Engineered tourmaline/g-C3N4 composites for photocatalytic Fenton-like oxidation: Synergy of spontaneous interface polarization and surface iron circulations induced by minerals

The peroxymonosulfate/peroxydisulfate (PMS/PDS) activation induced by photocatalytic reduction reaction is an economical and green means for oxidative degradation of organic pollutants in water. However, its efficiency is largely limited by the rapid recombination of photogenerated electron-holes. Herein, we report a graphitic carbon nitride (g-C3N4)-based photocatalytic persulfate activation system fine-tuned by a natural polarized Fe-containing mineral, tourmaline. The tourmaline/g-C3N4 composite photocatalyst was prepared to activate PMS for efficient carbamazepine (CBZ) degradation. In this system, the electrons and holes were produced by tourmaline/g-C3N4 composites under light excitation. Subsequently, PMS was activated by photogenerated electrons from g-C3N4 and Fe2+ on the surface of tourmaline to generate SO4•−, where partial SO4•− further reacted with H2O/OH– to produce •OH. Finally, the CBZ was oxidized by SO4•−, •OH and photo-induced holes. Under optimal conditions, with the presence of PMS, the degradation rate of CBZ conducted by tourmaline/g-C3N4 is 6.2 and 7.7 times of pristine g-C3N4 and tourmaline. It is revealed that the polarization electric field of tourmaline not only boosted the separation and migration of electron-hole of g-C3N4, but also optimized the electronic structure of g-C3N4 for intensified light absorption and improved reduction ability. Moreover, the Fe2+/Fe3+ cycle of tourmaline also facilitated the utilization of photogenerated electrons from g-C3N4 for PMS activation reactions. This study has innovatively constructed a photocatalytic PMS activation system enhanced by introducing natural Fe-containing polarized minerals, providing a new strategy for sustainable and low-cost advanced oxidation processes for water treatment.