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101.
Estimating the pore size distribution of activated carbons from adsorption data of different adsorbates by various methods 总被引:1,自引:0,他引:1
Gauden PA Terzyk AP Rychlicki G Kowalczyk P Cwiertnia MS Garbacz JK 《Journal of colloid and interface science》2004,273(1):39-63
Experimental adsorption isotherms of four adsorbates (N2, Ar, C6H6, and CCl4) as well as adsorption enthalpy (C6H6 and CCl4) measured on two strictly microporous carbons are used to evaluate the porosity of adsorbents (i.e., pore size distributions (PSDs) and average pore diameter ( Lav )). The influence of the diameter of adsorbates ( dA) as well as of the temperature ( T ) is analyzed in order to explain the differences or similarities between the above-mentioned quantities for all systems. Proposed previously, the general relationships between the parameters of the Dubinin-Astakhov (DA) isotherm equation (the characteristic energy of adsorption ( E0 ) and the exponent of this equation ( n )) and the average slit-width of carbon micropores are investigated. Moreover, the thermodynamic verification of the Horvath-Kawazoe (HK) theory and the ND model is presented based on data of the adsorption and enthalpy of adsorption of benzene and carbon tetrachloride on two carbons. Finally, the pore diameters calculated from calorimetry data using the Everett and Powl method and those calculated applying the recently developed equations are compared. In our opinion the change of apparent PSD should be monitored by performing a series of isotherm measurements from high (equal and higher than room temperature) to low temperatures (ca. 77.5 K) as was presented in the current study. Moreover, the analysis of the experimental data leads to the conclusion that the entropy of C6H6 and CCl4 can approach to the values characteristic of quasi-solid (a partially ordered structure). Therefore, this behavior of the adsorbate should be taken into consideration in the theoretical assumptions of model and its thermodynamic verification. 相似文献
102.
Sponer JE Spacková N Kulhanek P Leszczynski J Sponer J 《The journal of physical chemistry. A》2005,109(10):2292-2301
Large RNA molecules exhibit an astonishing variability of base-pairing patterns, while many of the RNA base-pairing families have no counterparts in DNA. The cis Watson-Crick/sugar edge (cis WC/SE) RNA base pairing is investigated by ab initio quantum chemical calculations. A detailed structural and energetic characterization of all 13 crystallographically detected members of this family is provided by means of B3LYP/6-31G and RIMP2/aug-cc-pVDZ calculations. Further, a prediction is made for the remaining 3 cis WC/SE base pairs which are yet to be seen in the experiments. The interaction energy calculations point at the key role of the 2'-OH group in stabilizing the sugar-base contact and predict all 16 cis WC/SE base-pairing patterns to be nearly isoenergetic. The perfect correlation of the main geometrical parameters in the gas-phase optimized and X-ray structures shows that the principle of isosteric substitutions in RNA is rooted from the intrinsic structural similarity of the isolated base pairs. The present quantum chemical calculations for the first time analyze base pairs involving the ribose 2'-OH group and unambiguously correlate the structural information known from experiments with the energetics of interactions. The calculations further show that the relative importance and absolute value of the dispersion energy in the cis WC/SE base pairs are enhanced compared to the standard base pairs. This may by an important factor contributing to the strength of such interactions when RNA folds in its polar environment. The calculations further demonstrate that the Cornell et al. force field commonly used in molecular modeling and simulations provides satisfactory performance for this type of RNA interactions. 相似文献
103.
Reactions of aryl aldehydes with styrene and (E)-β-methylstyrene in the presence of phenylboron dichloride regioselectively generate 1,3-diaryl-3-chloro-1-propanols and 1,3-diaryl-3-chloro-2-methyl-1-propanols in good to excellent yields with high stereoselectivity. 相似文献
104.
采用循环伏安法,稳态法,计时电位法等研究了SO2在聚钴卟啉膜电极上的电化学氧化过程,并和SO2在贵金属电极上的行为进行了比较。 相似文献
105.
A new calix[4]crown chemosensor based on dual sensing probes reveals Pb2+ ion selectivity over other metal ions, which arises from a hypsochromic shift of azo units in UV spectrum as well as a fluorescence enhancement of pyrenyl parts in fluorescence spectrum via a suppressed FRET. 相似文献
106.
Jerzy Strzelbicki Witold A. Charewicz Yung Liu Richard A. Bartsch 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(3):349-361
Separation efficiencies and selectivities in solvent extraction of Co(II) and Ni(H) ammine cations from aqueous solutions into chloroform and toluene and in transport through bulk toluene membranes by proton-ionizable crown ethers have been determined. Six proton-ionizable crown ethers with differing lipophilicities, polyether cavity sizes and ionizable groups (carboxylic and sulfonic acid functions) were examined. Higher selectivity and efficiency for Co(II) ammine cation extraction was observed for the more lipophilic, proton-ionizable crown ethers. Highly lipophilic crown carboxylic acids provided effective and selective transport of Co(II) ammine cations through bulk toluene membranes.Presented in part at the 6th International Symposium on High Purity Materials in Science and Technology: Preparation, Characterization and Application of Well-Defined Materials, Dresden, GDR, May 1985, Poster D91, Poster Abstracts, pp. 144, 145.All extraction and transport experiments were conducted at this location. 相似文献
107.
κ-卡拉胶热可逆凝胶化行为研究 总被引:3,自引:0,他引:3
用固体小角激光散射方法研究κ 卡拉胶 (KC)的热可逆凝胶化行为 .以散色斑点的突停点温度为体系的凝胶化点Tgel,考察了溶液中加入Na+ ,K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等抗衡离子对Tgel的影响 .结果是随抗衡离子浓度增大Tgel上升 ;Tgel与Na+ 的浓度呈线性关系 ,与K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等离子浓度的平方根成线性关系 ;另外 ,还得到 30℃时KC在KCl盐溶液中的溶胶 凝胶相图 ,并对比了KC在NaCl溶液中透析前后Tgel的变化 . 相似文献
108.
用同步荧光法研究细胞色素C在水溶液中的存在形态 总被引:3,自引:0,他引:3
用同步荧光光谱法研究细胞色素C在水溶液中的存在形态,发现细胞色素C中色氨酸残基的同步荧光光谱随浓度改变而发生变化,在较稀的溶液中,只观察到色氨酸残基的一个荧光峰,在较浓的溶液中也观察到一个荧光峰,而在这两个浓度之间时,这两个峰共存,可能反映了细胞色素C在不同浓度溶液中聚集状态的不同,当向存在两个荧光峰的溶液中加入不同浓度的脲,在一定脲浓度范围内,细胞色素C不发生变性,脲的作用使细胞色素C的单体浓度 相似文献
109.
110.
The influence of phase transition (PT) on the process of thermal development of a latent image arising after X-ray and uv irradiation of ammonium perchlorate (AP) crystals has been studied. Despite the production of a large number of new dislocations accompanying PT, it essentially does not influence the thermal development: The developed image does not smear at PT, remaining as clear as before it. By comparing mirror-symmetric surfaces of cleavage planes of AP crystals, it has been shown that at doses of X-ray and uv irradiation sufficient for obtaining an image, no production of new dislocations was observed in AP crystals. It is suggested that latent image arises due to formation during irradiation of chlorine oxidic products of radiolysis: ClO3, ClO2, and ClO as well as the corresponding ions ClO?, ClO?2, and ClO?3, i.e., initiators of AP low-temperature decomposition. 相似文献