Preparation and characterization of trilobal activated carbon fibers

The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N₂ adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO₂ flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N₂ adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m²/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N₂ adsorption measurements.     

Dielectric investigation of isotropic and anisotropic solutions of cellulose acetate in dioxane

The dielectric and optical characteristics of a sample of cellulose acetate (DS = 2.45) in dioxane solutions were studied at 10–50°C of concentration 10–50 wt% to include both isotropic and anisotropic phases. The study showed that the loss maximum, ε_max″, magnitude of polarization, (ε₀ ? ε_∞), static dielectric constant, ε₀, time of relation, (2πf_m)^?1, and refractive index, n_D, steadily increase with concentration up to the critical concentration (41 wt%) and then decrease. The mean-square dipole moment, 〈gμ²〉, decreases steadily up to the critical concentration then remains nearly constant, indicating that the isotropic solution changes to anisotropic, with smaller mean-square dipole moment. Comparison between the results of cellulose acetate (CA) and those of hydroxypropyl cellulose (HPC) reveals that, at the critical concentration in dioxane, the cholesteric structure of HPC possesses a greater mean-square dipole moment with higher temperature coefficient than does CA. The activation energy of the relaxation process for hydroxypropyl cellulose is higher, indicating a greater intrachain interaction compared with cellulose acetate.     

Preparation and properties of carbonaceous mesophase-II highly soluble mesophase from ethylene tar modified using aluminum chloride as a catalyst

A carbonaceous anisotropic mesophase, highly soluble in THF and quinoline, was prepared from ethylene tar pitch (ETP) modified using aluminum chloride as a catalyst. A mesophase pitch prepared at 360°C under vigorous nitrogen flow and stirring from ETP modified with 10 wt% of AlCl₃ at 250°C for 7 hr exhibited solubility of 80 wt% in quinoline at 90 vol% of anisotropic content, its solubilities in THF and pyridine being as high as 52 and 62 wt%, respectively. Such a high solubility of the mesophase pitch is ascribed to the naphthenic groups of its component molecules which are produced during the modifying reaction catalyzed by AlCl₃. The moderate molecular size of modified ETP is another advantage. The anisotropic mesophase of high solubility and low melting temperature is transformable into a flow domain texture by annealing. Easy spinning into highly oriented fibers is expected.     

Effects of chemical modification of petroleum cokes on the properties of the resulting activated carbon

Activated carbons have been prepared from petroleum cokes by the combination of a chemical treatment with HClO₄ or H₂O₂ and a chemical activation with KOH at a constant KOH/coke ratio of 3/1. The influence of different chemical treatments on the properties of the activated carbon precursors and final carbons activated with KOH was invested by using XRD, FTIR, and BET techniques. XRD results indicated that the value of interplanar distance d₀₀₂ increased by chemical treatment and the disappearance of the peak corresponding to 0 0 2 faces correlated to high specific surface area. FTIR studies showed that chemical modification promoted the formation of surface oxygen functionalities. Significant effects on BET surface area, pore texture and iodine adsorption capacity were evidenced. The results show that chemical modification prior to activation dramatically increased the BET surface area and total pore volume of the resulting activated carbon. Modified petroleum coke based activated carbon with chemical activation had higher specific surface area (2336 m²/g) and better iodine adsorption value (1998 mg/g).     

Optimization of borosilicate glass/CaTiO3-TiO2 composite via altering prefiring temperature and particle size

Low-temperature co-fired ceramic (LTCC) with middle permittivity is very crucial to the miniaturization of components. Based on our previous study on the glass/CaTiO₃-TiO₂ composite, prefiring temperature and particle size of CaTiO₃-TiO₂ ceramic were optimized in this study to promote the performance of the composites. Comparing with our previous study, after being sintered with 50 wt% glass at 875°C, CaTiO₃-TiO₂ ceramic prefired at 1275°C with particle size of 3.38 μm showed excellent properties of sintering density = 3.33 g/cm³, ε_r = 30.2, tan δ = 0.0005 (7 GHz). In addition, surface roughness of green tapes was also improved after optimization. The material has a good chemical stability and shrinkage matching with silver, making it a very promising candidate material for LTCC applications.     

