Temperature Dependence of the Adsorption of Carbon Tetrachloride on a Microporous Clay Adsorbent

Changes in the surface properties of montmorillonite and its porous structure after the replacement of exchangeable inorganic cations by tetramethylammonium cations were investigated. A thermal pretreatment in a vacuum significantly affects the adsorption properties of tetramethylammonium-montmorillonite with respect to carbon tetrachloride. From a set of sorption isosteres of CCl₄on the dehydrated organomontmorillonite measured over a wide temperature range, dependences of heats of adsorption and desorption on the adsorbed amount of substance were calculated.     

The influence of the preliminary adsorption of water on the adsorption of organic solvent vapors on fullerene materials

The preliminary adsorption of water considerably decreased the sorption capacity of fullerene-containing materials with respect to benzene. The effect grew stronger as the content of fullerenes in the adsorbent increased. The possibility of increasing adsorption capacity by treatment with water was studied. The dependence of the sorption capacity of fullerene materials with respect to benzene on the relative water vapor pressure and the sorption capacity with respect to water at the preadsorption stage was determined.     

Dynamics and isotherms of water vapor sorption on mesoporous silica gels modified by different salts

The mesoporous silica gels impregnated with different metal salts were prepared and studied. The pore structure and specific surface area of adsorbents were evaluated using nitrogen adsorption. Then, the sorption isotherms and dynamics of water vapor were carried out at 303 K and different relative humidity (RH). The temperature programmed desorption experiments were conducted to estimate the activation energy (E _d) of water desorption on the silica gels. The results showed that the sorption capacity for water decreased with the increase of the ionic radius (except the calcium ion) and that CaCl₂ and LiCl were particularly suitable for use in modification of the mesoporous silica gel to improve their sorption rates and capacities for water vapor at the lower and medium RH (RH < 80%). The larger the average pore diameter and pore volume of the initial silica gels, higher the accrual rates of the water vapor sorption rate and capacity were after modification with hygroscopic salts. The activation energy of the water desorption on the mesoporous silica gel modified by CaCl₂ were much higher than that on the silica gel modified by LiCl, because the polarizability of the Ca²⁺ was higher than that of Li⁺.     

Composite Water Sorbents of the Salt in Silica Gel Pores Type: The Effect of the Interaction between the Salt and the Silica Gel Surface on the Chemical and Phase Compositions and Sorption Properties

The influence of the inorganic salt-silica gel surface interaction on the chemical and phase compositions and sorption properties of composites of the salt in silica gel pores type is studied. Two possible interaction mechanisms are considered: (1) the ion-exchange adsorption of metal cations on the silica gel surface from a solution of a salt (CaCl₂, CuSO₄, MgSO₄, Na₂SO₄, and LiBr) and (2) the solid-phase spreading of a salt (CaCl₂) over the silica gel surface. The adsorption of metal cations on the silica gel surface in the impregnation step affords ≡Si-OM ⁿ⁺¹ surface complexes in the composites. As a result, two salt phases are formed in silica gel pores at the composite drying stage, namely, an amorphous phase on the surface and a crystalline phase in the bulk. The sorption equilibrium between the CaCl₂/SiO₂ system and water vapor depends on the ratio of the crystalline phase to the amorphous phase in the composite.     

The effect of polyoxometallate complexes of nickel and copper on the rate of their heterophase reaction with ammonia

It was established that the compounds formed by the cations in amine complexes of nickel(II) and copper(II) and the anions of polyoxometallates are capable of reacting stoichiometrically with gaseous ammonia when in the hydrated state. Some of the studied compounds are characterized by high sorption capacity (up to 40 molecules of adsorbate to a formula unit of the complex) and exhibit selectivity in the sorption of ammonia in the presence of water vapor. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 189–195, May–June, 2007.     

