Preparation of gold nanoparticles from jewelry industry wastewater by amido-amidoxime functionalized silica

Abstract

Silica gel was initially modified with 3-aminopropyltriethoxysilane and methylcyanoacetate and then reduced with hydroxylamine, yielding amido-amidoxime silica (Ami-SiO₂). The Ami-SiO2 was characterized by ¹³C-NMR, elemental analysis, FT-IR, and TGA techniques. A reducing capacity of 1.6±0.1 mEq / g Ami-SiO₂ was found by titration with KMnO₄. Various parameters affecting gold nanoparticle formation such as pH, concentration of gold ion, contact time, co ion were optimized. Residual gold in solution was determined by flame atomic absorption spectrometry. The characterization of gold nanoparticles were carried out by X-ray diffractometry, X-ray fluorescence spectrometry, Diffuse-reflectance ultraviolet visible spectrometry and the average particle size of gold nanoparticles of 37±6 nm was estimated by transmission electron microscopy. The [AuCl₄]- solution was best reduced at pH 3.0. The maximum capacity of reduction was 39±0.1 mg / g Ami-SiO₂. The preparation of gold nanoparticles was not affected by Ag+, Cu²+, Ni²+ and Zn²+. The [Au(CN)₄]- was not reduced into gold nanoparticles by the modified silica. The optimized conditions were applied for preparation of gold nanoparticles from jewelry industry wastewater.