Thiosulfate enhanced degradation of organic pollutants in aqueous solution with g-C3N4 under visible light irradiation.

Developing new strategies to design more practicable and efficient g-C3N4 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-C3N4 under visible light irradiation, resulting in a fast degradation of Rhodamine B (RhB) and other pollutants. The performance of g-C3N4 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-C3N4/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-C3N4, and initial solution pH on the performance of the system were also studied. The mechanism study suggests that STS is first oxidized to S2O3- radicals by photohole, which will be transformed to other oxysulfur radicals such as SO3- and finally to SO42- ions. At the same time, the rate of O2 reduction by photoelectrons to O2- 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.

The effects of nonredox metal ions on the activation of peroxymonosulfate for organic pollutants degradation in aqueous solution with cobalt based catalysts: A new mechanism investigation.

Herein, a new peroxymonosulfate (PMS) activation system was proposed employing nonredox metal ions as Lewis acids (LA), which have been widely recognized to play important roles in many biological and chemical oxidations. With Co2+ ions as model catalysts, it was found that oxidizing power of PMS was enhanced after binding weak LA such as Ca2+ ions, leading to its easier reduction to active radicals and substantial enhancement of dye degradation. The promoting effect of Ca2+ was also observed with other cobalt catalysts including CoFe2O4 and Co3O4. The rate of PMS decomposition in Co2++LA/PMS system was correlated with Lewis acidity; while in the presence of strong LA including La3+ and Y3+, the dye degradation rate declined. The interactions of LA with PMS were characterized and the detailed mechanism was proposed. The present study provides the first example of the promoting effect of weak LA on PMS activation with cobalt based catalysts.