The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell's characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.

Effect of surface state properties of TiO2 nanoparticle film on its photocatalytic activity

TiO2 nanoparticle film catalysts with different thicknesses were prepared by plasma-enhanced chemical vapor deposition(PECVD) method and the surfaces were subsequently treated by TiCl4 or O-2 plasma. Two kinds of TiO2 films with different surface properties were obtained. Their surface microstructures and energy levels of surface states were tested by AFM, XRD, SPS, The photocatalytic activities of the catalysts were determined via photodegradation experiments of phenol. The results demonstrated that photocatalytic activities of samples whose surface was treated by O-2 plasma were greater than those treated by TiCl4 plasma. Moreover, photodegradation ratio of phenol during the first hour catalyzed by 0. 17 mu m thickness TiO2 nanoparticle film was greater than other samples. Especially, the difference of photocatalytic activities of TiO2 nanoparticle films treated by TiCl4 or O-2 plasma was respectively explained by energy band theory.

Chemical vapour deposition of complex ferroic oxide thin films

Herein is presented a novel chemical vapour deposition (CVD) route for the fabrication of oxide ferroelectrics. A versatile layer-by-layer growth mode was developed to prepare naturally super-latticed bismuth based materials belonging to the Aurivillius phase family, with which good control over composition and crystal structure was achieved. In chapter 3, the effect of epitaxial strain on one of the very simple oxide materials TiO2 was studied. It has been found that the ultra-thin TiO2 films demonstrate ferroelectric behaviour when grown on NdGaO3 substrates. TiO2 exists in various crystal phases, but none of them show ferroelectric behaviour. The epitaxial strain due to the substrate, changes the crystal structure from tetragonal to orthorhombic which in turn leads to ferroelectric behaviour. In chapter 4, a unique growth method for multiferroic BiFeO3 (BFO) thin films is shown, where a phase pure BFO thin films can be prepared even in the presence of excess bismuth precursor during the growth process. This type of growth is usually called adsorption controlled growth and can be used for growing various bismuth containing compounds, where the volatility of bismuth can create various types of defects. Chapter 5 describes the growth of Bi4Ti3O12 thin films in a layer-by-layer growth mode. In this section, the effect of Bi and Ti precursor flows on the growth of thin films is discussed and it is shown that how change in precursor flows leads to out-ofphase boundary defects during the layer-by-layer growth mode. In chapter 6, the growth of a compound Bi5Ti3FeO15, which is a 1:1 mixture of BiFeO3 and Bi4Ti3O12, is presented. The growth mechanism of Bi5Ti3FeO15 thin films is presented, where the Fe precursor flow was controlled from zero to the insertion of one full BiFeO3 perovskite unit cell into the Bi4Ti3O12 structure in addition, the effect of iron precursor flow on crystalline properties is demonstrated. The methods presented in this thesis can be adopted to grow ferroelectric and multiferroic films for industrial applications.

An investigation into the effect of thickness of titanium dioxide and gold-silver nanoparticle titanium dioxide composite thin-films on photocatalytic activity and photo-induced oxygen production in a sacrificial system

Thin films of titanium dioxide and titanium dioxide with incorporated gold and silver nanoparticles were deposited onto glass microscope slides, steel and titanium foil coupons by two sol-gel dip-coating methods. The film's photocatalytic activity and ability to evolve oxygen in a sacrificial solution were assessed. It was found that photocatalytic activity increased with film thickness (from 50 to 500 nm thick samples) for the photocatalytic degradation of methylene blue in solution and resazurin redox dye in an intelligent ink dye deposited on the surface. Contrastingly, an optimum film thickness of similar to 200 nm for both composite and pure films of titanium dioxide was found for water oxidation, using persulfate (S2O82-) as a sacrificial electron acceptor. The nanoparticle composite films showed significantly higher activity in oxygen evolution studies compared with plain TiO2 films.

Light-driven oxygen scavenging by titania/polymer nanocomposite films

We demonstrate that UV illumination of nanocrystalline TiO2 films in the presence of excess organic hole scavengers can result in the deoxygenation of a closed environment. The kinetics of deoxygenation are investigated under continuous UV illumination as a function of film preparation and hole scavenger employed. Optimum deoxygenation is observed using methanol as a hole scavenger, although efficient deoxygenation is also observed for a range of different polymer/TiO2 nanocomposite films deposited on glass and plastic substrates. Transient absorption spectroscopy is used to probe the kinetics of the deoxygenation reaction, focusing on the kinetics of the reduction of oxygen by photogenerated TiO2 electrons. Under aerobic conditions, this oxygen reduction reaction is observed to exhibit first order kinetics with a rate constant of 70 s(-1), more than one order of magnitude faster than alternative reaction pathways for the photogenerated electrons. These observations are discussed in terms of the Langmuir-Hinshelwood equation for photocatalytic action. (C) 2004 Elsevier B.V. All rights reserved.

