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.     

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。     

Activation of carbon dioxide and carbon monoxide at aluminium surfaces

Dynamic photoelectron spectroscopy has shown that the adsorption of carbon dioxide at aluminium surfaces is followed by a dissociative reaction leading to the formation of a metastable surface carbonate in the temperature range 80-120 K. The carbonate is subsequently reduced (120–475 K) (deoxygenated) to generate two different forms of surface carbon, one carbidic C^δ- (a) and the other less ionic C⁰(a) possibly graphitic. Quantification of the C(ls) and O(ls) spectra enable each of the species O^2-(a), CO₃^2-(a), C^δ-(a) and C⁰ (a) to be distinguished and their surface concentrations calculated over a wide temperature range. The temperature and pressure dependences of CO₂ reduction suggest the participation of a precursor dimer state (CO₂^---CO₂)(a) which then disproportionates. Furthermore studies of the coadsorption of ammonia and carbon dioxide in analogous systems indicate that a discrete and specifically reactive species, O^- (s), is formed during carbonate formation. The results are discussed in the context of recent theoretical studies of FREUND and MESSMER and also comparisons made with metal-CO₂ complexes.The facile surface reduction of CO₂ via a surface carbonate suggested that a possible route to carbon-oxygen bond cleavage in carbon monoxide interaction with an sp-metal surface (aluminium) was a step-wise oxidation to CO₂ leading to surface carbonate which was then readily deoxygenated. Studies of carbon monoxide: dioxygen mixtures (100: I) confirmed that this indeed occurred. A modified ELEY-RIDEAL type mechanism involving a hopping "non-adsorbed" CO molecule and a short-lived surface O^- (s) species is suggested.     

Structure and thermodynamics of carbon and carbon/silicon precursors to nanostructures

The structures at the Hartree-Fock level, as well as the energetics, are reported for the unsaturated system C(36)H(16), its Si-doped analogue C(32)Si(4)H(16), and several smaller, unsaturated fragments. Structural effects on the electronic distribution are discussed in terms of a localized orbital energy decomposition. The standard heats of formation are calculated based on homodesmic and isodesmic reactions and the G2(MP2,SVP) method with a valence double-zeta plus polarization basis. The origin of the observed explosion of the all-carbon system (C(36)H(16)) to form carbon nanotubes was investigated by exploring a possible initial reactive channel (dimerization), which could lead to the formation of the observed onion-type nanostructures.     

纳米科学和碳纳米科学

介绍了纳米材料、纳米科学、碳纳米科学的研究领域及其重要的、潜在的应用价值。     

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.     

Preparation and characterization of carbon paste micro-electrode based on carbon nanoparticles

The present paper demonstrates the preparation and characterization of micro-electrodes based on carbon paste which is composed of carbon nano-particles with an average diameter of 30 nm and binding oil. The carbon paste electrode material is encased in pulled glass capillaries ranging in diameter from several tens down to less than ten micro-meters (r = 4.5 μm). Manipulation of the carbon paste micro-electrode (CPME) was accomplished via newly developed piston-driven system which construction and related problems are presented. Several parameters influencing the CPME performance including carbon paste composition and its electrochemical activation/preconditioning were investigated. Basic electrochemical behavior and properties were examined using typical redox system, i.e. potassium hexacyanoferrate. Applicability of the proposed carbon paste micro-electrode is illustrated by measuring some potentially interesting organic and inorganic analytes such as dopamine, ascorbic acid and selected heavy metals.     

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.     

Vibration—vibration energy exchange between carbon monoxide and carbon dioxide

Measurements have been made on the vibration—vibration (V—V) energy exchange rate between carbon monoxide and carbon dioxide in the temperature range 180 to 345 K. A steady-state vibrational fluorecence quenching technique was used in conjunction with an open flow gas system. Vibrational excitation of the carbon monoxide was accomplished by absorption of infrared radiation from prospane—oxygen flames. The measured rate constant for the process CO* (υ = 1) + CO₂ → CO + CO^*₂(001) increased linearly with temperature, and after correction for the V—V exchange rate fo the back reaction, the rate constant has a value of (2.2 ± 0.3) × 10³ torr^?1 s^?1 at 296 K. The data are compared to results at highest temperatures and to available theoretical calculations.     

Synthesis and characterization of core-shell selenium/carbon colloids and hollow carbon capsules

A novel Se/C nanocomposite with core-shell structures has been prepared through a facile one-pot microwave-induced hydrothermal process. The new material consists of a trigonal-Se (t-Se) core and an amorphous-C (a-C) shell. The Se/C composite can be converted to hollow carbon capsules by thermal treatment. These products were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS).     

Adsorption and diffusion of carbon dioxide and nitrogen through single-walled carbon nanotube membranes

We have used atomically detailed simulations to examine the adsorption and transport diffusion of CO2 and N2 in single-walled carbon nanotubes at room temperature as a function of nanotube diameter. Linear and spherical models for CO2 are compared, showing that representing this species as spherical has only a slight impact in the computed diffusion coefficients. Our results support previous predictions that transport diffusivities of molecules inside carbon nanotubes are extremely rapid when compared with other porous materials. By examining carbon nanotubes as large as the (40,40) nanotube, we are able to compare the transport rates predicted by our calculations with recent experimental measurements. The predicted transport rates are in reasonable agreement with experimental observations.     

Fullerenes inside carbon nanotubes and multi-walled carbon nanotubes: optimum and maximum sizes

The potential energies of interaction between carbon nanotubes and internal fullerenes of spherical and ellipsoidal shape, as well as between nanotubes in multi-walled nanotubes were calculated using the Lennard–Jones (LJ) potential for carbon–carbon interactions. The optimum and maximum size of internal fullerenes and multi-walled nanotubes are determined as a function of the external nanotube radius. It was found that at the potential energy minimum, the van der Waals distance is close to that in graphite for all studied cases. The calculated results agree with available experimental observations and could be used as a guide for future experiments.     

