In-situ synthesis of a novel ZnO/CuCo2S4 p-n heterojunction photocatalyst with improved phenol and rhodamine B degradation performance and investigating the mechanism of charge carrier separation

Designing high-performance ZnO-based photocatalysts can be a promising solution to environmental problems. However, pure ZnO with a large band gap has challenges such as excitation under UV light and high recombination of charge carriers. Construction of heterojunction with a narrow band gap semiconductor can be used as a suitable approach to increase the photocatalytic efficiency of ZnO. Considering that, in the present study, a novel ZnO/CuCo2S4 n-n heterojunction nanocomposite was successfully synthesized by the in-situ hydrothermal method. The purity of the prepared photocatalysts was confirmed by XRD, FT-IR, EDX, and XPS analyzes. FESEM, TEM, and HRTEM images disclosed the morphology of CuCo2S4 nanoparticles on spindle-like ZnO. The ZnO/CuCo2S4 photocatalyst showed 14 (63) and 4.6 (17) times higher photocatalytic performance than ZnO and CuCo2S4 for photodegradation of phenol (RhB) under visible light, respectively. The photocatalytic decomposition of phenol and RhB over ZnO/CuCo2S4 followed a pseudo-first-order kinetic with the rate constants of 109 × 10−4 and 485 × 10−4 min−1, respectively. The significantly enhanced photocatalytic activity of ZnO/CuCo2S4 nanocomposite can be attributed to the heterojunction formation, which provides more reaction active sites, excites semiconductors in the visible region, and increases the separation and transport of charge carriers. The narrow band gap of CuCo2S4 that led to the absorption of light by the nanocomposite in the higher wavelength range was also investigated by UV–vis DRS and Tauc plots. Suppressing the recombination of electron-hole pairs in the prepared nanocomposite relative to the components was shown by PL spectroscopy. Photocurrent and EIS data were also obtained, and based on them, the possible mechanism of photocatalytic degradation was proposed.