Thick titanium dioxide films for semiconductor photocatalysis

Thick paste TiO2 films are prepared and tested for photocatalytic and photoinduced superhydrophilic (PSH) activity. The films are effective photocatalysts for the destruction of stearic acid using near or far UV and all the sol-gel films tested exhibited a quantum yield for this process of typically 0.15 %. These quantum yields are significantly greater (4-8-fold) than those for titania films produced by an APCVD technique, including the commercial self-cleaning glass product Activ(TM). The films are mechanically robust and optically clear and, as photocatalysts for stearic acid removal, are photochemically stable and reproducible. The kinetics of stearic acid photomineralisation are zero order with an activation energy of ca. 2.5 Kj mol(-1). All titania films tested, including those produced by APCVD, exhibit PSH. The light-induced fall, and dark recovery, in the water droplet contact angle made with titania paste films are similar in profile shape to those described by others for thin titania films produced by a traditional sol-gel route. (C) 2003 Elsevier Science B.V. All rights reserved.

Anatase thin films on glass from the chemical vapor deposition of titanium(IV) chloride and ethyl acetate

Thin (50-500 nm) films of TiO2 may be deposited on glass substrates by the atmospheric pressure chemical vapor deposition (APCVD) reaction of TiCl4 with ethyl acetate at 400600 C. The TiO2 films are exclusively in the form of anatase, as established by Raman microscopy and glancing angle X-ray diffraction. X-ray photoelectron spectroscopy gave a 1:2 Ti:O ratio with Ti 2P(3/2) at 458.6 eV and O 1s is at 530.6 eV. The water droplet contact angle drops from 60degrees to

Antibacterial titania-based photocatalytic extruded plastic films

Photocatalytic antibacterial low density polyethylene (LDPE)–TiO2 films are produced by an extrusion method and tested for photocatalytic oxidation activity, via the degradation of methylene blue (MB) and photocatalytic antibacterial activity, via the destruction of Escherichia coli. The MB test showed that extruded LDPE films with a TiO2 loading 30 wt.% were of optimum activity with no obvious decrease in film strength, although the activity was less than that exhibited by the commercial self-cleaning glass, Activ®. UVC pre-treatment (9.4 mW cm−2) of the latter film improved its activity, with the level of surface sites available for MB adsorption increasing linearly with UVC dose. Although the MB test revealed an optimum exposure time of ca. 60 min photocatalytic oxidation activity, only 30 min was used in the photocatalytic antibacterial tests in order to combine minimal reduction in film integrity with maximum film photocatalytic activity. The photocatalytic antibacterial activity of the latter film was over 10 times that of a non-UVC treated 30 wt.% TiO2 film, which, in turn was over 100 times more active than Activ®.

Photocatalyst TiO2-Co: the effect of doping depth profile on methylene blue degradation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Highly ordered TiO2 nanotube arrays and photoelectrocatalytic oxidation of aromatic amine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of the morphology and microstructure on the photocatalytic properties of titanium oxide films obtained by sparking anodization in H3PO4

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

An improved three-dimensional model for growth of oxide films induced by laser heating

In this paper we consider a three-dimensional heat diffusion model to explain the growth of oxide films which takes place when a laser beam is shined on and heats a metallic layer deposited on a glass substrate in a normal atmospheric environment. In particular, we apply this model to the experimental results obtained for the dependence of the oxide layer thickness on the laser density power for growth of TiO2 films grown on Ti-covered glass slides. We show that there is a very good agreement between the experimental results and the theoretical predictions from our proposed three-dimensional model, improving the results obtained with the one-dimensional heat diffusion model previously reported. Our theoretical results also show the occurrence of surface cooling between consecutive laser pulses, and that the oxide track surface profile closely follows the spatial laser profile indicating that heat diffusive effects can be neglected in the growth of oxide films by laser heating. © 2001 Elsevier Science B.V.

Degradação de poluentes orgânicos utilizando filmes de TiO2 modificados com íons prata

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estrutura eletrônica e propriedades elétricas fotoinduzidas em filmes finos de SnO2 com dopagem de Sb, e formação de heteroestruturas com TiO2

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Otimização do processo de deposição de filmes TiO2:Mn usando RF magnetron sputtering

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)