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.