To see the other types of publications on this topic, follow the link: TiO2 nanotube.
Dissertations / Theses on the topic 'TiO2 nanotube'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'TiO2 nanotube.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Cummings, Franscious Riccardo. "TiO2 nanotube based dye- sensitised solar cells." University of Western Cape, 2012. http://hdl.handle.net/11394/3311.
Full textAbstract:
Philosophiae Doctor - PhD<br>This work investigated the synthesis of Al2O3-coated TiO2 nanotubes via the anodisation technique for application in DSCs. TiO2 nanotube arrays with
an average length of 15 μm, diameter of 50 nm and wall thickness of 15 nm
were synthesised via anodisation using an organic neutral electrolyte consisting
of 2 M H2O + 0.15 M NH4F + ethylene glycol (EG) at an applied voltage of 60 V
for 6 hours. In addition, scanning electron microscope (SEM) micrographs
showed that anodisation at these conditions yields nanotubes with smooth
walls and hexagonally shaped, closed bottoms. X-ray diffraction (XRD) patterns revealed that the as-anodised nanotubes were amorphous and as such were annealed at 450 °C for 2 hours in air at atmospheric pressure, which yielded crystalline anatase TiO2 nanotubes. Highresolution transmission electron microscope (TEM) images revealed that the nanotube walls comprised of individual nano-sized TiO2 crystallites.
Photoluminescence (PL) spectroscopy showed that the optical properties, especially the bandgap of the TiO2 nanotubes are dependent on the crystallinity, which in turn was dependent on the structural characteristics, such as the wall thickness, diameter and length. The PL measurements were supplemented by Raman spectra, which revealed an increased in the quantum confinement of the optical phonon modes of the nanotubes synthesised at low anodisation voltages, consequently yielding a larger bandgap
The annealed nanotubes were then coated with a thin layer of alumina (Al2O3) using a simple sol-gel dip coating method, effectively used to coat films of nanoparticles. Atomic force microscopy (AFM) showed that the average nanotube diameter increased post sol-gel deposition, which suggests that the nanotubes are coated with a layer of Al2O3. This was confirmed with HR-TEM, in conjunction with selected area electron diffraction (SAED) and XRD analyses, which showed the coating of the nanotube walls with a thin layer of amorphous Al2O3 with a thickness between 4 and 7 nm. Ultraviolet-visible (UVvis) absorbance spectra showed that the dye-adsorption ability of the nanotubes are enhanced by the Al2O3 coating and hence is a viable material for
solar cell application. Upon application in the DSC, it was found by means of photo-current density – voltage (I – V) measurements that a DSC fabricated with a 15 μm
thick layer of bare TiO2 nanotubes has a photon-to-light conversion efficiency of
4.56%, which increased to 4.88% after coating the nanotubes with a layer of
alumina. However, these devices had poorer conversion efficiencies than bare
and Al2O3-coated TiO2 nanoparticle based DSCs, which boasted with efficiencies of 6.54 and 7.26%, respectively. The low efficiencies of the TiO2 nanotube based DSCs are ascribed to the low surface area of the layer of nanotubes, which yielded low photocurrent densities. Electrochemical impedance spectroscopy (EIS) showed that the electron lifetime in the alumina coated nanotubes are almost 20 times greater than in a bare layer of nanoparticles. In addition, it was also found that the charge transfer resistance at the interface of the TiO2/dye/electrolyte is the lowest for an Al2O3-coated TiO2 layer.
2
Noeiaghaei, Tahereh. "Advanced treatment of wastewater effluents by multi-functional carbon nanotube-TiO2 nanotube membranes." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12846.
Full textAbstract:
Recently, the coupling of TiO2-photocatalysis with a membrane separation process has been perceived as a powerful tool for the recycling of wastewater effluents. While the membrane has the simultaneous task of supporting the photocatalyst as well as acting as a selective barrier for the species to be degraded, the photocatalyst degrades the organic compounds with the added advantage of mitigating membrane fouling. The focus of this thesis is to combine the specific features of TiO2 nanotubes with the unique properties of CNTs to design a multi-functional membrane for the enhanced removal of effluent organic matters (EfOMs) in wastewater effluents. Firstly, the kinetics of photocatalytic degradation of model organic compounds by TiO2 NPs were studied, and the experimental conditions for the enhancement of photocatalytic degradation efficiency were optimised. The photocatalytic reactivity and stability of TiO2 NPs were affected in the presence of natural organic matter (NOM). Secondly, TiO2 nanotube arrays (TNAs) were successfully fabricated via anodic oxidation of Ti substrates and their geometrical characteristics were optimised by controlling the synthesis parameters for enhancement of the photocatalytic removal efficiency of model organic compounds. Finally, multi-functional CNT/TiO2 nanotube membranes were fabricated via chemical vapour deposition (CVD) and anodic growth of TNAs on a porous Ti sheet. The performance of the hybrid CNT/TiO2 nanotube membrane (CNT/TNM) for removal of 4CBA was experimentally evaluated in a continuous filtration system under UV-A irradiation. The surface properties and the performance of the TNM were notably influenced by incorporation of CNTs. The CNT/TNM showed enhanced performance in removal of model compound compared to the TNM, which was attributed to the higher adsorption capacity of well-incorporated CNT/TNM.
3
Xu, Yanan. "Characterization of mechanical behaviour of TiO2 nanotube array." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/96480/1/Yanan_Xu_Thesis.pdf.
Full textAbstract:
This thesis presents a comprehensive investigation on mechanical behaviour of TiO2 nanotube arrays. Experimental investigation and numerical simulations have been carried out to understand the mechanical behaviour of single nanotube, micron-sized nanotube pillar and nanotube arrays. The deformation and failure mechanisms and their dependence on loading conditions are discussed. The outcomes of this work will be beneficial to future development of TiO2 nanotube arrays and other nanostructures.
4
Tshaka, Anele. "Synthesis of One-Dimensional TiO2 Nanotube Arrays by Potentiostatic Anodisation." University of the Western Cape, 2017. http://hdl.handle.net/11394/6198.
Full textAbstract:
Magister Scientiae - MSc (Microbiology)<br>TiO2 nanomaterials, in particular nanotubes, are some of the most studied materials, as they are
considerably important in technological and biological applications due to their unique
electronic properties and biocompatibility. For example, vertically aligned TiO2 nanotubes
play a crucial role in photovoltaics as they enhance the charge separation as a result of their
excellent photo-catalytic properties in the presence of organic dye molecules, and provide a
superior one-dimensional transport route compared to nanoparticle films. There are numerous
techniques used to synthesise TiO2 nanotubes, such as chemical vapor deposition (CVD),
template based techniques, anodisation, to name but a few. However, due to its non-toxicity
environmental friendliness and cost-effectiveness, anodisation is the most common technique
to synthesise TiO2 nanotubes. In addition anodisation allows for control over the morphology
when tailoring the anodisation parameters such as voltage, concentration, temperature and
duration. It is well-documented that the as-synthesised TiO2 nanotubes via anodisation
technique are amorphous and require post-treatment at elevated temperature (above 280 degrees C) to
induce crystallinity into anatase phase. Further increase in annealing temperature results in
crystallisation in either rutile or mixed phase structure.
5
Larue, Camille. "Impact de nanoparticules de TiO2 et de nanotubes de carbone sur les végétaux." Phd thesis, AgroParisTech, 2011. http://pastel.archives-ouvertes.fr/pastel-00765312.
Full textAbstract:
Dans le contexte du développement exponentiel des nanotechnologies, les nanomatériaux sont susceptibles de se disséminer dans l'environnement. Les végétaux sont un élément sensible des écosystèmes car ils constituent une interface entre l'eau, le sol et l'air et se situent à la base de la chaine trophique. Cette étude avait pour but d'évaluer l'impact des nanoparticules de TiO2 et des nanotubes de carbone sur les végétaux, et plus particulièrement sur le blé et le colza. L'accent a également était mis sur la caractérisation des nanomatériaux employés. Nous avons mis en évidence l'accumulation racinaire et le transfert vers les feuilles des nanoparticules de TiO2 et des NTC dans le blé et le colza après une exposition en hydroponie. Les nanoparticules de TiO2 sont également accumulées dans les plantes lors d'une exposition racinaire sur sol ou encore lors d'une exposition par voie aérienne. Les nanoparticules de TiO2 s'accumulent dans les végétaux à hauteur de quelques dizaines voire centaines de mg Ti/kg MS, leur phase cristalline n'est pas modifiée et ces nanoparticules ne se dissolvent pas lors de leur transfert dans le végétal. Les NTC s'accumulent en plus faible quantité (centaines de µg NTC/kg MS) et il semble qu'ils soient altérés par le contact avec le végétal. Ces nanomatériaux affectent peu le développement des végétaux. Sur huit tests réalisés, seule l'élongation racinaire s'est révélée être un critère sensible, avec une induction de l'élongation pour les NPs et les NTC présentant le plus faible diamètre nominal. Enfin, une nette influence du diamètre nominal des nanomatériaux a pu être mise en évidence, contrôlant ainsi leur internalisation, leur transfert et leurs effets biologiques sur les végétaux.
6
Madian, M., M. Klose, Tony Jaumann, et al. "Anodically fabricated TiO2–SnO2 nanotubes and their application in lithium ion batteries." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-225719.
Full textAbstract:
Developing novel electrode materials is a substantial issue to improve the performance of lithium ion batteries. In the present study, single phase Ti–Sn alloys with different Sn contents of 1 to 10 at% were used to fabricate Ti–Sn–O nanotubes via a straight-forward anodic oxidation step in an ethylene glycol-based solution containing NH4F. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. Our results reveal the successful formation of mixed TiO2/SnO2 nanotubes in the applied voltage range of 10–40 V. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage which turns Ti–Sn–O nanotubes into highly attractive materials for various applications. As an example, the Ti–Sn–O nanotubes offer promising properties as anode materials in lithium ion batteries. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at a current density of 504 μA cm−2. The results demonstrate that TiO2/SnO2 nanotubes prepared at 40 V on a TiSn1 alloy substrate display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. This electrode was tested at current densities of 50, 100, 252, 504 and 1008 μA cm−2 exhibiting average capacities of 780, 660, 490, and 405 μA cm−2 (i.e. 410, 345, 305 and 212 mA h g−1), respectively. The remarkably improved electrochemical performance is attributed to enhanced lithium ion diffusion which originates from the presence of SnO2 nanotubes and the high surface area of the mixed oxide tubes. The TiO2/SnO2 electrodes retain their original tubular structure after electrochemical cycling with only slight changes in their morphology.
7
Tsai, Hei-lok, and 蔡希樂. "Parametric study on the fabrication and modification of TiO2 nanotube arrays for photoeletrocatalytic degradation of organic pollutants." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45160259.
Full text
8
Madian, M., M. Klose, Tony Jaumann, et al. "Anodically fabricated TiO2–SnO2 nanotubes and their application in lithium ion batteries." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A30351.
Full textAbstract:
Developing novel electrode materials is a substantial issue to improve the performance of lithium ion batteries. In the present study, single phase Ti–Sn alloys with different Sn contents of 1 to 10 at% were used to fabricate Ti–Sn–O nanotubes via a straight-forward anodic oxidation step in an ethylene glycol-based solution containing NH4F. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. Our results reveal the successful formation of mixed TiO2/SnO2 nanotubes in the applied voltage range of 10–40 V. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage which turns Ti–Sn–O nanotubes into highly attractive materials for various applications. As an example, the Ti–Sn–O nanotubes offer promising properties as anode materials in lithium ion batteries. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at a current density of 504 μA cm−2. The results demonstrate that TiO2/SnO2 nanotubes prepared at 40 V on a TiSn1 alloy substrate display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. This electrode was tested at current densities of 50, 100, 252, 504 and 1008 μA cm−2 exhibiting average capacities of 780, 660, 490, and 405 μA cm−2 (i.e. 410, 345, 305 and 212 mA h g−1), respectively. The remarkably improved electrochemical performance is attributed to enhanced lithium ion diffusion which originates from the presence of SnO2 nanotubes and the high surface area of the mixed oxide tubes. The TiO2/SnO2 electrodes retain their original tubular structure after electrochemical cycling with only slight changes in their morphology.
9
Vesna, Despotović. "Fotolitička i fotokatalitička razgradnja odabranih herbicida u vodenoj sredini." Phd thesis, Univerzitet u Novom Sadu, Prirodno-matematički fakultet u Novom Sadu, 2014. https://www.cris.uns.ac.rs/record.jsf?recordId=86616&source=NDLTD&language=en.
Full textAbstract:
Ispitana je kinetika i mehanizam fotokatalitičke razgradnje herbicida kvinmeraka i klomazona u prisustvu UV/TiO<sub>2</sub> Degussa P25, odnosno piklorama i klopiralida primenom UV/TiO<sub>2</sub> Wackherr pri različitim eksperimentalnim uslovima. Praćena je i kinetika razgradnje odabranih herbicida direktnom fotolizom uz primenu sunčevog, UV i vidljivog zračenja, kao i u odsustvu svetlosti. Pored toga, upoređena je efikasnost UV/TiO<sub>2</sub> Degussa P25, odnosno UV/TiO<sub>2</sub> Wackherr sa vidljivim zračenjem, kao i direktnom fotolizom u prisustvu pomenutih izvora svetlosti. U cilju procene citotoksičnosti klomazona i klopiralida, kao i smeše klomazona i klopiralida i njihovih intermedijera nastalih tokom fotokatalitičke razgradnje ispitan je in vitro rast ćelijskih linija MRC-5 i H-4-II-E. Nakon ispitivanja fotokatalitičke razgradnje odabranih herbicida u dvaput destilovanoj vodi, praćena je njihova razgradnja i u prirodnim vodama. Takođe, ispitan je uticaj dodatka hidrogenkarbonata i huminske kiseline na efikasnost razgradnje odabranih herbicida. Fotokatalitička razgradnja klomazona, piklorama i mekopropa je ispitivana i u prisustvu UV/TiO<sub>2</sub> nanocevi. Aktivnost katalizatora TiO<sub>2 </sub>Wackherr i TiO<sub>2</sub> nanocevi je upoređena sa TiO<sub>2</sub> Degussa P25.<br>The kinetics and mechanism of photocatalytic degradation of the herbicides quinmerac and clomazone in the presence of UV/TiO<sub>2</sub> Degussa P25, and of picloram and clopyralid using UV/TiO<sub>2</sub> Wackherr under different experimental conditions were studied. The kinetics of degradation of selected herbicides by direct photolysis using sunlight, UV and visible radiation, and in the absence of light were followed. In addition, the efficiencies of UV/TiO<sub>2</sub> Degussa P25 and UV/TiO<sub>2 </sub>Wackherr were compared with visible radiation and direct photolysis in the presence of the above mentioned light sources. In order to evaluate the cytotoxicity of clomazone and clopyralid alone and in their mixture with intermediates formed during the photocatalytic degradation, in vitro growth of cell lines, MRC-5 and H-4-II-E was followed. After examining the photocatalytic degradation of selected herbicides in double distilled water, their decomposition in natural waters was also followed. Also, the influence of hydrogencarbonate and humic acid addition on the efficiency of degradation of selected herbicides was studied. Photocatalytic degradations of clomazone, picloram and mecoprop were investigated in the presence of UV/TiO<sub>2 </sub>nanotubes. Activities of the catalysts TiO<sub>2</sub> Wackherr and TiO<sub>2 </sub>nanotubes were compared to TiO<sub>2</sub> Degussa P25.
