High physisorption affinity of water molecules to the hydroxylated aluminum oxide (001) surface

The adsorption mechanism of water on the hydroxylated (001) plane of α-Al(2)O(3) was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al(2)O(3) samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al(2)O(3) surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365K, which is higher than that on the hydroxylated Cr(2)O(3) surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al(2)O(3) surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al(2)O(3) (001) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (001) plane of ice Ih.     

High resolution N2 adsorption isotherms at 77.4 K and 87.3 K by carbon blacks and activated carbon fibers--analysis of porous texture of activated carbon fibers by αs-method

The standard α(s)-data of N(2) at 87.3 K by graphitized and nongraphitized carbon black samples (GCB-I and NGCB) (cf.Figs. 3 and 4) have been determined on the basis of the high resolution adsorption isotherms of N(2) at 87.3 K, which were repeatedly measured in the pressure range of p/p(o)=5×10(-8)-0.4. The high resolution adsorption isotherms of N(2) by two kinds of activated carbon fibers (ACF-I and ACF-II) were measured from p/p(o)=10(-7) to p/p(o)=0.995 at 77.4 K and from p/p(o)=10(-7) to p/p(o)=0.4 at 87.3 K. Combination of the adsorption isotherms by ACF-I and ACF-II with the standard α(s)-data by NGCB at 77.4 K and 87.3 K make it possible to construct the high resolution α(s)-plots from very low filling (1%) to complete filling (100%). The high resolution α(s)-plots of N(2) at 77.4 K and 87.3 K were analyzed. On the basis of the analyzed result, the porous textures of ACF-I and ACF-II will be discussed.     

双头基两亲分子在气液界面的Langmuir铺展膜结构

用表面压-面积等温线,原子力显微镜（AFM）和X射线衍射（XRD）对两种具有不同取代位置的新型双头基两亲分子（bolaamphiphile）A和B在气液界面形成的Langmuir铺展膜的结构进行了研究,化合物1,20-二十碳二β-萘酯（B）在气液界面形成了拉伸型 Langmuir单分子膜,而化合物1,20-二十碳二α-萘酯（A）在气液界面则形成了具有三层分子厚度的二维结晶膜.     

Evaluations of the BET, I-point, and α-plot procedures for the routine determination of external specific surface areas of highly dispersed and porous silicas

Nitrogen adsorption isotherms of silicas and other oxidic materials are distorted by the presence of micropore adsorption and capillary condensation. This distortion affects the determination of the specific area of the material, depending on the chosen calculation procedure. Correction of the initial (total) isotherm for micropore capacity decreases or eliminates this source of error to give a useful estimate of the external surface area. In the present work, 26 silica-based adsorbent materials were studied to obtain total and external specific surface areas by the Brunauer-Emmett-Teller (BET), I-point, and α-plot procedures, using the micropore capacities from the α-plots to obtain the corrected (external) isotherms. Errors in the specific surface areas due to the presence of micropores are given by the equation ΔsA = 3.267 (m(2)/cm(3) STP) sV(mic), where sA is the specific surface area in m(2)/g and sV(mic) is the micropore capacity in cm(3) STP/g. A consistent set of conversion factors was obtained by which the external specific surface area obtained using one of these procedures can be converted, with part-per-thousand precision, to either of the others. Although the I-point procedure presents the advantage of not requiring a defined p/p(0) range, the α-plot procedure is recommended for routine determinations of external specific areas of silicas and other oxidic materials, except for cases in which the shapes of the adsorption isotherms of the sample and the reference differ significantly from one another in the p/p(0) range used for the determination.     

