Dissertations / Theses on the topic 'Inorganic Nanostructures - Synthesis'

Thesis (Ph. D.)--University of California, Riverside, 2009.
Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references. Also issued in print.

Organic semiconductors functionalized nanostructures are becoming as promising materials for electronic device applications including organic photovoltaics (OPVs). Perylenediimide (PDI) derivatives have also been known as one of the best n-type organic semiconductors. PDI derivatives can form bulk materials, which are both photochemically and thermally stable and have been widely used in various optoelectronic devices. Due to the formation of high electron mobility of crystalline domains, they prefer to incorporate into a silsesquioxane network. Here, we describe the potential applicability of perylenediimide functionalized silsesquioxane nanoribbons (PDI-dimethyl nanoribbons) as an acceptor for optoelectronic devices. We have developed synthetic procedures to make the PDI-dimethyl nanoribbons by the substitution reaction and the modified Stöber method. The PDI-dimethylethoxy silane precursor was produced in high yield by substituting 3-aminopropyldimethylethoxysilane on perylene-3,4,9,10-tetracarboxylicdianhydride as side chains. The optically active PDI-dimethyl nanoribbons were then formed upon hydrolysis with the certain concentration of ammonium hydroxide as a base. These nanoribbons were characterized using transmission electron microscopy (TEM), elemental analysis, and polarized optical microscopy. The photophysical properties in solution phase were also studied. The synthesis procedure developed here will have a great promise in large-scale manufacturing. Different shapes of PDI-dimethyl nanostructures, such as nanorods, nanochains, and nanoparticles, were discovered while varying the base concentrations. Also the morphologies of these PDI nanostructures were studied using TEM. Future studies will focus on optimizing procedures of PDI-dimethyl nanostructures and exploring new derivatives like perylenediimide dimer functionalized silsesquioxane polymers.

Encapsulation of nanoparticles within hexaniobate nanoscrolls presents interesting advances in the formation of nanocomposites exhibiting unique multi-dimensional properties. Building upon previous successes, facile yet versatile wet-chemical and microwave-irradiation synthetic protocols for the fabrication of a series of hexaniobate composites are presented herein. Solvothermal and, more recently, microwave-assisted methods have been developed that allow for the fabrication of peapod-like structures. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of preformed nanoparticles (NPs) to produce nanopeapods (NPPs). This approach offers versatility and high yields, in addition to the potential for advanced functional device fabrication. For the characterization of these materials, advanced techniques in atomic force microscopy (AFM) were used for investigating the surface of materials at the nanometer scale. Extensive physical, dynamic, and force modulation studies were performed on novel oxide nanocomposites by implementing particular scanning techniques to determine information such as topology, stress-induced behavior at the nanoscale, magnetic behavior, and frictional forces of the nanoscale materials. These composites were then analyzed by topological intermittent contact studies in tapping and contact mode, as well as with derivative techniques of these commonly used scanning probe approaches. In addition to studying surfaces using conventional modes of AFM, the mechanical properties of these nanocomposites were measured via dynamic lateral force modulation (DLFM) and magnetic properties of functionalized magnetic nanosheets were mapped via magnetic sampling modulation (MSM). By utilizing the capabilities of the DLFM imaging mode, elastic properties such as Young’s Modulus were measured from force-distance curves. In addition to this modulation mode, MSM was used to selectively map the vibrating magnetic nanomaterials from a modulated electromagnetic field. The information obtained from these AFM techniques can be helpful in determining the relative structural behavior of these nanocomposites and gauge their use in various applications such as structural engineering of nanoarchitectures as well as studying magnetic characteristics of metal oxide nanocomposites that exhibit characteristics different from their bulk counterparts.

Dye-sensitized solar cells (DSSC) have drawn much attention due to their higher versatility and lower production cost compared to inorganic photovoltaics. The top performers of DSSC have achieved power conversion efficiency over 10%, which is comparable to amorphous silicon solar cells. In this work, new photosensitizers and nanostructure for improving the photovoltaic performance of DSSC were developed and evaluated. Two series of cyclometalated ruthenium(II) complex photosensitizer were presented and their photosensitizing properties in DSSC were studied. Eight cyclometalated ruthenium(II) terpyridine complexes with three carboxylic acid groups on the terpyridine ligand were synthesized. Series A (M1 to M4) consist of C,N,N’ ligands substituted with phenyl group whereas series B (M5 to M8) consist of C,N,N’ ligands substituted with m-fluorophenyl group. All of the complexes exhibited broad aborption spectra covering the whole visible spectrum. The complexes in series B generally showed better photovoltaic performance than those in series A in the DSSCs. DSSC fabricated from M7 achieved the highest Voc, Jsc and power conversion efficiency among other DSSC, which were 0.56 V, 7.30 mAcm-2 and 2.63 % respectively. Truxene-core donor--acceptor dyes were presented and their photosensitizing properties in DSSC were studied. Eight dyes with either one donor two acceptors system (T2, B2, T2R and B2R) or two donor one acceptor system (T1, B1, T1R and B1R) were synthesized. Dyes with two acceptors have high molar extinction coefficients originated from the charge-transfer transition band, which are almost two times higher than those with only one accceptors. Both the enhanced absorption and better anchoring geometry on TiO2 contribute to the better photovoltaic performance of the two acceptors dyes in the DSSCs. Devices fabricated from B2 and volatile solvent electrolyte exhibited the best photovoltaic performance among the truxene-core dyes. The Voc, Jsc, FF and power conversion efficiency of the device were 0.59 V, 9.69 mAcm-2, 0.63 and 3.62 % respectively. Dyes based on cyanoacrylic acid anchoring groups (T1, T2, B1 and B2) were found to perform better than those based on rhodanine-3-acetic acid dyes (T1R, T2R, B1R and B2R) in both donor--acceptor configurations. ITO nanorod/TiO2 nanoparticle composite films with the three different types of ITO nanorod with different length (150 nm, 600 nm and 1.5 μm) were fabricated on FTO glass substrate. The transmittance and sheet resistance of the ITO nanorod array on the FTO glass substrate were found decreased with increasing the length of the ITO nanorod. When the ITO nanorod/TiO2 nanoparticle composite films were applied as the anode in DSSCs, the device fabricated from 600 nm ITO nanorod with TiO2 ‘double layer‘ film showed enhanced photocurrent generation. The improved photocurrent generation is suggested to be due to an improved charge collection efficiency at the ITO nanorod back electrode.
published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy

In this PhD thesis, several inorganic nanostructures were synthesized through a wetchemistry synthetic route. In particular, the miniemulsion approach was exploited to induce the formation in confined space of pure and doped binary (oxides, sulfides and fluorides) and ternary (hydroxides) compounds, of metal/oxide nanocomposites and of hybrid organic/inorganic nanoparticles. Through this methodology, the investigated systems were obtained in crystalline form already at room temperature. Various miniemulsion formulations were used to control the size and morphology of the investigated systems, achieving different emulsion stabilities and yields of crystalline powders. The obtained materials were thoroughly characterized through a wide array of techniques from the compositional, structural and functional points of view. In particular, XRD (X-Ray Diffraction) was employed to assess the formation of crystalline materials and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained were compared with micrographs collected through TEM (Transmission Electron Microscopy). This latter microscopy, coupled with SEM (Scanning Electron Microscopy), was also used to investigate the morphology of the synthesized nanostructures. In addition, the surface composition was explored through XPS (X-ray Photoelectron Spectroscopy) and, especially in the case of systems doped with transition metal or lanthanide ions, atomic ratios were compared to those obtained through ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) or ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) allowed to evaluate the presence and amount of residual surfactant moieties adsorbed on the materials surfaces. In the case of the doped systems, XAS (X-ray Absorption Spectroscopy) measurements were performed in order to study in detail the local structure of the doping ions, also with respect to the hosting matrices. The obtained data were further correlated to the photoluminescence properties. These materials, also due to the biocompatibility of the selected matrices, might indeed be potentially applied for optical bioimaging. At this regard, cytotoxicity and cell viability assays were also performed on selected systems.
In questa tesi di dottorato, diverse nanostrutture inorganiche sono state sintetizzate mediante un approccio sintetico per via umida. In particolare, l’approccio della miniemulsione è stato sfruttato per indurre la formazione in spazio confinato di composti binari (ossidi, solfuri e fluoruri) e ternari (idrossidi), sia in forma pura che drogati, e di nanocompositi metallo/ossido e nanoparticelle ibride organiche/inorganiche. Attraverso questa metodologia, i sistemi investigati sono stati ottenuti in forma cristallina già a temperatura ambiente. Miniemulsioni con varie formulazioni sono state usate per controllare le dimensioni e la morfologia dei sistemi investigati, ottenendo emulsioni con stabilità differenti e diversa resa in termini di prodotti cristallini. I materiali ottenuti sono stati caratterizzati in dettaglio attraverso numerose tecniche, sia dal punto di vista composizionale che da quello strutturare e funzionale. In particolare, l’XRD (X-Ray Diffraction) è stato utilizzato per valutare la formazione di materiali cristallini e, attraverso rifinimento Rietveld, calcolare le dimensioni medie dei cristalliti; i dati così ottenuti sono stati confrontati con le micrografie TEM (Transmission Electron Microscopy). Quest’ultima microscopia, affiancata al SEM (Scanning Electron Microscopy), è stata anche utilizzata per investigare la morfologia delle nanostrutture sintetizzate. In aggiunta, la composizione superficiale è stata esplorata attraverso XPS (X-ray Photoelectron Spectroscopy) e, specialmente nel caso dei sistemi drogati con ioni di metalli di transizione o lantanidi, i rapporti molari registrati sono stati confrontati con quelli ottenuti attraverso ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) o ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). Analisi TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) hanno invece permesso di valutare la presenza e la quantità di residui di tensioattivi adsorbiti sulla superficie del materiale. Nel caso dei sistemi drogati, sono state effettuate misure XAS (X-ray Absorption Spectroscopy) al fine di studiare in dettaglio la struttura locale intorno agli ioni droganti, in relazione alle matrici ospitanti. I dati così ottenuti sono stati inoltre correlati con le proprietà di fotoluminescenza. Questi materiali, anche grazie alla biocompatibilità delle matrici selezionate, potrebbero potenzialmente essere utilizzati nel campo del bioimaging ottico. A questo riguardo sono state quindi effettuate prove di citotossicità e di influenza sulla vitalità cellulare su alcuni dei sistemi sintetizzati.

The overall purpose of this work is to address several of the roadblocks to use of thermoelectric materials for generation of electricity, namely inefficient processing of materials and low performance, commonly rated by the figure of merit, ZT=T?2?/?tot. The ZT includes ? as the Seebeck coefficient, ? as electrical resistivity, T as the average temperature, and ?tot as total thermal conductivity. ?tot is the sum of electronic charge carrier (?C) and lattice (?L) contributions to thermal conductivity. Attempts to increase ZT in the literature to values >1 have focused on decreasing the thermal conductivity via nanostructuring or optimizing the electrical conductivity and Seebeck coefficient by doping. In this work, two separate approaches are taken to tackle these issues: (1) Target higher ZT by assembling lead telluride (PbTe) nanoparticles from a multi-gram synthesis utilizing ligand stripping techniques or deliberately including discrete lead sulfide (PbS) NCs. (2) Develop a rapid, convenient synthesis of tetrahedrite (Cu12Sb4S13). Approach (1): Nanostructuring of PbTe and PbTe?PbS. Nanostructured PbTe and nanocomposites of PbTe?PbS are hypothesized to increase ZT by lowering thermal conductivity, while ligand stripping of PbTe NCs by sulfide or iodide is expected to increase ZT because it has been demonstrated to increase electrical conductivity in thin films of PbS. A new synthesis is in demand because mixing PbTe and PbS NCs requires that the PbTe be dispersible, and literature syntheses of such NCs suffer from small yields (<200 mg). Thus, applications of dispersible PbTe NCs are largely limited to thin films. The ZT values of these thin films are not reported due to difficulty in quantifying thermal conductivity. In the dissertation research, nanostructured PbTe pellets are prepared by hot-pressing PbTe NCs after either mixing with PbS NCs by incipient wetness, or ligand stripping with sulfide salt, iodide salt, or both. The PbTe NCs themselves are prepared in multi-gram quantities by hot-injection methods in solution. The NCs are characterized for crystallinity by powder X-ray Diffraction (XRD). The size and morphology of the NCs are probed via Transmission Electron Microscopy (TEM), and their composition is determined by Energy Dispersive Spectroscopy (EDS). The thermoelectric properties are studied on hot-pressed pellets of each sample. Approach (2): Developing a facile route to tetrahedrite and doped derivatives. Tetrahedrite is exciting the thermoelectric community due to its lack of rare or toxic elements, the tunability of its electronic properties by doping, the ability to dope by ball-milling with the plentiful natural mineral, and the ability to achieve a ZT of unity. However, the natural mineral is unsuitable on its own due to an excess of natural dopant, and reported tetrahedrite syntheses require heating at high temperature 650 ?C in a three day process followed by two weeks of heating at 450 ?C. This work establishes a new synthesis amenable to industrial production that reduces the heating time from over 2 weeks to 2 days for simultaneous batch production at moderate temperature (155 ?C for one day and 430 ?C for 30 min, cooling naturally). The tetrahedrite powder is prepared from chloride-free metal salts and thiourea by solvothermal methods and characterized by XRD for crystallinity. The composition is determined by Inductively Coupled Plasma analysis. Products from multiple batches are mixed by ball-milling alone or combined with the natural mineral as a means to dope with Zn2+ as a solid solution. The resulting powder is then hot-pressed to pellet form for thermoelectric characterization. The tetrahedrite is also doped in-situ by zinc over a range of 0.79 to 1.40 mol equivalents using chloride-free metal salts.

