Revealing the mechanism of structure-electron effect in mechanochemistry-driven CuS-coupled layered g-C3N4 Schottky-junction for enhanced demercuration

Abstract

The development of cost-effective heterojunctions with heightened affinity for mercury (Hg0) presents a promising approach for mercury abatement from stationary source emissions. In this study, one novel hierarchical porous Schottky heterojunction composed of CuS-coupled layered g-C3N4 (CuS-CN) was synthesised via a mechanochemistry-driven acetate route. The prepared CuS-CN heterojunction exhibited a considerable Hg0 accommodation capacity of 33.04 mg/g at 70 °C and a breakthrough threshold of 60%, which was 40% higher than that of CuS-CN(mix) prepared by simply mixing CuS and CN without forming a heterojunction interface. Additionally, the CuS-CN heterojunction demonstrated satisfactory applicability against various simulated stationary source exhausts. Furthermore, the reason for the unparalleled and enhanced demercuration performance of the CuS-CN heterojunction was systematically deduced via experimental studies and first-principles calculations. Under-coordinated disulfides (S22−) on the CuS-CN surface served as the primary active centre for the oxidation of Hg0 to Hg2+ and simultaneous bonding site for Hg2+ to form HgS. The well-developed electron transport network and narrow bandgap energy of the CuS-CN heterojunction enhanced charge separation and transfer from Hg0 and CN to CuS, accelerating Hg0 oxidation reaction, which resulted in an enhanced adsorption energy of −344.52 kJ/mol. Additionally, the CuS-CN heterojunction exhibited stronger Hg0 oxidation and weaker HgS adsorption properties, attributed to the lower bond strength of HgS on the CuS-CN surface and lower energy barrier for HgS desorption. Thus, this study highlighted the effectiveness of the CuS-CN heterojunction in Hg0 abatement and presented a promising strategy for the mechanochemical synthesis of mercury removal agents for large-scale industrial applications.