Photocatalytic degradation of organic pollutants in wastewater with g-C3N4/sulfite system under visible light irradiation.

To develop low cost and high efficient sulfate radical (SO4-) based advanced oxidation processes (AOPs) for rapid remediation of contaminated waters is of great interest. In this study, a green and novel SO4- based AOPs, in situ visible light activation of sulfite by graphitic carbon nitride (g-C3N4), for the degradation of organic pollutants is reported. The g-C3N4+HSO3- + Vis system could achieve remarkably enhanced degradation of organic pollutants such as organic dyes and phenol in aqueous solution. The excellent reusability of the metal free catalyst was also observed during ten successive cycles. The efficiency of the system was dependent on the reaction conditions, which first increased and then decreased with the increase of HSO3- concentration and initial solution pH. The addition of HCO3- stimulated the pollutant degradation, but other water matrix components such as Cl- and humic acid showed nearly no influence on the reaction. The mechanism investigations suggested that sulfite is oxidized in the system to sulfite radicals, which then react with dioxygen and superoxide radicals to form SO5- radicals and HSO5- respectively. SO5- radicals can be also reduced by sulfite or photoelectron to HSO5-. SO4- radicals were then produced from HSO5- reduction by photoelectron, and contributed to dye degradation in the system together with superoxide radicals. This study provides a novel new approach for efficient degradation of organic degradation via sulfite activation.