Thiosulfate enhanced degradation of organic pollutants in aqueous solution with g-CN under visible light irradiation.

Developing new strategies to design more practicable and efficient g-CN based photocatalysts is important to solve the environmental issues. Thiosulfate (STS) is a common residual product found in wastewater and removal of STS remains a matter of great environmental concern. In this work, however, STS is activated by g-CN under visible light irradiation, resulting in a fast degradation of Rhodamine B (RhB) and other pollutants. The performance of g-CN prepared from urea was much higher than that from melamine, due to the higher surface area and more negative conduction band potential of the former catalyst. In addition, comparison with other oxidants and reductants such as peroxymonosulfate, peroxydisulfate, hydrogen peroxide and sulfite, the use of STS in g-CN/Vis system showed the highest efficiency for RhB degradation. During ten successive cycles, the excellent reusability of the catalyst was also obtained. The effect of different concentrations of STS and g-CN, and initial solution pH on the performance of the system were also studied. The mechanism study suggests that STS is first oxidized to SO radicals by photohole, which will be transformed to other oxysulfur radicals such as SO and finally to SO ions. At the same time, the rate of O reduction by photoelectrons to O radicals as well as RhB degradation increases. The finding of this study provides a promising advanced oxidation process for organic pollutants degradation via STS activation.