Basis Of Adsorption Isotherms Research Articles

Surface Modified Laterite Soil with an Anionic Surfactant for the Removal of a Cationic Dye (Crystal Violet) from an Aqueous Solution

The work aims to study the removal of crystal violet (CV) using laterite soil with surface modification by surfactant (SML). Surface modification of laterite soil was conducted by pre-adsorption of sodium dodecyl sulfate (SDS) at pH 4 and low ionic strength to enhance removal of CV. The effective conditions for CV removal through adsorption technique using SML were optimized and found to be contact time 60 min, pH 6, adsorbent dosage 5 mg/mL, and 5 mM NaCl as background electrolyte. The highest removal of CV using SML reached to 86.5% under optimum conditions. We used Fourier transform infrared spectroscopy (FT-IR) to evaluate the change of surface vibrational groups of laterite after SDS pre-adsorption and after CV adsorption while the different charged surface was determined by ζ potential measurements. The CV adsorption onto SML increased when increasing ionic strength from 1 to 10 mM. Nevertheless, at high ionic strength, this trend is reversal due to desorption of SDS from laterite surfaces. Adsorption isotherms of CV onto SML at different NaCl concentrations were tried to fit by Langmuir, Freundlich, and a two-step adsorption models. The adsorption kinetics were in good agreement with pseudo-second-order model. The removal efficiency of CV after four regenerations still reached higher than 85%. On the basis of adsorption isotherms, charged surface change by ζ potential and surface modification by FT-IR, we suggest that CV adsorption onto SML was induced by both non-electrostatic and electrostatic interactions. We also demonstrate that SML is a novel, reusable, and low-cost adsorbent for cationic dye removal from aqueous solution.

Adsorption of Anionic Surfactants onto Alumina: Characteristics, Mechanisms, and Application for Heavy Metal Removal

We investigated adsorption of anionic surfactants, sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS), onto alumina (Al2O3) with large size in the present study. The effective conditions for SDS and STS adsorption onto Al2O3 were systematically studied. The conditions for SDS and STS adsorption onto γ-Al2O3 were optimized and found to be contact time 180 min, pH 4, and 1 mM NaCl. Adsorption of both SDS and STS onto large Al2O3 beads increased with an increase of ionic strength, demonstrating that the adsorption is controlled by electrostatic attraction between anionic sulfate groups and positively charged Al2O3 surface, as well as hydrophobic interactions between long alkyl chains of surfactant molecules. Nevertheless, the hydrophobic interaction in terms of STS adsorption is much higher than that of SDS adsorption. The obtained SDS and STS adsorption isotherms in different NaCl concentrations onto Al2O3 beads were fitted well by two-step adsorption. Adsorption mechanisms were disused in detail on the basis of adsorption isotherm, the change in surface charge, and the change in functional surface groups by Fourier-transform infrared spectroscopy (FTIR). The application of surfactant adsorption onto Al2O3 to remove cadmium ion (Cd2+) was also studied. The optimum conditions for Cd2+ removal using surfactant-modified alumina (SMA) are pH 6, contact time 120 min, and ionic strength 0.1 mM NaCl. Under optimum conditions, the removal efficiency of Cd2+ using SMA increased significantly. We demonstrate that SMA is a novel adsorbent for removal of Cd2+ from aqueous solution.

Adsorption of phenol from aqueous solutions on original and oxidized multiwalled carbon nanotubes

The surface heterogeneity of the multiwalled carbon nanotubes is investigated on the basis of adsorption isotherms from dilute aqueous phenol solutions at various temperatures. The Dubinin–Astakhov...

Adsorption characteristics of anionic azo dye onto large α-alumina beads

Adsorption of anionic azo dye, new coccine (NC), onto large α-alumina beads in aqueous media was systematically investigated as functions of pH and NaCl concentration. Adsorption amounts of NC decrease with increasing pH of solutions due to less positive charges of α-Al2O3 surface at high pH. At a fixed pH, the NC adsorption increases with decreasing NaCl concentration, indicating that NC molecules mainly adsorb onto α-Al2O3 by electrostatic attraction. Experimental results of NC adsorption isotherms onto α-Al2O3 at different pH, and ionic strength can be represented well by two-step adsorption model. The effects of NC on surface charge and surface modification of α-Al2O3 at the plateau adsorption are evaluated by streaming potential and Fourier transform infrared spectroscopy with attenuated total reflection technique (FTIR-ATR), respectively. On the basis of adsorption isotherms, surface charge effect, and surface modification, we suggested that the formation of a bridged bidentate complex between aluminum ions of α-Al2O3 and two oxygen atoms of a sulfonic group induced the adsorption of NC onto α-Al2O3.

