Academic literature on the topic 'Nanoparticle Capping Agent'

This paper presents a simple and convenient procedure for the preparation of octyl amine capped silver nanoparticles. AgNO 3 has been reduced by octyl amine with benzene or toluene as solvent at 100°C to produce silver nanoparticles. Octyl amine plays its role both as reducing and capping agent and thus provides the advantage of avoiding the use of extra stabilizing agent. Time dependent formation mechanism of silver nanoparticle has been investigated. Thermo gravimetric analysis (TGA) shows weight change due to loss of capping agent. The reaction can easily be monitored from variation of color with time. The method is easy and reproducible. Very low concentration (1 mM) of metal ion is used. The particles synthesized were characterized by UV-Visible, FTIR, TGA, TEM and X-ray diffraction studies.

Green synthesis of silver nanoparticles using banana sap as a solvent, reducing agent and capping agent is reported in this work. Banana sap has also been used as a binder to incorporate silver nanoparticles into cotton fabric. UV-Visible spectroscopy was used to monitor the quantitative formation of silver nanoparticles. Silver nanoparticle coated fabric showed high antimicrobial activity against gram negative bacteria such asPseudomonas aureginosaandEscherichia coli, and gram positive bacteria such asBacillus subtilisandStaphylococcus aureus.KeywordsGreen synthesis, Silver nanoparticles, banana sap, antimicrobial activity

Castor oil (CO) is an inedible vegetable oil (VO) that has been employed extensively as a bioresource material for the synthesis of biodegradable polymers, cosmetics, lubricants, biofuels, coatings and adhesives. It is used in medicine, pharmaceuticals and biorefineries, due to its versatile chemistry. However, there has been less focus on CO as an alternative to toxic and expensive solvents, and capping/stabilizing agents routinely used in nanoparticle syntheses. It provides a richer chemistry than edible VOs as a solvent for green syntheses of nanoparticles. CO, being the only rich source of ricinoleic acid (RA), has been used as a solvent, co-solvent, stabilizing agent and polyol for the formation of polymer–nanoparticle composites. RA is a suitable alternative to oleic acid used as a capping and/or stabilizing agent. Unlike oleic acid, it provides a facile route to the functionalization of surfaces of nanoparticles and the coating of nanoparticles with polymers. For applications requiring more polar organic solvents, RA is more preferred than oleic acid. In this review, we discuss the production, chemical and physical properties, triglyceride and fatty acid (FA) compositions and applications of CO, focusing on the use of CO and RA as well as other VOs and FAs in syntheses of nanoparticles and surface functionalization.

Silver nanoparticles (AgNPs) are an interesting metal nanoparticle that can be incorporated into pharmaceutical products, including for diabetic foot ulcers as an antimicrobial agent. Green synthesis of AgNPs using plant extracts has been drawing much attention as it is simple, eco-friendly, stable, and cost-effective. This present study was performed to evaluate the potential of three Indonesian medicinal plant extracts, namely Phyllanthus niruri (PN), Orthosiphon stamineus (OS), and Curcuma longa (CL), as reducing and capping agents in the green synthesis of AgNPs, and to optimize their concentrations. Based on the yields and characteristics of the formed nanoparticles, which were analyzed using a UV-Vis spectrophotometer, particle size analyzer, scanning electron microscope, and X-ray diffractometer, Phyllanthus niruri extract at a concentration of 0.5% was concluded as the best extract in the green synthesis of AgNPs. It is thereby a prospective reducing and capping agent for further scale-up studies.

In this work, PtPd nanostructures have been synthesized via the chemical reduction method with different capping agents (i.e., PVA, PVP, and PEG), whilst the strong reducing agent, NaBH4, was used in this study to reduce the metal salt to zero-valent PtPd nanostructures. Both PtPd synthesized with PVP and PEG exhibit nanoparticle structures, whereas PtPd synthesized in PVA demonstrates large, interconnected network structures. Pt-Pd synthesized with PVP exhibits a high ECSA value of 692.68 m2/g compared to without capping agent (287.80 m2/g) indicating large active sites, which increases its catalytic function. This study concludes that the presence of a capping agent influences the morphological structure and the catalyst's efficiency in performing a redox reaction at the surface.

This investigation is motivated by interest in nanostructured FeOOH anodes for aqueous asymmetric supercapacitors operating in Na2SO4 electrolyte. The research goal is the fabrication of anodes with high active mass loading of 40 mg cm−2, high capacitance and low resistance. The influence of high-energy ball milling (HEBM), capping agents and alkalizer on the nanostructure and capacitive properties is investigated. HEBM promotes the crystallization of FeOOH, which results in capacitance reduction. Capping agents from the catechol family, such as tetrahydroxy-1,4-benzoquinone (THB) and gallocyanine (GC), facilitate the fabrication of FeOOH nanoparticles, eliminate the formation of micron size particles and allow the fabrication of anodes with enhanced capacitance. The analysis of testing results provided insight into the influence of the chemical structure of the capping agents on nanoparticle synthesis and dispersion. The feasibility of a conceptually new strategy for the synthesis of FeOOH nanoparticles is demonstrated, which is based on the use of polyethylenimine as an organic alkalizer-dispersant. The capacitances of materials prepared using different nanotechnology strategies are compared. The highest capacitance of 6.54 F cm−2 is obtained using GC as a capping agent. The obtained electrodes are promising for applications as anodes for asymmetric supercapacitors.

Abstract The wide application of gold nanoparticles has attracted much attention to the development of research in gold nanoparticles. In this study, the gold nanoparticles were prepared by chemical reduction method using potassium tetrachloroaurate as the gold source and sodium borohydride as reducer agent. The formation of gold nanoparticles was confirmed by surface plasmon spectra in ultraviolet-visible spectroscopy at wavelength 507 nm. The capping process of gold nanoparticles was studied using two different charges of amino acids. The asparagine had used as uncharge amino acid and lysine as a positive charge amino acid. The redshift in surface plasmon spectra showed the aggregation of the gold nanoparticles after being capped with amino acids that indicates the surface modification. The amine and carboxylate group was present on the gold nanoparticle surface after being capped with amino acids. The zeta potential results indicate the lysine capped gold nanoparticles have slightly higher stability than the asparagine capped gold nanoparticles. These stability and surface modification of gold nanoparticles are expected to increase their utilization on biological and medical applications.

Background: Owing to their remarkable chemical, physical and biological properties, silver nanoparticles have been widely used in water purification, electronics, bio-sensing, clothing, food industry, paint and medical devices. Various approaches, such as using harsh reducing and stabilising agents for reverse micelle and thermal decomposition, were proposed for silver nanoparticle production. However, these methods are not eco-friendly. Thus, the aim of this paper is to synthesise silver nanoparticles through a cost-effective and environmentally friendly approach. Materials and Methods: A green approach was presented for the synthesis of silver nanoparticles. This approach involved the treatment of silver nitrate and hibiscus leaf extract, which acts as reducing and capping agent. The synthesis was performed at room temperature. The resulting silver nanoparticles were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and Fourier transform infrared (FTIR) spectroscopy. Results: Spherical, rod-like, hexagonal and triangular silver nanoparticles were obtained through the proposed synthesis method. The crystalline nature of each nanoparticle was revealed by XRD and selected area electron diffraction (SAED). The average spherical size of the silver nanoparticles produced in this route was 44.3 nm. The obtained FTIR band at 1622 cm-1 corresponded to the C=O stretch in the amine I group, which is commonly found in protein. Thus, the protein was believed to serve as capping agent that was responsible for the stabilisation of silver nanoparticles. Conclusion: In conclusion, silver nanoparticles had been successfully synthesised using hibiscus leaf extract and a plausible formation mechanism of silver nanoparticles was proposed.

