Composite Adsorption Isotherms Research Articles

Influence of GO reinforcement on keratin based smart hydrogel and its application for emerging pollutants removal

In this work, the influence of graphene oxide (GO) reinforcement on keratin based smart hydrogel and its application for the emerging pollutant ciprofloxacin removal was studied. Firstly, the obtained material was characterized by Infrared Spectroscopy, Scanning Electronic Microscopy, Small angle X-ray Scattering and Swelling and Rheological behavior. The results showed that the keratin hydrogel and those nanocomposites containing GO present stimuli responsive behavior by changing the swelling along with the pH. Keratin hydrogels and the ones containing 0.5% of GO showed a similar behavior where swelling decreased between pH 6 and 5. The introduction of GO at 2% changed this inflection point at a value between pH 7 and 6. Also, the swelling of the shrunk hydrogels was higher when containing 2% GO. This effect was probably due to the steric hindrance generated by the nanosheets and their functional groups, partially interfering with keratin chains interaction. The antibiotic was adsorbed in the different active sites in the hydrogel provided by the keratin and the GO structures. After that, the composite adsorption isotherms against ciprofloxacin (CPX) and its kinetics were studied. The ability of the material to expand at high pH allowed a better desorption of the CPX. Thus, reusability presented a better performance when basic washings were used.

How Does Competition between Anionic Pollutants Affect Adsorption onto Mg–Al Layered Double Hydroxide? Three Competition Schemes

Competitive adsorption of three anionic orange-type dyes (i.e., methyl orange, orange II, orange G) and three inorganic anions (HPO42–, SO42–, CrO42–) onto Mg–Al layered double hydroxide (LDH) from bisolute aqueous solutions has been studied in view of potential application of the sorption-based technology in dye removal from textile wastewater effluents. The individual solute affinities for the LDH sample were inferred from the calorimetry measurements of the cumulative enthalpy of displacement in single-solute systems, thus leading to the following affinity order: CrO42– ≈ SO42– < OG2– ≈ HPO42– < OII– ≪ MO–. The individual and composite adsorption isotherms from bisolute aqueous solutions were determined by a solution depletion technique and supplemented by XRD studies on the well-defined adsorption systems corresponding to selected points on isotherms. Based on the shape of the individual adsorption isotherms for a dye and inorganic anion, it was possible to distinguish three different competition sche...

Characterization and adsorption properties of powders prepared from cactus pulp

Two cactaceous powders, labelled CACMM1 and CACMM2, are shown to contain calcium oxalate and to consist of globular or cubosome particles. The samples were characterized by X-ray diffractometry, spectroscopic, thermic, nitrogen and water adsorption methods and compared with other organic compounds. The pore systems have been analysed from adsorption isotherms, t-plots and pore size distribution curves. The bioadsorbents CACMM1 and CACMM2 exhibited low specific surface area values and presented pores in the mesopore range. Composite adsorption isotherms for the binary mixtures benzene-hexane and benzene-cyclohexane on cactaceous powders have been established and revealed preferential adsorption of hexane and cyclohexane in the respective system. Also the adsorption behavior of dyes from aqueous solution was studied to complete the diversity of adsorbate molecules. Linear adsorption isotherms were obtained up to 6 mM dye equilibrium concentration.

溶液中におけるシリカ表面へのアルコールの吸着およびアルコキシ化反応

The adsorption of alcohol and the alkoxylation reaction on a silica surface were studied in solution systems. The over-all adsorption equilibria are expressed by the composite adsorption isotherms, which can show the influence of the kind of particles and solvents. The volume-filling model can be successfully applied to determine the individual isotherms. The surface alkoxylation reaction in benzene solutions was studied in comparison with that in aqueous solutions. The number of the formed alkoxyl groups was measured against the equilibrium concentration in a solution containing silica particles. In this paper, the expression of equilibrium constant is discussed, and the values are reported for various systems. The equilibrium constant for methanol is much larger than for other alcohols both in aqueous and benzene solutions.

