Influence of Different Reducing Agents on the Ag Nanostructures and Their Electrokinetic and Catalytic Properties

This paper shows the impact of various reducing agents; sodium borohydride, trisodium citrate and polyvinyl pyrollidone (PVP) on the surface morphology of Ag nanoparticles (AgNPs). The AgNPs prepared by PVP are found to be much larger in size ca. ≈ 40-70 nm having red shifted surface plasmon band (SPR band) at 475 nm as compared to relatively smaller size ≈ 10-14 nm (SPR band ≈ 392 nm) prepared by reduction with sodium borohydride as confirmed by both TEM and DLS analysis. PVP act as a shape-control agent and results in well defined bipyramid shaped particles while sodium borohydride and trisodium citrate yields spherical, oval and polygonal morphologies. The measured zeta potential of AgNPs prepared by sodium citrate (-28.9 mV), sodium borohydride (-20.0 mV) and PVP (-6.0 mV) is notably decreased with geometric faces. Both co-catalytic and catalytic properties of various Ag nanostructures were evaluated for the photo oxidation of benzoic acid by AgNPs-TiO2 mixture, and for the reduction of p-nitrophenol to p-aminophenol, respectively. A significant increase in the catalytic (17 to 55%) and co-catalytic activity (20 to 50%) was found with decreasing size (50 to 12 nm) and increasing the surface to volume ratio (0.096 to 0.48 nm(-1)) of obtained AgNPs of different surface structure.