Characterization of Mg-substituted hydroxyapatite synthesized by wet chemical method

Mg-substituted hydroxyapatite made up of needle-like and plate-like particles containing different amounts of Mg (between 0.21 wt% and 2.11 wt%) were prepared via wet chemical precipitation method of a homogenous suspension of Mg(OH)₂/Ca(OH)₂ and an aqueous solution of H₃PO₄. According to the data of Brunauer–Emmett–Teller method and field emission scanning electron microscopy, high specific surface area Mg-substituted hydroxyapatite was obtained. Specific surface area of as-synthesized powders increased from 94.9 m² g⁻¹ to 104.3 m² g⁻¹ with increasing concentration of Mg up to 0.64 wt%. Fourier transform infrared spectroscopy, X-ray powder diffraction, differential thermal analysis, and heating microscopy, were used to evaluate thermal stability and sintering behavior of synthesis products. Increase in concentration of Mg in synthesis products (≥0.83 wt%) promoted decomposition of Mg-substituted hydroxyapatite to Mg-substituted β-tricalcium phosphate after thermal treatment.     

Performance as electrode of electrical double layer capacitor of activated carbon prepared from bamboo using guanidine phosphate and CO<Subscript>2</Subscript> activation

The electrochemical performances of an electrical double layer capacitor were investigated regarding the activated carbon prepared from bamboo by a new approach, that is, the combination of delignification, addition of guanidine phosphate, and CO₂ activation. In this study, a 1 M H₂SO₄ aqueous solution was used as the electrolyte of the capacitor. The physical properties, such as the BET specific surface area of the carbon material, depend on the preparation conditions of the activated carbon. A TEM image indicated that the addition of guanidine phosphate did not facilitate the graphitization and did not prevent activation by CO₂. The apparent reaction equation for the CO₂ activation was first-order, which is reasonable for physical activation. The electrochemical performances of the carbon material depended on the preparation conditions of the carbon material, such as the heat treatment temperature, amount of added guanidine phosphate, and CO₂ activation time. The sample prepared under the following conditions (the amount of added guanidine phosphate: 9 wt%, the heat treatment temperature: 800 °C, CO₂ activation time: 3 h) had the highest performance (153 F g^?1 at 1000 mA g^?1) because the sample had the highest BET specific surface area (2001 m² g^?1).     

Structure of K2Co3-loaded activated carbon fiber and its deodorization ability against H2S gas

Coal tar pitch containing finely dispersed KOH was spun centrifugally, followed by stabilization through heating to 330°C under a (1:1) mixture of air and CO₂ and carbonization/activation by heating to 850°C under CO₂. The activated carbon fiber obtained possessed of a specific surface area of 491 m²g⁻¹ and contained ca. 2% of K as K₂CO₃ over the peripheral region of fiber. The fiber showed high deodorization ability against 30 ppm of H₂S gas in air at ambient temperature. H₂S gas did not diffuse to the most interior parts of the fiber and was oxidized around outer regions of the fiber. Elemental sulphur was deposited in the fiber after H₂S absorption. The deodorization mechanism was discussed. The role and action of the K₂CO₃ supported was explained.     

