Pechini synthesis and characterization of Co₂MnO₄nanostructures and their application as a nano-photocatalyst for degradation of malachite green in contaminated water under sunlight

A spinel-type Co₂MnO₄ nanostructure was synthesized under various chelating and polymerizing conditions and systematically investigated for its ability to degrade malachite green (MG) in visible light. The structural, morphological, and optical properties of the samples were analyzed using XRD, FTIR, FESEM, EDX, TEM, BET, and DRS techniques. In this study, the catalyst synthesized from citric acid and propylene glycol (CMO-1) was most effective, with a generally uniform morphology and narrow particle size distribution (100–120 nm), a high surface area and a narrow 1.52 eV bandgap, among all samples examined. Under visible light, CMO-1 minimally degraded MG by 98.6% in 120 minutes with pseudo-first-order kinetics (k = 0.02542 min⁻¹). In scavenger experiments, it was determined that photogenerated holes (h⁺) contributed the most to degradation. Furthermore, the stability of the catalyst was assessed, in which it maintained 85% activity after 5 consecutive cycles of degradation without deteriorating structurally. A comparison of Co₂MnO₄ with other manganese-based and composite photocatalysts revealed similar or better performance when activated by visible light, demonstrating its potential as an effective and reusable photocatalyst for wastewater treatment.