Polyethylenimine modified potassium tungsten oxide adsorbent for highly efficient Ag + removal and valuable Ag 0 recovery.

Elemental Ag ⁰ is well known for its remarkable catalytic and antibacterial properties, thus the regeneration of valuable Ag ⁰ metal from Ag ⁺ wastewater is of great significance. In this study, a novel polyethylenimine (PEI) modified potassium tungsten oxide (N-K ₂ W ₄ O ₁₃ ) adsorbent was prepared for Ag ⁺ removal and reduction to Ag ⁰ using glutaraldehyde as crosslinking agent. XPS and FT-IR spectra verified PEI successfully anchored on the surface O and W atoms of K ₂ W ₄ O ₁₃ through aldehyde bridges. The content of PEI in N-K ₂ W ₄ O ₁₃ was calculated as 8.74wt% by TG curve. A heterogeneous PEI coating was observed in the SEM and TEM images. The N-K ₂ W ₄ O ₁₃ exhibited larger Ag ⁺ uptake (48.25mg/g) than the raw K ₂ W ₄ O ₁₃ (42.50mg/g) though required a longer equilibrium time. This was due to the combined results of strong chelation and weak electrostatic repulsion that meanwhile occurring on the positive-charged surface of N-K ₂ W ₄ O ₁₃ . The maximum Ag ⁺ uptake on N-K ₂ W ₄ O ₁₃ was 72.5mg/g, which was larger than many of the reported adsorbents. Furthermore, the prepared N-K ₂ W ₄ O ₁₃ displayed good anti-interference toward background ions (Na ⁺ , K ⁺ ) and hold a stable Ag ⁺ removal (>95%) after five runs of recycling tests. The mechanism studies elucidated that NH/N groups from the PEI modified N-K ₂ W ₄ O ₁₃ mainly accounted for the Ag ⁺ adsorption and Ag ⁰ recovery in the adsorption-reduction process. Ion-exchange between Ag ⁺ and K ⁺ from the N-K ₂ W ₄ O ₁₃ lattice also occurred. This work provided a facile method to synthesize a promising adsorbent for Ag ⁺ wastewater remediation and valuable Ag ⁰ recovery.
(Copyright © 2019. Published by Elsevier B.V.)