Content Of Oxygen-containing Groups Research Articles

Home-made epoxy emulsion sizing agent for treating carbon fibers: Thermal stability and mechanical properties

The thermal degradation kinetics of a home-made epoxy emulsion sizing agent for carbon fiber has been investigated by thermogravimetric analysis (TG). The thermal degradation activation energy, calculated by Flynn–Wall–Ozawa method and Friedman method, is in good agreement with each other, and the values are 214.03 and 220.87 kJ/mol, respectively. The reaction order n (4.7414) and frequency factor A (1.6906 × 1017) were determined by Friedman method. The studies by scanning electron microscope, X-ray photoelectron spectroscopy (XPS), tensile strength of single fiber and interlaminar shear strength (ILSS) revealed that the sizing agent had improved the content of oxygen-containing groups on carbon fiber, increased the tensile strength of single fiber, and effectively enhanced the interfacial properties of carbon fiber/epoxy composites.

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO2 particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO2 particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO2 particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO2, respectively, when the nano-SiO2 content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO2 containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO2. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO2-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO2 to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.

Humic acids-based hierarchical porous carbons as high-rate performance electrodes for symmetric supercapacitors.

Two kinds of hierarchical porous carbons (HPCs) with specific surface areas of 2000 m(2)g(-1) were synthesized using leonardite humic acids (LHA) or biotechnology humic acids (BHA) precursors via a KOH activation process. Humic acids have a high content of oxygen-containing groups which enabled them to dissolve in aqueous KOH and facilitated the homogeneous KOH activation. The LHA-based HPC is made up of abundant micro-, meso-, and macropores and in 6M KOH it has a specific capacitance of 178 F g(-1) at 100 Ag(-1) and its capacitance retention on going from 0.05 to 100 A g(-1) is 64%. In contrast, the BHA-based HPC exhibits a lower capacitance retention of 54% and a specific capacitance of 157 F g(-1) at 100 A g(-1) which is due to the excessive micropores in the BHA-HPC. Moreover, LHA-HPC is produced in a higher yield than BHA-HPC (51 vs. 17 wt%).

Hierarchical porous carbon derived from sulfonated pitch for electrical double layer capacitors

Hierarchical porous carbon (HPC) has been synthesized using sulfonated pitch as a precursor with a simple KOH activation process. Sulfonated pitch has a high content of oxygen-containing groups which enable it to be easily wetted in KOH solution and facilitate the activation process. The effect of the activation agent to precursor ratio on the porosity and the specific surface area is studied by nitrogen adsorption–desorption. A maximum specific surface area of 3548 m2 g−1 is achieved with a KOH to sulfonated pitch ratio of 3 and this produces a structure with micro-, meso- and macropores. Among the various HPC samples, the sample prepared with an activation agent to precursor ratio of 1.5 exhibits the best electrochemical performance as an electrode in an electrical double layer capacitor (EDLC) in 6 M KOH electrolyte. Its gravimetric specific capacitance is 157 F g−1 at a current density of 100 A g−1 and it has a capacitance retention ratio of 98.4% even after 10,000 cycles. The sample also presents outstanding electrochemical performance in 1 M Li2SO4 and 1 M TEA BF4/PC electrolytes. Thus, HPC derived from sulfonated pitch is a promising electrode material for EDLCs.

Ultrastrong Single-Walled Carbon Nanotubes/Graphene Oxide Nanosheets Hybrid Network Films as Flexible Electrode for Energy Storage

