Green synthesis of p-Co<sub>3</sub>O<sub>4</sub>/n-ZnO composite catalyst with Eichhornia Crassipes plant extract mediated for methylene blue degradation under visible light irradiation
Setegn Geta Aragaw, Fedlu Kedir Sabir, Dinsefa Mensur Andoshe, Osman Ahmed Zelekew
Abstract
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, CO 3 O 4 , and p-CO 3 O 4 /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, Co 3 O 4 , and Co 3 O 4 /ZnO were tested for MB dye degradation under visible light irradiation. The catalytic degradation of MB with p-CO 3 O 4 /n-ZnO composite catalyst was 95.5%; while 72% and 79% of MB dye was degraded by ZnO and Co 3 O 4 catalysts, respectively. The kinetic rate constants (k) in the degradation of MB dye with ZnO, Co 3 O 4 , and p-CO 3 O 4 /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-CO 3 O 4 /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.