Adsorption of carbon dioxide on microporous carbon adsorbents

Adsorption isotherms of carbon dioxide on microporous carbon adsorbents prepared by activation with potassium sulfide in water vapor were measured. The measurements were carried out in the pressure interval from 1 Pa to 0.1 MPa at temperatures from 216.2 to 293.15 K. Based on the theory of volumetric filling of micropores, the main structural and energetic parameters of the microporous carbon adsorbents were calculated. The adsorption isosters of carbon dioxide were calculated from the adsorption isotherms in the same pressure and temperature ranges and approximated by linear dependences. The plots of the differential mole isosteric heats of adsorption vs amount adsorbed were constructed by using the adsorption isosters.     

Lattice dynamics of carbon chain inside a carbon nanotube

Based on the density functional theory, we obtain the optimum geometry of carbon chain inside a carbon nanotube. The phonon spectrum and specific heat of such a chain and nanotube hybrid system are calculated in terms of lattice dynamics theory. Some new phonon branches that have been obtained come from the coupling vibrations of the nanotube and the chain. The bending and stretching modes of the chain appear at about 520 cm(-1)and 1935 cm(-1) at Gamma point, respectively. It is found that the softening of G modes results mainly from the chain induced variations in the bond length on nanotube, independent of van der Waals interaction, while the stiffening of radial breathing mode is developed by the competition between the two factors. In the low-frequency region, the vibrational density of states are very different from that of the bare nanotube. Its specific heat implies the underlying quantized phonon structures and much large thermal conductivity in the hybrid system. In addition, the chain-length dependent vibration modes are calculated, from which it is expected that a finite chain of about 14 carbon atoms in the nanotube may produce the experimental Raman peak at about 1850 cm(-1).     

Encapsulation of carbon chain molecules in single-walled carbon nanotubes

The vacuum space inside carbon nanotubes offers interesting possibilities for the inclusion, transportation, and functionalization of foreign molecules. Using first-principles density functional calculations, we show that linear carbon-based chain molecules, namely, polyynes (C(m)H(2), m = 4, 6, 10) and the dehydrogenated forms C(10)H and C(10), as well as hexane (C(6)H(14)), can be spontaneously encapsulated in open-ended single-walled carbon nanotubes (SWNTs) with edges that have dangling bonds or that are terminated with hydrogen atoms, as if they were drawn into a vacuum cleaner. The energy gains when C(10)H(2), C(10)H, C(10), C(6)H(2), C(4)H(2), and C(6)H(14) are encapsulated inside a (10,0) zigzag-shaped SWNT are 1.48, 2.04, 2.18, 1.05, 0.55, and 1.48 eV, respectively. When these molecules come inside a much wider (10,10) armchair SWNT along the tube axis, they experience neither an energy gain nor an energy barrier. They experience an energy gain when they approach the tube walls inside. Three hexane molecules can be encapsulated parallel to each other (i.e., nested) inside a (10,10) SWNT, and their energy gain is 1.98 eV. Three hexane molecules can exhibit a rotary motion. One reason for the stability of carbon chain molecules inside SWNTs is the large area of weak wave function overlap. Another reason concerns molecular dependence, that is, the quadrupole-quadrupole interaction in the case of the polyynes and electron charge transfer from the SWNT in the case of the dehydrogenated forms. The very flat potential surface inside an SWNT suggests that friction is quite low, and the space inside SWNTs serves as an ideal environment for the molecular transport of carbon chain molecules. The present theoretical results are certainly consistent with recent experimental results. Moreover, the encapsulation of C(10) makes an SWNT a (purely carbon-made) p-type acceptor. Another interesting possibility associated with the present system is the direction-controlled transport of C(10)H inside an SWNT under an external field. Because C(10)H has an electric dipole moment, it is expected to move under a gradient electric field. Finally, we derive the entropies of linear chain molecules inside and outside an open-ended SWNT to discuss the stability of including linear chain molecules inside an SWNT at finite temperatures.     

Control of carbon capping for regrowth of aligned carbon nanotubes

The regrowth of carbon nanotubes (CNTs) in a second growth stage after a first growth stage has been completely stopped has been found to be strongly related to the carbon capping present on their catalyst particles. It is shown that the undesirable carbon capping can be prevented from forming or removed and the nanotube growth can be rejuvenated by either control of plasma processing conditions during chemical vapor deposition or by inserting a room-temperature sputter etching process. The ability to cause sequential growth stages to take place in different directions makes it possible for us to clearly compare the occurrence and extent of CNT regrowth. Such a CNT regrowth process and understanding of controlling parameters can enable the creation of new nanowire configurations that could potentially be used for applications such as sharply bending nanointerconnections, nanosprings, bent AFM nanoprobes, or nanobarcodes.     