Heterogeneity of multiwalled carbon nanotubes based on adsorption of simple aromatic compounds from aqueous solutions

The surface heterogeneity of multiwalled carbon nanotubes (MWCNTs) is studied on the basis of adsorption isotherms from dilute aqueous phenol and dopamine solutions at various pH values. The generalized Langmuir–Freundlich isotherm equation was applied to investigate the cooperative effect of the surface heterogeneity and the lateral interactions between the adsorbates. The theoretical isosteric heats of adsorption were obtained assuming that the heat of adsorption profile reveals both the energetic heterogeneity of the adsorption system and the strength of the interactions between the neighboring molecules. The adsorption energy distribution functions were calculated by using algorithm based on a regularization method. The great advantage of this method is that the regularization makes no assumption about the shape of the obtained energy distribution functions. Analysis of the isosteric heats of adsorption for MWCNTs showed that the influence of the surface heterogeneity is much stronger than the role of the lateral interactions. The most typical adsorption heat is 20–22 kJ/mol for both phenol and dopamine. After purification of nanotubes, heat value for phenol dropped to 16–17 kJ/mol. The range of the energy distribution is only slightly influenced by the surface chemistry of the nanotubes in the aqueous conditions.

Sepiolite/calcium interactions in desiccant clay production

The aim of the present study is to determine the applicability of three different sepiolite samples received from the Eski şehir region of Turkey in the production of desiccant clay. Japanese (JIS-Z-0701) and British (BS 3482-6) standards dictate that effective sepiolite should uptake humidity of at least 8% of its weight at 20% RH. This value must be 20% at 50% RH and 30% at 90% RH. Therefore, the HAC of sepiolites was modified by subjecting them to heat treatment at 200 °C and different relative humidity (RH) values of 20 to 90% as a function of time. The data obtained was interpreted on the basis of adsorption isotherms. The results indicate that raw sepiolites at 50% RH do not conform to the desiccant standards. Therefore, sepiolite/CaCl 2 mixture at the different CaCl 2 additions was evaluated for its potential as a humidity adsorbent. However, it is shown that sepiolite mixed with 5% CaCl 2 at 50% RH or above exceeds the required specifications for a commercial desiccant.

The cooperative effect of the surface heterogeneity and of the lateral interactions between adsorbed molecules on adsorption of simple aromatic compounds from dilute aqueous solutions on activated carbons

Abstract The cooperative effect of the surface heterogeneity and of the interactions between adsorbed molecules on adsorption of simple aromatic compounds from aqueous solutions is presented. The phenomenon is investigated on the basis of adsorption isotherms of phenol and aniline from dilute aqueous solutions at various pH values on activated carbons prepared from different precursors. The literature experimental data concerning phenol adsorption from aqueous solutions on APET carbon prepared from polyethyleneterephthalate (PET) as well as the data of aniline adsorption on commercial ACP carbon prepared from peat have been utilized. The lateral interactions in the adsorbed phase are taken into account by use of the Fowler–Guggenheim (FG) isotherm, and by use of isotherms based on vacancy solution model (VSM) in conjunction with the Flory–Huggins (FH) and Wilson (W) activity coefficient equations. By assuming the definite form of the local isotherm of adsorption in the integral equation (IE) and quasi-Gaussian distribution of adsorption energy, the condensation approximation (CA) approach led to new isotherm equations for single-solute adsorption from dilute solutions.

Nanostructure of polymer layers formed upon the adsorption from binary and ternary solutions

Thicknesses of nanolayers formed upon the adsorption from dilute and semidilute solutions of polystyrene, poly(butyl methacrylate), and their mixtures on the surface of solid SiO2 are estimated on the basis of adsorption isotherms and atomic force microscopy measurements. It is established that the thickness of an adsorption layer is determined by the sizes of individual macromolecular coils and clusters arising in a solution. In the case of polymer blends, adsorption leads to the formation of mosaic structures with the alternation of polymeric components in the substrate plane; the characteristic size of a domain is ≈200 nm for each component. It is shown that adsorption layers formed on the surface of a silicon single crystal (covered with intact oxide) are fractal objects whose dimension depends on the nature of polymer and conditions of its adsorption.

