Inclusion of silver nanoparticles in host poly(perfluorosulfonic) acid membrane using ionic and non-ionic reductants

Abstract

Silver nanoparticles (Ag nps) in host poly(perfluorosulfonic) acid membrane (Nafion-117) were formed by in situ reduction of the Ag + ions with ionic (sodium borohydride) and non-ionic (dimethyl formamide, and formamide) reagents. Ag + ions were loaded in the membrane samples by the ion-exchange mechanism. Ag + ions were tagged with 110mAg radiotracer to monitor the process of Ag nps formation in the membrane matrix. Transmission electron microscopic analyses of cross-section of the reduced membrane samples were carried out to study the shape, size, and positioning of nps in the membrane. This study revealed that the shape of Ag nps in all the cases was spherical, but size and spatial distributions varied depending upon reducing conditions of the membrane. The bulk concentration of Ag nps having 15 ± 4 nm size was found to be located near the surface of BH 4 − ions reduced membrane sample. In case of slow dimethyl formamide reduction, the non-uniform and bimodal size distribution (5 ± 1 and 18 ± 5 nm) of Ag nps was observed in the membrane matrix. The reduction with formamide at 65 °C was found to produce Ag nps dispersed uniformly in the membrane matrix with narrow size distribution (9 ± 2 nm). EDXRF and radiotracer analyses were carried out to quantify Ag contents of the nanoparticles formed in the reduced membrane samples. The mechanism of formation of Ag nps in the membrane by ionic and non-ionic reductant was interpreted in terms of ion-exchange process operating during the reduction. The self-diffusion coefficients of Na +, Cs +, and Eu 3+ counterions in the Ag nps embedded membrane samples were measured by the isotopic-exchange method. It was observed that the presence of Ag nps enhanced the diffusion mobility of slow moving Cs + and Eu 3+ counterions ions in the membrane matrix by 2 and 5 times, respectively.