Ultrasonic-enhanced Fenton-like degradation of bisphenol A using a bio-synthesized schwertmannite catalyst

Schwertmannite (Sch) was synthesized by Acidithiobacillus ferrooxidans and used as Fenton-like catalyst for bisphenol A (BPA) degradation combining with ultrasonic technology (US). Physicochemical characterizations showed that the bio-synthesized Sch particles had a pompon-like morphology with high BET surface area of 92.92m²/g. The degradation reaction showed a two-stage pseudo-first-order kinetic process consisting of an induction period and a followed rapid degradation period. A synergistic effect existed between US and Sch on activating H₂O₂ and the synergy factor was calculated to be 2.32. The catalytic efficiency of the system was mainly affected by pH, Sch dosage and temperature, but less relevant to H₂O₂ concentration. Free OH radicals in the bulk solution were identified to be the dominant oxidant, which were produced by both heterogeneous and homogeneous processes. The promotional effect of US on Fenton-like degradation of BPA can be ascribed to the reasons of (1) increasing the radical generation by ultrasonic cavitation; (2) reducing the apparent activation energies of degradation reaction; (3) accelerating the dissolution of iron and (4) keeping the high surface area of catalyst by continuous surface cleaning. Ecotoxicity tests indicated lower toxicities of intermediates than BPA. In addition, Sch exhibited high reusability in the recycle study.