Standard nitrogen adsorption data for α-alumina and their use for characterization of mesoporous alumina-based materials

Nitrogen adsorption isotherm measured at ?196 °C for a macroporous α-alumina (α-Al₂O₃) is reported. This isotherm is compared with the previously reported adsorption data measured on LiChrospher 1000 silica and with available reference isotherms measured at moderate and high relative pressures on macroporous aluminas. The isotherm reported in this work for α-Al₂O₃ and that recorded previously on LiChrospher 1000 silica were used as reference data for adsorption characterization of ordered and disordered mesoporous aluminas by α _s -plot analysis and pore size analysis. It is shown that both reference isotherms provide almost identical adsorption characteristics of the aforementioned mesoporous aluminas, indicating that the available reference data for the silica surface are also suitable for adsorption analysis of alumina-based materials.     

Gravimetric studies of the sorption of toluene and propanol by copper phthalocyanines

Sorption isotherms of toluene and n-propanol were determined at 25°C on well-characterised samples of the α and β forms of copper phthalocyanines, the measurements being made with a Cahn RG electrobalance and a McBain-Bakr spring balance. A study of sorption hysteresis was undertaken with each solid—vapour system. The work demanded reliability of instrumentation for the measurement of small changes in mass over long periods of time (up to several months).The toluene isotherm data obtained with the sample of β-copper phthalocyanine appear to be fairly straightforward to interpret: the solid—vapour interaction is relatively weak and hysteresis is confined to the capillary condensation range. On the other hand, the sample of α-copper phthalocyanine underwent considerable ageing when exposed to toluene vapour; the toluene isotherms show low-pressure hysteresis and indicate strong solid—vapour interaction.The initial n-propanol adsorption isotherms on the β-copper phthalocyanine is Type III in character, but desorption resulted in the strong retention of alcohol molecules at very low pressure. The uptake of n-propanol by the α-copper phthalocyanine was much larger than that given by the β form and appreciable ageing occurred on exposure of the sample to n-propanol vapour.These results reveal that the β-copper phthalocyanine sample was more stable when exposed to toluene or n-propanol than the α form (although the original surface areas were similar). Toluene adsorption appears to be restricted to the crystal surface of the β-copper phthalocyanine, whereas the sorption of toluene and n-propanol by the α form involves penetration within the pigment aggregates. The irreversible sorption of n-propanol may be partly due to slow intercalation.     

Isobaric thermal expansivities of polyethylenes with various crystallinities over the pressure range from 0.1 to 300 MPa and over the temperature range from 303 to 393 K

A pressure-controlled scanning calorimeter (PCSC) has been applied for measuring the isobaric volume thermal expansivities (α_p) of crystalline polymers as a function of pressure up to 300 MPa at various temperatures. The measurements have been performed for several well-defined polyethylenes with various degrees of crystallinity at 302.6, 333.0, 362.6, and 393.0 K. The results are reported as values of coefficients in a correlation equation, which facilitates the use of reported data over large ranges of temperature and pressure. The general pressure-temperature behavior of α_p for all polyethylenes under study is such that α_p increases with temperature and decreases with pressure. The increase with temperature is smaller at high pressures and the isotherms of α_p have a tendency to converge at high pressures; α_p decreases linearly with the crystallinity of the polyethylene over the whole range of pressure and temperature under investigation. From the linear approximation of experimental data for polyethylenes with various crystallinities the estimated α_p for both crystal and amorphous phases of polyethylenes have been determined as a function of pressure up to 300 MPa at 302.6, 333.0, and 362.5 K. The obtained results have been compared with available literature crystallographic data and with the values derived from the Pastine theoretical equation of state for both crystalline and amorphous phases. © 1996 John Wiley & Sons, Inc.     

Wetting films

Wetting films of nonpolar liquids are stabilized due to action of the repulsion dispersion forces. For aqueous films, it is necessary to takes additionally into account action of electrostatical and structural forces.Disjoining pressure isotherms of a thick methastable β -films of electrolyte and surfactant solutions can be quantitavely described on the basis of theory of long-range electrostatical forces. Thicknesses of thinner α-films of water formed as a result of vapour adsorption depend on the surface hydrophilicity and are controlled by the action of structural repulsion forces.     