The ability to encapsulate linear nanoparticle (NP) chains in scrolled nanosheets is an important advance in the formation of nanocomposites.These nanopeapods (NPPs) exhibit interesting properties that may not be achieved by individual entities. Consequently, to fully exploit the potential of NPPs, the fabrication of NPPs must focus on producing composites with unique combinations of morphologically uniform nanomaterials. Various methods can produce NPPs, but expanding these methods to a wide variety of material combinations can be difficult. Recent work in our group has resulted in the in situ formation of peapod-like structures based on chains of cobalt NPs. Building on this initial success, a more versatile approach has been developed that allows for the capture of a series of preformed NPs in NPP composites. In the following chapters, various synthetic approaches for NPPs of various material combinations will be presented and the key roles of various reaction parameters will be discussed. Also, uniform hexaniobate nanoscrolls were fabricated via a solvothermal method induced by heating up a mixture of TBAOH, hexaniobate crystallites, and oleylamine in toluene. The interlayer spacing of the nanoscrolls was easily tuned by varying the relative amount and chain lengths of the primary alkylamines. To fabricate NPPs, as-synthesized NPs were treated with hexaniobate crystallite in organic mixtures via solvothermal method. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of NPs to produce the target NPP structures in high yield. Reaction mixtures were held at an aging temperature for a few hours to fabricate various new NPPs (Fe3O4@hexaniobate, Ag@hexaniobate, Au@hexaniobate, Au-Fe3O4@hexaniobate, TiO2@hexaniobate, CdS@hexaniobate, CdSe@hexaniobate, and ZnS@hexaniobate). This versatile method was first developed for the fabrication of magnetic peapod nanocomposites with preformed nanoparticles (NPs). This approach is effectively demonstrated on a series of ferrite NPs (≤ 14 nm) where Fe3O4@hexaniobate NPPs are rapidly (~ 6 h) generated in high yield. When NP samples with different sizes are reacted, clear evidence for size selectivity is seen. Magnetic dipolar interactions between ferrite NPs within the Fe3O4@hexaniobate samples leads to a significant rise in coercivity, increasing almost four-fold relative to free particles. Other magnetic ferrites NPPs, MFe2O4@hexaniobate (M = Mn, Co, Ni), can also be prepared. This synthetic approach to nanopeapods is quite versatile and should be readily extendable to other, non-ferrite NPs or NP combinations so that cooperative properties can be exploited while the integrity of the NP assemblies is maintained. Further, this approach demonstrated selectivity by encapsulating NPs according to their size. The use of polydispersed NP systems is also possible and in this case, evidence for size and shape selectivity was observed. This behavior is significant in that it could be exploited in the purification of inhomogeneous NP samples. Other composite materials containing silver and gold NPs are accessible. Partially filled Fe3O4@hexaniobate NPPs were used as templates for the in situ growth of gold to produce the bi-functional Au- Fe3O4@hexaniobate NPPs. Encapsulation of Ag and Au NP chains with a hexaniobate nanoscroll was shifted the surface plasmon resonance to higher wavelengths. In these composites NPs can be incorporated to form NPP structures, decorated on nanosheets before scrolling, or attached to the surfaces of the nanoscrolls. The importance of this advancement is the promise it holds for the design and assembly of active nanocomposites. One can create important combinations of nanomaterials for potential applications in a variety of areas including catalysis, solar conversion, thermoelectrics, and multiferroics.

Although the study of biominerals may be traced back many centuries, it is only recently that biological principles have been applied to synthetic systems in processes termed "biomimetic" and "bioinspired" to yield materials syntheses that are otherwise not possible and may also reduce the expenditure of energy and/or eliminate toxic byproducts. Many investigators have taken inspiration from interesting and unusual minerals formed by organisms, in a process termed biomineralisation, to tailor the nanostructure of inorganic materials not necessarily found biogenically. However, the fields of nanoparticle synthesis and biomineralisation remain largely separate, and this thesis is an attempt to apply new studies on biomineralisation to nanomaterials science.Principally among the proteins that influence biomineralisation is a group comprised largely of negatively charged aspartic acid residues present in serum. This study is an investigation determining the ability of these serum proteins and other anolagous biomolecules to stabilise biologically relevant amorphous minerals and influence the formation of a variety of materials at the nanoscale. Three different materials were chosen to demonstrate this effect; gold was templated into nanosized single crystals by the action of bioorganic molecules, and the utility of these nanoparticles as a biosensor was explored. The influence of bioorganic molecules on the phase selection and crystal size restriction of titanium dioxide, an important semiconductor with many applications, was explored. The use of bioorganically derived nanoparticles of titanium dioxide was then demonstrated as a highly efficient photocatalyst. Finally, calcium carbonate, a prevalent biomineral was shown to form highly ordered structures over a variety of length scales and different crystalline polymorphs under the influence of a templating protein. In addition, an alternative route to producing calcium phosphate nanoparticle dispersions by mechanical filtration was explored and use as a transfection vector was optimised in two cell lines.Several significant achievements are presented: (i) the assessment of the relative ability of serum, serum derived proteins and their analogues to stabilize the amorphous state, (ii) the formation of single crystalline gold templated by an antibody, (iii) the formation of highly photocatalytically active nanoparticulate anatase by a phosphorylated cyclic esther, (iv) the formation of conical structures at the air liquid interface by the templating ability of a protein and (v) the optimisation of calcium phosphate nanoparticle mediated transfection in two cell lines by mechanical filtration.
Malgré le fait que l'étude des biomatériaux remonte à plusieurs siècles, ce n'est que récemment que des principes biologiques furent appliqués à des systèmes synthétiques dans des procédés de "biomimetic" et "bioinspirés", permettant ainsi de nouveaux matériaux de synthèses tout en réduisant l'expansion d'énergie et/ou d'éliminer les résultantes toxiques. Plusieurs chercheurs se sont inspirés des formes inusuelles dès plus intéressantes créées par des organismes, formés par un procédé de biominéralisation, qui modifie la nanostructure des matériaux synthétiques. Toutefois, les champs d'études des synthèses de nanoparticules et de la biominéralisation demeurent grandement à part, et cette thèse tente d'appliquer de nouvelles études de biominéralisation par rapport à la science des nanomatériaux.Les protéines sériques qui influencent la biominéralisation sont chargées négativement de résidus d'aspartate. Cette recherche déterminera l'habileté de ces protéines et des diverses molécules bio–organiques qui stabilisent biologiquement d'important minéraux aux multiples formes qui influencent la formation de matériaux non biogènes sur une nano échelle; l'or et le dioxyde de titane ont permis de démontrer ce résultat. L'or fut transformé en nanoparticules de cristal par l'action des protéines sériques, et c'est l'utilité de ces nanoparticules en tant que biocapteurs qui fut explorée. L'influence des molécules bios-organiques sur le choix de la phase ainsi que sur la restriction de la grosseur du cristal de dioxyde de titane, un important semi-conducteur dans plusieurs applications, fut explorée. Les nanoparticules dérivant bio-organiquement du dioxyde de titane ont dès lors démontrées leur action hautement efficace comme photo catalyseur. Le carbonate de calcium, un biominéral commun, a su démontré sa capacité à auto-former des structures à multiples échelles ainsi que différents polymorphes cristallins sous l'influence d'une protéine modèle. De plus, la manipulation des structures à former divers arrangements est une variable qui fut démontrée. Finalement, la stabilité des nanoparticules du phosphate de calcium à se disperser dans le sérum de culture fut modifiée afin d'optimiser l'efficacité du transfert dans deux lignes de cellules.Plusieurs grandes recherches ont accomplis de façon significative; (i) l'évaluation de l'habileté relative du sérum, le dérivé des protéines sériques et de leur capacité à stabiliser les phases de leurs multiples formes, (ii) la formation simple cristalline de l'or former par un anticorps, (iii) la formation de nanoparticules très actives photocatalytiquement d'anatase formées par un ester cyclique phosphorylée, (iv) la formation de structures coniques à l'interface air liquide par la capacité de gabarits d'une protéine, (iv) l'optimisation de transfection médiation par des nanoparticules de phosphate de calcium dans deux lignées cellulaires par filtration méchanique.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2002.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thin film nanocomposites consisting of inorganic matter embedded within a soft polymeric matrix on the nanometer length scale are an important class of materials with potential application in optoelectronics and photonics, magnetic media, and batteries and fuel cells. In addition to the component material properties, the properties and performance of the nanocomposite depend crucially on the interaction between and the nanoscale organization of the components. The polymeric matrix plays a critical role in controlling and mediating this interaction and organization. Polyelectrolyte multilayers formed by the layer-by-layer electrostatic assembly of oppositely charged polymers are a versatile new form of thin film in which the physical and chemical architecture can be precisely controlled over the nanoscale. This thesis addresses the elucidation, development, and application of polyelectrolyte multilayers as nanostructured matrices for inorganic synthesis. Multilayers formed from poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), possessing ion-exchangeable carboxylic acid groups, were used to bind metal cations within the film. Metallic and semiconducting nanoparticles, including Ag, Pd, and ZnS, were formed in situ by reduction or sulfidation of the bound metal cations. The size and concentration of Ag nanoparticles were controlled by the concentration of metal-binding carboxylic acid groups as determined by multilayer assembly pH. In addition, the metal cation exchange and reaction methodology could be repeatedly cycled to increase nanoparticle size and concentration. An alternative method to increase nanoparticle size was also developed using electroless metal deposition on catalytic Pd particles.
(cont.) The nanoparticles were homogeneously dispersed and randomly distributed within the film due to the high degree of interpenetration between PAH and PAA chains in the multilayer. Stratified films were prepared by assembling fully ionized polyelectrolyte pairs with PAH/PAA during multilayer formation; the nanoparticles were spatially selective for only the PAH/PAA regions. One effect of the embedded Ag nanoparticles was the dramatic enhancement of the nanocomposite refractive index. The ability to control both multilayer architecture and nanoparticle properties via assembly conditions facilitated the controlled modulation of the nanocomposite refractive index over the entire film thickness. Photonic bandgap structures based on stratified polyelectrolyte multilayer nanocomposites were demonstrated.
by Tom Chih-Hung Wang.
Ph.D.

Thesis (Ph.D.) - University of Glasgow, 2007.
Ph.D. thesis submitted to the Department of Chemistry, Faculty of Physical Sciences, University of Glasgow, 2007. Includes bibliographical references. Print version also available.

Thesis advisor: Dunwei Wang
The performance of advanced energy storage devices is intimately connected to the designs of electrodes. To enable significant developments in this research field, we need detailed information and knowledge about how the functions and performances of the electrodes depend on their chemical compositions, dimensions, morphologies, and surface properties. This thesis presents my successes in synthesizing and characterizing electrode materials for advanced electrochemical energy storage devices, with much attention given to understanding the operation and fading mechanism of battery electrodes, as well as methods to improve their performances and stabilities. This dissertation is presented within the framework of two energy storage technologies: lithium ion batteries and lithium oxygen batteries. The energy density of lithium ion batteries is determined by the density of electrode materials and their lithium storage capabilities. To improve the overall energy densities of lithium ion batteries, silicon has been proposed to replace lithium intercalation compounds in the battery anodes. However, with a ~400% volume expansion upon fully lithiation, silicon-based anodes face serious capacity degradation in battery operation. To overcome this challenge, heteronanostructure-based Si/TiSi2 were designed and synthesized as anode materials for lithium ion batteries with long cycling life. The performance and morphology relationship was also carefully studied through comparing one-dimensional and two-dimensional heteronanostructure-based silicon anodes. Lithium oxygen batteries, on the other hand, are devices based on lithium conversion chemistries and they offer higher energy densities compared to lithium ion batteries. However, existing carbon based electrodes in lithium oxygen batteries only allow for battery operation with limited capacity, poor stability and low round-trip efficiency. The degradation of electrolytes and carbon electrodes have been found to both contribute to the challenges. The understanding of the synergistic effect between electrolyte decomposition and electrode decomposition, nevertheless, is conspicuously lacking. To better understand the reaction chemistries in lithium oxygen batteries, I designed, synthesized, and studied heteronanostructure-based carbon-free inorganic electrodes, as well as carbon electrodes whose surfaces protected by metal oxide thin films. The new types of electrodes prove to be highly effective in minimizing parasitic reactions, reducing operation overpotentials and boosting battery lifetimes. The improved stability and well-defined electrode morphology also enabled detailed studies on the formation and decomposition of Li2O2. To summarize, this dissertation presented the synthesis and characterization of inorganic nanostructured materials for advanced energy storage. On a practical level, the new types of materials allow for the immediate advancement of the energy storage technology. On a fundamental level, it helped to better understand reaction chemistries and fading mechanisms of battery electrodes
Thesis (PhD) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: electrodeposition; chemical vapor deposition; AAO template-assisted nanofabrication; 1 D nanomateirals; inorganic nanomaterials; nanostructured electrode. Includes bibliographical references (leaves 102-103).