Green synthesis of silver nanoparticles is of great importance in the field of nanoscience and nanotechnology. Various phytochemical constituents present in whole or parts of plants can act as reducing, capping and stabilizing agents in the synthesis of silver nanoparticle (AgNPs) by green method. In this work, AgNPs have been successfully synthesized in the laboratory by chemical reduction and green method. NaBH4 was used as a reducing agent in chemical reduction method whereas Zingiber officinale leaf extract was used as reducing and capping agent in green method. The properties of as synthesized AgNPs by both green and chemical methods have been examined by UV-Vis spectroscopy, XRD and FTIR method. Besides these, biological activities of as synthesized AgNPs were tested against Bacillus subtilis and Escherichia coli which exhibited remarkable antimicrobial activities in green method. Based on the result, it is found that AgNPs synthesized from ginger plant (Zingiber officinale) leaf extract exhibited significant antimicrobial effect than that by chemically synthesized AgNPs.

Abstract In this Ph.D. project, the effective parameters in the sol-immobilization method which can affect catalytic reactivity including: capping agent, solvent of synthesis, and support were studied. The synthesized catalysts were employed in the liquid phase hydrogenation reactions of two biomass derived molecules namely furfural and vanillin. In this regard, the role of protective agents, which are used to stabilize colloidal nanoparticles (NPs) in solutions, for Pd NPs supported on carbon support in the liquid phase hydrogenation of furfural was explored. The use of Pd as a hydrogenation catalyst is well documented, as hydrogenation reactions can only be performed by metals that can easily chemisorb hydrogen. Pd is one of such metals capable of dissociate hydrogen even at room temperature. The capping agent adsorbed on the surface of the NPs can alter their activity and selectivity, by modifying the particle size, size distribution, morphology, and stability against leaching and agglomeration. Besides, the effect of the amount of protective agent and the synthesis solvents have been investigated, allowing better insight into the metal-support interaction in Pd/TiO2 catalysts for the hydrogenation of furfural. Then, the effect of using different carbonaceous supports with various chemical-physical properties on the activity and selectivity towards the hydrodeoxygenation of vanillin as a lignin model compound was explored. To better understand the role of the capping agents in controlling the activity and the selectivity of the furfural hydrogenation, a series of carbon-supported Pd nanoparticles were prepared through controlled sol-immobilization method using different capping agents, including polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly(diallyldimethylammonium) chloride (PDDA) containing oxygen and/or nitrogen groups. The catalysts were characterized by different techniques. UV-Vis and Fourier-transform infrared (FTIR) spectroscopy were used to evaluate the interaction between capping agents and Pd precursor, while transmission electron microscopy (TEM) was performed to study the final morphology of the catalyst. Finally, X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface chemistry of the carbon support, the chemical state, and the exposure of supported palladium species. The UV-Vis spectra of the system composed of Pd precursor plus capping agent demonstrated the interaction of the metal with PVA and PVP. In the case of PDDA, changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. The disappearance of the peaks associated with Pd2+ and the observed scattering indicated a complete reduction to Pd0 and the formation of metal nanoparticles. The interaction of the capping agents with the Pd precursor was studied by FTIR spectroscopy. For PVA, the peaks corresponding to the stretching vibrations of C–O–C linkage were observed, which suggested the presence of cross-linked PVA molecules, and the slight modification observed for the peaks in the spectrum of PVA + Na2PdCl4 suggested a weak interaction between the metal precursor and the –OH groups present in PVA. In the case of PVP, a decrease in the intensity of the peak after the addition of Pd was observed which confirmed that both O and N groups are present in PVP interaction with the metal precursor. For PDDA, after the addition of Pd, the intensity of the peaks decreased, which indicated that the activity of the vibrational modes is modified in the mixture, probably due to PDDA–Pd interaction. The morphological characteristics of the synthesized catalysts were evaluated by HRTEM. We noticed that the capping agent has a major effect on the size and distribution of Pd NPs when using activated carbon as the support. All catalysts had an average particle size of 3–4 nm, with the presence of isolated larger particles in the case of PdPDDA/C. The XPS survey data revealed that only Pd, C, N, and O species were present on the surface of the catalysts. Depending on the capping agent used, substantial differences were observed in the relative amount of Pd on the surface: PdPVA/C (1.30 %) > PdPDDA/C (0.76 %) > PdPVP/C (0.50 %). The data also showed a different oxygen content in the samples. PdPVA/C displayed the highest relative amount of O (14.7 % compared to PdPDDA/C (9.70 %) and PdPVP/C (9.10 %)), respectively. The highest oxygen content on the surface of PdPVA/C catalyst is probably due to the presence of –OH groups in PVA. PdPVP/C exhibited the highest N content (2.95 %), higher than PdPDDA/C (1.86 %) due to the presence of a pyrrole-type N species in PVP and dimethyl-ammonium groups in PDDA, while in the PdPVA/C N was not detected on the surface, as expected. The performance of the prepared catalysts was examined for the liquid-phase hydrogenation of furfural (furfural 0.3 M; furfural/metal ratio 500 mol/mol, 5 bar H2, temperature range of 25–75 °C) with 2-propanol as solvent. The catalytic results revealed that the activity of catalysts is correlated to the relative amount of Pd at the surface: PdPVA/C (1.3%) > PdPDDA/C (0.76%) > PdPVP/C (0.50%). At 75 °C the catalysts exhibit similar reactivity. We ascribed this effect to the partial removal of a capping agent during the reaction, thereby exposing a higher number of active sites to the reactant. In the next step, since the best results were obtained using PVA, this latter was chosen as the protective agent, focusing on the effects that its amount and the change of the solvent of synthesis to methanol-water mixtures might have on the preparation of Pd/TiO2 catalysts. This new approach indicates the necessity of using the capping agent, and results also show that the acidification step, which lowers the isoelectric point (IEP) to afford anchoring of the NPs to the surface of the support, can be eliminated while still maintaining the same degree of Pd immobilization (≥ 96%) and particle size control (< 2 nm). These samples were evaluated for furfural hydrogenation; there was an improvement in selectivity towards furfuryl alcohol and tetrahydrofurfuryl alcohol, whereas ether by-products were suppressed. Supported Pd NPs were prepared in accordance with the standard sol-immobilization method, in which the temperature of the chemical reduction was maintained at 1 °C. This temperature was chosen as earlier research in our workgroup reviled the formation of smaller nanoparticles when lower temperatures were used. UV-Vis spectroscopy was performed to characterize the precursor salt and colloidal solutions during NPs preparation. Changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. Catalysts prepared with increasing volumes of MeOH showed shifts in the distinctive ligand to metal charge transfer (LMCT) and d-d transitions. This confirms a change to the Pd metal precursor complex when it is solvated in either the MeOH/H2O mixture or in pure MeOH. One reason for this is the exchange of ligands between the Pd salt complex and the solvent synthesis. The Pd % loading of each catalyst was measured using microwave plasma – atomic emission spectroscopy (MP-AES). All catalysts were characterized using TEM, in order to get information of their average NP sizes and particle size distributions/dispersions. An initial comparison of catalysts, showed that an acidified immobilization step increases the average NP size. The bigger NP size and dispersion was found for the sample prepared by H2O as the solvent, PVA, and acidification step, which it can be ascribed to the interaction of the stabilizer agent (PVA) with acid during