A step ahead towards the green synthesis of monodisperse gold nanoparticles: the use of crude glycerol as a greener and low-cost reducing agent

Abstract

Owing to their widespread application, the preparation of monodisperse gold nanoparticle (AuNPs) by green methods and using low-cost and environment friendly reagents is of great importance. In this study, the formation of nearly monodisperse spherical AuNPs of around 8 nm has been achieved, for the first time, using the as-received crude glycerol (CG) from the biodiesel plant. As a proof of concept, two different crude glycerol samples with different glycerol contents (65% and 73%) and different impurities levels (low and high) and types (organic and inorganic) were employed to prepare AuNPs. No special chemical or physical treatment of CG except simple filtration was carried out. The effect of possible impurities in CG as well as synthesis parameters (pH, glycerol concentration, and stabilizing agent concentration) on the shape and size distribution of AuNPs was studied. The shape and particle size distribution of AuNPs was found to be greatly affected by the concentration of stabilizing agent polyvinylpyrrolidone (PVP) and polydiallyldimethylammonium chloride (PDAC) while the number of particles formed is strongly dependent on pH of the reaction media. Uniformly distributed AuNPs of around 7 ± 1.5 nm were produced under a wide range of glycerol concentration (0.1–0.4 mol L⁻¹) and OH⁻ concentration (0.1–0.4 mol L⁻¹) using 1.0% stabilizing agents concentration. Both PVP and PDAC, besides acting as stabilizing agents, also help in reduction of metal salts in basic media. For comparison, AuNPs were also prepared using commercial glycerol (purity ≥ 99.5%) under identical experimental conditions. AuNPs with similar size and shape were obtained in both cases (commercial pure glycerol as well as CG of varying glycerol content and impurities) indicating that commercial glycerol can be replaced with CG in the AuNPs synthesis and the organic and inorganic impurities do not significantly affect the particle size distribution of prepared AuNPs. This study opens up new possibilities for the environment-friendly preparation of metallic nanoparticles using the low-cost, non-toxic and biodegradable CG as a reducing agent.