Amount Of Oxygen-containing Groups Research Articles

Secondary silane grafting on aramid fibers improves the interfacial bonding performance in textile composite materials

To improve the chemical and physical surface features of aramid fibers and the bonding quality at the interface, carbon nanotubes, dopamine and silane coupling reagent KH560 were used to modify the surface of aramid fibers. The fiber surface was characterized by FTIR, XPS, SEM and AFM. The single-fiber specific strength, surface roughness, wettability and interfacial shear strength of the modified fiber were quantified. Finally, the uniaxial tensile behaviour of the textile composite laminate with the modified fibers was tested. The experimental results show that: after the grafting of silane coupling reagent as a second modification step, the amount of oxygen-containing groups on the surface of aramid fibers, and the surface roughness, and the ability to impregnate resin are further improved. The single-fiber specific strength, the interfacial shear strength by fiber pull-out tests, and the tensile strength of the laminate are increased by 21.62%, 73.57%, and 51.60%, respectively. This work demonstrates a general surface modification strategy working for diverse types of fibers, synthetic or natural. The present findings help to develop a broad range of high-performance textile composites to address long-term challenges in structural engineering.

Natural rubber as a renewable carbon source for mesoporous carbon/silica nanocomposites.

This study is the first report on the preparation of mesoporous carbon/silica (MCS) nanocomposites with tunable mesoporosity and hydrophobicity using natural rubber (NR) as a renewable and cheap carbon source. A series of mesoporous nanocomposites based on NR and hexagonal mesoporous silica (HMS) were prepared via an in situ sol–gel process and used as precursors; then, they were converted into MCS materials by controlled carbonization. The NR/HMS precursors exhibited a high dispersion of rubber phase incorporated into the mesostructured silica framework as confirmed by small-angle X-ray scattering and high-resolution transmission electron microscopy. An increase in the carbonization temperature up to 700 °C resulted in MCS nanocomposites with a well-ordered mesostructure and uniform framework-confined wormhole-like channels. The NR/HMS nanocomposites possessed high specific surface area (500–675 m2 g−1) and large pore volume (1.14–1.44 cm3 g−1). The carbon content of MCS (3.0–16.1 wt%) was increased with an increase in the H2SO4 concentration. Raman spectroscopy and X-ray photoelectron spectroscopy revealed the high dispersion of graphene oxide-like carbonaceous moieties in MCS materials; the type and amount of oxygen-containing groups in obtained MCS materials were determined by H2SO4 concentration. The enhanced hydrophobicity of MCS nanocomposites was related to the carbon content and the depletion of surface silanol groups, as confirmed by the water sorption measurement. The study on the controlled release of diclofenac in simulated gastrointestinal environment suggests a potential application of MCS materials as drug carriers.

High electrocapacitive performance of bowl-like monodispersed porous carbon nanoparticles prepared with an interfacial self-assembly process

Bowl-like monodispersed porous carbon nanoparticles (BMPCNs) have been successfully prepared with a facile and scalable approach, and the as-prepared BMPCNs are examined thoroughly by various physical characterizations. Physical measurements display that BMPCNs have the high surface area (1255m2g−1), hierarchical porosity, a certain amount of oxygen-containing groups and high graphitization degree. These unique structure features endow BMPCNs with a high capacitance (281Fg−1 at 0.5Ag−1), excellent rate capability (209Fg−1 at 50Ag−1), and outstanding cycling stability (94.8% capacity retention after 10,000 cycles at 10Ag−1) in electrochemical double-layer capacitors, suggesting its promising applications in field of energy conversion and storage. Further, the studies on formation mechanism of BMPCNs suggest that, the CTAB wormlike micelles assembling with silica/resorcinol-formaldehyde oligomers at the interface of tetraethyl orthosilicate droplets under Stöber condition determines the morphology of BMPCNs.

Composition of fulvic acids after the mechanical activation of peats

It was found that a structural rearrangement related to a change in the amount of functional groups in the composition of fulvic acids occurred upon the mechanoactivation of peat: the amount of oxygen-containing groups and unsubstituted aliphatic structures increased. Carboxyl groups at the aromatic rings of fulvic acids are most reactive; this fact is responsible for their role in sorption and detoxification processes.