Homogeneous free-standing SWCNT/GO hybrid network films were fabricated using vacuum filtration method and their performances to be used as flexible electrodes in electrochemical capacitors were studied. Firstly, the SWCNT/GO hybrid films were treated under different temperature to investigate the influence of oxygen-containing groups on GO nanosheets on capacitive performance of them. Our results showed that the content of oxygen-containing groups had great influence on the capacitive performance of SWCNT/GO hybrid films and that the film annealed at 250 degrees C under 5% H2/Ar flow displayed an optimal capacitive performance. For the film with SWCNT/GO mass ratio of 1:4, specific capacitances of 171.85, 162.9, 148.98, 133.8, 112.8 and 82.24 F/g corresponding to discharge current of 5, 10, 20, 40, 80 and 160 A/g, respectively, were achieved. Secondly, the influence of mass ratio of SWCNT/GO on capacitive performance of SWCNT/GO hybrid films was also demonstrated. The hybrid films exhibited extremely high mechanical strength with tensile strength up to 461 MPa and specific capacitance of 105.2 F/g at current density of 5 A/g in case of 1:1 mass ratio of SWCNT/GO. A higher specific capacitance of 206.7 F/s at discharge current of 5A/g was obtained for the films with SWCNT/GO mass ratio of 1:8. Our SWCNT/GO hybrid network films showed good flexibility and durability over 2000 bending cycles test, indicating the potential to be used in flexible energy-storage devices.

Electrochemical‐Reduction‐Assisted Assembly of a Polyoxometalate/Graphene Nanocomposite and Its Enhanced Lithium‐Storage Performance

Herein, we present an electrochemically assisted method for the reduction of graphene oxide (GO) and the assembly of polyoxometalate clusters on the reduced GO (rGO) nanosheets for the preparation of nanocomposites. In this method, the Keggin-type H4 SiW12O40 (SiW12) is used as an electrocatalyst. During the reduction process, SiW12 transfers the electrons from the electrode to GO, leading to a deep reduction of GO in which the content of oxygen-containing groups is decreased to around 5%. Meanwhile, the strong adsorption effect between the SiW12 clusters and rGO nanosheets induces the spontaneous assembly of SiW12 on rGO in a uniformly dispersed state, forming a porous, powder-type nanocomposite. More importantly, the nanocomposite shows an enhanced capacity of 275 mAh g(-1) as a cathode active material for lithium storage, which is 1.7 times that of the pure SiW12. This enhancement is attributed to the synergistic effect of the conductive rGO support and the well-dispersed state of the SiW12 clusters, which facilitate the electron transfer and lithium-ion diffusion, respectively. Considering the facile, mild, and environmentally benign features of this method, it is reasonable as a general route for the incorporation of more types of functional polyoxometalates onto graphene matrices; this may allow the creation of nanocomposites for versatile applications, for example, in the fields of catalysis, electronics, and energy storage.

Capacitive Performance of Ordered Mesoporous Carbons in Ionic Liquids

Ordered mesoporous carbons (BOMC) were prepared by doping boric acid using a hard-templating method, while a CMK-3 carbon (OMC) was also prepared for comparison. The capacitive performance of these two carbons was investigated in ionic liquid of EMImBF4 and EMImTSFI. As demonstrated by the structure analysis, BOMC possesses almost same surface area and pore size as OMC, while the former carbon possesses higher content of oxygen-containing groups. In ionic liquid electrolyte, the carbons mainly show typical electric double layer capacitance, and the capacitance retention ratio and ion diffusion of electrolyte is determined to the surface chemical property. BOMC present visible pseudo-capacitance due to the oxygenated groups in hydrophilic EMImBF4, while no visible pseudo-capacitive behavior was observed in hydrophobic EMImTSFI.

Surface properties and adsorption characteristics to methylene blue and iodine of adsorbents from sludge

Adsorbent materials created from wastewater sludge have unique surface characteristics and could be effective in adsorption applications. In this research, the sludge-adsorbents were generated by pyrolyzing mixtures of sewage sludge and H(2)SO(4). Scanning electron microscope (SEM), thermal analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) were used to analyze the properties of sludge-adsorbent. XPS results show that the adsorbent surface functional groups with high contents of oxygen-containing groups serve as active sites for the adsorption and affect the surface characteristics; the adsorption mechanism of methylene blue (MB) is mainly Brönsted acid-base reaction between the adsorbent surface and MB; and iodine atoms are bonded to the surface of the adsorbent mainly by dispersive interactions rather than by electrostatic interactions. The results also show that H(2)SO(4) level, pyrolysis temperature and sulfuric acid/sludge weight ratio actually affected the adsorption characteristics. Using the conditions (H(2)SO(4) level of 1-18 M, pyrolysis temperature of 650°C, and weight ratio of 0.8), the adsorption capacities for MB and iodine were 74.7-62.3 mg g(-1) and 169.5-209.3 mg g(-1), respectively.