Despite of the huge number of applications of titania (TiO2), a no-toxic, low cost and very promising photocatalyst, there are some critical factors that limit its photoactivity, first of all the fact that titania is a semiconductor only active in the UV region of the light spectrum. Several methods have been proposed to reduce its energy-gap value, among which noble metal deposition, surface modifications and doping with transition metal ions or rare earth elements Ceria (CeO2) has attracted great attentions due to its unique properties, such as biocompatibility, chemical inertness and strong oxidizing capability related to the formation of oxygen defects. CeO2-TiO2 systems seem to exhibit improved photocatalytic activity due to the enhanced mobility of excitons and/or reduced band gaps. In the present dissertation, nanostructured TiO2 samples containing different CeO2 loadings were synthesized and characterized by many techniques. Surface and bulk chemistry was evaluated by using X-ray powder diffraction (XRPD), X-ray photoelectron Spectroscopy (XPS) and infrared spectroscopy (DRIFT-IR); morphological and textural characterization was carried out by high resolution transmission electron microscopy (HRTEM); porosity was measured by N2 physisorption and the optical properties were studied by UV-vis spectroscopy (DRIFT UV-vis). Finally the samples were tested in the photodegradation of methylene blue (MB) in aqueous suspension under UV light.The CeO2-TiO2 nanostructured photocatalysts were found active in the test reaction attaining very high MB degradation values of dye oxidation after the monitored reaction period (120 min), with cerium-doped TiO2 (CeO2 loading less than 2.5 wt%) nanomaterials displaying a MB degradation rate higher than that of pure TiO2.

The purpose of following thesis is synthesizing nanostructured TiO2 samples using hydrothermal method containing different CeO2 loadings ranging from 0.1 to 5.0 wt% and investigating their photocatalytic activity. Prepared samples characterized by different techniques to analyze them. Textural and structural characterization (surface and bulk properties) by using X-ray diffraction, the surface area and pore size distribution of synthesized samples were calculated by N₂ physisorption. morphological characterization and optical characterization, the size, shape and composition of synthesized nanoparticles were characterized by high resolution transmission electron microscopy (HRTEM) and energy dispersive x-ray (EDX) and optical properties were investigated by measuring their band gap energy (Eg ). Figure shows the change in diffuse reflectance optical spectra with increased ceria doping. To evaluate the synthesized photocatalysts, the degradation of two industrial dyes, methylene blue (MB) and methylene orange (MO) were chosen as a test reaction in aqueous suspension under light irradiation at room temperature and atmospheric pressure. Under UV light the CeO2-TiO2 nanostructured photocatalysis were found active in the reaction, obtain high degradation values after the monitored reaction period (120 min), with all CeO2-containing nanomaterials exhibit a degradation rate higher that that of pure TiO2 samples. The most promising materials, displaying a convenient energy gap value, were also tested in the same operating conditions under simulated solar light irradiation. The conclusion of the test experiment confirmed that the amount of ceria in the bodywork of titania and undoubtedly lowering the band gap to match with visible light absorption, can elevate the photocatalytic activity. Eventually, Ce-containing nanoparticles synthesized by a hydrothermal approach, demonstrate a higher rate of photodegradation than that of pure titania samples.

Carbon materials constitute a large family of diverse structures and textures that underlie an increasing range of applications suggested by the impressive number of papers published on this topic. Several hundreds of thousands of publications have appeared since 1900, out of which, thousands were published during the last decade (Web of Science™, Thomson Reuters, Scopus, SciFinder using as searching topics “carbon materials,” “carbon chemistry,” “carbon nanomaterials,” “carbon nanotubes,” and “graphene”). The popularity of carbon materials is due to a unique combination of physical and chemical properties such as high electrical conductivity, high surface area, good resistance to corrosion, high thermal stability, and high chemical stability in non-oxidizing environments and particular mechanical properties. Carbon materials are easy to process, provide a wide variety of structures and textures, have diverse surface chemical properties and are compatible with other materials, thus are ideal for composites as well. This unique combination of properties is a consequence of the different hybridization of orbitals in C atoms and the possibility of combining with other heteroatoms. Carbon materials form the basis of numerous applications in a wide variety of research and engineering areas. This causes publications on carbon-based materials to appear traditionally in various journals from both scientific and engineering domains. Certainly, new uses will appear considering the versatility of carbon materials. In this thesis, the use of carbon materials for applications in energy storage, gas sensing and additive manufacturing is taken into account. In addition, particular attention is given to different approaches of nanomaterials syntheses either chemical or electrochemical route. Integration of carbon materials (especially nanocarbons) into other components to design functional or structural materials is a critical issue. Functional materials constituted by a carbon material and another component such as metal oxides, polymers and conductive polymers, are very much studied for energy storage. In this case, synthetic methods to achieve an adequate distribution of both components and improve synergies are considered. In summary, research on carbon-based materials is a very dynamic and growing area of study with nearly unlimited possibilities. We still have plentiful theoretical and applied issues to be understood regarding the structure, texture, and properties of carbon materials.

Amino-functionalized organic–inorganic hybrid materials with a narrow distributed nanostructure of 2–4 nm in size were obtained by means of a template-free and non-aqueous procedure. Simultaneous twin polymerization of novel amino group containing twin monomers with 2,2′-spirobi[4H-1,3,2-benzodioxasiline] has been applied for this purpose. The amino groups of the organic–inorganic hybrid material are useful for post derivatization
Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

In recent years water contamination is reaching alarming levels, since the concentration of pollutants present in seas, lakes and streams has far exceeded water self-purifying capacity. The most widespread sources responsible for water pollution are urban and industrial dumps containing a vast range of dangerous substances. Despite wastewaters are always subjected to purification treatments, a complete remediation is not always possible. The most common pollutants are heavy metal ions and organic compounds such as phenolic compounds, polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pesticides and synthetic dyes. All these substances are highly stable and can easily bioaccumulate in living organisms as xenobiotic molecules, causing chronic and acute toxicity or carcinogenic and mutagenic effects. Furthermore, substances as dyes can cause changes to the aquatic ecosystem as they absorb the sunlight limiting its penetration into deep waters, thus inhibiting the photosynthesis of aquatic plants and thus limiting the water re-oxygenation capacity. In such a scenario, in the last few decades the scientific community has put a great deal of effort into the improvement of wastewater remediation processes. Among the various treatments, adsorption is one of the most useful thanks to its simplicity and low cost. The great advancement in nanotechnology has paved the way for new highly effective nanostructured adsorbent materials. These generally porous nanoadsorbents are characterized by a high surface area and high surface/volume ratio, which greatly influence their adsorption capacity. The purpose of this thesis work was the development of new mesoporous adsorbents, namely functionalized ordered mesoporous silica (OMS) and metal organic frameworks (MOFs) for the removal of heavy metal ions and organic dyes two types of pollutants commonly present in wastewaters.. Both OMS and MOFs are characterized by high surface area, high surface/volume ratio, geometrical order, and easy synthesis or functionalization. SBA-15 OMS and Fe-BTC type MOF have been successfully synthesized and characterized by means of different techniques, such as small angle X rays scattering (SAXS), powder X-rays diffraction (XRD), N2 physisorption, transmission and scanning electron microscopy (TEM and SEM), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). SBA-15 was functionalized with two different organic ligands, namely triethylenetetramine (TETA) and 2,8-dithia-5-aza-2,6-pyridinophane macrocycle (PyNS2), to obtain two different adsorbents, named SBA-TETA and SBA-PyNS2 which have been tested against some heavy metal ions (Cu2+, Zn2+ and Cd2+). The Fe-BTC, without further modifications, was instead tested as an adsorbent of two highly toxic organic dyes, such as Alizarin red S (ARS) and Malachite Green (MG). All adsorption experiments were monitored using Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES) or UV-Vis Spectroscopy. This allowed the experimental determination of the adsorption capacity q of the three adsorbents, their thermodynamic and kinetic parameters. In the case of SBA-15-based adsorbents, further investigations on their properties were carried out by means of potentiometric titrations.

The effect of acoustic and hydrodynamic cavitation on the precipitation of inorganic catalytic materials was investigated. The overall objective was to understand the fundamental factors involved in synthesizing nanometer-size catalytic materials in the 1-10 nm range in a cavitating field. Materials with grain sizes in this range have been associated with enhanced catalytic activity compared to larger grain size materials. A new chemical approach was used to produce titania supported gold by coprecipitation with higher gold yields compared to other synthesis methods. Using this approach, it was determined that acoustic cavitation was unable to influence the gold mean crystallite size compared to non-sonicated catalysts. However, gold concentration on the catalysts was found to be very important for CO oxidation activity. By decreasing the gold concentration from a weight loading of 0.50% down to approximately 0.05%, the rate of reaction per mole of gold was found to increase by a factor of 19. Hydrodynamic cavitation at low pressures (6.9-48 bar) was determined to have no effect on gold crystallite size at a fixed gold content for the same precipitation technique used in the acoustic cavitation studies. By changing the chemistry of the precipitation system, however, it was found that a synergy existed between the dilution of the gold precursor solution, the orifice diameter, and the reducing agent addition rate. Individually, these factors were found to have little effect and only their interaction allowed gold grain size control in the range of 8-80 nm. Further modification of the system chemistry and the use of hydrodynamic cavitation at pressures in excess of 690 bar allowed the systematic control of gold crystallite size in the range of 2-9 nm for catalysts containing (2.27 ± 0.17)% gold. In addition, it was shown that the enhanced mixing due to cavitation led to larger gold yields compared to classical syntheses. The control of gold grain size was gained at the loss of CO activity, which was attributed to the formation of non-removable sodium titanate species. The increased mixing associated with cavitation contributed to the activity loss by partially burying the gold and incorporating more of the sodium titanate species into the catalysts. This work produced the first evidence of hydrodynamic cavitation influencing the gold crystallite size on titania supported gold catalysts and is the only study reporting the control of grain size by simple mechanical adjustment of the experimental parameters. Despite the low activity observed due to sodium titanate, the methodology of adjusting the chemistry of a precipitating system could be used to eliminate such species. The approach of modifying the chemical precipitation kinetics relative to the dynamics of cavitation offers a general scheme for future research on cavitational processing effects.

The rise of graphene has attracted great interest in low-dimensional materials (0D, 1D and 2D). A joint effort among the different branches of science (chemistry, physics, materials science and related areas) is directed towards the production of new intriguing materials with tuneable graphene-like properties. Promising is the direct synthesis of organic nanostructures on metal surfaces under ultrahigh-vacuum conditions (UHV). Perfect tuning of the reaction conditions, high control of the surface symmetry and of its corrugation, a rich variety of substrate materials are only some of the advantage that UHV may offer. Although several reactions have been tested, it seems clear that to achieve ordered covalent monolayers more complex approaches are needed. In this thesis, the on-surface polymerization of covalent nanostructures has been studied for different coupling reactions, substrate materials and reaction conditions. Scanning tunneling microscopy and X-ray photoelectron spectroscopy are used for the characterization, allowing complementary analysis of molecular structures and chemical states. In particular, thermally activated reactions were used to gradually polymerize the 4,4”-dibromo-terphenyl precursor into poly-paraphenylene wires, through an Ullmann-like reaction scheme on Au(111), and then into graphene nanoribbons, after activation of the C-H bonds. A fine balance between the catalytic activity of the surface, molecular mobility and favourable molecular organization allowed us to get extended and ordered covalent structures. Taking advantage of this synthetic pathway, three different mono-dimensional polymers were obtained, namely poly-paraphenylene and two pyridinic derivatives, with gradually increased nitrogen content. Macroscopically anisotropic samples have been prepared by taking advantage of the vicinal surface templating effect. Using angle resolved photoemission spectroscopy, we reveal that the electronic structure of doped polymers is monotonically downshifted with respect to the metal Fermi level as the pyridine substitution is increased within the molecular scaffold. Finally, the photochemical activation of different functional groups has been explored. These studies represents a step forward in the application of organic photochemistry to on-surface synthesis, which is currently limited to the use of diacetylene groups, and it opens up new opportunities for using several organic functional groups as photoactive centres for the synthesis of covalent organic frameworks.
La scoperta del grafene ha suscitato grande interesse verso i materiali a bassa dimensionalità (0D, 1D e 2D) e uno sforzo congiunto tra i diversi rami della scienza è orientato verso la produzione di nuovi materiali con proprietà analoghe a quelle del grafene, ma controllabili. La sintesi su superficie in condizioni di ultra-alto vuoto (UHV) sembra essere promettente per la produzione di nanostrutture organiche. Infatti, in queste condizioni, è possibile avere un’ampia varietà di materiali, un perfetto controllo delle condizioni di reazione, della simmetria della superficie e della sua corrugazione. Questi sono solo alcuni dei vantaggi che l’UHV offre. Sebbene varie reazioni siano state testate negli ultimi anni, sembra chiaro che per realizzare monostrati polimerici ordinati siano necessiari approcci più complessi. In questo lavoro di Tesi, la sintesi di nanostrutture polimeriche su superficie è stata studiata per diverse reazioni, substrati e condizioni di reazione. La microscopia ad effetto tunnel e la spettroscopia di fotoemissione a raggi X sono state utilizzate per la caratterizzazione dei diversi sistemi permettendo un'analisi complementare delle strutture molecolari e dei loro stati chimici. In particolare, le reazioni attivate termicamente sono state utilizzate per polimerizzare gradualmente il 4,4"-dibromo-terfenile e ottenere, in un primo step di reazione, per mezzo della reazione di Ullmann su Au (111), il poli-parafenilene, ,e poi nanoribbons di grafene dopo l'attivazione del legami C-H. Un delicato equilibrio tra l'attività catalitica della superficie, la mobilità molecolare e l’organizzazione molecolare ha permesso di ottenere strutture ordinate estese. Inoltre, sfruttando questa metodica, sono stati ottenuti tre differenti polimeri 1D, caratterizzati da un crescente contenuto di azoto. Campioni macroscopicamente anisotropici sono stati preparati sfruttando l'effetto templante delle superfici vicinali e, grazie alla spettroscopia di fotoemizzione risolta in angolo, è stato rivelato che la struttura elettronica dei polimeri drogati è rigidamente spostata verso energie minori rispetto al livello di Fermi del metallo all'aumentare del contenuto di azoto. Infine, è stata esplorata l'attivazione fotochimica di diversi gruppi funzionali. Questi studi rappresentano un passo avanti verso l’applicazione della fotochimica alla sintesi su superficie, che attualmente sfrutta solo gruppi diacetilenici, e apre nuove opportunità per l'utilizzo di diversi gruppi funzionali organici come centri fotoattivi.