the immobilization step. XAFS was performed to investigate both changes to Pd oxidation state (XANES) and the local structural environment with respect to Pd (EXAFS). The results confirmed that by using PVA in the solvent system, the Pd oxidation state contains a greater quantity of Pd2+. Interestingly, by removing the acidification step during the synthesis, an increase in the oxidized Pd state was observed. This was consistent with the TEM data indicating this increase in Pd2+ is related to the observed particle sizes. Pd surfaces are known to form passivating oxide layers when exposed to air with an increase in the temperature needed to form a bulk oxide structure. Therefore, the Pd2+ fraction refers to the quantity of the available Pd surface and hence the particle size. Fitting of the 1st shell Pd K edge EXAFS data was consistent with the trends observed through TEM and XANES characterization. The presence of small Pd NPs is confirmed by the decreased magnitude of Pd-Pd scattering, signified by smaller CNPd-Pd. All catalysts were tested for the hydrogenation of furfural at 50°C. Although the XANES, EXAFS, and TEM data have all confirmed that sample prepared by the pure MeOH contains smaller NPs than the sample prepared by pure H2O, the initial catalytic activity showed that the sample synthesized by H2O has a significant increase in initial TOF h-1. In addition, furfural hydrogenation performed over the bare TiO2 support displayed 98.4 % selectivity to the acetal product (2-(diisopropoxymethyl) furan), at isoconversion, while sample prepared by H2O revealed less selectivity to the acetal (18.8%). To understand these differences in activity/selectivity we performed further HRTEM investigations of the fresh samples. These studies have identified a 'halo' of PVA around NPs produced using MeOH (e.g. PdMeP) and at the interface between NPs and support. We suggest that the poor solubility of PVA in methanol is responsible for this increase in PVA clustering on the catalytic surface/support interface identified with HRTEM. We also propose that the active sites on TiO2 are formed through the spillover of hydrogen onto the support and accounts for the superior yield of acid catalysed products for Pd/TiO2 compared to TiO2 alone. In the case of Pd/TiO2, the catalysts prepared using MeOH result in aggregation of PVA at the Pd-TiO2 interface, which restrict spillover effects and decreases the amount of acid catalysed products. For the catalysts prepared without the addition of PVA, we observed a higher proportion of ethers than for the analogous catalysts prepared with PVA. This further supports our hypothesis that PVA at the metal-support interface limits the spillover of hydrogen. Catalyst recycle tests were carried out over six consecutive hydrogenation cycles. The catalysts prepared without PVA quickly deactivated with almost negligible performance by the sixth consecutive run. The TEM analysis of the spent sample confirmed that when PVA is not present the samples quickly agglomerate and effective surface area of Pd rapidly diminishes. Finally, the effect of support on both activity and selectivity of the catalyst in the hydrogenation of vanillin to vanillyl alcohol and the subsequent hydrodeoxygenation (HDO) to creosol was studied. Four types of carbonaceous materials (three activated carbon: Norit, KB, G60, and a carbon nanofiber: HHT) were used as support for Pd nanoparticles. Catalysts were synthesized with sol immobilisation method using PVA as the capping agent, and tested in the hydrodeoxygenation reaction of vanillin under mild reaction conditions (50 °C, 5 bar H2 and isopropanol as solvent). Catalysts have been extensively characterized by TEM, XPS and BET in order to correlate the surface properties with the catalytic behaviour and selectivity to the target products. In the end, recycle tests were carried out on the most active catalyst to determine the reusability of the material used. BET analysis was conducted on Pd-supported catalysts. Pd/Norit catalyst has the highest surface area (2000 m2/g), whereas Pd/HHT has the lowest surface area (40 m2/g). The average pore radius of all samples was in the range of 2 nm for Pd/KB to 25,4 nm for Pd/HHT. XPS analysis were performed on the synthesized catalysts to determine the oxidation state of the Pd, the graphitization order and the presence and abundance of oxygen functionality. Pd/Norit, Pd/KB and Pd/G60 had a similar amount of C1s species (84.4 %, 87.3 % and 91.1 %, respectively), while Pd/HHT had the highest number of C 1s (98.8 %). Evaluation of O1s species revealed that the Pd/HHT catalyst has the lowest amount of functionalisation (0.9 %), while Pd/Norit the highest one (14.3 %). The results showed that the Pd/HHT catalyst has the highest amount of C=C (82.1 %), therefore the support can be considered highly graphitised. TEM analysis were performed to determine the mean particle size and size distribution. In all samples, the nanoparticles are homogeneously distributed on the support. Pd/Norit and Pd/KB had similar mean Pd particle sizes (2.5 and 2.7 nm respectively). Whereas, Pd/G60 and Pd/HHT displayed higher mean Pd nanoparticle diameters (3.5 and 3.9 nm, respectively). The catalysts were tested in the vanillin HDO reaction. The reaction profile shows the features of a typical consecutive reaction, with vanillyl alcohol as the intermediate product, and creosol as the final product. Interesting, an additional product was detected in the reaction mixture, namely vanillyl isopropyl ether. The ether is produced by reaction of vanillyl alcohol with a molecule of solvent (isopropanol) and it is consumed with time since it is in equilibrium with the alcohol. The results revealed that the rate of conversion of vanillin enhances with increasing degree of graphitisation. These results can be explained by the strong interaction between the graphitic plane of the support and the aromatic ring of the substrate that allows a better interaction with the active metal nanoparticles. At the same time, the activity in the vanillin hydrogenation reaction decreases with an increase in oxygen content at the carbon surface. The support-substrate interaction is responsible for the change in activity; the increase in oxygen functionality actually disrupts the graphical plane structure of the support. The support affected the selectivity at the lower conversion. In fact, at 50 % of conversion, vanillyl alcohol was the main product of Pd/Norit, Pd/HHT and Pd/KB (selectivity in the 73-82 %), while Pd/G60 provided high levels of both vanillyl isopropyl ether and creosol (23 and 21 %, respectively). The formation of ether was associated with the amount of carboxylic support functionality (COOH groups). The recycling tests were carried out on the most active catalyst: Pd/HHT. After five consecutive reactions, the conversion did not significantly decrease, demonstrating the high stability of the catalyst. Comparably, the selectivity of vanillyl alcohol remained almost unchanged.

>Magister Scientiae - MSc
During the course of this study iron oxide nanoparticles, which have been researched for drug-targeted delivery, were synthesised via the co-precipitation method and characterised using various methods. This study focused on the role of relevant capping agents for the inhibition of agglomeration of the particles; chitosan, polyvinyl alcohol (PVA) and poly lactic glycolic acid (PLGA) were the capping agents of interest. The study is an assessment of the effects brought about the different capping agents used for this work. The prepared particles were then capped with the different capping agents followed by the loading of the drug curcumin. Various analytical methods were used to analyse the particles such as High resolution transmission electron microscopy (HR-TEM), Superconducting quantum interference device (SQUID), Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and zeta potential. PVA, chitosan and PLGA capped SPIONS were successfully prepared and verified by FT-IR spectrometry, various sizes were prepared almost ranging the same for the successfully prepared particles verified by XRD. The resultant particles were found to be spherical with an average particles size between 13- 22 nm. From the study it was concluded that the addition of the different capping agents resulted in the reduction of the intensity of the peaks in XRD, it was also found out the presence of the capping agents did not alter the crystalline phase of the particles. From the study it was also observed that higher saturation magnetization was experienced where PVA was used as the capping agents.

