Studies of LPCVD and anodised TiO2 thin films and their photoelectrocatalytic photochemical properties for destruction of organic effluents

TiO2 thin films prepared by CVD and anodisation methods and their applications for the photoelectrocatalytic and photocatalytic destruction of organic effluents are described in this thesis. The theoretical background of CVD, photoelectrocatalysis (PEC) and photocatalysis (PC) is introduced in Chapter 1. This chapter also contains an intensive literature review about TiO2 thin film preparation, mainly by CVD, and about PEC and PC destruction of organic effluents by TiO2 thin films. The experimental methods, which include CVD reactors, PEC cells and film characterisation and chemical analysis, are described in Chapter 2. The results for TiO2 films deposited by LPCVD on SnO2 coated glass using either TTIP or TTB precursors in the presence of O2, with or without water as a reagent, are discussed in Chapter 3 for a small CVD reactor and Chapter 4 for a large reactor. The effects of precursor, water and annealing on the crystal structure of the films have been investigated and compared. It was found that phase transition temperatures for changes from amorphous to anatase and anatase to rutile with TTIP were higher than those obtained with TTB. Water also had an effect by decreasing the temperature for depositing crystalline films. The other kind of TiO2 films prepared by anodisation of titanium mesh was studied and the results are presented in Chapter 5. PEC or PC destruction of MPA, RDX and 4-CP have been studied using TiO2 thin film anodes in small and large PEC reactors which are described in Chapter 6 and Chapter 7, respectively. PC destruction rates of organics are found to be improved significantly with an applied potential; i.e. by a PEC process. The effects of film properties, such as film crystallinity, thickness and film type on the PEC and PC efficiencies have been investigated. It was found that the different behaviour of films in PEC processes probably was due to surface effects rather than internal electric field differences. The extent of PEC and PC destruction of organics for CVD films was higher than for anodised films. The thesis concludes with an overall summary of the results and some suggestions for future work (Chapter 8). (author)