烟酰胺腺嘌呤二核苷酸在纳米α-氧化铝上的吸附作用

用紫外-可见吸收光谱、X射线衍射、荧光光谱和衰减全反射傅里叶变换红外(ATR-FTIR）光谱等方法,研究了烟酰胺腺嘌呤二核苷酸(NAD+)在纳米α-Al2O3粒子上的吸附行为。 实验结果显示,NAD+的吸附量受pH值和离子强度影响较大,说明NAD+主要通过静电作用吸附在纳米α-Al2O3粒子上。 采用ATR-FTIR光谱分析了不同pH值溶液中及被吸附的NAD+,发现吸附后的NAD+与溶液中NAD+ 的ATR-FTIR光谱相似,但磷酸根的吸收峰向高波数位移,说明磷酸根参与了表面静电作用。 吸附过程符合Langmuir和Freundlich等温式。 荧光实验结果显示,随着吸附剂α-Al2O3用量的变化,NAD+构象也发生变化。     

Sheet-like assemblies of charged amphiphilic α/β-peptides at the air-water interface

There is growing interest in the design of molecules that undergo predictable self-assembly. Bioinspired oligomers with well-defined conformational propensities are attractive from this perspective, since they can be constructed from diverse building blocks, and self-assembly can be directed by the identities and sequence of the subunits. Here we describe the structure of monolayers formed at the air-water interface by amphiphilic α/β-peptides with 1:1 alternation of α- and β-amino acid residues along the backbone. Two of the α/β-peptides, one a dianion and the other a dication, were used to determine differences between self-assemblies of the net negatively and positively charged oligomers. Two additional α/β-peptides, both zwitterionic, were designed to favor assembly in a 1:1 molar ratio mixture with parallel orientation of neighboring strands. Monolayers formed by these α/β-peptides at the air-water interface were characterized by surface pressure-area isotherms, grazing incidence X-ray diffraction (GIXD), atomic force microscopy and ATR-FTIR. GIXD data indicate that the α/β-peptide assemblies exhibited diffraction features similar to those of β-sheet-forming α-peptides. The diffraction data allowed the construction of a detailed model of an antiparallel α/β-peptide sheet with a unique pleated structure. One of the α/β-peptide assemblies displayed high stability, unparalleled among previously studied assemblies of α-peptides. ATR-FTIR data suggest that the 1:1 mixture of zwitterionic α/β-peptides assembled in a parallel arrangement resembling that of a typical parallel β-sheet secondary structure formed by α-peptides. This study establishes guidelines for design of amphiphilic α/β-peptides that assemble in a predictable manner at an air-water interface, with control of interstrand orientation through manipulation of Coulombic interactions along the backbone.     

Affinity of human thrombin for insoluble polystyrene substituted with sulfonate,n-hydroxyethylsulfamoyl and n-substituted amidine functions

A new polymeric material was prepared from polystyrene beads with N-substituted amidines and rendered hydrophilic with sulfonate and N-hydroxyethylsulfamoyl groups. It was synthesized by reacting the p-chlorosulfonyl polystyrene with ethanolamine followed by the Michael-like addition of the terminal OH of the polymer (PSEa) to N-t-butyl-N'-phenylpropenamidine 1 thus leading to the final polymer PSEaAm. Its affinity constant for human α-thrombin calculated from the Langmuir adsorption isotherms was about 10⁶ M⁻¹, a value comparable to the one estimated for polystyrene modified with L-arginine methyl ester. This new material was used as stationary phase in affinity chromatography of thrombin confirming a strong and specific interaction between the positively charged amidinium groups and the enzyme at pH = 7.4 and desorption at pH = 10 and high ionic strength.     

