| Titanium dioxide (TiO2) as a well-known wide band gap semiconductor, has a lot of applications such as solar energy conversion, photoluminescence, photocatalytic and nano-electronics because of its unique optical, electrical, magnetic, catalytic and chemical properties. The synthesis, characterization and modification of nano-TiO2 has become core contents in semiconductor photoelectrochemical and photocatalytic for TiO2 material application, the functionalization of TiO2 nano-materials has alwaysly been a focus research area in basic research. Preparation mechanism investigation of nano-TiO2 materials was carried out to optimize the dimensions, size, morphology and composition of nano-TiO2 materials, which has important significance to obtain functional oriented nano-TiO2 materials. Based on that state, we prepared nano-TiO2 materials with different morphologies and functions by different methods such as sol-gel, hydrothermal, anodic oxidation and template methods. Different morphologies of nano-Ti02 materials such as nano-particle, nano-tube, nano-fiber and ordered porous film were studied for the functional modification of nano-TiO2 materials. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-Vis spectroscopy were employed to characterize the structures and properties of nano-TiO2 materials. Photocatalytic activity of nano-TiO2 materials was evaluated using self-made photocatalysis reaction system. Optoelectronic property of nano-TiO2 materials was investigated under simulated solar illumination (Newport 1.5AM) by using TiO2 film an electrode in dye-sensitized solar cells (DSSC) with a sandwich structure.A series of doping TiO2 nano-particles, nano-fibers and nano-tubes were prepared with above methods. The controllability in preparation and the performance of the functional doping nano-TiO2 materials were also investigated. Experiment results showed that:(1) The RE-doped nano-TiO2 materials were prepared by sol-gel method using tetrabutyl titanate and rare-earth salts as precursors. Photocatalytic ability of nano-TiO2 materials doped with RE (Pr, La, Gd, Ho, Nd) has improved significantly. And its photocatalysis activity was closely related to different kind of RE, its adding amount and the doping approach. Among all the RE employed, Gd doped specimen compound possessed the highest photocatalysis activity. (2) The Gd3+and B3+co-doping TiO2 nanotubes prepared by hydrothermal method, where the caliber is approximately 5nm and the wall thickness is 1nm. The micro-morphology, crystalline structure and photo-absorption of the as-produced samples were also characterized. Various influence factors on preparation process were also discussed. (3) A two-step synthesis method was also used. First, Potassium tetratitanate (K2Ti4O9) nano-fibers doped with gadolinium were prepared by mixing P25 and K2CO3 with Gd(NO)3 solution through the kneading-drying-calcination method (KDC). Then, using K2Ti4O9 fibers as the precursor, the doping nano-TiO2 fiber consist of primary anatase crystallites were synthesized after dispersed in glycerine and heat treated under reflux. The average length of the formed TiO2 nano-fiber was tens of microns and the average diameter was approximately 50nm. The results showed that the TiO2 nano-fiber doped Gd3+exhibits high photocatalysis activity, the degrading rate of methyl orange could be above 70% under natural light. (4) Gd/N co-doped nano-TiO2 photocatalyst was synthesized by sol-gel method. The photocatalytic activity was evaluated by the photodegradation of methyl orange in an aqueous solution under natural light irradiation.The results indicated that Gd/N co-doped simple was anatase, had synergistic effect and increased absorption in visible range, its average particle diameter was about 13nm; Several different doping method were carried in preparation of Gd/N co-doped TiO2 samples and their photocatalytic activity was compared, the sample with urea as nitrogen source had higher photocatalytic activity than other's, the degradation rate for methyl orange was 92%.Ordered nano-tube arrays with regular structure were prepared by the electrochemical anode oxidation method with control of certain reaction conditions. Zn (NO3)2 was added during the oxidation process to load a certain amount of Zn in the nano-tube. The influence of the oxidation voltage, temperature, time, pH value, electrolyte concentration, and content of Zn, as well as the photoelectric effect, on the structure and morphologies of the TiO2 nanotubes were investigated as well. The current-time curves scanned by an electrochemical workstation were adopted to quantitatively monitor the growth process of TiO2 nano-tube arrays and investigate their growth mechanism. Scanning electron microscopy (SEM) and x-ray diffraction spectroscopy (XRD) were applied to characterise their morphology and crystalline structures. The photo-electrochemical properties were studied by electrochemical impedance spectrum (EIS). The optimum working conditions for TiO2 nano-tube arrays were found to be pH 1,0.5wt%HF concentration, and 20 V anodized oxidation for 2 h. The produced sample was in anatase form, with a length of around 70～100 nm, a thickness of 10 nm, uniform diameter, and structure that does not collapse at the preparation conditions. The EIS results showed that TiO2 nano-tube arrays prepared with 0.5wt%HF concentration presented low resistance and the TiO2 nano-tube arrays loaded by Zn could decrease the resistance. This decrease could likely accelerate the transfer of carriers and even increase photoelectric conversion.Ordered porous TiO2 film doped with Gd3+and La3+were prepared by PS template. The influence of concentration of styrene, initiator (K2S2O8), surfactant (SDBS) to the particle size PS beads and the void structure of the template was studied. Based on the template, an ordered porous TiO2 film doped with Gd3+and La3+was deposited on a conductive glass. The results shown that rare earth dopant, the lattice of PS template and the TiO2 precursor exhibit influences on the performance of ordered porous TiO2 film. The photoelectric properties of TiO2 film were characterized by electrochemical analysis system to investigate the mechanism of dopant and TiO2. The as-produced film was used as an electrode in dye-sensitized solar cells (DSSC) with a sandwich structure. Under simulated solar illumination, a short circuit current of 0.618 mA and an open circuit voltage of 0.538 V were attained by the ordered porous TiO2 electrode doped with 0.5% Gd3+, which were better than the performances of TiO2 film electrode and ordered porous TiO2 film electrode. As the synergistic effect of Gd3+and La3+, the photoelectric properties of ordered porous TiO2 electrode co-doped with 0.5%Gd3+and 0.3%La3+is the best, which attained a short circuit current of 0.696 mA and an open circuit voltage of 0.539 V.Gd3+/Eu3+-codoped TiO2-multi walled carbon nano-tubes (Gd3+/Eu3+-codoped MWCNTs/TiO2) multiplex photocatalysts were successfully synthesized with sol-gel method and hydrothermal method respectively. SEM, TEM and FL (photoluminescence) spectra were applied to characterise their morphology and properties. Methyl orange was employed as a modal pollutant to investigate the photocatalytic activity of the obtained photocatalysts. The experiment results shown that nano-TiO2 particles distribute evenly along MWCNT in samples prepared with the hydrothermal method. Meanwhile, their photocatalysis activity is higher than that prepared with the sol-gel method. Co-doping proper proportioning Gd3+/Eu3+can increase the photocatalysis activity of multiplex photocatalyst, and the optimal dopant contents for Gd3+, Eu3+are 0.1 wt%and 1.0wt%respectively.The above mentioned results were possible to promote the photoelectric properties of TiO2 nano-materials and even make breakthrough in this filed. Studies on the preparation technology and functional modification, investigate the effect mechanism between doped ions and TiO2 matrix, which were hopeful to provide new ideas and ideal research systems for the exploration of the photoelectric properties and electron transmission between nano-materials matrix and the interface. Meanwhile, the results were hopeful to provide theoretical basis and technical support for the development of TiO2 dye-sensitized solar cells (DSSC) and the application of TiO2 nano-materials in photocatalysis filed.
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