Different Degrees Of Oxidation Research Articles

Structural and Electronic Properties of Graphene Oxide for Different Degree of Oxidation

In the last year, the investigation of two-dimensional materials as graphene oxide is a fundamental goal to produce innovative devices with wide range of applications in many areas. In the present work, we report a systematic study of structural and electronic properties of graphene oxide for different oxidations levels (25%, 50%, 75%, 100%) using density functional calculations for electronic ground state and a statistical approach on carbon-carbon bond length obtained after the geometric optimization of graphene covered with epoxide and hydroxyl functional groups. The theoretical models proposed and studied here are accord with the well-known experimental data. Our statistical results of the carbon-carbon bond length shown that hydroxyl groups disturbs the structure of graphene more than epoxide groups, however, both hydroxyl and epoxide groups are responsible of the change of hybridization sp2 to sp3, while the degree of oxidation increase. In addition, our electronic structure calculations confirm that with low degree of oxidation, the graphene oxide is semiconductor, and with full degree of oxidation graphene oxide is an insulating material. The minimum of total energy is found when the graphene oxide has full coverage. This work can contribute to understand the plasticity and ductility properties of graphene oxide recently reported.

Recycling Oxidized Model Polyethylene Powder as a Degradation Enhancing Filler for Polyethylene/Polycaprolactone Blends

Polyethylene (PE) powder with different degrees of oxidation was prepared to model end-of life polyethylene that has been oxidized during processing and/or service-life. The nonoxidized and preoxidized PE powders were blended with PCL to evaluate the possibility to recycle PE powder in PCL blends. Good elongation at break was reached for all 25/75 (w/w) PE/PCL films and the elongation at break correlated well with the carbonyl index of the original PE powder, indicating that the oxidation of PE increased the interfacial adhesion with PCL and improved the blend properties. The preoxidized PE powder in combination with surfactant and pro-oxidant greatly accelerated the degradation rate of PCL as measured by molecular weight decrease during low temperature thermo-oxidative aging. This coincided with the fast initial increase in PE carbonyl index. The degradation accelerating effect was larger when preoxidized PE was blended with PCL as compared to when nonoxidized PE was added. However, the degree of preoxidation had minor impact on PCL degradation rate. Without PE powder the degradation rate of PCL was not enhanced by the addition of pro-oxidant and surfactant alone.

Cellulose nanocrystal reinforced oxidized natural rubber nanocomposites

Natural rubber (NR) latex particles were oxidized using KMnO4 as oxidant to promote the insertion of hydroxyl groups in the surface polyisoprene chains. Different degrees of oxidation were investigated. Both unoxidized and oxidized NR (ONR) latex were used to prepare nanocomposite films reinforced with cellulose nanocrystals (CNCs) by casting/evaporation. The oxidation of NR was carried out to promote chemical interactions between the hydroxyl groups of ONR with those of CNCs through hydrogen bonding. The effect of the degree of oxidation of the NR latex on the rheological behavior of CNC/NR and CNC/ONR suspensions, as well as on the mechanical, swelling and thermal properties of ensuing nanocomposites was investigated. Improved properties were observed for intermediate degrees of oxidation but they were found to degrade for higher oxidation levels.

Conformation of carboxylated schizophyllan in aqueous solution

Carboxylated schizophyllan (sclerox) samples of different degrees of oxidation were molecularly characterized by size exclusion chromatography equipped with a multi-angle light scattering detector (SEC-MALS) in 0.10M aqueous NaCl solution. The molar mass distribution obtained by SEC-MALS shows that sclerox of low degree of oxidation is dissolved mainly as the trimer, whereas the trimer and single chain coexist in solution of sclerox of high degree of oxidation. The trimer of sclerox is much more flexible than the fully ordered triple helix of the parent schizophyllan and easily dissociates into single chains upon heating.

Friction and Wear Behavior of Pressureless Solid State Sintered SiC

In the present work, SiC was pressureless solid state sintered with 3 wt% C and 0.6 wt% B4C as sintering additives. The friction and wear behavior of the PSSS SiC ceramics was investigated by using a block-on-ring tribometer. The wear volume and friction coefficient was measured. It is as expected that the friction coefficient increased with the elevation of the normal load and sliding speed. The microstructure of the worn surface was observed, based on which the wear mechanism was analyzed. Different degrees of oxidation during the friction process was found and the degree of oxidation was related to the severity of wear. The normal load was found to exert great influence on the wear of the SSiC ceramics.