磁性有序介孔炭的制备及药物吸附行为研究

采用纳米共铸法将磁性纳米粒子包埋到有序介孔炭的骨架中, 制成含有磁性纳米粒子的有序介孔炭(Fe/OMCs). 实验通过氮气吸附、扫描电镜、X射线衍射、磁性测试等手段对Fe/OMCs进行了系统的表征. 研究表明, Fe/OMCs基本保持了有序介孔结构, 磁性粒子在材料中以纳米α-Fe粒子的形式存在, 并且具有超顺磁特性. 盐酸四环素(TH)在Fe/OMCs上的吸附研究表明, Fe/OMCs的介孔表面积和介孔孔容是决定TH吸附量的关键因素. 脱附动力学研究表明, Fe/OMCs的孔尺寸是影响脱附速率的关键因素, 孔径越大, TH的脱附速率就越大.     

A theory of hydrogen absorption with interactions

The multiplateau theory of hydrogen absorption isotherms is extended to include interactions between hydrogen atoms absorbed on different kinds of site. Techniques are developed for finding the stable phases and the positions of the phase transitions. For the case of two kinds of site, it is shown that there can be no, one, two or three phase transitions. Typical isotherms of each of these types are presented.     

Preparation of SnO2 supported membranes with ultrafine pores

The colloidal route of the sol-gel process was used to prepare supported SnO₂ membranes. The influence of the sol and monoelectrolyte concentrations on the formation of the gel layer by sol-casting on the top of macroporous α-Al₂O₃ support was described. The stability of the colloidal suspension as a function of the concentrations was analyzed from creep-recovery measurements. The calcined supported membranes were characterized by nitrogen adsorption-desorption isotherms and scanning electron microscopy. The set of results show that homogeneous membrane layers containing the smallest quantity of cracks are formed in a critical interval of sol (1.0<-[SnO₂]<-1.4 M) and electrolyte (2.0<-[Cl⁻]<-4.0 mM) concentrations. The samples prepared from concentrated suspensions present a lot of interconnected cracks which favors the peeling of the coated layer. The membranes have pores of average diameter of about 1 nm.     

Self-assembled 3D porous flowerlike α-Fe2O3 hierarchical nanostructures: synthesis, growth mechanism, and their application in photocatalysis

In this work, a facile route using a simple solvothermal reaction to synthesize 3D porous flowerlike hierarchical nanostructures (HNs) of α-Fe(2)O(3) without employing templates or matrices for self-assembly is presented. The morphology and compositional characteristics of the 3D HNs were investigated by various techniques. The 3D HNs composed of 2D nanopetals, were intercrossed with each other and constructed from nanobricks with a length of about 100 nm and a diameter of about 30 nm. Influencing factors such as the reaction time, dosage of reactants and the solvents are systematically investigated. A possible formation mechanism for the 3D HNs is proposed. On the basis of characterization results, the growth of such 3D HNs has been proposed as a self-assembly followed by Ostwald ripening process. The specific surface area of the 3D HNs also was investigated by using nitrogen adsorption and desorption isotherms. The as-prepared α-Fe(2)O(3) HNs have a comparatively large Brunauer-Emmett-Teller (BET) surface area of about 52.51 m(2) g(-1). The photocatalytic properties of the as-obtained α-Fe(2)O(3) 3D HNs are systematically investigated, which was evaluated by the degradation of RhB dye under ultraviolet light irradiation. The result shows that photocatalytic activity is greatly affected by the hierarchical and porous structure.     

Water adsorption with hysteresis effect onto microporous activated carbon fabrics

Understanding the adsorption of water vapor onto activated carbons is important for designing processes to remove dilute contaminants from humid gas streams, such as providing protection against chemical warfare agents (CWAs), or against toxic industrial compounds (TICs) used in a terrorist chemical attack. Water vapor isotherms for Calgon BPL granular activated carbon (GAC), military ASZM-TEDA GAC, electrospun activated carbon nanofibers (ACnF), Calgon Zorflex^™ activated carbon cloth, and Novoloid-based activated carbon fiber cloth (ACFC) are presented. Of particular interest are the ACFC isotherms, which exhibit an unusually high degree of hydrophobicity. The ACFC isotherms also show a correlation between water vapor adsorption hysteresis and the level of activation. Water vapor isotherm models from the literature are compared.     

