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 ∼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 N/L 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.

Research highlights
► nZVI was controllably immobilized within two polymeric hosts.
► Host surface chemistry greatly affects nZVI size and efficiency.
► Chloride and sulfate impose considerably effect on both hybrids for nitrate reduction.
► Effect of host surface chemistry should be considered for fabrication of similar nanocomposites.