A visible-light active p-n heterojunction ZnO/Co3O4 composites supported on Ni foam as photoanode for enhanced photoelectrocatalytic removal of methylene blue

A series of ZnO/Co3O4 composites supported on nickel foam were prepared by a rapid liquid deposition of ZnCo-MOF precursor and a subsequent calcination process. The prepared electrodes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, UV–visible diffuse reflection spectroscopy (UV–Vis DRS), transient photocurrent (TPC) measurements, and electrochemical impedance spectroscopy (EIS). The experimental results showed that the ZnO/Co3O4 composite calcined at 500 °C with a Zn/Co molar ratio of 3:1 represents the best photoelectrocatalytic performance; such electrode exhibited a high methylene blue (MB) dye degradation rate of 92.5% after 140 min. Moreover, the activity can be well-maintained, with a degradation rate of 85.4% being obtained after 5 cycles. The photoelectrocatalytic efficiency was increased by 14.1% compared with photocatalytic efficiency due to the synergistic effect of light and external potential. The possible photoelectrocatalytic mechanism was analyzed and discussed. Mott-Schottky (M-S) experiment verified the existence of p-n heterojunction constructed by ZnO and Co3O4 in the composite, which overcomes the disadvantages of high photoelectron-hole recombination rate and weak visible light response of ZnO catalyst. The quenching experiments of the prepared electrode showed that h+, •OH and •O2− contribute to the degradation of MB, with •OH being the main active radical.Graphical abstractZnO/Co3O4 composite electrode was prepared by calcination of ZnCo-MOF precursor grown on nickel foam by liquid deposition method. The ZnO/Co3O4 composite electrode exhibits excellent photoelectrocatalytic degradation performance for methylene blue.