Study of sodium interaction with calcium nitrate and carbonate in alkali metal chloride melts by IR and Raman spectroscopy

In the IR and Raman spectra of molten eutectic mixtures of alkali metal chlorides with additions of calcium nitrate and carbonate (without the introduction of sodium), vibrations of NO 3 − and CO 3 2− groups of symmetry D 3h were detected. After the introduction of sodium metal into the melts of oxygen-containing salts in amounts equal to the stoichiometric content of oxygen-containing groups, the spectra did not show the characteristic frequencies of the NO 2 − group or CO 3 2− vibrations, which is evidence of the complete oxidation of the alkali metal accompanied by reduction of the nitrate and carbonate groups to nitrogen dioxide and carbon dioxide, respectively. The results of spectroscopic studies are presented.

Improving Polarity of UHMWPE Through γ-Ray Irradiation and Its Application

Gamma-ray irradiation treatment in air has been used to induce some oxygen-containing groups onto the molecular chains of ultra-high molecular weight polyethylene (UHMWPE) to improve its polarity. The effect of γ-ray irradiation on the structure and polarity of UHMWPE was studied by the Fourier transform infrared spectroscopy, gel content measurement, and static contact angle measurement. Gamma-ray-irradiated UHMWPE was then blended with two commonly used engineering plastics, polyamide (PA) and polycarbonate (PC), and their mechanical and frictional properties were studied. The experimental results show that the content of oxygen-containing groups increased with irradiation dose, improving the polarity of UHMWPE. Both the friction coefficient and the yield strength of the blends with PA and PC decreased with increasing UHMWPE content. However, compared with the nonirradiated blends of the same UHMWPE content, the yield strength and notched impact strength of the irradiated blends were improved, while the friction coefficient decreased.

Thermal conversion of coal-tar pitch in the presence of silicon compounds

The effect of SiO2 and polycarbosilane (PCS) additives on the thermal degradation of coal-tar pitch at temperatures to 900°C was studied by thermogravimetric analysis, differential thermal analysis, mass-spectrometric analysis, IR spectroscopy, and electron microscopy. It was found that, in the presence of the test additives, the character of release and the quantitative composition of volatile degradation products changed, the degree of aromaticity of the carbon residue decreased, and the concentration of oxygen-containing groups in this residue increased. In the case of the PCS additive, the combined thermal conversion of both of the components occurred. In this case, the contribution of structurization processes increased to cause a nonadditive increase in the yield of solid residue. Silicon mainly occurred as organosilicon fragments with Si-C and Si-O-C bonds, an oxycarbide, and, probably, silicon carbide. In the case of the SiO2 additive, oxidation processes were enhanced; the yield of carbon somewhat decreased, and siloxane groups were present in the solid residue.

Electrochemistry of bilirubin oxidase at carbon nanotubes

In this paper, we compared the direct electron transfer and electrocatalytic properties of bilirubin oxidase (BOD) immobilized at two kinds of carbon nanotubes (CNTs), bamboo-CNTs and uniform-CNTs. X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the ratio of sp2 band to sp3 band and the content of oxygen-containing groups at the surface of uniform-CNTs were higher than that of bamboo-CNTs. Moreover, uniform-CNTs can be well separated at the surface of the electrode. Better electrochemical and electrocatalytic properties of BOD immobilized at uniform-CNTs were shown.

