Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis

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.

Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3N4

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

The characterization of activated carbons with oxygen and nitrogen surface groups

Roles of water for chemical reactions in high-temperature water

Thiophenes are the simplest aromatic sulfur-containing compounds and are stable and widespread in fossil fuels. Regulation of sulfur levels in fuels and emissions has become and continues to be ever more stringent as part of governments’ efforts to address negative environmental impacts of sulfur dioxide. In turn, more effective removal methods are continually being sought. In a chemical sense, thiophenes are somewhat obdurate and hence their removal from fossil fuels poses problems for the industrial chemist. Sulfur K-edge X-ray absorption spectroscopy provides key information on thiophenic components in fuels. Here we present a systematic study of the spectroscopic sensitivity to chemical modifications of the thiophene system. We conclude that while the utility of sulfur K-edge X-ray absorption spectra in understanding the chemical composition of sulfur-containing fossil fuels has already been demonstrated, care must be exercised in interpreting these spectra because the assumption of an invariant spect...

https://pubs.acs.org/doi/pdf/10.1021/jp505766f

Long-range chemical sensitivity in the sulfur K-edge X-ray absorption spectra of substituted thiophenes.

A bituminous coal, Illinois No. 6, has been treated under Friedel--Crafts alkylation conditions, some as mild as 0 to 5/sup 0/C and atmospheric pressure. The tools of mass spectroscopy and classical analytical techniques were employed to confirm unequivocally that the coal was alkylated. The alkylated product has both a higher hydrogen content and higher solubility in benzene and pyridine than the untreated coal. This work demonstrates that coal is very much more reactive than is conventionally believed. 5 tables.

Friedel-crafts isopropylation of a bituminous coal under remarkably mild conditions

Disclosed in this invention are novel road paving binder compositions and the method of making same. The compositions are made by combining an asphalt that contains sulfonate or sulfonic acid groups, a polymer preferably of butyl rubbers, styrene-butadiene linear diblock polymer, styrene-butadiene-styrene linear or radial triblock polymer and EPDM that has been sulfonated, and mixtures thereof, and a basic neutralizing agent that contains cations having a valence from +1 to +3. The amounts of each are effective to allow formation of one continuous phase or two interdispersed phases that do not segregate on standing at elevated temperatures associated with road paving. The amount of polymer is an amount less than 7 wt. % of total polymer-asphalt composition that is sufficient to produce an asphaltic composition having a viscosity at 135° C. in the range of from about 150 cPs to about 2000 cPs or from about 3000 cPs to about 8000 cPs. The novel road paving asphaltic compositions have improved viscoelasticity, softening point, and storage stability. The compositions can be used as binders in road paving applications.

Martin L. Gorbaty

Papers

Long-range chemical sensitivity in the sulfur K-edge X-ray absorption spectra of substituted thiophenes.

Friedel-crafts isopropylation of a bituminous coal under remarkably mild conditions

Polymer-modified functionalized asphalt compositions and methods of preparation (C-2747)

Stability of adamantane and its derivatives to coal-liquefaction conditions, and its implications toward the organic structure of coal

Evaluation of several methods of extraction of oil from a Jordanian oil shale