Surface atomic oxygen species mediated the in-situ formation of hydroxyl radicals on Fe3C decorated biochar for enhancing catalytic ozonation

Developing highly efficient and anti-interference catalysts was still a challenge for the practical application of heterogeneous catalytic ozonation (HCO) in water decontamination. Herein, a magnetic Fe3C decorated biochar (Fe3C/BC) was prepared for HCO to achieve efficient degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The Fe3C/BC catalytic ozonation system promoted the degradation ratio of 2,4-D from 58.7% (ozonation alone) to 90.0% within 10 mins when the ozone dosage was 1.0 mg/L. And the observed degradation rate constant (kobs) of 2,4-D under catalytic ozonation system was 2.58 times that of ozonation alone. Fe3C/BC exhibited negligible adsorption on 2,4-D but with a significant enrichment to ozone, which realized the cooperating process of "adsorption-catalysis" at the solid–liquid interface, thus avoiding the ineffective decomposition of ozone. The dissociative adsorption of ozone molecules on the surface Fe3C generated surface atomic oxygen species (O* and O2*), which mediated the in-situ formation of hydroxyl radicals (·OH). ATR-FTIR, in-situ Raman, isotope tracing tests, and theoretical calculations were used to disclose the interface reaction processes and reveal the ·OH formation mechanism. Free radical reactions at the interface efficiently avoid the interference of coexisting ions dissolved in water. The presence of 3 mM (183 mg/L) bicarbonate had essentially little effect on the degradation of 2,4-D. The consecutive use of Fe3C/BC did not influence its catalytic performance and stable structure. This study provided new insight into the ·OH-dominated interfacial reaction in the HCO process.