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

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.