Electrochemical behavior of pyrite in sulfuric acid solutions containing silver ions

A systematic electrochemical study of pyrite in H₂SO₄ solutions containing dissolved silver was undertaken to gain more information about the transfer of silver ions to pyrite and their role in enhancing the direct oxidation of pyrite. The results of cyclic voltammetry experiments provide additional evidence of the formation of metallic silver on the FeS₂ surface under open-circuit conditions. A pyrite electrode held at the open-circuit potential for 2 h in the presence of 10^–3 m Ag⁺ exhibits a large and sharp anodic peak at about 0.7V. The current associated with this peak is the result of the dissolution of metallic silver deposited during the initial conditioning period. There is no evidence of silver deposition without preconditioning until the potential drops below about 0.6V for Ag⁺ concentrations ranging from 10^–4 to 10^–2 m. However, subsequent silver deposition appears to be very sensitive to the dissolved silver concentration in this range. There is also evidence that the state of the pyrite surface has a pronounced influence on its interaction with silver ions. Agitation has also been found to have a significant effect on the electrochemistry of the Ag–FeS₂ system.     

Preparation of micro-porous monolithic activated carbon from anthracite coal using coal tar pitch as binder

Monolithic activated carbon (MAC) has been produced from steam activation of monoliths prepared by mixing coal powders with high-temperature coal tar binder for a long time. However, this process leads to poor working conditions, environmental pollution, and waste of resource. This study investigated the use of coal tar pitch as binder to prepare MAC with high surface area, micro-pore structures, and strong mechanical strength. The performances of the MACs with both coal tar and coal tar pitch as binders were compared. The product yield of MAC bonded with coal tar pitch (MAC_p) was 10% higher than that with coal tar (MAC_T). The BET surface area, micropore volume, and average pore diameter of MAC_P were 837.99 m² g^?1, 0.346 m³ g^?1, and 1.776 nm, respectively, which were all superior to the corresponding values of MAC_T. Only the attrition resistance strength of MAC_P was slightly lower than that of the MAC_T. The SEM images showed that the cokes on the surface of both MACs distributed identically and uniformly. Furthermore, XRD results revealed that the pore-expanding reactions mainly led to the reduction of carbon crystallite along with the stacking direction rather than horizontal direction during steam activation process. This work demonstrates that cost-effective MAC can be prepared with the coal tar pitch as binder and the results of the investigation presented in this work provide new and important information necessary to the successful application of MACs in industrial field.     

Effect of vanadium surface density and structure in VOx/TiO<Subscript>2</Subscript> on selective catalytic reduction by NH<Subscript>3</Subscript>

We investigated the correlation between vanadium surface density and VOx structure species in the selective catalytic reduction of NOx by NH₃. The properties of the VOx/TiO₂ catalysts were investigated using physicochemical measurements, including BET, XRD, Raman spectroscopy, FE-TEM, UV-visible DRS, NH₃-TPD, H₂-TPR, O₂-On/Off. Catalysts were prepared using the wet impregnation method by supporting 1.0-3.0 wt% vanadium on TiO₂ thermally treated at various calcination temperatures. Through the above analysis, we found that VOx surface density was 3.4 VOx/nm², and the optimal V loading amounts were 2.0-2.5 wt% and the specific surface area was 65-80m²/g. In addition, it was confirmed that the optimal VOx surface density and formation of vanadium structure species correlated with the reaction activity depending on the V loading amounts and the specific surface area size.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

Double layer capacitance of high surface area carbon nanospheres derived from resorcinol–formaldehyde polymers

Micro-mesoporous bimodal carbon nanospheres with high surface areas were synthesized by a combined use of surfactant templating technique and BaO₂ chemical activation one. Starting spherical nanopolymer/surfactant composites were prepared by the NaOH-catalyzed reaction of resorcinol (R) and formaldehyde (F) in the presence of cetyltrimethylammonium bromide (CTAB) as a core template and 1,3,5-trimethylbenzene (TMB) and tert-butanol (t-BuOH) as cosurfactants. After pretreatment with hydrochloric acid, the composite materials were calcined at 1000 °C in N₂ coexistent with varying weight ratios of BaO₂ to RF polymer ranging from 0 to 11. It produced micro-mesoporous bimodal carbon nanospheres of 124–143 nm diameter, with specific surface areas as high as 1884 m² g⁻¹ or up to 3301 m² g⁻¹, in contrast to microporous ones with smaller surface areas obtained at low BaO₂-loadings. The electrochemical double layer capacitance of the resulting nanocarbons in 0.5 M H₂SO₄ showed a marked increase with specific surface areas, up to as high as 219 F g⁻¹ for the highest surface area carbon material.     

