Sulfur surface chemistry

In this section, the surface chemistry of non-metals adsorbed as thin layers, films or SAMs on gold surfaces is discussed. Although attachment by a sulfur atom is by far the most predominant binding motif, many other elements may be used to bind to gold. Particular focus is given here to surface binding through atoms other than those already extensively covered in the literature. 

If you move left one column in the periodic table from the halides, the chalcogenides need two electrons to complete their valence shell, and thus can bond to the surface and each other simultaneously. This appears to account for much of the interesting surface chemistry of chalcogenide atomic layers. Chalcogenides, including oxides (corrosion), are some of the most studied systems in surface chemistry. The oxides are clearly the most important, but significant amounts of work have been done with sulfur, selenium and tellurium. 

XANES spectra measured the surface chemistry and the TEY probe indicated that sulfur for all concentrations was in the sulfide form. 

In the absence of mechanical activation, the XPS spectrum is different from that obtained in the presence of mechanical activation. Thus, sulfur compounds that are formed on the surface (162 eV) appear in the spectra that are not present in the spectra for static immersion. Cutting produces a change in the surface chemistry and the reaction product formed appears to be similar to that obtained by mechanical activation. Thus, mechanical activity plus increased surface temperatures on a solid surface tend to promote surface chemical reactions. A lubricant interacting with metal oxide can produce entirely different reaction products from that of a lubricant interacting with rubbing metal surfaces. 

Mechanical activity at the surface such as load, speed, and variations in surface energetics, play a role in surface chemistry. For example, if a clean metal surface is exposed to materials such as oxygen, chlorine, and sulfur, an interaction goes on. There is no activation energy necessary to achieve the reaction of the species with the metal surface to form surface compounds. 

Stark, J. V., Park, D. G., Lagadic, I. and Klabunde, K. J. Nanoscale metal oxide particles/ clusters as chemical reagents. Unique surface chemistry on magnesium oxide as shown by enhanced adsorption of acid gases (sulfur dioxide and carbon dioxide) and pressure dependence, Chem. Mater., 1996, 8, 1904-1912. 

Stark JV, Park DG, Lagadic I, Klabunde KJ (1996) Nanoscale Metal Oxide Particles/Clusters as Chemical Reagents. Unique Surface Chemistry on Magnesium Oxide As Shown by Enhanced Adsorption of Acid Gases (Sulfur Dioxide and Carbon Dioxide) and Pressure Dependence, Chem Mater 8 1904-1912... 

The benzene surface chemistry was not qualitatively altered by the presence of carbon or sulfur impurities (up to V0.2-0.3... 

Extensive efforts have been made to characterize the surface chemistry of carbon blacks. Although carbon blacks are nearly all carbon, impurities of oxygen, sulfur, nitrogen and small amounts of other elements are present. Most of the work has centered around the identification and quantification of oxygen containing... 

Another interesting observation is almost identical behavior of samples exposed for SOj adsorption. Regardless the carbonization temperature the same amounts of SO, are adsorbed on the samples exhausted in the HjS breakthrough test. This suggests that after exhaustion of all active centers responsible for HjS adsorption the differences in surface chemistry, which play a role in sulfur dioxide adsorption/oxidation on fresh surfaces, seem to be somehow screened by HjS adsorption products. Nevertheless, it is interesting that still some capacity exists. 

Results presented in this paper show that differences in the chemical composition of sewage sludge derived adsorbents lead to differences in their performance as adsorbents of acidic gases. It has been demonstrated that however some adsorption centers can be common for both gases, there are surface features on the sample pyrolized at 950 C which favor oxidation of hydrogen sulfide to elemental sulfur. This is likely due to the catalytic action of the iron species. When adsorption of SOj takes part calcium species play a crucial role. Surface chemistry has also its effect on the physical form of sulfur deposited on the surface. It is either rhombic or monoclinic depending on the pyrolysis temperature and chemical changes imposed by heat treatment. 

While the effect of cation impurities on the surface chemistry of MgO has been investigated in detail, very little is known about anion substitution. Defect formation and excitation energies for S and Se -doped bulk MgO have been calculated [182,183] but there are no data for the surface. In the bulk it has been estimated that the presence of S or Se impurities result in a outward relaxation of the Mg neighbors of 6% and 8%, respectively [182]. A recent report of the 0 "-S exchange reaction on MgO has been reported [184]. The reaction involves adsorption of CS2 on MgO powders and the subsequent exchange reaction with formation of COS and of S ions probably located at the low coordinated sites. It has been found that the basicity of the MgO surface doped with sulfur ions is drastically modified with respect to that of pure MgO [184]. 

The high temperatures and pressures drive chemical reactions of CO2, SO2, OCS, H2S, HCl, and HF with rocks and minerals on Venus surface. A possible exception is sulfur vapor chemistry initiated by absorption of blue sunlight. After the Mariner 2 flyby Mueller (1963) wrote that Venus surface temperature corresponds with those [temperatures] attained during moderately high degrees of metamorphism on Earth. It is... 

Sulfur and sulfur compounds and their relationship to volcanic silicate rocks are at the heart of lo s surface chemistry. The satellite s low ultraviolet albedo combined with high visible and near-infrared reflectance suggested elemental sulfur to a number of researchers studying telescopic spectra (Wamsteker, 1973 Wamsteker et al., 1974), although laboratory measurements of pure sulfur differ somewhat from lo s average color. The presence of sulfur ions detected in Jupiter s magnetosphere near lo (Kupo et al., 1976) also pointed toward an lo source of sulfur. 

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