Superior photo-Fenton activity toward tetracycline degradation by 2D α-Fe2O3 anchored on 2D g-C3N4: S-scheme heterojunction mechanism and accelerated Fe3+/Fe2+ cycle

Photo-Fenton advanced oxidation process has received intense attention since it can exert the synergistic effect of photocatalysis and Fenton reaction. Herein, 2D/2D α-Fe2O3/g-C3N4 S-scheme heterojunctions were successfully fabricated and applied in photo-Fenton degrading tetracycline hydrochloride (TC). The crystalline phases, morphologies, microstructures, textural structures and optical properties of as-prepared heterojunctions were thoroughly characterized. By comparison and optimizing, the 5.26 wt% 2D/2D α-Fe2O3/g-C3N4 heterojunction exhibited the best photo-Fenton catalytic activity for TC degradation. The outstanding photo-Fenton catalytic performance could be ascribed to the efficient separation and utilization of photogenerated charges by an S-scheme transfer route, as well as accelerating the cycle of Fe3+/Fe2+. The active species trapping tests, photoluminescence (PL) spectra, electron spin resonance (ESR) measurements and density functional theory (DFT) calculations were implemented, which not only evidenced that the hydroxyl radicals (·OH), superoxide radicals (·O2-) and holes (h+) were all involved in the photo-Fenton reaction, but also further corroborated the S-scheme charge transfer mechanism. Additionally, the possible degradation pathways of TC were reasonably proposed by the high-performance liquid chromatography mass spectrometry (LC-MS) analytic results. This current work provided an insight into the construction of 2D/2D S-scheme heterojunction photo-Fenton catalysts for environment remediation.