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 (PPh₃), dodecanamine (C₁₂H₂₇N) and dodecanethiol (C₁₂H₂₆S). XAFS and TEM results indicate that the surface interaction intensity between Au nanoparticles and surfactants is in the order of C₁₂H₂₆S, C₁₂ H₂₇ N and PPh₃. The head-group P atom in the PPh₃ 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 C₁₂H₂₇N and S atom in C₁₂H₂₆S 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 Å for PPh₃ capping to 2. 79 Å for C₁₂H₂₆S capping, along with the decrease of Au-Au coordination number from 11. 3 to 10. 1, indicating the strongest interaction between C₁₂H₂₆S and Au nanoparticles. The XANES results indicate that the significant charge transfer of Au nanoparticles only occurs for the case of C₁₂H₂₆S capping.