Surface characterization of industrial fibers with inverse gas chromatography

Inverse gas chromatography (IGC) was applied for the determination of the surface characteristics of Tenax carbon fibers and Akzo Nobel Twaron fibers. Furthermore, IGC procedures for the determination of dispersive and acid-base interactions were validated. The data show that too high values for the dispersive component of the surface energy are obtained when the adsorption area occupied by a single adsorbed n-alkane molecule is estimated from parameters of the corresponding liquid. Comparable values are obtained when the Doris-Gray methodology (area per methylene unit) or measured probe areas are employed. For the fibers studied in this work meaningful Gibbs energy values of the acid-base interaction were only obtained with the polarizability approach. When the dispersive interaction of the polar probes with the fiber surface was scaled to the n-alkane interaction via surface tension, the boiling point, or the vapor pressure of the probes often negative acid-base interaction energies were found. From the temperature dependence of the Gibbs energy, the enthalpy of the acid-base interactions of various probes with the carbon and Twaron aramid fibers was determined. However, from these enthalpy values no meaningful acid-base surface parameters could be obtained. Generally, the limited accuracy with which these parameters can be obtained make the usefulness of this procedure questionable. Also the Gibbs energy data of acid-base interaction can provide a qualitative basis to classify the acidity-basicity of the fiber surface. This latter approach requires only a limited data set and is sufficiently rapid to enable the use of IGC as a screening tool for fibers at a production site. For several polar probes significant concentration effects on carbon fibers were observed. At very low probe loadings the interaction with the fiber surface suddenly increases. This effect is caused by the heterogeneity of the interaction energy of the active sites at the surface. A simple procedure to measure the adsorption isotherm at infinite dilution was developed. The determination of the concentration dependence of the interaction of an n-alkane, an acidic and a basic probe was incorporated in the IGC screening procedure of carbon fibers to monitor this heterogeneity.     

Acid-base Vapor Sensing Enabled by ESIPT-attributed Cd(II) Coordination Polymer with Switchable Luminescence

Fluorescence materials based on excited state intramolecular proton transfer(ESIPT) have attracted great attention due to the unique four-level energy states. Herein, we report the assembly of a Cd-L_F coordination polymer from purposely designed L_F(H₂hpi2cf) ligand, which can present switchable luminescence behavior by gain or loss protons originated in uncoordinated ESIPT sites and serve as acid-base vapor sensors. Fabricated into in-situ grown film or transparent ink by simple methods, Cd-L_F presents facile and portable amine sensor for food spoilage detection and fluorescent anti-counterfeiting ink applications.     

A novel silver catalyst prepared by using superheated-steam as a heating medium for ethylene oxide production

A high-performance catalyst for the production of ethylene oxide by vapor phase oxidation of ethylene was developed and commercialized. High performance was achieved by the usage of a high surface area carrier with controlled pore distribution and surface acid-base properties, by the adoption of mixed amines to dissolve heat-decomposable silver salt, by the addition of effective additives, and by the introduction of a uniquely developed heat-treatment technology using superheated-steam as the heating medium. The catalyst thus prepared showed high activities because of homogeneously and highly dispersed silver and additive elements within the carrier. As a result, the reaction temperature could be lowered, which led to the improvement of not only the selectivity but also the catalyst life. Heat treatment with superheated-steam proved to have many advantages in producing high-performance catalysts and it is commercially favorable because it needs only a very short processing time.     

铁锆氧化物催化剂上苯酚和甲醇气相邻位烷基化反应

采用共沉淀法制备了不同锆含量的铁锆氧化物催化剂, 考察了它们在苯酚和甲醇气相邻位烷基化反应中的催化性能. 结果表明, 铁锆两组分氧化物催化剂具有良好的催化活性和邻位选择性, Zr、Fe摩尔比为0.5/100的催化剂上苯酚的转化率达到99.2%, 主要产物邻甲酚和2,6-二甲酚的选择性分别为22.6%和77.0%, 随着反应温度的提高, 2,6-二甲酚的选择性增加. 铁锆氧化物表面存在的相对较强的酸碱中心可能是获得较高苯酚转化率和2,6-二甲酚选择性的主要原因.     