Spherical activated carbon derived from spherical cellulose and its performance as EDLC electrode

Spherical activated carbons (ca. 30–100 μm in diameter) were synthesized from commercial spherical cellulose beads. The addition of guanidine phosphate was performed as the pretreatment, and CO₂ activation was applied for enhancing the specific surface area. The addition of guanidine phosphate drastically improved the yield of carbon during the activation process. The specific surface area reached 1545 m² g^?1 for the sample heat‐treated at 850°C for 1 h in flowing N₂ and continuously for 3 h in flowing CO₂ activation. The calculated capacitance values per area (F m^?2) for the pore size of less than 1 nm was large in the case of small current density. The distortion of the solvation shell could be the reason for the large capacitance value for the small pore size of less than 1 nm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40950.     

A study of the water–gas shift reaction in Ru-promoted Ir-catalysed methanol carbonylation utilising experimental design methodology

The water–gas shift reaction occurs competitively to the main reaction of the Ir-catalysed methanol carbonylation process. To study the effect of seven factors including temperature, pressure, iridium, ruthenium, methyl iodide, methyl acetate and water concentrations on the formation of hydrogen and carbon dioxide as a result of the water–gas shift reaction and other side reactions in the carbonylation of methanol to acetic acid, the experimental design method combined with response surface methodology (RSM) was utilised. Central composite design at five levels (with α=1.63) was used to design experiments. A quadratic model that included the main and interaction effects of variables for H₂ and CO₂ formation was developed. For two responses, R² was in reasonable agreement “Adj-R²”. Furthermore, statistical tests confirmed the accuracy and the precision of models developed in this research. For CO₂ formation, pressure, iridium and methyl iodide concentrations and for H₂ formation, water and iridium concentrations had the most pronounced effects. Optimum conditions to minimise H₂ and CO₂ and CH₄ formation were determined as follows: temperature of 189 °C, pressure of 32.0 bar, iridium content of 859 ppm, ruthenium concentration of 528 ppm, methyl iodide content of 8.68 wt%, methyl acetate concentration of 23.9 wt% and water content of 6.49 wt%. Ultimately, an experiment at optimum conditions revealed satisfactory agreement between the experimental and predicted data.     

Catalytic synthesis of 1,6‐dicarbamate hexane over MgO/ZrO2

MgO/ZrO₂ catalyst was prepared for the synthesis of 1,6‐dicarbamate hexane (HDC) using dimethyl carbonate (DMC) and 1,6‐diamine hexane (HDA) as raw materials. When the catalyst is calcined at 600 °C and MgO load is 6 wt%, the catalyst exhibits better activity. When the concentration of catalyst is 2 g (100 mL)^?1 DMC, n(HDA):n(DMC) = 1:10, reaction time is 6 h under reflux temperature, and the yield of 1,6‐dicarbamate hexane is 53.1%. HDC yield decreases from 53.1% to 35.3% after MgO/ZrO₂ being used for three times. The decrease in specific surface area may be attributed to deactivation of MgO/ZrO₂. Copyright © 2007 Society of Chemical Industry     

Catalytic NO–H2–CO–O2 reactions over Pt-supported mesoporous yttrium oxide

Catalytic light-off of a stream of NO, H₂, CO in an excess O₂ has been studied over various metal oxides loading 1 wt% Pt. Because a low-surface area Y₂O₃ (<5 m² g⁻¹) was found to exhibit the highest de-NO_x activity, a mesoporous Y₂O₃ was then synthesized from an yttrium-based surfactant mesophase templated by dodecyl sulfate , which was anion-exchanged by acetate (AcO = CH₃COO⁻). The product showed a 3-D mesoporosity with a large surface area (396 m² g⁻¹) and the Pt-supported catalyst achieved much improved light-off characteristics suitable for the low-temperature de-NO_x in the presence of CO and excess O₂.     

