Oxidation Of Carbon Materials Research Articles

ChemInform Abstract: Carbocatalyzed Oxidative C(sp2)—C(sp2) Homocouplings of Benzo‐Fused Heterocycles.

AbstractAppropriate treatment of amorphous carbon with aqua regia or concentrated nitric acid leads to oxidized carbon material which is able to catalyze homocoupling reactions of benzo‐fused heterocycles as well as β‐naphthol.

Li-decoration on the edge oxidized graphyne and graphdiyne: A first principles study

In recent years, the new two-dimensional planar carbon allotropes, graphyne and graphdiyne, have received significant research attention. Accordingly, the present study is devoted to investigate how the electronic structures of graphyne and graphdiyne nanoflakes are modified upon the edge oxidizing as well as Li-decoration. Different oxygen containing groups such as carbonyl, ketone, hydroxyl, carboxylic, formyl, and epoxide are considered for oxygenation of these carbon surfaces. The stability of oxidized surfaces with respect to the bare sheets has been discussed in terms of Gibbs free energy of formation. We showed that carbon surfaces terminated with carboxylic group are more stable than other oxidized surfaces. It is also found that the band gap in considered surfaces can be tuned (0.53–1.51eV) by changing the type of oxygen containing group. Moreover, we report the binding energies for the Li adsorption at hollow sites on the basal plane and on the oxygen of functional group. Our calculations reveal that the interaction between oxygen group and carbon atoms at the edge increases the reactivity of considered sheets toward Li adsorption. The band gap of fuctionalized surfaces can be engineered by selective lithiation over a wide range between 0.01 and 1.31eV. We found that the oxygen species plays the key role on the Li adsorption on the edge oxidized surfaces leading to either semiconducting or metallic behaviors. However, this study offers critical information for further theoretical and experimental studies on oxidized carbon materials for their possible applications in lithium ion batteries as well as hydrogen storage materials.

Temperature influence on the synthesis of pristine graphene oxide and graphite oxide

Derivative oxide carbon materials, such as graphene or graphite oxides, have been recently considered to be a promising material in a wide scenarios of emerging technologies due to their physical and chemical properties, as well as, for their low production costs. Even if apparently similar, these materials exhibit different physical and chemical properties. One of the critical issue is associated with the exfoliation process and contributes to the formation of graphene oxide and graphite oxide material. Here, we show a single synthetic wet method to produce graphene or graphite oxide by applying a control of the operational temperature during the reaction. The process was optimised to obtain the pristine graphite oxide at low temperature (T = 0 °C) and the pristine graphene oxide at higher temperature (T = 30 °C). Finally, the peculiar features of these materials were described using spectroscopic, structural and morphological measurements.

Impacts of acidity and textural properties of oxidized carbon materials on their catalytic activity for hydrolysis of cellobiose

Hydrolysis of cellobiose was investigated in the presence of oxidized carbon materials with different textural properties and concentrations of surface acidic groups. Specifically, oxidized microporous activated carbon, graphite-like mesoporous Sibunit carbon, and graphite-like multi-walled carbon nanotubes were studied. Catalytic activity was found to correlate with the concentration of surface acidic sites. Activated carbon oxidized with HNO3 at 130 °C exhibited superior catalytic activity due to highest acidity of this material. The catalytic performance was predominantly dependent on acidity, while textural properties only played a minor role, and no mass transfer limitations were observed for microporous catalysts.

Synthesis and characterization of carbon fiber/silica aerogel nanocomposites

Nanoporous silica aerogel–carbon fiber composites were prepared via a sol–gel process by surface modification at ambient pressure. Oxidizing modification of the carbon microfibers improved the adhesion between hydrophilic silica gel and the carbon material surface. Suggested solution contributed to the blocking of hydroxide bonds of silica gel via reaction with the oxidized carbon material surface, which lowered the contraction of gel volume during its drying in atmospheric pressure and led to the more stable structure.