10
Su, Lusheng. "Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126.
Full text
11
Tilly, Trevor. "DISPERSION OF GEOMETRIC TITANIUM DIOXIDE NANOMATERIALS AND THEIR BIOLOGIC EFFECT." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1387488387.
Full text
12
Sahu, Gayatri. "Investigating the Electron Transport and Light Scattering Enhancement in Radial Core-Shell Metal-Metal Oxide Novel 3D Nanoarchitectures for Dye Sensitized Solar Cells." ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1478.
Full textAbstract:
Dye-sensitized solar cells (DSSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Electron transport is one of the prominent processes in the cell and it is further a complex process because the transport medium is a mesoporous film. The gaps in the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, the electron transport in these so called state-of-the-art systems has a practical limit because of the low electron diffusion coefficient (Dn) in this mesoporous film photoanode. This work focuses on the influence of the advanced core-shell nanoarchitecture geometry on electron transport and also on the influence of electron-ion interactions. In order to achieve the proposed goals, DSSCs based on ordered, highly aligned, 3D radial core-shell Au-TiO2 hybrid nanowire arrays were fabricated, using three different approaches. J-V, IPCE, and EIS characteristics were studied. The efficiency, light scattering and charge transport properties of the core-shell nanowire based devices were compared to TiO2 nanotube as well as TiO2 mesoporous film based DSSCs. The Au nanowires inside the crystalline TiO2 anatase nanoshell provided a direct conduction path from the TiO2 shell to the TCO substrate and improved transport of electrons between the TiO2 and the TCO. The optical effects were studied by IPCE measurement which demonstrated that Au-TiO2 nanowires showed an improved light harvesting efficiency, including at longer wavelengths where the sensitizer has weak absorption. The metal nanostructures could enhance the absorption in DSSCs by either scattering light enabling a longer optical path-length, localized surface plasmon resonance (LSPR) or by near-field coupling between the surface plasmon polariton (SPP) and the dye excited state. Rapid, radial electron collection is of practical significance because it should allow alternate redox shuttles that show relatively fast electron-interception dynamics to be utilized without significant sacrifice of photocurrent. A combination of improved electron transport and enhanced light harvesting capability make Au-TiO2 core-shell nanowire arrays a promising photoanode nanoarchitecture for improving photovoltaic efficiency while minimizing costs by allowing thinner devices that use less material in their construction.
13
Tian, Yujing. "Boosting Reaction Kinetics of N2 Electrocatalysis via Adsorption Enhancement and Confinement of Adsorbates." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin159239534417192.
Full text
14
Zheng, Zhanfeng. "Synthesis and modifications of metal oxide nanostructures and their applications." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/31728/1/Zhanfeng_Zheng_Thesis.pdf.
Full textAbstract:
Transition metal oxides are functional materials that have advanced applications in many areas, because of their diverse properties (optical, electrical, magnetic, etc.), hardness, thermal stability and chemical resistance. Novel applications of the nanostructures of these oxides are attracting significant interest as new synthesis methods are developed and new structures are reported. Hydrothermal synthesis is an effective process to prepare various delicate structures of metal oxides on the scales from a few to tens of nanometres, specifically, the highly dispersed intermediate structures which are hardly obtained through pyro-synthesis. In this thesis, a range of new metal oxide (stable and metastable titanate, niobate) nanostructures, namely nanotubes and nanofibres, were synthesised via a hydrothermal process. Further structure modifications were conducted and potential applications in catalysis, photocatalysis, adsorption and construction of ceramic membrane were studied. The morphology evolution during the hydrothermal reaction between Nb2O5 particles and concentrated NaOH was monitored. The study demonstrates that by optimising the reaction parameters (temperature, amount of reactants), one can obtain a variety of nanostructured solids, from intermediate phases niobate bars and fibres to the stable phase cubes. Trititanate (Na2Ti3O7) nanofibres and nanotubes were obtained by the hydrothermal reaction between TiO2 powders or a titanium compound (e.g. TiOSO4·xH2O) and concentrated NaOH solution by controlling the reaction temperature and NaOH concentration. The trititanate possesses a layered structure, and the Na ions that exist between the negative charged titanate layers are exchangeable with other metal ions or H+ ions. The ion-exchange has crucial influence on the phase transition of the exchanged products. The exchange of the sodium ions in the titanate with H+ ions yields protonated titanate (H-titanate) and subsequent phase transformation of the H-titanate enable various TiO2 structures with retained morphology. H-titanate, either nanofibres or tubes, can be converted to pure TiO2(B), pure anatase, mixed TiO2(B) and anatase phases by controlled calcination and by a two-step process of acid-treatment and subsequent calcination. While the controlled calcination of the sodium titanate yield new titanate structures (metastable titanate with formula Na1.5H0.5Ti3O7, with retained fibril morphology) that can be used for removal of radioactive ions and heavy metal ions from water. The structures and morphologies of the metal oxides were characterised by advanced techniques. Titania nanofibres of mixed anatase and TiO2(B) phases, pure anatase and pure TiO2(B) were obtained by calcining H-titanate nanofibres at different temperatures between 300 and 700 °C. The fibril morphology was retained after calcination, which is suitable for transmission electron microscopy (TEM) analysis. It has been found by TEM analysis that in mixed-phase structure the interfaces between anatase and TiO2(B) phases are not random contacts between the engaged crystals of the two phases, but form from the well matched lattice planes of the two phases. For instance, (101) planes in anatase and (101) planes of TiO2(B) are similar in d spaces (~0.18 nm), and they join together to form a stable interface. The interfaces between the two phases act as an one-way valve that permit the transfer of photogenerated charge from anatase to TiO2(B). This reduces the recombination of photogenerated electrons and holes in anatase, enhancing the activity for photocatalytic oxidation. Therefore, the mixed-phase nanofibres exhibited higher photocatalytic activity for degradation of sulforhodamine B (SRB) dye under ultraviolet (UV) light than the nanofibres of either pure phase alone, or the mechanical mixtures (which have no interfaces) of the two pure phase nanofibres with a similar phase composition. This verifies the theory that the difference between the conduction band edges of the two phases may result in charge transfer from one phase to the other, which results in effectively the photogenerated charge separation and thus facilitates the redox reaction involving these charges. Such an interface structure facilitates charge transfer crossing the interfaces. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process. Moreover, the fibril titania photocatalysts are of great advantage when they are separated from a liquid for reuse by filtration, sedimentation, or centrifugation, compared to nanoparticles of the same scale. The surface structure of TiO2 also plays a significant role in catalysis and photocatalysis. Four types of large surface area TiO2 nanotubes with different phase compositions (labelled as NTA, NTBA, NTMA and NTM) were synthesised from calcination and acid treatment of the H-titanate nanotubes. Using the in situ FTIR emission spectrescopy (IES), desorption and re-adsorption process of surface OH-groups on oxide surface can be trailed. In this work, the surface OH-group regeneration ability of the TiO2 nanotubes was investigated. The ability of the four samples distinctively different, having the order: NTA > NTBA > NTMA > NTM. The same order was observed for the catalytic when the samples served as photocatalysts for the decomposition of synthetic dye SRB under UV light, as the supports of gold (Au) catalysts (where gold particles were loaded by a colloid-based method) for photodecomposition of formaldehyde under visible light and for catalytic oxidation of CO at low temperatures. Therefore, the ability of TiO2 nanotubes to generate surface OH-groups is an indicator of the catalytic activity. The reason behind the correlation is that the oxygen vacancies at bridging O2- sites of TiO2 surface can generate surface OH-groups and these groups facilitate adsorption and activation of O2 molecules, which is the key step of the oxidation reactions. The structure of the oxygen vacancies at bridging O2- sites is proposed. Also a new mechanism for the photocatalytic formaldehyde decomposition with the Au-TiO2 catalysts is proposed: The visible light absorbed by the gold nanoparticles, due to surface plasmon resonance effect, induces transition of the 6sp electrons of gold to high energy levels. These energetic electrons can migrate to the conduction band of TiO2 and are seized by oxygen molecules. Meanwhile, the gold nanoparticles capture electrons from the formaldehyde molecules adsorbed on them because of gold’s high electronegativity. O2 adsorbed on the TiO2 supports surface are the major electron acceptor. The more O2 adsorbed, the higher the oxidation activity of the photocatalyst will exhibit. The last part of this thesis demonstrates two innovative applications of the titanate nanostructures. Firstly, trititanate and metastable titanate (Na1.5H0.5Ti3O7) nanofibres are used as intelligent absorbents for removal of radioactive cations and heavy metal ions, utilizing the properties of the ion exchange ability, deformable layered structure, and fibril morphology. Environmental contamination with radioactive ions and heavy metal ions can cause a serious threat to the health of a large part of the population. Treatment of the wastes is needed to produce a waste product suitable for long-term storage and disposal. The ion-exchange ability of layered titanate structure permitted adsorption of bivalence toxic cations (Sr2+, Ra2+, Pb2+) from aqueous solution. More importantly, the adsorption is irreversible, due to the deformation of the structure induced by the strong interaction between the adsorbed bivalent cations and negatively charged TiO6 octahedra, and results in permanent entrapment of the toxic bivalent cations in the fibres so that the toxic ions can be safely deposited. Compared to conventional clay and zeolite sorbents, the fibril absorbents are of great advantage as they can be readily dispersed into and separated from a liquid. Secondly, new generation membranes were constructed by using large titanate and small ã-alumina nanofibres as intermediate and top layers, respectively, on a porous alumina substrate via a spin-coating process. Compared to conventional ceramic membranes constructed by spherical particles, the ceramic membrane constructed by the fibres permits high flux because of the large porosity of their separation layers. The voids in the separation layer determine the selectivity and flux of a separation membrane. When the sizes of the voids are similar (which means a similar selectivity of the separation layer), the flux passing through the membrane increases with the volume of the voids which are filtration passages. For the ideal and simplest texture, a mesh constructed with the nanofibres 10 nm thick and having a uniform pore size of 60 nm, the porosity is greater than 73.5 %. In contrast, the porosity of the separation layer that possesses the same pore size but is constructed with metal oxide spherical particles, as in conventional ceramic membranes, is 36% or less. The membrane constructed by titanate nanofibres and a layer of randomly oriented alumina nanofibres was able to filter out 96.8% of latex spheres of 60 nm size, while maintaining a high flux rate between 600 and 900 Lm–2 h–1, more than 15 times higher than the conventional membrane reported in the most recent study.
15
Fraga, Tiago Marques. "Produção de nanotubos de TiO2 visando sua aplicação em células solares." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-18062013-154723/.
Full textAbstract:
Nesse trabalho foram obtidos nanotubos de TiO2 pelo processo de anodização do titânio em soluções fluoradas visando sua aplicação em células solares, pois estes apresentam melhores propriedades que o TiO2 em forma de filme fino ou de nanopartículas, devido a sua maior área superficial e melhores propriedades de transporte de carga. Os processos de anodização foram realizados em lâminas de titânio com soluções de HF e NH4F e diferentes tensões e tempos de anodização, pois a tensão elétrica aplicada no processo pode ser utilizada para controlar o diâmetro, espessura e comprimento dos nanotubos. As amostras obtidas com as soluções de NH4F foram as que apresentaram os melhores resultados, com tubos de paredes mais lisas, comprimentos maiores e forma mais definida, pois as soluções de NH4F apresentam menor taxa de corrosão que as soluções de HF. Portanto, nesse trabalho as soluções de NH4F também foram utilizadas para crescer nanotubos sobre substratos de vidro, onde foi possível obter matrizes de nanotubos altamente ordenadas, e formar matrizes de nanotubos com padrões geométricos, para aplicação em células solares, sensores integráveis e cristais fotônicos. Porém nesse trabalho, os nanotubos foram utilizados somente para fabricar as células solares sensibilizadas por corante. Foram produzidas células solares utilizando lâminas de vidro cobertas por ITO e FTO, lâminas de titânio sem polimento, lâminas de Ti eletropolidas e também lâminas polidas utilizando polimento químico. Os processos de eletropolimento e polimento químico foram realizados para a obtenção de matrizes de nanotubos mais uniformes e células solares mais eficientes, utilizando esses processos foi possível obter células solares com curvas de J - V bem definidas e com fator de preenchimento (FF) de 0,5.<br>In this work TiO2 nanotube arrays were obtained by anodization of titanium foils in fluoride-based electrolytes, aiming their application in solar cells, due to its improved proprieties compared to TiO2 thin films or nanoparticles as a consequence of their large surface area and good electron transport. The anodization processes were performed utilizing HF and NH4F solutions with different anodization voltages and times, in order to study the effect of these parameters in the arrays morphology and structure. The samples obtained from NH4F solutions presented better results, with nanotubes exhibiting smoother walls, enhanced length and well defined shape, due to the lower NH4F solution etching rate compared to HF solution. Therefore the NH4F solutions were also utilized to grow nanotubes on glass substrates, allowing to obtain highly oriented of nanotubes arrays. Also patterned nanotube arrays were obtained for integrated sensors and photonic crystals applications. However, in this work, the nanotubes were only used to manufacture the dye sensitized solar cells. Were performed solar cells with glass substrates coating by thin films of ITO and FTO, unpolished titanium foils, eletropolished Ti foils and chemical polished Ti foils. The eletropolishing and chemical polishing process was performed to obtain more uniform nanotube arrays and more efficient solar cells, with well defined J-V curve and FF of 0,5.
