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-K2W4O13) 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 K2W4O13 through aldehyde bridges. The content of PEI in N-K2W4O13 was calculated as 8.74 wt% by TG curve. A heterogeneous PEI coating was observed in the SEM and TEM images. The NK2W4O13 exhibited larger Ag - uptake (4825 mg/g) than the raw K2W4O13 (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-K2W4O13. The maximum Ag-0 uptake on NK2W4O13 was 72.5 mg/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 Ag-0 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 Ag-0 recovery. (C) 2019 Elsevier B.V. All rights reserved.