Modification Of Titanium Dioxide And Its Photoelectrochemical Properties

TiO₂ semiconductor nanomaterials are considered as promising candidates in the fields of solar cells, water photosplitting, and photodegradation of pollutants, etc. However, the two main problems of TiO₂, i.e., the wide band gap and the high recombination rate, considerably limit the photoelectrochemical conversion efficiency of TiO₂, and hinder their practical applications.In this thesis, to solve the above problems, the chemical modification methods such as combining TiO₂ with noble metal and carbon materials are adopted. TEM, XRD, IR and UV-Vis measurements are used to analyze the morphological, structural and spectroscopic properties of the chemically modified TiO₂. Moreover, the mechanism of photoelectrochemical reactions is explored by the photoelectrochemical measurements, electrochemical impedance spectra and Mott-Schottky measurements. These attempts will contribute to the investigation of TiO₂ and its applications in solar cells and photodegradation.This thesis contains three parts:1. Tuning Photoelectrochemical Performances of Ag-TiO₂ Nanocomposites via Reduction/Oxidation of Ag.The role of chemical states of Ag in the photoelectrochemical properties of Ag-TiO₂ remains controversial in research. Ag (0)-TiO₂ and Ag(I)-TiO₂ were prepared via photoreduction-thermal treatment method, respectively. Spectroscopic, elemental and electrochemical measurements were adopted to investigate and compare the photoelectrochemcial properties of the two composites. It was found that silver contributed to the enhancement in photocurrent due to the surface plasmon resonance effect; while the silver ions could serve as the electron acceptors and suppress the charge recombination, which benefited the promotion in photocatalysis. This work could provide possibility to achieve better photoelectrochemical performances of Ag-TiO₂ by tuning the chemical states of Ag species for promising photoelectrochemical applications in solar energy conversion and photocatalysis.2. P25-Graphene Composite as a High Performance Photocatalyst. The TiO₂ (P25)-graphene composite was prepared via one step hydrothermal reaction. Due to the excellent photocatalytic properties of TiO₂ and unique properties of graphene, such as the high specific surface area and ultrahigh conductivity, the obtained P25-graphene possessed the advantages of great adsorptivity of dyes, extended light absorption, and efficient charge separation. Hence, the composite showed great potential in various photoelectrochemical applications.3. Energy-Efficient Photodegradation of Azo Dyes with TiO₂ Nanoparticles Based on Photoisomerization and Alternate UV-visible LightTo reduce the energy cost in conventional UV photocatalysis of azo dyes with TiO₂. A UV-visible light alternate photocatalysis strategy was put forward, which availed of the photoisomerization property of azo dyes. The trans state of azo dyes, compared to the cis state, benefited the charge transfer and separation on the surface of catalyst due to both conductance and spatial effects, and thus the promotion of the photocatalysis. Therefore, UVLAP showed a 40% increase in the photocatalytical rate than conventional mode, when the energy cost was taken account. This work is anticipated to open new possibilities in reducing the energy cost and promoting photodegradation of azo dyes and other pollutants with isomerization properties.