Existence of chloride ions in high salinity wastewater accelerates the removal of micropollutants over light-driven catalysts

Photocatalytic removal of micropollutants from highly saline water purification is challenging because of the interference and quenching of active species by chloride ions (Cl). Herein, anthraquinone-2-carboxylic acid (AQC) was anchored on aminated graphene sheets (AGR) to construct a metal-free photocatalyst (AQC/AGR) via a mild two-step method. We demonstrated efficient degradation of micropollutants on AQC/AGR, in which trimethoprim (TMP)-removal efficiency reached 97.7 % under solar irradiation for 40 min at high NaCl concentration (500 mM). A novel mechanism for the electron-transfer interaction of AQC/AGR with Cl and in situ generation of radicals from photoactivated Cl was explored through characterization measurements, radical quenching experiments and theoretical calculations. This system removed micropollutants mainly through radical processes mediated by superoxide radical (O2•), hydroxyl radical (•OH) and dichloride radical anion (Cl2•−). This work presents a novel family of catalysts for solar-energy-enabled removal of organic micropollutants to purify saline wastewater with high chloride concentration.