Theoretical analysis of pyrrole anions addition to carbon disulfide and carbon dioxide

Quantum chemical analysis (MP2/6‐31+G*) of the pyrrole anions addition to carbon disulfide and the substitution effects therein shows that pyrrole‐2 (5)‐carbodithioates are thermodynamically the most stable compounds, while 1‐isomer obtained from the unsubstituted pyrrole is likely a kinetic product. Steric hindrances destabilize N‐adducts when a methyl substituent appears in a 2(5) position and the 2,5‐dimethyl‐1‐pyrrolecarbodithioate anion turns out to be even less stable than the 2,5‐dimethyl‐3‐pyrrolecarbodithioate anion. By contrast, pyrrole‐1‐carboxylates are calculated to be the most stable adducts of CO₂ with pyrrole anions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Determination of total carbon and total organic carbon from volatile air pollutants

Summary The method developed based on the determination of TC and TOC in the form of the total amount of CO₂ requires application of the proper techniques for the final determination of CO₂. The possibility of using a stream of carrier gas at a convenient flow-rate for desorbing quantitatively CO₂ concentrated on a molecular sieve permits use of a wide variety of known analytical techniques for the final determination of CO₂. Various methods were compared on the basis of both absolute and calibration measurements. The absolute methods chosen were gravimetric (classical or an automated version based on application of a gravimetric automat and automatic recording balance), thermogravimetric analysis and coulometry. The calibration methods included thermal conductivity, the flame-ionization detector (after conversion of CO₂ into methane) and infrared absorption. Usefulness of the methods was evaluated on the basis of comparative statistical analysis of experimental data with respect to precision (Snedecor'sF-test and Bartlett'sU ²-test) and accuracy (Student'st-test).

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Zusammenfassung Das entwickelte Verfahren zur Bestimmung des TC- und TOC-Gehaltes in Form der gesamten Menge CO₂ erfordert die Anwendung geeigneter Analysentechniken zur Endbestimmung dieser Verbindung. Die Möglichkeit einer Desorption des am Molekularsieb angereicherten CO₂ in einem Gasstrom mit geeignetem Durchfluß erlaubt zur Endbestimmung von CO₂ die Anwendung einer Reihe verschiedener Analysenverfahren. Die Anwendbarkeit verschiedener, auf Absolutverfahren und auch auf relativen Messungen beruhender Methoden wurde vergleichend untersucht. Die folgenden Methoden zur CO₂-Bestimmung wurden gewählt: die Gravimetrie (klassische oder automatisierte unter Einsatz eines Wägeautomaten und einer registrierenden Waage), die Thermogravimetrie und die Coulometrie. Von den relativen Methoden wurden die Thermokonduktometrie, der Flammenionisationsdetektor (nach Umsetzung von CO₂ zu Methan) und das IR-Absorptionsmeßverfahren geprüft. Die Anwendbarkeit der Methoden wurde mit Hilfe statistischer Prüfverfahren beurteilt, wobei die Präzision (SnedecorsF-Test und BartlettsU ²-Test) und die Genauigkeit (Studentst-Test) der erhaltenen Analysenwerte verglichen wurden.

     

Voltammetric determination of Celiptium with carbon paste and lipid-modified carbon paste electrodes

The electrooxidation of the antitumour drug 2-methyl-9-hydroxyellipticinium (Celiptium) was investigated by cyclic, differential-pulse and adsorptive voltammetry at carbon paste (CPE) and lipid-modified carbon paste electrodes (LM-CPE). The influence of the paste composition, i.e., the ratio of graphite to binder, was studied in order to elucidate the nature of the accumulation process at the surface of the CPE. The electrode surface coverage at saturation was calculated. A.c. measurements at the CPE and at the LM-CPE during the accumulation of Celiptium demonstrated an increased differential double layer capacity of the LM-CPE. The influence of several parameters that affect the adsorptive step at the CPE was investigated, such as pH, ionic strength and interfering ions. Improved signals were obtained at the CPE and the detection limit in 0.1 M sodium perchlorate (t_acc.=3 min) was found to be 2 × 10^?10 M. Measurements of the drug in dilute standard serum samples were done using the medium-exchange technique.     

Stable carbon and oxygen isotopic analysis of carbon monoxide in natural waters

Techniques have been developed to allow on-line simultaneous analysis of concentration and stable isotopic compositions ((13)C and (18)O) of dissolved carbon monoxide (CO) in natural water, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The analytical system consisted sequentially of a He-sparging bottle of water, a gas dryer, CO(2)-trapping stage using both Ascarite trap and silica-gel packed gas chromatography (GC), on-line oxidation to CO(2) using the Schütze reagent, cryofocusing, GC purification using a capillary column and measurement by CF-IRMS. Each sample analysis takes about 40 minutes. The detection limit with delta(13)C standard deviation of 0.5 per thousand is 300 pmol and that with delta(18)O deviation of 1.0 per thousand is 750 pmol. Analytical blanks associated with these methods are 21+/-9 pmol. The procedures are evaluated through analyses of temporally varying concentration and isotopic compositions of CO in an artificial lake on the university campus. The delta(13)C and delta(18)O values of CO showed wide variation in accordance with diurnal variation of CO concentration, probably due to significant isotopic effects during photochemical production and microbial oxidation of CO in the aquatic environment. The delta(13)C and delta(18)O values of CO should be a useful tool in studies of the mechanism and pathways of CO production and consumption in natural waters.