On the photocatalytic activity of the sulfur doped titania nano-porous films derived via micro-arc oxidation

摘要

Sulfur doped TiO2 layers containing nano/micro-sized pores were synthesized by micro-arc oxidation process. Effect of the applied voltage and the electrolyte composition on physical and chemical properties of the layers was investigated using SEM, AFM, XRD, XPS, and EDS techniques. A UV-vis spectrophotometer was also used to study optical properties of the layers. It was found that the doped layers were porous with a pore size of 40-170 nm. They consisted of anatase and rutile phases with varying fraction depending on the applied voltage and electrolyte concentration. Our XPS investigations revealed the existence of sulfur in the forms of S~(4+) and S~(6+) states which substituted Ti~(4+) in the titania lattice. The sulfur concentration in the layers also increased with the voltage and the electrolyte concentration. Furthermore, the absorption edge of the doped layers shifted significantly toward longer wavelengths as compared to the pure TiO2 layers. The band gap energy was calculated as 2.29 eV for sulfur doped TiO2 layers, respectively. Finally, photocatalytic activity of the layers was studied by measuring the degradation rate of methylene blue on their surface under UV and visible illuminations. The doped layers showed a slightly enhanced photoactivity than the pure layers under UV-irradiation, while their photocatalytic performance was much higher than that of pure layers under visible-irradiation. It was measured that about 92% and 66% of methylene blue was decomposed over doped layers under UV and visible irradiations, respectively.