共查询到20条相似文献,搜索用时 15 毫秒
1.
Zhou Z Zhao J Chen Z Gao X Yan T Wen B Schleyer Pv 《The journal of physical chemistry. B》2006,110(27):13363-13369
The physisorption and chemisorption of hydrogen in BN nanotubes, investigated by density functional theory (DFT), were compared with carbon nanotubes. The physisorption of H2 on BN nanotubes is less favorable energetically than on carbon nanotubes; BN nanotubes cannot adsorb hydrogen molecules effectively in this manner. Chemisorption of H2 molecules on pristine BN nanotubes is endothermic. Consequently, perfect BN nanotubes are not good candidates for hydrogen storage by either mechanism. Other strategies must be utilized if BN nanotubes are to be employed as hydrogen storage media such as utilizing them as supporting media for hydrogen-absorbing metal nanoclusters. 相似文献
2.
Sh. T. Lyu E. G. Rakov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(10):2011-2015
The ion-exchange sorption of La(III) and Ce(III) from nitrate solutions using oxidized carbon nanotubes with a solubility of 4.2 g/L is studied at metal concentration С = 5–160 mg/L, рН 2.5–6.0, ratio S: L = 0.002–0.06, and room temperature. At С = 35 mg/L, the equilibrium capacity is shown to grow dramatically with рН rising from 3.0 to 4.0–4.5 and reaching 840 mg/g in La and 950 mg/g in Се when S: L < 0.006 and рН > 4.0–4.5. The introduction of ionic salts is found to reduce the capacity (at рН > 4 and concentrations of 0.01 М and 0.1 М NaCl, the Се capacity is reduced to ~500 and ~200 mg/g). It is concluded that the sorption equilibrium is better described by the Langmuir equation, while the process kinetics, by pseudo-first and pseudo-second order equations. 相似文献
3.
Acid-base titrations of oxidized multiwall carbon nanotubes (MWCNTs), Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs were conducted to investigate the surface charge characteristics of oxidized MWCNTs and the surface complexation interactions between Sr(II)/Eu(III) and oxidized MWCNTs. The results suggested that Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs increased with increasing pH, and decreased with increasing ionic strength, and the affinity of oxidized MWCNTs for Eu(III) was much higher than that for Sr(II). The diffuse layer model (DLM) fitted the experimental data of Sr(II) and Eu(III) adsorptions well with the aid of FITEQL 3.2. 相似文献
4.
Comparative characterization study of microporous carbons by HRTEM image analysis and gas adsorption 总被引:1,自引:0,他引:1
Lozano-Castello D Cazorla-Amoros D Linares-Solano A Oshida K Miyazaki T Kim YJ Hayashi T Endo M 《The journal of physical chemistry. B》2005,109(31):15032-15036
The present work presents a useful comparison of micropore size distributions (MPSDs) obtained from gas adsorption and image analysis of high-resolution transmission electron micrographs. It is shown that the MPSD obtained for a chemical activated carbon is concordant with that obtained from CO2 adsorption. In addition, this technique has allowed us to obtain the MPSD of a carbon molecular sieve (CMS) prepared in our laboratory by a copyrolysis process, which could only be characterized by CO2 adsorption at 273 K (not by N2 adsorption at 77 K due to diffusional problems). The MPSD obtained by high-resolution transmission electron microscopy (HRTEM) for the CMS is wider than that obtained by CO2 adsorption, suggesting that HRTEM is detecting the closed porosity existing in this sample, which is not accessible to gas adsorption. The existence of closed porosity in the CMS is explained considering the preparation method used. Thus, HRTEM combined with image analysis seems to be useful for structural analysis of narrow micropores including closed porosity. 相似文献
5.
Summary Specific retention volumes, adsorption isotherms, molar heats of solution and changes of the entropy were determined from
chromatographic data, which was obtained by the gas chromatographic separation of metal acetylacetonates. The retention data
for Cr(III), Co(III) and Al(III) acetylacetonates were measured at different temperatures and different flow rates. From the
retention data other values associated with adsorption and solution phenomena were calculated. 相似文献
6.
