Adsorption of aromatic compounds from solutions in <Emphasis Type="Italic">n</Emphasis>-heptane by modified nanoporous silica

The adsorption of anisole, anthracene, benzoic acid, benzene, naphthalene, phenanthrene, phenol, and carbon tetrachloride from dilute solutions in n-heptane on the modified nanoporous silica sorbents, Silasorb C18 and Phenyl-Silasorb, at 298 K is investigated by developing liquid chromatography. The Henry law constants and Helmholtz energy of adsorption for these aromatic compounds are calculated from their retention values. The adsorption isotherms of the aromatic compounds are calculated from their chromatographic peaks with allowances made for longitudinal smearing. A correlation is made between the Henry law constants calculated from the retention values of the aromatic compounds and from their adsorption isotherms. The influences of the surface modification of the silica adsorbents and the molecular structure of the aromatic compounds on their elution from the chromatographic column with n-heptane as the eluent are discussed. Contributions of functional groups in the molecules of the aromatic compounds to the Helmholtz energy of adsorption on different surfaces are estimated.     

Comparison of Adsorption Isotherms of Methylxanthines on C18 Column

A comparison of the adsorption isotherms of caffeine, theophylline and theobromine and the competitive adsorption of the three compounds on a C 18 column were investigated. The experimental parameters of the equilibrium isotherms were estimated by linear and nonlinear regression analyses. The linear equation as a function of the adsorption concentration of the single compound in its solution and the competitive adsorption of a single compound in a mixed solution were then determined. The adsorption equilibrium data were then correlated to the linear, Langmuir, Freundlich, Langmuir-Freundlich and stoichiometric displacement theory for adsorption(SDT-A) isotherm models. The mixed compounds of the three compounds were competitively adsorbed on the C 18 particles. The expression of stoichiometric displacement theory for adsorption was found to be more suitable for adsorption of methylxanthines on a C 18 column.     

Adsorption of 1-tetradecene/dodecane mixtures on different types of zeolites

The influence of heterogeneity parameters on the shape of excess adsorption isotherms has been discussed. These isotherms have been calculated according to the equations corresponding to different energy distributions. Next, the isotherm equations have been applied to examine the experimental excess isotherms for 1-tetradecene/dodecane mixture adsorption on different types ofX-zeolites at 293 K, 313 K and 333 K. The zeolite samples have been prepared from NaX-zeolite by exchanging the sodium ions for ions of alkalines and calcium group. Analysis of the above adsorption data by means of different isotherm equations showed that the parameters of aDubinin-Radushkevich-type equation change correctly with temperature and the contents of alkalines in the zeolite samples.     

分子连接性指数与溶液吸附自由能的相关性

测定了硅胶自四氯化碳中吸附脂肪醇及活性炭自水中吸附芳香化合物的吸附等温线, 等温线均可用Langmuir方程描述。利用Langmuir参数计算了各体系的吸附标准自由能变化。计算了各种吸附质的分子连接性指数。各种分子的分子连接性指数与吸附标准自由能变化间有相关性, 并给出了相关方程, 同时作了初步的讨论。     

Adsorption Isotherms of Quercetin and Catechin Compounds on Quercetin-MIP

A molecular imprinted polymer(MIP)was prepared with quercetin as the template and methacrylic acid(MAA)as the functional monomer.Acetonitrile and methanol were used as the porogen with ethylene glycol dimethacrylate(EGDMA)as the crosslinker and 2,2'-azobis(isobutyronitrile)(AIBN)as the initiator.The experimental parameters of the equilibrium isotherms were estimated via linear and nonlinear regression analyses.The linear equation as the functions of the adsorption concentration of the single compound in its solution and the competitive adsorption of the single compound in its mixed compounds solution was then expressed,and the adsorption equilibrium data were correlated to Langmuir and Freundlich isotherm models.The mixture compounds show competitive adsorption on the specific binding sites of quercetin-MIP.Furthermore,the competitive Langmuir isotherms were applied to the mixture compounds.The adsorption concentrations of quercetin,( )catechin( C),and(-)epicatechin(EC)on the quercetin molecular imprinted polymer were compared.The quercetin-imprinted polymer shows extraordinarily higher adsorption ability for quercetin than for the two catechin compounds that were also assessed.     