Fungal degradation of elemental carbon in Carbonaceous gold ore

Phanerochaete chrysosporium was used to decompose elemental carbon in Carbonaceous gold ore and enhance cyanide recovery of gold. The degradation of elemental carbon amounted to 34% due to fungal treatment for 14days. A positive correlation between the fungal degradation of elemental carbon and the activity of degradation enzymes was noted. Organic acids and nitrogenous bases, which are generated by the fungi, caused the degradation of elemental carbon indirectly. P. chrysosporium caused a surface exfoliation of elemental carbon in the form of layers and the destruction of the microcrystalline and pore structure. The amount of oxygen-containing groups and of aliphatic groups was increased. The amount of aromatic rings, the specific surface area, the pore volume and the condensation index of aromatic rings were decreased. Also the thermal properties of elemental carbon changed significantly, whereas the amount of the low-stability compounds was increased. P. chrysosporium can reduce the interference of elemental carbon with the cyanide recovery of gold. The amount of gold recovery increased from 44% to 62%. This improvement is ascribed to the combined effect of degradation and passivation of elemental carbon by P. chrysosporium.

Analysis of Structural Features of Humic Acids Fractions after Mechanochemical Modification

Humic substances are the major components of soil, peat and brown coal. They can be fractionating into fulvic acids (FA), brown humic acids (BHA) and gray humic acids (GHA). In this work we investigated the influence of mechanochemical modifications on structural composition of HAs main fractions using the methods of IR and 1H MRS spectroscopy. The IR spectroscopy results has shown that HA has different chemical composition in comparison with GHA and BHA. Potentiometric titration showed that mechanoactivation (MA) with thiourea increases the amount of oxygen-containing groups up to 2.5. For the first time we studied the impact of modifying agent of thiourea on the structural composition and acid-base properties of HAs major fractions - GHA and BHA during the mechanoactivation process.

Catalytic Oxidative Carbonylation over Cu2O Nanoclusters Supported on Carbon Materials: The Role of the Carbon Support

AbstractStable catalysts prepared by dispersing Cu2O nanoparticles on activated carbon were investigated in the oxidative carbonylation of methanol to dimethyl carbonate. The effect of the surface oxygen containing groups (OCGs) on the rate of dimethyl carbonate formation and the selectivities of the catalyst for dimethyl carbonate and the byproduct methyl formate were determined. The carbon support surface OCGs played a key role in the oxidative carbonylation. For carbon supports with the same amount of OCGs, the highest catalytic activity was achieved at a certain level of Cu loading. The optimal Cu loading as well as catalytic activity increased linearly with the amount of OCGs. The active sites of the catalysts were the Cu2O nanoparticles that coordinated to the OCGs on the carbon surface.

Longitudinal unzipping of carbon nanotubes and their electrochemical performance in supercapacitors

The capacitive properties of graphene nanoribbons (GNRs) with different reduction levels were investigated. GNRs have been synthesized through thermal reduction of oxidized GNRs in the temperature range 100–400 °C. Oxidized GNRs were synthesized by longitudinal unzipping of multi-walled carbon nanotubes (MWCNTs) by means of chemical treatments. Scanning electron microscopy and transmission electron microscopy observations showed, that the efficient tube unzipping yielded improved effective surface area without any tube annihilation by the unzipping process of MWCNTs. Electrochemical studies indicated that through unzipping of MWCNTs, specific capacitance increased from 8 to 28 F g−1 at discharge current density of 0.5 A g−1, confirming increased active surface area and increased defect density in the MWCNTs surface. Unzipping of MWCNTs resulted in decreased rate capability of the electrode because of low electrical conductivity due to oxidization during the unzipping process. Thermal reduction of unzipped sample affected both specific capacitance and rate capability of electrodes. The highest specific capacitance of 62 F g−1 at discharge current density of 0.5 A g−1 was obtained for the sample unzipped and thermally annealed at about 150 °C. The amount of oxygen-containing groups was shown to be an important factor influencing the performance of the GNRs. These results make unzipped MWCNTs promising electrode materials for supercapacitor applications.

