Highly efficient degradation of Ponceau S using a solar-light-driven Z-scheme ZnMn2O4/ZnO heterojunction photocatalyst

A ZnMn 2 O 4 /ZnO heterojunction was prepared via a solid dispersion method for the photocatalytic degradation of Ponceau S (PS) under solar irradiation. The structural, textural, morphological, optical, and electrochemical properties of the synthesized materials were systematically characterized. UV–Vis DRS revealed band gap energies of 1.92 eV for ZnMn 2 O 4 and 3.14 eV for ZnO, supporting the formation of a direct Z -scheme heterojunction, which promotes efficient charge separation. The ZnMn 2 O 4 /ZnO heterostructure exhibited superior photocatalytic performance compared to the individual components, achieving 97.21% degradation efficiency under optimized conditions (photocatalyst dosage: 0.3 g/L; PS concentration: 15 mg/L; reaction time: 180 min and pH: 5.9) with a short half-life of 39.72 min. The low relative standard deviation (RSD = 0.25%) confirms the excellent reproducibility of the results. Scavenger experiments identified O 2 •- and h + as the dominant reactive species. The heterojunction retained a removal efficiency of 79.91% after six cycles, demonstrating good stability without significant structural deterioration. Monte Carlo and molecular dynamics simulations revealed strong interactions and high adsorption affinity of PS on the ZnMn 2 O 4 /ZnO surface. Furthermore, toxicity analysis confirmed that the degradation byproducts exhibit lower acute toxicity than the parent dye.