Simple Preparation of Exfoliated Graphene Oxide Sheets via Simplified Hummer’s Method

Today, research on graphene and other two-dimensional sp2-hybridized carbon nanomaterials has tremendously impacted the areas of modern chemistry, physics, and materials science and engineering. The significant attraction of these materials can be attributed to the outstanding electrical, optical, electrochemical, and mechanical properties of graphene-like materials, especially in comparison to other carbon materials. In this manner, graphene oxide as a substrate for graphene-like materials reduction process is getting more and more interesting. Although early routes to these materials were challenging, significant advances in synthetic and processing methods have enabled access to high-quality exfoliated graphene oxide sheets in appreciable quantities. Herein, we introduced a simple and efficient method for the high-conversion preparation of graphene oxide using a simplified hummer’s method from large graphite flakes (an average flake size of 100 μm). One-pot chemical oxidation of graphite was carried out at room temperature for the preparation purpose. It was found that different degree of oxidation of graphite flakes could be realized by stirring graphite in a mixture of sulphuric acid and potassium permanganate under different oxidation durations, resulting in exfoliated graphene oxide sheets with large lateral dimension and area. The simplified Hummer’s method provides a facile approach for the preparation of large-area exfoliated graphene oxide sheets.

Dispersibility-Dependent Biodegradation of Graphene Oxide by Myeloperoxidase.

Understanding human health risk associated with the rapidly emerging graphene-based nanomaterials represents a great challenge because of the diversity of applications and the wide range of possible ways of exposure to this type of materials. Herein, the biodegradation of graphene oxide (GO) sheets is reported by using myeloperoxidase (hMPO) derived from human neutrophils in the presence of a low concentration of hydrogen peroxide. The degradation capability of the enzyme on three different GO samples containing different degree of oxidation on their graphenic lattice, leading to a variable dispersibility in aqueous media is compared. hMPO fails in degrading the most aggregated GO, but succeeds to completely metabolize highly dispersed GO samples. The spectroscopy and microscopy analyses provide unambiguous evidence for the key roles played by hydrophilicity, negative surface charge, and colloidal stability of the aqueous GO in their biodegradation by hMPO catalysis.

Green preparation of reduced graphene oxide using a natural reducing agent

A simple and efficient method was introduced for the high-conversion preparation of graphene oxide (GO) from large graphite flakes (average flake size=100μm) using a simplified Hummer׳s method. Natural reducing agents such as lemon juice and vinegar were compared with hydrazine (N2H4) as potential reducing agents. Graphene was prepared by chemical reduction of GO because this method was low cost and could be used for large-scale graphene production. This one-pot graphene preparation was performed at room temperature. Different degrees of oxidation of graphite flakes were obtained by stirring graphite in a mixture of sulfuric acid and potassium permanganate at different oxidation times, and highly exfoliated GO sheets were produced. GO was subsequently reduced effectively by lemon juice, a new, green, and potential reducing agent with pH 2.3. This reduced GO exhibited a high electrical conductance of 24.6μS attributed to its higher C/O ratio (≈8:2) compared with other samples.

Oxidation of coal in industrial conditions. 5. limiting storage times

The limiting storage times of coking coal in open heaps at coke plants in summer and winter are determined. There are considerable differences between the limiting storage times determined on the basis of the degree of oxidation, clinkering, coking, and temperature of the coal in the heap. For coal of low (G coal) and high (OS coal) metamorphic development, the change in clinkering and coking properties generally occurs before or at the onset of intense oxidation. For coal of moderate metamorphic development (Zh and K coal), significant change in clinkering and coking properties accompanies intense oxidation. Selection of the limiting storage time on the basis of the coking of the coal is proposed—in particular, in terms of the mechanical strength of blast-furnace coke produced from batch containing coal of different degrees of oxidation. The limiting storage times recommended for coal in summer and winter, respectively, are as follows: 30 and 60 days for G coal; 145 and 200 days for Zh coal; 80 and 95 days for K coal; and 20 and 30 days for OS coal. In revising the Operational Rules, a provision requiring verification of the coking properties of any coal stored in open heaps for more than the standard time must be introduced.