Properties of Pt/C catalysts prepared by adsorption of anionic precursor and reduction with hydrogen. Influence of acidity of solution

Carbon-supported Pt/C catalysts prepared with H2PtCl6 as metal precursor have been studied by temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and CO chemisorption in order to investigate the effect of acidity of the solution on the catalyst properties. The catalytic activity of the samples has been tested in structure insensitive reaction of cyclohexene hydrogenation. The catalysts were prepared by adsorption of platinum precursor on activated carbons with different pore structure followed by drying and reduction in flowing hydrogen at 523 K. The use of acidic and highly basic solution during the impregnation of microporous carbons led to highly dispersed catalysts with low activity. It has been suggested that a part of the supported metal became inaccessible to the organic substrate due to localization of metal particles in narrow pores of the support. However, in the range of intermediate solution pH, the activity per surface metal atom remained at a high level. Such phenomenon is attributed to the formation of bulky species of platinum precursor, which hardly penetrates into the small pores of the support, thus preventing a blocking effect. Effect of acidity of the solution proved significant for Pt/C catalysts on the activated carbons with the smaller micropores and higher concentration of oxygen-containing groups.

The oxidative modification of polypropylene surface in electrolytic-cathode atmospheric-pressure discharge

The effect of electrolytic-cathode atmospheric-pressure discharge in air on the surface of polypropylene immersed in a solution and on the hydrogen peroxide formation efficiency was studied. It was found that iron(II) sulfate admixtures lead to a substantial increase in the concentration of oxygen-containing groups on the surface and to a decrease in the concentration of hydrogen peroxide in the solution. A possible interpretations of the results is given.

The structural transitions of rayon under the promotion of a phosphate in the preparation of ACF

The molecular and physical structures of cellulosic rayon fiber during the stepwise heat treatment for the fabrication of activated carbon fiber (ACF) were researched by Fourier transform infrared spectroscopy, wide angle X-ray diffraction and elemental analysis. Dibasic ammonium phosphate (DAP) lowers the dehydration temperature of rayon evidently and acts also as a reactant besides as a catalyst. Group C=O is generated at 200 °C while group C=C appears at 250 °C. About 220–250 °C is a key temperature range where the chain, ring and crystal structures of rayon macromolecules are damaged completely to lose the basic characteristics of cellulose by dehydration. The drastic changes of weight loss, discoloration and shrinkage occur simultaneously. The bands of chemical groups decrease rapidly and go to disappear during carbonization. The activation at a lower temperature (750 °C) decreases the contents of oxygen-containing groups, but increases them at a higher temperature (950 °C). The microcrystalline structures are gradually formed near 800 °C and activation seems to be favor to the crystallization. A higher usage of the phosphate does not only affect the weight-losses of rayon fiber significantly, it also enhances the specific surface areas of ACF obviously.

Activated carbon sorbent with thioetheric sites—preparation and characterization

An activated carbon sorbent containing thioetheric sites (ACTS) was prepared by modification of the activated carbon with 2,2′-thiodiethanol. The specific surface area, pore volume, concentration of oxygen-containing groups and sulfur content of the sorbent were determined. The sorption behavior towards ions of some precious metals—Au(III), Pt(IV), Pd(II) and heavy metals—Ni(II), Zn(II), Fe(III), Cu(II), Pb(II), Cd(II) and Co(II) was studied. Selectivity towards gold, palladium and platinum in the pH range 1–9 was observed. The capacity for gold was 80 mg g−1. The sorption of Au(III) at pH 1 is not affected by milligram amounts of Ni(II), Zn(II), Fe(III), Cu(II), Pb(II), Cd(II) and Co(II). The sorbed gold species is Au(0).

Radiation degradation of blends polypropylene/poly(ethylene- co-vinyl acetate)

Physicochemical and mechanical characteristics of irradiated electron beam polypropylene/ethylene-vinyl acetate (PP/EVA) blends and individual components were investigated. Although oxidation of alkyl radicals in the blends proceeds slower than in PP, the total oxidation effect monitored by content of oxygen-containing groups shows opposite tendency. Blending with EVA does not affect degree of PP crystallinity. The enthalpy of melting and crystallization of the blends reveal phase separation between dispersed copolymer and PP matrix. In all studied blends, degradation prevails over tendency of EVA to cross-linking.

