X-ray and optical characterization of the intermediate products in the Au3+ reduction process by oleylamine.

Formation of gold nanoparticles (NPs) from the mixture containing NaAuCl 4 as a precursor, octadecene as a solvent and oleylamine as a reducing agent was studied in situ by means of optical and X-ray spectroscopies. Dynamic light scattering (DLS) revealed the presence of initial aggregates of 500 nm average size which split into nanoparticles of about 8 nm width shortly after the reduction from Au3+ to Au+ has been completed. Based on Density Functional Theory (DFT) simulations and analysis of X-ray absorption spectra (XAS) we identified the structure of Au3+ and Au+ gold complexes. Quantitative analysis shows that Au NPs formation proceeds in following steps: substitution of chlorine ligands in Au3+ complex by four oleylamines; reduction of Au3+ to Au+ coordinated by two oleylamines. Latter process occurs in oleylamine micelles in octadecene. The third step is a fragmentation of large micelles into smaller ones shortly after reduction Au3+ to Au+, and subsequent slow growth of Au NPs via reduction of Au+ to Au0. • Initial agglomerates are split into small 8 nm particles during the reduction of Au. • Au(III) complex is coordinated by four N located at 2.04 Å. • Au(I) complex is coordinated by two N atoms at 2.05 Å. • No Cl atoms are present in the first coordination of Au at all stages of nanoparticle formation. [ABSTRACT FROM AUTHOR]