FeC2O4-ball milled biochar for simultaneous removal of cadmium and tetracycline: A strategy coupling oxygen vacancies with carboxyl groups

The concurrent removal of heavy metals and antibiotics from water and soil continues to pose a substantial challenge. In this work, FeC 2 O 4 -assisted ball milling was utilized to prepare a novel bifunctional biochar composite (FeC 2 O 4 @BC) to achieve the simultaneous removal of Cd 2 + and tetracycline (TC). Batch experiments in binary-solute system showed that FeC 2 O 4 @BC can simultaneously remove 69.6 % of Cd 2+ and 93.4 % of TC, while 86.4 % of TC was degraded, which conquered competitive effects between Cd 2+ and TC and exhibited faster kinetic and higher capacity than raw biochar. In this study, FeC 2 O 4 -assisted ball milling for BC provided FeC 2 O 4 @BC with endogenous oxygen vacancies (OVs) by losing lattice oxygen of FeC 2 O 4 , and simultaneously induced exogenous -COOH formation on composite. Mechanistic analysis revealed that OVs in FeC 2 O 4 @BC greatly improved 1 O 2 production for efficient TC degradation by reducing O 2 adsorption energy and accelerating electron transfer to adsorbed O 2 from adjacent Fe(Ⅱ) atoms, which lowered the free energy barrier for the O 2 to singlet oxygen ( 1 O 2 ) conversion. Meanwhile, -COOH significantly increased Cd 2+ complexation on FeC 2 O 4 @BC, which coupled with cation exchange and Cd-π conjugation contributing to Cd 2+ removal. Overall, FeC 2 O 4 @BC holds considerable potential for dealing with combined heavy metals and antibiotics pollution in environment systems.