High-efficiency photocatalyst based on bis(dimethylglyoximato)nickel(II) complex and Fe3O4 (magnetite) nanoparticles for rapid degradation of toxic dyes in aqueous medium

The discharge of toxic dyes like methylene blue (MB) and nigrosin black (NB) from industrial effluents poses a severe environmental threat. While photocatalysis is a promising solution, developing efficient and environmentally benign catalyst remains a significant challenge. In order to address it, a mesoporous metal-organic framework (MOF) heterostructured composite is prepared through the functionalization of bis(dimethylglyoximato)nickel(II) complex microrods with magnetite Fe₃O₄ nanoparticles. SEM analysis depicts large (0.2–1.0 μm), well-defined facets with sharp, terraced steps on these parallel structures apparent as semi-nano rods of [Ni(DMG)₂] complex. Spherical Fe₃O₄ nanoparticles (50–100 nm in diameter) were immobilized on the surface of the [Ni(DMG)₂] microrods. Fe₃O₄ nanoparticles exhibited crystallite sizes of 20–50 nm, while the [Ni(DMG)₂] microrods displayed a semi-crystalline periphery with finer crystallites of 1–2 nm. XRD validated retention of spinel Fe₃O₄ and [Ni(DMG)₂] crystallinity, and DRS showed a reduced bandgap of 1.45 eV as compared to 2.13 eV for pure Fe₃O₄ due to enhanced visible-light absorption by organic complex. The mesoporous structure of [Ni(DMG)₂]-Fe₃O₄-MOF have a surface area of 18.09m²/g was confirmed with BET. The composite demonstrated exceptional photocatalytic performance under visible light, achieving 95 % degradation of MB within 30 min and 91 % degradation of NB within 50 min using minimal catalyst doses of 0.05 g and 0.06 g, respectively. Kinetic studies adhered to a pseudo-second-order model, and mineralization was confirmed by the 89 % reduction from 1800 mg/L to 200 mg/L after 90 min in chemical oxygen demand (COD). This work establishes that the [Ni(DMG)₂]-Fe₃O₄-MOF composite is a highly efficient, reusable, and practical photocatalyst for sustainable wastewater treatment.