Insight into the mechanisms for hexavalent chromium reduction and sulfisoxazole degradation catalyzed by graphitic carbon nitride: The Yin and Yang in the photo-assisted processes

Abstract As robust polymeric catalysts, graphitic carbon nitride (g-C 3 N 4 ) has been known to have great application potential in environmental remediation. However, the mechanisms in the photo-assisted catalytic processes during the reduction or oxidation of pollutants are still difficult to discern and therefore not well studied. In this work, visible-assisted catalytic reduction of hexavalent chromium (Cr(VI)) or oxidation of sulfisoxazole (SIZ) by g-C 3 N 4 with the addition of formic acid (FA) or potassium peroxydisulfate (PS) were systematically investigated. Effects of operation parameters such as g-C 3 N 4 dosage, FA concentration, Cr(VI) concentration, solution pH, PS concentration were studied. The results showed g-C 3 N 4 can be effective and robust catalyst for both the reduction ( Yin ) and oxidation ( Yang ) reactions in the environmental remediation. Mechanisms were studied by using electron spin resonance (ESR) spectroscopy. The results revealed the CO 2 – is the predominant radical for Cr(VI) reduction in the g-C 3 N 4 /FA/Vis system and the SO 4 – and OH are all the main radicals for the oxidation of SIZ in the g-C 3 N 4 /PS/Vis system. The photo-generated carriers by g-C 3 N 4 , act as radical initiator, were responsible for the production of the reactive radical species in aqueous solution. This work not only shed a new light on the application of semiconductor polymers for the removal of micropollutants and also will expand the applicability of the polymeric photocatalysts for environmental remediation.