>Magister Scientiae - MSc
Magnetic luminescent nanoparticles of an iron oxide (Fe₃O₄) superparamagnetic core and an indium phosphide/zinc selenide (InP/ZnSe) quantum dot shell are reported. The magnetic nanoparticles (MNP’s) and quantum dots (QD’s) were each synthesized separately before conjugation. The MNP’s were functionalized with a thiol-group allowing the QD shell to bind to the surface of the MNP by the formation of a thiol-metal bond. The nanocomposite was capped with 3-mercaptopropionic acid, 1-propanethiol, 2-methyl-1-propanethiol and their properties investigated using the characterization techniques: high- resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), UV-vis, scanning electron microscopy (SEM), superconducting quantum interference device (SQUID), and photoluminescence. These techniques yielded significant information on particle size, morphology, dispersion, and chemical composition including luminescence and florescence.

Due to their small size and large surface area-to-volume ratios, nanoparticles (particles with limiting dimensions smaller than 100 nm) have been widely applied as catalysts. Metal nanoparticles are typically produced in suspensions from metal ion precursors, reducing agents, and organic ligands called capping agents. Capping agents help prevent particle agglomeration, fix nanoparticle size, and promote monodispersity. However, capping agents also affect the morphology and the physico-chemical surface properties of nanoparticles, which can influence catalytic properties in unpredictable ways. While there have been extensive studies focused on examining the relationship between nanoparticle size, shape, composition and catalytic activity, relatively few have investigated the effects of capping agent properties on catalysis, and most studies involving nanoparticle catalysts have been conducted on collections, ensembles, or arrays of particles rather than single nanoparticles. Results obtained for systems composed of multiple nanoparticles dispersed on solid surfaces can be difficult to interpret due to variations in particle loading and interparticle distance, which are often challenging or impossible to control and characterize. The complexity of these unavoidable experimental variables may explain some of the seemingly inconsistent conclusions that have been drawn between nanoparticle properties and catalytic activity in recent reports. Single nanoparticle studies should help overcome limitations associated with investigations based on collections of nanoparticles by helping uncover direct relationships between nanoparticle size, surface properties, and catalytic activity that are unobscured by complex factors such as interparticle distance and particle loading. In this work, we aim to use nitrided carbon fiber ultramicroelectrodes to examine electrocatalytic properties of bare (uncapped) and capped gold nanoparticles at the single nanoparticle level.

Eu has been placed instead of In in Cu-In-S2 which is used for CIS solar cells and effect of different capping agents on composition, size, distribution and morphology of the nanoparticles was investigated by scanning electron microscopy equipped with energy dispersive X-ray and transmission electron microscopy with the corresponding selected area electron diffraction pattern. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35300

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In this work the single-step/single-phase synthesis of hybrid organic-inorganic core-shell gold nanoparticles (AuNPs), facilitated by amino-functionalized amphiphilic block copolymers that simultaneously play the roles of reductant and stabilizer, was investigated in this study. Experiments were devised with emphasis on the pH-responsive poly(ethylene oxide)-b-poly(2,3-dihydroxypropyl methacrylate)-b-poly[2-(diisopropylamino)ethyl methacrylate] triblock copolymer, which allows direct chemical cross-linking of the micellar structures to be performed. The polymer structure-reactivity relationship associated with the AuNP formation was established using a set of six structurally related macromolecules. AuNP formation was dependent on the aqueous dissociation equilibrium involving tertiary amino groups, the Au(III) speciation, and electrochemical redox potentials. The effects of these parameters on the synthesis of AuNPs change as the solution pH is increased from pH 3.5 (molecularly dissolved polymer chains; no AuNP formation) to 6.8 or higher (polymer chains self-assembled into spherical micelles; stable gold sols are produced), and Au(III) reduction potentials shift toward the cathodic region whilst the oxidation potential of deprotonated amino groups decreases. Sigmoidal nanoparticle growth kinetics was observed in all cases after a characteristic induction period. Stable, well-defined, uniform polymer-coated gold colloids with localized surface plasmon resonance centered at 530 nm can be conveniently produced in one-pot, two-reactant, no work-up reactions when the stoichiometry is [N]/[Au] = 3.5 - 25.0.
Neste trabalho a síntese em única fase/etapa de nanopartículas de ouro híbridas orgânico-inorgânicas do tipo casca núcleo (AuNPs) facilitadas por copolímeros em bloco anfifílicos funcionalizados com grupos aminos e que simultaneamente atuam como agente redutor e estabilizante foi investigada. Os experimentos foram realizados com ênfase nas respostas frente ao pH do copolímero tribloco poli(óxido de etileno)-b-poli(metacrilato de 2,3-diidroxipropila)-b-poli(metacrilato de 2-(diisopropilamino)etila) e que permite a química direta de reticulação das estruturas micelares. A relação entre estrutura e reatividade do copolímero associada à formação das AuNPs foi estabelecida usando uma série de seis macromoléculas semelhantes aos blocos constituintes do copolímero. A formação das AuNPs é dependente do equilíbrio de dissociação envolvendo grupos aminos terciários, espécies de Au(III) e também do potencial eletroquímico redox. Os efeitos desses parâmetros levam a formação de AuNPs quando da mudança de pH de 3,5 (cadeias poliméricas dissolvidas não formam AuNPs) para pH 6,8 ou maior (polímero auto-organizado em micelas esféricas coloides estáveis de ouro são produzidos), e quando o potencial de redução dos íons Au(III) mudam para a região catódica e o potencial de oxidação dos grupos aminos desprotonados presentes no copolímero diminui. A cinética de crescimentos das AuNPs apresentou em todos os casos perfil sigmoidal após o período de indução característicos da síntese. Coloides de ouro estáveis, bem definidos e estabilizados pelo copolímero com ressonância plasmônica de superfície centrado em cerca de 530 nm foram produzidos em etapa única, dois reagentes, sem reações paralelas na estequiometria [N]/[Au(III)] entre 3,5 e 25.

