Hierarchical NH2-MIL-88B(Fe)-derived Fe3O4@porous carbon/g-C3N4 nanocomposite for magnetically recoverable visible light photocatalysis of azo dyes

Abstract

A hierarchical Fe3O4@porous carbon/g-C3N4 nanocomposite was synthesized from NH2-MIL-88B(Fe) through controlled pyrolysis and heterojunction assembly for visible-light photocatalytic degradation of azo dyes. Structural and optical characterization confirmed the formation of a porous heterostructure with enhanced visible-light absorption and charge separation. Under visible-light irradiation (λ > 420 nm), the composite achieved degradation efficiencies of 98.6% for methyl orange and 96.8% for Congo red within 90 min. The catalyst exhibited a saturation magnetization of 32.4 emu g⁻¹, enabling rapid magnetic separation within approximately 20 s. Radical trapping experiments indicated that •OH and •O2- were the dominant reactive species, supporting a Z-scheme charge-transfer mechanism. The nanocomposite retained 92.3% of its initial photocatalytic efficiency after five cycles, demonstrating good stability, reusability, and potential for sustainable wastewater treatment.