How does ball-milling elevate biochar as a value-added peroxydisulfate activator for antibiotics removal?

Biochar, a promising carbonaceous material, has gained increasing attention for its role in catalytic degradation of organic pollutants. Currently, how ball-milling improve the catalytic performance of biochar is poorly understood. In this study, ball-milled biochar was prepared to activate peroxydisulfate (PDS) to degrade tetracycline hydrochloride (TCH), focusing on the insights into ball-milling mechanism. The extension of ball-milling time caused the increase of surface area, the reduction of particle size, and the development of oxygen-containing groups and carbon defects in biochar, which were instrumental in improving the catalytic performance of biochar for TCH degradation. When the ball-milling time of biochar was increased to 120 min, the degradation of TCH increased from 62.3% to 86.9%. The study also delved into the influence of process factors (PDS dosage, TCH concentration, reaction temperature, initial pH, anions, and humic acid) on the TCH degradation. Application potential in real water was verified by treatment of different antibiotics and in different water matrices. Radical quenching experiments and electron paramagnetic resonance analysis affirmed that singlet oxygen and electron hole contributed more to the degradation of TCH than sulfate radicals and hydroxyl radicals. Electrochemical experiments uncovered that ball-milling treatment boosted the biochar's ability to transport electrons, thereby enhancing it to activate PDS for TCH degradation. Quantitative structure-activity relationships revealed that the increase of surface area and oxygen-containing groups induced by ball-milling contributed to adsorption and catalytic degradation of TCH. The degradation pathways and mineralization of TCH in the catalytic system was also manifested. This research provides novel insights into the potential of ball-milled biochar for activating PDS to degrade TCH, holding promise for environmental applications.