The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

/pdf/the-chemistry-of-graphene-oxide-507zcedhhu.pdf

The chemistry of graphene oxide

An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers’ method (KMnO4, NaNO3, H2SO4) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 mixture of H2SO4/H3PO4 improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers’ method or Hummers’ method with additional KMnO4. Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers’ method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers’ method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the ...

https://www.researchgate.net/file.PostFileLoader.html?id=54ca19b4cf57d79a768b4618&assetKey=AS%3A273691751976961%401442264606356

Improved Synthesis of Graphene Oxide

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

/pdf/graphene-and-graphene-oxide-synthesis-properties-and-2q80uaujok.pdf

Graphene and Graphene Oxide: Synthesis, Properties, and Applications

Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.

/pdf/processable-aqueous-dispersions-of-graphene-nanosheets-4pl49qkwvn.pdf

Processable aqueous dispersions of graphene nanosheets


 Reservoir wettability is a parameter of crucial importance for oil recovery1. However, its definition and its measurement are quite complex. For a flat surface, wettability is directly related to the contact angle of a water droplet on a surface controlled by the hydrophilicity of the surface. For an arbitrary surface, the contact angle, however, does not only depend on the hydrophilicity of the surface but also depends on the surface roughness at various length scales. Therefore, wetting is a macroscopic property that is only directly related to the hydrophilicity of the surface if the surface is flat and smooth. The hydrophilicity of the surface is a microscopic property that determined the surface interactions with water and hydrocarbons and plays a crucial role in oil production and recovery. The unknown surface roughness of internal surfaces of rock porous media makes wettability definition and measurement of such internal surfaces extremely challenging. Identifying a wettability index of porous media surfaces with broad applicability is a primary objective in oil and gas industry.
 Here we demonstrate an NMR-detected isotherm technique for measuring surface wettability of porous media. This technique is not only related directly to the traditional measure of wettability using macroscopic contact angles, it is also directly related to the microscopic surface property of hydrophilicity. It is shown that NMR-detected isotherms of both water and isopropanol (IPA) are needed to obtain the wettability index. Through systematic studies of quartz glass beads and quartz slides that are hydrophilic- or hydrophobic-modified, we established a quantitative relationship between the NMR isotherm-based wettability index and the traditional measure of wettability using contact angle. Therefore, the proposed wettability index derived from NMR isotherms provides a clear link to both macroscopic and microscopic properties of internal surfaces of porous media and can be a reliable measure of interactions between water and hydrocarbon with internal surfaces of rock porous media, as evidenced by preliminary studies of rock samples.

Connection Between Wettability and NMR-Detected Isotherms

The passivation and reactivation of As donor dopants in n-type Si was studied with both monatomic hydrogen and deuterium. Hydrogenated Schottky diodes were characterized with C-V and DLTS measurements. The reactivation kinetics of the As-H and As-D complexes were studied in the space-charge layer of reverse biased diodes in the temperature range from 60°C to 120°C. These bias-anneals yield dissociation time constants for As-H, from which an averaged activation energy of 1.17±0.1 eV was determined. Although the dissociation of the As-H complex is appreciably slower than that previously measured for P-H, the activation energy is within about 0.05 eV of that determined previously for the P-H complex (1.2 eV). The depth redistribution of the As-H complexes after bias-annealing agrees with the previous conclusion that hydrogen can assume a negative charge state in n-type Si.

Donor Reactivation Kinetics and Hydrogen Redistribution in the Space Charge Layer of N-Type Silicon

Within the Hydrogen Sorption Center of Excellence (HSCoE), our task is to use NMR to provide microscopic information on hydrogen adsorption in materials synthesized by HSCoE partners. NMR furnishes microscopic and quantitative information on adsorption processes. It also provides information on the structure of adsorption sites. Such information provides feedback to efforts in materials synthesis and theory in designing materials to reach the DOE targets.

/pdf/iv-c-1j-characterization-of-hydrogen-adsorption-by-nmr-4d2eu19r6n.pdf

IV.C.1j Characterization of Hydrogen Adsorption by NMR

Magnetic susceptibility is predicted to be sensitive to structural disorder in the group IV elemental semiconductors. A proton nuclear magnetic resonance (NMR) technique is shown to precisely measure bulk magnetic susceptibilities (χ) of hot-wire (HW) CVD a-Si:H films as- deposited on quartz substrates. Differences in χ correlate with growth rate, but not with hydrogen content or deposition temperature. Qualitative agreement is found between smaller diamagnetic susceptibility (less average disorder) and desirable electronic properties measured by photo- and dark conductivity on the same samples. Comparing films with similar hydrogen distribution and content (as evidenced by the NMR spectra) allows the unambiguous identification of the importance of overall Si network structural disorder in the metastability of a-Si:H.

Yue Wu

Papers

Connection Between Wettability and NMR-Detected Isotherms

Donor Reactivation Kinetics and Hydrogen Redistribution in the Space Charge Layer of N-Type Silicon

IV.C.1j Characterization of Hydrogen Adsorption by NMR

Diamagnetic susceptibility of micron thick a-Si: H films measured via proton NMR: A probe of structural disorder