Mechanochemical (MC) destruction of pollutants is effective; however, the emerging electron transfer mechanism is ambiguous owing to a lack of systematic evaluation. Therefore, this study aims to evaluate the contribution of electrons to perfluorooctanoic acid (PFOA) defluorination during MC process. A synergistic effect was obtained by activating BaTiO 3 to generate piezoelectrons and applying zero-valence aluminum (ZVAl) to facilitate electron transfer, with 95.66% PFOA defluorination and reaction time decreasing from 6 h to 3 h. The mechanism of piezoelectric catalysis of the BaTiO 3 /ZVAl system was further investigated through kinetic analyses and intersystem comparisons. The major contribution of piezo-excited electrons was revealed through probe detection and quantitative determination. A positive correlation between electron generation and PFOA defluorination was ascertained, and the calculation of the electron utilization ratio revealed an electron transfer mechanism. The detached fluorides were confirmed to be bonded directly to the additives. Furthermore, PFOA decomposition was identified as a cyclical process with constant dissociation of the CF 2 groups.
Hexabromocyclododecane (HBCD) is one of the priority persistent organic pollutants (POPs), yet a cost-effective technology has been lacking for the removal and degradation of HBCD. Zero-valent aluminum (ZVAl) is an excellent electron donor. However, the inert and hydrophilic surface oxide layer impedes the release of the electrons from the core metallic Al, resulting in poor reactivity towards HBCD. In this research, a new type of modified mZVAl particles (AC@mZVAl bm/NaCl ) were prepared through ball milling mZVAl in the presence of activated carbon (AC) and NaCl, and tested for adsorption and reductive degradation of HBCD in water. AC@mZVAl bm/NaCl was characterized with a metallic Al core with newly created reactive surface coated with a thin layer of crushed carbon nanoparticles . AC@mZVAl bm/NaCl was able to rapidly (within 1 h) adsorb HBCD (C 0 = 2 mg L −1 ) and thus effectively enriched HBCD on the carbon surface of AC@mZVAl bm/NaCl . The pre-enriched HBCD was subsequently degraded by the electrons from the core Al, and ∼63.44% of the pre-sorbed HBCD was completely debrominated after 62 h of the contact. A notable time lag (∼12 h) from the onset of the adsorption to the debromination was observed, signifying the importance of the solid-phase mass transfer from the initially adsorbed AC particles to the reactive Al-AC interface. Overall, AC@mZVAl bm/NaCl synergizes the adsorptive properties of AC and the high reactivity of metallic Al, and enables a novel two-step adsorption and reductive degradation process for treating HBCD or likely other POPs.
Yang Liu,Xiaowen Zhang,Fashuai Yang,Cuili Xing,Peng Fan,Yuankui Sun,Xiaohong Guan
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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