Nanočástice perovskitů halogenidů kovů vykazují unikátní vlastnosti, především výjimečně vysoké hodnoty kvantových výtěžků fluorescence, které předurčují tyto materiály pro aplikace v optoelektronických a fotonických zařízeních. Tato práce popisuje přípravu nanočástic perovskitů halogenidů kovů pomocí stabilizačních činidel inspirovaných přírodou. Stabilizační činidla zde slouží nejen ke stabilizaci, ale i k modifikaci povrchu nanočástic za účelem zvýšení funkčnosti výsledných nanostruktur. Úvod práce popisuje optimalizaci přípravy nanočástic precipitační technikou za použití stabilizačních činidel; jako stabilizační činidlo byl zvolen adamantan-1-amin spolu s hexanovou kyselinou. Bylo prokázáno, že klíčový vliv na optické vlastnosti výsledných koloidních roztoků má volba rozpouštědel a teploty při precipitaci. Mimo jiné byl zkoumán vliv koncentrace prekurzorů na výslednou morfologii a optické vlastnosti nanočástic a jejich koloidních roztoků. V neposlední řadě byly nanočástice stabilizovány adamantan-1-aminem spolu s různými karboxylovými kyselinami a byly studovány optické vlastnosti a koloidní stabilita výsledných koloidních roztoků. V dalším kroku byly nanočástice perovskitů stabilizovány pomocí proetogenních aminokyselin L-lysinu and L-argininu. Takto stabilizované nanočástice vykazovaly úzká emisní spektra ve viditelné oblasti a kvantové výtěžky fluorescence dosahující hodnot téměř 100 %. Stabilizace nanočástic prostřednictvím postranních skupin aminokyselin byla prokázána navázáním chránící terc-butoxykarbonylové skupiny na -amino skupinu. Nanočástice stabilizované modifikovaným lysinem v průběhu jejich přípravy vykazovaly závislost optických vlastností na přítomnosti vody. Předpokládá se, že molekuly vody jsou schopné kontrolovat růst krystalové mřížky po navázání na prekurzory perovskitů a ovlivňovat tak výslednou velikost nanočástic, což vede k projevení kvantových jevů. Spojení nanočástic perovskitů s peptidy představuje nový typ materiálů kombinujících výjimečné optické vlastnosti se samoorganizačními a senzorickými vlastnostmi. Tento koncept byl představen přípravou nanočástic perovskitů stabilizovaných cyklo(RGDFK) pentapeptidem. Vzhledem k citlivosti peptidů na jejich byly nanočástice stabilizovány peptidovými nukleovými kyselinami, robustními analogy nukleových kyselin. Ke stabilizaci nanočástic byl připraven monomer a trimer peptidové nukleové kyseliny obsahující thymin jako dusíkatou bázi. Thymin byl na povrchu nanočástic dostupný k interakci s adeninem přes vodíkové můstky umožňující přenos náboje. Kombinace peptidových nukleových kyselin a perovskitů s unikátními optickými vlastnostmi otevírá aplikační možnosti zejména v oblasti optických senzorů.

In order to better predict the aggregation state of nanomaterials, the factors that influence aggregation must be understood. The combined effects of natural and engineered coatings have been shown to factor into nanoparticle aggregation behavior in preliminary research. In this study, aggregation behaviors of gold nanoparticles with two different engineered coatings were investigated in the presence of the monovalent electrolyte KCl and the divalent electrolyte CaCl���. Aggregation studies were conducted using dynamic light scattering to determine the relative stability of the NMs in environments of varying ionic strength in the absence and presence of Suwannee River Natural Organic Matter (SRNOM). Coatings which provided primarily electrostatic stabilization were found to adhere closely to DLVO theory, while coatings which provided steric stability inhibited aggregation over a wide range of ionic strengths for both electrolytes. The presence of SRNOM was found to provide some electrostatic stability in the presence of KCl, but appeared to form agglomerates with calcium ions, especially at higher SRNOM concentrations.
Graduation date: 2013

The present thesis entitled “Design and Synthesis of Novel Soft Composites from Physical Gels and Nanomaterials” deals with soft materials derived from low molecular weight gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular weight gel (LMOG) which forms the basis of the work. It delves with the history of research in physical gel field, design of different types of gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design new gelator molecules. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. The aspect of liquid crystallinity in the gel phase is also discussed to throw light on the pattern of assembly and potential uses of these materials. Towards the end there is a comprehensive discussion on the smart nanocomposites derived from LMOGs and nanomaterials. The design, synthesis and numerous applications of inorganic-organic hybrid composites are discussed. Chapter 2A describes the synthesis and characterization of a variety of fatty acid amides of different naturally occurring L-amino acids whose molecular structures are shown in Chart 2A.1. Some of them were found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, rheology and it was found that gelation was critically dependent on the fatty acid chain length and nature of the amino acid. Among them, L-alanine based gelators were found to be the most efficient and versatile as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. (Structural formula) Chart 2A.1. Molecular structures of various fatty acid amides of different amino acids. Chapter 2B describes efficient gelation of both aliphatic and aromatic hydrocarbon solvents by a fatty acid amide, n-lauroyl-L-alanine (Chapter 2B.1). In addition, this compound was found to gelate the binary solvent mixtures comprised of aromatic hydrocarbon e.g. toluene and aliphatic hydrocarbon e.g. n-heptane. SEM and AFM showed that the fiber thickness of the gel assembly increases progressively in the binary mixture of n-heptane and toluene with increasing percentage of toluene. The self- Chart 2B.1. Molecular structure of the gelator. assembly patterns of the gels in individual solvents, n-heptane and toluene are however, different. The toluene gel consists of predominantly one type of morphological species while n-heptane gel has more than one species leading to polymorphic nature of the gel. The n-heptane gel is thermally more stable than the toluene gel as evident from the measurement using differential scanning calorimetry. The thermal stability of the gels prepared in the binary mixture of n-heptane and toluene is dependent on the composition of solvent mixture. Rheology of the gels shows that they are shear-thinning material and show characteristic behavior of soft viscoelastic solids. For the gels prepared from binary solvent mixture of toluene and n-heptane, with incorporation of more toluene in the binary mixture, the gel becomes a more viscoelastic solid. The time sweep rheology experiment demonstrates that the gel made in n-heptane has faster gel formation kinetics than that prepared in toluene. Chapter 2C describes lyotropic mesophase formation by organogels of different fatty acid amides of L-alanine in aromatic solvents. The helical assembly, characteristic of the cholesteric mesophase was found to exhibit reflection bands in circular dichroism spectra. The reflection bands corresponded to the pitch of the helical arrangement of the gelator molecules in the aromatic solvent. Transmission Electron Microscopy (TEM) showed presence of twist in the gel fibres. Polarising optical microscopy of the organogel exhibited weak birefringence confirming lyotropic nature of the assembly. Chapter 3 deals with synthesis and characterization of a new class of molecules with molecular structures shown in Chart 3.1. Among a variety of amino acid based molecules only alanine and serine based molecules were found to form translucent gels in aliphatic hydrocarbons such as n-heptane. TEM showed presence of fiber like structures for alanine whereas serine based gelator produces unique network like structures. SEM of the dried gels exhibited presence of three dimensional fibrous networks to spongy globular cauliflower like structures depending on the molecular structure of the gelators. Rheological studies of the organogels showed that they behave like typical LMOG gels. The oscillatory rheological studies demonstrated that the L-serine based gelator, 5 formed more viscoelastic solid like gel than that of L-alanine based gelator, 1 in n-heptane. Chart 3.1. Molecular structures of different amino acid derivatives from 3,4,5-tri-dodecyloxybenzoic acid scaffold. Chapter 4A presents design and properties of new nanocomposites from LMOG and metal nanoparticles (Chart 4A.1). The profound influence of nanoparticle (NP) incorporation into physical gels was evident from various microscopic and bulk properties. The interaction of nanoparticles with the gelator assembly was found to depend critically on the capping agent coating the nanoparticles. TEM showed long range Chart 4A.1. Molecular structures of the gelator and various AuNPs synthesized. directional assembly of the certain AuNPs along the gel fibers. SEM of the dried gels and nanocomposites indicated that the morphological transformation in the composite microstructures depended profoundly on the capping agent of the nanoparticle. Differential Scanning Calorimetry showed that gel formation from sol postponed to lower temperature with incorporation of AuNPs having capping agents which were able to interact with the gel fibers. Rheological studies indicated that the gel-nanoparticle composites exhibit greater rigidity as compared to the naked gel only when the capping agents were able to interdigitate into the gelator assembly. Also, very low percentage of the AuNPs incorporation could switch the cholesteric mesophase of gel assembly, as evident from circular dichroism. We have been able to define a relationship between materials and molecular properties via manipulation of the molecular structures of NP capping agents. Chapter 4B discusses the design and preparation of novel organogel-carbon nanotube composites by incorporation of single-walled carbon nanotubes (SWNT) into physical gels formed by an L-alanine based Low Molecular Mass Organogelator (Chart 4B.1). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized (Chart 4B.1). Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon incorporation of SWNTs. The microstructures of nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of SWNT incorporation. Again, more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Also, the helical cholesteric mesophase formed by the toluene gel could be switched to a layer stacked assembly by doping functional SWNT. Remarkably, by using a near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting. Chart 4B.1. Molecular structures of the gelator and different functionalized SWNT synthesized. Chapter 5A presents design of two component hydrogels and their potential utilization as a template for metal nanoparticle synthesis. Among a variety of acids and amines (Chart 5A.1) only stearic acid or eicosanoic acid when mixed with di- or oligomeric amines in specific molar ratios form stable gels in water. The formation of such hydrogels depends on the hydrophobicity of the fatty acid, and also on the type of amine used. The gelation properties of these two component systems were investigated using electron microscopy, FTIR, 1H NMR spectroscopy, differential scanning calorimetry (DSC) and both single crystal and cast film X-ray diffraction. FTIR spectral analysis suggests salt formation during gelation. 1H NMR of the gels indicates that the fatty acid chains are immobilized in the gel state and when the gel is melted, these chains regain their mobility. Analysis of DSC data indicates that increase in spacer length in the di-/oligomeric amine lowers the gel melting temperature. Two of these gelator salts developed into crystals and structural details of such systems could be secured by single-crystal X-ray diffraction analysis. The structural information of the salts thus obtained was compared with the XRD data of the self-supporting films of those gels. Such analyses provided pertinent structural insight on the supramolecular interactions that prevail within these gelator assemblies. From the crystal structure it is confirmed that the multilayered lamellar aggregates exist in the gel and it also showed that only one plane of symmetry is present in the gel state. Finally, the hydrogel was used as a medium for the synthesis of silver nanoparticles. The nanoparticles were found to position themselves on the fibers and produce a long ordered assembly of gel-nanoparticle composite (Figure 5A.1). Chart 5A.1. Structures and abbreviations of different acids and amines checked for gelation. Figure 5A.1. TEM images of gel-Ag-NP composite. (a) Ag-NP synthesized in hydrogel of SA-IBPA (1:3.5), (b) Magnified images of Ag-NP preferentially residing on gel fibers. Chapter 5B demonstrates the aptitude of supramolecular hydrogel formation using simple bile acids e.g. lithocholic acid (LCA) in aqueous solution containing di- or oligomeric amines (Chart 5B.1). By variation of the choice of the amines in such mixture the hydrogelation properties could be modulated. However, replacement of LCA by cholic acid or deoxycholic acid resulted in no hydrogelation. FT-IR studies show that the carboxylate and ammonium residues of the two components are primarily involved in salt formation. This promotes further assembly of the components reinforced by continuous Chart 5B.1. Structures and abbreviations of different bile acids and amines checked for gelation. hydrogen bonded network leading to gelation. Electron microscopy shows that the morphology of the gels of two component systems which also depends strongly on the amine part. Variation of amine component from the simple ethanediamine (EDA) to oligomeric amine with lithocholic acid changes the morphology of the assembly from long one dimensional nanotubes to three dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines participate with the carboxylate and hydroxyl moiety through H-bonding and electrostatic forces. The rheological properties of this class of two component system provide clear evidence that this system is a shear-sensitive hydrogel and the flow behavior can be modulated varying the acid-amine ratio. From small angle neutron scattering study, it becomes clear that loose gel from LCA-EDA shows scattering oscillation due to the presence of non interacting nanotubules while for gels of LCA with oligomeric amine the individual fibers come together to form complex three dimensional structures of higher length scale.(For structural formula pl refer the pdf file)

