Green synthesis of p-Co3O4/n-ZnO composite catalyst with Eichhornia crassipes plant extract mediated for methylene blue degradation under visible light irradiation

Abstract

The water pollution due to industrial effluents causes a great health problem. Hence, it is important to treat wastewater before discharging to the environment. In this work, water hyacinth (Eichhornia Crassipes) plant extract mediated ZnO, CO3O4, and p-CO3O4/n-ZnO composite catalysts were synthesized by green co-precipitation routes. The resulting samples were characterized by x-ray diffractometer (XRD), scanning electron microscope (SEM), Fortier transform infrared (FT-IR), and with other instruments. The catalytic activities of ZnO, Co3O4, and Co3O4/ZnO were tested for MB dye degradation under visible light irradiation. The catalytic degradation of MB with p-CO3O4/n-ZnO composite catalyst was 95.5%; while 72% and 79% of MB dye was degraded by ZnO and Co3O4 catalysts, respectively. The kinetic rate constants (k) in the degradation of MB dye with ZnO, Co3O4, and p-CO3O4/n-ZnO composite catalysts were also 0.014 min−1, 0.018 min−1, and 0.028 min−1, respectively. The results showed that the presence of plant extract during the synthesis of the catalysts makes the catalyst more active and enhances the catalytic performances. Moreover, the formation of p-n junction in the p-CO3O4/n-ZnO catalyst also facilitates the photogenerated electron-hole separation and further enhances the catalytic efficiency. Hence, the formation of p-n junction is the key factor for enhancing the photodegradation of MB dye under visible light irradiation and the plant extract mediated catalyst synthesis also further improves its performance.