Boron-doped biochar with dual C-B-O/O-B-O sites as a super-anchor and electron-accelerator for nZVI-activated persulfate oxidation of imidacloprid.

Removing imidacloprid from water by persulfate oxidation remains challenging because the iron-based activators commonly used in these systems are prone to aggregation, passivation, and loss of reactivity. Among available advanced oxidation processes, nZVI-activated peroxydisulfate (PDS) is attractive for IMI degradation, but its performance is often compromised by inefficient oxidant utilization and poor catalyst durability. Herein, boron-doped biochar (BBC) with atomically dispersed functional sites was engineered to enhance nZVI catalytic performance. C-B-O sites served as robust anchoring sites, exhibiting a calculated Fe-binding energy of 391.98 kJ/mol and contributing to nZVI stabilization and improved activity retention after air exposure. Concurrently, O-B-O sites created polar microenvironments that promoted PDS enrichment and accelerated interfacial electron transfer, yielding an electron efficiency of 0.62 e- per PDS molecule. This dual-site architecture promoted the generation of O2·-, 1O2, SO4·-, and ·OH, as evidenced by radical-scavenging and electron paramagnetic resonance measurements. PBQ quenching caused the most pronounced suppression of IMI removal, indicating an important role of O2·-, whereas the characteristic TEMP-1O2 signal confirmed the involvement of a 1O2-associated non-radical pathway. DFT calculations further showed that the selected reaction pathways of O2·-, 1O2, SO4·-, and ·OH toward IMI exhibited different intrinsic energy barriers. Collectively, these results support the important involvement of O2·--mediated oxidation and 1O2-associated non-radical processes in IMI transformation under the investigated conditions. The catalyst achieved 91% IMI removal within 160 min and retained >96% of its initial activity after 30 days of air exposure. These findings provide a practical interfacial regulation strategy for designing carbon-supported iron catalysts with improved stability and enhanced PDS activation performance for persulfate-based water purification.