Fundamental electrochemistry of three-dimensional graphene aerogels

3D-architectured graphene is an emerging electrode material because of its ultra-low mass density and hierarchically connective pore-structure, which can provide a large accessible surface area and also enhance mass and electron transport. However, few reports are concerned with the fundamental electrochemical study of this fascinating material. In this work, we prepared reduced graphene oxide aerogel (RGOA) samples by thermal reduction of the original graphene oxide aerogel (GOA) at different temperatures and comparatively studied their structure and fundamental electrochemical performance. By using three representative inner- and outer-sphere redox probes, we found that RGOA, which was reduced at 250 °C outperforms its analogues by providing the lowest ΔEp as well as the highest k0. This is due to its abundant accessible active sites, which can effectively interface with electrolytes, facilitate electron transfer, and provide multiplexed and highly conductive pathways. In contrast to 2D-structured graphene, the electrochemical performance of 3D-architectured graphene is influenced by not only the amount of oxygen-containing groups and structural defects, but also by the macropores and surface roughness, which enhance hydrophilicity/hydrophobicity. The as-constructed RGOA-based sensor shows good sensitivity and selectivity for the detection of dopamine. This study adds a new dimension to the electrochemical performance and applications of 3D-architectured graphene.

Template-assisted low temperature synthesis of functionalized graphene for ultrahigh volumetric performance supercapacitors.

We demonstrated the fabrication of functionalized graphene nanosheets via low temperature (300 °C) treatment of graphite oxide with a slow heating rate using Mg(OH)2 nanosheets as template. Because of its dented sheet with high surface area, a certain amount of oxygen-containing groups, and low pore volume, the as-obtained graphene delivers both ultrahigh specific gravimetric and volumetric capacitances of 456 F g(-1) and 470 F cm(-3), almost 3.7 times and 3.3 times higher than hydrazine reduced graphene, respectively. Especially, the obtained volumetric capacitance is the highest value so far reported for carbon materials in aqueous electrolytes. More importantly, the assembled supercapacitor exhibits an ultrahigh volumetric energy density of 27.2 Wh L(-1), which is among the highest values for carbon materials in aqueous electrolytes, as well as excellent cycling stability with 134% of its initial capacitance after 10,000 cycles. Therefore, the present work holds a great promise for future design and large-scale production of high performance graphene electrodes for portable energy storage devices.

Influence of Functional Groups on Desorption of Organic Compounds from Carbon Nanotubes into Water: Insight into Desorption Hysteresis

Adsorption-desorption of nitrobenzenes, phenols, and anilines on five multiwalled carbon nanotubes (MWCNTs) with different degrees of surface oxidation were investigated to examine the influence of functional groups of both organic chemicals and CNTs on desorption hysteresis. Desorption hysteresis was not observed for nitrobenzenes, phenols, and 4-nitroaniline from all MWCNTs. Significant desorption hysteresis was observed for aniline and 4-methylaniline on surface-oxidized MWCNTs but not on unoxidized MWCNTs. Formation of an irreversible amide bond (i.e.,-CONH-) by amidation reaction of amino group of anilines with oxygen-containing groups (i.e., carboxyl or lactonic groups) on MWCNTs was observed. We proposed that desorption hysteresis could be attributed to the immobilization of organic compounds on the surface of CNTs resulting from the irreversible chemical reaction/binding. The irreversible chemical immobilization is compound functional group selective and dependent on the surface oxygen-containing groups of CNTs. Hysteresis index (HI) values of aniline or 4-methylaniline on MWCNTs increased with the amounts of oxygen-containing groups on MWCNTs. Moreover, HI values of anilines on a given oxidized MWCNT followed an order of 4-nitroaniline < 4-chloroaniline < aniline < 4-methylaniline.

Prolonged exposure of graphite oxide to soft X-ray irradiation during XPS measurements leads to alterations of the chemical composition

X-ray photoelectron spectroscopy is an indispensable technique to analyse the structural and chemical features of graphene-based materials. Such detailed characterization is often imperative prior to the usage of these materials for various applications. In this work, the effects of the continuous irradiation with soft X-rays during the analysis of graphite oxide with X-ray photoelectron spectroscopy were investigated. Prolonged exposure to the X-ray source was observed to cause an overall decrease in the amount of oxygen-containing groups, which could consequently lead to the wrong interpretation of the XPS analysis result. Proper and careful consideration on the time span of XPS analysis of graphite oxide is, thus, highly advocated.