Determination of mercury in aquatic ecosystems

Small concentrations of mercury are determined by the example of the quantitative recovery of a toxicant from snow water in a segregating system with no organic solvent (water-antipyrine-sulfosalicic acid). The organic component of the system in situ forming as a result of acid-base interactions was used in microliter amounts to modify a graphite indicator electrode and register an analytical signal of mercury. The reliability of the results of voltammetric determination was checked by the independent cold vapor method. Organic components obtained by segregation were used to extract mercury from the conservative ecosystem component, solid snow particles, snow water preconcentrated with a membrane filter, river suspensions from surface water and floodplain soils, and also fish samples. The characteristic features of mercury extraction with a mixture if mineral acids and the liquid organic component of a segregating system with no organic solvent are discussed.     

Kinetic Aspects of the Adsorption on Aluminum Oxide Drying Agents Doped with Alkali Metal Ions

Fundamental dynamic (kinetic) aspects of the process in which water vapor interacts with the surface of drying agents that are synthesized on the basis of low-temperature modification of aluminum oxide produced from a pseudoboehmite-containing hydroxide and are modified (doped) with alkali atoms (K, Na). It is shown that the kinetics of adsorption on the samples under study, formed from the fine fraction (0.5–1.0 mm) of aluminum oxide adsorbents, can be described with the Glueckauf equation, which rather well describes the dynamics of water vapor absorption in the course of time. The equation parameters were determined: adsorption rate constants and the equilibrium adsorption capacities (a*). It was found that the alkaline modification of the surface of aluminum oxide adsorbents results in that a* increases (by ~40%) as compared with the unmodified drying agent. A correlation is observed between the equilibrium adsorption capacity of the samples under study and the acid-base properties of the surface.     

Pervaporation from a dense membrane: roles of permeant-membrane interactions, Kelvin effect, and membrane swelling

Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation.     

Thermal characterization of aminium nitrate nanoparticles

Amines are widely used and originate from both anthropogenic and natural sources. Recently, there is, in addition, a raised concern about emissions of small amines formed as degradation products of the more complex amines used in CO(2) capture and storage systems. Amines are bases and can readily contribute to aerosol mass and number concentration via acid-base reactions but are also subject to gas phase oxidation forming secondary organic aerosols. To provide more insight into the atmospheric fate of the amines, this paper addresses the volatility properties of aminium nitrates suggested to be produced in the atmosphere from acid-base reactions of amines with nitric acid. The enthalpy of vaporization has been determined for the aminium nitrates of mono-, di-, trimethylamine, ethylamine, and monoethanolamine. The enthalpy of vaporization was determined from volatility measurements of laboratory generated aerosol nanoparticles using a volatility tandem differential mobility analyzer set up. The determined enthalpy of vaporization for aminium nitrates range from 54 up to 74 kJ mol(-1), and the calculated vapor pressures at 298 K are around 10(-4) Pa. These values indicate that aminium nitrates can take part in gas-to-particle partitioning at ambient conditions and have the potential to nucleate under high NO(x) conditions, e.g., in combustion plumes.     

ACID-BASE INTERACTIONS BETWEEN POLYMERS AND FILLERS

Inverse gas chromatography(IGC) and Fourier-transform infrared (FT-IR) techniques were applied to determining the relative acid-base strength of polymers and coupling agents. The acid-base characteristics of fillers such as CaCO_3 could be altered by treatment with different coupling agents. It was shown that some mechanical properties of filled polymers were obviously associated with acid-base interactions between polymers and fillers.     

Vapor phase reduction of cyclohexanone to cyclohexanol on CexZr1-xO2 solid solutions

Reduction of cyclohexanone to cyclohexanol using propane-2-ol as hydrogen donor has been carried out in vapor phase on Ce_xZr_1-xO₂ solid solutions synthesized by ombustion synthesized at 302°C. The solid solutions around 0.4 mol% cerium content show better catalytic activity compared to pure ZrO₂ and the selectivity to cyclohexanol is 98%. A moderate acid-base and good redox properties of Ce_xZr_1-xO₂ solid solutions are seen to be responsible for the catalytic activity. A possible mechanism of hydride transfer has been proposed with cerium ions as promoters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Activity of Water and Osmotic Coefficients of Histidine Derivatives in Aqueous Solutions at 310.15 K

