Fine structure of gold nanoparticles stabilized by buthyldithiol: Species identified by Mössbauer spectroscopy

Stabilized gold nanoparticles (Au NPs) were prepared with 4:2.6 Au to buthyldithiol stoichiometry using modified Brust synthesis. The size of the particles falls into the 1.3-4 nm range in which the molecular cluster - metallic particle transition takes place. Stabilized particles were characterized by transmission electron microscopy (TEM/HRTEM). Moreover, numerous spectroscopic techniques like UV-vis, infrared (FTIR), X-ray diffraction (XRD), Raman, photoacoustic and Mossbauer spectroscopies were also used for detailed structural identification of the functionalized Au NPs. The presence of Ausingle bond S bonds was proven by FTIR and Raman spectra. It was found that the distribution of covering thiol layer is uneven, therefore the presence of uncovered surface gold atoms can be assumed at the applied stoichiometry. In good coincidence, four types of gold species could be identified in the corresponding Mossbauer spectrum. They can be attributed to metallic gold in the core, to bare gold in the surface layer, to surface gold atoms attached to thiol, and finally, to gold atoms pulled out from the particle, located in Ssingle bond Ausingle bond S bridges.