Thesis (Ph.D.)--Chulalongkorn University, 2007

This research focuses on preparation and characterization of TiO[subscript 2], WO[subscript 3] and composite films using two techniques: electrodeposition and anodization. Optimization of SS/TiO[subscript 2], SS/WO[subscript 3] and composite films prepared by electrodeposition on the stainless steel (SS) type 304 was investigated. This study also probes the relationship between the morphology of anodic TiO[subscript 2] and WO[subscript 3] layers grown on Ti or W foil substrates and their subsequent photoelectrochemical response in 0.5 M Na[subscript 2]SO[subscript 4] supporting electrolyte. The effects of anodization variables (voltage and time) and anodization medium composition [water, glycerol, poly(ethylene glycol) (PEG), ethylene glycol (EG)] along with fluoride ion concentration on the oxide layer morphology and photoresponse are described. Well define nanotube morphology of TiO[subscript 2] was observed when the fluoride ion containing electrolyte was modified by PEG400 or EG while the nanotube morphology could not be observed on W substrate. In fabrication of composite film by pulse anodization technique, two types of composite film (W/WO[subscript 3]/TiO[subscript 2] and Ti/TiO[subscript 2]/WO[subscript 3]) were conducted. These composite films exhibit better photoelectrochemical response than the pure W/WO[subscript 3] and Ti/TiO[subscript 2], respectively. In addition, the well organized composite Ti/TiO[subscript 2]/WO[subscript 3] nanotube films were fabricated and gave the excellent photoelectrochemical performance reaching 7.7 mA cm[superscript -2]. Finally, photocatalytic reduction of hexavalent chromium and photocatalytic oxidation of methylene blue were studied under ultraviolet light using anodically growth Ti/TiO[subscript 2], W/WO[subscript 3] and composite films. Furthermore, visible light ([lambda] > 400 nm) degradation of methylene blue using W/WO[subscript 3] films was studied. The photocatalytic degradation rate follow Langmuir–Hinshelwood model yields k = 0.687 [mu]M min[superscript -1] and K = 0.021 [mu]M[superscript -1].