Mechanistic insight into the bifurcated pH-dependent decontamination trends in zero-valent aluminum systems
Zero-valent aluminum (ZVAl) shows promise for environmental remediation, yet its decontamination performance under circumneutral conditions remains debated. To unravel this paradox, we employed Se(IV) and nitrate (NO 3 − ) as model pollutants to probe how contaminant-specific modulation of Al 2 O 3 transformation dictates ZVAl performance across pH 0 2.0–11.0. Results revealed that Se(IV) sequestration exhibited U-shaped kinetics with minimum efficiency at pH 0 4.0–7.0 (5.8–14.2 %), whereas NO 3 − reduction displayed an inverted U-shaped trend with maximum efficiency (> 95 %) obtained in the same pH range. Mechanistic studies demonstrated that these contrasting trends originate from pollutant-mediated Al 2 O 3 evolution. Specifically, Lewis-basicity-dependent competition for Al 2 O 3 surface sites dictates whether hydration or dissolution dominates activation. Se(IV), acting as a strong Lewis base, inhibited Al 2 O 3 hydration by competing with OH − for Al 2 O 3 surface sites and/or forming passivating Al-O-SeO 3 2− complexes , thereby self-limiting its own removal. Conversely, NO 3 − with weak Lewis basicity negligibly affected Al 2 O 3 hydration to form porous Al(OH) 3 , which can enhance electron transfer by reducing interfacial charge transfer resistance. This work resolves the long-standing pH limitation paradox in ZVAl systems by elucidating the role of Al 2 O 3 evolution, thereby offering a mechanistic framework for the design of adaptive metal-based remediation technologies.
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