AbstractThe synthesis of silver nanoparticles using plant extract as a capping agent has been very easy, economical and environment friendly method. The Madhuca longifolia is one of the well-known trees for its various benefits from food industry to its medicinal applications. It is indigenous to India, Nepal, Sri Lanka and Myanmar. In the present aqueous extract was used from leaves of M. lngifolia has been used as a capping agent to form AgNPs by reducingsilver nitrate with the help of green synthesis route. UV-visible spectroscopicy gave maximaat 420 nmconfirmed the synthesis of M. longifolia AgNPs. Characterization was done by TEM, SEM, XRD and FTIR techniques. FTIR confirmed the presence of various phytochemicals and formation of nanoparticles. XRD confirmed the formation of crystalline structure of synthesized silver nanoparticles. The shape of silver nanoparticles was irregular and spherical. The reaction solution turned brown which is the primary indication of formation of AgNPs. Crystalline size was calculated and found to be 10–25 nm; and TEM showed the size of nanoparticles around 5–40 nm. The M. longifolia based Silver nanoparticles were evaluated for their antibacterial and antibiofilm activity on Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative) by disc diffusion and percentage inhibition methods was confirmed.

Nanoparticles are often associated with their small size and numerous applications. However, the synthesis process is equally important as it determines the size and properties of the nanoparticles. While traditional nanoparticle synthesis methods require the use of hazardous chemicals and high-energy consumption, green synthesis offers a sustainable, cost-effective, and environmentally friendly alternative. This approach utilizes natural resources and biologically active compounds that can act as reducing, stabilizing, or capping agents in the one-step synthesis of nanoparticles. Green synthesis offers numerous advantages, including the development of processes with minimal environmental impact and improved safety for nanoparticle synthesis. Overall, the synthesis of nanoparticles using green chemistry is a promising approach for sustainable and efficient production. This chapter provides a general overview of nanoparticles, their applications, and green synthesis, and highlights the various biological resources used in these processes and the factors affecting their synthesis.

Nanotechnology is a recent technology which is developing rapidly and it has a wide range of potential applications. It is the atomic-level tailoring of materials to achieve unique features that may be controlled for the intended purposes. Nanomaterials can be prepared via several physico-chemical methods but bioreduction of bulk to nanomaterials via green synthesis has developed as a viable alternative to physico-chemical methods in order to overcome their limitations. Plant-mediated nanomaterial synthesis has been found to be environmentally friendly, less costly, and safe with no use of chemicals for medicinal and biological applications where the nanoparticles purity is of major concern. Plant extract is used for the reduction of materials from bulk into nano scale instead of other toxic reducing agents used in chemical methods. The phytochemicals present the extract of plant not only facilitate the synthesis of nanomaterials but act as stabilizing and capping agent, also the shape and size of nanoparticles can be tailored by changing the nature and concentration of plant extract. The present chapter focuses on the green synthesis of nanoparticles mediated by various Brassica species and their potential medicinal and biological applications.

Nanotechnology is growing as an essential discipline in research with several applications. For the synthesis of nanoparticles, distinct methods such as chemical, physical and biological entities have been adopted. Among these, green synthesis of metal nanoparticles has gained wider attention owing to its simplicity, non-toxicity, cost-effective, sustainable and easy availability. The phyto compounds existing in the plant extract either acts as reducing, stabilizing and capping agents; thereby, it reduces the cost and consumptions of energy and hazardous chemicals. This review mainly focused on the recent trend in the utilization of the plant material for the synthesizing of various metal nanoparticles and their catalytic application with special reference to their morphological features.

