Silver nanoparticles embedded cation-exchange membrane for remediation of Hg species and application as the dip catalyst in organic transformation

Abstract

Silver nanoparticles (Ag NPs) embedded in poly(perfluorosulfonic) acid cation-exchange membrane (Nafion-211) were synthesized by in situ reductions of Ag+ ions by sodium borohydride at room temperature and formamide at 65 °C. The formamide-reduction formed Ag NPs uniformly distributed in the membrane matrix. Therefore, the formamide-reduced Ag NPs embedded membranes were used for the sorption-preconcentration of Mercury (Hg)2+ ions by the galvanic reaction with Ag NPs in the membrane matrix. The replacement of Ag0 in NPs with Hg2+ ions resulted in the formation of Hg0 accumulated as nanodroplets in the membrane matrix as indicated by the field emission scanning electron microscopy studies. The sorption of Hg2+ ions via galvanic reaction in the Nafion membrane was found to be maximum (>93%) from pH = 2.5 to pH = 6.5. The Ag NPs embedded membrane was studied for Hg2+ ions sorption from the aqueous samples by radiotracer (203Hg), spectrophotometry, energy dispersive X-ray fluorescence and cold vapor atomic absorption spectrophotometry. This membrane was successfully applied for the determination and quantification of Hg2+ ions in the real water samples and safe storage of Hg for the remediation objective. The Hg0 embedded membrane was also found to be promising as the dip catalyst in the representative organic transformation of phenylacetylene to acetophenone. The Hg0 embedded membrane dip catalyst was reused in four consecutive cycles under similar conditions and found to be successful by giving an almost similar yield (%) of the product. This demonstrated a possibility of safe application of Hg0 stored in the matrix of poly(perfluorosulfonate) membrane for catalysis.