From the data of vapor pressure osmometry the activity of water, osmotic coefficients, and the values of activity coefficients of two derivatives of histidine: N-Boc-L-histidine (Boc-His-OH, m=0.005–0.14 mol⋅kg⁻¹) and N-Boc-L-histidine-methyl ether (Boc-His-OMe, m=0.005–0.05 mol⋅kg⁻¹) are obtained in aqueous solutions at 310.15 K. From the comparison of water activity and osmotic coefficient values it follows that Boc-His-OMe shows a more pronounced deviation from ideality than Boc-His-OH. Both components exhibit a stronger non-ideality than histidine and a weaker one than His⋅HCl. By means of potentiometric titration the acid-base properties of Boc-His-OMe are investigated and the ionization constant at 298.15 K is determined. The pK value related to the acid-base equilibrium of the nitrogen atom in the imido group of the imidazole ring is higher (6.47) than the corresponding value of histidine (6.00).     

Adhesion of polymers: New approaches to determination of surface properties of metals

Determination of the acid-base properties of metal surfaces used as substrates in adhesive compounds was performed by a two-liquid method. It was shown that the suggested method provides a possibility of scientifically grounded selection of a substrate for creating adhesive polymeric-adhesive-metal compounds with a high level of interphase acid-base interaction.     

酸碱型磺化聚芳醚腈酮质子交换膜材料的性能研究

以合成的一系列不同磺化度的碘化聚芳醚腈酮(SPPENKs)为acidic聚合物,以聚芳醚酰亚胺(PEI)为basic聚合物,并将其溶解在N-甲基-2-吡咯烷酮(NMP)中配成质量分数为10%的成膜液,60℃下刮制成膜,制得acid-base型磺化聚芳醚腈酮质子导电了聚合物膜.用红外(FT-IR)谱图表征了acid-base型质子导电聚合物的结构,并测试了acid-base型质子导电聚合物膜的溶胀率、含水率、水解、氧化和热稳定性以及膜材料的离子交换容量IEC(IEC=meqSO3H/gdrymembrane)值等.测试结果初步表明新型质子导电聚合物膜具有良好的物化性能和较高的质子导电性,在80℃下acid-base型质子导电聚合物膜的水解断裂时间除SPPENK-40/PEI外,都超过2000h;SPPENK-60/PEI和SPPENK-80/PEI膜(IEC分别为1·08mmol/g、1·32mmol/g)与Nafion117相比,在具有较高质子交换能力的同时具有较低的溶胀率。     

A new design strategy for dispersion stabilization of Ni particles based on the surface acid and base properties of Ni particles

A dispersion technology for Ni particles suspended in a non-aqueous medium based on the quantitative evaluation of surface acid-base properties of Ni particles is described. A quantitative analysis of surface acid-base properties of Ni particles was performed using non-aqueous titration. Dimethylamino ethanol and acetic acid were used as probe molecules to detect surface acid-base amounts of Ni particles. The dispersion system was designed on the basis of the amounts of surface acid-base sites on the Ni particle surface. Rheological behavior and agglomerate particle size data demonstrate that the dispersion stability of the designed Ni suspension is markedly improved, as expected. Therefore, the design strategy to improve the dispersion stability of Ni particles was successful. This strategy is expected to be applicable to dispersion systems of other particles suspended in a non-aqueous medium.     

Comparison of contact angle measurement and microbial adhesion to solvents for assaying electron donor-electron acceptor (acid-base) properties of bacterial surface

The electron donor-electron acceptor (acid-base properties) of cell surfaces of a series of bacteria were determined by two methods, namely, Microbial Adhesion to Solvents (MATS) and Contact Angle Measurements (CAM) combined with equation of Van Oss. The efficiency of these two methods was then compared. Pseudomonas aeruginosa ATCC 27853, Bacillus subtilis ILP 142B, Staphylococcus aureus ATCC 25923 and four Escherichia coli strains including HB101, AL52, O128B12 and ATCC 25922, acid-base properties were examined under the two different conditions mentioned above. The results showed that the correlation between acid-base properties determined by MATS and CAM was very weak. We have also found that when the microbial cell surface was electron donor by CAM method, similar result was found by MATS, but the reverse was not always true. In contrast, a good correlation between the two methods was obtained when the four E. coli strains were examined.     

