Novel cow dung-doped sludge biochar as an efficient ozone catalyst: Synergy between graphitic structure and defects induces free radical pathways.

A composite material, cow dung-doped sludge biochar (Zn@SBC-CD), was synthesized by one-step pyrolysis using ZnCl 2 as an activating agent and applied to a catalytic ozonation process (COP) for methylene blue (MB) removal. SEM, XRD, FTIR, XPS and BET analyses were performed to characterize the biochar (BC) catalysts. Zn@SBC-CD had high graphitization degree, abundant active sites and uniform distribution of Zn on its surface. Complete removal of MB was achieved within 10 min, with a removal rate much higher than that of ozone alone (32.4%), implying the excellent ozone activation performance of Zn@SBC-CD. The influence of experimental parameters on MB removal efficiency was examined. Under the optimum conditions in terms of ozone dose 0.04 mg/mL, catalyst dose 400 mg/L and pH 6.0, COD was completely removed after 20 min. Electron paramagnetic resonance (EPR) analysis revealed radical and non-radical pathways were involved in MB degradation. The Zn@SBC-CD/O 3 system generated superoxide anion radicals ( • O 2 −), which were the main active species for MB removal, through adsorption, transformation, and transfer, Furthermore, Zn@SBC-CD exhibited good reusability and stability in cycling experiments. This study provides a novel approach for the utilization of cow dung and sludge in synthesis of functional biocatalysts and application in organic wastewater treatment. • First use of cow dung-doped sludge to prepare biochar through pyrolysis. • Cow dung doping improved the catalytic performance of sludge biochar. • Radical and non-radical pathways were involved in MB degradation. • Superoxide anion radicals (. • O 2 −) acted as the main active species. • Zn@SBC-CD showed good reusability and stability. [ABSTRACT FROM AUTHOR]