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

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.

Highlight

•	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.

Funding

National Natural Science Foundation of China(41671331)

Innovative Approaches Special Project of the Ministry of Science and Technology of China(2020IM020300)

Beijing–Tianjin–Hebei Collaborative Innovation Promotion Project of China(Z201100006720001)