Structural control of Au and Au-Pd nanoparticles by selecting capping ligands with varied electronic and steric effects

Weakly interacting ligands including three Gemini surfactants, didodecyldimethylammonium bromide (DDAB), and amines (RNH2, R2NH, and R3N) were used to prepare Au nanoparticles (NPs). Aqueous Au NPs capped with DDAB and Gemini surfactants showed similar sizes (3-4 nm), whereas toluene-based NPs stabilized with DDAB, amines, and their mixtures range from 2.5 to 9.3 nm. Ligand effect on Au-Pd NP structure was also studied with EXAFS. These findings were consistently accounted for by considering the ligand's electronic/steric effects and mixed ligands coadsorption, and suggest useful ways to control NP structure by manipulating the two effects and using mixed capping ligands.