Porous carbon and carbon composite hollow spheres

In this communication, we propose a template approach toward synthesis of carbon hollow spheres by direct carbonization of highly crosslinked sulfonated polystyrene gel hollow spheres (sPS). The sulfonic acid group can facilitate carbonization. Moreover, the acid group can also induce a favorable growth of other materials within the sPS gel-forming carbon-based composite shell such as bi-continuous C/SiO₂ and their derivative ceramic SiC. Release of small molecules during polymers decomposition results porous shell.     

Multi-wall carbon nanotubes with nitrogen-containing carbon coating

Polyaniline coating was deposited on the surface of multi-wall carbon nanotubes of Russian and Taiwanese origin in situ during the polymerization of aniline. The deposited polyaniline film was subsequently carbonized under an inert atmosphere at various temperatures to produce coaxial coating of the carbon nanotubes with nitrogen-containing carbon. The new materials were investigated by infrared and Raman spectroscopies, which demonstrated the conversion of the polyaniline coating to a carbonized structure. X-ray photoelectron spectroscopy proved that the carbonized overlayer contains nitrogen atoms in various covalent bonding states. Transmission electron microscopy confirmed the coaxial structure of the composites. The Brunauer-Emmett-Teller method was used to estimate the specific surface area, the highest being 272 m² g^?1. The conductivity of 0.9–16 S cm^?1 was measured by the four-point method, and it was only a little affected by the carbonization of the polyaniline coating.     

Adsorption of carbon dioxide on microporous carbon adsorbent PAU-10

Carbon dioxide adsorption on the microporous carbon adsorbent PAU-10 within the 177.8—423 K temperature and 0.1—5.13·10⁶ Pa pressure intervals was studied. The isosteres of absolute adsorption are well approximated by straight lines, which do not change their slope on going to temperatures higher than the critical temperature of CO₂. An increase in the differential molar isosteric heat of adsorption (q _st) at 0 < a < 1 mmol g^–1 is explained by the influence of the endothermic effect of adsorption expansion of the adsorbent. In the region of high pressures and nonideal gas phase, q _st is temperature-dependent.     

Regeneration of cobalt-contaminated activated carbon by supercritical carbon dioxide extraction

A mixture of Di-(2-ethylhexyl) phosphoric acid (D2EPHA) and n-hexane or methanol is used as the extractant solution for extracting cobalt from activated carbon using supercritical carbon dioxide extraction technology. In this work, a semi-continuous pilot unit of SFE is employed to conduct the extraction. In order to feed the viscous extractant by HPLC pump, n-hexane or methanol is added as a diluent to reduce the viscosity of the extractant. The amount of cobalt removed along the time course of the extraction is recorded and plotted as an extraction curve. A kinetic model is also established and fit to the extraction curve, and the obtained parameters of the model are used to explain the regeneration mechanism. The effects of temperature ranged from?40 to?80?°C and the effect of the concentration of diluents on the extraction are investigated and discussed based on the established model. It is also found that the removal of cobalt ions reaches a maximum; this varies with the operational conditions and is known as maximum removal efficiency. It is presumed that the maximum removal efficiency is affected by the adsorption kinetics of the extractant and the rate of ion exchange between the extractant and metal ions on the surface of the activated carbon. After increasing the extraction temperature from?60 to?80?°C it is observed that the maximum removal efficiency is greatly increased, presumably resulting from the diminishing competitive adsorption between the extractant and diluents. The established model can help to reveal the extraction mechanism and to promote maximum removal efficiency for regenerating activated carbon without secondary pollution.     

Kinetics of the gas-phase chlorination of activated carbon with carbon tetrachloride

The chlorination of activated charcoals KAU and SCN with CCl₄ vapor in the temperature range 300–600 °C and also the thermal stability of the added chlorine has been studied. It is shown that chlorination with CCl₄ vapor led to the addition of up to 22 mass % (6.2 mmol/g) of chlorine to the surface layer of the carbon. The added chlorine is desorbed from the surface with formation of HCl, while at temperatures above 500 °C desorption of chlorine goes practically to completion. The effective rate constants and the energies of activation of the processes of chlorination and desorption have been found.     

Surface control of activated carbon fiber by growth of carbon nanofiber

Carbon nanofiber/activated carbon fiber (CNF/ACF) composites with multifunctional surfaces were prepared through catalytic growth of CNFs on an ACF. Because of selective deposition of catalyst particles in ACF micropores, partial oxidation of ACF after catalyst impregnation was a critical step to control the surface area of the CNF/ACF composites, of which the surface functions can be synergistically performed by both the microporous surface of ACF and free edges of CNFs. CNF/ACF composites of this study are expected to provide an improved performance in SOx or NOx removal.     