Fractal Analysis of Composite Adsorption Isotherms Obtained by Using Density Functional Theory Data for Argon in Slitlike Pores

Two methods of calculation of the fractal dimension from single adsorption isotherms were examined by employing the composite adsorption isotherms obtained on the basis of the density functional theory for argon in slitlike pores at 87 K. In addition, the fractal analysis of the adsorption isotherms calculated under the assumption of the condensation approximation was performed. It was shown that the tested methods are valid but their application is not as simple as it was previously thought.

Experimental Approach to the Competitive Adsorption of Benzene/Water and Tetrahydrothiophene/Water Binary Vapors onto Quartz

This paper describes an experimental approach to the competitive adsorption of two different vapor molecules at room temperature on natural solids. We report firstly the isotherms of benzene, tetrahydrothiophene (THT), and water on quartz at 25 °C. The isotherms of water and THT present a hysteresis. The adsorption of benzene is fully reversible. Secondly we present results of adsorption of one vapor on a solid precovered by the other molecule. In this latter experiment, the quartz is covered by a chosen quantity of statistical layers of water (or benzene or THT). Another vapor species is then introduced in the closed experimental system. Our experimental device allows the displacement of both molecules to be followed. The first important conclusion in the analysis of the displacement of water by benzene is the fact that the displacement depends on the precoverage value. If the coverage is greater than 1 statistical monolayer, it is necessary to increase the partial pressure of benzene up to a “critical” value, in order to displace a small quantity of water from the quartz. The benzene is displaced by water in the very low partial pressure region, compared to previous results of displacement of water by benzene. The individual and composite adsorption isotherms of one component in the presence of the second are compared. In this latter case, the quantities of adsorbed water are greater than those obtained in preceding experiments. The displacement of preadsorbed THT by water is impossible in the studied range of pressure.

Verification of selected relationships for fractally porous solids by using adsorption isotherms calculated from density functional theory

Methods of calculating the fractal dimension (D) on the basis of single adsorption isotherms were critically tested by using argon composite adsorption isotherms for fractally porous solids. These isotherms were obtained from adsorption data for homogeneous slit-like pores calculated by employing the density functional theory (DFT). The composite adsorption isotherms were used to test the validity of the method based on the Frenkel-Halsey-Hill equation and so called “thermodynamic method” proposed by Neimark. The applicability of these methods was confirmed. However, our studies reveal new aspects of practical usage of both approaches, which need to be taken into consideration in analysis of experimental data.

水溶液中におけるシリカゲルへのアルコールの吸着

The adsorption of alcohol molecules on silica gel was investigated in a wide range of the alcohol concentrations in a water solution. Adsorption isotherms of ethanol and 1-propanol from the aqueous solutions were measured and analyzed in terms of the surface excess amount of adsorption. The composite adsorption isotherms were well expressed by a Dubinin-Radushkevich type equation. The individual isotherm, which was calculated by assuming a simple volume-filling model, showed that the pores of the silica were filled with the alcohol at a mole fraction higher than about 0.8.The surface hydroxyl groups of silica gel were partially alkoxylated to the alkoxyl groups even in contact with the alcohol in the presence of water. The number of formed alkoxyl groups increased with increase in the concentration of the alcohol in the solution. The equilibrium constant for the alkoxylation reaction was calculated.