Note Water Vapor Sorption by the Polyelectrolyte Complex of Poly (Acrylic Acid) and Poly (4-Vinyl-N-Ethylpyridinium Bromide)

A great number of studies of polyelectrolyte complexes have been carried out by various investigators; most of them concentrated on the reaction between oppositely charged polyelectrolytes [1-3]. The structure and properties of the resultant complexes have been investigated to a lesser extent, and the understanding of this new class of polymer materials is still insufficient. Thus, we have been investigating the sorption of water vapor by the complexes and the morphological changes caused by this sorption [4,5].     

Porous Structure of Aluminum–Tin Phosphate

The sorption isotherms of water and tetrachloromethane vapors are studied, and the porous structures of aluminum tin phosphate gels coprecipitated at various Al/Sn molar ratios are analyzed. The resultant samples contain both micro- and mesopores. The structure of aluminum tin phosphate is suggested to contain slitlike pores that do not change during drying because of the presence of polyaquahydroxoaluminum cations introduced via an exchange with interlayer cations of tin(IV) hydrophosphate.     

Adsorption of nickel on synthetic hydroxyapatite from aqueous solutions

The sorption of nickel on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite samples used in experiments were a commercial hydroxyapatite and hydroxyapatite of high crystallinity with Ca/P ratio of 1.563 and 1.688, respectively, prepared by a wet precipitation process. The sorption of nickel on hydroxyapatite was pH independent ranging from 4.5 to 6.5 as a result of buffering properties of hydroxyapatite. The adsorption of nickel was rapid and the percentage of Ni sorption on both samples of hydroxyapatite was >98 % during the first 15–30 min of the contact time for initial Ni²⁺ concentration of 1 × 10^?4 mol dm^?3. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on a commercial hydroxyapatite and hydroxyapatite prepared by wet precipitation process was calculated to be 0.184 and 0.247 mmol g^?1, respectively. The sorption of Ni²⁺ ions was performed by ion-exchange with Ca²⁺ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Co²⁺ and Fe²⁺ towards Ni²⁺ sorption was stronger than that of Ca²⁺ ions. NH₄ ⁺ ions have no apparent effect on nickel sorption.     

Determining the effects of vapor sorption in polymers with the quartz crystal microbalance/heat conduction calorimeter

The quartz crystal microbalance/heat conduction calorimeter (QCM/HCC) is a versatile instrument coupling both gravimetric and calorimetric techniques. The QCM/HCC is used to probe vapor sorption in thin films. Three parameters are measured simultaneously as a thin film undergoes vapor sorption, namely: mass changes in the film (±10 ng), corresponding thermal effects upon vapor sorption (±100 nW), and motional resistance (±0.5Ω) changes within the film. A range of film thicknesses (0.75 to 8.5 μm) of the polymer, Tecoflex? are cast on QCMs and the interaction of each film with ethanol and water is determined. From the direct calorimetric measurements, sorption enthalpies (Δ_sorptionH kJ/mol) are determined for the film–vapor interactions. Sorption isotherms are then analyzed for each film. The isotherms shown here generally display a linear Henry's Law dissolution relationship between the vapor pressure and the amount of vapor sorbed into the film. Motional resistance data provides a window to view viscoelastic effects of the polymer films upon vapor sorption. Motional resistance data are compared for ethanol sorption in a relatively thin (0.75 μm) and thicker (8.5 μm) Tecoflex? film. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3893–3906, 2004     

Water vapor sorption by fibers of aromatic polyamides

Isotherms of water vapor sorption by fibers of aromatic polyamides of several types have been obtained in a wide range of relative pressures (p/p _s from 0 to 0.8–0.9). It has been shown that different values of moisture sorption determined from sorption isotherms correlate with molecular and structural characteristics, such as the thermodynamic rigidity of macromolecules, the integral specific surface area with respect to an inactive sorbate (krypton), the average off-orientation angle, and the phase state of the structure. It has been speculated that a difference in the moisture sorption of the test fibers is primarily related to their phase structure, particularly, to the prevalence of either a mesophase or crystalline order.     

