Nitrate reduction using nanosized zero-valent iron supported by polystyrene resins: Role of surface functional groups

To probe the role of host chemistry in formation and properties of the inside nano-zero valent iron (nZVI), we encapsulated nZVI within porous polystyrene resins functionalized with -CH2Cl and -CH2N+(CH3)(3) respectively and obtained two hybrid nZVIs denoted Cl-S-ZVI and N-S-ZVI. 14.5% (in Fe mass) of nZVI particles were distributed in N-S within a ring-like region (about 0.10 mm in thickness) of size around similar to 5 nm, whereas only 4.0% of nZVI particles were entrapped near the outer surface of Cl-S of size > 20 nm. -CH2N+(CH3)(3) is more favorable than -CH2Cl to inhibit nZVI dissolution into Fe2+ ions under acidic pH (3.0-5.5). 97.2% of nitrate was converted into ammonium when introducing 0.12 g N-S-ZVI into 50 mL 50 mg NIL nitrate solution, while that for Cl-S-ZVI was 79.8% under identical Fe/N molar ratio. Under pH = 2 of the effectiveness of nZVI was 88.8% for nitrate reduction, whereas that for Cl-S-ZVI was only 14.6% under similar conditions. Nitrate reduction by N-S-ZVI exhibits relatively slower kinetics than Cl-S-ZVI, which may be related to different nZVI distribution of both composites. The coexisting chloride and sulfate co-ions are favorable for the reactivity enhancement of N-S-ZVI whereas slightly unfavorable for Cl-S-ZVI. The results demonstrated that support chemistry plays a significant role in formation and reactivity of the encapsulated nZVI, and may shed new light on design and fabrication of hybrid nZVIs for environmental remediation. (C) 2011 Elsevier Ltd. All rights reserved.