甲烷在石墨化热解碳黑和活性炭上的吸附

为研究影响碳基吸附剂吸附超临界温度气体的主要因素,选择石墨化热解碳黑BP280和Ajax活性炭,分析超临界温度高压甲烷在其上的吸附平衡。应用容积法,在压力0~20.5 MPa、温度253 K~313 K测定甲烷的吸附平衡数据,并由等量吸附线标绘和亨利定律常数确定等量吸附热。引入通用吸附等温方程,再由方程的Langmuir标绘确定最大吸附容量,进而通过方程的线性化计算吸附平衡态中甲烷分子的作用能。结果表明,甲烷在两种吸附剂上的最大吸附容量均随温度而变化,并都小于液态甲烷的密度;甲烷在碳黑和活性炭上的等量吸附热分别为11.9 kJ/mol~12.5 kJ/mol和17.5 kJ/mol~22.5 kJ/mol,体现了两种吸附剂不同的表面能量分布;甲烷分子间作用能随吸附量的变化特点反映了超临界温度甲烷以类似于压缩气体状态聚集的特点和吸附剂结构上的差异。碳基吸附剂的比表面积和微孔容积是影响其储存甲烷容量的重要因素。     

Multifunctional molecular carbon materials--from fullerenes to carbon nanotubes

This critical review covers the timely topic of carbon nanostructures-fullerenes and carbon nanotubes-in combination with metalloporphyrins as integrative components for electron-donor-acceptor ensembles. These ensembles are typically probed in condensed media and at semi-transparent electrode surfaces. In particular, we will present a comprehensive survey of a variety of covalent (i.e., nanoconjugates) and non-covalent linkages (i.e., nanohybrids) to demonstrate how to govern/fine-tune the electronic interactions in the resulting electron-donor-acceptor ensembles. In the context of covalent bridges, different spacers will be discussed, which range from pure "insulators" (i.e., amide bonds, etc.) to sophisticated "molecular wires" (i.e., p-phenylenevinylene units, etc.). Furthermore, we will elucidate the fundamental impact that these vastly different spacers may exert on the rate, efficiency, and mechanism of short- and long-range electron transfer reactions. Additionally, a series of non-covalent motifs will be described: hydrogen bonding, complementary electrostatics, pi-pi stacking and metal coordination-to name a few. These motifs have been successfully employed by us and our collaborators en route towards novel architectures (i.e., linear structures, tubular structures, rotaxanes, catenanes, etc.) that exhibit unique and remarkable charge transfer features.     

Adsorption of dyes on activated carbon and graphitic thermal carbon black

The adsorption of a basic dye (Methylene Blue; MB) and an acidic dye (Acid Orange; AO) has been studied on three activated carbons (ACs; FAS, SKD, and BAU) significantly differing in their porous structures and surface concentrations of ion-exchange groups and on graphitic thermal carbon black (GTCB). The effective specific surface area of FAS, SKD, and BAU determined by dye adsorption is, respectively, 60, 50, and 40% of the BET nitrogen adsorption surface area. The MB uptake on ACs and GTCB increases with rising pH, while the AO uptake decreases. Addition of an electrolyte (0.3 M NaCl) virtually does not effect the adsorption of dyes on ACs and GTCB. It is suggested that hydrophobic interactions, and not ionic ones, are the major contributors to the adsorption of dyes on ACs.     

Synthesis of carbon nanotubes using scrap tyre rubber as carbon source

Carbon nanotubes(CNTs) were successfully synthesized through chemical vapor deposition(CVD) method over cobalt catalysts using scrap tyre rubber as carbon source.The CNTs as produced were investigated by means of X-ray diffraction, thermogravimetric analysis,scanning electron microscope,transmission electron microscopy and Raman spectrum techniques.It was found that the obtained carbon material mainly existed in the form of CNTs.     

Transition-metal-catalyzed reactions of propargylamine with carbon dioxide and carbon disulfide.

The reactions of propargylamine derivatives with carbon dioxide and carbon disulfide have been systematically examined in the presence of transition-metal catalysts. Pd(OAc)(2) is the best catalyst for the formation of the corresponding oxazolidinones. In addition, we found that, in the reaction of propargylamine with carbon dioxide catalyzed by palladium(0) metal catalyst in toluene, both oxazolidinone 1 and imidazolidinone 2 could be obtained under mild reaction conditions at the same time. The reaction of 1 with primary and secondary amines has been examined. A plausible reaction mechanism for the formation of 2 was proposed. In addition, in this paper, we first disclosed the ligand's effect on this reaction. Using PBu(t)(3) as a ligand with Pd(2)(dba)(3), 1 was exclusively formed in 90% yield.