Synthesis of chitosan resin possessing 3,4-diamino benzoic acid moiety for the collection/concentration of arsenic and selenium in water samples and their measurement by inductively coupled plasma-mass spectrometry

A chitosan resin functionalized with 3,4-diamino benzoic acid (CCTS-DBA resin) was newly synthesized by using a cross-linked chitosan (CCTS) as base material. The adsorption behavior of trace amounts of elements on the CCTS-DBA resin was examined by the pretreatment with a mini-column and measurement of the elements by inductively coupled plasma-Mass spectrometry (ICP-MS). Arsenic(V) could be retained on the CCTS-DBA resin at pH 3 as an oxoanion of H₂AsO₄⁻. Selenium(VI) is strongly adsorbed at pH 2 and pH 3 as an oxoanion of SeO₄²⁻, while selenium(IV) as HSeO₃⁻ is adsorbed on the resin at pH 3. The sorption capacities are 82, 64, and 88 mg g⁻¹resin for As(V), Se(IV), and Se(VI), respectively. The effect of common anions and cations on the adsorption of As(V), Se(IV), and Se(VI) were studied; there was no interference from such anionic matrices as chloride, sulfate, phosphate, and nitrate up to 20 ppm, as well as from such artificial river water matrices as Na, K, Mg, and Ca after passing samples through the mini-column containing the resin. The CCTS-DBA resin was applied to the collection of arsenic and selenium species in bottled drinking water, tap water, and river water.     

Experimental and numerical study on water sorption over modified mesoporous silica

–SO₃H modified mesoporous silica adsorbent with water sorption capacity and fast desorption kinetics for water sorption was synthesized and studied via a combined experimental and numerical approach. Mesoporous silica was synthesized using sol–gel method in H₂SO₄ medium. The water adsorption isotherms and kinetics over the silica were evaluated by a dynamic water vapor sorption analyzer. Mesoporous silica was modeled using annealing simulation with CVFF forcefield. –SO₃H modified mesoporous silica was modeled by the attachment of –SO₃H to the surface hydroxyl groups and validated. Simulation results show water sorption capacity at low relative humidity (RH) increases with –SO₃H loading on mesoporous silica. Energy distribution of intermolecular interaction and micro-view of water sorption over –SO₃H modified mesoporous silica reveal that although strong interaction (intermolecular interaction of ?40 to ?20 kcal/mol) between hydrophilic groups (–SO₃H) with water can increase water sorption capacity at low RH, weak H₂O–H₂O interaction (intermolecular interaction of ?20 to ?10 kcal/mol) dominated water sorption capacity at both low and high RH.     

Structural Transformations and adsorption of fuel-related gases of a structurally responsive nickel phosphonate metal-organic framework, Ni-STA-12

The structure of the nickel N,N'-piperazinebismethylenephosphonate, Ni-STA-12 (St. Andrews porous material-12), has been determined in the hydrated (Ni2L x 8 H2O, L = O3PCH2NC4H8NCH2PO3), partially dehydrated (Ni2L x 2 H2O), and fully dehydrated (Ni2L) forms from high-resolution synchrotron X-ray powder diffraction. The framework structures of Ni2L x 8 H2O and Ni2L x 2 H2O are almost identical (R, a = 27.8342(1) A, c = 6.2421(2) A; R, a = 27.9144(1) A, c = 6.1655(2) A) with additional physisorbed water of the as-prepared Ni-STA-12 present in an ordered hydrogen-bonded network in the channels. Ab initio structure solution of the fully dehydrated solid indicates it has changed symmetry to triclinic (P1, a = 6.03475(5) A, b = 14.9157(2) A, c = 16.1572(2) A, alpha = 112.5721(7) degrees, beta = 95.7025(11) degrees, gamma = 96.4950(11) degrees) as a result of a topotactic structural rearrangement. The fully dehydrated solid possesses permanent porosity with elliptical channels 8 A x 9 A in free diameter. The structural change results from the loss of water coordinated to the nickel cations, so that the nickel coordination changes from edge-sharing octahedral NiO5N to edge- and corner-sharing five-fold NiO4N. During this change, two out of three phosphonate groups rotate to become fully coordinated to nickel cations, leaving the remainder of the phosphonate groups coordinated to nickel cations by two oxygen atoms and with a P=O bond projecting into the channels. This transformation, which is completely reversible, causes substantial changes in both vibrational and electronic properties as shown by IR, Raman, and UV-visible spectroscopies. Complementary adsorption, calorimetric, and infrared studies of the probe adsorbates H2, CO, and CO2 reveal the presence of several distinct adsorption sites in the solid, which are attributed to their interactions with nickel cations which are weak Lewis acid sites, as well as with P=O groups that project into the pores. At 304 K, the adsorption isotherms and enthalpies of adsorption on dehydrated Ni-STA-12 have been measured for CO2 and CH4: Ni-STA-12 gives adsorption uptakes of CO2 of 2.5 mmol g(-1) at 1 bar, an uptake ca. 10 times that of CH4.     

