An efficient and Durable α-Al₂O₃@ g-C₃N₄ system for high-performance Cr(VI) photoreduction

The removal of hexavalent chromium Cr(VI)) from wastewater through photocatalysis remains a critical environmental challenge, necessitating the development of efficient and stable photocatalysts. In this study, hierarchical α-Al₂O₃@CNS (Al₂O₃@g-C₃N₄) composites with abundant heterojunctions were synthesized through a simple one-step thermal condensation process, leading to the formation of thin g-C₃N₄ nanosheets spatially distributed around submicron α-Al₂O₃ particles. The optimized 15Al₂O₃@CNS heterostructure achieved over 96 % Cr(VI) reduction within 120 min, outperforming pure α-Al₂O₃, bulk g-C₃N₄, 15TiO₂@CNS, and 15In₂O₃@CNS, as well as many previously reported g-C₃N₄-based heterojunction systems. Kinetic studies confirmed that Cr(VI) reduction followed a pseudo-first-order reaction, with the 15Al₂O₃@CNS composite exhibiting a rate constant of 0.02996 min^-1, which is about 8.7 times higher than bulk g-C₃N₄ (0.00344 min^-1) and more than 20 times higher than α-Al₂O₃ (0.00148 min^-1). The superior activity is attributed to enhanced interfacial contact, increased surface area, and efficient electron trapping by α-Al₂O₃, which together promote effective charge separation and suppress recombination. This work highlights the potential of α-Al₂O₃ as an excellent support in heterojunction photocatalysts, offering a new strategy for designing highly efficient materials for environmental remediation.