Bifunctional green nanoferrites as catalysts for simultaneous organic pollutants reduction and hydrogen generation:...

The upcycling strategy is an approach that includes the conversion of waste into new higher value-added products. This study reports on a new methodology for the environmentally friendly synthesis of MFe₂O₄ spinel nanoferrites (M = Co, Cu, Fe and Mn) to be used as catalysts applied in the upcycling method. Thus, the reduction of 4-nitrophenol (4-NP), methyl orange, and methyl red to commercially valuable compounds was evaluated, as well as the simultaneous generation of hydrogen in a short time. Therefore, an eco-friendly synthesis was proposed, according to the 12 principles of green chemistry and sustainability. Product were obtained with satisfactory properties in terms of crystallinity, magnetic particle size, and magnetization. The materials exhibited excellent performance in catalytic reduction of 4-NP, whose reduction time decreased in the order MnFe₂O₄ > Fe₃O₄ > CoFe₂O₄ > CuFe₂O₄. This behavior highlighted the CuFe₂O₄ nanoferrite, which achieved 4-NP reduction in just 10 s. It proved that it could also be reused for 10 consecutive cycles while maintaining its crystalline structure. The catalyst was also effective in the reduction of azo dyes and subsequent production of substituted aromatic compounds suitable for use in chemical processes. Under the optimized conditions, the green CuFe₂O₄ catalyst was effective in producing hydrogen by hydrolysis. HGR and activation energy (E_a) values were of the order of 19,600 mL g^-1 min^-1 and 25.5 kJ mol^-1, respectively. The results demonstrated the potential of this simple strategy for the environmental pollutant elimination and power generation.