Synthesis and characterization of gold nanoparticles for mercury adsorption

Abstract

This research was carried out to synthesize and characterize different sizes and shapes of gold (Au) nanoparticles in order to find the optimum synthesis parameters for maximum mercury adsorption. The different sizes and shapes of Au nanoparticles were prepared using microwave (MW) polyol method. By using different polyvinylpyrrolidone (PVP) concentrations (1.9-33.3 mM), different concentration of sodium chloride (NaCl) (10-30 mM) and different amount of [Au]1/[Au]0 molar ratio (1-9), different sizes and shapes of Au nanoparticles were obtained. The Au nanoparticles were characterized using ultra violet-visible (UVVis) absorption spectroscopy and transmission electron microscopy (TEM). The different sizes and various mixtures of spherical, triangular, cubic, hexagonal, octahedral, decahedral, icosahedral and one-dimension (1-D) particles were obtained using those methods. Mercury adsorption was determined based on different sizes and shapes of Au nanoparticles and measured using atomic absorption spectrophotometer (AAS). The optimum PVP concentration is 22.2 mM for 92 % spherical particles of a size in range less than 10 nm. It was found that, using 11.1 mM of PVP solution, the sizes and shapes can be further reduced in the presence of chloride ions. It was also found that, 20 mM of NaCl is sufficient to produce stable Au nanoparticles with most of the particles are spherical in which 97 % of particles diameter is less than 10 nm. The different of [Au]1/[Au]0 molar ratio led to the high yield of polygonal nanoparticles and the size is increase with increasing [Au]1/[Au]0 molar ratio. However, the optimum values of [Au]1/[Au]0 molar ratio cannot be determined because the sizes and shapes are irregular. High mercury adsorption was obtained for spherical nanoparticles (263.18 mg/g) with 99 % particles size less than 10 nm. The defect on spherical nanoparticles surface contributes to high mercury adsorption. In addition, smaller sizes of Au nanoparticles increase the total surface area available for mercury adsorption. It was found that the formation of sizes and shapes of Au nanoparticles was depend on parameters such as the concentration of PVP, NaCl, as well as [Au]1/[Au]0 molar ratio, and thus affects the mercury adsorption.