A study on gold nanoparticle synthesis using oleylamine as both reducing agent and protecting ligand

The growth kinetics and mechanism of a gold nanoparticle synthesis using water as a single phase solvent and oleylamine as both reducing agent and monolayer protection agent were studied. FT-IR and H-1 NMR spectroscopic analysis revealed a conversion of oleylamine ligands to oleylamides when gold(III) was reduced to gold(I) and gold atoms. During the reaction, it was found by UV-Vis absorption spectroscopy and transmission electron microscopic study that oleylamine ligands formed large complex aggregates with gold salt instantly upon mixing these two agents together. At an elevated temperature of 80 degrees C, the complex decomposed first into very small particles and then the small particles recombined together into larger and thermally stable particles with an average core size around 9-10 nm. The oleylamide ligands formed a protecting monolayer around the nanoparticles through a hydrogen bonding network between the amide groups. The recombination of small particles into larger ones was found to follow a logistic model, as confirmed by a nonlinear regression fitting of the UV-Vis absorption data of the reaction solution with the mathematical model.