Highly efficient activation of sulfite by p-type S-doped g-C3N4 under visible light for emerging contaminants degradation

Abstract

The photocatalytic activation of sulfite is a one-electron oxidation process of SO32− or HSO3−, and therefore the property of photo-generated holes is essential in determining the activation performance. The n-type g-C3N4 (pCN) was successfully converted to p-type by substituting N2C positions by S (SCN), which not only increased the hole density but also positively shifted the valence band (VB). Whereafter, the SCNs were for the first time applied in sulfite activation under visible light irradiation to degrade diclofenac (DCF). The 1:1SCN showed the highest VB potential of 2.45 V, which exhibited the best performance in activating S(IV). Moreover, the 1:1SCN also demonstrated improved photoelectric properties and enhanced adaptability to complex water qualities (pH, different emerging contaminants, high pollutant concentration and water matrices). The density functional theory (DFT) calculations implied that the doping of S improved the sulfite adsorption capability of 1:1SCN, favorably producing SO3•− as the primary active species. Diverse reactive oxidation species including h+, •OH, SO3•− and SO5•− were present, and h+ and SO5•− were identified as the dominant contributors to DCF degradation. Based on DFT calculations and LC/MS analysis, four pathways were proposed for DCF degradation. This work provides new insights into the sulfite activation technologies and a promising alternative for efficient degradation of emerging contaminants in water.