g-C3N4/rectorite as a highly efficient catalyst for peroxymonosulfate activation to remove organic contaminants in water

In recent years, modification of graphite carbon nitride (g-C3N4) has drawn considerable attention because of its catalytic potential. In this study, rectorite was designed as a carrier for g-C3N4, and g-C3N4/rectorite was synthesized via pyrolysis under nitrogen protection. The efficiency of g-C3N4/rectorite for peroxymonosulfate (PMS) activation was evaluated using acid Orange 7 dye (AO7) as a model organic contaminant. Material characterization suggested the successful synthesis of g-C3N4/rectorite. The removal of AO7 was significantly enhanced by the composite, compared to pure g-C3N4, rectorite, or their physical mixture. The g-C3N4 content in the composite affected its catalytic ability, while the g-C3N4/rectorite with 41% g-C3N4 content showed the highest catalytic efficiency. Furthermore, the removal of AO7 was affected by catalyst concentration, oxidant concentration, and solution pH. Notably, under the optimized condition (i.e., 0.8 g/L of g-C3N4/rectorite, 0.20 mg/L of PMS, and 6.0 of pH), an initial concentration of 50 mg/L AO7 was removed to a level below the detection limit (i.e., 0.25 mg/L) within 8 min. A recycling test demonstrated the reusability of the g-C3N4/rectorite in six repeated reactions. Singlet oxygen played a key role in PMS activation, suggesting that the non-radical degraded process is the dominated AO7 removal pathway. The rectorite has a confined effect preventing g-C3N4 from agglomeration, inhibiting the electron-hole recombination, and improve the exposure of active sites such as CO groups, -OH groups, and pyridinic N. Overall, g-C3N4/rectorite is a low-cost and environment-friendly catalyst exhibiting high catalytic activity for PMS activation to remove organic contaminants in water.