CuO/Co3O4 heterojunctions for catalytic nitroarenes reduction and oxygen evolution reaction

[Display omitted] •CuO/Co3O4 composites with heterojunctions were prepared via solution combustion method using Benincasa hisipida juice as fuel.•Catalytic reduction of nitroarenes and electrocatalytic oxygen evolution were studied over the pristine and composite oxides.•Heterojunctions in the C3 composite are highly active for nitroarenes reduction.•The composite is found to have good recyclability and versatility.•Heterojunctions of the C5 composite unveiled high current density and low overpotential for oxygen evolution reaction. Heterojunctions of copper oxide (CuO) and cobalt oxide (Co3O4) were synthesized by simple and scalable solution combustion method using Benincasa hispida juice extract as a green fuel. X-ray diffraction (XRD) confirms the presence of CuO and Co3O4 particles in monoclinic and face centered cubic phases respectively in the composites. Transmission electron microscopy (TEM) confirms the presence of heterojunctions in the composites. The nitrogen adsorption–desorption measurements demonstrate appreciable surface area of the composites and X-ray photoelectron spectroscopy (XPS) studies confirm the presence of the metal ions in variable oxidation states. The composite obtained with 1:1 ratio of Cu:Co precursors displayed very good catalytic activity towards reduction of noxious 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) with rate constant of 0.477 min−1 and 0.429 min−1 respectively. An admirable reduction efficiency of greater than 98 % within 6 min is observed with this composition. Also, this catalyst could effectively reduce other nitro compounds such as 4-nitroaniline, nitrobenzene, nitroacetophenone and 4-bromonitrobenzene. The catalyst could be reused up to three cycles without any noticeable loss in efficiency. The catalyst prepared with 0.25:0.75 ratio of Cu:Co precursors displayed fairly low overpotential and Tafel slope towards electrocatalytic oxygen evolution reaction (OER) with very good long-term stability. The improved performance of the composites arises from the synergistic effects at the numerous heterojunctions formed between the Cu and Co oxides that are favorable for OER kinetics and reduction reactions.