Peroxydisulfate activation using B-doped biochar for the degradation of oxytetracycline in water

In the present study, B-doped biochar (BBC) materials with different B contents were prepared and used for the adsorption/degradation of oxytetracycline (OTC) through the activation of peroxydisulfate (PDS). The catalytic activity of BBC was improved to different degrees compared with that of pristine BC owing to enhanced OTC adsorption and PDS activation. Furthermore, the best adsorption and degradation achieved in this study was when the ratio of boric acid to biochar was 2:1, and we defined it as BBC2. The degradation rate of OTC (20 mg/L) after 120 min was increased to 94% by adding BBC2 and PDS. Furthermore, B-doping increased the BC pore size and introduced Lewis-acidic sites to its surface for PDS activation. The effects of PDS concentration, initial pH, and catalyst dosage on the removal of OTC were also evaluated. Using free-radical-quenching experiments, two main pathways for OTC degradation were identified, i.e., that via radicals on the BBC surface and that via non-radicals (O-1(2)) in solution. B atom doping positively charged the adjacent C atoms, thus allowing direct electron transfer with S2O82- and facilitating the generation of O-1(2). Furthermore, the C=O groups generated upon BBC activation also generate O-1(2) in a similar manner. Finally, nine OTC degradation products were identified and two possible degradation pathways were proposed.