Improving the Compatibility of Polycarbonate/UHMWPE Blends through Gamma-Ray Irradiation

Gamma-ray irradiation treatment in air has been used as an alternative to the common surface treatment of ultrahigh molecular weight polyethylene (UHMWPE) powders to induce some oxygen-containing groups onto the molecular chain of UHMWPE to enhance its compatibility with polycarbonate (PC). The effect of gamma-ray irradiation on the structure and properties of UHMWPE was studied by FTIR, gel content measurement, mechanical property testing, and melt flow rate measurement. The mechanical properties and compatibility of polycarbonate/gamma-ray irradiated UHMWPE (γ-UHMWPE) blend were also studied. The experimental results show that gamma-ray irradiation partly causes oxidative degradation of UHMWPE and the content of oxygen-containing groups increases with irradiation dose. The surface hydrophilicity of UHMWPE is improved due to the presence of oxygen-containing groups. SEM observation of the fractured surface of the PC/UHMWPE blends indicates the compatibility is improved through γ-ray irradiation. Meanwhile, improved fracture toughness and mechanical strength can also be achieved; both yield and notched impact strength of PC/γ-UHMWPE blends are greatly increased from 39.7 MPa and 9.9 kJ/m2 to 49.2 MPa and 24.9 kJ/m2, respectively, compared with the PC/UHMWPE (85/15) blend. Gamma-ray irradiation treatment is efficient for enhancing the compatibility of polycarbonate/UHMWPE blends.

Pt/C stabilization for catalytic wet-air oxidation: Use of grafted TiO 2

The wet-air oxidation (WAO) process is effective in converting organic pollutants in wastewater to innocuous carbon dioxide. Supported Pt catalysts, particularly Pt/C, are effective but unstable. A novel catalyst, Pt on TiO 2-grafted carbon (Pt/TiO 2-C), has been developed for WAO. This catalyst is characterized by high activity and stability in WAO processes. Using transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), and Fourier transform infrared (FTIR) spectroscopy, the fresh and aged Pt/C catalysts were characterized, and the mechanism of catalyst deactivation was elucidated. The average Pt cluster size increased from about 2 to 10 nm after WAO of methanol in water at 220 °C for 200 h. These results indicate that Pt/C catalyst was deactivated due to migration and aggregation of the Pt clusters into large Pt particles. The increase in the content of oxygen-containing groups and carbonate species, as characterized by FTIR spectra in the aged catalyst, further suggests that the oxidation of carbon surface decreases the affinity between Pt and the carbon support, leading to extensive Pt aggregation. Thus, TiO 2 was grafted on to the carbon support to anchor and keep Pt from migrating and agglomerating, thereby obtaining a stable Pt/TiO 2-C catalyst. The efficacy of TiO 2 grafted on activated carbon in stabilizing the Pt/C catalyst was demonstrated in long-term catalytic performance tests. The efficacy of TiO 2 in anchoring and maintaining the Pt clusters in small ensembles were further demonstrated by characterizing the Pt–TiO 2 interactions and the morphology of Pt clusters using EXAFS.

Preparation and characterization of NaOH-activated carbons from phenolic resin

Chemically (NaOH) activated carbons (CACs) from phenolic resin were prepared at temperatures from 600 to 800 °C in N2. The effect of the NaOH/phenolic resin ratio and activation temperature on the BET surface area and carbon yield of the resulting carbons was investigated. The optimum NaOH/phenolic ratio is from 1.5 to 2.0 to produce high surface area and carbon yield at 600 °C. With increasing activation temperature from 600 °C to 800 °C, the BET surface area increased but the carbon yield decreased. NaOH-activated carbons have a higher concentration of narrow micropores (<10 Å) and a lower concentration of mesopores than a commercially available activated carbon, GAC-F400. Lower temperature (600 °C) NaOH-activated CAC-600 has a higher concentration of narrow micropores (<7 Å) than an 800 °C NaOH-activated carbon, CAC-800. Much higher adsorption capacity for CO2 and H2 is obtained with a NaOH-activated carbon as compared to GAC-F400. A higher content of oxygen-containing groups but without any hydrogen in CAC-600 is observed by EA and XPS. The adsorption isotherms of methyl tert-butyl ether (MTBE) show that CAC-800 has a higher adsorption capacity than GAC-F400 and CAC-600.