Environmentally friendly and recyclable Dawson-type polyoxometalate: A novel homogeneous catalytic system for degradation of dye pollutants

This research paper investigates the catalytic potential of a Dawson-type polyoxometalate-based metal complex (Co-POM) in the efficient degradation of Indigo Carmine (IC) and Methyl Orange (MO) dyes. The synthesized complex was characterized using a variety of characterization techniques, and its catalytic activity was evaluated during the degradation of these dyes under different experimental conditions. The results of the study reveal that this new environmental homogeneous catalytic system (H₂O₂/Co-POM/Dye) exhibits notable catalytic efficiency, leading to effective degradation of the dyes under consideration. The influence of various parameters on catalytic performance was systematically investigated.The cobalt-substituted complex (Co-POM) showed the best catalytic efficiency compared with other transition metal-substituted POMs {Ni(II), Cu(II), Mo(II)} and the parent POM, with a degradation of 87.4 % for IC and 94.3% for MO under the following optimized conditions: an initial hydrogen peroxide (H₂O₂) concentration of 0.02 M, a catalyst concentration of 0.2 mM, and an initial dye concentration of 5 mg/L at pH 3 and room temperature (25 °C). It revealed the oxidative role of hydroxyl radicals (OH^●), hydroperoxyl radicals (HO₂^●), and superoxydes (O₂•) as reactive species, on the basis of which a plausible degradation mechanism is proposed.The recyclability test indicated good catalyst stability over five consecutive cycles with a very low loss of catalytic efficiency (∼5 %). Their stability and robustness were verified by various characterization techniques such as UV–vis spectroscopy, FT-IR spectroscopy, single crystal X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), and Energy Dispersive X-ray analysis (EDX).