16
Bonelli, Thiago Scremin. "Produção, caracterização morfológica e nitretação de nanotubos de TiO2." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-08012018-103731/.
Full textAbstract:
Nos últimos anos, óxidos metálicos têm sido amplamente estudados para uma série de aplicações na indústria eletrônica e metalúrgica, sendo empregados em revestimentos anticorrosivos, sensores químicos, em dispositivos optoeletrônicos sensíveis, entre outros. Dentre os óxidos metálicos, o TiO2 (óxido de Titânio) tem enorme potencial em aplicações como sensor de gás, sensor de pH e em dispositivos fotossensíveis como células solares sensibilizadas por corante e para degradação fotocatalítica de compostos orgânicos. Há várias morfologias que podem ser obtidas para o TiO2, porém a de maior interesse atualmente é a de arranjos ordenados de nanotubos de TiO2 produzidos pelo processo de anodização do Ti, que por terem maior área superficial que outras morfologias como por exemplo, filmes finos, nanopilares e nanobastões, apresenta também maior sensibilidade à presença dos gases e/ou soluções a serem analisados, assim como maior absorção de fótons, além de uma menor recombinação de pares elétron-lacuna no material. Apesar destas várias vantagens, a atividade fotocatalítica do TiO2 é limitada por absorver apenas radiação ultravioleta devido a seu largo gap de aproximadamente 3,2 eV. Assim, neste trabalho foram produzidos nanotubos de TiO2 pelo processo de oxidação anódica do Ti, com diferentes parâmetros, correlacionando-os com a morfologia resultante. Com isso foi possível observar que o comprimento e diâmetro externo dos nanotubos de TiO2 crescem proporcionalmente com o aumento da tensão, sendo aproximadamente linear até um dado valor de saturação. A exceção a isto refere-se a nanotubos de TiO2 crescidos a partir de Ti depositado e substratos de vidro, no qual, há uma limitação de Ti a ser anodizado, de modo que após a conversão total do Ti em óxido não há mais o crescimento de nanotubos, porém os diâmetros gerados respeitam os mesmos valores para os casos em que não há essa limitação. Os nanotubos de TiO2 crescidos foram submetidos a processos de nitretação em um reator de deposição química a vapor assistida por plasma e os parâmetros foram avaliados com o intuito de encontrar as melhores condições para diminuição de seu gap, afim de aumentar sua atividade fotocatalítica. Pressão e potência de rádio frequência foram variados de 0,66 a 2,66 mBar (0,50 a 2,00 Torr) e 0,22 a 3,51 W/cm2 respectivamente. A maior diminuição no valor do gap, para 2,80 eV, foi obtida usando-se a pressão de 1,33 mBar (1,00 Torr), 1,75 W/cm2 de potência de rádio frequência durante um processo de 2 h a 320 °C, levando a uma diminuição de 14% no valor do gap e a um aumento de 25% na atividade fotocatalítica (redução de Azul de Metileno). Essa diminuição no valor do gap óptico dobra a abrangência de absorção de fótons de 5% para 10% do espectro solar. Os nanotubos de TiO2 nitretados produzidos com gap de 2,80 eV foram facilmente integrados a um microcanal de polidimetilsiloxano, produzindo um dispositivo fotocatalítico para estudo na fotodegradação de compostos orgânicos, podendo ser usado inclusive para redução de poluentes. O dispositivo fotocatalítico reduziu completamente 5 µL de solução de Azul de Metileno em cerca de 12 min, com uma taxa aproximadamente linear de 130 µM/h, enquanto os nanotubos de TiO2 como preparados apresentaram taxa de cerca de 115 µM/h. Logo, o dispositivo com nanotubos de TiO2 nitretados teve um aumento de 13% em sua eficiência de redução.<br>In recent years, metal oxides have been widely studied for a number of applications in the electronics and metallurgical industry, being used in anticorrosive coatings, chemical sensors, sensitive optoelectronic devices, among others. Among the metal oxides, TiO2 (titanium oxide) has enormous potential in applications such as gas sensor, pH sensor and in photosensitive devices such as dye sensitized solar cells and for photocatalytic degradation of organic compounds. There are several morphologies that can be obtained for TiO2, but the most interesting one today is ordered arrangements of TiO2 nanotubes produced by the Ti anodization process, which have a larger surface area than other morphologies such as thin films, nanopillars and nanobastones, also presents greater sensitivity to the presence of the gases and/or solutions to be analyzed, as well as greater absorption of photons, besides a smaller recombination of electron-hole pairs in the material. Despite these several advantages, the photocatalytic activity of TiO2 is limited by absorbing only ultraviolet radiation due to its wide gap of approximately 3.2 eV. Thus, in this work, TiO2 nanotubes were produced by the anodic oxidation process of Ti, with different parameters, correlating them with the resulting morphology. With this, it was possible to observe that the length and external diameter of the TiO2 nanotubes grow proportionally with the increase of the voltage, being approximately linear up to a given value of saturation. The exception to this relates to TiO2 nanotubes grown from Ti deposited and glass substrates, in which, there is a limitation of Ti to be anodized, so that after the total conversion of Ti to oxide, there is no longer growth of nanotubes, but the diameters generated respect the same values for cases in which there is no such limitation. The as grown TiO2 nanotubes were submitted to nitriding processes in a plasma assisted chemical vapor deposition reactor and the parameters were evaluated in order to find the best conditions to decrease their gap in order to increase their photocatalytic activity. Pressure and radio frequency power were varied from 0.66 to 2.66 mBar (0.50 to 2.00 Torr) and 0.22 to 3.51 W/cm2 respectively. The largest decrease in the gap value, to 2.80 eV, was obtained using the pressure of 1.33 mbar (1.00 Torr), 1.57 W/cm2 of radio frequency power during a process of 2 h in 320 °C, leading to a 14% decrease in gap value and a 25% increase in photocatalytic activity (reduction of Methylene Blue). This decrease in the value of the optical gap doubles the absorption range of photons from 5% to 10% of the solar spectrum. The nitrided TiO2 nanotubes produced with a gap of 2.80 eV were easily integrated into a microchannel of polydimethylsiloxane, producing a photocatalytic device for the study of photodegradation of organic compounds, and could be used to reduce pollutants. The photocatalytic device completely reduced 5 µL of Methylene Blue solution in about 12 min, with an approximately linear rate of 130 µM/h, whereas the TiO2 nanotubes as grown presented a rate of about 115 µM/h. Therefore, the device with nitrided TiO2 nanotubes had a 13% increase in its reduction efficiency.
17
Santos, Thais Cristina Lemes dos. "Síntese de nanotubos de TiO2 pelo processo de anodização e caracterização para aplicações fotoeletroquímicas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/165225.
Full textAbstract:
Nos últimos anos, a utilização de nanotubos (Nts) de dióxido de titânio (TiO2) têm atraído interesse tecnológico e científico de forma significativa devido às suas propriedades únicas, tais como grande área de superfície específica, alta capacidade de absorção e apresentam excelentes atividades fotoeletroquímicas e um meio para melhorar essas propriedades está relacionada ao controle da morfologia dos Nts durante a sua sintetização no processo de anodização. O objetivo desse estudo é avaliar a influência do potencial aplicado durante o processo de anodização para obtenção de Nts de TiO2, tendo em vista a utilização desses nanotubos como catalisador fotoeletroquímico. Para que houvesse a cristalização do óxido, realizou-se tratamento térmico a 400 °C ao ar, durante 3 h com taxa de aquecimento de 10 °C / min. Analisou-se a relação do potencial aplicado durante o processo de anodização com a morfologia dos nanotubos e a sua resposta fotoeletroquímica. As caracterizações foram realizadas através das técnicas de microscopia eletrônica de varredura com emissão de campo (MEV-FEG), difração de raios X (DRX), espectrofotometria no ultravioleta visível (UV-VÍS), voltametria linear e espectroscopia de impedância eletroquímica (EIE).Observou-se que o potencial de anodização exerce influência na geometria do nanotubo, isto é, no comprimento, na espessura da parede e no diâmetro, alterando a absorção de luz e, consequentemente, o desempenho fotoeletroquímico das amostras. Os resultados obtidos por espectroscopia de impedância eletroquímica mostraram pouca diferença na resistividade das amostras estudas. Contudo, as correntes desenvolvidas no ensaio de voltametria linear, indicaram que a amostra Nt30 é um fotoeletrodo promissor para formar heteroestruturas baseado em nanotubos de dióxido de titânio.<br>In recent years, the use of TiO2 nanotubes (Nts) has attracted technological and scientific interests in a significant way due to its unique properties, such as large specific surface area, high absorption capacity and excellent photoelectrochemical activities. One way to improve these properties is to control the nanotubular morphology during its synthesis through the anodizing process. The objective of this study is to evaluate the influence of the applied potential during the anodization process to obtain titanium dioxide (TiO2) nanotubes and applying these nanotubes as a photoelectrochemical catalyst. In order to crystallize the Nts, heat treatment was carried out at 400 ° C in air for 3 h at a heating rate of 10 ° C / min. The effect of the applied potential during the anodizing process on the morphology of the nanotubes and their photoelectrochemical response were analyzed. The characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), visible ultraviolet spectrophotometry (UV-VIS) and electrochemical impedance spectroscopy (EIS). It was observed that the anodization potential influences the geometry of the nanotubes, that is, their length, wall thickness and diameter, altering their light absorption properties; consequently, influencing the photoelectrochemical performance of the samples. The results obtained from the electrochemical impedance spectroscopy showed a slightly small difference in the charge transportation resistance of the studied samples. However, the currents developed in the linear voltammetry tests indicated that the Nt30 sample is a promising photoelectrode to apply for other applications such as heterostructures and cationic/anionic doped structures based on titanium dioxide nanotubes.
18
Oliveira, Aline Maxiline Pereira. "Preparação de nanoestruturas de TiO2 por meio de tratamento hidrotérmico e aplicação no processo de fotocatálise heterogênea." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-22102013-085301/.
Full textAbstract:
Entre os processos oxidativos avançados, a fotocatálise heterogênea tem se destacado na degradação de poluentes recalcitrantes aos tratamentos convencionais. Neste processo, a geração de espécies radicalares ocorre a partir de uma fotoreação catalisada por materiais semicondutores, sendo o dióxido de titânio um dos mais utilizados, principalmente, devido a sua estabilidade química e baixo custo. A estrutura do TiO2 possui grande influência no processo fotocatalítico. Neste trabalho buscou-se preparar, a partir do TiO2 comercial e do TiO2 sintetizado pelo método sol gel, diferentes nanoestruturas do dióxido de titânio e avaliar o desempenho fotocatalítico destes materiais na degradação de fenol. Utilizando o tratamento hidrotérmico em meio fortemente alcalino, foi possível obter materiais nanoestruturados com maior área superficial, de até 308 m2 g-1. O tratamento foi aplicado em três diferentes precursores, com diferentes morfologias inicias. Avaliou-se o efeito de diferentes temperaturas (120 e 200 ºC) e tempos de tratamento (12, 24 e 48 horas), a fim de avaliar a influência das condições de tratamento e da morfologia inicial nos materiais obtidos. As amostras obtidas foram empregadas como catalisadores na degradação do poluente fenol por fotocatalise heterogênea. Em dois dos precursores estudados foram obtidas estruturas nanotubulares quando empregou-se condições mais brandas de tratamento. Em temperaturas mais severas, observou-se a formação de nanobastões. As amostras nanotubulares derivadas do TiO2 comercial anatásio, quando aplicadas na degradação do fenol, permitiram porcentagens de degradação superiores ao do precursor. Quando calcinadas, as amostras apresentaram resultados ainda melhores. O material tratado por 48 horas à 120 ºC possibilitou uma degradação de cerca de 100% do poluente, após 3 horas de irradiação. Utilizando três precursores com morfologias iniciais distintos foram observados resultados diferentes quanto a formação de nanoestruturas e atividade fotocatalítica, sendo o material obtido utilizando o TiO2 comercial anatásio, o que apresentou melhores resultados na degradação do fenol.<br>Among the advanced oxidation processes, heterogeneous photocatalysis has attracted great attention due the degradation of pollutants recalcitrant to conventional treatments. In this process, the generation of radical species takes place from a photoreaction catalyzed by semiconductor materials. Titanium dioxide is the most used catalyst mainly because of its chemical stability and low cost. The TiO2 structure has great influence on the photocatalytic process. In this study, different nanostructures of titanium dioxide were prepared from commercial TiO2 and TiO2 synthesized by sol gel method. The performance of these materials was evaluated the on the photocatalytic degradation of phenol. Using the hydrothermal treatment in strongly alkaline media, it was possible to obtain nanostructured materials with higher surface area, up to 308 m2 g-1. The treatment was employed in three different precursors with different initial morphology. It was evaluated the effect of different temperatures (120 and 200 °C) and treatment times (12, 24 and 48 hours) to assess the influence of processing conditions and of the initial morphology. The different materials were employed as catalysts in the phenol degradation by heterogeneous photocatalysis. In two precursors studied, nanotubular structures were obtained when it was used milder conditions of treatment. In more severe temperatures, it was observed nanorods formation. Nanotubular samples were obtained from commercial TiO2 anatase. When applied to the degradation of phenol, this material allowed degradation percentages higher than the precursor. When calcined, these samples showed even better results. The material treated for 48 hours at 120 °C allowed a phenol degradation of almost 100% after 3 hours of irradiation. Using three precursors with different initial morphologies it was observed different results regarding the formation of nanostructures and photocatalytic activity. The material obtained from the commercial anatase TiO2 it was the sample which presented the best result in the degradation of phenol
19
Arruda, Pâmella Marques de. "Membranas de nanotubos de TiiO2 aplicadas na fabricação de sensores e células solares." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-28022018-134042/.
