Polyethylenimine modified potassium tungsten oxide adsorbent for highly efficient Ag+ removal and valuable Ag0 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 8.74   wt% 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 (48.25   mg/g) than the raw K 2 W 4 O 13 (42.50   mg/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 72.5   mg/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.