Enhanced degradation of organic water pollutants by photocatalytic in-situ activation of sulfate based on Z-scheme g-C3N4/BiPO4

In recent years, the excellent performance of sulfate radical (SO4·−) in advanced oxidation process has attracted more and more attention. However, it requires the consumption of expensive persulphate (PMS/PDS), and the resulting sulfate ion (SO42−) requires subsequent processing procedures, which limits its practical application value. In this work, a Z-scheme heterojunction g-C3N4/BiPO4 (CNBx) photocatalyst was constructed to in-situ activate the residual SO42− , H2O and dissolved O2 in organic wastewater simultaneously and produce SO4·−, ·OH and O2·− efficiently, so as to realize enhanced organic pollutant treatment by using clean and renewable solar energy resources. Under the condition of 10 mM SO42− addition and 100 mW·cm−1 illumination, the degradation rate of BPA (C0 = 20 mg·L−1) by optimized CNB150 catalyst was 0.30 min−1, which was 50% higher than that without SO42− (0.20 min−1). Detailed characterizations shown that a direct Z-scheme heterojunction was formed between g-C3N4 and BiPO4, which could be simultaneously stimulated by light, and then effective charge separation and migration could be achieved through the internal electric field caused by the Fermi-level difference between the g-C3N4 (-0.12 eV) and BiPO4 (0.01 eV). In general, this study makes full use of renewable solar energy and provides a feasible path for promoting the simultaneous in-situ utilization of small molecules (SO42−, H2O and O2) that originally exist in water, which makes organic wastewater treatment more economic, eco-friendly and sustainable.