Recent Advances in Solid Acid-Base Catalysis and Future Problems

Recent advances in acid-base catalysis are summarized. Several examples of solid acid, base, and acid-base bifunctional catalysis which have brought significant progress of the field or are considered to give strong impacts to industrial application are presented. Selected commercialized processes developed by using solid acid-base catalysts are demonstrated, their significance being discussed. The future problems in this field are speculated and important fundamental research subjects are pointed out.     

Energy-based prediction of amino acid-nucleotide base recognition

Despite decades of investigations, it is not yet clear whether there are rules dictating the specificity of the interaction between amino acids and nucleotide bases. This issue was addressed by determining, in a dataset consisting of 100 high-resolution protein-DNA structures, the frequency and energy of interaction between each amino acid and base, and the energetics of water-mediated interactions. The analysis was carried out using HINT, a non-Newtonian force field encoding both enthalpic and entropic contributions, and Rank, a geometry-based tool for evaluating hydrogen bond interactions. A frequency- and energy-based preferential interaction of Arg and Lys with G, Asp and Glu with C, and Asn and Gln with A was found. Not only favorable, but also unfavorable contacts were found to be conserved. Water-mediated interactions strongly increase the probability of Thr-A, Lys-A, and Lys-C contacts. The frequency, interaction energy, and water enhancement factors associated with each amino acid-base pair were used to predict the base triplet recognized by the helix motif in 45 zinc fingers, which represents an ideal case study for the analysis of one-to-one amino acid-base pair contacts. The model correctly predicted 70.4% of 135 amino acid-base pairs, and, by weighting the energetic relevance of each amino acid-base pair to the overall recognition energy, it yielded a prediction rate of 89.7%.     

Structure and Thermodynamics of NaF-AlF(3) Melts with Addition of CaF(2) and MgF(2)

The NaF-AlF(3) system with additions of CaF(2) and MgF(2) has been studied with Raman and vapor pressure measurements for 3 >/= CR (NaF/AlF(3) molar ratio) >/= 1 and up to 50 mol % additive. The results show that the binary melt can be described using the two equilibria AlF(6)(3)(-) = AlF(6)(2)(-) + F(-) and AlF(5)(2)(-) = AlF(4)(-) + F(-) with equilibrium constants 0.25 and 0.05, respectively, at 1293 K. Both reactions have positive reaction enthalpies. The first equilibrium is strongly shifted to the right resulting in a melt mixture with very low AlF(6)(3)(-) concentrations even at the Na(3)AlF(6) composition. Evidence for nonideal mixing of anions was found. For the ternaries, models based on Raman data are presented and compared with vapor pressure measurements. Good agreement is observed when association between the additives, CaF(2) or MgF(2), with the AlF(5)(2)(-) ions in the melt was considered. This association could be experimentally observed through a band broadening and a slight shift in the AlF(5)(2)(-) band frequency. Our vapor pressures and Raman data both indicate that MgF(2) clearly acts as an acid when added to NaF-AlF(3) melts of any composition. When CaF(2) is added, a slight decrease of vapor pressure occurs. Raman data indicate a decrease of AlF(4)(-) concentration, corresponding to a dissociation of CaF(2) with liberation of F(-) ions. All these results are, however, very much dependent on the initial melt composition. These data are explained in terms of acid-base, dilution, and association reactions of the solute with the solvent.     

Acid-base properties of the surface of the α-Al2O3 suspension

The distribution of the acid-base centers on the surface of α-Al₂O₃ suspension particles was studied by potentiometric titration, and the corresponding pK spectra were constructed. It was inferred that the double electric layer created by the supporting electrolyte substantially affected the screening of the acid-base centers on the particle surface of the suspension.     

Catalytic activity of a ceria-lanthana system for 4-methylpentan-2-ol dehydration

A ceria-lanthana catalytic system prepared by the sol-gel technique proved to be active in 4-methylpentan-2-ol conversion, mainly leading to 4-methylpent-1-ene, a monomer for manufacturing polymers of high technological properties. The product distribution strongly depends on the acid-base features of the catalyst. The catalytic behavior of the samples was examined in the light of their acid-base properties. This revised version was published online in June 2006 with corrections to the Cover Date.