Silver nanoparticles (AgNPs) biosynthesized using by-products of tomatoes extracts as reducing and capping agents show multiple possibilities for solving various biological problems. The aim of this study was to expand the boundaries on AgNPs using novel low toxicity and production cost phytochemical method for the biosynthesis of nanoparticles from tomatoes aqueous extracts. Biosynthesized AgNPs were characterized by various methods (SEM, EDS). Determined antioxidative and antimicrobial activity of plant extracts was compared with the activity of the AgNPs. TEM results show mainly spherical-shaped AgNPs, size distribution of which depends on the plant leaf extract type; the smaller AgNPs were obtained with tomatoes extract (6–45 nm AgNPs). Besides, AgNPs show strong antimicrobial activity against broad spectrum of Gram-negative and Gram-positive bacteria strains and fungi.

The development in nanotechnology, specifically the nanoparticulate system, has a great impact on medicine, engineering and other scientific areas. Inorganic nanoparticles such as silver, gold, zinc oxide, selenium, iron, lead, platinum and copper, etc. were found to exhibit antimicrobial, antioxidant and other biological activities, used as biosensors and also used in different fields of engineering. In the 21st century, microorganisms and plant parts are playing a major role in the synthesis of inorganic nanoparticles. Green synthesis of inorganic nanoparticles becomes preferable to other approaches because of its eco-friendly and non-toxic approach. Additionally, the active molecules of plants (Tannins, flavonoids, terpenoids, saponins, proteins and glycosides) which act as capping and reducing agents in the synthesis of metal nanoparticles could make them most suitable for biomedical applications. This green approach fascinated researchers across the globe to explore the potential of different microorganisms and plants in the synthesis of inorganic nanoparticles. Selenium nanoparticles are one of the inorganic nanoparticles which are widely used in the area of medicine and engineering. In this chapter, we discussed the green synthesis using microorganism and Agri based products, characterisation and various applications of selenium nanoparticles.

Nanoscience has opened new vistas to manage phytopathogens, improve crop productivity by the development of new varieties, and control infectious diseases in humans. Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) are highly acclaimed for their wide potential application in various fields. Chemical and physical methods of synthesis of AgNPs and AuNPs are widely used; however, such methods possess numerous setbacks, such as the production of toxic residues and indispensable need for high energy. Biosynthesis of nanoparticles is a cost-effective and environmentally friendly method. A plethora of species of plant, bacteria, fungi, etc. is available with potential biosynthesis ability. Fungi are a highly preferred organism owing to the ability to secrete a large number of extracellular enzymes, metal toxicity tolerance and bioaccumulation ability, and ease of handling of its biomass. Extracellular enzymes act both as reducing as well as capping agents. Two different methods are used by fungi for synthesis viz., intercellular and extracellular synthesis. Extracellular synthesis is preferred over intercellular as it bypasses several down streaming processes. During the reduction process, the metal ions (Ag2+ and Au3+) are converted to an elemental state (Ag0 and Au0 ) which is in the nano range. Due to their large surface-to-volume ratio and other properties, they become very effective against other pathogens. There is an excellent prospect of the use of nanoparticles in the field of agriculture and health and nanoparticles synthesized using a biological method involving fungi could be a boon.

A controlled synthesis method for preparing narrow-dispersed copper nanoparticles, using water and ethylene glycol as the reaction mediums respectively, has been reported. In order to obtain pure-phase copper nanoparticles using water, the reaction time of 8h is essential. Owing to the reduction property of ethylene glycol, the reaction rate using ethylene glycol is higher. In addition, the amount of reduction agent can reduce largely. Polyvinyl pyrrolidone plays great role on the size of copper particles, and the increasing of polyvinyl pyrrolidone concentration attributes to the smaller dimension particles. The mean diameter is about 4 nm when the concentration of polyvinyl pyrrolidone is 0.5 mmol/L. Polyvinyl pyrrolidone acts as the polymeric capping agents in the reaction, preventing the agglomeration of the copper nanoparticles. When water is the reaction medium, Cu2+ complex is reduced to Cu+ complex firstly, and the further reduction of Cu+ forms the pure copper nanoparticle.

Silver nanoparticles have been the focus of extensive research for many decades due to their unique physical, chemical and electrical properties. Introducing new environmentally benign methods for the synthesis of silver nanoparticles is of great interest in the research community. In this work we propose a new method for the simple synthesis of stable heterostructured biopolymer (sodium alginate)-capped silver nanoparticles (Ag-NPs) based on green chemistry.The as-prepared nanoparticles were characterized using the ultraviolet–visible (UV–Vis) absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Dynamic light scattering (DLS) techniques. The results showed that the as-prepared Ag-NPs have a heterostructured morphology with particle size in the range 30 ± 18 – 60 ± 25 nm, showing a zeta potential of -62 mV. The silver nanoparticle formation was confirmed from UV-Vis spectra showing 424 nm as maximum absorption. The particle size and crystallinity of the as- synthesized nanoparticles were analyzed using TEM and XRD measurements respectively. FTIR spectra confirmed the presence of alginate as capping agent to stabilize the nanoparticles. The Ag-NPs also showed excellent sensing capability, with a linear response to hydrogen peroxide spanning a wide range of concentrations from 10-1 – 10-7 M, which indicates their high potential for water treatment applications, such as pollution detection and nanofiltration composites.

Graphene quantum dots (GQDs) are famously known for large surface area, good dispersibility, good conductivity, and high transparency with good photochemical, electrochemical, and optical properties that are utilized in many biomedical and biotechnological applications. Interestingly, GQDs were reported to serve as an excellent reducing reagent in the synthesis of noble metal nanoparticles such as silver nanoparticles (AgNPs). Moreover, GQDs eradicate the limitation of impurities of AgNPs synthesized using plant extracts as a stabilizer and reducing agents. Therefore, we experimented GQDs synthesis from moringa oleifera (MO) plant extracts compared to citric and urea synthesized GQDs. And used the synthesized GQDs to synthesize, reduce and functionalize AgNPs. MO contains about 110 compounds, high nutrients, vitamins, oleic oil, and phytoconstituents such as alkaloids, flavonoids, glucosinolates, saponins, tannins, terpenes, steroids, phenolic acids, which suggested to us that, MO extracts can serve as a capping agent in the synthesis of nanoparticles. Initially, MO leaves and seeds water phase extracts were obtained by overnight distillation and lyophilized to create a stock solution of 1mg/ml. Next, following Das, R. et al and slightly modifying the followed method by varying the MO extract concentration from 20µL to 60 µL, AgNPs were synthesized by hydrothermal method. GQDs were separately synthesized adopting Tran, H.V. et al method and later added to the AgNPs forming a more stable hybrid structure that was characterized using the UV-vis spectroscopy (UV-Vis), Nano zeta sizer, Raman spectroscopy, and the Fourier Infrared transmission resonance (FTIR). As the concentration of MO extract increased, the color change intensity increased symbolizing the formation of AgNPs while the luminous bright solutions under the UV light symbolized the formation of GQDs. This study lay the foundation for further research and analysis to be done on the nanozyme or biosensor application of enhanced functionalized and stable hybrid AgNPs with GQDs.

