Electrochemical in-situ probing of heterocatalytic green reduction of 4-nitroaniline by novel non-noble CuO/Co3O4 nanocomposites

Abstract

Nobel metals are commonly used catalysts in reactions due to their excellent catalytic activities. Transition metals, too, possess good catalytic activity due to the availability of vacant d-orbitals that provide avenues for electron exchange during reactions. In this work, the performance of CuO/Co3O4 (CCO) catalyst is evaluated. The catalyst is prepared by a facile coprecipitation method. X-ray diffraction, Fourier transform infrared spectroscopy, HRTEM, Ultraviolet spectroscopy, Scanning electron microscopy and X-ray photoelectron spectroscopy techniques were used to study the material properties. XRD analysis confirms the formation of CCO heterostructure with supporting evidence from FTIR, HRTEM and XPS. The catalyst shows optical bandgap contributions of CuO and Co3O4 at 1.6 eV and 2.4 eV, respectively. The SEM analysis shows the presence of agglomerates with a mean length of 111 ± 3 nm. The prepared catalyst is employed for the 4-nitroaniline reduction using sodium borohydride. The kinetics of the reduction reaction were studied, and an apparent rate constant of 0.323 min−1 was estimated. The catalyst shows a turnover frequency of 1.44 min−1 and 100% recyclability up to 5 cycles that are competitive with noble metal and rare-earth-based catalysts. The fast reduction of 4-NA is attributed to the novel p-p type isojunction formed by the heterostructure of CCO. Additionally, extensive electrochemical analysis has been used as an in situ probe to monitor the reduction reaction. Accordingly, the study shows the different intermediary reduction species formed in the process of reduction, adding evidence to the proposed mechanism.