Photocatalytic reduction of nitroarene derivatives by impressive visible-light active Co3O4-QDs/Mn3O4 nanocomposite

A visible light active Co₃O₄-quantum dots (QDs)/Mn₃O₄ nanocomposite was successfully synthesized by a straightforward precipitation approach. Notably, the formation of Mn₃O₄ nanosheets in composite structure was evidenced by different physicochemical techniques especially transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and N₂ sorption analyses, which indicated the uniform distribution of Co₃O₄-QDs with small size of around 5 nm on the surface of Mn₃O₄ nanosheets along with the enhancement of specific surface area for final composite. Also, the persistence of Co₃O₄-QDs during nanocomposite synthesis was analyzed by X-ray diffraction (XRD), FT-IR and TEM techniques. The diffuse reflectance UV–Vis and electrochemical impedance spectroscopies revealed the reduction of band gap energy and enhanced charge separation efficiency for Co₃O₄-QDs/Mn₃O₄ nanocomposite, respectively, which consequently led to improved photocatalytic response in comparison with bare Co₃O₄-QDs and Mn₃O₄ nanosheets. The as-prepared nanocomposite exhibited excellent photocatalytic activity in the reduction of a wide range of substituted nitroarenes with the yields of higher than 80 % relative to the corresponding arylamines, using N₂H₄·H₂O as the hydrogen source and ethanol as green solvent at 25 °C and ambient pressure under visible light illumination. The synergistic effect could improve the production of active hydrogen atoms, therefore, the reasons for this transformation over the prepared nanocomposite under benign conditions are fully discussed. Furthermore, the nanocomposite could be easily recycled without decay in photocatalytic activity for at least five successive cycles.