Sulfidization of Au(111) from Thioacetic Acid: An Experimental and Theoretical Study

We have studied the adsorption of thioacetic acid (TAAH) on Au(111) from solution deposition. The close proximity of the SH groups to CO groups makes this molecule very attractive for exploring the effect of the functional group on the stability of the S–C and S–Au bonds. Although thioacetic acid was supposed to decompose slowly in water by hydrolysis supplying hydrogen sulfide, this behavior is not expected in nonpolar solvents such as toluene or hexane. Therefore, we have used these solvents for TAAH self-assembly on the Au(111) surface. The characterization of the adsorbates has been done by electrochemical techniques, X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). We have found that even in nonpolar solvents thioacetic acid decomposes to S. The results have been discussed on the basis that the adsorbed species suffer a cleavage on the Au surface, leaving the S attached to it. The dissociation is a spontaneous process that reaches the final state very fast once it is energetically favorable, as can be interpreted from DFT calculations. The thioacetic acid adsorption reveals the strong effect that produces a functional group and the key role of the S–H bond cleavage in the self-assembly process

New Insights into the Chemistry of Thiolate-Protected Palladium Nanoparticles

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand place-exchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV–visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method