Construction of Chitosan-biochar/ZnO/NiO composites for efficient photocatalytic removal of Congo red and tetracycline

The combination of photocatalyst and biochar is an effective strategy to improve the overall photocatalytic activity, but it is still a challenge to find photocatalyst with excellent photocatalytic activity and biochar with large surface and rich oxygen functional groups. In this study, a novel CS-biochar/ZnO/NiO composite with adsorption-photocatalytic performance was constructed using chitosan as biochar source, and exploited for visible-light-driven photocatalytic degradation of tetracycline (TC) and Congo red (CR). The superior photocatalytic activity of CS-biochar/ZnO/NiO than pristine ZnO, NiO and CS-biochar/ZnO under visible light, and 63 %-CS/ZnO/NiO composite has the best photocatalytic activity. The photodegradation efficiency for CR was 94.5 % within 100 min, and the apparent rate constant (k) was 0.0206 min(-1), which is about 1.87 and 3.89 times that ZnO and NiO, respectively. For TC, the photodegradation efficiency was 90 % within 45 min, and k was 0.0377 min(-1), which is about 1.74 and 2.86 times that bare NiO and ZnO, respectively, which attribute to the synergistic effect between ZnO/NiO and CS-biochar improved the activity of photocatalysts. This work presents a straightforward approach for improving photocatalytic antibiotic and dye degradation through the construction of bifunctional "hybrid" material, which have great potential for application in the removal of contaminants.