Application of the persulfate activated by molten anhydrous CuCl2 modified biochar to degrade antibiotics: Performance and the role of C-O-Cu structure

[Display omitted] •Catalytic degradation of TCs by molten anhydrous CuCl2 modified lotus leaf biochar.•DFT calculations show that the C-O-Cu structure exists on the catalyst surface and changes the charge distribution on the catalyst surface.•The C-O-Cu structure contributes to the cyclic conversion of Cu(I) and Cu(II), promoting the emergence of more active species.•Cu-HBC/PDS can be applied to the actual engineering of continuous operation. The misuse of tetracycline antibiotics had caused extremely serious problems in the water environment. The molten metal salt technique was used in this work to co-pyrolyze anhydrous CuCl2 with lotus leaf biomass to prepare Cu-modified lotus leaf biochar (Cu-HBC) and used it to activate persulfate (PDS) for removing tetracycline antibiotics (TCs) from water bodies. According to the experimental findings, the removal of tetracycline (TC) and oxytetracycline (OTC) by Cu-HBC activated PDS (Cu-HBC/PDS) improved by 55.47 % and 51.60 % compared to lotus leaf biochar (HBC)/PDS. The characterization results showed that only Cu2O crystals and monomer Cu were found on the surface of Cu-HBC rather than CuO crystals. Interestingly, Cu(II) was unexpectedly found in XPS, based on which we proposed a possible the C-O-Cu structure on the surface of Cu-HBC, and the structure was accurately confirmed by FT-IR. Density Functional Theory (DFT) indicated the C-O-Cu structure made the electrons collect around the Cu, caused the formation of electron-rich centers on the Cu-HBC surface, then sparked cyclic disproportionation reaction at the monomeric Cu, Cu(I), and Cu(II), resulting in the interconversion of Cu(I) and Cu(II). In the procedure, Cu-HBC completed the activation of PDS, generating the primary active species (1O2) to oxidize TCs and reduce their toxicity.