Solvothermally synthesized narrow band gap Mg2Co7O12: A novel photocatalytic material for methylene blue dye degradation

Abstract

This work reports the first experimental synthesis and comprehensive characterization of a novel triclinic, spinel-derived oxide, Mg2Co7O12, and its application as an efficient photocatalyst for the degradation of methylene blue dye under natural solar irradiation. The material was synthesized via a solvothermal route followed by controlled calcination, yielding a phase-pure compound confirmed by X-ray diffraction and crystallized in the P1 space group. Raman spectra of calcined Mg2Co7O12 show characteristic peaks at 676.8 cm-1 (A1g), 470.2 cm-1 (Eg), 611.4�517.2 cm-1 (F2g), and 193.6 cm-1 (3F2g), confirming the formation of crystalline Mg2Co7O12 phase. Morphological investigation shows uniformly distributed microparticles, while Brunauer-Emmett-Teller (BET) analysis indicates a surface area of 46.626 m2g-1. UV�Vis spectra demonstrate a narrow bandgap of 1.89 eV, enabling efficient absorption across the visible region. The photocatalytic activity was evaluated under natural sunlight, exhibiting a maximum degradation efficiency of 98.73% at pH 12 within a short reaction time of 30 min without using any oxidizing agents. Kinetic analysis follows pseudo-first-order behavior. Mechanistic studies using radical scavengers confirm that hydroxyl radicals (�OH) are the dominant reactive species responsible for dye degradation. The enhanced photocatalytic performance is attributed to the synergistic effects of mixed-valence Co2+/Co3+ redox cycling, structural distortion, and efficient charge separation within the lattice. These findings demonstrate that Mg2Co7O12 is a promising and previously unexplored photocatalyst for wastewater remediation, offering a sustainable and efficient approach for the removal of organic pollutants under solar irradiation. � 2026 Elsevier B.V.