The Evolution Rule of Three-Dimensional Structures of Graphite During Oxidation

The graphite oxidation samples with different degrees of oxidation were prepared from natural flake graphite via a modified Hummers method with controlled addition of KMnO 4. The evolution of oxygen-containing functional groups was analyzed by Fourier transform infrared spectrometry (FT-IR) and X-ray photoelectron spectroscopy (XPS). The evolution rule of three-dimensional (3D) graphite structures during oxidation has been verified via X-ray diffraction (XRD). Experimental results show that the evolution of the interplanar spacing of samples during oxidation can be approximately divided into four stages. When the dosage of KMnO 4 is 0.5 g per 1 g of graphite (g/g), a graphite intercalation compound (GIC) is formed through intercalating reactions, and a slight increase is observed in the values of d100 and d110, suggesting that the π–π interactions which decrease the length of carbon–carbon bonds were partially disrupted. Adding additional KMnO 4 initiates the second stage, in which GIC begins to oxidize. The insertion of oxygen-containing functional groups in the graphene basal plane leads to dramatic changes in the values of d100 and d110. The d100 is greatly reduced while d110 increases slightly. These trends are attributed to the fact that the basal plane is stretched during the oxidation process. Further addition of KMnO 4 in the third stage leads to relatively small increases in the values of d100 and d110. This result is consistent with the evolution rule of hydroxyl groups. In this research, the evolution rule of the value of d001 is also clearly demonstrated. When the concentration of KMnO 4 is not more than 3.0 g/g, the value of products d001 keeps gradually increasing, indicating that oxygen-containing groups continue to form bonds with carbons in the basal plane, and that additional water molecules are adsorbed between the layers of the samples. All the interplanar spacing values (d001, d100 and d110) are reduced significantly in the fourth stage, when the amount of KMnO 4 added up to 4.0 g/g. FT-IR and XPS analyses demonstrate that the decrease in the values of d100 and d110 is due to a reduction in the content of external hydroxyl groups. The change in d001 is attributed to the partial release of water molecules confined in the interlayer spaces between adjacent sheets are partly released.

Adsorption in micro and mesoporous slit carbons with oxygen surface functionalities

Microscopic surface heterogeneity has in general significant effects on the overall adsorption characteristics of porous solids. However these effects may differ to a large extent when different adsorbates are used. Here, we present and compare simulations of N2 and CO2 adsorption in slit shaped pore models having a graphitic surface with oxygen functionalities. We use models with three different degrees of oxidation, to study the impact of the surface oxygen content on gas adsorption in both micro- and small mesopores. Significant contribution on the energies and densities stems from the electrostatic interactions used in the solid–fluid force fields. Therefore adsorption is strongly influenced by the presence of partial charges on surface sites and functional groups. By using CO2 instead of N2 we get a clearer picture of the surface energetic details, as revealed on the computed isotherms and on the isosteric heats of adsorption. CO2 adsorption can be used as a complementary tool to N2 porosimetry, for the surface chemistry characterization of carbon solids.

Composition of PbTe oxides obtained by different methods

The widespread use of PbTe nanocomposites requires knowledge regarding the composition of their grain boundaries. Cathodoluminescence (CL), TOF-SIMS and Rutherford backscattering spectroscopy (RBS) were used to explore the composition of surface layers formed via thermal, electrochemical, and wet chemical oxidation of lead telluride. Surface layers obtained by these methods contained components with different degrees of oxidation. RBS and CL results show that thermal and anodic oxidation produced ternary PbTeO3 and Pb2TeO4 oxides, respectively. For the chemical oxide we observed a substantially lower concentration of oxygen described by PbO1−xTeO2−x, a significant amount of non-oxidized PbTe ions detected by SIMS, and low CL stability under electron beam radiation. Thus, the chemical oxide is likely a mixture of binary suboxides.

Impact of Electrode Oxidation on the Current Transport Properties at Platinum/(Niobium-Doped Strontium-Titanate) Schottky Junctions

The current transport properties and resistance-switching (RS) behavior at platinum/niobium-doped strontium-titanate (Pt/NSTO) Schottky junctions were investigated for junctions with different degrees of oxidation (PtOx) in the Schottky electrode. It was found that the rectifying current-voltage (I–V) profile strongly depends on the heat-treatment of the NSTO crystal and oxidation of the Pt electrode. The hysteresis in the I–V relationships was larger for the PtOx/NSTO junction than for the pure Pt/NSTO junction, and heat-treatment of the NSTO crystal suppresses the hysteresis in I-V and increases the leakage current. The change in the rectifying I–V profiles can be reasonably explained by the increase in the built-in potential caused by partial oxidation of the electrode interface, as determined by soft X-ray photoemission spectroscopy. The experimental results indicate that control of the built-in potential and the partial oxidation of the electrode, which affects the homogeneity of the potential profile, is the key to improving and controlling the rectification and RS properties in Pt/NSTO junctions.

