Efficient adsorption-photocatalytic removal of tetracycline hydrochloride over La2S3-modified biochar with S,N-codoping

Abstract

The adsorption instability and weak visible-light utilization of biochar restrain the industrial application in wastewater and soil remediations. Hence, S,N-codoped biochar is modified with La2S3 (La2S3/SN-biochar) via the one-pot sulfurization approach to boost the adsorption and photocatalytic activities for tetracycline hydrochloride (TCH) removal. Among the biochar-based composites, the optimal 3c-La2S3/SN-biochar with the La content of 15.43 wt% and the N content of 0.49 wt% exhibits the best removal efficiency of TCH. Its calculated adsorption capacity is 419.18 mg g−1, and the solar-light driven removal efficiency is 98.45 % for 200 mg L−1 TCH solution within 120 min. However, the long-term photo-corrosion induces to the declined adsorption-photocatalytic efficiency of 3c-La2S3/SN-biochar from 98.45 % to 93.26 % after 5 cycles, and the inadequate vacant sites result in the decreased adsorption capacity from 313.44 to 286.36 mg g−1 after 7 cycles. Langmuir isotherms and second-order kinetics well fit with the adsorption isotherms and kinetics of La2S3/SN-biochar composites, respectively. The Z-scheme junction between La2S3 and S,N-codoped biochar favors the rapid migration and separation of photoinduced electron-hole pairs. Meanwhile, the negative surface discharge is suitable for the efficient electrostatic attraction of TCH adsorption.