A Simple Nickel Activation Process for Electroless Nickel-Phosphorus Plating on Carbon Fiber

A new nickel activation process was developed for metalizing the carbon fiber (CF) surface with electroless nickel plating. The oxidation and activation processes were examined using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and X-ray Diffractometry (XRD). XPS analysis showed that HNO3 oxidation improved the O/C ratio of the CF surface, which resulted in an increase in the amount of oxygen-containing groups. As activation time increased, both Nio cluster and Ni-P deposits increased. More than 50 mg of Nio clusters formed on the surface of 1g CF. SEM observations illustrated that particles and island-like shapes were developed from the Nio cluster, which helped to initiate the electroless nickel-plating on the CF surface. A continuous and compact coating with a thickness of about 2 to 3 μm was obtained. EDS results showed that the nickel and phosphorus content in the deposits was 97.34 wt.% and 2.66 wt.%, respectively. XRD indicated that the Ni-P coating was crystalline and the maximum deposition on 1 g CFs was as high as 9000 mg. As the results of the observations reveal, the activation method is a feasible alternative to Pd activation.

High performance supercapacitor electrode based on graphene paper via flame-induced reduction of graphene oxide paper

Reduced graphene oxide (r-GO) paper is easily synthesized by a flame-induced reduction of graphene oxide (GO) paper under ambient conditions. The X-ray diffraction and X-ray photoelectron spectroscope results confirm the effectivity of the flame-induced reduction. The resulting r-GO paper has a high surface area of 274.9 m2 g−1 and contains a certain amount of oxygen-containing groups. Electrochemical behaviors of the electrode built with the r-GO paper are investigated in two kinds of electrolytes, 2 M KOH aqueous solution and 1 M Et4NBF4-acetonitrile solution, respectively. The results show that the high values of the specific capacitance for the r-GO can be obtained in both electrolytes, which reach 212 and 160 F g−1 at the same current density of 1 A g−1 respectively. Also, the r-GO-based electrode and supercapacitor exhibits stable cycling performance. The good capacitive performances in KOH aqueous electrolyte are due to the high surface area and the remaining oxygen containing groups of the r-GO paper.

A thermodynamic approach to assess organic solute adsorption onto activated carbon in water

In this paper, the hydrophobicity of 13 activated carbons is determined by various methods; water vapour adsorption, immersion calorimetry, and contact angle measurements. The quantity and type of oxygen-containing groups on the activated carbon were measured and related to the methods used to measure hydrophobicity. It was found that the water-activated carbon adsorption strength (based on immersion calorimetry, contact angles) depended on both type and quantity of oxygen-containing groups, while water vapour adsorption depended only on their quantity. Activated carbon hydrophobicity measurements alone could not be related to 1-hexanol and 1,3-dichloropropene adsorption. However, a relationship was found between work of adhesion and adsorption of these solutes. The work of adhesion depends not only on activated carbon–water interaction (carbon hydrophobicity), but also on solute–water (solute hydrophobicity) and activated carbon–solute interactions. Our research shows that the work of adhesion can explain solute adsorption and includes the effect of hydrogen bond formation between solute and activated carbon.

Oxidation behavior of multiwall carbon nanotubes with different diameters and morphology

Multiwall carbon nanotubes (MWNT) with three medium diameters (20–22, 9–13, and 6–8nm) and different morphology were chemically oxidized using concentrated nitric acid, mixture of nitric and sulfuric acids (“mélange” solution) and mixture of sulfuric acid and hydrogen peroxide (“piranha” solution). Influence of MWNT type and structure as well as type of oxidizer on the surface composition and structure of nanotubes after oxidation was investigated. Acid–base titration, X-ray photoelectron spectroscopy and thermal gravimetric analysis were used for quantitative and qualitative investigation of surface group composition of initial and oxidized nanotubes. Amount of oxygen-containing groups on the surface of oxidized MWNT depends on the type of initial MWNT. It was found that ratio of different oxygen containing groups is less dependent on the type of oxidizer. Electrophysical properties of initial and oxidized nanotubes were investigated in temperature range 4–293K and main types of electrical conductivity were determined. It was shown that oxidation results in decrease in electrical conductivity of all samples with simultaneous change in the conductivity mechanism. Dispersive behavior of initial and oxidized nanotubes in different commonly used solvents was investigated. It was shown that oxidation leads to the improvement of sedimentation stability of MWNT in polar solvents.