Study on Surface Properties of PAN-Based Carbon Fiber Oxidized in a Static Electrochemical Oxidation Process

PAN-based carbon fibers (CFs) were oxidized in a static electrochemical oxidation process. The surface color and chemical composition were investigated by means of digital camera and XPS. The results showed that, with the increasing distance from anodic roller, the surface color of CFs changed and the degree of oxidation got weaker and weaker. A close correlation was found between its surface color and chemical properties. It indicates that the electrochemical oxidation performance of one kind of carbon fiber can be handily studied using static electrochemical oxidation process because we can get CFs of different degree of oxidation through one experiment.

Targeted functionalization of spruce O‐acetyl galactoglucomannans—2,2,6,6‐tetramethylpiperidin‐1‐oxyl‐oxidation and carbodiimide‐mediated amidation

ABSTRACTModified spruce O‐acetyl galactoglucomannans (GGMs) can be used as molecular anchors to alter the surface properties or to activate the surface of cellulose. To selectively introduce functionalities, GGMs were oxidized on C‐6 of hexoses by 2,2,6,6‐tetramethylpiperidin‐1‐oxyl‐mediated oxidation. Different degrees of oxidation were successfully obtained by varying the reaction parameters. Low degrees could be obtained by performing the oxidations in bromide‐free conditions. The formed uronic acids were further modified by a carbodiimide‐mediated amidation reaction, which opens a window for introducing various functionalities selectively on hexoses. The adsorption of the modified GGMs to various cellulose samples was investigated. Indirect bulk sorption to fibers was compared to direct adsorption to nanofibrillated cellulose ultrathin films. GGMs with low degrees of oxidation showed high affinity to cellulose surfaces and could be sorbed onto cellulose in pure water. Moderate amounts of GGMs with high degree of oxidation could be sorbed onto cellulose in the presence of salts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3122–3129, 2013

Combinatorial Generation of Complexity by Redox Enzymes in the Chaetoglobosin A Biosynthesis

Redox enzymes play a central role in generating structural complexity during natural product biosynthesis. In the postassembly tailoring steps, redox cascades can transform nascent chemical scaffolds into structurally complex final products. Chaetoglobosin A (1) is biosynthesized by a hybrid polyketide synthase-nonribosomal peptide synthetase. It belongs to the chaetoglobosin family of natural products, comprising many analogs having different degrees of oxidation introduced during their biosynthesis. We report here the determination of the complete biosynthetic steps leading to the formation of 1 from prochaetoglobosin I (2). Each oxidation step was elucidated using Chaetomium globosum strains carrying various combinations of deletion of the three redox enzymes, one FAD-dependent monooxygenase, and two cytochrome P450 oxygenases, and in vivo biotransformation of intermediates by heterologous expression of the three genes in Saccharomyces cerevisiae. Five analogs were identified in this study as intermediates formed during oxidization of 2 to 1 by those redox enzymes. Furthermore, a stereochemical course of each oxidation step was clearly revealed with the absolute configurations of five intermediates determined from X-ray crystal structure. This approach allowed us to quickly determine the biosynthetic intermediates and the enzymes responsible for their formation. Moreover, by addressing the redox enzymes, we were able to discover that promiscuity of the redox enzymes allowed the formation of a network of pathways that results in a combinatorial formation of multiple intermediate compounds during the formation of 1 from 2. Our approach should expedite elucidation of pathways for other natural products biosynthesized by many uncharacterized enzymes of this fungus.

Methane Catalytic Combustion on Pd9/?-Al2O3 with Different Degrees of Pd Oxidation

This research is focused on the analysis of adsorbed CH4 intermediates at oxidized Pd9 nanoparticles supported on gamma-alumina. From first-principle density functional theory (DFT) calculations, several configurations, charge transfer and electronic density of states have been analyzed in order to determine feasible paths for the oxidation process. Furthermore methane oxidation cycles have been investigated on Pd nanoparticles with different degrees of oxidation. In case of low oxidized Pd nanoparticles, activation of methane is observed, whereby hydrogen from methane is adsorbed at one oxygen atom. This reaction is exothermic. In a subsequent step, two water molecules desorb. Additionally, a very interesting structural effect becomes evident; Pd-carbide formation, which is also an exothermic reaction. Furthermore, oxidation of such carbidized Pd-nanoparticles leads to CO2 formation, which is an endothermic reaction. One important result is that the support is involved in the CO2 formation. A different mechanism of methane oxidation was discovered for highly oxidized Pd nanoparticles. When the Pd nanoparticle is more strongly exposed to oxidative conditions, adsorption of methane is also possible, but it leads to carbonic acid production at the interface between the Pd nanoparticles and support. This process is endothermic.

