Polyethylenimine modified potassium tungsten oxide adsorbent for highly efficient Ag⁺ removal and valuable Ag⁰...

Elemental Ag⁰ is well known for its remarkable catalytic and antibacterial properties, thus the regeneration of valuable Ag⁰ metal from Ag⁺ wastewater is of great significance. In this study, a novel polyethylenimine (PEI) modified potassium tungsten oxide (N-K₂W₄O₁₃) adsorbent was prepared for Ag⁺ removal and reduction to Ag⁰ using glutaraldehyde as crosslinking agent. XPS and FT-IR spectra verified PEI successfully anchored on the surface O and W atoms of K₂W₄O₁₃ through aldehyde bridges. The content of PEI in N-K₂W₄O₁₃ was calculated as 8.74wt% by TG curve. A heterogeneous PEI coating was observed in the SEM and TEM images. The N-K₂W₄O₁₃ exhibited larger Ag⁺ uptake (48.25mg/g) than the raw K₂W₄O₁₃ (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-K₂W₄O₁₃. The maximum Ag⁺ uptake on N-K₂W₄O₁₃ was 72.5mg/g, which was larger than many of the reported adsorbents. Furthermore, the prepared N-K₂W₄O₁₃ 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-K₂W₄O₁₃ mainly accounted for the Ag⁺ adsorption and Ag⁰ recovery in the adsorption-reduction process. Ion-exchange between Ag⁺ and K⁺ from the N-K₂W₄O₁₃ lattice also occurred. This work provided a facile method to synthesize a promising adsorbent for Ag⁺ wastewater remediation and valuable Ag⁰ recovery.