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

X-ray photoelectron spectroscopy (XPS) has been used in the study of the surface composition of iron and inorganic sulfur forms in coals from the Argonne Premium Sample Program. The concentration of iron at the coal surface can be very different than the bulk average. XPS and elemental analysis of selected particle size distributions show that the differences at the surface cannot be explained solely on the basis of particle size effects

Surface composition of iron and inorganic sulfur forms in Argonne Premium coals by x-ray photoelectron spectroscopy

Comparison of the yields and structure of fuels derived from freshwater algae (torbanite) and marine algae (El-Lajjun oil shale)

Disclosed in this invention are novel road paving asphaltic compositions having improved viscoelastic properties and storage stability and unexpected phase compatibility. They contain neutralized mixtures of oxidized asphalt and an acid functionalized polymer, which polymer is selected from the group consisting of sulfonated EPDM, sulfonated styrene-butadiene, and acrylic acid terpolymers, in an amount that is sufficient to result in an asphaltic composition having a softening point greater about 55° C. and a viscosity in the range from about 150 cPs to 2000 cPs or from about 3000 cPs to about 8000 cPs at 135° C. and effective to allow the formation of one continuous phase or two interdispersed phases that do not segregate on standing at elevated temperatures. The basic neutralizing agent used in these compositions contain cations having a valence of from +1 to +3, preferably +2. The invention also relates to the products produced by the process and method of making the compositions. The compositions can be used as a binder in paving applications, particularly as a binder in dense graded and in open graded hot mix pavements.

Martin L. Gorbaty

Papers

Surface composition of iron and inorganic sulfur forms in Argonne Premium coals by x-ray photoelectron spectroscopy

Comparison of the yields and structure of fuels derived from freshwater algae (torbanite) and marine algae (El-Lajjun oil shale)

Polymer-modified, oxidized asphalt compositions and methods of preparation

Coal physical structure: porous rock and macromolecular network

A comparison of the NaOH-HCl and HCl-HF methods of extracting kerogen from two different marine oil shales