공침법으로 제조된 TiO₂/WO₃복합산화물의 미세구조 천이와 광전기화학 특성
Phase transition and photoelectrochemical characteristics of mixture of TiO2/WO3 oxides prepared by coprecipitation method
v, 57 p.
TiO₂ WO₃ 공침법;
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Mixture of TiO2/WO3 oxides were processed by coprecipitation and calcination using TiCl4 and WCl6 as starting materials. Phase transition of the oxides with varying tungsten addition was studied as well as the microstructures and variation of bandgap energy of TiO2/WO3 powders. The mixture of as-precipitated Ti(OH)4 and WO(OH)6 particles were calcined a 800℃ for 4 hours under air atmosphere. For the pure TiO2 particles calcination in air at 800℃ resulted in the formation of stable rutile phase. However, as W doping into TiO2 increases, phase transition of the anatase TiO2 into rutile phase is retarded by calcinations at 800℃ with the presence of both anatase and rutile phases. Increasing W addition resulted in formation of WO3 presented up to 30 wt.% of W addition for a given calcination temperature of 800℃. It indicates that tungsten is not doped at all completely into TiO2. The band gaps of TiO2/WO3 powders, as measured using UV-vis measurements of TiO2/WO3, decrease as the content of tungsten is increasing. Lattice parameters of TiO2/WO3 powders were measured in very precise manner by X-ray diffraction. It reveals a consistent result that the lattice parameter does not either decrease nor increase as the tungsten addition increases. The ionic radii of Ti4+ is 6.05 nm, whereas the ionic radii of W6+ is 6.20 nm with the charge of +6. It is quite difficult for Ti to be substituted by W due to large ionic radius and charge difference. Thus, regardless of the tungsten contents, the formation of Ti1-xWxO2 is not expected. However, due to the difference of band gap height(CV and VB), electron and hole charge can be separated between the two particles, which will decrease the charge life time resulting in increased electrical resistivity.