Enhanced tetracycline removal via Z-scheme activation by a novel magnetic ZnO/Fe3O4-modified biochar

At present, tetracycline (TC) is among the most widely utilized antibiotics and its widespread usage can bring the contamination in the environment, especially in water, leading to many ecological and health risks. In this research, a novel magnetic photocatalyst with Z-scheme heterostructure, ZnO/Fe 3 O 4 /BC (MZB), was developed by co-doping ZnO/Fe 3 O 4 on biochar derived from poplar wood powder. In 50 mL of 40 mg L −1 TC solution, a dose of 10 mg 0.8-MZB achieved a 90.4 % elimination of TC through adsorption-photocatalysis, with a photocatalytic degradation rate of 20.27 × 10 −3 min −1 , which was 2.1 and 5.8 times greater than ZnO and Fe 3 O 4 , respectively. The highest adsorption of TC by 0.8-MZB was 23.17 mg g −1 , and the adsorption behavior could be described by the pseudo-second-order kinetic models. The enhanced adsorption performance was attributed to its increased specific surface area, while the improved photocatalytic capability was primarily due to the Z-scheme heterojunction formed between ZnO and Fe 3 O 4 . Additionally, the BC functioned as a conductive channel, facilitating the separation of photogenerated electron-hole pairs (e − /h + ) and offering more active sites for electron transfer. The 0.8-MZB had excellent stability as the removal rate only slightly decreased by about 8 % after 5 cycles, and showed a high steady efficiency under different water matrices. In the toxicity assessment, the optimum concentration of 0.8-MZB could effectively promote the growth of mung bean seedlings, but the higher concentrations (400, 800 mg L −1 ) of 0.8-MZB inhibited them. This study provides a factual foundation for the implementation of photocatalytic technology in water pollution remediation as well as the utilization of agricultural and forestry residues. • Magnetic ZnO/Fe 3 O 4 /BC was synthesis by combining coprecipitation and pyrolysis method. • BC as the onductive channel promoted the absorption property and charge separation. • 0.8-MZB showed the excellent removal, stability and recyclability. • Detailed reaction pathways and mechanism during the TC photodegradation was proposed.