Computer modeling and analysis of heterogeneous structures of microporous carbonaceous materials

The aim of this work was to study the problems connected with computer modeling and analysis of heterogeneous structures of microporous carbonaceous materials. The research was focused on the numerical properties of original mathematical models for heterogeneous multilayer adsorption on microporous carbonaceous materials presented in our earlier papers and their applicability to examination of real microporous materials. These models are aimed at drawing information on pore structure and capacity on the basis of adsorption isotherms of small molecule adsorbates. They easily fit typical adsorption data in wide relative pressure ranges. In the theory presented, adsorption of small nearly spherical molecules in irregular pores of molecular size has been considered and side adsorbate-adsorbate interactions are neglected. The molecules mentioned are located in pores by forming aggregates, the size of which is limited by the geometry of the pores. The set of adsorbate molecules, which were adsorbed mainly due to adhesive interactions with the adsorbent matter, is treated as the first layer adsorption. Joining further molecules is viewed as the second, third,... layer adsorption. The main idea of the approach to modeling microporous structure presented, consists of introducing of realistic relationships between geometrical properties of pores and adsorption energy. Special attention was focused on the analysis of the influence of the number of model parameters on identification reliability and evaluation errors of porous structure parameters. This paper gives more information on properties of the identification technique presented in our earlier papers. The five-parameter and six-parameter identification reliability is analyzed in more detail, for different values of the system parameters. In this context, the efficiency of simultaneous examination of two isotherms is also studied.

Investigation of Chromium(III)-Picolinate Adsorption on Some Soil Types

In the experiment adsorption characteristics of different soil types (humic sand, meadow soil, leached chernozem and meadow solonec) was examined on the basis of adsorption isotherms for Cr(III)-picolinate. The Langmuir equation was used to describe the isotherms by which the amounts of metal ions actually and maximally adsorbed by the soils were determined concerning the given complex. A comparison was made among the organically bound Cr(III)-picolinate, an inorganic Cr(III) compound and a Cr(VI) form examined in a previous study. Based on the adsorption isotherms, adsorption capacity of the Cr(III)-picolinate was found 20 times smaller on sandy soil and 50 times smaller on the chernozem comparing to that of the inorganic Cr(III)-chloride, thus, the bio-availability of the chromium for the plants is 20 and 50 times higher in case of the given soil types. For the well-known toxic Cr(VI)-form, the adsorption was 2 times higher in case of sandy soil and 5 times higher for chernozem than in case of the organic Cr(III)-complex compound.

Validation of the Reliability of the Porous Structure Parameters for Activated Carbons as Evaluated on the Basis of Adsorption Isotherms from the Gaseous Phase

Adsorption/desorption isotherms from the gaseous phase (benzene vapour, nitrogen) have been determined consecutively a number of times on the same activated carbon sample. The porous structure parameters were evaluated on the basis of the experimental data using the Dubinin-Radushkevich, Dubinin-Astakhov, Finger-Büllow, Dubinin-Stoeckli and Horvath-Kawazoe equations for the calculations. Analyses of the mean values and relative errors of particular structural parameters were made as well as comparisons of the stability of the adsorption models used. It was found that the reliability of the results obtained was better for the benzene vapour adsorption isotherms determined by a gravimetric method than for those determined by a volumetric method using nitrogen as the adsorbate.

Variable thickness of the liquid sorption layers on solid surfaces

Calculations of the adsorption capacity and the thickness of the adsorption layer are of primary importance for studies of the adsorption of binary mixtures. Earlier methods were applicable to the determination of real adsorption capacity only in the case of monolayers and/or layers of constant thickness, independent even of mixture composition. In the case of the adsorption isotherms of binary mixtures of non-electrolytes these conditions are often not fulfilled, and neither the Schay–Nagy extrapolation method nor reciprocal isotherm representations can be used for the determination of adsorption capacity on the basis of adsorption isotherms. Here we present a method of calculation suitable for the computation of surface composition and adsorption layer thickness in the whole composition range. Thus, instead of a single value of adsorption capacity, the system is characterized by the layer thickness isotherm given as a function of the composition of the bulk phase.

Effect of Different Factors on the Adsorption of Phosphamidon on Two Different Types of Indian Soil

The effect of exchangeable cations (H+ and Na+). autoclaving, organic matter, anionic surfactants and temperature on the adsorption of phosphamidon on two different types of Indian soil was studied. The adsorption isotherms for all the effects/treatments were in close agreement with the Freundlich equation and yielded S-shaped isotherms. The amount of phosphamidon adsorbed in all cases was higher in medium black (silt loam) soil than alluvial soil (sandy loam) and was related to the organic matter content, clay content, CaCO3 content, surface area and cation-exchange capacity of the soils. The adsorption on both types of soil follows the order H+-soil > Na+-soil > natural soil at 10°C > natural soil at 20°C > autoclaved soil > organic matter-removed soil > anionic surfactant > natural soil at 40°C, which was in accordance with the Freundlich constant, KF, and distribution coefficient, Kd, values. The adsorption capacity of phosphamidon for organic matter and clay content for both the soils was evaluated by calculating the Kom and Kc values when it was found that phosphamidon adsorption was better correlated with the clay content than with the orgnic matter content on the basis of adsorption isotherms. Various thermodynamic parameters such as the thermodynamic equilibrium constant (K0), the standard free energy (ΔG0), the standard enthalpy (ΔH0) and the standard entropy (ΔS0) changes have been calculated as a means of predicting the nature of the isotherms.

