One-pot ligand-free synthesis of gold nanoparticles: The role of glycerol as reducing-cum-stabilizing agent

The synthesis of gold nanoparticles (AuNPs), especially by green methods, has attracted great attention due to their unique size-dependent optical properties, biocompatibility and diverse applications in various fields. The formation of stable AuNPs with control of size and shape often requires the use of a surfactant or some surface stabilizing ligands. Unfortunately, these stabilizing agents may hinder the catalytic activity and adversely affect the biocompatibility of the surfactant/AuNPs assembly. In this article, we report a one-pot, green synthesis of ligand-free AuNPs employing the eco-friendly glycerol both as reducing agent and stabilizing agent, thereby, greatly simplifying the synthesis process. The effect of glycerol:water (G:W) ratio, pH, temperature, dilution, ionic strength and aging on the stability and particle size distribution was studied. Stable AuNPs with reasonably good size distribution (8 +/- 2 nm) were obtained which, at room temperature, showed no significant agglomeration or size change up to 04 days and only slight changes were seen after 08 days. The stability and size distribution of the particles was found to be dependent on the G:W ratio, temperature and pH of the reaction media. Owing to their clean surface, the synthesized ligand-free AuNPs exhibit advantage of lower energy requirement for glycerol electro-oxidation when compared to bulk Au and AuNPs-PVP materials. Such surfactant-free biocompatible AuNPs prepared using the eco-friendly glycerol may find useful applications in catalysis and biomedical applications.