Visible light introduced photocatalytic degradation of tetracycline using δ-MnO2@BC

Birnessite-type (δ-MnO 2 ) exhibits a high adsorption and catalytic performance to remove organic contaminants, but it still suffers from agglomerates, low specific surface area, and uneven distribution of active sites. Here, a novel birnessite-loaded biochar (δ-MnO 2 @BC, MBC) was prepared by chemical precipitation and used for the catalytic degradation of tetracycline under visible light. The biochar provides a large number of birnessite loading sites, which increases the specific surface area of the material, and reduces the electron–hole pair complexation rate. Photocatalytic results showed that under optimal conditions, 91.89% of TC could be degraded by 20% MBC(m(δ-MnO 2 )/m(BC) = 20%) at a pH value of 3.0, with a negligible effect by solid–liquid ratio and temperature. Our evidences demonstrate that photogenerated electrons and holes serve as the key active species, whereas superoxide radicals play a supplementary role. The MBC photocatalyst exhibits excellent stability, maintaining an 85% TC removal efficiency after five recycling cycles. In addition, the proposed degradation pathways of TC were presented, suggesting a partial mineralization by visible light photocatalysis using MBC. This study provides new ideas for the treatment of antibiotic wastewater with manganese oxides and biochar materials. Graphical abstract