Photodegradation of methyl orange from wastewater on TiO2/SnS combined powders

The photodegradation of an aqueous solution of methyl orange by the TiO2/SnS powders was studied in different ratios of SnS against TiO2. The effects of the initial pH value and light resource were investigated. The SnS extends the light absorption edge of the TiO2 to ~940 nm of the SnS (1.32 eV). The results indicated that the optimal SnS proportion for the maximum degradation efficiency increased in relation to a decrease in the initial pH in both sunlight and visible light, and decreased when changing from visible light to sunlight. The pure TiO2 powder had maximum efficiency in conditions of pH 9 and visible light irradiation or in conditions of pH 7 and sunlight irradiation. In visible light, the degradation efficiency on the powders containing the SnS was larger than that on the pure TiO2 powder in a range of pH 3–7. The maximum efficiency in visible light was found to be in conditions of pH 5 and TiO2:SnS = 3:2 and 2:3, beyond which the efficiency decreased. The efficiency was, overall, larger in sunlight than in visible light. The mechanism of the effects of pH and light resource was discussed in view of the surface charge of the catalysts.