Synthesis and Characterization of Microporous Silica Prepared with Sodium Silicate and Organosilane Compounds

Microporous silica gels were prepared in the pH range of 3–4 using sodium silicate as a silica source. Surface polarity of these gels was modified by grafting hydrophobic groups into the silica gel matrix with the help of hydrophilic solvents (acetone, acetonitrile, ethanol and methanol) and alkoxysilane compounds containing nonhydrolyzable alkyl groups. The porous framework and hydrophobicity of the silica gels were evaluated using nitrogen adsorption/desorption and water adsorption measurement techniques. All the measured isotherms were found to be type I which is indicative of microporosity. The surface area and microporosity of these samples were estimated by analyzing the measured nitrogen adsorption/desorption data using BET, Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. The micropore size distribution was determined from their nitrogen adsorption isotherms using the slit-pore model of the Horvath-Kawazoe equation. Silica gels with high surface area (over 500 m²/g) as well as high microporosity (over 0.2 cc/g) were obtained at gelation pH of 3.50 from the water-solvent system.     

The adsorption of gases on the surface of solid solutions and binary compounds of the GaSb-ZnTe system

The adsorption of ammonia, carbon monoxide, and oxygen on solid solution and binary compound films of the GaSb-ZnTe system was studied. The mechanism of adsorption and rules governing adsorption processes depending on adsorption conditions and system composition were determined by analyzing adsorption isobars, equilibrium and kinetic isotherms, the thermodynamic and kinetic characteristics of adsorption, and the electronic nature of adsorbate molecules. The behavior of (GaSb)_x(ZnTe)_1?x solid solutions was similar to that of binary compounds (GaSb and ZnTe) and had special features characteristic of multicomponent systems. The latter manifested themselves by the presence of extrema in adsorption characteristic-composition diagrams. The use of such diagrams allowed us to identify system components most active with respect to NH₃, CO, and O₂ and use them to create high-sensitivity and selectivity sensors.     

Band splitting in overloaded isocratic elution chromatography II. New competitive adsorption isotherms

The equations of two new binary competitive isotherms models are derived. The first of these models assumes that the isotherms of the two pure, single compounds have distinct monolayer capacities. Its derivation is based on kinetic arguments. The ideal adsorbed solution (IAS) framework was applied to derive the second model that is a thermodynamically consistent competitive isotherm. This second model predicts the competitive adsorption isotherm behavior of a mixture of two compounds that have single-component adsorption behavior following a BET and/or a Langmuir isotherms. Both models apply well to the binary adsorption of ethylbenzoate and 4-tert.-butylphenol on a Kromasil-C18 column (with methanol-water, 62:38, v/v, as the mobile phase). The best single-solute adsorption isotherms of these two compounds are the liquid-solid extended multilayer BET and the Langmuir isotherms, respectively. The kinetic and thermodynamic new competitive models were compared, regarding the accuracy of their prediction of the elution band profiles of mixtures of these two compounds. A better agreement between experimental and calculated profiles was observed with the kinetic model. The IAS model failed because the behavior of the ethylbenzoate/4-tert.-butylphenol adsorbed phase mixture is probably non-ideal. The most striking result is the qualitative prediction by these models of the peak splitting of 4-tert.-butylphenol during its elution in presence of ethylbenzoate.     

Amine-functionalized low-cost industrial grade multi-walled carbon nanotubes for the capture of carbon dioxide

Industrial grade multi-walled carbon nanotubes (IG-MWCNTs) are a low-cost substitute for commercially purified multi-walled carbon nanotubes (P-MWCNTs). In this work, IG-MWCNTs were functionalized with tetraethylenepentamine (TEPA) for CO₂ capture. The TEPA impregnated IG-MWCNTs were characterized with various experimental methods including N₂ adsorption/desorption isotherms, elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Both the adsorption isotherms of IG-MWCNTs-n and the isosteric heats of different adsorption capacities were obtained from experiments. TEPA impregnated IG-MWCNTs were also shown to have high CO₂ adsorption capacity comparable to that of TEPA impregnated P-MWCNTs. The adsorption capacity of IG-MWCNTs based adsorbents was in the range of 2.145 to 3.088 mmol/g, depending on adsorption temperatures. Having the advantages of low-cost and high adsorption capacity, TEPA impregnated IG-MWCNTs seem to be a promising adsorbent for CO₂ capture from flue gas.     

