Optical, Catalytic and Electrokinetic Properties of Silver Nanoparticles of Different Sizes

Abstract

Silver nanospheres (AgNS) of five different sizes in the range between 10 to 80 nm have been prepared by reduction with sodium borohydride (NaBH4) and sodium citrate (C6H5O7Na3) and by solvothermal process using Polyvinylpyrrolidone (PVP) and dimethylformamide (DMF). These AgNS were characterized by UV-Visible absorption spectra, transmission electron microscopy, Zeta potential (ζ) and diffuse light scattering measurements and studied their comparative catalytic properties. The AgNS prepared by utilizing PVP and DMF are found to be much larger in size ca. ≈ 30-80 nm having red shifted surface plasmon band at 474.6 nm as compared to relatively smaller AgNS sizes ca. ≈13.5 nm (SP band ≈ 392.6 nm) as obtained by reduction with NaBH4 and C6H5O7Na3. The effects of silica (SiO2) and PVP coating and the influences of various solvents on the optical absorption, ζ, conductance and catalytic activity of these AgNS were studied comparatively. The aqueous suspension of SiO2 coated AgNS (SiO2/AgNS) displayed highest zeta potential (-24.6 mV) and conductance (1927 µS) values as compared to the bare AgNS (-5.59 mV and 86 µS) in water dispersion. The catalytic activity of various AgNS depending on its size and coating agents (silica and PVP) is evaluated and compared by the reduction of p-nitrophenol to p-aminophenol. A significant increase (17.5 % to 55 %) in the catalytic activity has been found with decreasing the size (80 nm to 13.5 nm) of AgNS. An optimum amount (10.92 × 1018 atoms) of AgNS is the prerequisite for the reaction to be carried out at a higher pace (with in 36 min).