The interaction of water with solid surfaces: Fundamental aspects

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis

We developed a simple chemical method to obtain bulk quantities of N-doped, reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia. X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various reaction temperatures reveals that N-doping occurs at a temperature as low as 300 °C, while the highest doping level of ∼5% N is achieved at 500 °C. N-doping is accompanied by the reduction of GO with decreases in oxygen levels from ∼28% in as-made GO down to ∼2% in 1100 °C NH3 reacted GO. XPS analysis of the N binding configurations of doped GO finds pyridinic N in the doped samples, with increased quaternary N (N that replaced the carbon atoms in the graphene plane) in GO annealed at higher temperatures (≥900 °C). Oxygen groups in GO were found responsible for reactions with NH3 and C−N bond formation. Prereduced GO with fewer oxygen groups by thermal annealing in H2 exhibits greatly reduced reactivity with NH3 and a lower N-doping level. Electrical measurements of individua...

Simultaneous Nitrogen Doping and Reduction of Graphene Oxide

Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen- and oxygen-containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H2SO4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X-ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea- and melamine-treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 A. On the other hand, pores between 5 A and 6 A are most effective in a double-layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic-N-oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen. (C)2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

A combination of solid-state 13C NMR, X-ray photoelectron spectroscopy (XPS) and sulfur X-ray absorption near edge structure (S-XANES) techniques are used to characterize organic oxygen, nitrogen, and sulfur species and carbon chemical/structural features in kerogens. The kerogens studied represent a wide range of organic matter types and maturities. A van Krevelen plot based on elemental H/C data and XPS derived O/C data shows the well established pattern for type I, type II, and type III kerogens. The anticipated relationship between the Rock−Eval hydrogen index and H/C is independent of organic matter type. Carbon structural and lattice parameters are derived from solid-state 13C NMR analysis. As expected, the amount of aromatic carbon, measured by both 13C NMR and XPS, increases with decreasing H/C. The correlation between aromatic carbon and Rock−Eval Tmax, an indicator of maturity, is linear for types II and IIIC kerogens, but each organic matter type follows a different relationship. The average al...

Direct characterization of kerogen by x-ray and solid-state **13c nuclear magnetic resonance methods

X-ray photoelectron spectroscopy (XPS) was used to identify and quantify the organically bound nitrogen forms present in fresh Argonne Premium coals. XPS spectra obtained on a wide variety of model compounds were used to establish a curve resolution methodology. Pyrrolic nitrogen is the moat abundant form of organically bound nitrogen, followed by pyridinic types. Quaternary nitrogen species were also identified. An analysis of the sensitivity of XPS for primary amines indicates that these species are not detected at concentrations above 5 mol %. A trend of decreasing level of quaternary nitrogen forms along with increasing levels of pyridinic nitrogen was observed with increasing coal rank. The formation and reactivity of quaternary nitrogen forms in several coals were examined

Quantification of nitrogen forms in Argonne Premium coals

Direct determination and quantification of sulphur forms in heavy petroleum and coals: 1. The X-ray photoelectron spectroscopy (XPS) approach

The present work explores the potential of Raman spectroscopy to provide maturity information about catagenesis stage kerogens and coals. The first-order Raman spectra of coals and kerogens show a broad amorphous A band between 1310 and 1360 cm-1 and a graphite-like G band near 1580−1600 cm-1. As vitrinite reflectance (R0) increases, the Raman A band becomes narrower and shifts to lower frequencies while the absorption strength of the A band relative to the G band decreases. The area ratio of the A band to G band (R = fA/fG) decreases from 3.2 to 2.4 in going from the least mature sample up to R0 = 2.0%. Similar trends were observed for maturation suites of Type II and other Type III kerogens. Laboratory thermolysis produced a range of samples with well-defined laboratory R0. The changes in the Raman A and G bands from the laboratory matured samples directionally paralled the natural samples. These results demonstrate that the Raman spectra of catagenesis stage samples vary in regular ways with sample mat...

Maturity trends in Raman spectra from kerogen and coal

A combination of XPS and solid-state 15N NMR have been used to characterize the nitrogen forms in a variety of different carbonaceous samples having high natural nitrogen abundance. It is currently difficult to unequivocally interpret and quantify individual 15N NMR and XPS spectra. The advantages of using a multiple technique approach for nitrogen speciation as well as the limitation of XPS nitrogen (1s) and 15N NMR spectroscopy are discussed. XPS and 15N NMR results show that pyridinic and pyrrolic nitrogen are present in quinoline and isoquinoline pyrolysis chars. Pyridinic nitrogen is the most abundant form in quinoline pitch while isoquinoline pitch produced the most pyrrolic nitrogen. A small amount of quaternary nitrogen (∼10 mol %) appeared in the XPS spectrum of the chars, however, no additional nitrogen forms were identified above the noise level in the 15N NMR spectra. The 15N NMR spectrum of Green River kerogen shows a single broad feature centered around −245 ppm in the 15N NMR, consistent wi...

Simon R. Kelemen

Papers

Direct characterization of kerogen by x-ray and solid-state **13c nuclear magnetic resonance methods

Quantification of nitrogen forms in Argonne Premium coals

Direct determination and quantification of sulphur forms in heavy petroleum and coals: 1. The X-ray photoelectron spectroscopy (XPS) approach

Maturity trends in Raman spectra from kerogen and coal

XPS and 15N NMR study of nitrogen forms in carbonaceous solids