Adsorption of acidified multiwalled carbon nanotubes (MWCNTs) to heavy metal using Pb(II) as a model was investigated and characterized by many techniques. The main adsorption mechanism of acidified MWCNTs to Pb(II) is proposed on the basis of adequate analysis. The results show that the oxygenous functional groups can be formed on MWCNTs after MWCNTs were treated by concentrated nitric acid. The oxygenous functional groups play an important role in Pb(II) adsorption to form chemical complex adsorption, which accounts for 75.3% of all the Pb(II) adsorption capacity. The Pb(II) in the form of PbO, Pb(OH)(2), and PbCO(3) adsorbed on the surface of the acidified MWCNTs is only 3.4% of the total Pb(II) adsorption capacity. The Pb(II) species adsorbed on acidified MWCNTs mainly aggregate on the ends and at the defects sites on the acidified MWCNTs. 相似文献
7.
Farag H 《Journal of colloid and interface science》2007,307(1):1-8
Adsorption technique could be a reliable alternative in removing to a certain remarkable extent the sulfur species from the feedstock of petroleum oil. The performance of various carbons on adsorption of model sulfur compounds in a simulated feed solution and the sulfur containing compounds in the real gas oil was evaluated. The adsorption experiments have been carried out in a batch scale at ambient temperature and under the atmospheric pressure. In general, the most refractory sulfur compounds in the hydrotreatment reactions were selectively removed and adsorbed. It was found that the adsorbents affinities to dibenzothiophene and 4,6-dimethyldibenzothiophene were much more favored and pronounced than the aromatic matrices like fluorene, 1-methylnaphthalene and 9-methylanthracene. Among the sulfur species, 4,6-dimethyldibenzothiophene was the highest to be removed in terms of both selectivity and capacity over all the present adsorbents. The studied adsorbents showed significant capacities for the polyaromatic thiophenes. The electronic characteristics seem to play a certain role in such behavior. Regeneration of the used adsorbent was successfully attained either by washing it with toluene or by the release of the adsorbates through heat treatment. A suggested adsorptive removal process of sulfur compounds from petroleum distillate over carbon supported CoMo catalyst was discussed. 相似文献
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9.
The synthetic crystalline hydrous titanium(IV) oxide (CHTO), an anatase variety and thermally stable up to 300 °C, has been used for adsorption of Cr(III) and Cr(VI) from the aqueous solutions, the optimum pH-values of which are 5.0 and 1.5, respectively. The kinetic data correspond very well to the pseudo-second order equation. The rates of adsorption are controlled by the film (boundary layer) diffusion, and increase with increasing temperature. The equilibrium data describe very well the Langmuir, Redlich–Peterson, and Toth isotherms. The monolayer adsorption capacities are high, and increased with increasing temperature. The evaluated ΔG° (kJ · mol?1) and ΔH° (kJ · mol?1) indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (ΔS° = positive), and the mean free energy (EDR) values obtained by analysis of equilibrium data with Dubinin–Radushkevick equation indicate the ion-exchange mechanism for Cr(III) and Cr(VI)-adsorptions. 相似文献
10.
G. M. Plavnik M. A. Davydova S. P. Vnukov D. V. Fedoseev M. M. Dubinin 《Russian Chemical Bulletin》1988,37(5):862-865
Conclusion Using the method of small-angle x-ray scattering, it was shown that precipitation of carbon in the micropores of active carbons does not take place in thermal decomposition of methane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 991–994, May, 1988. 相似文献
11.
Kinetics and thermodynamic study of aniline adsorption by multi-walled carbon nanotubes from aqueous solution 总被引:3,自引:0,他引:3
Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as ΔG°, ΔH° and ΔS°, respectively, were all negative. 相似文献
12.