Activation of coal tar derived needle coke with K2CO3 into an active carbon of low surface area and its performance as unique electrode of electric double-layer capacitor

Raw needle coke from coal tar pitch was activated with K₂CO₃ at a coke:carbonate weight ratio of 1:4, to prepare an electrode for an electric double-layer capacitor (EDLC). Although the surface area of the coke activated at 900 °C for 3 h was as small as 20 m²/g, with a very high yield, the coke achieved capacitances per weight and volume of 20 F/g and 20 F/ml, respectively, in the two-electrode system, by charging at 2.7 V. The surface area of KOH-activated coke with a similar ratio (coke:hydroxide = 1:4, wt:wt) was over 2300 m²/g, and it exhibited capacitance per weight and volume values of 42 F/g and 17 F/ml, respectively. The coke activated by K₂CO₃ was found to be further activated by the charging. This electrochemical activation, which has been reported as activation in an electric field, was investigated by cyclic voltammetry in order to clarify it. The graphitic and pore structures of the coke after the electrochemical activation were analyzed by XRD to confirm retention of the graphene structure. Xe-NMR showed that the formation of small new pores was induced in the cathode material, increasing the surface area from 6 m²/g to 18 m²/g before use, although the pore volume was around 0.015-0.017 m³/g both before and after the charging. This activation with K₂CO₃ and a deeper understanding of the activation on charging suggest future directions for the preparation of electrode carbon for EDLCs.     

Kinetics of Silver Extraction with Triisobutylphosphine Sulfide

Abstract

Kinetics of silver extraction from nitrate solutions with triisobutylphosphine sulfide dissolved in n-octane was studied. Experiments were carried out in a rotating diffusion cell. The rate constants of forward and reverse chemical reactions were evaluated: the former k^? _f = 1.064 × 10^?3 m⁹/(mol³·s) and the latter k^? _f = 2.085 × 10^?1 s^?1. The value obtained for the activation energy shows that the process of silver extraction with triisobutylphosphine sulfide is a predominantly diffusion-controlled process.     

Synthesis of superhydrophobic nanocomposite coating films for self-cleaning glass using nanoemulsion technique

This work aims to fabricate new potent superhydrophobic-hybrid coated nanocomposites used as a self-cleaning coating on the glass surface. Three (styrene/vinyl acetate) copolymers with monomer molar ratios of 0.06:0.17, 0.12:0.11, and 0.17:0.06 denoted as Z1-, Z2-, and Z3-copolymers were synthesized using the emulsion phase inversion concentration (EPIC) method. Two functionalized SiO₂-NPs using dodecyl triethoxysilane and hexadecyl trimethoxysilane as coupling agents denoted as E-NPs and F-NPs, respectively were fabricated by a sol–gel process to promote the hydrophobicity properties of the synthesized SiO₂-NPs. New hybrid composites denoted as P_y and T_y(y = 1, 2, and 3) were fabricated by incorporating 1, 3, and 5 wt% of the functionalized SiO₂-NPs (E-NPs or F-NPs) into the Z3-copolymers matrix, respectively. The chemical structures of the synthesized copolymers, unfunctionalized SiO₂-NPs, and the hybrid composites were elucidated by FTIR and ¹HNMR spectroscopes. The surface wettability and topography of the glass-surface coated by synthesized (styrene/vinyl acetate) copolymers and the silica hybrid composites were analyzed using water contact angle, scanning electron, and atomic force microscopes. The results showed that a highly superhydrophobic coated hybrid composite with a contact angle of 161.48° was achieved by Z3-copolymer/F5-NPs denoted as T3-composite at F5-NPs concentration of 5 wt%.