In this Thesis, metal sulfides were synthesized through water-based and ligand-free synthetic routes. A simple batch approach was successfully employed for the synthesis of ZnS, CuS, PbS, MnS and Ag2S in a crystalline form at a temperature near 0 °C without employing ligands or stabilizing agents. Particles dimension, crystal structure, surface composition and susceptibility to oxidation phenomena of these materials were assessed. In the case of the batch synthesis of ZnS, a SAXS (Small Angle X-Ray Scattering) in-situ study was also performed to elucidate the dimensional evolution of the obtained NPs (nanoparticles) as function of time. Moreover, for ZnS, the behavior in water suspension and the interaction with probe molecules at the liquid/solid interface were also assessed. Microfluidic and CHFS (Continuous Flow Hydrothermal Synthesis) approaches were employed for the synthesis of pure and doped ZnS NPs. In the case of the pure samples, the synthesis conditions were varied in order to gain insights on the growth mechanism of the NPs and to analyze the potential over the control of dimensional and structural properties of the samples. For the doped samples, the uptake of dopants was determined and their inclusion in the ZnS matrix discussed. The functional properties of selected samples were assessed. In particular, the catalytic activity for the HER (Hydrogen Evolution Reaction) was studied for pure ZnS NPs, while PL (Photoluminescence) was measured in the doped ones. Cytotoxicity assays on doped ZnS NPs obtained with the microfluidic route were also performed in view of bioimaging applications. The effect of thermal treatment and oxidation phenomena on ZnS NPs as a function of the NPs size was also in-depth analyzed. The study addressed the variations of size, morphology, structure, composition of the nanostructures and their effect on the photocatalytic activity. The characterization strategy relied on the complementary use of different techniques. XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) analyses were performed to assess mainly dimensional and structural features of the materials, while the surface composition was analyzed combining XPS (X-ray Photoelectron Spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy). The characterization of the materials was also complemented by Raman spectroscopy. The results showed the potential of the proposed methods to control relevant features of different materials, even without the use of stabilizing agents, and allowed to assess the surface chemistry of the synthesized naked particles.
In questa tesi sono stati sintetizzati solfuri metallici utilizzando metodi in soluzione acquosa che non prevedono l’uso di leganti. In particolare, ZnS, CuS, PbS, MnS e Ag2S sono stati ottenuti in forma cristallina ad una temperatura prossima a 0 °C e senza l’uso di leganti mediante un semplice metodo batch. Sono stati studiati la dimensione, la struttura cristallina, la composizione e i fenomeni di ossidazione delle particelle ottenute. È inoltre stato eseguito uno studio SAXS (Small Angle X-Ray Scattering) in-situ risolto nel tempo relativo alla sintesi di ZnS per valutarne la crescita nella miscela di reazione durante la sintesi batch. Sono inoltre stati studiati il comportamento in sospensione acquosa di particelle di ZnS e la loro interazione con sonde molecolari all’interfaccia liquido/solido. La sintesi di nanoparticelle di ZnS pure e drogate è stata eseguita mediante un metodo microfluidico ed uno CHFS (Continuous Flow Hydrothermal Synthesis). Nel caso di ZnS puro, le condizioni di sintesi sono state variate per ottenere informazioni sul meccanismo di formazione del materiale e valutare le potenzialità dei metodi utilizzati per controllare le proprietà dimensionali e strutturali delle nanoparticelle. Nel caso di ZnS drogato, l’incorporazione dei droganti nel materiale è stata quantificata e discussa. Le proprietà funzionali di alcuni campioni selezionati sono state studiate. Nel caso di ZnS puro è stata quantificata l’attività fotocatalitica per la HER (Hydrogen Evolution Reaction), mentre per il materiale drogato sono state misurate le proprietà di fotoluminescenza. È inoltre stata determinata la citotossicità di alcuni campioni ottenuti per via microfluidica in vista di potenziali applicazioni nella diagnostica per immagini. È stato eseguito uno studio approfondito sull’effetto di trattamenti termici e fenomeni di ossidazione sulle proprietà dimensionali, morfologiche, strutturali e composizionali delle nanostrutture e sui loro effetti sulla di attività fotocatalitica di nanoparticelle di ZnS di diversa dimensione. La strategia di caratterizzazione si è basata sull’uso complementare di tecniche diverse, quali l’XRD (X-Ray Diffraction) e la microscopia TEM (Transmission Electron Microscopy) per lo studio di proprietà dimensionali e strutturali, mentre XPS (X-ray Photoelectron Spectroscopy) e FTIR (Fourier Transform Infrared Spectroscopy) sono state usate per la determinazione della composizione superficiale. La caratterizzazione dei campioni è stata completata dalla spettroscopia Raman. I risultati ottenuti hanno mostrato la potenzialità dei metodi di sintesi proposti nell’ottenere il controllo di importanti proprietà dei materiali senza sfruttare l’uso di leganti superficiali, e hanno consentito lo studio della chimica della superficie esposta delle nanoparticelle sintetizzate.

Come è ormai ben noto i livelli di anidride carbonica nell’atmosfera stanno costantemente aumentando a causa delle attività umane contribuendo ogni giorno di più all’incremento dell’effetto serra la cui lotta rappresenta attualmente una delle più grandi sfide per la società contemporanea. In questo contesto la conversione elettrocatalitica dellaCO2 rappresenta un’interessante approccio a questo problema dal momento che permette di pensare a quello che fino ad oggi non può essere considerato altrimenti se non un prodotto di scarto, come ad una nuova ed interessante risorsa virtualmente ad impattoambientale nullo. Attraverso i processi riduttivi proposti in questo lavoro è infatti possibile accedere a molecole di grande importanza industriale ed energetica e dall’elevato valore aggiunto come ad esempio acido formico, metano e Syngas (una miscela di CO ed H2 alla base dei processi industriali di tipo Fisher-Tropsch utilizzati per la sintesi di idrocarburi). Tra i molti metalli che manifestano attività catalitica in questi processi il rame occupa sicuramente un ruolo centrale. Il lavoro principale esposto in questa tesi è infatti incentrato nello sviluppo di tecniche nuove ed innovative per incrementare la selettività di questo metallo attraverso procedure di nanostrutturazione e funzionalizzazione con diverse specie metalliche. Una delle vie maggiormente percorsa consiste nella formazione controllata di ossidi di rame sottoposti poi ad una successiva riduzione nello stesso ambiente di CO2R. Numerose strategie sono state riportate in letteratura a questo proposito. Sulla base di questi lavori è descritto un metodo puramente elettrochimico ed innovativo per la sintesi di interfacce rame-indio dalle ottime proprietà catalitiche. Questo tipo di catodi è stato studiato nel dettaglio e caratterizzato morfologicamente ed elettrochimicamente permettendo di poter osservare efficienze riduttive in grado di eccedere il 70% in solo monossido di carbonio con una conseguente selettività verso il Syngas attorno al 100% dipendentemente dal potenziale applicato e dalla quantità di indio fissata sulla superficie. La letteratura in merito ad elettrodi Cu-In è tuttora molto limitata, in particolare i catodi Cu-In descritti in questa tesi sono in grado di produrre selettivamente miscele di Syngas ideali per la sintesi di metanolo ed aldeidi (oltre che di idrocarburi a più elevato peso molecolare) a potenziali particolarmente accessibili contenuti in una finestra che va da -1.3V a -1.6V vs SCE con delle correnti associate compatibili per applicazioni su più ampia scala. Durante questo lavoro di ricerca sono stati sperimentati anche diversi altri metalli per la funzionalizzazione delle interfacce di rame, in particolare risultati interessanti sono stati ottenuti anche con la deposizione di Cerio, che ha modificato la selettività verso la produzione del metano con efficienze massime osservate attorno al 40%. Inoltre grazie ad una collaborazione con l’università di Milano è stato possibile studiare le caratteristiche di particolari catodi in oro depositati su FTO tramite PLD che si sono dimostrati particolarmente selettivi nei confronti del CO e dell’acido formico. La deposizione PLD ha infatti permesso di accedere a nuove e peculiari nano strutture non ottenibili tramite le tecniche tradizionali di deposizione. Sono infatti descritte interfacce decorate da nanostrutture di forma colonnare e porosa, quest’ultima particolarmente selettiva per miscele di Syngas 40% CO e 60% H2 (ideale per la sintesi di idrocarburi a vario range di pesi molecolari) prodotte a potenziali relativamente blandi attorno a -1.1V vs SCE. Il lavoro contenuto in questa tesi di dottorato è stato oggetto di pubblicazioni su riviste di settore ed ha portato al deposito di un brevetto italiano ed europeo grazie alla collaborazione con realtà industriali interessate all’applicazione di questo tipo di tecnologie.
The level of carbon dioxide in the atmosphere is constantly growing mainly due to anthropogenic activities causing the well known greenhouse effect that represent one of the greatest challenges to contemporary society. On this regard electroreduction of CO2 represents an appealing strategy to rethink a waste and an environmentally dangerous product as an innovative feedstock for the formation of value-added carbon neutral compounds. Among metal electrodes able to catalyze such process, copper plays a central role. The work of this thesis focuses into the development of new and innovative strategies aimed at tuning Cu selectivity comprise nanostructuring and alloying with heterometals. One of the more investigated nanostructuring strategies consist in the controlled formation of Cu oxides, which then undergo to a re-reduction in CO2R conditions. Several strategies have been reported for the oxidation of Cu foils’ surface. In this contribution, are reported straightforward electrochemical methods for the formation of Cu-In interfaces. The latter were fully characterized and then used as cathodes for CO2 electroreduction, leading to the selective production of Syngas with efficiencies that exceed 70% only for carbon monoxide, whose composition varies upon changing the applied bias and Indium content. Literature examples of copper-indium nanostructured catalysts for CO2R are now still limited.[5] In particular, the proposed Cu-In cathode in this work is able to efficiently catalyze gaseous mixtures compatible with the Fischer-Tropsch synthesis of methanol or aldehydes, that are produced at a relative low (i.e. -1.3 V vs SCE up to -1.6 V vs SCE) applied bias with the development of interesting stable current densities. During this research work was investigated the co-functionalization of also other metallic species than indium such as Cerium that was able to drive the selectivity of the copper interface towards an enhanced production of methane (up to 40% in faradic efficiency). Furthermore, thanks to a collaboration with the Milan University a detailed study of gold nanostructures deposited via PLD on FTO substrates was also performed leading to the development of a particularly efficient electrocatalyst for the production of Syngas and formic acid. In particular with the pulsed laser deposition it was possible to generate particular nanostructures that are not achievable by standard synthetic methodologies, two of these were found to be interesting in terms of catalytic performance. In fact the study was centered into the description of a columnar cathodic interface and a “foam” like surface, the latter was the most interesting due to it’s selectivity towards a Syngas mixture of 40% CO and 60% H2 at a low applied bias of -1.1V vs SCE, ideal for the synthesis of hydrocarbons with a wide range of molecular weight. The work described in this thesis leads to the publications in multiple scientific journal and the deposition of an Italian and European patent due to the collaboration of interested industries in the application of this know how, on this regard also a lot of specific studies were carried out with the aim of clarify the technoeconomic potential of this technology and the possibility to scale up from the laboratory scale to a plant simulation not only in theory but also with the design and development of larger electrochemical cells and setup.

