Sulfur K-edge x-ray absorption spectroscopy of petroleum asphaltenes and model compounds
26 Apr 1989-Journal of the American Chemical Society (American Chemical Society)-Vol. 111, Iss: 9, pp 3182-3186
TL;DR: In this article, the utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated and the results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
Abstract: The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra were obtained for a selected group of model compounds and for several petroleum asphaltene samples. For the model compounds the sulfur XANES was found to vary widely from compound to compound and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfidic and thiophenic model compounds and allowed approximate quantification of the amount of each component in the mixtures and in the asphaltene samples. These results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
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TL;DR: The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and the excellent photoreactivity of C(3)N(4-x)S(x), which may shed light on general doping strategies for designing potentially efficient photocatalysts.
Abstract: Electronic structure intrinsically controls the light absorbance, redox potential, charge-carrier mobility, and consequently, photoreactivity of semiconductor photocatalysts. The conventional approach of modifying the electronic structure of a semiconductor photocatalyst for a wider absorption range by anion doping operates at the cost of reduced redox potentials and/or charge-carrier mobility, so that its photoreactivity is usually limited and some important reactions may not occur at all. Here, we report sulfur-doped graphitic C(3)N(4) (C(3)N(4-x)S(x)) with a unique electronic structure that displays an increased valence bandwidth in combination with an elevated conduction band minimum and a slightly reduced absorbance. The C(3)N(4-x)S(x) shows a photoreactivity of H(2) evolution 7.2 and 8.0 times higher than C(3)N(4) under lambda > 300 and 420 nm, respectively. More strikingly, the complete oxidation process of phenol under lambda > 400 nm can occur for sulfur-doped C(3)N(4), which is impossible for C(3)N(4) even under lambda > 300 nm. The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of C(3)N(4-x)S(x). The results acquired may shed light on general doping strategies for designing potentially efficient photocatalysts.
1,762 citations
TL;DR: Asphaltenes, the most aromatic components of crude oil, are critical to all aspects of petroleum use, including production, transportation, refining, upgrading, and heavy-end use in paving and coating materials as mentioned in this paper.
Abstract: Asphaltenes, the most aromatic of the heaviest components of crude oil, are critical to all aspects of petroleum use, including production, transportation, refining, upgrading, and heavy-end use in paving and coating materials. As such, efficiency in these diverse disciplines mandates proper chemical accounting of structure−function relations of crude oils and asphaltenes, the vision of petroleomics (Asphaltenes, Heavy Oils and Petroleomics; Mullins, O. C., Sheu, E. Y., Hammami, A., Marshall, A. G., Eds.; Springer: New York, 2007). Indeed, the molecular characterization of asphaltenes is required as well as the detailed understanding of the hierarchical colloidal structures of asphaltenes and petroleum. With great prescience, Professor Teh Fu Yen and co-workers proposed a hierarchical model of asphaltenes to account for many of their characteristics known at that time (Dickie, J. P.; Yen, T. F. Macrostrucutres of asphaltic fractions by various instrumental methods. Anal. Chem. 1967, 39, 1847−1852). This m...
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TL;DR: In this article, the authors review applications of the near-edge X-ray absorption fine structure (NEXAFS) technique in the investigations of electronic and structural properties of transition metal compounds.
518 citations
TL;DR: The rotational correlation times of individual asphaltene molecules have been determined using fluorescence depolarization techniques, addressing an active, long-standing controversy as discussed by the authors, using simple...
Abstract: The rotational correlation times of individual asphaltene molecules have been determined using fluorescence depolarization techniques, addressing an active, long-standing controversy. Using simple ...
499 citations
TL;DR: A review of the developments of the 1980s in the characterisation of organically-bound sulphur in the geosphere and summarises the geochemical significance of the results obtained by these studies can be found in this paper.
487 citations