Full textAbstract:
A proposta deste trabalho é a produção de matrizes de nanotubos de dióxido de titânio seguindo os métodos de anodização eletroquímica de titânio estabelecidos da literatura. O objetivo central é a compreensão aprofundada das etapas do processo de crescimento dos nanotubos de TiO2, para posterior otimização de sua síntese visando as diferentes aplicações. Com este propósito foram realizados sistematicamente os seguintes estudos: das diferentes fases de crescimento dos nanotubos de TiO2, do efeito dos diferentes parâmetros de anodização na morfologia dos nanotubos e da reprodutibilidade dos processos. Visando as diferentes aplicações foram estudados métodos para obtenção de membranas autossustentadas e remoção de nanoresíduos. O método de camada sacrificial de fotoresiste positivo apresentou melhor resultado para remoção de nanoresíduos do topo dos nanotubos de TiO2 do que as demais técnicas. Por último, os arranjos obtidos com esta método foram aplicados na fabricação dos sensores de pH.<br>This work proposes the production of titania nanotubes arrays following the electrochemical anodization methods of a titanium sheet established in the literature. The main goal is a deep comprehension of the different TiO2 nanotubes growth stages for further optimization aiming the diverse applications. In this way the following systematic studies were performed: of the initial growth stages, of the effect of each anodization parameter on the nanotubes morphology and of the process reproducibility. In addition, methods for the production of self-sustained membranes as well as for obtaining a nanotube array surface free of nanoremnants were studied aiming the different applications. Positive photoresist bases sacrificial layer method presented a better result to eliminate nano-remnants on top of TiO2 nanotubes than other techniques. Finally, the nanotubes arrays obtained with this method were utilized for pH sensors fabrication.
20
Bagnara, Mônica. "Estudo da atividade fotocatalítica de nanotubos de TiO2 dopados com nitrogênio." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/49291.
Full textAbstract:
Este trabalho apresenta o estudo do desempenho de catalisadores nanoestruturados de dióxido de titânio, TiO2, dopados com nitrogênio, visando melhorar sua atividade fotocatalítica sob radiação visível. Os nanotubos de TiO2 foram preparados pelo método hidrotérmico, onde partículas de TiO2 reagem com NaOH a temperatura e pressão elevadas. Em seguida o material é tratado, através de uma lavagem ácida e calcinação, de modo a apresentar as características desejáveis para a aplicação como fotocatalisador. Foram determinadas as melhores condições de obtenção dos nanotubos avaliando-se sua atividade fotocatalítica, variando-se o pH da solução de lavagem e temperatura de calcinação. Determinadas essas condições, buscou-se em três compostos nitrogenados o melhor desempenho para dopagem de nanotubos. Foram eles: amônia, uréia e tiouréia. A reação de degradação do corante rodamina B foi utilizada para avaliar a atividade fotocatalítica dos catalisadores. Os experimentos foram realizados em um reator batelada agitado, com o catalisador em suspensão e na presença de aeração, sob radiação UV e visível. Avaliaram-se inicialmente as condições de reação, como concentração de catalisador e de corante, com o catalisador comercial e precursor de Ti, P25 Degussa. Além da determinação da atividade fotocatalítica, foram feitas as seguintes análises para caracterização dos materiais: difração de raios X (DRX), espectroscopia de refletância difusa (ERD), microscopia eletrônica de transmissão (MET) e determinação da área específica e volume de poros. A partir dos ensaios fotocatalíticos observou-se que os tratamentos a que foram submetidos os materiais tiveram grande influência na sua atividade catalítica. Sob radiação UV nenhum catalisador foi mais ativo que o P 25. Sob radiação visível, as amostras dopadas com tiouréia (NTT-4-500/TiouréiaI) e amônia (NTT-7-600/NH3I) apresentaram os melhores resultados, com um aumento na fotodegradação de 16 e 30 % em relação às amostras não dopadas, respectivamente.<br>This work presents the study of the catalytic performance of nanostructured titanium oxide, TiO2, doped with nitrogen in order to improve its photocatalytic activity under visible light. TiO2 nanotubes were prepared by hydrothermal method, where TiO2 particles react with NaOH at high temperature and pressure. Then the material was handled through an acid wash and calcination, in order to produce desirable characteristics for the photocatalyst applications. The best conditions for titania nanotubes preparation were determined by varying the pH of the wash water and calcination temperature. Established these conditions, the research focused on obtaining among three nitrogen doping the one that provided best performance of nanotubes. They were: ammonium hydroxide, urea and thiourea. The degradation reaction of rhodamine B dye was used to evaluate the photocatalytic activity of catalyst. The experiments were performed in a stirred batch reactor, with the catalyst in suspension and in the presence of aeration, in the presence of UV and visible radiations. Initially the reaction conditions, such as catalyst and dye concentrations, were determined with the commercial catalyst and Ti precursor, P25 Degussa. In addition to determining the photocatalytic activity, the material characterization was made by X-ray diffraction (XRD), diffusive reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and determination of specific area and pore volume by N2 absorption isotherms. The photocatalytic tests showed that the acid washed and calcination had a strong influence on its photocatalytic activity. No synthesized catalyst presented a larger photodegradation activity under UV light than P25. Under visible light, the samples doped with thiourea (NTT-4-500/TiouréiaI), and ammonia (NTT-7-600/NH3I) showed the best results with an increase in the photodegradation activity of 16 and 30% compared to the undoped samples, respectively.
21
Silva, William Leonardo da. "Síntese, caracterização e atividade fotocatalítica de catalisadores nanoestruturados de TiO2 dopados com metais." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/61062.
Full textAbstract:
No presente trabalho foi realizado o estudo do desempenho de catalisadores nanoestruturados de dióxido de titânio, TiO2, dopados com diferentes metais (prata, ouro, cobre, paládio e zinco), a fim de promover um aumento da atividade fotocatalítica sob radiação visível. Os experimentos foram realizados em um reator batelada de vidro, com controle de temperatura e catalisador em suspensão, sob radiação UV e visível, usando-se rodamina B (RhB) como molécula teste. Além disso, foram avaliadas as condições de reação, como as concentrações de catalisador e de corante, e do catalisador comercial P-25 Degussa. Para síntese dos nanotubos de TiO2 utilizou-se o método hidrotérmico, que consiste na reação de partículas de TiO2 com uma solução aquosa de NaOH sob temperatura e pressão elevadas, seguida de lavagem ácida e calcinação. Foram determinadas as melhores condições de obtenção dos nanotubos, variando-se o pH da solução de lavagem e temperatura de calcinação, antes da dopagem com metais. Além da avaliação da atividade fotocatalítica, a difração de raios X (DRX), espectroscopia de reflectância difusa (ERD), microscopia eletrônica de transmissão (MET) e a determinação da área específica e volume de poros foram utilizadas para caracterização dos fotocatalisadores dopados e dos nanotubos de TiO2 (NTTs). Pelos ensaios fotocatalíticos observou-se que os tratamentos a que foram submetidos os materiais tiveram grande influência na sua atividade catalítica. Sob radiação UV apenas o catalisador dopado com paládio foi mais ativo que o P 25, com uma degradação de 93%. Sob radiação visível, as amostras dopadas com prata (NTT-4-600/Ag+UV e NTT-4-600/Ag+escuro), paládio (NTT-4-500/Pd) e ouro (NTT-4-500/AuI) apresentaram os melhores resultados, em relação às amostras não dopadas, com degradação de 19%, 11%, 17% e 16% respectivamente.<br>The performance of nanostructured titanium dioxide catalysts doped with different metals was studied (silver, gold, copper, palladium and zinc), in order to promote an increase in the photocatalytic activity under visible light. The experiments were performed in a glass batch reactor with controlled temperature and catalyst in suspension under UV and visible radiation for rhodamine B (RhB) degradation. In addition, was evaluated the reaction conditions such as catalyst and dye concentration, and the performance of the commercial catalyst TiO2 Degussa P-25. TiO2 nanotubes were synthesized by hydrothermal method, which consists of the reaction of TiO2 particles with aqueous NaOH solution under elevated temperature and pressure, followed by acid washing and calcining. Before the doping metals were determined the best conditions for to obtain nanotubes, by varying the pH of the wash and calcination temperature. In addition to the evaluation of photocatalytic activity, the X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and determine the specific area and pore volume were the techniques used for characterization of doped photocatalysts and TiO2 nanotubes (NTTs). The photocatalytic tests showed that the treatments had a great influence on its catalytic activity. Under UV radiation only doped with palladium catalyst was more active than the P 25, with a 93% degradation. Under visible light, the samples doped with silver (NTT-4-600/Ag+UV e NTT-4-600/Ag+dark), palladium (NTT-4-500/Pd) and gold (NTT-4-500/ AuI) showed the best results, with a degradation 19%, 11%, 17% e 16% respectively.
22
Saboo, Tapish. "Chimie organométallique de surface sur l’oxyde de titane." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1061/document.
Full textAbstract:
La chimie organométallique de surface (COMS) est une technique utilisée pour concevoir des catalyseurs structurellement bien définis. Elle a été employée ici pour établir les fondements de la COMS sur des supports photoactifs. L’oxyde de titane, TiO2 à savoir l’anatase a été utilisé comme support photo-catalytique en raison de sa haute stabilité, photo-activité and non toxicité. La nature chimique et la densité des sites réactifs de surface ont été établies. Un complexe de Ta bien connu de la littérature a été utilisé pour mener les premières études d’interaction entre la surface et le complexe organométallique. Les résultats ont permis d’observer le greffage organométallique couplé à des mécanismes transfert de charge métal sur métal, en route vers des photo-catalyseurs bien définis<br>Surface organometallic chemistry (SOMC) is used to design well-defined catalysts. It has been employed here to lay the foundation of SOMC on photocatalytic support, a previously little if any explored area. TiO2 anatase was used as the photocatalytic support due to its high stability, photoactivity and nontoxicity. The chemical nature and the surface density of the reactive moieties found on anatase support has been determined. A Ta complex, well-known in literature, was used to conduct the first principal studies regarding the interaction between the surface and the organometallic complex. The results provide solid insights into organometallic grafting and metal to metal charge transfer mechanisms for developing well-defined photocatalysts by SOMC
23
Monteiro, Gleydson Zeca. "Sensoriamento de ph baseado em nanotubos de TiO2." reponame:Repositório Institucional da UFABC, 2015.
Find full textAbstract:
Orientadora: Prof. Dra. Kátia Franklin Albertin Torres<br>Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2015.<br>A medição do pH tem se mostrado de grande valia em diversos campos como em agricultura, saúde, indústria e meio ambiente. Na saúde, a identificação de áreas com células cancerígenas no corpo humano pode ser feita através da medição do pH nestas áreas. Os métodos e sensores utilizados atualmente não se mostram os melhores para isto. Os nanotubos de dióxido de titânio (TiO2) podem ser utilizados para esta medição, superando as dificuldades atuais, dadas as suas dimensões reduzidas, características morfológicas e baixo custo de processo. No presente trabalho obtiveram-se nanotubos de TiO2 em lâminas de Ti utilizando um processo de anodização em solução orgânica de etileno glicol, fluoreto de amônia (NH4F) e água, com diferentes tensões e tempos de processo e, posteriormente, caracterizados como sensores de pH. Para controle e definição da geometria dos nanotubos em região pré-determinada da lâmina, utilizou-se isolamento da área por meio de mascaramento mecânico utilizando Polidimetilsiloxano (PDMS). As amostras de nanotubos obtidos foram caracterizadas através da técnica de microscopia eletrônica de varredura (MEV). Os sensores de pH à base de nanotubos de TiO2 foram fabricados e caracterizados utilizando soluções padrões de valores de pH de 4,01; 5,50; 7,01; 8,50 e 10,01. Verificou-se que o tempo de anodização influi diretamente no comprimento dos nanotubos, enquanto que a tensão influi diretamente no diâmetro das bocas dos nanotubos, bem como da espessura de sua parede. Além disso, observou-se que, os sensores que apresentaram melhor sensibilidade foram produzidos em uma anodização com tensão de 40 V e com tempo de 45 minutos, valores estes intermediários em relação aos demais produzidos. Esta sensibilidade chegou ao valor de -51 mV/pH, bem próximo aos -59 mV/pH da equação teórica de Nernst. Ainda na caracterização elétrica dos sensores notou-se que não necessariamente o maior nanotubo em comprimento trará o melhor resultado, bem como nem o de maior diâmetro como foi constatado através do sensor anodizado com tensão de 40 V e com tempo de 45 minutos.<br>The pH measurement has proved of great value in several fields as, agriculture, health, industry and environment. In health, pH measurement can be used to identify cancer cells in the human body. The currently methods and sensors, due some limitation, are not the best mode to make cancer investigation. Titanium dioxide (TiO2) nanotubes, due their small size, morphological characteristics and biocompatibility, overcome the currently difficulties, and it is very interesting to be used for pH measurement to identify cancer cells in the human body. In the present study were obtained TiO2 nanotubes Ti blades anodizing process using an organic solution in ethylene glycol, ammonium fluoride (NH4F) and water, with different voltages and process times and subsequently characterized as pH sensors. In order to control and defined the geometry of the nanotubes, a predetermined region of the TiO2 nanotubes arrays were defined by a mechanical masking with Polydimethylsiloxane (PDMS). The TiO2 nanotube arrays were characterized by scanning electron microscopy (SEM). The pH sensors based on TiO2 nanotubes were characterized using standard pH solutions of 4.01, 5.50, 7.01, 8.50 and 10.01. It was observed that the anodizing time influences directly the nanotubes length, while the anodizing voltage influences directly the nanotubes diameter, as well as the thickness of its wall. Furthermore, the pH sensors that shows the best sensitivity value were produced by anodization process with 40V voltage during 45 minutes. This sensitivity reached value of -51 mV/pH, very close to -59 mV/pH of theoretical Nernst equation. It is possible to observe that not necessarily the most nanotube length gives the best sensors results as well as the larger diameter.