Li adsorption on edge-oxidized graphene nanoribbons predicted by DFT calculations

Motivated by the increased interest in graphene oxide derivatives for Li-ion battery applications, the interaction of Li atoms and various oxygen-terminated graphene nanoribbons was studied using the spin-polarized density functional theory and periodic boundary conditions calculations. Li binding energies were calculated at the edge regions and on the basal plane considering zigzag and armchair morphologies terminated at the edges with different oxygen-containing groups, such as hydroxyl, carboxyl, carbonyl, and ether groups. A relation between the adatom binding energies and the electronic properties of the chemically modified substrate is investigated. The main factors contributing to favorable Li adsorption energies are edge morphologies and sites, electronic behavior, and the presence of ketone groups at the edge. This work suggests that the formation of covalent bonds within Li and certain group terminations could explain the much larger irreversible capacity found in experimentally oxidized carbon materials. Our calculations offer critical information to further optimize the structure of oxidized carbon materials for Li-ion battery applications.

Enhancing the efficiency of AuCl4− ion removal from aqueous solution using activated carbon and carbon nanomaterials

The removal of AuCl4− ion from acidic aqueous solutions is studied using a series of non-oxidized and surface oxidized carbon materials (activated carbon, carbon nanotubes, carbon-encapsulated iron nanoparticles and carbon black). The studied sorbents differ in crystallinity, porosity and morphology. In the case of non-oxidized carbon materials the maximum removal efficiency (74%) is found for activated carbon, whilst graphitized nanomaterials (i.e. carbon nanotubes and carbon-encapsulated iron nanoparticles) are able to remove 42–45% of gold ion from the solution. The oxidation in nitric acid significantly improves the removal efficiencies. The uptake of Au(III) increases two times (to 91–92%) for oxidized carbon nanotubes and carbon-encapsulated iron nanoparticles. The same oxidation procedure applied to activated carbon and carbon black moderately enhances the uptake efficiency to 88% and 55%, respectively. The observed substantially distinct uptakes are discussed in the frames of textural properties, morphology, surface chemistry characteristics and crystallinity of the studied carbon materials. Moreover, the possibility of a galvanic exchange reaction between AuCl4− and metallic Fe in the carbon encapsulate core is also evaluated.

The influence of structure and surface chemistry of carbon materials on the decomposition of hydrogen peroxide

Carbon materials with different structural and chemical properties, namely activated carbons, carbon xerogels, carbon nanotubes, graphene oxide, graphite and glycerol-based carbon materials, were tested under different operating conditions for their ability to catalyse hydrogen peroxide (H2O2) decomposition in aqueous solutions. Activated carbons treated with concentrated sulphuric acid (ACS) are the most active catalytic materials for H2O2 decomposition in most of the conditions studied, due to the presence of sulphur containing functional groups at their surface. In addition, ACS proved to be a stable catalyst in reutilization tests for H2O2 decomposition. Methanol was used as selective scavenger of hydroxyl radicals (HO), to show that activated carbons with a markedly basic character lead to the highest yield of HO formed during the H2O2 decomposition process (14%, after 150min of reaction). Overall, from the mechanistic interpretation of H2O2 decomposition, it is concluded that the presence of sulphur containing functional groups at the surface of the activated carbons improves the removal of H2O2 in aqueous solutions, but, on the other hand, the selective decomposition of H2O2 via HO formation is enhanced by the presence of basic active sites on the carbon surface.

Abstract TP271: Novel Carbon-Based Particle Antioxidants in Reversible Hyperglycemic MCA Occlusion

Introduction: We have demonstrated that nanoscale PEG-ylated oxidized carbon materials, which we refer to as hydrophilic carbon clusters (PEG-HCCs), have antioxidant characteristics favorable for their use in ischemia. These materials are rich in conjugated carbon double bond domains, and unlike conventional antioxidants, are able to quench rather than transfer oxidative radicals thus not requiring regeneration (Marcano et al, JNT in press). They have shown no acute or 6 week toxicity in rodents, excellent uptake into endothelial cells and protection against TBI-induced neurovascular dysfunction (Bitner et al, ACS Nano, 2012), but were not designed for blood-brain barrier (BBB) transport. We were able to synthesize PEG-HCCs bound to adamantane (ADM), a well characterized moiety that increases lipophilicity. We tested these agents in a severe example of oxidative stress, reversible middle cerebral artery occlusion (MCAO) in acutely hyperglycemic rats (Martini and Kent, JCBFM 2006). Methods: 16 Male, Long Evans rats received an ip injection of streptozotocin or vehicle 2 days prior to 90 minutes MCAO using the suture technique. Physiological and post-op monitoring was performed. PEG-HCCs or ADM-PEG-HCCs were injected IV at suture removal. The endpoints investigated thus far are: mortality; nitric oxide (NO) expression, reflected in the ratio of perivascular DAF-2AC intensity in penumbra to contralateral region after 5 min. circulation (Fabian and Kent AJP 2008); and presence of the PEG-HCCs detected by reaction product from an anti-PEG antibody to the tightly bound PEG moiety. Results: Mortality by 24 hours was 100% in untreated hyperglycemic rats, 66% with PEG-HCCs and 33% after ADM-PEG-HCCs. Ratio of penumbral perivascular NO expression to control hemisphere was: untreated: 0.29; PEG-HCCs: 0.52; and ADM-PEG-HCCs: 0.59. There was considerable vascular and parenchymal staining with ADM-PEG-HCC but was restricted to the vasculature with PEG-HCCs. Conclusion: Addition of an ADM moiety to PEG-HCCs reduced mortality. This may have occurred because of BBB transport and partial recoupling of endothelial NO synthase, thought to be impaired in hyperglycemic stroke. Further characterization of the range of actions of these materials is underway.