Influence of parent graphite particle size on the electrochemistry of thermally reduced graphene oxide

Electrochemical applications of graphene are of very high importance. For electrochemistry, bulk quantities of materials are needed. The most common preparation of bulk quantities of graphene materials is based on oxidation of graphite to graphite oxide and subsequent thermal exfoliation of graphite oxide to thermally reduced graphene oxide (TR-GO). It is important to investigate to which extent a reaction condition, that is, composition of the oxidation mixture and size of graphite materials, influences the properties of the resulting materials. We characterised six graphite materials with a range of particle sizes (0.05, 11, 20, 32, 35 and 41 μm) and the TR-GO products prepared from them by use of scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetric performance of the TR-GO samples was compared using ferro/ferricyanide and ascorbic acid. We observed no correlation between size of initial graphite and properties of the resultant TR-GO such as density of surface defects, amount of oxygen-containing groups, or rate of heterogeneous electron transfer (HET). A positive correspondence between HET rate and high defect density as well as low amounts of oxygen functionalities was noted. Our findings will have profound influence upon practical fabrication of graphene for applications in sensing and energy storage devices.

A Facile Approach to the Synthesis of Graphene Nanosheets Under Ultra-Low Exfoliation Temperature

High specific surface area graphene nanosheets have been obtained from graphite oxide by using an effective modified exfoliation method under vacuum, the exfoliation temperature (135 degrees C) is much lower than that conventionally applied (1050 degrees C) to obtain monolayer graphene sheets via rapid thermal shock. These products have fluffy and highly porous structure and with a lateral size typically of a few micrometers. Transmission electron microscopy (TEM) observation shows that it looks like a wrinkled transparent ultrathin film consisting of single or few-layer graphene sheets, and their Brunauer-Emmett-Teller surface area is as large as 750 m2/g. Simultaneously, X-ray photoelectron spectroscopy analysis revealed that considerable amount of oxygen-containing groups (C/O ratio, 5:1) retained on the graphene sheets after exfoliation process, which would provide convenience for further modification of the surface properties and chemistry of graphene sheets. This work offers a facile and scalable approach to fabricate graphene oxide and opens up a new vista of various potential applications electronics and composite materials.

Chemically-modified graphenes for oxidation of DNA bases: analytical parameters

We studied the electroanalytical performances of chemically-modified graphenes (CMGs) containing different defect densities and amounts of oxygen-containing groups, namely graphite oxide (GPO), graphene oxide (GO), thermally reduced graphene oxide (TR-GO) and electrochemically reduced graphene oxide (ER-GO) by comparing the sensitivity, selectivity, linearity and repeatability towards the oxidation of DNA bases. We have observed that for differential pulse voltammetric (DPV) detection of adenine and cytosine, all CMGs showed enhanced sensitivity to oxidation, while for guanine and thymine, ER-GO and TR-GO exhibited much improved sensitivity over bare glassy carbon (GC) as well as over GPO and GO. There is also significant selectivity enhancement when using GPO for adenine and TR-GO for thymine. Our results have uncovered that the differences in surface functionalities, structure and defects of various CMGs largely influence their electrochemical behaviour in detecting the oxidation of DNA bases. The findings in this report will provide a useful guide for the future development of label-free electrochemical devices for DNA analysis.

Synthesis of nanoporous carbons from mixtures of coal tar pitch and furfural and their application as electrode materials

Synthetic nanoporous carbons are prepared by polymerization of mixtures containing coal tar pitch and furfural in different proportions, followed by carbonization of obtained solid product and steam activation of the carbonizate. The chemical composition of the initial mixture significantly affects the physicochemical properties (surface area, pore structure, electro resistance and amount of oxygen-containing groups on the surface) of the obtained materials. The incorporation of oxygen in the precursor mixture by means of furfural, has a strong influence in the synthetic step; increasing the furfural content facilitates the formation of a solid product characterized by a large oxygen content. Moreover, the solid product is more reactive towards activation as the furfural content increases, giving rise to nanoporous carbons with large surface areas and unique chemical features (high density of oxygen functionalities of basic nature). These nanoporous carbons have been investigated as electrodes in electrochemical applications.