Over the last decades optical sensors assumed a major role in the analytical field. In particular, plasmonics, that is the branch of sensors that exploits the excitation of surface plasmons due to the collective oscillation of the electrons in the conduction band, allowed to achieve excellent results in terms of detection limits and accuracy. This kind of sensors exploits the interaction between the metal nanoparticles that possess plasmonic properties (Au, Ag, Cu) and an interacting molecules. In fact, under resonance conditions, a strong localized electric field is produced on the surface of the nanostructure, that, by the interaction with a molecule located at the interface, may amplify or attenuate its optical properties. In this thesis various methods of synthesis of substrates based on silver nanostructures, ordered or otherwise, as thin films for applications in Raman and UV-Visible (LSPR) sensors were explored. The samples were characterized in terms of chemical, physical and morphological properties and were systematically tested to assess their efficiency and quality. In the first part of the thesis, commercially available digital versatile discs (DVDs) were used to fabricate SERS easy&cheap substrates. DVDs contain a silver-coated spiral distribution of rectangular-shaped grooves (AgDVD): for the first time, they were used to produce surface-enhanced Raman scattering (SERS) substrates by electrochemical deposition of silver nanoparticles (AgNPs@AgDVD). The overall procedure only requires cheap and widely available materials and can be easily accomplished. Scanning electron microscopy images of AgNPs@AgDVD revealed that small Ag NPs (average diameter about 15 nm) are present within the valleys of AgDVD, whereas over the ridges, the Ag NPs are bigger, more densely packed and with a dendrite-like morphology somewhere. The SERS properties of these substrates were studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample-to-sample repeatability. It turned out that high SERS EF and good reproducibility are both fulfilled. As for repeatability, remarkably better results than typical literature values were achieved. Such an easy&cheap preparation along with efficient SERS properties make DVD-derived SERS substrates very good candidates for the development of convenient and disposable sensing platforms. In the second part of the thesis, Ag nanostructures (Ag NSs) were grown by AC electrodeposition on Anodic Alumina Oxide (AAO) connected membranes acting as templates. Depending on the thickness of the template and on the voltage applied during the growth process, different Ag NSs with different optical properties were obtained. When ca 1 µm thick AAO membranes are used, the Ag NSs consist in Ag nanorods, at the bottom of the pores, and Ag nanotubes (Ag NTs) departing from the nanorods and filling the pores almost for the whole length. When ca 3 µm thick AAO membranes are used, the nanostructures are Ag spheroids, at the bottom of the pores, and Ag nanowires (Ag NWs) that do not reach the upper part of the alumina pores. The samples were characterized by Angle Resolved X-Ray Photoelectron Spectroscopy, Scanning Electron Microscopy measurements and UV-Vis and Raman Spectroscopies. In the case of µm thick AAO membranes, a simple NaOH etching procedure, followed by sonication in ethanol, allows one to obtain an exposed ordered array of Ag nanorods (Ag NRs), suitable for Surface Enhanced Raman Spectroscopy, while in the other case (3 µm thick AAO membranes) the sample can be used in Localized Surface Plasmon Resonance sensing. The AC electrodeposition procedure was extended to copper in order to obtain Cu NSs to be used as sacrificial anodes for the subsequent deposition of Ag. Also in this case the samples were chemically, physically and morphologically characterized and finally tested as sensors. Finally, SERS substrates were produced by electrophoretic deposition (EPD) of Ag NPs. The Ag NPs colloidal suspension was prepared by simply using [Ag(NH3)2]+ as silver source and glucose as reducing agent. This simple “green synthesis” allows to obtain an Ag NPs suspension with a good dimensional monodispersion and good optical performances. The obtained Ag NPs are characterized by a negative z-potential and therefore suitable for EPD. The stability of the suspension, obtained by this simple way, is guaranteed by the “protection” of the adsorbed gluconic acid on the Ag NPs surface, that forms during the redox reaction between the [Ag(NH3)2]+ complex and glucose. Because of the gluconic acid protection the Ag NPs maintain their original dimension even after the EPD. Moreover, molecules that bind more strongly to Ag, like thiols or amines, can easily substitute the gluconic acid adsorbed on the Ag NPs surface (weak interaction). Such samples were characterized by XPS, SEM, UV-Vis and finally tested as SERS substrates
Nel corso degli ultimi decenni la sensoristica ottica ha assunto un ruolo di primaria importanza in campo analitico. In particolare, la plasmonica, ovvero quella branca della sensoristica che sfrutta l’eccitazione dei plasmoni di superficie, dovuta all’oscillazione collettiva degli elettroni in banda di conduzione, ha permesso di raggiungere risultati eccellenti in termini di limiti di rivelabilità e accuratezza. Questo tipo di sensoristica sfrutta l’interazione tra le nanoparticelle metalliche che godono di proprietà plasmoniche (Au, Ag, Cu) e le molecole interagenti. Infatti, in condizioni di risonanza, si sviluppa sulla superficie della nanostruttura un fortissimo campo elettrico localizzato che, interagendo con una molecola posizionata all’interfaccia, può amplificare o attenuare le sue proprietà ottiche. In questo tesi sono state esplorate diverse metodiche di sintesi di substrati basati su nanostrutture di argento, ordinate e non, su film sottile per applicazioni in Sensoristica Raman e UV-Visibile (LSPR). I campioni sono stati caratterizzati dal punto di vista chimico, fisico e morfologico e sono stati testati sistematicamente per valutarne l’efficienza e la qualità. Nella prima fase della tesi sono stati preparati dei campioni su substrati di basso costo e facilmente reperibili. A tale scopo sono stati utilizzati dei DVD scrivibili disponibili in commercio, che contengono una distribuzione a spirale di scanalature di forma rettangolare ricoperte da un film sottile di Ag (AgDVD): per la prima volta sono stati usati per produrre substrati per surface-enhanced Raman scattering (SERS) tramite deposizione elettrochimica di nanoparticelle di Ag (AgNPs@AgDVD). La procedura generale richiede solo materiali economici, ampiamente disponibili e può essere facilmente realizzata. Le immagini effettuate tramite Scanning electron microscopy (SEM) mostrano che nelle valli dell’AgDVD sono presenti piccole nanoparticelle di Ag (Ag NPs, diametro medio di circa 15 nm), mentre sulle creste, le Ag NPs sono più grandi, più densamente impaccate e in alcune zone presentano una morfologia di tipo dendritico. Le proprietà SERS di questi substrati sono state studiate in termini di enhancement factor (EF), di ripetitibilità da punto a punto e di riproducibilità da campione a campione. Si è scoperto che i requisiti di alti SERS EF e di una buona riproducibilità sono entrambi soddisfatti. Per quanto riguarda la ripetibilità, sono stati raggiunti risultati di gran lunga migliori rispetto ai valori tipici riportati in letteratura. Tale preparazione easy&cheap con efficienti proprietà SERS rende i substrati SERS derivati dai DVD ottimi candidati per lo sviluppo di sensori convenienti e monouso. Nella seconda fase della tesi sono state cresciute nanostrutture di Ag (Ag NSs) mediante elettodeposizione in corrente alternata utilizzando come template delle membrane di allumina nanoporosa (AAO) direttamente connesse al substrato metallico. A seconda dello spessore del template e del voltaggio applicato durante il processo di crescita è possibile ottenere differenti Ag NSs con differenti proprietà ottiche. Quando si usano AAO da circa 1 µm di spessore, le nanostrutture che si formano sono nanobarre di Ag (Ag NRs), alla base dei pori, e nanotubi di Ag (Ag NTs) che partono dalle nanobarre e riempiono il poro in quasi tutta la sua lughezza. Quando si usano AAO da circa 3 µm di spessore, le nanostrutture che si formano sono sferoidi, alla base dei pori, e nanofili di Ag (Ag NWs) che non raggiungono la parte superiore dei pori dell’allumina. Nel caso delle AAO da circa 1 µm di spessore, un semplice trattamento di erosione in NaOH, seguito da sonicazione in etanolo, permette di ottenere una disposizione ordinata (array) di Ag NRs, adatta per il SERS, mentre nell’altro caso (per le AAO da 3 µm di spessore) i campioni possono essere utilizzati per misure di Localized Surface Plasmon Resonance sensing (LSPR). La procedura di elettrodeposizione in corrente alternata è stata estesa anche al rame al fine di ottenere Cu NSs da utilizzare come anodi sacrificali per la successiva deposizione di Ag. Anche in questo caso i campioni sono stati caratterizzati chimicamente, fisicamente e morfologicamente ed infine testati come sensori. Infine sono stati preparati dei substrati SERS tramite deposizione elettroforetica (EPD) di Ag NPs. La sospensione colloidale di Ag NPs è stata preparata utilizzando semplicemente [Ag(NH3)2]+ come precursore d'argento e glucosio come agente riducente. Questa semplice "sintesi verde" permette di ottenere una sospensione di Ag NPs con una buona monodispersione dimensionale e buone prestazioni ottiche. Le Ag NPs ottenute sono caratterizzate da un potenziale z negativo e quindi adatte per l’EPD. La stabilità della sospensione, ottenuta in questo modo semplice, è garantita dalla "protezione" offerta dall’acido gluconico adsorbito sulle Ag NPs, che si forma durante la reazione redox tra il complesso [Ag(NH3)2]+ e il glucosio. Grazie alla protezione offerta dall’acido gluconico le Ag NPs mantengono la loro dimensione originaria anche dopo l’EPD. Inoltre, le molecole che si legano più fortemente all’Ag, come tioli o ammine, possono facilmente sostituire l'acido gluconico adsorbito sulla superficie delle Ag NPs (interazione debole). Tali campioni sono stati caratterizzati tramite XPS, SEM, UV-Vis e infine sono stati testati come substrati SERS

ZnO based materials, such as Zn1-xTMxO (TM = Mn, Co, Cu) nanopowders, were synthesised by a Sol gel route to investigate their properties in three fields: catalysis, optics and magnetism. These materials were characterised by complementary techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and UV-Vis Spectroscopy. The fine structure and electronic properties of these nanomaterials were studied by X-ray Absorption Spectroscopy (XAS) and Electron Paramagnetic Resonance (EPR). These techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the functionality of the system. The catalytic performance of undoped and Cu-doped ZnO nanosystems were tested with respect to the Methanol Steam Reforming (MSR) reaction. Contrary to what is generally accepted in literature, the results obtained in this study demonstrate that ZnO also plays a prominent role in this catalytic process. The structure–activity relationship of ZnO and copper-doped ZnO catalysts described in this work give an insight into the effective function of each component which is vital to enable the rational design of improved catalysts. The luminescence properties of the doped Zn1-xTMxO nanopowders were investigated with X-ray Excited Optical Luminescence (XEOL) techniques: these experiments provided a better understanding of the relationship between the electronic structure of the systems and their properties. Results showed how it is possible to manipulate the luminescence of ZnO grown by Sol gel by modifying synthesis conditions – i.e. the annealing temperature and the nature and concentration of the transition metal ion. Finally, preliminary results were presented on the materials' magnetic properties, obtained by SQUID (Superconducting Quantum Interference Devices) magnetometry, where the coexistence of different contributions has been detected. Even though further characterisation is still needed, this study is a step towards the determination of the nature of magnetic interactions in such systems, of which there has been considerable debate in the scientific community.
Materiali a base di ZnO, in particolare nano-polveri di Zn1-xTMxO (TM = Mn, Co, Cu), sono stati sintetizzati via Sol gel per studiarne le proprietà in tre diversi campi applicativi quali la catalisi, l’ottica ed il magnetismo. Tali materiali sono stati caratterizzati utilizzando diverse tecniche, complementari tra loro, quali X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) e UV-Vis Spectroscopy. X-ray Absorption Spectroscopy (XAS) ed Electron Paramagnetic Resonance (EPR) vengono invece impiegate per studiare le proprietà elettroniche e di struttura fine delle nano-polveri. Tali caratterizzazioni si sono dimostrate fondamentali per la comprensione delle proprietà del sistema ed, in particolare, per cercare di identificare le interazioni sussistenti tra struttura, composizione, morfologia dei materiali e la loro capacità di espletare una determinata funzionalità. Nano-polveri di ZnO tal quali e drogate con ioni rame vengono testate come catalizzatori nella reazione di Steam Reforming del metanolo. I risultati ottenuti in questo studio dimostrano il ruolo attivo dell’ossido di zinco nel processo catalitico, contrariamente a quanto solitamente accettato in letteratura. La relazione sussistente tra struttura-attività nei catalizzatori a base di ZnO permette di ottenere informazioni circa l’effettiva funzione di ogni componente, aspetto di estrema importanza per la progettazione razionale di catalizzatori con elevate performance. Le proprietà di luminescenza dei sistemi drogati Zn1-xTMxO vengono studiate mediante spettroscopia X-ray Excited Optical Luminescence (XEOL); tali esperimenti forniscono una migliore comprensione del rapporto che sussiste tra la struttura elettronica dei sistemi in esame e le loro proprietà di emissione. I risultati mostrano come sia possibile modulare la luminescenza di ZnO prodotto via Sol gel modificando le condizioni di sintesi – i.e. temperatura di trattamento, natura e concentrazione del metallo di transizione utilizzato come drogante. Infine, risultati preliminari sulle proprietà magnetiche dei materiali ottenuti mediante SQUID magnetometer (Superconducting Quantum Interference Devices) hanno rivelato la coesistenza di diversi contributi magnetici. Nonostante ulteriori caratterizzazioni siano sicuramente necessarie, questo studio si è rivelato un passo avanti verso una comprensione della natura delle interazioni magnetiche in tali sistemi, da tempo causa di vivace dibattito nella comunità scientifica.

Im Fokus dieser Arbeit stand die Methode Zwillingspolymerisation zur Synthese organisch-anorganischer Hybridmaterialien. Die simultane Zwillingspolymerisation wird als neues Konzept zur gezielten Herstellung homogener, nanostrukturierter Hybridmaterialien unterschiedlicher Zusammensetzung vorgestellt. Hierfür wurden die Zwillingsmonomere 2,2’-Spirobi[4H-1,3,2-benzodioxasilin] und 2,2 Dimethyl-4H-1,3,2-benzodioxasilin in einem Arbeitsschritt gemeinsam polymerisiert. Die erhaltenen Phenolharz-Siliciumdioxid/Dimethylsiloxan-Hybridmaterialien weisen aufgrund einstellbarer Syntheseparameter unterschiedliche Eigenschaftsprofile auf, die systematisch analysiert wurden. Die Charakterisierung der Produkte erfolgte mit Hilfe der Festkörper-NMR-Spektroskopie, Elektronenmikroskopie, DSC, TGA-MS, sowie durch Extraktionsversuche und die Erzeugung und Analyse poröser Materialien. Neben der simultanen Zwillingspolymerisation wird die Synthese, Charakterisierung und thermisch induzierte Polymerisation literaturunbekannter Silicium-Spiroverbindungen mit einfach- oder zweifach substituierter Salicylalkohol-Einheit beschrieben. Hierbei wurden nanostrukturierte Hybridmaterialien mit teils hohem löslichen Anteil erhalten. Die Produktbildung wird in Abhängigkeit von der Entstehung und Weiterreaktion gefundener Chinonmethid-Strukturen diskutiert.

