Macroporous alginate substrate-bound growth of Fe0 nanoparticles with high redox activities for nitrate removal from aqueous solutions

• Macroporous alginate substrate (MAS)-supported Fe0 NPs were newly synthesized.
• Fe0 NPs were covalently immobilized on the MAS via a reductive growth method.
• Enhanced nitrate removal was achieved by agglomeration-prevention of Fe0 NPs/MAS.
• A synergistic effect of Fe0 NPs/MAS on nitrate removal was observed.

The agglomeration of zero-valent iron nanoparticles (Fe0 NPs) can significantly decrease the effective surface area of nanoparticles and thus reduce their catalytic performance. To avoid such agglomeration, a two-part Fe0 NP-immobilization approach was developed: (1) The fabrication of a macroporous alginate substrate (MAS) that provided a large surface area capable of sustaining a high load of stable and well-dispersed Fe0 NPs (26.06 wt.%). (2) A facile chemical reductive growth procedure to generate Fe0 NPs (ca. 50–100 nm) that are covalently anchored to the surface of the MAS. The macroporous alginate substrate-supported Fe0 nanoparticles (Fe0 NPs/MAS) removed >96.5% of nitrates from an aqueous solution within 30 min, whereas unsupported Fe0 NPs removed only 44.7% of nitrates over a longer period of time. These results demonstrate that MAS acts in a way to prevent the agglomeration of Fe0 NPs and, in turn, to promote their redox activity compared to unsupported Fe0 NPs. On the basis of our experimental results, a grow mechanism of Fe0 NPs on the MAS was proposed, and potential implications for environmental applications of Fe0 NPs/MAS were discussed.

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