Semiconductor nanocrystals have unique optical properties due to quantum confinement effects, and a variety of promising approaches have been devised to interface the nanomaterials with biomolecules for bioimaging and therapeutic applications. Such bio-interface can be facilitated via a DNA template for nanoparticles as oligonucleotides can mediate the aqueous-phase nucleation and capping of semiconductor nanocrystals.[1,2] Here, we report a novel scheme of synthesizing fluorescent nanocrystal quantum dots (NQDs) using DNA aptamers and the use of this biotic/abiotic nanoparticle system for growth inhibition of MCF-7 human breast cancer cells for the first time. Particularly, we used two DNA sequences for this purpose, which have been developed as anti-cancer agents: 5-GGT GGT GGT GGT TGT GGT GGT GGT GG-3 (also called, AGRO) and 5-(GT)15-3.[3–5] This study may ultimately form the basis of unique nanoparticle-based therapeutics with the additional ability to optically report molecular recognition. Figure 1a shows the photoluminescence (PL) spectra of GT- and AGRO-passivated PbS QD that fluoresce in the near IR, centered at approximately 980 nm. A typical synthesis procedure involves rapid addition of sodium sulfide in the mixture solution of DNA and Pb acetate at a molar ratio of 2:4:1. The resulting nanocrystals are washed to remove unreacted DNA and ions by adding mixture solution of NaCl and isopropanol, followed by centrifugation. The precipitated nanocrystals are collected and re-suspended in aqueous solution by mild sonication. Optical absorption measurements reveal that approximately 90 and 77% of GT and AGRO DNA is removed after the washing process. The particle size distribution in Figure 1b suggests that the GT sequence-capped PbS particles are primarily in 3–5 nm diameter range. These nanocrystals can be easily incorporated with mammalian cells and remain highly fluorescent in sub-cellular environments. Figure 1c serially presents an optical image of a MCF-7 cell and a PL image of the AGRO-capped QD incorporated with the cell. Figure 1. (a) Normalized fluorescence spectra of PbS QD synthesized with GT and AGRO sequences, which were previously developed as anti-cancer agents. The DNA-capped QD fluoresce in the near IR centered at ∼980 nm. (b) TEM image of GT-templated nanocrystals ranging 3–5 nm in diameter. (c) Optical image of an MCF-7 human breast cancer cell after a 12-hour exposure to aptamer-capped QD. (d) PL image of AGRO-QD incorporated with the cell, indicating that these nanocrystals remain highly fluorescent in sub-cellular environments. One immediate concern for interfacing inorganic nanocrystals with cells and tissue for labeling or therapeutics is their cytotoxicity. The nanoparticle cytotoxicity is primarily determined by material composition and surface chemistry, and QD are potentially toxic by generating reactive oxygen species or by leaching heavy metal ions when decomposed.[6] We examined the toxicity of aptamer-passivated nanocrystals with NIH-3T3 mouse fibroblast cells. The cells were exposed to PbS nanocrystals for 2 days before a standard MTT assay as shown in Figure 2, where there is no apparent cytotoxicity at these doses. In contrast, Pb acetate exerts statistically significant toxicity. This observation suggests a stable surface passivation by the DNA aptamers and the absence of appreciable Pb2+ leaching. Figure 2. Viability of 3T3 mouse fibroblast cells after a 2-day exposure to DNA aptamer-capped nanocrystals. There is no apparent dose-dependent toxicity, whereas a statistically significant reduction in cell viability is observed with Pb ions. Note that Pb acetate at 133 μM is equivalent to the Pb2+ amount that was used for PbS nanocrystal synthesis at maximum concentration. Error bars are standard deviations of independent experiments. *Statistically different from control (p&lt;0.005). Finally, we examined if these cyto-compatible nanoparticle-aptamers remained therapeutically active for cancer cell growth inhibition. The MTT assay results in Figure 3a show significantly decreased growth of breast cancer cells incorporated with AGRO, GT, and the corresponding templated nanocrystals, as anticipated. In contrast, 5-(GC)15-3 and the QDs synthesized with the same sequence, which were used as negative controls along with zero-dose control cells, did not alter cell viability significantly. Here, we define the growth inhibition efficacy as (100 − cell viability) per DNA of a sample, because the DNA concentration is significantly decreased during the particle washing. The nanoparticle-aptamers demonstrate 3–4 times greater therapeutic activities compared to the corresponding aptamer drugs (Figure 3b). We speculate that when a nanoparticle-aptamer is internalized by the cancer cells, it forms an intracellular complex with nucleolin and nuclear factor-κB (NF-κB) essential modulator, thereby inhibiting NF-κB activation that would cause transcription of proliferation and anti-apoptotic genes.[7] The nanoparticle-aptamers may more effectively block the pathways for creating anti-apoptotic genes or facilitate the cellular delivery of aptamers via nanoparticle uptake. Our additional investigation indicates that the same DNA capping chemistry can be utilized to produce aptamer-mediated Fe3O4 nanocrystals, which may be potentially useful in MRI and therapeutics, considering their magnetic properties and biocompatibility. In summary, the nanoparticle-based therapeutic schemes developed here should be valuable in developing a multifunctional drug delivery and imaging agent for biological systems. Figure 3. Anti-proliferation of MCF-7 human breast cancer cells with aptamer-passivated nanocrystals. (a) Viability of MCF-7 cells exposed to AGRO and GT sequences, and AGRO-/GT-capped QD for 7 days. The DNA concentration was 10 uM, while the particles were incubated with cells at 75 nM. (b) Growth inhibition efficacy is defined as (100 − cell viability) per DNA to correct the DNA concentration after particle washing.

Two potential molecular imaging vectors are investigated for material properties and magnetic resonance imaging (MRI) contrast improvement. Monodisperse magnetite (Fe3O4) nanocrystals ranging in size from 7 to 22 nm are solvothermally synthesized by thermolysis of Fe(III) acetylacetonate (Fe(AcAc)3) both with and without the use of heptanoic acid (HA) as a capping ligand. For the resulting Fe3O4 nanocrystals, X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device magnetometry (SQUID) is used to identify the average particle size, monodispersity, crystal symmetry, and magnetic properties of the ensembles as a function of time. The characterization study indicates that the HA synthesis route at 3 hours produced nanoparticles with the greatest magnetic anisotropy (15.8 × 104 J/m3). The feasibility of Fe8 single molecule magnets (SMMs) as a potential MRI contrast agent is also examined. SQUID magnetization measurements are used to determine anisotropy and saturation of the potential agents. The effectiveness of the Fe3O4 nanocrystals and Fe8 as potential MRI molecular probes is evaluated by MRI contrast improvement using 1.5 mL phantoms dispersed in de-ionized water. Results indicate that the magnetically optimized Fe3O4 nanocrystals and Fe8 SMMs hold promise for use as contrast agents based on the reported MRI images and solution phase T1/T2 shortening.

Clay-supported silver nanoparticles were green synthesized using the aqueous leaf extract of Parkia biglobosa. The phytochemical analysis and FTIR results of the Parkia biglobosa showed that the leaf contains phenol, tanning, and flavonoids, which act as reducing, capping, and stabilizing agents required for the synthesis of the silver nanoparticles. The prepared adsorbent has good morphology, is rich in silica, and contains functional groups suitable for heavy metal binding. The adsorptions of Zn, Cu, and Pb from pharmaceutical wastewater onto the silver-modified clay were studied as an adsorbent dosage and contact time. From the percentage removal results obtained, the adsorbent had up to 99.96%, 99.5%, and 99.44% removal efficiency for Zn, Pb, and Cu, respectively. The present work shows that the synthesized silver nanoparticles supported on local clay can be used as a potentially low-cost adsorbent to remove heavy metal ions from industrial wastewater.