The Oxidation Erosion in Carbon Materials for CZ Furnace

In this work, on the basis of carbon materials microstructure and morphology, we study on the influence of carbon fiber content , graphite degree and metal impurities on oxidation performance of carbon materials. The result of oxidation test shows that there are more crystal defects at the interface of carbon fiber and carbon matrix, and oxidation activity of carbon atoms near the area of crystal defects is higher than others.Carbon materials with higher fiber content and higher graphite degree, has a better anti-oxidation performance. The presence of impurities, especially metal impurities play a catalysis role in oxidation of carbon materials. After purification, impurities escape from the graphite microcrystal,resulting that the distortion of lattice decreased, that cause the better anti-oxidation performance.

Highly dispersed Pd nanoparticles on chemically modified graphene with aminophenyl groups for formic acid oxidation

A novel electrode material based on chemically modified graphene (CMG) with aminophenyl groups is covalently functionalized by a nucleophilic ring-opening reaction between the epoxy groups of graphene oxide and the aminophenyl groups of p-phenylenediamine. Palladium nanoparticles with an average diameter of 4.2 nm are deposited on the CMG by a liquid-phase borohydride reduction. The electrocatalytic activity and stability of the Pd/CMG composite towards formic acid oxidation are found to be higher than those of reduced graphene oxide and commercial carbon materials such as Vulcan XC-72 supported Pd electrocatalysts.

Ozonized activated carbon as catalyst for MTBE-cleavage

The application of oxidized carbon materials for the cleavage of methyl-tert-butyl ether has been investigated under technical relevant conditions in a fully automated apparatus with paralleled tube reactors. The carbon spheres oxidized for 60 min (SAC60) are active for MTBE cleavage at 498 K and 6 bar(g). MTBE is selectively converted into isobutene ( S > 99%) and MeOH ( S > 99.9%) at 80% conversion. The catalytic activity of the oxidized activated carbon can be traced back to the surface groups generated by ozonization of the carbon as the untreated sample did not show any conversion of MTBE at all. Broensted acidic carboxylic acid and anhydride surface groups are responsible for the activity of oxidized carbon as was concluded from simulation of the ex situ DRIFT spectra of the applied materials. In contrast to commonly used amorphous alumosilicates, the modified carbon completely inhibited the production of the undesired by-product dimethylether. Therefore, as no Lewis-acid sites are present on SAC60 and none of the present surface groups (carboxylic acids, anhydrides, lactones and carbonyl groups) cause the dehydration of methanol into dimethylether, it can be concluded that DME formation most probably occurs purely on Lewis-acidic or on basic sites. The decrease in conversion over time-on-stream obtained for the oxidized carbon material is ascribed either to poisoning of present active sites or to a decarboxylation of the activated carbon.