The initial stage of adsorption of water vapors on active carbons is due to the reaction of the water molecules with inorganic and organic polar sites. For the lowest degrees of filling, the heats of adsorption of H2O on active carbons evacuated at 500°C are overestimated due to the strong physical and chemical reaction with the primary active sites. Adsorption on secondary active sites (second coordination sphere of the active site) results in the formation of aqueous clusters with stressed hydrogen bonds and with heats below the heat of vapor condensation (). Filling of micropores containing water clusters and capillary condensation in mesopores simultaneously take place in the middle region and in the region of saturation. Micropores containing no water clusters do not fill with water even for P/Ps=1. In this region, q > by 3%. Desorption of water from the micropores is almost totally controlled by capillary evaporation of the liquid from the mesopores, and the sorption volume distribution curve by Kelvin radii reflects the distribution of the total volume of meso- and micropores by the radii of the cylindrical mesopores.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2183–2186, October, 1989. 相似文献
13.
A. V. Mamchenko 《Theoretical and Experimental Chemistry》1986,22(1):70-74
A model is proposed for the intradiffusional kinetics of adsorption, taking into account the different mobilities of the molecules adsorbed in micro-, supermicro-, and mesopores and the bonding of such pores in an active carbon particle. Within the framework of the model it has been shown that the effective diffusion coefficient of the adsorbed molecules depends on the structural and sorption characteristics of the material and the concentration conditions of the process being carried out. The model has been used to make an analysis of experimental data for adsorption of organic materials dissolved in water by active carbon having nonuniform pores.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 79–83, January–February, 1986. 相似文献
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15.
Mohammad Reza Nabid Roya Sedghi Roya Hajimirza Hossein Abdi Oskooie Majid M. Heravi 《Mikrochimica acta》2011,175(3-4):315-322
We describe a new method for the separation and preconcentration of traces of Au(III) in environmental samples. Sorbents made from modified multiwalled carbon nanotubes and conducting polymers (PANI and PEDOT) were used for solid-phase extraction. The Au(III) ions are adsorbed as a result of the interaction with the electron pairs of =N- and -S- groups. Effects of pH value, flow rate and volume of sample, type, volume and concentration of eluent, and the adsorption capacity were investigated. The maximum adsorption capacity of MWCNTs/PANI and MWCNTs/PEDOT are 159 and 176?mg?g?1, and the detection limits of this method are below 0.3 and 0.5?ng?mL?1, respectively. The procedure was successfully applied to the determination of traces of Au(III) in a reference material and in environmental samples. Figure
The multiwalled carbon nanotubes/conducting polymers (PANI and PEDOT) were used for solid-phase extraction of Au(III) ions. The Au(III) adsorbed on macromolecules chains; resulting from sharing an electron pair of = N?C and ?CS?C groups of conducting polymers with gold ions. The final results demonstrate that nanocomposites are convenient for preconcentration and determination of gold from environmental samples. 相似文献
16.
Speciation of Cr(III) and Cr(VI) can be attained by flow injection analysis with amperometric detection. Cr(VI) is reduced in an acidic medium to Cr(III) with a glassy carbon electrode at —0.1 V vs. Ag/AgCl and the current is recorded. Cr(III) is oxidised on-line to Cr(VI) with alkaline hydrogen peroxide solution. From the difference of the total chromium and Cr(VI), the amount of Cr(III) was obtained. A linear calibration curve for Cr(VI) was obtained for the concentration ranges 0.01-5.0ppm of Cr(VI) and we have calculated the limit of determination to be about 0.5ppb. We have studied the degree of reproducibility obtained using the solid electrodes under various conditions. The influence of flow rate, coil length, interfenences and the extent of reaction were studied. 相似文献
17.
Applying activated carbons for SO2 adsorption and conversion to H2SO4, as a dry process, has been considered the development direction of desulfurization technology. Coal-based activated carbon, coconut shell activated carbon, single wall carbon nanotube and multi-wall carbon nanotubes were used as typical carbonaceous materials to study the SO2 adsorption mechanism. SEM, N2 adsorption, XPS and fixed-bed reaction system were employed to study the morphology, pore structure, surface functional groups and SO2 adsorption behaviors of the four adsorbents. The fixed-bed experiment was carried out at normal pressure and SO2 concentration was set 1,000 ppm. According to SEM and N2 adsorption results, hierarchical pore structure was an important characteristic of activated carbon. Aggregation was an important characteristic of CNTs. Mesopores and macropores took the dominance of pore structure in CNTs. According the SO2 adsorption data and correlation analysis, it can be concluded that the dominant adsorption type on activated carbons does not alter with adsorption temperature changing. However, the adsorption type of SO2 adsorption on CNTs changes with adsorption temperature varying. With adsorption temperature increasing, the dominant adsorption type transforms to chemisorption by physisorption. Higher-density π–π* in carbon nanotubes may be the active sites for the SO2 chemical adsorption. Micropores with the diameter smaller than 0.7 nm were the best SO2 adsorption place for both activated carbons and carbon nanotubes. The results provided a profound insight into the microstructure and SO2 adsorption mechanism of the two kinds of carbonaceous materials. 相似文献
18.
