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

Abstract

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.