Comparison of degradation behaviors for open-ended and closed proton exchange membrane fuel cells during startup and shutdown cycles

As catalyst support materials, the oxidation of carbon materials is considered one of the major factors for performance decay during the startup and shutdown process of proton exchange membrane fuel cells, which must be mitigated to achieve acceptable durability. In this paper, the effect of cathode exhaust conditions on the degradation behaviors of fuel cells is investigated using two single cells named the open-ended and closed cells. The cathode inlet pressure during the introduction of the dummy load is an important factor in analyzing the performance decay of membrane electrode assemblies under different conditions. Electrochemical techniques, including the measurement of polarization curves, cyclic and linear sweep voltammetry, and cross-sectional scanning electron microscopy of tested membrane electrode assemblies, are employed to evaluate the performance decay of fuel cells. The results show that a closed cathode exhaust valve during the introduction of the dummy load would significantly alleviate both the performance decay and the decrease in the electrochemically active surface area, resulting in an improvement in fuel cell durability. No significant deterioration of the membranes is observed for both the open-ended and the closed cells during frequent startup and shutdown processes.

Removal of chromium Cr(VI) by low-cost chemically activated carbon materials from water

Low-cost, chemically activated carbon materials, Pellet-600 and PVA-300, were prepared at relatively low temperatures and show more effective removal efficiency of Cr(VI) from water than commercially available activated carbons tested. The Pellet-600 is a pelletized carbon material with high mesoporous volumes and surface area, and the PVA-300 is composed of a high surface area carbon coating on a fiberglass mat substrate. A much faster adsorption kinetics and a much higher adsorption capacity for Cr(VI) are achieved by the Pellet-600. At very low concentrations of Cr(VI), the PVA-300 displays a strong adsorption ability for Cr(VI). XPS data show an increase in the atomic ratio of Cr/C and oxidation of carbon materials after adsorption of Cr(VI). These results suggest that a high content of mesopores with a high surface area and surface functional groups greatly improve the Cr(VI) removal efficiency from water.

Infrared Spectroscopy of Carbon Materials: A Quantum Chemical Study of Model Compounds

The present work reports a theoretical study of the infrared spectra of chemical structures that are suitable to the description of the surface chemistry of carbon materials. Prior to any consideration, the computational approach was tested and adapted by comparing the predicted IR spectra to those obtained experimentally for various reference compounds. Several models were considered, subsequently accounting for the most relevant functional groups that have been postulated to decorate the edges of graphene layers on carbon materials (i.e., anhydrides, carboxyls, lactones, phenolic, quinones, and pyrones). For each of the previous functional groups, different structures involving a different number of fused rings were considered. This strategy allowed us to establish the effect of conjugation on the shift of the IR frequencies corresponding to a given functional group. Cooperative effects between different functional groups (phenol−carboxyl, phenol−lactone, and so on) were another aspect that revealed itself to be an interesting issue when assigning frequencies in the IR spectra of highly oxidized carbon materials. Thus, it was found that the frequencies of the CO bonds present in acid functional groups were systematically lowered when phenolic groups were close enough to establish hydrogen bonds. Special attention was also paid to the elucidation of the origin of the 1600-cm-1 band of carbons. It was found that, in the case of acid carbons, this band can be assigned to CC stretching of carbon rings decorated mainly with phenolic groups. Cyclic ethers in basic carbons would also promote absorption in the 1600-cm-1 region of the IR spectrum. Finally, the predicted assignments are employed to interpret the IR spectra obtained experimentally for several activated carbons.

Oxidation behavior of fine-grained SiC–B 4C/C composites up to 1400 °C

Fine-grained B 4C–SiC/C composites were fabricated using a ball-milling dispersion process. The oxidation behaviors of both fine-grained B 4C–SiC/C composites and coarse-grained B 4C–SiC/C composites at temperatures of up to 1400 °C were analyzed by the differential thermal analysis technique, and the surface morphology of the composites after isothermal oxidation at 800, 1200 and 1400 °C was examined by scanning electron microscopy (SEM). The results indicated that fine-grained B 4C–SiC/C composites had excellent oxidation resistance with self-healing properties at 1400 °C. A general model and mechanism for self-protection against oxidation of carbon materials were proposed.

Surface fluorination and oxidation of carbon materials for negative electrode of lithium ion secondary battery

The effect of surface modification of carbon materials on their electrochemical behavior has been studied. Fluorination, ozonization and air-oxidation of carbon surfaces increased the charge-discharge capacities. The change in the d-spacings of carbon materials due to surface modification was negligibly small. XPS measurement indicated that surface oxygen contents slightly increased not only in oxidized samples but also in fluorinated one. XPS also revealed the existence of nearly ionic and semi-covalent fluorines at the surface of the fluorinated sample.