24
LAMBERTI, ANDREA. "Metal-oxide nanostructures for energy applications." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506221.
Full textAbstract:
One of the most important challenges for our society is providing powerful devices for energy conversion and storage. The number of proposed technologies in today’s green and renewable energy science is large and still increasing: among all the dye-sensitized solar cells (for energy generation) and Li-ions batteries (for energy storage) have attracted a lot of interest thanks to the easy fabrication processes and the cheap materials involved.
Great attention has been paid on the investigation of one-dimensional metal-oxide nanostructures for a new generation of power sources, because of their unique electronic properties, such as high electron mobility and low carrier recombination rate, high surface-to-volume ratio and excellent surface activity.
Among the large number of semiconductive metal oxide nanostructures, TiO2 and ZnO are of particular interest due to the fact that they are the best candidates as active materials in electrochemical devices thanks to their chemical and electronic properties.
Several approaches have been proposed for TiO2 nanostructure synthesis and among them anodic oxidation is now a well-established technique that can provide large area uniform nanotubular arrays on Ti foil with relatively high specific surface.
Regarding zinc oxide, many papers report on the synthesis of ZnO nanostructures performed by means of different techniques. Most of them exploits high temperature processes often using catalyst particles, requires the presence of a sacrificial template, introduces chemical contamination or exhibit slow kinetics.
This PhD thesis investigates the fabrication of different metal-oxide nanostructures and their integration as electrodes into DSCs and LiBs: in particular the work deals with TiO2 nanotube arrays obtained by anodic oxidation and with ZnO sponge-like films obtained by combined sputtering/thermal oxidation techniques.
Vertically oriented TiO2 NTs were obtained by anodic oxidation of titanium foil and fully characterized in terms of stoichiometry, crystalline phase and morphology. TiO2 nanotubes were tested both in DSC and in LiBs showing improved charge transport properties due to the 1-dimensional structures and a reduced recombination rate (and a subsequent higher carrier lifetime value) that could be attributed to the reduced presence of defects and trap-sites in the nanotubes with respect to the nanoparticle-based electrodes.
As competitive alternative to TiO2 nanotubes, porous ZnO films were obtained by a simple two-step method, involving the sputtering deposition of a sponge-like layer of metallic zinc, followed by a low-temperature treatment allowing for the complete oxidation of zinc, thus forming sponge-like ZnO films. Also in this case ZnO nanostructured films were fully characterized tested both in DSC and in LiBs showing interesting performance. Thanks to the its 3D nanostructuration, the superimposition of small branches able to grow in length almost isotropically and forming a complex topography, ZnO sponge-like can combine the fast transport properties of one dimensional material and the needed surface area usually provided by nanocrystalline electrodes.
25
MOYA, Johan René González. "Nanotubos de TiO2 sensibilizados com quantum dots de CdS e suas aplicações para a geração de hidrogênio mediante fotocatálise e fotoeletrocatálise." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/17768.
Full textAbstract:
Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-08-31T13:00:29Z
No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
Tese Doutorado Johan CD.pdf: 3689018 bytes, checksum: 956c4e0d76742d36ffe10e5bd9f4fa90 (MD5)<br>Made available in DSpace on 2016-08-31T13:00:29Z (GMT). No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
Tese Doutorado Johan CD.pdf: 3689018 bytes, checksum: 956c4e0d76742d36ffe10e5bd9f4fa90 (MD5)
Previous issue date: 2016-02-29<br>CNPq<br>No presente trabalho foi investigado o desempenho de nanotubos de TiO2 sensibilizados com quantum dots de CdS na geração de hidrogênio por meio da reação de dissociação da água por meio da fotocatálise e fotoeletrocatálise. Os nanotubos de TiO2 foram obtidos pelo método de anodização (30 V, 1 hora) de chapas de Ti, em etilenoglicol e água contendo íons fluoreto. As amostras anodizadas foram submetidas a tratamento térmico 400°C durante 3 horas. Posteriormente as amostras foram sensibilizadas com quantum dots de CdS via síntese hidrotérmica in situ usando o ácido 3-mercaptopropiônico como agente estabilizante. A eficiência fotocatalítica dos materiais na produção de hidrogênio foi investigada por meio da reação de dissociação da água utilizando como fonte de irradiação um simulador solar. A quantificação do hidrogênio gerado foi determinada por meio de cromatógrafia gasosa. Por outro lado, para estimar a eficiência de geração de hidrogênio via fotoeletrocatálise, as amostras foram avaliadas como fotoânodos e medidas da fotocorrente gerada pela irradiação em uma célula fotoeletroquímica (PEC) de três eletrodos foram realizadas. A sensibilização dos nanotubos de TiO2 com os quantum dots de CdS a partir da síntese hidrotérmica in situ, permitiu uma boa impregnação e distribuição uniforme dos quantum dots ao redor da superfície dos nanotubos, de acordo com as análises de EDS e XPS. O perfil de profundidade de XPS mostrou que a concentração de CdS permaneceu praticamente inalterada (homogênea) ao longo da matriz nanotubular. A presença de ânions sulfato evidenciou a oxidação do material preferentemente na superfície. Os nanotubos conferem uma proteção ao CdS frente à oxidação e protegem também os quantum dots quanto à fotocorrosão na solução de sacrifício S2-/SO32- utilizada. Este comportamento define uma boa estabilidade na fotocorrente gerada como mostrado em experimentos de longa duração (20 horas) sob irradiação. Os resultados experimentais mostraram três comportamentos diferentes para a geração de H2 quando o tempo de síntese dos QDs de CdS aumenta. Foram observados, efeitos similares, antagônicos e sinérgicos frente à atividade fotocatalítica em relação aos nanotubos de TiO2. O efeito antagônico parece estar relacionado com a presença de duas populações de tamanhos de QDs de CdS, onde a população com um band gap menor atua como uma armadilha para os elétrons fotogerados pela população com um band gap maior, diminuindo a atividade fotocatalítica do TiO2 na região ultravioleta. A transferência de elétrons a partir dos QDs de CdS para o TiO2 foi comprovada pelos resultados de UPS combinados com as medidas do band gap óptico. A maior absorção no visível após a sensibilização com o CdS combinada com a transferência de elétrons possibilita um incremento na taxa de geração de hidrogênio por meio da fotocatálise a partir de luz visível de quase zero para os nanotubos de TiO2 até cerca de 0,3 μmol cm-2 h-1 após sensibilização com os QDs de CdS. No caso da fotoeletrocatálise em uma PEC, a taxa de geração de H2 a partir de luz visível estimada pela fotocorrente gerada após a sensibilização (1,79 μmol cm-2 h-1) chega a ser até 12 vezes maior que para os nanotubos de TiO2 sem sensibilizar (0,15 μmol cm-2 h-1).<br>In the present work, we investigated the performance of TiO2 nanotubes sensitized with CdS quantum dots on the photocatalytic and photoelectrocatalytic H2 production reaction. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogenous), while the concentration relative to the sulfate anion decreases by more than 80 % with respect to the initial value after ~200 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix also protected the CdS from photocorrosion in sacrificial solution leading to good stability properties proved by a long duration photocurrent measurements. The effect of the sizes of CdS quantum dots attached to TiO2 nanotubes on the hydrogen production via photocatalysis was investigated. The experimental results showed three different behaviors when the CdS size is increased in the sensitized samples, e.g., similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related with two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS combined with optical band gap measurements. This property facilitates an improvement of the visible-light photocatalytic hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmolcm-2h-1 for TiO2 nanotubes sensitized with CdS quantum dots. The hydrogen generation rate estimated from photocurrents measurements via photoelectrocatalysis in PEC systems was also investigated. The hydrogen generation rate after sensitization was improved from 0,15 μmol cm-2 h-1 to 1,79 μmol cm-2 h-1, near to 12 times better performance under visible-light irradiation.
26
Rosa, Yeison Núnez De la. "Síntese e caracterização de nanotubos de TiO2 preparados eletroquimicamente." Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/7883.
Full textAbstract:
Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-10-05T13:31:10Z
No. of bitstreams: 1
DissYNNR.pdf: 3683311 bytes, checksum: e9291665cc68d8dd4abaf96989d12269 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-14T14:26:43Z (GMT) No. of bitstreams: 1
DissYNNR.pdf: 3683311 bytes, checksum: e9291665cc68d8dd4abaf96989d12269 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-14T14:26:52Z (GMT) No. of bitstreams: 1
DissYNNR.pdf: 3683311 bytes, checksum: e9291665cc68d8dd4abaf96989d12269 (MD5)<br>Made available in DSpace on 2016-10-14T14:27:02Z (GMT). No. of bitstreams: 1
DissYNNR.pdf: 3683311 bytes, checksum: e9291665cc68d8dd4abaf96989d12269 (MD5)
Previous issue date: 2016-04-20<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>In the field of nanotechnology, the titanium dioxide (TiO2) has been widely studied for its optical and electrical properties. This oxide is an n-Type semiconductor and is found naturally in
different crystalline phases. Recently, this material has attracted much attention as photocatalyst for the electrochemical photolysis of water displaying a high efficiency, chemical stability and a large surface area. Furthermore, for this application has been proposed that the synthesis of TiO2 nanotubes (Nts-TiO2)
prepared by anodization are promising. Thus, we aimed to study the correlation between the synthesis - morphological and microstructural properties for the optical properties of Nts-TiO2 prepared electrochemically, using the
photoelectrochemical decomposition reaction of water as a reaction target optical properties. For this, the Nts-TiO2 were prepared by anodizing the titanium substrate in Ethylene glycol solutions /water/ ionic liquid (BMIM-BF4), followed
by a heat treatment at 450 °C. In this study, we performed a factorial design 23 to: i) evaluate the statistical significance of synthesis variables: applied potential (Eapl), bath temperature (Tbanho) and percentage of water in the electrolyte (%A); and ii) quantify the correlation between synthesis, morphological, microstructural and optical properties of Nts-TiO2. The synthesized nanotubes were characterized by their morphology and photoelectrochemical properties. The characterization by X-ray diffraction indicated characteristic peaks only the anatase phase interest. The band gap determined by the Wood-Tauc method were calculated values near
3.2 eV. The scanning electron micrographs showed the formation of Nts-TiO2 in all conditions of synthesis, with an internal diameter with values between 23 and 65 nm, being statistically significant main effects Tbanho and %A and interactions effects of Eapl -%A. To study the photoelectrochemical properties of the
electrodes, linear voltammetry experiments were carried out in the light and dark in 0, 5 M H2SO4 solution, the photocurrent density values obtained in the course showed values up to 300 μA cm-2 at 1.01 V vs Ag/AgCl/KClsat. (Water oxidation
potential for the system studied) compared with the response obtained in the dark. With the results obtained, is observed the variability in current density in function of morphological, microstructural and semiconducting properties of Nts-TiO2. Key words: Titanium dioxide, photoelectrochemical cell, TiO2<br>No campo de estudo da nanotecnologia, o dióxido de titânio (TiO2), vem sendo amplamente investigado por suas propriedades ópticas e elétricas. Este óxido é um semicondutor do tipo n
e é encontrado na natureza em diferentes fases cristalinas. Recentemente, este material tem atraído muito interesse como fotocatalisador para a fotóliseeletroquímica da água por apresentar uma alta eficiência, estabilidade química e
uma grande área superficial. Além disso, para esta aplicação tendo sido proposto que a síntese de nanotubos de TiO2 (Nts-TiO2), preparados por anodização são promissores. Deste modo, teve como objetivo principal estudar a correlação
síntese-propriedades morfológicas e microestruturais com as propriedades ópticas
dos Nts-TiO2 preparados eletroquimicamente, fazendo uso da reação de decomposição fotoeletroquímica da água como reação alvo das propriedades ópticas. Para isso, os Nts-TiO2 foram preparados através da anodização do
substrato de titânio em soluções de Etileno glicol/Água/Líquido iônico (BMIM-BF4), seguido de um tratamento térmico a 450 °C. Neste estudo foi
realizado um planejamento fatorial 23 para: i) avaliar a significância estatística das variáveis de síntese: potencial aplicado (Eapl), temperatura do banho (Tbanho) e porcentagem de água no eletrólito (%A); e ii) quantificar a correlação entre
síntese, propriedades morfológicas, microestruturais e ópticas dos Nts-TiO2. Os
eletrodos sintetizados foram caracterizados quanto a sua morfologia e propriedades fotoeletroquímicas. A caracterização por difração de raios-X indicou apenas os picos característicos da fase de interesse anatase. Os band gaps determinados através do método de Wood-Tauc tiveram os valores calculados
próximo a 3,2 eV. As micrografias eletrônica de varredura mostraram a formação de Nts-TiO2 em todas as condições de síntese, com diâmetro interno com valores entre 23 e 65 nm, sendo estatisticamente significativos os efeitos principais Tbanho e %A e as interações dos efeitos Eapl - %A. Para estudar as propriedades
fotoeletroquímicas dos eletrodos, foram realizados experimentos de voltametria
linear no claro e escuro em solução de H2SO4 0.5M, os valores de densidade de
fotocorrente obtidas no claro mostraram valores de até 300 μA cm2- em 1,01 V vs Ag/AgCl/KCl sat. (Potencial de oxidação da água para o sistema estudado) quando comparado com a resposta obtida no escuro. Com os resultados
obtidos, foi observada a variabilidade na densidade de fotocorrente em função dos
parâmetros morfológicos, microestruturais e semicondutores dos Nts-TiO2. Palavras chaves: Dióxido de titânio, célula fotoeletroquímica, nanotubos de TiO2.
