Various Sensitizations Of TiO₂Nanomaterials And Their Applications

Titanium dioxide (TiO2) is the most intensively investigated binary transitionmetal oxide due to its excellent corrosion resistance, environment-friendly,bio-compatibility, photo-catalytic activity as well as its great accessibility andmoderate cost. Numerous and diverse applications based on TiO2nanomaterials havealso been developed, such as photovoltaic cell/photoelectrochemical cell,photo-catalytic degradation of pollutants, bio-sensing and drug delivery, and so on.Many of these applications depend not only on the properties of the TiO2nanomaterialsitself but also on the modification of the TiO2nanomaterials host and on the interactionof TiO2nanomaterials with the environment due to its large band gap and limitedproperties. So, various modification strategies playing an important role in improvingperformance and expanding application fields of TiO2based devices have hugepractical and theory significance. Besides, it is very important to control the shape andstructure of various nanomaterials. Because the nanomaterial performances greatlydepend on the shape and structure except for the properties of itself. Meanwhile,different research fields always need different shape and structure. In this thesis, westudy the applications of TiO2nanomaterials mainly in spectral analysis/purifyingcontaminated water and energy exploitation with the help of composition design, shapecontrol and structure optimization of the TiO2nanomaterials and sensitizes. The detailsare summarized as follows:(1) Preparation of TiO2nanomaterials: Preparation of equally distributed andorderly one dimension TiO2nanotube and nanowire arrays in titanium foil by anodicoxidation and hydrothermal methods, respectively (in chapter2). Preparation ofvarious nanostructures, including nano-leaves, nano-flowers, nano-wires/nano-leaves,nano-wires/nano-flowers, nano-leaves/nano-flowers through change hydrothermalmethod parameters. Study the formation mechanism of various TiO2nanostructuresprepared by hydrothermal method (in chapter3).(2) Modification of TiO2nanotube arrays with metal nanoparticles: Throughphotocatalytically deposition of Au nanoparticles inside TiO2nanotube arrays, a threedimensions electromagnetic field is generated in the nanotubular structure of theAu-nanoparticles/TiO2nanotube arrays. Raman enhancement occurs when targetmolecules are spatially confined within the zone of the nanotubular structure. Polycyclic aromatic hydrocarbons are well detected using surface enhanced Ramanscattering signals in such substrate(in chapter4).(3) Modification of TiO2nanotube arrays with metal and metal oxidenanoparticles: Direct fabrication of vertically aligned one-dimensional singlecrystalline CuO nanowires on TiO2nanotube arrays using thermal oxidation andelectrodeposition methods. Present CuO nanowires growth model is confirmed: Bothstress-driven grain-boundary diffusion mechanism and stress accumulation andrelaxation mechanism are proposed to account for CuO nanowires growth.Nano-mushrooms and nanosheets can be easily obtained by varying growth conditions.Mass transport channel of Cu ions in horizontal and vertical is confirmed, which isproposed to adjust nanowires diameter and length. Ag nanocrystals are successfullymodified upon CuO nanowires and TiO2nanotube arrays using photocatalyticallydeposition strategy, the photoelectrode exhibits superior properties in monitoring andremoving environmental contaminants, a recycling has been achieved (in chapter5).(4) Modification of TiO2nanotube arrays with II-VI semiconductor nanocrystals:Coupled the hydrothermal method with successive ionic layer adsorption and reactionprocess to assemble type-II core/shell CdTe/CdS quantum dots onto TiO2nanotubearrays using a bi-functional linker molecule. Spatial separation of the electron and holewave functions within the core/shell heterostructured nanocrystals appears to result inan extended charge separation state, resulting in a significant increase in photocurrentof composite photoelectrodes. Upon coating CdS shell onto CdTe core, CdTephotocorrosion is greatly suppressed, and device stability increase. Photoelectrodesdisplay a remarkable hydrogen evolution rate (in chapter6).(5) Modification of TiO2nanotube arrays with I-III-VI2semiconductornanocrystals: Different from lead or cadmium-based II-VI and IV-VI semiconductornanocrystals, I-III-VI2semiconductor nanocrystals are potential candidates due to itshigh photoresponse ability (visible and near infrared region) and environmentallybenign feature, for example CuInSe2. However, limited by complex growth process ofternary nanocrystals and synthesis route, it is very difficult to prepare shape andsize-controllable CuInSe2nanocrystals. By careful control technical parameters duringsynthesis, solid and hollow spherical CuInSe2nanocrystals and quantum dots can beeasily obtained with tunable size. Study the mechanisms of small nanocrystalsformation and morphology evolution from solid to hollow. Using monodisperse solidand hollow spherical CuInSe2nanocrystals modifying TiO2nanotube arrays confirm astructure-dependent photocatalytic property (in chapter7). Hollow chalcopyrite CuInSe2nanocrystals are then assembled inside TiO2nanotube arrays as highperformance photocatalyst for hydrogen evolution. In order to improve chargesseparation and transport, we engineer the CuInSe2-based photoelectrode with a novelstrategy: a quasi-quantum well structure. Cyclic voltammetry and electrochemicalimpedance analysis are used to study charges transport path andtransport/recombination resistance. Open-circuit dark-light-dark photovoltage responseand photoluminescence spectroscopy support above results (in chapter8)..