Endogenous Fe-Al self-doped biochar derived from rubber sludge for effective peroxymonosulfate activation: Dominant...

The treatment of rubber sludge and removal of antibiotics is significant, but still challenging. Herein, rubber sludge was recycled into a novel Fe-Al self-doped biochar (FeAlBC) without exogenous dopants to activate peroxymonosulfate (PMS) for efficient removal of tetracycline (TC). The pyrolysis temperature regulation revealed that a higher pyrolysis temperature induces structural reconstruction of Fe and Al species in rubber sludge into self-doped crystalline phases. Among all the FeAlBC samples, FeAlBC800 achieved the highest PMS activation performance due to the crystallization of active phases and its balanced adsorption capability. The high TC degradation performance was associated with the synergism of the strong activation capability of Fe²⁺, the electron-mediating role of C=O groups, the conductive graphitized carbon structure, and the strong Lewis acid sites by Al³⁺. The optimal system of 0.1 g/L FeAlBC800, 10 mg/L PMS reached 93.5 % TC (5 mg/L) degradation in 90 min. The quenching experiments and electron spin resonance spectroscopy revealed that ¹O₂ and electron transfer were responsible for TC degradation. The assessments of pH tolerance, interference resistance, reusability and ecotoxicity demonstrated the promising practical applicability of FeAlBC800/PMS system. This study offers a promising approach for antibiotics removal and a value-added route for converting rubber sludge into functional materials for environmental remediation.