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TiTanate NanoTubes (TTNT) were synthesized by hydrothermal alkali treatment of TiO2 anatase followed by repeated washings with distinct degrees of proton exchange. TTNT samples with different sodium contents were characterized, as synthesized and after heattreatment (200-800?C), by X-ray diffraction, scanning and transmission electron microscopy, electron diffraction, thermal analysis, nitrogen adsorption and spectroscopic techniques like FTIR and UV-Vis diffuse reflectance. It was demonstrated that TTNTs consist of trititanate structure with general formula NaxH2−xTi3O7?nH2O, retaining interlayer water in its multiwalled structure. The removal of sodium reduces the amount of water and contracts the interlayer space leading, combined with other factors, to increased specific surface area and mesopore volume. TTNTs are mesoporous materials with two main contributions: pores smaller than 10 nm due to the inner volume of nanotubes and larger pores within 5-60 nm attributed to the interparticles space. Chemical composition and crystal structure of TTNTs do not depend on the average crystal size of the precursor TiO2-anatase, but this parameter affects significantly the morphology and textural properties of the nanostructured product. Such dependence has been rationalized using a dissolution-recrystallization mechanism, which takes into account the dissolution rate of the starting anatase and its influence on the relative rates of growth and curving of intermediate nanosheets. The thermal stability of TTNT is defined by the sodium content and in a lower extent by the crystallinity of the starting anatase. It has been demonstrated that after losing interlayer water within the range 100-200?C, TTNT transforms, at least partially, into an intermediate hexatitanate NaxH2−xTi6O13 still retaining the nanotubular morphology. Further thermal transformation of the nanostructured tri- and hexatitanates occurs at higher or lower temperature and follows different routes depending on the sodium content in the structure. At high sodium load (water washed samples) they sinter and grow towards bigger crystals of Na2Ti3O7 and Na2Ti6O13 in the form of rods and ribbons. In contrast, protonated TTNTs evolve to nanotubes of TiO2(B), which easily convert to anatase nanorods above 400?C. Besides hydroxyls and Lewis acidity typical of titanium oxides, TTNTs show a small contribution of protonic acidity capable of coordinating with pyridine at 150?C, which is lost after calcination and conversion into anatase. The isoeletric point of TTNTs was measured within the range 2.5-4.0, indicating behavior of a weak acid. Despite displaying semiconductor characteristics exhibiting typical absorption in the UV-Vis spectrum with estimated bandgap energy slightly higher than that of its TiO2 precursor, TTNTs showed very low performance in the photocatalytic degradation of cationic and anionic dyes. It was concluded that the basic reason resides in its layered titanate structure, which in comparison with the TiO2 form would be more prone to the so undesired electron-hole pair recombination, thus inhibiting the photooxidation reactions. After calcination of the protonated TTNT into anatase nanorods, the photocatalytic activity improved but not to the same level as that exhibited by its precursor anatase
Titanatos nanoestruturados, particularmente TiTanatos NanoTubulares (TTNT), foram sintetizados por tratamento hidrot?rmico alcalino de TiO2-anat?sio seguido de repetidas lavagens com diversos graus de troca prot?nica. Amostras de TTNT com diferentes teores de s?dio foram caracterizadas na forma de p? seco e ap?s calcina??o (200-800?C) por difra??o de raios-X, microscopia eletr?nica de varredura e transmiss?o, difra??o de el?trons, an?lise t?rmica, adsor??o de nitrog?nio e t?cnicas espectrosc?picas de infravermelho e de reflet?ncia difusa no UV-Vis?vel. Demonstrou-se que tais materiais de paredes multilamelares s?o trititanatos de f?rmula geral NaxH2−xTi3O7?nH2O, retendo ?gua entre as lamelas. A remo??o de s?dio da estrutura reduz a quantidade de ?gua contraindo o espa?o interlamelar levando, combinado a outros fatores, ao aumento da ?rea e do volume de poros espec?ficos. Os TTNTs s?o materiais mesoporosos com duas contribui??es principais: poros menores que 10 nm devido ao volume interno dos nanotubos e poros entre 5 e 60 nm devido aos espa?os interpart?cula. A composi??o qu?mica e a estrutura cristalina do TTNT n?o dependem do tamanho de cristalito do TiO2-anat?sio precursor, todavia este par?metro afeta significativamente a morfologia e as caracter?sticas texturais do produto nanoestruturado. Tal depend?ncia foi racionalizada atrav?s de um mecanismo de dissolu??o-recristaliza??o que leva em conta a velocidade de dissolu??o do TiO2 de partida e sua influ?ncia sobre a taxa de crescimento de nanofolhas intermedi?rias em rela??o ? taxa de seu curvamento a nanotubos. A estabilidade t?rmica do TTNT ? definida pelo teor de s?dio e em pequena extens?o pelo tipo de anat?sio de partida. Foi demonstrado que o TTNT ap?s perder a ?gua intercalada entre 100 e 200?C se transforma pelo menos parcialmente num hexatitanato NaxH2−xTi6O13 intermedi?rio ainda nanotubular. A transforma??o t?rmica do tri- e hexatitanato nanoestruturados ocorre em maior ou menor temperatura e segue diferentes rotas dependendo do teor de s?dio. No caso de alto s?dio sinterizam e crescem at? grandes cristais de Na2Ti3O7 e Na2Ti6O13 na forma de bast?es e fitas acima de 600?C. No caso da amostra protonizada evoluem para nanotubos de TiO2(B) que facilmente se convertem em nanobast?es de anat?sio acima de 400?C. Al?m de hidroxilas e acidez de Lewis t?picos dos ?xidos de tit?nio, os TTNTs apresentam uma pequena contribui??o de acidez prot?nica capaz de se coordenar com a piridina a 150?C, e que ? perdida ap?s sua calcina??o e transforma??o ? anat?sio. O ponto isoel?trico do TTNT variou dentro da faixa 2,5- 4,0, indicando o comportamento de um ?cido fraco. Apesar de se revelar um semicondutor exibindo banda de absor??o t?pica no espectro de UV-vis?vel com energia de bandgap ligeiramente superior ao do respectivo TiO2-anat?sio precursor, os TTNTs apresentaram baixo desempenho fotocatal?tico na degrada??o de corantes cati?nico e ani?nico. Concluiu-se que a causa fundamental reside em sua estrutura de titanato lamelar que, em rela??o ? forma TiO2, apresentaria maior probabilidade de recombina??o do par el?tron-lacuna (e-/h+), inibindo as rea??es de fotoxida??o. A transforma??o do TTNT prot?nico ? nanobast?es de anat?sio melhorou a atividade fotocatal?tica, por?m ainda sem atingir o mesmo desempenho do TiO2-anat?sio precursor

This dissertation combines coordination and materials chemistry studies. The oxide materials and nanoparticles formed are produced from decomposition of known or brand new coordination compounds. Chapters I and II discuss the synthesis, characterization, and functionalization of shaped nanoparticles. Fe(II)(O2CH)2 and Mn(II)(O 2CH)2 were used as precursors for the controlled synthesis of wustite (FexO), manganosite (MnO), and iron-manganese (Fe 1-yMnyO) nanocrystals with non-thermodynamic shapes, such as concave cubes, nanocrosses, and 'dogbones'. An acid-base surfactant system under thermal conditions and atmospheric pressure was employed. The nanoparticle morphology was studied as a function of reaction parameters, of which water and surfactants were found most critical for shape control. Shaping progress is described as a function of crystal defects and dissolution-precipitation processes. Nanoparticles were successfully oxidized to the magnetic phases, Fe3O4 (magnetite) and Mn3O4 (hausmannite), while retaining original shape. Iron oxide-gold and manganese oxide-gold nanoshells were produced, and these maintained the magnetic behavior of magnetite and hausmannite, as demonstrated by magnetic measurements.

Surfaces and interfaces are of fundamental importance from the nucleation to growth of crystals formed under different conditions such as vapor phase, liquid phase including biomineralisation conditions. Recently there is lot of interest in controlling the shape of nanoparticles during the synthesis due to their excellent shape dependent properties. Understanding the role of surfaces and interfaces is vital for such shapecontrolled synthesis of nanomaterials. On the surface, coordination number, structure, density and composition are different from that of bulk and hence the properties are completely different in the surfaces and interfaces of any crystalline material. Especially when the length scale become nanoscale, the surface and interface play a dominant important role and leads to several new and interesting phenomena. In this dissertation, the role of surfaces and interfaces on the synthesis and the properties of inorganic functional nanostructures have been studied. The work primarily relies on basic chemistry to synthesize nanostructures that brings the importance of surfaces/interfaces into the picture. Though several basic characterization techniques have been used, electron microscopy has been the emphasis and has been used extensively through the work to probe and explore the materials for characterizing the structures over a variety of length scales. The entire thesis based on the results and findings obtained from the present investigation are organized as follows: Chapter1 gives a general introduction to the surfaces and interfaces to create a background for the investigation. This emphasizes the role of surfaces and interfaces in several aspects starting from nucleation, growth to the properties of inorganic crystals. It gives some exposure in to the different type of surface phenomenon which is common in nanoscale materials. Chapter 2 deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter 3 deals with predicting the morphology of 2D nanostructures by combining the crystal growth theory into chemical thermodynamics. Morphology diagrams have been developed for Au, Ag, Pt and Pd to predict conditions under which two-dimensional nanostructures form as a result of a chemical reaction. In addition, it provides the general understanding of shape control in 2D nanostructures with atomistic mechanism. The validity of the morphology diagram has been tested for various noble metals by carrying out critical experiments. As a result, 2D nanostructures of metals projecting the lowest energy facet resulted in a complete novel way in the absence of any capping/reducing agents. Chapter 4 deals with predicting the formation of 2D nanostructures of inorganic crystals formed as a result of precipitation reaction. Morphology diagram has been developed for the case of hydroxyapatite, an inorganic part of the human bone. This answers some of the long standing question related to the shape of the HA crystals formed in the bone by biomineralisation. The generality of the method has been tested to few other inorganic crystals such as CaCO3, ZnO and CuO formed through precipitation reaction. The key finding of the above two chapter is that the low driving force of the chemical reactions results in two dimensional nanostructures. On contrary, high chemical driving force combined with the optimum zeta potential results in porous aggregate of nanoparticles. Chapter 5 discusses the formation of porous clusters of metals and ceramics at specific conditions. The mechanism behind the formation of monodisperse aggregates are investigated based on the interaction energies of nanoparticles in aqueous medium. This chapter reveals the role of surface charge and the surface energy in controlling the stability of nanoparticles in aqueous medium. In addition, it provides the simple methodology to produce well controlled porous clusters by exploiting the competition between surface charge and surface energy during the aggregation. The application of the porous clusters of Pt has been tested for methanol oxidation which is essential for fuel cell applications. Chapter 6 deals with the development of porous biphasic scaffolds through the morphology transition of nanorods. Rod shape is not stable when subjected to high temperature due to instability and spherodisation takes place to minimize the surface energy. Here in this chapter, by exploiting spherodisation along with the phase transition, highly interconnected porous structure of hydroxyapatite and tricalcium phosphate is achieved. Combined with the morphology transition, by adding naphthalene as a template, the possibility of achieving hierarchical porous structure also presented. The mechanical strength of the biphasic porous scaffold has been tested by microindentation. Mechanical properties of apatite are generally poor and there are lots of efforts to improve the mechanical properties apatite by the composite approach. Chapter 7 deals with the HA-Alumina and HA-TCP composites. In spite of much attention given to the mechanical properties of the composites, the interfacial phenomenon that takes place between the components of the nanocomposite has not been studied in detail. In the present study, interfacial reactions in hydroxyapatite-alumina nanocomposites have been investigated and new reaction mechanism also proposed. The degradation of densification process has been observed for the HATCP composites due to the creation of porous interface between HA crystals and TCP matrix. Mechanical properties of these two composites have been studied using microindentation. The mechanical properties of HA and TCP single crystals are important for developing the biphasic composites with reliable mechanical properties. Chapter8deals with the mechanical behavior of hydroxyapatite and tricalcium phosphate single crystals. The mechanical properties of HA and TCP have been studied by performing nanoand microindentation on specific crystallographic facets. In case of hydroxyapatite, the anisotropy in mechanical properties has been explored by performing indentation on its prism and basal planes. Nanoscale plasticity is observed in both HA and TCP crystals which arise due to the easy movement of surface atoms with lesser coordination compared to the bulk. Nanoindentation has been performed in the calciumdeficient HA platelets provides important clues about the role of calcium deficiency on the mechanical behavior of bone and has implications for the properties of osteoporotic bones.