27
CARNEIRO, José Vinícius Oliveira. "Construção de microrreatores nanoestruturados para a degradação de diclofenaco sódico mediante fotocatálise heterogênea." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18634.
Full textAbstract:
Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-04-25T14:08:17Z
No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
DISSERTAÇÃO José Vinícius O. Carneiro-Final (BC).pdf: 3473579 bytes, checksum: 53d2c12ba53b539b7c125ce7329018ff (MD5)<br>Made available in DSpace on 2017-04-25T14:08:17Z (GMT). No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
DISSERTAÇÃO José Vinícius O. Carneiro-Final (BC).pdf: 3473579 bytes, checksum: 53d2c12ba53b539b7c125ce7329018ff (MD5)
Previous issue date: 2016-09-01<br>Diante da necessidade de tratar os contaminantes emergentes (CEs) presentes em águas
residuais, o presente trabalho surge como uma rota alternativa de processo terciário a ser
implantada nas estações de tratamento de efluentes (ETEs) convencionais. A fotodegradação do
diclofenaco de sódio (DCF) mediante processos oxidativos avançados (POA), ocorreu via
fotocatálise heterogênea utilizando nanotubos de TiO2 (NTs de TiO2) como fotocatalisadores.
Empregou-se um reator em batelada com fotocatalisadores em placa (NTs de TiO2 e NTs de
TiO2-Au ) e um reator tubular carregado com um microrreator (fotocatalisador) dotado de NTs de
TiO2 sensibilizado ou não com nanopartículas de ouro (NPs Au). A síntese dos NTs de TiO2
ocorreu pelo processo de anodização utilizando como substrato folhas de titânio metálico (Ti). As
matrizes nanotubulares foram cristalizadas por tratamento térmico (400°C por 3h). A
sensibilização com NPs de Au foi realizada in situ por redução através da radiação UV. A
fotodegradação foi realizada a partir da irradiação do simulador solar NEWPORT modelo 67005
com uma lâmpada de Xenônio-Mercúrio (com potência calibrada para 1 SOL), na ausência ou
presença de filtro (UV ou visível). A fase cristalina anatase dos NTs de TiO2 foi identificada pela
difração de raios X (DRX). Foi estimada pelo refinamento de Rietveld uma cristalinidade de 77%
para a superfície fotocatalítica, com a anatase (NTs de TiO2 cristalizados) representando 92,4%
desta fase cristalina. A energia de band gap dos fotocatalisadores de 3,23 eV foi determinada pela
espectroscopia de reflectância difusa. Através da microscopia eletrônica de varredura (MEVEDD)
foi possível visualizar para a folha de Ti lisa, estruturas cilíndricas dos NTs de TiO2 que
cresceram perpendicular ao substrato, apresentando um diâmetro médio de 78,87 nm e
comprimentos na ordem de 2 µm, no caso da folha de Ti ondulada os NTs de TiO2 cresceram em
direções variadas apresentando um diâmetro médio de 81,09 nm e comprimentos na ordem de 3
µm. A presença das NPs Au foi identificada pela espectroscopia de energia dispersiva (EDD). A
determinação e quantificação de produto e reagente da fotocatálise heterogênea na degradação do
DCF foram realizadas pela combinação de métodos analíticos (Cromatografia líquida de alta
eficiência, Ressonância Magnética e Infravermelho por transformada de Fourier), obtendo uma
conversão de 100% do DCF para testes no reator em batelada e de 37,0% no reator com
recirculação para o melhor sistema fotocatalítico. Foi estimado através da análise de carbono
orgânico total (COT) uma mineralização de 18,5% do DCF inicial para o sistema fotocatalítico
mais eficiente utilizando o reator com recirculação. A ecotoxicidade do DCF e seus produtos de
fotodegradação foi avaliada utilizando microcrustáceos (Artêmias Salinas) como bioindicador.<br>Faced with the need to address emerging contaminants (ECs) in waste water, this work
is an alternative route of tertiary process to be implemented in conventional wastewater treatment
plants (WTPs). Sodium diclofenac photodegradation (DCF) by advanced oxidation processes
(AOP), occurred via heterogeneous photocatalysis using TiO2 nanotubes (TiO2 NTs) as
photocatalysts. He employed a batch reactor with photocatalysts plate (TiO2 NTs and TiO2 - Au
NTs) and a tubular reactor charged with a microreactor (photocatalyst) having TiO2 NTs
sensitized or not with gold nanoparticles (NPs Au).
The synthesis of TiO2 NTs occurred by anodization process using as substrate sheets of metallic
titanium (Ti). The nanotubulares matrices were crystallized by heat treatment (400 ° C for 3h).
The sensitization Au NPs was performed in situ by reduction by UV radiation. The
photodegradation was carried from the irradiation NEWPORT solar simulator 67005 model with
a xenon-mercury lamp (calibrated power for 1 SUN) in the absence or presence of filter (UV or
visible). The anatase crystalline phase of TiO2 NTs was identified by X-ray diffraction (XRD). It
was estimated by Rietveld refinement a crystallinity of 77% at the photocatalytic surface with
anatase (TiO2 crystallized NTs) representing 92.4% of this crystalline phase. The energy band
gap of 3.23 eV photocatalysts was determined by diffuse reflectance spectroscopy. By scanning
electron microscopy (SEM-EDS) it was possible to view the Ti smooth sheet, cylindrical
structures of TiO2 NTs that grew perpendicular to the substrate, with an average diameter of
78.87 nm and lengths in 2 µm order, in the case of the corrugated Ti sheet the TiO2 NTs grew in
different directions with a mean diameter of 81.09 nm and lengths on the order of 3 µm. The
presence of NPs Au was identified by energy dispersive spectroscopy (EDS). The determination
and quantification of product and reactant of heterogeneous photocatalytic on the degradation of
DCF were performed by a combination of analytical methods (high-performance liquid
chromatography, Magnetic Resonance and Infrared Fourier transform ), whereby a conversion of
100 % DCF for testing in batch reactor and 37.0 % in the reactor for recirculating the best
photocatalytic system. It was estimated by analyzing total organic carbon (TOC) a mineralization
of 18.5 % of the initial DCF for more efficient photocatalyst system using the reactor with
recirculation. The ecotoxicity of DCF and its photodegradation products was evaluated using
microcrustaceans (Artemias Salinas) as bioindicator.
28
Wei-KangChang and 張維剛. "Study of TiO2 Nanotube Arrays Based Gas Sensors." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/66993330159249546605.
Full textAbstract:
碩士<br>國立成功大學<br>化學工程學系碩博士班<br>98<br>In this study, the TiO2 nanotube arrays (NTAs)/quartz fabricated by anodization were used as resistive-type gas sensors. Firstly, a thin Ti film was deposited on the quartz substrate by RF sputtering. Subsequently, the sample was anodized in an NH4F-H2O-EG electrolyte to form highly ordered TiO2 NTAs. Then, a metal electrode was deposited onto the TiO2 surface to obtain TiO2 NTA/quartz device. Furthermore, the sensing characteristics of the studied devices were investigated on H2, NH3 and NO2 gases, respectively. The effects of metal electrode on gas sensing performance were emphasized. In addition, the gas sensing mechanism was also deduced.
From the experimental results, it indicated that three sensor devices with metal electrodes of Pt, Au and Pd all showed superior sensing ability to H2 more than NH3 and NO2. Comparing these three kinds of gas sensors, it was found that the hydrogen sensitivity was decreased in the sequence as Pt ＞ Pd ＞ Au. The sensitivity of TiO2 NTA/quartz device exposed to 1% H2/N2 at 373K could reach up to 2.85×104. Even at extremely low hydrogen concentration, e.g., 100 ppb H2/N2, the sensitivity still approached to about 1 order. From results of I-t transient responses, the response rate of the Pt/TiO2 NTA/quartz was increased with increasing either temperature or hydrogen concentration. For the hydrogen sensing at 473K under 1% H2/N2 ambience, the response time was only 15s.
When the hydrogen sensing experiments performed in the air ambience, the adsorbed oxygen (O2) was removed from the TiO2 surface by the reaction with hydrogen, and then the oxygen vacancies would be backfill by oxygen from air ambience and formed O2 again. Consequently, the sensing current could reach to the steady-state value rapidly. As compared with the sensitivity in N2 ambience, it showed that the hydrogen sensitivity in air was relatively low (373K, 1% H2/air, S=304.9), which deviated even reaching to about 2 order.
29
Yang, Jing-Yi, and 楊靜怡. "Photocatalytic activity of carbon nanotube supported TiO2 photocatalyst." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/78552954350234675924.
Full textAbstract:
碩士<br>東海大學<br>環境科學與工程學系<br>96<br>Abstract
The main objective of this work is to coat multi-walled carbon nanotube surface with TiO2 and to investigate its photocatalytic activity. Commercial multi-walled carbon nanotubes were modified with nitric acid under microwave heating. The TiO2/MWCNT photocatalysts were prepared by sol-gel method under ultrasonic condition; they were characterized with BET, XRD, SEM, TEM, UV-Vis, XAS and photodegradation of methylene blue in water under ultraviolet illumination. The results show that the BET surface area of the catalysts is 72.4—167.6 m2/g . From XRD results, TiO2 is the photocatalyst composites calcined at 450 ◦C are in anatase form structure. SEM and TEM results indicate that TiO2 has been successfully deposited on the surface of multi-walled CNT. The UV-Vis and XAS results indicate the existence of interaction between TiO2 and MWCNT. The photocatalytic activities of the composite catalysts were evaluated by photodegradation of methylene blue under ultraviolet illumination. TiO2/MWCNT has better photocatalytic activity than both TiO2 and MWCNT. TiO2 coated on the surface of MWCNT could improve the efficiency of the photocatalytic reaction.
30
Yang, Ya-Ting, and 楊雅婷. "Dye-Sensitized Solar Cell using TiO2 Nanowires on Anodic TiO2 nanotube Arrays (TNWs/TNAs)." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/g644t9.
Full textAbstract:
碩士<br>國立交通大學<br>照明與能源光電研究所<br>101<br>Dye-sensitized solar cell (DSSC), a new generation solar cell, has the potential to be widely used due to its advantages of low cost, compatibility for flexible devices, and enhanced performance with temperature. Specifically, the morphology of TiO2 film is one of the major factors affecting the conversion efficiency. Among various structures, TiO2 nanotube has great potential due to the highly ordered could provide a direct transport route and higher stability for flexible device.
In this study, a TNWs/TNAs hybrid structure was first fabricated using a one-step method by anodizing a titanium foil in electrolytes consisting of NH4F and H2O, under different voltage and processing time. The evolution and the mechanism of TNWs/TNAs hybrid structure prepared by using mechanical stirring were examined and proposed. The DSSC performance of TNWs/TNAs was measured and compared to TNAs and conventional TiO2 nanoparticle film. Based on the I-V characteristics and dye absorption measurement by an UV-visible spectroscopy, nanowires in the TNWs/TNAs (12 贡m) hybrid structure enhance the surface area and improve the redox couple diffusion in TiO2 electrode to raise the photocurrent, resulting in enhanced conversion efficiency. For TNWs/TNAs hybrid structure (30V, 8 hours), the conversion efficiency and Jsc are 1.85%, 5.27 mA/cm2, compared to 1.04% and 3.81 mA/cm2 in a TNA only film. The 44.3% improvement in conversion efficiency can be attributed to the enhanced dye adsorption (21%) and better electron transport in TNWs/TNAs compared to TNAs only. Overall, TNWs/TNAs films show great potential to be a simple and flexible DSSC.
31
Wong, Pei-Chieh, and 翁培傑. "TiO2-nanotube Surface for Investigation of Biocompatibility and Hemocompatibility." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/51290338618555160380.
Full textAbstract:
碩士<br>國立中興大學<br>生醫工程研究所<br>103<br>Nanoscale metallic substrates for improved biocompatibility and hemocompatibility are a persistent theme in biomaterials research and biomedical applications. For example, the need to improve the long¬term prognosis of commercially available bare-metal stents has drawn a lot of attention. In this study, we focused on surface modification of titanium (Ti) for simultaneously investigating the effects of nanoscale surface structure and angstrom-scale chemicals on biocompatibility and hemocompatibility. The technique of electrochemical anodization was used to create uniform nanotubular structure of titanium oxide on the surface of titanium (ATN). After the process of anodization, the ATN samples were individually either coated by NO or modified by 3-mercaptopropyltrimethoxysilane (MPTMS). Ti, ATN, NO coated ATN (NO-ATN), MPTMS modified ATN (MPTMS-ATN), NO coated MPTMS-modified ATN (NO-MPTMS-ATN), and MPTMS modified NO-coated ATN (MPTMS-NO-ATN), were separately examined their material properties using electron spectroscopy for chemical analysis (ESCA) and contact angle goniometer. The results of ESCA showed the specific chemical bondings after each step of modification. In addition, all the surface modified samples displayed better hydrophilic property in comparison with Ti. Endothelial cells on NO-MPTMS-ATN and MPTMS-NO-ATN were respectively increased to 1190±14.74 cells/mm2 and 1167±24 cells/mm2 in five days of culture. Although the tests of prothrombin time (PT) and activated partial thromboplastin time (aPTT) exhibited normal in all samples, the fibrinogen concentration was 193.18±6.0 mg/dl on MPTMS-NO-ATN and less than other five groups and reference value. Collectively, the modified surfaces showed augmented proliferation of endothelial cells and improved hemocompatibility. This cost-effective and industrially-scalable technique of metallic surface modification can be successfully utilized to offer a cell/hemo-friendly solution to the inherent limitations pertinent to bare metallic stents in the future.
32
Huang, Yi-Ching, and 黃怡晶. "Syntheses and photocatalytic properties of TiO2 nanotube-based heterostructures." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/91736560814934946481.