The effect of heat treatment on the adsorption properties of solids. II. The effect of heat treatment on the character of the adsorption isotherm

In this study the nitrogen adsorption isotherms of heat-treated zinc oxalate, sintered magnesium oxide, and some oxidised pitch resins are considered. It is shown that characterisation of the adsorption isotherm can be via the monolayer capacity, the BET constant C, or plots of the degree of coverage of the surface at various relative vapour pressures. These parameters are critically assessed and shown to be dependent upon the closeness to the manner in which the complete adsorption isotherm is described by the BET equation. In considering the complete adsorption isotherm it is considered best to characterise the adsorption data by quoting the statistical monolayer capacity and the value of C at this point on the adsorption isotherm. The adsorption isotherms are then best compared by plotting as the number of statistical layers against the relative pressure. The further characterisation by plotting the apparent variation in C or the degree of coverage of the surface against the relative pressure has a usefulness if the limitations of the method are noted.     

Effects of pore structure and surface chemical characteristics on the adsorption of organic vapors on titanate nanotubes

Effects of pore structure and surface chemical characteristics of titanate nanotubes (TNTs) on their adsorptive removal of organic vapors were investigated. TNTs were prepared via a hydrothermal treatment of TiO₂ powders in a 10 M NaOH solution at 150?°C for 24?h, and subsequently washed with HCl aqueous solution of different concentrations. Effects of acid washing process (or the sodium content) on the microstructures and surface chemical characteristics of TNTs were characterized with nitrogen adsorption-desorption isotherms, FTIR, and water vapor adsorption isotherms. For the adsorption experiments, gravimetric techniques were employed to determine the adsorption capacities of TNTs for four organic vapors with similar heats of vaporization (i.e., comparable heats of adsorption) but varying dipole moments and structures, including n-hexane, cyclohexane, toluene, and methyl ethyl ketone (MEK), at isothermal conditions of 20 and 25?°C. The experimental data were correlated by well-known vapor phase models including BET and GAB models. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms of organic vapors on TNTs were type II, characterizing vapor condensation to form multilayers. The specific surface area (and pore volume) and hydrophilicity of TNTs were the dominating factors for the determination of their organic vapors adsorption capacity. The GAB isotherm equation fitted the experimental data more closely than the BET equation. The heats of adsorption showed that the adsorption of organic vapors on TNTs was primarily due to physical forces and adsorbates with larger polarity might induce a stronger interaction with TNTs.     

Kinetics and isotherms of asphaltene adsorption in narrow pores

New data relating to the kinetics and adsorption isotherms of asphaltene in consolidated sandstone core samples are reported. The data were obtained from the measurements of electrokinetics of consolidated sandstone core samples in asphaltene/toluene solutions and petroleum oils. The numerical reduction in the (negative) zeta potential of the sandstone samples were attributed to the adsorption of positively charged molecules of asphaltenes. The hydrodynamics thickness δ of adsorption of asphaltene were followed by monitoring the pressure increase that occurred as the adsorbed layer restricted the rock pores and applying Poiseuille's equation. The flow rates indicated a plateau of asphaltene adsorption at a pore blocking thickness of about δ/r = 0.3, which was also the point at which the streaming current reached a plateau. After increasing to about 30% of the pore radius, the adsorbed layer thickness δ stopped growing either with time or with concentration of asphaltene in the flowing liquid. Alternative hypotheses involving asphaltene adsorption isotherms have been investigated. A theoretical treatment advanced describing particle adsorption in the same terms as molecular adsorption and the Langmuir isotherm, with the free energy of asphaltene adsorption on the rock surface (modeled on silica) calculated on the basis of van der Waals attraction. Acceptable agreement was obtained with the electrokinetic measurements.     

相对分子质量对烷基芳基磺酸盐复配体系固液吸附性能的影响

测定了5种平均相对分子质量和相对分子质量(以下简称分子量)分布不同的烷基芳基磺酸盐复配体系的吸附等温线,分别考察了分子量、分子量分布、温度和无机盐对复配体系在油砂/石英砂表面的吸附量的影响。 结果表明,对5种分子量分布复配体系吸附量依次降低的顺序为递增分布、正态分布、反正态分布、递减分布和均匀分布;复配体系在油砂表面的吸附量随着磺酸盐的平均分子量的增大而增大,随温度的升高而降低,随NaCl浓度的增加而增加。另外,在低浓度时,MgCl2、CaCl2和Na2SO4比NaCl对吸附的影响显著。 NaCl对复配体系在油砂表面的吸附影响比对石英砂表面吸附的影响略大。     

π-Selective stationary phases: (II) Adsorption behaviour of substituted aromatic compounds on n-alkyl-phenyl stationary phases

The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute–solute interactions that are likely caused by π–π interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weight aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.     