Porosity and surface properites of SBA-15 with grafted PNIPAAM: a water sorption calorimetry study

Mesoporous silica SBA-15 was modified in a three-step process to obtain a material with poly-N-isopropylacrylamide (PNIPAAM) grafted onto the inner pore surface. Water sorption calorimetry was implemented to characterize the materials obtained after each step regarding the porosity and surface properties. The modification process was carried out by (i) increasing the number of surface silanol groups, (ii) grafting 1-(trichlorosilyl)-2-(m-/p-(chloromethylphenyl) ethane, acting as an anchor for (iii) the polymerization of N-isopropylacrylamide. Water sorption isotherms and the enthalpy of hydration are presented. Pore size distributions were calculated on the basis of the water sorption isotherms by applying the BJH model. Complementary measurements with nitrogen sorption and small-angle X-ray diffraction are presented. The increase in the number of surface silanol groups occurs mainly in the intrawall pores, the anchor is mainly located in the intrawall pores, and the intrawall pore volume is absent after the surface grafting of PNIPAAM. Hence, PNIPAAM seals off the intrawall pores. Water sorption isotherms directly detect the presence of intrawall porosity. Pore size distributions can be calculated from the isotherms. Furthermore, the technique provides information regarding the hydration capability (i.e., wettability of different chemical surfaces) and thermodynamic information.     

Interaction of water-soluble vitamins with a new HPLC stationary phase based on zinc phthalocyanate

The adsorption of water-soluble vitamins on the surface of Diaspher-110-C₁₈ sorbent modified with zinc octa-4,5-carboxyphthalocyanate is studied. Adsorption isotherms are constructed and calculated by the Glücauf method at 20°C. It is established that the shape of the isotherms depends on the nature of vitamins and their structure: the isotherm of vitamin C is a Henry-type isotherm, the isotherms of vitamins B₃ and B₆ are of S-type, and the isotherm of vitamin PP-amide is of L-type. Monolayer capacities, adsorption equilibrium constants, and Gibbs energy changes are calculated.     

Solving the adsorption integral equation with Langmuir-kernel and the influence of temperature on the stability of the solution

Adsorption energy distribution functions can be calculated from measured adsorption isotherms by solving the adsorption integral equation. In this context, it is common practice to use general regularization methods, which are independent of the kernel of the adsorption integral equation, but do not permit error estimation. In order to overcome this disadvantage, we present in this paper a solution theory which is tailor-made for the Langmuir kernel of the adsorption integral equation. The presented theory by means of differentiation and Fourier series is the basis for a regularization method with explicit terms for error amplification. By means of simple and complicated adsorption energy distribution functions we show for ideal gas adsorption isotherms without measurement error that reliable distribution functions can be obtained from the isotherms. Furthermore we show how the stability of the solution depends on temperature.     

Modeling of the adsorption behavior and the chromatographic band profiles of enantiomers : Behavior of methyl mandelate on immobilized cellulose

The adsorption isotherms of (−)- and (+)-methyl mandelate from a hexane-isopropanol (90:10) solution were measured on a chromatographic column packed with 4-methylcellulose tribenzoate coated on silica. These isotherms are accounted for by a bi-Langmuir isotherm model, the two Langmuir terms having widely different initial slopes and saturation capacities, but each term having the same saturation capacity for the two enantiomers. The competitive isotherms were also measured. They are in excellent agreement with the prediction of a competitive bi-Langmuir model based on the single-component isotherms. The individual band profiles are in agreement with the profiles calculated from these isotherms. Thus, a simplified competitive isotherm can be used to model a separation on a chiral stationary phase the recognition mechanism of which is not well identified and the adsorption behavior of which is certainly not ideal.