Surfaces and interfaces are of fundamental importance from the nucleation to growth of crystals formed under different conditions such as vapor phase, liquid phase including biomineralisation conditions. Recently there is lot of interest in controlling the shape of nanoparticles during the synthesis due to their excellent shape dependent properties. Understanding the role of surfaces and interfaces is vital for such shapecontrolled synthesis of nanomaterials. On the surface, coordination number, structure, density and composition are different from that of bulk and hence the properties are completely different in the surfaces and interfaces of any crystalline material. Especially when the length scale become nanoscale, the surface and interface play a dominant important role and leads to several new and interesting phenomena. In this dissertation, the role of surfaces and interfaces on the synthesis and the properties of inorganic functional nanostructures have been studied. The work primarily relies on basic chemistry to synthesize nanostructures that brings the importance of surfaces/interfaces into the picture. Though several basic characterization techniques have been used, electron microscopy has been the emphasis and has been used extensively through the work to probe and explore the materials for characterizing the structures over a variety of length scales. The entire thesis based on the results and findings obtained from the present investigation are organized as follows: Chapter1 gives a general introduction to the surfaces and interfaces to create a background for the investigation. This emphasizes the role of surfaces and interfaces in several aspects starting from nucleation, growth to the properties of inorganic crystals. It gives some exposure in to the different type of surface phenomenon which is common in nanoscale materials. Chapter 2 deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter 3 deals with predicting the morphology of 2D nanostructures by combining the crystal growth theory into chemical thermodynamics. Morphology diagrams have been developed for Au, Ag, Pt and Pd to predict conditions under which two-dimensional nanostructures form as a result of a chemical reaction. In addition, it provides the general understanding of shape control in 2D nanostructures with atomistic mechanism. The validity of the morphology diagram has been tested for various noble metals by carrying out critical experiments. As a result, 2D nanostructures of metals projecting the lowest energy facet resulted in a complete novel way in the absence of any capping/reducing agents. Chapter 4 deals with predicting the formation of 2D nanostructures of inorganic crystals formed as a result of precipitation reaction. Morphology diagram has been developed for the case of hydroxyapatite, an inorganic part of the human bone. This answers some of the long standing question related to the shape of the HA crystals formed in the bone by biomineralisation. The generality of the method has been tested to few other inorganic crystals such as CaCO3, ZnO and CuO formed through precipitation reaction. The key finding of the above two chapter is that the low driving force of the chemical reactions results in two dimensional nanostructures. On contrary, high chemical driving force combined with the optimum zeta potential results in porous aggregate of nanoparticles. Chapter 5 discusses the formation of porous clusters of metals and ceramics at specific conditions. The mechanism behind the formation of monodisperse aggregates are investigated based on the interaction energies of nanoparticles in aqueous medium. This chapter reveals the role of surface charge and the surface energy in controlling the stability of nanoparticles in aqueous medium. In addition, it provides the simple methodology to produce well controlled porous clusters by exploiting the competition between surface charge and surface energy during the aggregation. The application of the porous clusters of Pt has been tested for methanol oxidation which is essential for fuel cell applications. Chapter 6 deals with the development of porous biphasic scaffolds through the morphology transition of nanorods. Rod shape is not stable when subjected to high temperature due to instability and spherodisation takes place to minimize the surface energy. Here in this chapter, by exploiting spherodisation along with the phase transition, highly interconnected porous structure of hydroxyapatite and tricalcium phosphate is achieved. Combined with the morphology transition, by adding naphthalene as a template, the possibility of achieving hierarchical porous structure also presented. The mechanical strength of the biphasic porous scaffold has been tested by microindentation. Mechanical properties of apatite are generally poor and there are lots of efforts to improve the mechanical properties apatite by the composite approach. Chapter 7 deals with the HA-Alumina and HA-TCP composites. In spite of much attention given to the mechanical properties of the composites, the interfacial phenomenon that takes place between the components of the nanocomposite has not been studied in detail. In the present study, interfacial reactions in hydroxyapatite-alumina nanocomposites have been investigated and new reaction mechanism also proposed. The degradation of densification process has been observed for the HATCP composites due to the creation of porous interface between HA crystals and TCP matrix. Mechanical properties of these two composites have been studied using microindentation. The mechanical properties of HA and TCP single crystals are important for developing the biphasic composites with reliable mechanical properties. Chapter8deals with the mechanical behavior of hydroxyapatite and tricalcium phosphate single crystals. The mechanical properties of HA and TCP have been studied by performing nanoand microindentation on specific crystallographic facets. In case of hydroxyapatite, the anisotropy in mechanical properties has been explored by performing indentation on its prism and basal planes. Nanoscale plasticity is observed in both HA and TCP crystals which arise due to the easy movement of surface atoms with lesser coordination compared to the bulk. Nanoindentation has been performed in the calciumdeficient HA platelets provides important clues about the role of calcium deficiency on the mechanical behavior of bone and has implications for the properties of osteoporotic bones.

This thesis details the synthesis and characterization of anisotropic cadmium and lead sulfide nanostructures from single-source molecular precursors. Six new precursors were synthesized for cadmium and lead sulfide each, by the reaction of the appropriate metal acetate with picolinic (HPic), 2,6-dipicolinic (H2dipic) or salicylic acid (H2sal) followed by the addition of thiourea (th) or thiosemicarbazide (ths). The precursors for CdS are [Cd(Hsal)2(tu)2] (Cd1a), [Cd(Hsal) 2(ths)2]·nH2O (Cd1b), [Cd(pic) 2(tu)2]·0.5H2O (Cd2a), [Cd(pic) 2(ths)2]·2H2O (Cd2b), [Cd(dipic)(tu) 2] (Cd3a) and [Cd(dipic)(ths)2(H2O)]·2H 2O (Cd3b) and the precursors for PbS are [Pb(Hsal) 2(th)2] (Pb1a), [Pb(Hsal)2(ths) 2] (Pb1b), [Pb(pic)2(th)2] ( Pb2a), [Pb(pic)2(ths)2] (Pb2b), [Pb(dipic)(th)(H2O)]2·2H2O ( Pb3a) and [Pb(dipic)(ths)2]·H2O ( Pb3b). All of the compounds were characterized spectroscopically and by elemental analysis. Cd1a, Cd2a, Cd2b, Cd3a, Cd3b, Pb2b Pb3a and Pb3b formed well-defined crystals and were characterized by single crystal X-ray diffraction. The precursors were decomposed at or around 170°C using n-cetyltrimethylammonium bromide (CTAB), sodium dodecylsulphate (SDS), ethylenediamine, oleic acid, oleylamine, trioctylamine or hexadecylamine as surfactants. Systematic variations of surfactants gave small spherical nanoparticles, micro-sized flowers, multipods and nanorods for CdS and nanocubes, truncated nanocubes, hexapods, octahedrons and dendritic stars for PbS. From XRPD studies it was found that most of the CdS nanostructures were of the stable hexagonal phase. However, in two cases the nanostructures were found to be predominantly of a metastable orthorhombic phase. For PbS system, all the decompositions yielded pure crystalline galena. For CdS system, TEM studies revealed planar defects (such as polysynthetic and multiplet twinning) in the nanocrystals, which gave an explanation for mechanism of growth. For PbS system, in order to elucidate the effect of single source precursors on the mechanism of growth of nanoparticles, the decomposition results were compared with PbS nanostructures synthesized from multiple-source precursors, lead acetate and thiourea or thiosemicarbazide. It was found that in the reactions of multiple source precursors, acidic components in the reaction mixture (oleic acid, acetic acid) led to etching and crystal splitting, which played a crucial role in the formation of anisotropic nanostructures.

The thesis is divided into two parts. The first part deals with the research work carried out on the synthesis and chemical modification of nanomaterials whereas the second part describes the preparation and characterisation of polymer films and their use as separation membranes. Part I of the thesis describing the synthetic strategies and chemical manipulation schemes employed on various types of nanomaterials is divided into six chapters. Chapter 1 describes a chemist’s approach towards synthesizing and tuning the properties of different classes of nanomaterials along with a brief account of their potential applications. Chapter 2 of the thesis describes the synthesis and characterization of various metal nanostructures (viz. nanoparticles, nanorods, nanosheets etc.) of nickel, ruthenium, rhodium and iridium using a solvothermal procedure. Chapter 3 deals with the nanoparticles of the novel oxide metal ReO3. ReO3@Au, ReO3@Ag, ReO3@SiO2 and ReO3@TiO2 core-shell nanostructures with ReO3 as the core nanoparticle have been synthesized through a two-step process and characterized. Dependence of the plasmon band of the ReO3 nanoparticles on the interparticle separation has been examined by incorporating the nanoparticles in various polymer matrices and the results compared with those obtained with gold nanoparticles. Chapter 4 presents the dispersion of nanostructures of metal oxides such as TiO2, Fe3O4 and ZnO in solvents of differing polarity (water, DMF and toluene) in the presence of several surfactants. In Chapter 5 of the thesis, fluorous chemical method of separation of metallic and semiconducting single-walled carbon nanotubes is described. This method involves the selective reaction of the diazonium salt of a fluorous aniline with the metallic nanotubes in an aqueous medium and subsequent extraction of the same in a fluorous solvent leaving the semiconducting nanotubes in the aqueous layer. Chapter 6 presents the studies on the interaction of single walled nanotubes and graphene with various halogen molecules (I2, IBr, ICl and Br2) of varying electron affinity probed by employing Raman spectroscopy and electronic absorption spectroscopy. Part II of the thesis describes a general method of fabricating ultrathin free-standing cross-linked polymer films and their subsequent use as separation membranes. A particular class of 1-D nanomaterials namely cadmium hydroxide nanostrands were used in this method throughout, to generate a sacrificial layer upon which the polymer films were generated.

The thesis is divided into two parts. The first part deals with the research work carried out on the synthesis and chemical modification of nanomaterials whereas the second part describes the preparation and characterisation of polymer films and their use as separation membranes. Part I of the thesis describing the synthetic strategies and chemical manipulation schemes employed on various types of nanomaterials is divided into six chapters. Chapter 1 describes a chemist’s approach towards synthesizing and tuning the properties of different classes of nanomaterials along with a brief account of their potential applications. Chapter 2 of the thesis describes the synthesis and characterization of various metal nanostructures (viz. nanoparticles, nanorods, nanosheets etc.) of nickel, ruthenium, rhodium and iridium using a solvothermal procedure. Chapter 3 deals with the nanoparticles of the novel oxide metal ReO3. ReO3@Au, ReO3@Ag, ReO3@SiO2 and ReO3@TiO2 core-shell nanostructures with ReO3 as the core nanoparticle have been synthesized through a two-step process and characterized. Dependence of the plasmon band of the ReO3 nanoparticles on the interparticle separation has been examined by incorporating the nanoparticles in various polymer matrices and the results compared with those obtained with gold nanoparticles. Chapter 4 presents the dispersion of nanostructures of metal oxides such as TiO2, Fe3O4 and ZnO in solvents of differing polarity (water, DMF and toluene) in the presence of several surfactants. In Chapter 5 of the thesis, fluorous chemical method of separation of metallic and semiconducting single-walled carbon nanotubes is described. This method involves the selective reaction of the diazonium salt of a fluorous aniline with the metallic nanotubes in an aqueous medium and subsequent extraction of the same in a fluorous solvent leaving the semiconducting nanotubes in the aqueous layer. Chapter 6 presents the studies on the interaction of single walled nanotubes and graphene with various halogen molecules (I2, IBr, ICl and Br2) of varying electron affinity probed by employing Raman spectroscopy and electronic absorption spectroscopy. Part II of the thesis describes a general method of fabricating ultrathin free-standing cross-linked polymer films and their subsequent use as separation membranes. A particular class of 1-D nanomaterials namely cadmium hydroxide nanostrands were used in this method throughout, to generate a sacrificial layer upon which the polymer films were generated.

Surfactant bound stable colloids of Au, Ag, and Pd were prepared by the solvated Metal Atom Dispersion (SMAD) method, a method involving co-condensation of metal and solvent vapors on the walls of a reactor at 77 k. The as=prepared dodecanethiol-capped Au and Ag colloids consisting of polydisperse nanoparticles were transformed into colloids consisting of highly monodisperse nanoparticles by the digestive ripening process. In the case of Pd colloids, digestive ripening led to the formation of thiolate complexes. The [Pd(SC12H25)2]6 complex formed from the dodecanethiol-capped Pd nanoparticles was found to be a versatile precursor for the synthesis of a variety of Pd nanophases such as Pd(0), PdS, and Pd@PdO by soventless thermolysis. Co-digestive ripening of as-prepared dodecanethiol-capped Au or Ag colloids with Pd colloid resulted in Au@Pd and Ag@Pd core-shell nanoparticles, respectively; attempts to transform the core-shell structures into alloy phases even at high temperatures were unsuccessful. Phosphine-capped Au nanoparticles were also prepared by the SMAD method and refluxing of this colloid resulted in an Ostwald ripening process rather than the expected digestive ripening due to the labile nature of bound PPh3. The labile nature of the bound phosphine was studied using 31P NMR spectroscopy and utilized in the adsorption of CO. Palladium nanoparticles obtained from the SMAD Pd-butanone colloids and Pd@PdO nanoparticles prepared by the solventless thermolysis of Pd-dodecanethiolate complex were found to be good catalysts for the generation of H2 from AB via either hydrolysis and methanolysis. The active hydrogen atoms produced during the hydrolysis and methanolysis diffuse into the Pd lattice. It was also noticed that hydrogen atoms that were buried deep inside the Pd lattice cannot be removed completely by heating the sample even at 600°C. Wet chemical reduction method was employed for the synthesis of PVP capped, nearly monodisperse, spherical Ir nanoparticles which undergo a polymer driven self-assembly at 80°C to afford rectangular structures and interlinked particles.

Surfactant bound stable colloids of Au, Ag, and Pd were prepared by the solvated Metal Atom Dispersion (SMAD) method, a method involving co-condensation of metal and solvent vapors on the walls of a reactor at 77 k. The as=prepared dodecanethiol-capped Au and Ag colloids consisting of polydisperse nanoparticles were transformed into colloids consisting of highly monodisperse nanoparticles by the digestive ripening process. In the case of Pd colloids, digestive ripening led to the formation of thiolate complexes. The [Pd(SC12H25)2]6 complex formed from the dodecanethiol-capped Pd nanoparticles was found to be a versatile precursor for the synthesis of a variety of Pd nanophases such as Pd(0), PdS, and Pd@PdO by soventless thermolysis. Co-digestive ripening of as-prepared dodecanethiol-capped Au or Ag colloids with Pd colloid resulted in Au@Pd and Ag@Pd core-shell nanoparticles, respectively; attempts to transform the core-shell structures into alloy phases even at high temperatures were unsuccessful. Phosphine-capped Au nanoparticles were also prepared by the SMAD method and refluxing of this colloid resulted in an Ostwald ripening process rather than the expected digestive ripening due to the labile nature of bound PPh3. The labile nature of the bound phosphine was studied using 31P NMR spectroscopy and utilized in the adsorption of CO. Palladium nanoparticles obtained from the SMAD Pd-butanone colloids and Pd@PdO nanoparticles prepared by the solventless thermolysis of Pd-dodecanethiolate complex were found to be good catalysts for the generation of H2 from AB via either hydrolysis and methanolysis. The active hydrogen atoms produced during the hydrolysis and methanolysis diffuse into the Pd lattice. It was also noticed that hydrogen atoms that were buried deep inside the Pd lattice cannot be removed completely by heating the sample even at 600°C. Wet chemical reduction method was employed for the synthesis of PVP capped, nearly monodisperse, spherical Ir nanoparticles which undergo a polymer driven self-assembly at 80°C to afford rectangular structures and interlinked particles.

