Surface interaction between Au nanoparticles and surfactants studied by XAFS

X-ray absorption fine structure (XAFS) was used to study the atomic and electronic structure of Au nanoparticles affected by three kinds of surfactants, triphenylphosphine (PPh3), dodecanamine (C12H27N) and dodecanethiol (C12H26S). XAFS and TEM results indicate that the surface interaction intensity between Au nanoparticles and surfactants is in the order of C12H26S, C12H27N and PPh3. The head-group P atom in the PPh3 molecule is weakly bonded Au adatoms of Au nanoparticles, and the resulting nanoparticle size is about 72 nm. However, the head-group N atom in C12H27N and S atom in C12H26S are strongly bonded to Au adatoms, forming Au—N and Au—S covalent bonds, respectively, which effectively inhibits the aggregation of nanoparticles and leads to the smaller size of 31 nm. Furthermore, the bond length of the first nearest Au—Au coordination decreases from 282  for PPh3 capping to 279  for C12H26S capping, along with the decrease of Au—Au coordination number from 113 to 101, indicating the strongest interaction between C12H26S and Au nanoparticles. The XANES results indicate that the significant charge transfer of Au nanoparticles only occurs for the case of C12H26S capping.