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.