Mixed-linker Ni-MOF/ZIF-8 heterojunctions with hierarchical porosity for broadband dye degradation

The excessive use of azo dyes in industrial processes has caused severe environmental pollution due to their high stability in aquatic systems. Herein, a mixed-linker-modified Ni-MOF/ZIF-8 heterojunction was synthesized via a facile room-temperature strategy as an efficient photocatalyst for dye degradation. The Ni-MOF core, modified with mixed ligands, was encapsulated by a ZIF-8 shell to enhance interfacial charge transfer and structural stability. Diffuse reflectance spectroscopy revealed enhanced light absorption extending into the visible region arising from ligand-to-metal charge transfer and d–d transitions, leading to improved charge separation efficiency. The optimized Ni-MOF(7.5)/ZIF-8 composite exhibited outstanding photocatalytic performance, achieving degradation efficiencies of 93.85% for methylene blue and 69.42% for methyl orange within 180 min. The superior activity is attributed to synergistic effects of hierarchical porosity, enlarged surface area, and enhanced light-harvesting capability. Additionally, the photocatalyst demonstrated excellent recyclability, maintaining 87.82% efficiency after five cycles. Radical trapping experiments identified superoxide radicals as the primary active species. This study highlights the potential of mixed-ligand MOF heterojunctions as stable, renewable, and highly efficient photocatalysts for broad-spectrum dye removal from wastewater.