Biotemplated-processes To Au/TiO₂ Nanostructured Films And Their Photoelectrochemical Activities

TiO₂ based composite film, one of the most promising photoelectric catalysts,has broad application prospects in photo-splitting water hydrogen production, degradation of pollutants, sensitized solar cells and other fields. By constructing heterojunctions with precious metals or other semiconductors, TiO₂ can remarkably improve the photoelectric catalysis performance. It is of great significance in basic research and practical application. In this dissertation, a dialysis method is used to prepare TiO₂ nanoparticles, Au and CdS nanoparticles are prepared through a biotemplate synthetic process. With these nanoparticles as nanobuilding blocks, Au/TiO₂, CdS/TiO₂, and Au/CdS/TiO₂ nanocomposite films are successfully prepared. The structures and photoelectrochemical properties are thoroughly investigated by using the following techniques including transmission electron microscope（TEM）, scanning electron microscope（SEM）, X-ray powder diffraction（XRD）, ultraviolet visible diffuse reflection（UV-vis DRS）, Zeta potentiometer, Fourier Transform Infrared Spectrometer（FTIR） and the photoelectrochemical measurements, and so on. And the main research results obtained are list as follows:（1） A dialysis process is applied to prepare a TiO₂ sol solution with great high purity. The TiO₂ sol is used as precursor to prepare TiO₂ nanoparticles through a sol-gel process. By using the doctor blade method, TiO₂ films are prepared with FTO as the conducting substrate. The photoelectrochemical measurements prove that the dialysis process can remarkably improve the the photoactivity of the TiO₂ films. The photoactivity enhancement is attributed to dialysis induced improvements of the purity and interparticle connections of the TiO₂ nanoparticles.（2） By using flagella as biotemplates, a highly stable Au nanoparticle dispersion is prepared. The flagella stabilized Au nanoparticle and dialyzed TiO₂ sol are further used to prepare Au/TiO₂ composite films which show high photoactivity. Herein, the mechanism of flagella stabilizing Au nanoparticles are mainly investigated, finding that flagel a act as both the nucleation sites and growth control agents of the CdS nanoparticles.（3） In the third part, much more complex nanostructure systems, that is, CdS/TiO₂ and Au/CdS/TiO₂ composite films are prepared through a similar flagel a-template synthetic process. The visible light photoactivities of the CdS/TiO₂ and Au/CdS/TiO₂ composite films are improved significantly. Flagella can effectively reduce the particle size and aggregation of CdS nanocrystals. Moreover, a remarkable quantum size effect of the CdS nanocrystals is detected. The above factors lead to the photoactivity enhancement of the nanocompsite films.Our results in this thesis can be good references to further researches for the preparation of advanced photoactive nanostructured semiconductor films which have promising application potentials in photovoltage devices, water splitting hydrogen production, photocatalytic degradation of pollutants.