A series of interesting core/shell silver/phenol formaldehyde resin (PFR) nano/microstructures were also synthesized through an efficient microwave process by self-assembly growth. Various morphologies, including monodispersed nanospheres, nanocables, and microcages were obtained by changing the fundamental experimental parameters, such as the reaction time and the surfactants (Pluronic P123 or CTAB). The results indicated that the presence of triblock copolymer Pluronic P123 would result in hollow silver/PFR microcages, while CTAB would prefer the formation of ultralong silver/PFR coaxial nanocables. In the absence of surfactants, monodispersed core/shell silver/PFR nanospheres could be obtained. The size of the nanospheres can be controlled in the range of 110 to 450 nm by changing the molar ratio of reagents (phenol:hexamine). The morphology and composition of the as-prepared products were characterized. The formation mechanism of the products was discussed based on the obtained results.
Bifunctional mesoporous core/shell Ag FeNi3 nanospheres were synthesized by reducing iron(III) chloride, nickel(II) chloride and silver nitrate with hydrazine in ethylene glycol under microwave irradiation. The efficient microwave-hydrothermal process significantly shortened the synthesis time to one minute. The toxicity of Ag FeNi3 nanospheres were tested by exposing to zebrafish, they were less toxic than silver nanoparticles. In vitro MRI confirmed the effectiveness of the Ag FeNi3 nanospheres as sensitive MRI probes. The interaction of Rhodamine Band nanospheres showed greatly enhanced fluorescence over the FeNi3 nanoparticles.
Finally, a series of ZnO microarchitectures including monodispersed spindles, branches, flowers, paddies, and sphere-like clusters were prepared by an efficient microwave-hydrothermal process. The ZnO mophologies could be effectively controlled by changing the reaction conditions such as the reaction temperature, the reactant concentrations and the solvent system. Simple microspindles, interesting flowers and paddies could be obtained in the presence of hexamine, and the more attractive sphere-like clusters could be synthesized by introducing phenol. The formation mechanisms of different morphologies are discussed in detail. These interesting ZnO structures may have potential applications in electronic and optoelectronic devices.
Inorganic nanostrucured materials have attracted much attention owing to their unique features and important applications in biomedicine. This thesis describes the development of rapid and efficient approaches to synthesize inorganic nanostructures, and introduces some potential applications.
Magnetic nanostructures, such as necklace-like FeNi3 magnetic nanochains and magnetite nanoclusters, were synthesized by an efficient microwave-hydrothermal process. They were used as magnetic resonance imaging (MRI) contrast agents. Magnetic FeNi3 nanochains were synthesized by reducing iron(III) acetylacetonate and nickel(II) acetylacetonate with hydrazine in ethylene glycol solution without any template under microwave irradiation. This was a rapid and economical route based on an efficient microwave-hydrothermal process which significantly shortened the synthesis time to mins. The morphologies and size of the materials could be effectively controlled by adjusting the reaction conditions, such as, the reaction time, temperature and concentrations of reactants. The morphology and composition of the as-prepared products were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The size of the aligned nanospheres in the magnetic FeNi 3 chains could be adjusted from 150nm to 550nm by increasing the amounts of the precursors. Magnetic measurements revealed that the FeNi3 nanochains showed enhanced coercivity and saturation magnetization. Toxicity tests by exposure of FeNi3 nanochains to the zebrafish larvae showed that the as-prepared nanochains were biocompatible. In vitro magnetic resonance imaging (MRI) confirms the effectiveness of the FeNi 3 nanochains as sensitive MRI probes. Magnetite nanoclusters were synthesized by reducing iron(III) acetylacetonate with hydrazine in ethylene glycol under microwave irradiation. The nanoclusters showed enhanced T2 relaxivity. In vitro and in vivo MRI confirmed the effectiveness of the magnetite nanoclusters as sensitive MRI probes. We also investigated the biodistribution of the nanoclusters in rat liver and spleen.
Jia, Juncai.
Adviser: Jimmy C. Yu.
Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.

The thesis consists of eight chapters of which the first chapter presents a brief overview of inorganic nanostructures. Synthesis and magnetic properties of MnO and NiO nanocrystals are described in Chapter 2, with emphasis on the low-temperature ferromagnetic interactions in these antiferromagnetic oxides. Chapter 3 deals with the synthesis and characterizations of nanocrystals of ReO3, RuO2 and IrO2 which are oxides with metallic properties. Pressure-induced phase transitions of ReO3 nanocrystals and the use of the nanocrystals for carrying out surface-enhanced Raman spectroscopy of the molecules form Chapter 4. Use of ionic liquids to synthesize different nanostructures of semiconducting metal sulfides and selenides is described in Chapter 5. Synthesis of Mn-doped GaN nanocrystals and their magnetic properties are described in Chapter 6. A detailed investigation has been carried out on the growth kinetics of nanostructures of a few inorganic materials by using small-angle X-ray scattering and other techniques (Chapter 7). The study includes the growth kinetics of nanocrystals of Au, CdS and CdSe as well as of nanorods of ZnO. Results of a synchrotron X-ray study of the formation of nanocrystalline gold films at the organic-aqueous interface are also included in this chapter. Chapter 8 discuses the use of the organic-aqueous interface to generate Janus nanocrystalline films of inorganic materials where one side of the film is hydrophobic and other side is hydrophilic. This chapter also includes the formation of nanostructured peptide fibrils at the organic-aqueous interface and their use as templates to prepare inorganic nanotubes.

The thesis consists of eight chapters of which the first chapter presents a brief overview of inorganic nanostructures. Synthesis and magnetic properties of MnO and NiO nanocrystals are described in Chapter 2, with emphasis on the low-temperature ferromagnetic interactions in these antiferromagnetic oxides. Chapter 3 deals with the synthesis and characterizations of nanocrystals of ReO3, RuO2 and IrO2 which are oxides with metallic properties. Pressure-induced phase transitions of ReO3 nanocrystals and the use of the nanocrystals for carrying out surface-enhanced Raman spectroscopy of the molecules form Chapter 4. Use of ionic liquids to synthesize different nanostructures of semiconducting metal sulfides and selenides is described in Chapter 5. Synthesis of Mn-doped GaN nanocrystals and their magnetic properties are described in Chapter 6. A detailed investigation has been carried out on the growth kinetics of nanostructures of a few inorganic materials by using small-angle X-ray scattering and other techniques (Chapter 7). The study includes the growth kinetics of nanocrystals of Au, CdS and CdSe as well as of nanorods of ZnO. Results of a synchrotron X-ray study of the formation of nanocrystalline gold films at the organic-aqueous interface are also included in this chapter. Chapter 8 discuses the use of the organic-aqueous interface to generate Janus nanocrystalline films of inorganic materials where one side of the film is hydrophobic and other side is hydrophilic. This chapter also includes the formation of nanostructured peptide fibrils at the organic-aqueous interface and their use as templates to prepare inorganic nanotubes.

PhD. (Chemistry)
Well-defined palladium and platinum nanoparticles were synthesized by two template methods, namely dendrimer template and reverse microemulsions. For dendrimer template, three dendrimers, generation 4, 5, and 6 hydroxyl terminated poly(amidoamine) dendrimers (PAMAM), G4-OH, G5-OH, and G6-OH, were used as stabilizing agent, with PdCl4 2- or PtCl4 2- metal ions to dendrimer ratio of 40, 80, and 160, respectively. For reverse microemulsions, we employed water/AOT surfactant/isooctane system with water to surfactant ratios (ω0) of 5, 10, and 13, capped with thiol, to produce Pd and Pt nanoparticles. A total of twelve catalysts were characterized by techniques such as UV-Vis spectroscopy, TEM, EDX, and p-XRD. In the dendrimer template method, the synthesis of Pd and Pt nanoparticles in lower concentrations produced smaller sizes with narrower size distributions (2.02 ± 0.45 ~ 2.35 ± 0.58 nm Pd nanoparticles, 1.90 ± 0.44 nm ~ 2.48 ± 0.60 nm Pt nanoparticles) compared to those in higher concentrations (2.74 ± 0.44 ~ 3.32 ± 0.86 nm Pd nanoparticles, 2.81 ± 0.70 nm ~ 3.03 ± 0.47 nm Pt nanoparticles). In the case of thiol-capped Pd and Pt nanoparticles by reverse microemulsions, the range of average particle sizes were 3.47 - 7.51 nm and 3.51 - 4.23 nm for Pd and Pt nanoparticles, respectively. This indicated that a wider size regime was obtained by the reverse microemulsion method as compared to the dendrimer template method. Overall, smaller sizes with narrower size distributions were achieved by using the dendrimer-templated synthetic method rather than reverse microemulsions for both Pd and Pt nanoparticles.

Catalysts play a vital role in almost every aspect of our lives and are used in the production of fuels, polymers, chemicals, foods, and pharmaceuticals. One challenge facing the heterogeneous catalysis community is the targeted synthesis of dispersed catalyst ensembles. The Barnes research group has developed a general methodology for the synthesis of nanostructured silicate building block supports and heterogeneous catalysts. This methodology provides researchers with the ability to control the dispersion of surface functionality, the dispersion of metal cation centers, the number of linkages from the metal cation center to the support, the surface area of the support, and the porosity of the support. This dissertation describes work aimed at synthesizing and characterizing nanostructured silicate building block supports and heterogeneous catalysts. Nanostructured silicate building block supports were synthesized by reacting SiCl4py2 with Si8O12(OSnMe3)8. The resulting supports contained spatially isolated Me3Sn groups and the density of Me3Sn groups was targeted by varying the stoichiometric ratio of reactants. The stoichiometric ratio of reactants also controlled the surface area and porosity of the supports. Nanostructured heterogeneous catalysts with isolated tungsten(VI) or zirconium(IV) centers were synthesized by reacting a limiting amount of a metal chloride with either Si8O12(OSnMe3)8 or a premade silicate building block support. Two types of catalysts ensembles were targeted: embedded and surface. Embedded ensembles were successfully targeted using WOCl4 and ZrCl4 while the reaction between WCl6 and the building block did not result in the preparation of the targeted ensemble. However the resulting ensemble was thoroughly characterized even though the targeted ensemble was not produced. In all three cases a single type of catalyst ensembles was synthesized and a high surface area silicate support was generated around the embedded ensembles without disrupting the ensemble itself. Surface ensembles were successfully targeted using ZrCl4. The reaction between the tungsten chlorides (WOCl4 and WCl6) and the premade support did not result in the preparation of the targeted ensembles however the resulting ensembles were thoroughly characterized.

Using two different model systems, this thesis considers the old, but fascinating question: how do atoms or particles possessing a particular set of individual characteristics combine to form assemblies with quite distinct, ensemble characteristics, and how do those characteristics evolve as a function of the size of the assembly? For the last thirty years, numerous experiments studying the emergence of collective material properties have focused on a class of semiconducting, colloidal nanocrystals commonly known as quantum dots, which are notable for the size-dependence of their optical properties. Despite years of effort, even the most uniform quantum dot samples possess some heterogeneity in size, shape, and composition, which has prevented complete structure determination and hindered understanding of structure-property relationships. Chapter 1 of this thesis presents an approach to overcoming this challenge and reports the synthesis of a set of four, new, atomically precise cadmium selenide nanocrystal samples, which we call CdSe(350 nm), CdSe(380 nm), CdSe(408 nm), and CdSe(435 nm) after their lowest energy absorption features. We determine their structures and formulas through a combination of single crystal and powder X-ray diffraction measurements, elemental analysis, and spectroscopy. We also describe the optical properties of these samples and their sensitivity to ligand coverage, compare them to other previously reported cadmium selenide nanomaterials, and discuss ongoing experiments. Because CdSe(350 nm), CdSe(380 nm), CdSe(408 nm), and CdSe(435 nm) are atomically precise, they allow us to correlate specific structural features with material properties, which is the focus Chapter 2. Here we present a series of Raman scattering experiments designed to probe the evolution of vibrational structure with size. We find that the Cd-Se stretching region of the Raman spectra exhibits two peaks, which are assigned to primarily surface-derived and interior-derived atomic motions using density functional theory calculations. By performing variable temperature measurements, we discover that the smallest sample, CdSe(350 nm), exhibits behavior that can be well-described using a model developed for small molecules while the vibrations of the largest measured cluster, CdSe(408 nm), are better described by a model developed for bulk materials. This observation is evidence that the transition to a more bulk-like vibrational structure occurs relatively rapidly when cadmium selenide materials are approximately 2 nm in size. The emergence of collective material properties is also the subject of Chapter 3, but the topic is approached from a different perspective. Instead of focusing on a series of atomically precise clusters that differ in size, Chapter 3 presents a series of molecules composed of atomically precise clusters. We prepare octahedral hexaruthenium carbonyl clusters, [Ru₆C(CO)₁₆]²⁻, and use them as building blocks to assemble oligomers linked by single metal atom bridges. We synthesize and structurally characterize a set of compounds varying in length (from monomer to trimer) and linker atom identity (cadmium and mercury) and study the effect on electronic structure using infrared and UV-Visible absorption spectroscopies and density functional theory calculations. With increasing oligomer length, the UV-Vis absorption profile changes and shifts to lower energy, which we attribute in part to the development of coupling between neighboring clusters. Our calculations show that the infinite polymer composed of [Ru₆C(CO)₁₆]²⁻ linked by Hg²⁺ would be a one-dimensional semiconductor with a 1.5 eV direct band-gap. More detailed abstracts can be found at the beginning of each chapter.