Binary adsorption of globular proteins on ion-exchange media

Adsorption equilibrium of binary pairs of lysozyme (LYS), cytochrome c (CYC) and ribonuclease A (RNase) has been measured on different cation-exchange media at various solution conditions. Adsorption patterns largely follow the intrinsic protein–surface interactions, but can differ significantly for different pairs or even for one pair at different solution conditions. LYS/CYC adsorption shows similar behavior on all the adsorbents examined, with competitive adsorption dominated by LYS and the presence of LYS reducing the adsorption of CYC significantly. Simultaneous and sequential measurements for LYS/CYC show that the order of adsorption does not have a significant effect on the adsorption equilibrium. For LYS/RNase, LYS is consistently more strongly adsorbed. For CYC/RNase, both proteins can display significant adsorption, depending on the pH and salt concentration. A model based on colloidal energetics is developed to calculate the binary adsorption isotherms using parameter values obtained from single-component isotherms. The calculated adsorption is in good agreement with experimental results, with significantly better representation than for other commonly used binary isotherms.     

Characteristics of phenol and chlorinated phenols sorption onto surfactant-modified bentonite

Surfactant-modified bentonite was synthesized by replacing adsorbed Na+ with long-chain alkyl quaternary ammonium cation, hexadecyltrimethylammonium bromide (HDTMAB). The sorption isotherms of phenol, p-chlorophenol, and 2,4-dichlorophenol were modeled according to the Langmuir and Freundlich equations. The Langmuir isotherm was found to describe the equilibrium adsorption data well. The mechanisms and characteristics of sorption of these ionizable organic contaminants onto surfactant-modified bentonite from water were investigated systematically and described quantitatively. The sorption properties are affected by the treatment conditions, such as amount of organobentonite, and the properties of organic compounds. Results indicated that adsorption of phenols from water was in proportion to their hydrophobicities, which increased with chlorine addition (phenol相似文献   

Biosorption of uranium (VI) and thorium (IV) onto Ulva gigantea (K��tzing) bliding: discussion of adsorption isotherms, kinetics and thermodynamic

Ulva gigantea (Kützing) bliding (UGB) obtained from sea inlet of Izmir-Turkey has been studied as a biosorbent for removal of radioactive metals from water. In this study, unmodified UGB and modified UGB with glutaraldehyde (GUGB) characterized by FTIR spectroscopy were used as biosorbents for removal of U(VI) and Th(IV) ions from aqueous solution. Adsorption experiments performed under batch process with initial pH, contact time, adsorbent mass and temperature as variables. In order to determine the adsorption characteristics, Langmuir, Freundlich and Dubinin-Raduschkevich adsorption isotherms were applied to the adsorption data. Adsorption experiments showed that the adsorption isotherms correlated well with the Freundlich model. The sorption followed pseudo-second-order kinetics. The thermodynamic parameters such as variations of ??H°, ??G° and ??S° were estimated as a function of temperature. The thermodynamics of the adsorption of U(VI) and Th(IV) onto UGB and GUGB indicates that the spontaneous and exothermic nature of the process. The results showed that UGB and GUGB were potential for application in removal of U(VI) and Th(IV) from aqueous solution.     

Modeling of the adsorption of organic compounds on polymeric nanofiltration membranes in solutions containing two compounds.

The adsorption of organic compounds in aqueous solution on polymeric nanofiltration membranes is studied; this process is one of the most important fouling mechanisms influencing the flux and retention behavior of nanofiltration membranes. It is shown that the adsorption of dissolved organic compounds on polymeric nanofiltration membranes is comparable to that on activated carbon. Freundlich and Langmuir isotherms are used to describe the relation between the adsorbed mass on the membrane and the equilibrium concentration of the organic compound in a single-compound solution. Based on these results, three models for the adsorption of solutions containing several compounds [i.e., the simple competitive adsorption model (SCAM), the model of Jain-Snoeyinck, and the model of Butler-Ockrent] were used to predict the adsorption behavior of an organic compound in an aqueous solution containing two compounds. The results of the three models were compared to experimental observations. It is shown that the SCAM allows a good prediction of the adsorption behavior.