Synergy effect between tetracycline and Cr(VI) on combined pollution systems driving biochar-templated Fe₃O₄@SiO₂/TiO₂/g-C₃N₄ composites for enhanced removal of pollutants

Highlights

•	Synthesized biochar-based catalyst enhanced adsorption and photocatalytic activity.
•	The catalys simultaneously removed 91% of TC and 79% of Cr(VI) in combined systems.
•	Synergistic photocatalytic effect accelerated TC and Cr(VI) removal in combined systems.

Abstract

Biochar-coupled Fe₃O₄@SiO₂/TiO₂/g-C₃N₄ composites were successfully constructed through simple sol–gel and calcination methods. The composites efficiently removed high-concentration toxic tetracycline (TC) by means of ·OH and ·${\rm O}_2^{-}$, whose removal rate exhibited 91.88% during 3 h, and the degradation rate constant reached up to 0.0068 min⁻¹. The excellent performance can be attributed to the high specific surface area, enhanced visible light response, the introduction of magnetic nanoparticles and biochars expediting charge transfer, Z-scheme heterojunction enhancing the spatial separation of photo-generate carriers and, importantly extraordinary adsorption capacity of 147.96 mg g⁻¹. Moreover, the composites showed the most excellent efficiency under the calcination temperature of 450 ℃, and exhibited good stability with tolerance to a wide range of pH and anions. Interestingly, a synergistic photocatalytic effect was discovered in the TC/Cr(VI) combined pollution systems, resulting in significantly improved removal of Cr(VI). Besides, the photocatalytic mechanism and degradation path of tetracycline were also elucidated. All these findings suggested the as-synthesized catalyst was an excellent photocatalyst for removal of TC/Cr(VI)-contaminated water.

Funding

National Natural Science Foundation of China(42220104004); Innovative Approaches Special Project of the Ministry of Science and Technology of China(2020IM020300); Beijing–Tianjin–Hebei Collaborative Innovation Promotion Project of China(Z201100006720001)