Moliner-Martínez Y Barrios M Cárdenas S Valcárcel M 《Journal of chromatography. A》2008,1194(1):128-133
The use of carbon nanostructures in different modalities is a topic of growing interest. This article provides a systematic comparison of surfactant-coated single-wall carbon nanotubes, multi-wall carbon nanotubes and C(60) fullerenes as pseudostationary phases (PSPs) in electrokinetic chromatography. The differences on the electrophoretic behaviour as a function of the pseudostationary phase for phenolic compounds, triazines and nitroimidazole derivatives have been explored. Phenolic compounds, triazines and nitroimidazole derivatives has been selected as model compounds of aromatic compounds, pi-exceeding heteroaromatic compounds and pi-deficient heteroaromatic compounds, respectively. Resolution was also evaluated on the basis of the differences in the electrophoretic behaviour and in this sense the best PSP for each group of compounds can be proposed. 相似文献
19.
Hai‐ming Chen Jie Chen Li‐na Shao Jing‐hui Yang Ting Huang Nan Zhang Yong Wang 《Journal of Polymer Science.Polymer Physics》2013,51(3):183-196
Organic montmorillonite (OMMT) and the one‐dimensional functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into poly(L ‐lactide) (PLLA) to prepare PLLA/OMMT and PLLA/FMWCNT nanocomposites, respectively. The effects of nanofillers on melt crystallization and cold crystallization of PLLA were comparatively investigated by using polarized optical microcopy, differential scanning calorimetry and wide angle X‐ray diffraction. The results show that FMWCNTs exhibit higher nucleation efficiency for the melt crystallization of PLLA, whereas OMMT is the better one for the cold crystallization of PLLA. Rheological properties show that both OMMT and FMWCNTs at relatively higher concentrations can form the percolated network structure in the PLLA matrix, however, the latter nanocomposites exhibit relatively denser or more compact percolated networks. The difference of the networks between OMMT and FMWCNTs is suggested to be the main reason for the different cold crystallization behaviors observed in the PLLA/OMMT and PLLA/FMWCNT nanocomposites. The dynamic mechanical analysis measurements show that OMMT is the better one to improve the stiffness of the nanocomposites in the present work. The thermogravimetric analysis measurements show that FMWCNTs have higher efficiency in improving the thermal stability of PLLA compared with OMMT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
20.
K. M. El-Azony M. Ismail Aydia A. A. El-Mohty 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(2):381-388
Triton X-100 cerium(IV) phosphate (TX-100CeP) was synthesized and characterized by using IR, X-ray, TGA/DT and the elemental
analysis. The chemical stability of TX-100CeP versus the different concentrations of HCl acid was studied before and after
its exposure to the radiation dose (30 K Gray). The effect of HCl concentration on separation of Cr(III) from Cr(VI) by using
TX-100CeP as surface active ion exchanger was also studied. A novel method was achieved for the quantifying of Cr(III) and
Cr(VI) ions by using the high-performance liquid chromatography (HPLC) at wavelength 650 nm, a stationary phase consists of
reversed phase column (Nucleosil phenyl column; 250 × 4.6 mm, 5 μm), and a mobile phase consists of 0.001 M di-(2-ethylhexyl)
phosphoric acid (DEHPA) in methanol:water (70:30 v/v). The retention times were 7.0 and 8.5 min, for the Cr(III) and Cr(VI),
respectively. The exchange capacity of Cr(III) was quantified (2.1 meq/g) onto the TX-100CeP. 相似文献