Adsorption of binary solvent mixtures in reversed-phase chromatographic systems : Surface excess isotherms and enthalpies of displacement

An adsorption study of binary polar solvent mixtures by hydrocarbon-bonded chromatographic silica is presented which emphasizes the role of interfacial thermodynamics in the interpretation of retention volumes in reversed-phase liquid—solid chromatography. The composite adsorption isotherms of the three binary systems formed by acetonitrile (A), methanol (M) and water (W) on a C 18-modified silica surface were determined over the entire composition range by frontal analysis chromatography, and the thermodynamic consistency of these results was tested. In addition, the enthalpies of displacement, Δ ji H, of solvent i by solute j at the surface of two alkyl-modified porous-layer-bead materials was measured for the same liquid systems by flow calorimetry. The systems W + A and W + M exhibit S-shaped surface excess isotherms with negative (exothermic) Δ ji H values at both ends of the composition range. The molar enthalpy of displacement, Δ ji h, (defined in terms of a simple surface phase model) for A and M from dilute aqueous solutions is about −7 kJ/mol, and is attributed to hydrophobic interactions with the surface alkyl chains. Adsorption of W from dilute solutions in A yields much greater Δ ji h values which are attributed to hydrogen-bond interactions of water with free surface silanol groups. In the system W + A (which exhibits large positive deviations from ideal mixing behaviour) multi-layer adsorption of A occurs on the non-polar surface at compositions near the maximum of the surface excess isotherm.

Dipolar effects in adsorption from mixtures

A statistical mechanical theory of monolayer adsorption on to a plane charged surface from a mixture of two polar solvents is described. The region of the mixed monolayer containing adsorbed molecules with permanent and induced dipoles is treated as a vacuum situated between two continuous dielectric media. The ratio of areas occupied by the two components equals 2 and each adsorbed molecule is assigned two dipole orientation states in the monolayer. Preferential dipole orientation at the point of zero charge is achieved by postulating a residual energy. Because of the strong lateral dipole-dipole interactions and the molecular polarisability, the mean dipole moment per unit area of monolayer is small enought to give an acceptable potential drop across the monolayer. By introducing a replacement or exchange condition, the theoretiacal individual and composite adsorption isotherms are determined at different surface charges.

Composite adsorption isotherms corrected for solution-adsorbate molar volume differences

The components of a binary solution do not necessarily “see” the same volume of the pores of an adsorbent. If this difference in behavior is not taken into account, the calculated composite adsorption isotherms can be in error by several percent, even in normal cases. Three reasons pure liquid or solution species can have a molar volume in the bulk phase different from that in the adsorbate phase are discussed. The pore volume of silica gel, measured assuming that the gel does not swell, depends upon the liquid used to measure it; for one batch of gel, values are reported using water and 19 organic liquids. Equations are derived that show: (1) how composite isotherms can be calculated, taking into account this volume effect and using the pore volume data; and (2) the extent of the error if the pore volume difference is not noted. The method is applied to the composite isotherms of three representative pairs of liquids, and the effect of various assumptions on the calculation of these isotherms is shown. For spherical solute species, such as solvated ions, size comparisons can be made using the volume effect even if the solvent species is not spherical, providing ion reaction with the surface is prevented. The method used in earlier work to obtain the relative sizes of hydrated ions is shown to be in fair agreement with a thermodynamic analysis of the volume effect developed by Giddings et al. for use in other solution-gel systems.

Solid/solution interface equilibria for aromatic molecules adsorbed from non-aromatic media. Part 2.—Aromatic carboxylic acids

Data have been obtained for benzoic acid, 1-naphthoic acid and 2-naphthoic acid adsorption on the carbon blacks Graphon and Spheron 6, and on the oxides Alcoa C730, Alon C, titanium dioxide and Cab–O–Sil using some or all of the solvents cyclohexane, carbon tetrachloride and cyclohexanone. Individual isotherms were calculated from the composite adsorption isotherms by well-established methods, thus enabling an assessment of the nature of the adsorbed phase. For the carbon blacks and some of the oxide adsorbents, the results are consistent with an adsorbed phase confined to a monolayer with a flat orientation of aromatic molecules; on the more polar oxide adsorbents however there is evidence of perpendicular orientation of the aromatic molecules in some cases, as well as of multilayer adsorption.

The use of ternary phase diagrams in the study of composite adsorption isotherms

The use of ternary phase diagrams in the study of composite adsorption isotherms