Full textAbstract:
博士<br>國立中興大學<br>材料科學與工程學系所<br>103<br>Photocatalytic nanostructure effectively solved the problem of environmental pollution and as an alternative energy which could to degrade pollutants, produce H2 by water splitting and convert CO2 to orgainic molecule. However, bare semiconductor photocatalyst had bad photocatalytic activity because of the rapid recombination of photoinduced electron-hole pairs. In the study, synthesising 3D heterostucture photocatalyst by growing ZnO nanorods, Ag nanoparticles and Pd nanodendrtie on the TiO2 nanotube array improved photocatalytic activity on the bases of an enhanced separation of photoexcited elelctron-hole pairs. The electron microscopes and X-ray photoelectron spectroscopy were used to analysze the morphologies, lattice structure and the element composites of the TiO2 nanotube-based heterostructures. For determining SERS efficiency, the Raman spectra of the TiO2 NT based heterostructure were detected Raman signal by using visible Raman spectroscopy. Finally, it was evaluated that the photocatalytic activity of the photocatalyst heterostructure by analyzing dye degradation and hydrogen generation.
In the study, we successfully grafted ZnO nanorod on the TiO2 nanotube by hydrothermal method to form 3D TiO2/ZnO arrayed heterostructure as supporting platform for nanoparticle deposition. or be a sacrifice for Pd dendrite forming. Crystal structure between ZnO and TiO2 followed specific lattic direction in order to reduce surface energy: ZnO(100) // TiO2(103), ZnO growth along [002] direction; Ag nanoparticle crystallized to follow specific direction, too: Ag(101) // TiO2(103) and Ag(101) // ZnO(002); The arm/branch angle of Pd dendrite was 70°C and grew along [111] direction. The first and recylce degradation of TiO2 nanotube based heterostructure showed excellent photocatalytic activity. TiO2 nanotube/Pd nanodendrite heterostructure was excited more electron-hole pairs due to strong surface plasmon resonance effect. In addition, the separation of electron hole pairs and high surface area provided more reactive positions to enhance photocatalytic activity. At last and the most important of all is that in this study, we use theoretical calculation to prove that carrier charge numbers had specific exponential relationship with dye degradation and hydrogen generation. The photocatalytic mechanism is mainly controlled by the carrier charger numbers.
33
Hsu, Way-Chih, and 徐偉智. "Electrochemically prepared TiO2-xCx nanotube arrays for water splitting." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/33744737927443565439.
Full textAbstract:
碩士<br>國立交通大學<br>分子科學研究所<br>98<br>TiO2-xCx nanotube arrays have been grown by anodic oxidation. Two kinds of carbon sources: ethylene glycol and phenol have been employed. The optimum condition for anodization is to employ 10 g DI water, 0.5 g NH4F, 89.5 g ethylene glycol and 16 g phenol with annealing at 500 ℃. Water splitting efficiency was found to be 16.31% at 330 ±70 nm and 0.068% at 520 ± 46 nm. The observed XPS result shows that the higher binding energy of carbon is related to better water splitting efficiency. Besides, there is a unique peak in the valence band which is consistent with the result of quantum chemical (density functional theory) calculations which reveal three possible structures.
34
Huang, Jia-Sheng, and 黃嘉聖. "Application of TiO2 Nanotube on Dye-Sensitized Solar Cells." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/01677909059938039541.
Full textAbstract:
碩士<br>國立臺灣師範大學<br>機電科技研究所<br>98<br>In the study, TiO2 nanotube was manufactured by anodization with electrolyte of mixed solution of ethylene glycol (EG), ammonium fluoride (NH4F) and DI water, high purity titanium (99.7%) as anode and platinum as cathode, dye-sensitized solar cells contribute to efficiency.
By sensitizing the anode with N719 dye and exposing under a light which light intensity is 100 mW/cm2, the length for 30 μm which measured by the highest photoelectric conversion efficiency, the Jsc = 11.30 mA/cm2, Voc = 0.71 V, FF = 0.48, η = 3.92%.
35
Huang, Yung-Chi, and 黃泳騏. "Preparation and Photocatalytic Activity of TiO2 Nanotube/Pd Nanodendrite Heterostructures." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/38665319466341637155.
Full textAbstract:
碩士<br>國立中興大學<br>材料科學與工程學系所<br>102<br>Stable, nontoxic, and low cost TiO2 with high redox potential has been widely used in optoelectronics devices, solar cells, photocatalysts, and biomaterials. Particularly, anodized TiO2 nanotubes of easy synthesis and low cost can generate electron-hole pairs under UV-light irradiation guide the transfer of electrons. However, the rapid recombination of the electrons holes will reduce the photocatalytic activity. Therefore, surface modifications and TiO2 heterostructures have been intensively studied. In this study, ZnO nanorods were first grown on anodized TiO2 nanotubes by a hydrothermal method, and the TiO2/ZnO heterostructures were then sensitized and activated to form TiO2/Pd nanodendrite heterostructures by a non-uniform Zn+2 electric field. With increasing sensitization/activation time, Pd nanodendrites became particles of low surface energy. Because of the large surface area of the dendrite structure for reactions and the enlarged light absorption range, the photocatalytic activity was markedly enhanced. The photodegradation rates of dye pollutants in the presence of the TiO2/Pd nanodendrite heterostructures were much higher than those only in the presence of TiO2 nanotubes.
36
Liang, Yu-Chuan, and 梁育銓. "The Synthesis and Photocatalysis of Ag-loaded TiO2 Nanotube Arrays." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/41724120503312817905.
Full text
37
Wu, Kuan-Lin, and 吳冠霖. "Preparation and Characterization of TiO2 Nanotube Arrays by Anoding Process." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/11858744737722903944.
Full textAbstract:
碩士<br>元智大學<br>化學工程與材料科學學系<br>99<br>The highly ordered TiO2 nanotube arrays were fabricated by using electrochemical anodization in ethylene glycol electrolyte containing 0.3 wt% NH4F and 2 wt% H2O. TiO2 nanotubes were then manufactured under various temperature and anodization potential using plumbum (Pb) plate and platinum (Pt) coated titanium-made (Ti) net as a cathode, respectively. Field emission scanning electron microscopy, X-ray diffraction and UV-visible light spectrum meter were applied to analyze the characteristics of TiO2 nanotubes. Varied concentrations of Pt catalysts on TiO2 nanotubes were implemented by impregnation method. The efficiency of varied Pt catalysts was independently measured by the evaluation of hydrogen production under UV light irradiation. Our results showed that the increase in working temperature facilitated the growth of TiO2 nanotubes at 50V. TiO2 nanotubes were 16.8 μm in length using Pt coated Ti net cathode and 11 μm in length using Pb cathode, respectively. The temperature was controlled at 40℃, TiO2 nanotubes raised from 32 nm to 80 nm in diameter and from 1.7 μm to 16.8 μm in length using Pb cathode when the anodization potential was increased. By contrast, the diameter of TiO2 nanotubes reached from 33 nm to 83 nm and the length increased from 1.7 μm m to 16.8 μm using Pt coated Ti net cathode. The highest efficiency of hydrogen production was found in the TiO2 nanotube substrate with 0.05 % Pt catalyst. On the contrary, the increased concentration of Pt catalyst on TiO2 nanotube resulted in lower hydrogen production.
38
Chang, Chieh-Chun, and 張傑鈞. "N-doped TiO2 Nanotube for PtRu Catalysts in Fuel Cells." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/45690321136101285431.
Full textAbstract:
碩士<br>國立中央大學<br>化學研究所<br>98<br>This research pertains to the development of novel anodic catalyst of direct methanol fuel cells. The use of nitrogen doped titanium nanotubes improves electronic conductivity and the interaction between metal and support, leading to the improvement of methanol oxidation efficiency and the performance of fuel cell.
Titania nanotube bears much higher surface area and favorable low dimension conducting property. Through replacing the oxygen atoms on the surface of the TiO2 nanotube by nitrogen, the N-dopped TiNT raised electronic conductivity from 10-7 Scm-1to 10-1 Scm-1. The N-doped TiO2 tube shows higher surface area compared to conventional carbon materials. Using HRTEM observes some wrinkling on the surface differ from un-annealing one. Additional, EELS mapping helps to realize the nitrogen atoms are dispersion well；XRD to realize the morphology and the phase transfer, the phase is transferred from Anatase to TiN follow by temperature increase； The XPS revealed nitrogen content of about 27.55 wt%, and the binding energy is 396eV and 400eV, which confirms the bonding of Ti-N and TiO-N.
Synthesize the PtRu alloy catalyst is achieved by alcohol reduction method. The study shows the majority of metal nano particle reside on the metal oxide tube surface and the Pt-Ru nanoparticles are well dispersed and indicate, that the metal oxide is effective in preventing the particle aggregation, giving rise to higher electrochemical active surface area. The N-TiNT/C/PtRu exhibited a mass current density of 653 A/g Pt, which is much higher than that of E-TEK (358 A/g Pt) measured under the same condition.；.The If/Ib ratio is higher to 5.69, which mean highly CO tolerance. In addition, present study shows that the nitrogen doped TiO2 as the support for metal nano-particle, nitrogen improve both the electrocatalytic oxidation activity and benefit CO-tolerance. CO-stripping measure the ECSA (Electrochemical Surface Area) can reach to 104 m2/g. The catalyst with N-TiNT support displayed a relatively lower CO to CO2 oxidation potential compare to E-TEK, which implies better CO oxidation capability compared to commercial E-TEK catalysts and the MEA performance is substantially improved.
39
Jian, Li-Shin, and 簡立欣. "Silver Halide/TiO2 Nanotube Composite Photocatalyst in Visible Light Photocatalytic Application." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/69068879184565818989.
Full textAbstract:
碩士<br>國立中興大學<br>化學工程學系所<br>102<br>TiO2 is an important photocatalyst due to its high chemical stability, low cost, non-toxicity. However, it possesses high energy gap of 3.2eV, TiO2 is only responsive to ultraviolet irradiation. Thus, how to prepare the photocatalyst has good photocatalytic activity under visible light is one of our goals. We try to prepare photocatalyst that can produce electron-hole under visible light by combining the high specific surface area of TiO2 nanotube and the strong photosensitivity of silver halide. The factors we are trying to enhance the photocatalytic activity including the temperature in the hydrothermal process, kinds of silver halide, the proportion of silver halide to TiO2 nanotube, and the temperature of calcination.
The characteristic analysis of silver halide-doped TiO2 nanotube were performed by XRD、BET、SEM、TEM、ICP. From the XRD images, we can confirm the crystal lattice of TiO2 nanotube and silver halide. From the SEM and TEM images, we can observe the structure of TiO2 nanotube. From BET analysis, we know the specific surface area of our samples. By ICP analysis, we can determine how much silver halide has been doped on our TiO2 nanotube. From Uv-vis analysis, the absorbance wavelength range can be determined. Finally, we have concluded that TiO2 nanotube preparing at 140℃ hydrothermal temperature, load 20 mole% AgBr, and calcine at 400℃ has the best photocatalytic activity. A 0.1g photocatalyst degradation in 100ml of methyl orange, which concentration is 10 ppm. The decomposition rate can reach up to 90% in a hour.
40
Hsu, Ching-Wen, and 許淨雯. "Opening direction of TiO2 nanotube arrays for Dye-Sensitized Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/v6zyr6.
Full textAbstract:
碩士<br>國立臺北科技大學<br>有機高分子研究所<br>100<br>The aim of this thesis is to fabricate a TiO2 nanotube based dye-sensitized solar cells (DSSCs) with the front-side illumination. In this work, the formation of ordered anatase TiO2 nanotube (TNT) arrays was carried out by potentiostatic anodization process followed by annealing at 450 oC for particular time. Subsequently, tube-shaped and pipe-shaped free standing TNT arrays were fabricated by voltage-pulse method, in which voltage pulses were applied for a short time at the end of the anodization process. The TNT arrays were detached and transferred onto the FTO substrate using TiO2 NP paste as an interface and used as a photoanode in DSSCs for front-side illumination.
The first part of this work is the preparation of tube-shaped TNT arrays by varying the second anodization voltage. The free-standing TNT arrays were attached on the FTO substrate in two directions, one as upright (face-up) and another one is inverted (bottom-up). In order to investigate the effect of TNT array direction in DSSCs performance, the characteristics analysis of N719-based DSSCs, such as current density-voltage (J-V) and incident photo-to-current conversion efficiency (IPCE) measurements were performed.
The second part of this work is the preparation of pipe-shaped TNT arrays by elevating the anodizing voltage at the end of second anodization process. Elevating the voltage helps to break the adhesion of the TNT arrays from the underlying Ti substrate and simultaneously open their closed bottom. Adsorption of N719 dye for the closed bottom and opened bottom TNT array photoanodes were studied. The photoelectrical performance of DSSCs with closed bottoms and opened bottoms TNT arrays were investigated and compared with each other.
Hereby, from the above two works we can conclude that the front-side illuminated TNT arrays based DSSCs demonstrated a better improvement in the photoconversion efficiency. The free-standing TNT arrays were attached on the FTO substrate in three directions, one as upright (face-up), another is inverted (bottom-up), and the other is open-end. In order to investigate the effect of TNT array direction in DSSCs performance, inverted (bottom-up) has the best efficiency is 6.93 %. And incident photo-to-current conversion efficiency (IPCE) measurements were 47.63 % at 530 nm wavelength in open-end.
41
Wu, Jen-Wei, and 吳哲瑋. "Electronic Properties of TiO2-nanotube arrays studied by x-ray spectroscopies." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/8fuvn6.
Full textAbstract:
碩士<br>國立臺北科技大學<br>製造科技研究所<br>101<br>The TiO2 nanotubes (TiNT) arrays were fabricated by electrochemical anodic oxidation method at room temperature using Ti foil in ethanol containing ammonium fluoride (NH4F) and hydrogen peroxide solution (H2O2). The TiO2-nanotube arrays exhibit favorable electron transport properties and superior light-harvesting efficiency. The high quality arrayed nanotubes can be used to the wide range of applications in photovoltaic cells and optoelectronic devices. In this report, the conduction/valence band and electron/hole transportation of the TiNTs are investigated by scanning photoelectron microscopy (SPEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy(XAS) . The electronic structural characterization reveal that the catalytic property strongly correlates with the Ti 3d-O 2p hybridization. It reveals that the electronic structure around Ti site is varied in the bottom and the top of the nanotube. In addition, the local atomic structure of these TiNTs are also investigated by extended X-ray absorption for fine structure (EXAFS).