Adsorption characteristics of trichloroethylene on plasma‐treated activated carbon

The adsorption characteristics of trichloroethylene (TCE) on untreated activated carbon (U‐AC) and plasma‐treated activated carbons (PT‐ACs) were investigated on the basis of adsorption isotherms, differential heat of adsorption and entropy of adsorption to elucidate the difference between the U‐AC and PT‐ACs interactions with TCE. Differences in the amount of TCE adsorbed between U‐AC and PT‐ACs seemed to be attributable to the surface properties and micropore structure of the activated carbon. The interaction of the TCE ‐ PT‐AC surface was stronger than that of the TCE ‐ U‐AC surface. The amount of TCE adsorbed and strength of the TCE ‐ activated carbon binding for the surface of the PT‐AC depended on the hydrophobicity with inner the surface area of the activated carbon, that is, the porosity due to tetrafluoromethane plasma treatment.

Adsorption of .BETA.-Carotene from Alkali-Refined Rape Seed and Soybean Oils with Attapulgite and Sepiolite.

The difference in amounts of β-carotene adsorbed on attapulgite and sepiolite was discussed on the basis of adsorption isotherm from alkali-refined rape seed and soybean oils. The amounts adsorbed on attapulgites were larger than those on sepiolites. The difference in the amounts adsorbed on attapulgite and sepiolite could not be explained using their surface area, pore size distribution, acid strength, acidity or free fatty acids. It was concluded that triolein was competing with β-carotene for adsorption sites of attapulgite and sepiolite and that sepiolite was more accessible to triolein competition than attapulgite.

Interaction between Methylchloroform and Surface Modified Activated Carbon in CF4 Plasma

Abstract The interaction between methylchloroform and a surface modified activated carbon, which was treated with tetrafluoromethane plasma, was evaluated on the basis of adsorption isotherms and physicochemical properties of the activated carbon. Tetrafluoromethane plasma-treated activated carbon could be used for the complete recovery of methylchloroform.

Influence of different factors on the adsorption of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl- N-methyl carbamate) on soils

The effects of exchangeable cations (H + and Na +), autoclaving, organic matter, cationic and anionic surfactants, and temperature on the adsorption of carbofuran on two different types of soils were studied. The adsorption isotherms for all effects/treatments were in close agreement with the Freundlich equation and yielded S-shaped isotherms. The amount of carbofuran adsorbed in all cases was higher in Jhansi red loam soil than in Pilibhit sandy loam soil and was related to organic matter content, clay content, CaCO 3 content, surface area, and cation-exchange capacity of the soils. The adsorption on soils from both sites follows the order H soil → Na soil → natural soil at 25°C → autoclaved soil → soil from which organic matter had been removed → cationic surfactant → anionic surfactant → natural soil at 50°C and was in accordance with Freundlich constant K values and distribution coefficient K d values. The adsorptive capacity of carbofuran for organic matter and clay content for both the Jhansi and the Pilibhit soils was also evaluated by calculating K om and K c values, and it was found that the carbofuran adsorption was better correlated with clay content than with organic matter content of soils. On the basis of adsorption isotherms, various thermodynamic parameters such as the thermodynamic equilibrium constant K 0, standard free energy ( ΔG°) changes, standard ethalpy ( ΔH°) changes, and standard entropy ( ΔS°) changes have been calculated in order to predict the nature of isotherms.

Influence of different factors on the adsorption of phosphamidon on soils

The effect of exchangeable cations (H+ and Na+), organic matter and temperature on the adsorption of phosphamidon on two different types of Indian soils was studied. The adsorption isotherms for all the effects/treatments were in close agreement with the Freundlich equation and yielded (S) shaped isotherms. The amount adsorbed in all the cases was lower in tarai loam soil than black silt clay loam soil and was related to organic matter content, clay content, CaCO3 content, surface area and CEC of the soils. The adsorption on both the soils follows the order as H‐soil > Na‐soil > natural soil at 25°C > natural soil at 50°C > organic matter removed soil. This order of adsorption was in accordance with Freundlich constant K values and distribution coefficient K d‐values. The adsorptive capacity of phosphamidon for organic matter and clay content for both the soils was. also evaluated by calculating Kom and Kc values and found that phosphamidon adsorption was slightly better correlated with clay content than organic matter content. On the basis of adsorption isotherms, various thermodynamic parameters such as thermodynamic equilibrium constant (Ko) standard free energies (?G°), standard enthalpies (?H°) and standard entropies (?S°) changes have been calculated for predicting the nature of isotherms.

Calculation of internal-mass-transfer coefficients in porous bodies on the basis of adsorption isotherms

Formulas relating the mass-transfer coefficients in porous bodies to the adsorption isotherms and coefficients of internal diffusion of vapor and adsorbed material are derived.