Covalently bonded aluminum-iron modified activated carbon moderately activated ferrate(VI) through enhanced interaction path: pH-driven efficacy on active species evolution and synergic mechanistic

Recent studies have predominantly focused on improving the oxidation capability of ferrate (Fe(VI)) by promoting the formation of Fe(IV)/Fe(V) through various activation methods. However, the low utilization rate of intermediate active iron species caused by the rapid self-decomposition of Fe(VI) limits its water treatment application. This study proposed to use covalently bonded aluminum-iron modified activated carbon (CAFM@PAC) to moderately activate Fe(VI) for carbamazepine (CBZ) degradation. The mutual interfacial between Fe(VI) and CAFM@PAC was explored, especially the mechanism of moderately activating to enhance the stability and utilization of activated intermediate iron and reactive oxygen species through metal modification modulation and pH-driven processes. Results showed that CBZ removal in Fe(VI)/CAFM@PAC system was higher than that of Fe(VI) alone system, especially in acidic conditions, which should be attributed to the enhanced interfacial reaction and electron transfer path through the synergistic effect of aluminum, iron and carbon. The interaction of Fe(VI) and CAFM@PAC had a moderate activating effect on Fe(VI) and inhibited its excessive self-decomposition, stabilizing and improving the utilization of active species. pH showed great influence on the high-valent iron species (Fe(IV)/Fe(V)) and reactive oxygen species (·OH, ·O₂^–, and ¹O₂) evolution and active species played different roles within varying pH. Moreover, the freshly generated rich aluminum-iron oxides enhance adsorption by effectively capturing and complexing CBZ degradation intermediate products. Fe(VI)/CAFM@PAC system possessed strong anti-interference ability and universality across a broad pH spectrum. The system integrated the advantages of highly active free radicals and selective metal active substances, achieving efficient removal of refractory organic pollutants. This study provided a new insight into the moderate activation effect for Fe(VI) by CAFM@PAC within dynamic pH and enriched the fundamental knowledge of Fe(VI) activation.