A microcalorimetric study of the interaction between water and poly(hexamethylene guanidine)-modified kaolinite surface

The isotherms and differential heats of water vapor adsorption on kaolinite modified with poly(hexamethylene guanidine) hydrochloride are measured. Modification efficiency is, to a high extent, determined by the compliance (complementarity) between the structure of the modifying agent and the chemical nature of the kaolinite surface. It is shown that the individual stages of the interaction between water and the modified sorbent comprise sorption of four or five molecules on triads of amino groups of the modifying layer, conformational changes in the layer, the formation of additional adsorption sites, partial rupture of the modifying layer, and the dispersion of kaolinite particles induced by adsorbed water. Alternative opinions are presented on the reason for the appearance of the additional adsorption sites. It is proven that not only the adsorbate, but also the adsorbent, undergoes efficient changes during the adsorption.     

Sorption of nickel on chitosan

The sorption of nickel on chitosan was studied using batch method. As a tracer was used radioisotope ⁶³Ni. The effect of pH and contact time to reach sorption equilibrium was investigated. During the sorption of Ni²⁺ ions occur mostly to ion-exchange reactions on the surface of sorbent. The time to reach the sorption equilibrium of nickel on chitosan was 14 h. The percentage of sorption after 14 h achieved the value of 84 %. On the sorption of nickel used solutions with initial pH in the range from 3.9 to 8.1. In the monitored range of pH after 24 h of contact was the sorption of nickel on chitosan >97 %. The sorption of nickel was reduced by increasing concentrations of Ni²⁺ ions in the solution. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on chitosan was 2.71 × 10^?3 mol g^?1.     

医用多孔壳聚糖膜的制备及性能研究

以邻苯二甲酸二丁酯为致孔剂,制备了多孔壳聚糖膜,并用扫描电镜对其表面和断面形貌进行了分析,同时对膜的吸水性、水蒸气透过性、比表面积、力学性能及生物相容性等进行了考察。分析结果表明:以邻苯二甲酸二丁酯为致孔剂,制备的多孔壳聚糖膜孔径均匀,吸水性好,孔隙率高,比表面积大,膜的最大吸水率、孔隙率和比表面积分别为196%、71.5%和1.0472 m2.g-1;膜的力学性能好,最大抗拉强度为273.17MN/m2。     

Kinetic peculiarities of <Emphasis Type="Italic">Quillaja Saponaria Molina</Emphasis> saponin sorption by chitosan

A relationship between adsorption layer structure at different stages of sorbent filling, hydrophilicity, and spatial orientation of saponin in chitosan phase is revealed by joint analysis of the kinetic curves of saponin sorption, IR spectra of chitosan and saponin samples, and computer-simulation data. The sorbent–sorbate complex is formed due to electrostatic interactions between protonated amino groups in chitosan and carboanions of glucuronic acid in saponin, as well as hydrogen bonding between NH₂ and OH groups in chitosan molecules and OH groups in the carbohydrate moiety of saponin molecules.     

