Preparation of S-TiO2 photocatalyst and photodegradation of L-acid under visible light

S-doped TiO2 (S-TiO2) photocatalyst was synthesized by sol–gel method with tetrabutyl titanate and thiourea as precursor. S-TiO2 was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis absorption spectroscopy, transmission electron microscopy (TEM) and the photocatalytic activity was evaluated by 1-naphthol-5-sulfonic acid (L-acid) under UV, visible light and solar light radiation. The results showed that doped S could improve photoabsorption property of TiO2 in the visible region, leading the increase in the photocatalytical activity of TiO2. The average particle size of the S-TiO2 photocatalyst is about 10 nm. The S-TiO2-4 photocatalyst contains 100% anatase crystalline phase of TiO2. In the S-TiO2-4 photocatalyst, S does not exist independently, but is incorporated into the crystal lattice of TiO2. In the inner crystal lattice of the S-TiO2-4 photocatalyst, S as S2− replaces O in TiO2, while on the surface of crystal lattice, S exists as S4+ and S6+. The photocatalytical activity of S-TiO2-4 photocatalyst for the photodegradation of L-acid is better than that of pure TiO2. Under the same conditions, the photodegradation efficiency of L-acid for the S-TiO2-4 photocatalyst and the solar light irradiation is 85.1%, while it is only 26.4% for pure TiO2. In addition, the final products of the photocatalysis of L-acid using the S-TiO2-4 photocatalyst are not organic compounds with low molecular weight, but the inorganic compounds.