42
Chen, Si-Fan, and 陳思帆. "Preparation and Photocatalytic Properties of TiO2 Nanotube /Sn-Pd Nanoparaticle Heterostructures." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/08513717388699933172.
Full textAbstract:
碩士<br>國立中興大學<br>材料科學與工程學系所<br>98<br>Titanium dioxide (TiO2) with many excellent properties is promising for the applications to optoelectronic devices, solar cells, photocatalytic, biomaterials, etc. The growth of TiO2 nanotube arrays by anodization processes has many advantages because of a low manufacture temperature, simple prossces, and low cost. However, the recombination of photoexcited electron-hole pairs in the TiO2 nanotubes will reduce the photocatayltic efficiency. Therefore, surface modification or hetrostructure on the TiO2 nanotubes has been extensively studied. In this study, TiO2 nanotube arrays were fabricated by anodization first. Sn-Pd nanoparticles were then deposited on the TiO2 nanotube arrays by a sensitization-activation method. It was found that the diameter and length of TiO2 nanotubes were depended on the anodic voltage and anodization time, respectively. Anatase TiO2 nanotubes were obtained by heat treatment at 450℃. The deposition of the Sn-Pd nanoparticles was dominated by the concentration of hydrochloric acid in the solution and also the sensitization-activation time. The growth Sn-Pd nanoparticles was found on anatase TiO2 nanotubes at specific sites and a orientation. However, before heat treatment, the TiO2 nanotubes deposited with Sn-Pd nanoparticles were amorphous and then crystallized into a rutile phase at 450℃. In photocatalytic properties, anatase phase TiO2 nanotubes with Sn-Pd nanoparticles have a better degradation rate for methylene blue (MB) and methyl orange (MO).
43
Shang, Wei-Ting, and 商維庭. "Photocatalytic Oxidation of Methyl Orange over Boron-doped TiO2 Nanotube Arrays." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/81071707444358989282.
Full textAbstract:
碩士<br>國立臺灣大學<br>環境工程學研究所<br>98<br>The objective of this study was to modify TiO2 nanotube arrays with boron via two doping methods including chemical vapor deposition and electrodeposition. With various characterizations including Field-Emission Scanning Electron Microscope (FE-SEM), Raman Spectrophotometer, X-Ray Diffractometer (XRD), UV-Visible Spectrophotometer (UV-Vis) and Fourier Transform Infrared Spectrophotometer (FT-IR), the effects of aspect ratios of TiO2 nanotube arrays on the doping performance were investigated. The photoactivity of B-doped TiO2 nanotube arrays was also examined in terms of the oxidation efficiency of methyl orange (MO).
The XRD patterns of TiO2 nanotube arrays calcined at 500 ℃ showed that the intensity of anatase peak increased with increasing the aspect ratio. After boron doping, the intensity of anatase peaks decrease. The UV-Vis DRS spectra indicated that the absorption intensity of the B-doped TiO2 nanotube arrays was enhanced both in the UV and visible regions. In addition, all the B-doped TiO2 nanotube arrays exhibit red shifts.
The results indicated that the photoactivity of TiO2 nanotube arrays is significantly dependent on the aspect ratio. An increase in the aspect ratio of TiO2 nanotube arrays leads to an improved efficiency of MO oxidation. Furthermore, the photoactivity of TiO2 nanotube arrays was enhanced after B doping via either chemical vapor deposition or electrodeposition. The optimum boron doping concentration prepared by electrodeposition was lower than that by chemical vapor deposition. Meanwhile, the enhancement of photocatalytic performance of B-modified TiO2 nanotube arrays is apparent when the aspect ratio is lower. This result is probably owing to the fact that the larger the aspect ratio, the less TiO2 nanotube arrays can be modified. Based on the FT-IR spectra, the intensity of MO absorption bands over B-modified TiO2 nanotube arrays vanished after 0.5 h UV illumination whereas the MO signal over unamended TiO2 nanotube arrays remained obvious after 2 h UV illumination.
44
Lin, Jui-Yang, and 林瑞陽. "Study of the Bamboo-type TiO2 Nanotube Array： Synthesis and Application." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/89137224227004144485.
Full textAbstract:
碩士<br>國立中興大學<br>化學工程學系所<br>100<br>Hydrogen is a source of clean energy. The photocatalyst has been applied to water splitting generate hydrogen when it is activated by the light. Many studies have investigated the photocatalysis, and the most extensive photocatalyst is titanium oxide(TiO2). Due to its photo-electrochemical stability, non-toxicity, and low cost for fabrication. High surface area TiO2 and highly ordered TiO2 nanotubes can enhance the photocatalysis activity, and lead to a potential application for hydrogen generation application from photo electrochemical cell.
This study will synthesize Bamboo-type TiO2 nanotube array by alternating voltage system under the anodization method. To achieve the highly order Bamboo-type TiO2 nanotube array, the high voltage system in alternating voltage condition, anodization time, calcinations temperature and switch of voltage have been effectively controlled. Studying the structural properties of the highly order Bamboo-type TiO2 nanotube array has used the instructments of Field Emission Scanning Electron Microscope(FE-SEM), X-ray Diffraction Spectrometer(XRD), Electrochemical Chromatography, and Gas Chromatography(GC). The Bamboo-type TiO2 nanotube arrays have the higher surface area than the tranditional TiO2 nanotube arrays, it could enhance the photocatalytic activity. The photoconversion efficiency of Bamboo-type TiO2 nanotube array achieves 15.04%.
45
Lu, Jun-Lin, and 盧俊霖. "The photodegradation of Bisphenol A by highly-ordered TiO2 nanotube array." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/79211255125863719125.
Full textAbstract:
碩士<br>輔英科技大學<br>環境工程與科學系碩士班<br>98<br>Bisphenol A (BPA) is often used the raw materials of manufacturing baby bottles, beverage cans, plastic and resin. Many scholars discovered that bisphenol A is a kind of environmental hormone, which will affect female cells and result in ether deformity or reproductive impairment of biological organisms. In recent years bisphenol A existed in environmental water body has attracted increasing attention, the treatment of the bisphenol A is widely studied. Because of the time-consuming and poor results of biological decomposition method, the built-in photocatalytic degradation is a potential technology, which is a rapid degradation, solve the traditional disadvantages of catalyst recycling problems, and except high-energy ultraviolet light the visible light also has some degradation effect. It was found that mineralization reduced 80% TOC during photocatalytic degradation. In the future, there are many efforts to do in technology development, such as handling the scale of toward practical application.
In this study, a self-made highly-ordered array of TiO2 nanotubes plate was used to degrade bisphenol A and explore the effects of pH, the initial concentration of bisphenol A, inorganic ions, dissolved organic matter and other factors on the degradation of bisphenol A. The results showed that pseudo-first order reaction could be used to describe this photocatalytic degradation reaction. The initial concentration of bisphenol A had no significant effect on photocatalytic degradation of bisphenol A in this study. The estimated degradation rate constants revealed that the effect of pH was in the order of pH 4> pH 10> pH 7. The Cl- and SO42- ions were found to suppress the photocatalytic degradation of bisphenol A, but there is a positive effect for NO3- on photocatalytic degradation reaction. And the effect of copper ion is not obvious. Dissolved organic matter HA (humic acid, salt form) restrained the photocatalytic degradation of bisphenol A.
46
Tsai, Shuei-Feng, and 蔡水蜂. "TiO2/ZnO nanotube arrays synthesis for dye-sensitized solar cell application." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/83884567635648082721.
Full textAbstract:
碩士<br>崑山科技大學<br>綠色材料研究所<br>98<br>A chemical bath deposition (CBD) method was applied to grow zinc oxide nanorod (nanowire) arrays on transparent conductive oxides (TCO, ITO or FTO) acting as templates for the synthesis of TiO2/ZnO nanorod arrays by spin procedures, and then these arrays were assembled as anodes in dye-sensitized solar cells. The physical properties and photovoltaic efficiency were studied in relation to the procedure variables including concentration of TiO2 sol for the bottom layer, deposited times of the ZnO seeds and ZnO nanorods (nanowires) , number of TiO2 spin coat layer and calcination temperature and time. Etching of ZnO from TiO2/ZnO nanorods was also carried out to obtain top-end opening structure to improving the DSSC efficiency. Results indicates that samples prepared from 0.05M TiO2 sol, 4 times of ZnO seed deposition, 3 times of ZnO nanorod array growth, 1 TiO2 layer by spin coat and calcination at 450℃for 60 min exhibits the highest photovoltaic efficiency.
Etching by HCl solution can change the morphology of TiO2/ZnO nanorod arrays and cause an increased photovoltaic efficiency. Particularly, this effect is more significant with the samples by a spin rate 3000 rpm than 1000 rpm in coating TiO2 on ZnO nanorod arrays. A maximum efficiency 3.4% was obtained by optimizing the procedure variables of the etched sample. Photoluminescence (PL) analysis reveals that etching by 3% HCl solution for 3 minutes can decrease both the band to band and excitonic PL intensities; however, increasing TiO2 coating number increases both the PL intensities, leading to a decreased photovoltaic efficiency. Finally, the dark current measurements and open-circuit voltage decay (OCVD) techniques were adopted to examine the charge recombination of electrons between the semiconductors and electrolytes.
47
Hsu, Chih-Hao, and 許致豪. "Synthesis TiO2 nanotube and applied in dye sensitized solar cell electrode." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/yw9fyk.
Full textAbstract:
碩士<br>國立臺北科技大學<br>材料科學與工程研究所<br>97<br>On this study,we use reflux method to synthesize titanium dioxide nanotubes, and the use of different titanium dioxide powder source(P25, Anatase, Rutile) and heat temperature (130 ℃, 160 ℃, 190 ℃), and reaction time (12h, 24h, 48h , 96h) and concentration of sodium hydroxide (5M, 10M) to explore the synthesis mechanism. Which found that titanium dioxide dissolved in alkali to TiO3-exist in aqueous solution, and the use of dissolution - precipitation growth approach with a view to grow into tubular shape, compared with the previous literature, not by law to the formation of nanometer curly tube structure. We synthesized nanotubes by length of microns up to more than 100 nm in diameter; in the process of growth can also be found in sheet (sheet), nano-band (nanoribbon) the existence of flake length and width not more than 1 micron, nanotechnology is long with nearly 1-micron width of 100 nm. While the formation and morphology of titanium dioxide in the solubility of sodium hydroxide. As regards the structure, the original anatase or rutile return characteristics of the summit in the process of gradually weakened disappeared and been replaced by titanate structure, but can be by way of pickling will be out of sodium ion replacement, at the same time re-heated to above 450 ℃ can be returned to anatase or rutile structure.
48
Yang, Min-Kai, and 楊閔凱. "Preparation and Dye-Sensitized Solar Cell Application of TiO2 nanotube array electrode." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/t2paa4.
Full text
49
Kuang-LeeLee and 李光麗. "CuInS2 Quantum Dot Sensitized TiO2 Nanotube Arrays as Photoelectrode for Photovoltaic Reactions." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/84840155966342819640.
Full textAbstract:
碩士<br>國立成功大學<br>化學工程學系碩博士班<br>98<br>Our laboratory had already synthesized colloidal CuInS2 nanoparticles via solvothermal method under lower temperature, which was employed as sensitizers for photoelectrochemical cells while using TiO2 nanaoparticle as electron conductor. In this study, try to improve the photoresponcse under visible light illumination though changing the TiO2 nanoparticle to the TiO2 nanotube and doping zinc into CuInS2 quantum dot (QD).
Compare to nanoparticle, nanotube structures has higher degree of crystallinity and high surface area to volume ratio which provides better electron transport, so we focus our research on using nanotube as electron conductor. On the other hand, introduction of Zn into CuInS2 system can enhance the photoluminescence(PL) intensity and the band gap can be tuned while changing the solvothermal temperature or altering the concentration of zinc. Higher PL strength of doping Zn into CIS system had been confirmed, which can improve the photoresponse, however, is the topic of this work.
From this experiment, after find out the optima tube length for loading quantum dot, discuss the optical properties, band gap energy, and PL intensity of chalcopyrite-type nanocystals. Finally, discuss the results of photovoltaic reaction.
50
Dewi, Cynthia, and 辛西亞. "The Synthesis of TiO2 Nanotube Arrays as Electron Conductor for Photovoltaic Reactions." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/61347614839220684980.
Full textAbstract:
碩士<br>國立成功大學<br>化學工程學系碩博士班<br>97<br>Nanotubes structures have drawn interests for its high degree of crystallinity and high surface area to volume ratio which provides better electron transport when it is used as the electron conductor. Anatase TiO2 has been known as a good material for photocatalytic applications since it has wide band gap (3.1 eV) which relates to the UV light absorption. This research is focused on synthesizing the TiO2 nanotubes as the electron conductor for photovoltaic reactions; by anodizing Ti foil (vs Pt foil as the counter electrode) in F- ions containing electrolyte solution. The electrolyte solutions used for the anodic oxidation are 0.5 wt% NH4F in ethylene glycol or glycerol, modified by adding 10 wt% dimethyl sulfoxide (DMSO) to enhance the nanotube formation. TiO2 nanotubes obtained were then used as the substrate for CdS deposition using chemical bath deposition (CBD) method, and then were tested for the photoresponse under visible light illumination.
It is found that the TiO2 samples obtained from the anodization of Ti foil for 24 hours gave the highest photocurrent under UV light illumination. It is also found that the samples anodized in glycerol electrolytes are more organized and the nanotubes wall is smoother than those anodized in ethylene glycol electrolytes. The addition of DMSO has been proven to enhance the nanotubes structure uniformity and hence performed higher photoresponse. The CdS deposited TiO2 nanotubes exhibit high photocurrent, showing that the TiO2 nanotubes synthesized in this research can be used as the electron conductor for the photovoltaic reactions.