Enhanced degradation of Bisphenol AF by Fe/Zn modified biochar/ferrate(VI): Performance and enhancement mechanism

The use of ferrate (Fe(VI)) as an oxidizing agent is gaining popularity due to its eco-friendly and efficient properties. However, its practical application is constrained by its significant pH-dependence. Consequently, finding cost-effective and environmentally friendly catalysts that can activate Fe(VI) over a wide pH range is crucial for the removal of organic pollutants. In this study, the Fe/Zn-modified biochar (Fe/Zn-BC) was synthesized and it was employed to activate Fe(VI) for the purpose of accelerating the breakdown of bisphenol AF (BPAF). The Fe(VI)+Fe/Zn-BC system can effectively degrade 90.1% of BPAF within three minutes, which is nearly twice as efficient as the single Fe(VI) system and the Fe(VI)+BC system, and significantly higher than the Fe/Zn-BC system alone. During the reaction, the pH increase caused a reduction in the reactivity of Fe(VI), resulting in the observation of a distinct segmentation phenomenon in the results of pseudo-first-order kinetics fitting. Besides, the removal rate of BPAF was influenced by key operating parameters (i.e., Fe/Zn-BC dosage, Fe(VI) concentration, initial pH). Additionally, the study demonstrated that Fe/Zn-BC could still effectively activate Fe(VI) even under higher initial pH conditions. Fe(IV) and Fe(V) were identified as the major active oxidizing species in the system through free radical scavenging and PMSO conversion experiments and a possible activation mechanism was proposed based on results of experiments (including XPS and FTIR). Overall, this study provides a practical and cost-effective approach to improve the oxidation performance of Fe(VI).