Transition Metal (Mn, Fe, Co, Ni)‐Doped Graphene Hybrids for Electrocatalysis

The development of electrocatalysts is crucial for renewable energy applications. Metal-doped graphene hybrid materials have been explored for this purpose, however, with much focus on noble metals, which are limited by their low availability and high costs. Transition metals may serve as promising alternatives. Here, transition metal-doped graphene hybrids were synthesized by a simple and scalable method. Metal-doped graphite oxide precursors were thermally exfoliated in either hydrogen or nitrogen atmosphere; by changing exfoliation atmospheres from inert to reductive, we produced materials with different degrees of oxidation. Effects of the presence of metal nanoparticles and exfoliation atmosphere on the morphology and electrocatalytic activity of the hybrid materials were investigated using electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Doping of graphene with transition metal nanoparticles of the 4th period significantly influenced the electrocatalysis of compounds important in energy production and storage applications, with hybrid materials exfoliated in nitrogen atmosphere displaying superior performance over those exfoliated in hydrogen atmosphere. Moreover, nickel-doped graphene hybrids displayed outstanding electrocatalytic activities towards reduction of O2 when compared to bare graphenes. These findings may be exploited in the research field of renewable energy.

High-temperature thermomagnetic properties of vivianite nodules, Lake El'gygytgyn, Northeast Russia

Abstract. Vivianite, a hydrated iron phosphate, is abundant in sediments of Lake El'gygytgyn, located in the Anadyr Mountains of central Chukotka, northeastern Russia (67°30′ N, 172°05′ E). Magnetic measurements, including mass-specific low-field AC magnetic susceptibility, field-dependent magnetic susceptibility, hysteresis parameters, temperature dependence of the induced magnetization, as well as susceptibility in different heating media, provide ample information on vivianite nodules. Electron microprobe analyses, electron microscopy and energy dispersive spectroscopy were used to identify diagnostic minerals. Vivianite nodules are abundant in both sediments of cold (anoxic) and warm (oxic) stages. Magnetic susceptibility of the nodules varies from 0.78 × 10−6 m3 kg−1 to 1.72 × 10−6 m3 kg−1 (average = 1.05 × 10−6 m3 kg−1) and is higher than the susceptibility of sediments from the cold intervals. Magnetic properties of vivianite are due to the respective product of oxidation as well as sediment and mineral inclusions. Three types of curves for high-temperature dependent susceptibility of vivianite indicate different degrees of oxidation and inclusions in the nodules. Vivianite acts as a reductant and reduces hematite to magnetite and masks the goethite–hematite transition during heating. Heating vivianite and sulfur mixtures stimulates the formation of monoclinic pyrrhotite. An additive of arsenic inhibits the formation of magnetite prior to its Curie temperature. Heating selective vivianite and pyrite mixtures leads to formation of several different minerals – magnetite, monoclinic pyrrhotite, and hexagonal pyrrhotite, and makes it difficult to interpret the thermomagnetic curves.

Electrooxidation Methods to Produce Pseudocapacitance-containing Porous Carbons

Surface oxygen groups play a key role on the performance of porous carbon electrodes for electrochemical capacitors in aqueous media. The electrooxidation method in NaCl electrolyte using a filter press cell and dimensionally stable anodes is proposed as a viable process for the generation of oxygen groups on porous carbon materials. The experimental set-up is so flexible that allows the easy modification of carbon materials with different configurations, i.e. cloths and granular, obtaining different degrees of oxidation for both conformations without the requirement of binders and conductivity promoters. After the electrooxidation method, the attained porosity is maintained between 90 and 75% of the initial values. The surface oxygen groups generated can increase the capacitance up to a 30% when compared to the pristine material. However, a severe oxidation is detrimental since it may decrease the conductivity and increase the resistance for ion mobility.