氧化硅-石墨烯气凝胶介孔复合材料的合成及其对苯的吸附性能

采用水热法快速合成了一种新型介孔氧化硅-石墨烯气凝胶复合吸附材料(MSGA)。通过X射线衍射、扫描电镜等方法对MSGA进行表征。结果表明,经过水热反应和冻干处理后的MSGA材料的介孔结构保持完好,介孔氧化硅在MSGA中的分散具有高度均一性。当介孔氧化硅的含量达到88.2(wt)%时,MSGA的比表面积可达395.5m~2/g。MSGA材料对苯蒸汽的常温常压吸附量为10.77mL/g,是石墨烯气凝胶的13倍,吸附穿透时间达到石墨烯气凝胶的34.4倍。在0.8%的环境湿度下,由于材料表面羟基的亲和性,进一步提升了对苯的吸附。得益于超低密度和丰富的内部孔隙结构,MSGA能够适应高达500mL/min的气流量。上述结果表明,该复合材料在VOCs消除领域具有广阔的应用前景。     

Hydration mechanism of polysaccharides: A comparative study

Water sorption was studied at 20 °C on films composed of different natural polymers. Three polysaccharides were investigated: chitosan, cellulose, and alginate. The major differences between these polymers, from a structural point of view, lay in the substitution of an OH group by an NH₂ function for chitosan and by an ionic COO^?Na⁺ group for alginate. An analysis of the experimental water sorption isotherms, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the enthalpy profile related to the water sorption allowed us to propose a water sorption mechanism in two steps for all the polymers: water sorption on polymer‐specific sites in the first step and water clustering around the first sorbed water molecules in the second step. It was determined that two water molecules interacted with the polymer chains for cellulose and chitosan, whereas four water molecules were bonded to alginate chains. The specific sorption sites were identified as OH groups for cellulose, OH and NH₂ groups for chitosan, and ionic and OH groups for alginate. A systematic reduction of the half‐sorption time was observed in the activity range corresponding to this first sorption step, and it was explained by a water plasticization effect. On the other hand, an increase in the half‐sorption time was observed in the second sorption step, at a high activity (>0.8), for chitosan and alginate. A modelization associating the Guggenheim–Anderson–de Boer model and the clustering theory, applied to our systems, allowed us to relate the occurrence of this last phenomenon to the formation of water clusters containing more than two water molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 48–58, 2005     

Effect of acetonitrile on the hydration of human serum albumin films: a calorimetric and spectroscopic study

A new experimental approach based on the combination of calorimetric and FTIR spectroscopic measurements was proposed to study simultaneously the sorption of water and organic solvent, and corresponding changes in the structure of protein films in the water activity range from 0 to 1.0. Enthalpy changes (ΔH_tot) on the interaction of water with the dried human serum albumin (HSA) in the presence and absence of acetonitrile (AN) have been measured using a Setaram BT-2.15 calorimeter at 298 K. Spectroscopic data on water and organic solvent vapor sorption by the HSA films and the corresponding changes in the protein secondary structure were determined by means of a Bruker Vector-22 FTIR spectrometer. By using a water activity-based comparison we characterised the effect of acetonitrile on the hydration and structure of the HSA films. Acetonitrile (AN) sorption isotherm resembles a smooth curve. HSA film binds about 250 mol AN/mol protein at the lowest water activities. As the water activity increases from 0 to 0.8, the sorption of AN gradually decreases from 250 to 150 mol AN/mol HSA. At a_w > 0.8, the sorption of AN sharply decreases to zero. Acetonitrile decreases markedly the water content at a given a_w. This behavior suggests that the suppression in the uptake of water is due to a competition for water-binding sites on the HSA films by acetonitrile. Changes in the secondary structure of HSA were determined from infrared spectra by analyzing the structure of amide I band. Acetonitrile increases the intensity of the 1654 cm⁻¹ band that was assigned to the α-helix structure. Changes in the intensity of the 1654 cm⁻¹ band agree well with the decrease in water uptake in the presence of AN. An explanation of the acetonitrile effect on the hydration and structure of the HSA films was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the initially dried protein.