Hill-de Boer Research Articles

Adsorption of isopropanol and cyclohexane on zinc oxide

Adsorption isotherms of isopropanol and cyclohexane are obtained in the range of 234–303 K on an initial surface of zinc oxide and after its treatment with glow-discharge plasma in O2 and high-frequency plasma in Ar. The values of isosteric heat and adsorption entropy are shown to be only slightly affected by these treatments. It is found that the acidity of the surface increases by 38 and 97%, respectively, and the acidic sites are not adsorption sites for either adsorbate. At low degrees of occupation, the adsorption isotherms of (CH3)2CHOH are described by an equation of induced adsorption whose parameters are dependent on the plasma-chemical treatments. It is concluded that adsorbed isopropanol particles exist in positively and negatively charged forms. The adsorption of cyclohexane is described by the Hill-de Boer equation for the initial ZnO surface, and by the Langmuir equation after plasma-chemical treatments.

CORROSION INHIBITION OF ALUMINUM IN 0.1 M HCL SOLUTION BY GLUTAMIC ACID

The inhibition effect of glutamic acid (Glu) on corrosion of aluminum in 0.1 M HCl solution was investigated using linear polarization (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. Polarization curves revealed that Glu acted as a mixed-type inhibitor. The values of polarization resistance obtained by LPR and EIS were consistent in showing that inhibition efficiency increased with increasing concentration of Glu. The inhibition occurs by adsorption of Glu on the metal surface, and evidence of this was given by the equivalent circuit analysis of EIS results. The adsorption process was found to obey the Hill-de Boer isotherm with a standard free energy of adsorption of −60.45 kJ mol−1. Surface analysis by means of X-ray photoelectron spectroscopy (XPS) was performed to provide chemical characterization of the adsorbed layer. The N 1 s spectrum showed the presence of ionized () and neutral (NH2) amino group. The corrosion inhibition was attributed to a chemisorption process with Glu molecules forming a stable chelate on the metal surface.

Equilibrium and thermodynamic studies on adsorption of BSA using PVDF microfiltration membrane

It was the aim of this work to investigate equilibrium and thermodynamic aspects for static adsorption of bovine serum albumin (BSA) as model protein of extracellular polymer substances (EPS) from membrane bioreactor (MBR) on hydrophilic polyvinylidene fluoride (PVDF) microfiltration membrane. In present paper, the influences of temperature, pH and ionic strength were studied and eight different isotherm models were used to fit equilibrium data by nonlinear regression method. The obtained results showed that the best-fitted adsorption isotherm models were in the order of: Langmuir and Freundlich>BET>Langmuir≈Redlich–Peterson≈Temkin>Freundlich>Fowler and Guggenheim (Hill–De Boer), of which, Langmuir–Freundlich isotherm is the best suitable. Thermodynamic investigation indicated that this process was not spontaneous and endothermic and maybe attributed to physicosorption, and the distribution of BSA adsorbed on PVDF membrane was more chaotic than that in the aqueous solution. The results from the static adsorption of BSA on PVDF membrane can be a useful tool to evaluate the behavior of membrane biofouling in MBR and also provide basis for performance comparison among different membranes.

Modeling of adsorption isotherms of phenol and chlorophenols onto granular activated carbon: Part I. Two-parameter models and equations allowing determination of thermodynamic parameters

The adsorption equilibrium isotherms of five phenolic compounds from aqueous solutions onto granular activated carbon (GAC) were studied and modeled. Phenol (Ph), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) were chosen for the adsorption tests. To predict the adsorption isotherms and to determine the characteristic parameters for process design, seven isotherm models: Langmuir (five linear forms), Freundlich, Elovich, Temkin, Fowler–Guggenheim, Kiselev, and Hill–de Boer models were applied to experimental data. The results reveal that the adsorption isotherm models fitted the data in the order: Fowler–Guggenheim > Hill–de Boer > Temkin > Freundlich > Kiselev > Langmuir isotherms. Adsorption isotherms modeling shows that the interaction of phenolic compounds with activated carbon surface is localized monolayer adsorption, that is adsorbed molecules are adsorbed at definite, localized sites. Each site can accommodate only one molecule. The interaction among adsorbed molecules is repulsive and there is no association between them, adsorption is carried out on energetically different sites and is an exothermic process. Uptake of phenols increases in the order Ph < 2-CP < 4-CP < DCP < TCP, which correlates well with respective increase in molecular weight, cross-sectional area, and hydrophobicity and decrease in solubility and p K a. Additionally, for the four tested chlorophenols, it seems that the magnitude of adsorption is directly proportional to their degree of chlorination.

3-Hydroxybenzoic acid as AISI 316L stainless steel corrosion inhibitor in a H2SO4?HF?H2O2 pickling solution

3-Hydroxybenzoic acid (3-HBA) was studied for possible use as a AISI 316L stainless steel (SS) corrosion inhibitor in an environmental-friendly aqueous pickling solution of 75 g l−1 sulphuric acid (H2SO4), 25 g l−1 hydrofluoric acid (HF) and 30 g l−1 hydrogen peroxide (H2O2). 3-HBA was tested in concentrations from 5 × 10−5 to 5 × 10−1M at 298 and 313 K temperature. Inhibition efficiency increased with the 3-HBA concentration. The inhibitor mechanism is discussed in terms of the properties of the isotherm equations of Frumkin, Hill-de Boer and Kastening–Holleck mainly. The shape, the trend of the slopes along the curve and the existence of inflection points, were analysed as the characteristics that differentiate one adsorption equation from another. The best fit was obtained using the Frumkin isotherm model. The projected molecular area of 3-HBA was calculated as a structural parameter to elucidate its optimal inhibition mechanism.

Two-dimensional gas and vacancy solution approaches in the thermodynamic description of adsorption equilibrium

We present two approaches to description of the adsorption equilibrium in adsorbate–adsorbent systems, the treatment where the adsorbate is considered as a two-dimensional gas, and the treatment where the adsorbate and adsorbent form a solution where the adsorbate is the solute and vacancies play the role of the solvent. In the first case the application of different equations describing the state of a two-dimensional gas leads to some fundamental adsorption isotherm equations, for example, Henry, Volmer, Hill–deBoer, Fowler–Guggenheim, and Langmuir. In contrast, the application of different equations (existing in the theory of solutions) describing the activity of the solvent (e.g., the Wilson model or the model of Flory and Huggins) leads to some new adsorption equations and the assumption of the ideality of the solvent leads to the Langmuir adsorption isotherm. We present some new adsorption equations basing on the second method described above and on the Redlich–Kister and Wohl expansions. Assuming that the activity coefficients are given by the one-constant Margules equation, the two-constant Margules equation, the van Laar equation, the Wilson equation, and, finally, the Flory–Huggins equation, we derive the respective adsorption isotherm formulas. We also present the assumptions leading to the best-known adsorption equations derived applying the first method. The equation developed by Cochran et al. is also corrected, taking into account the fundamental assumptions of the Flory–Huggins theory.

Analysis of Adsorption of Gases and Vapors on Nonporous Graphitized Thermal Carbon Black

In this paper we analyzed the adsorption of a large number of gases and vapors on graphitized thermal carbon black. The Henry constant was used to determine the adsorbate-adsorbent interaction energy, which is found to be a modest decreasing function of temperature. Analysis of the complete adsorption isotherm over a wider range of pressure yields information on the monolayer coverage concentration and the adsorbate-adsorbate interaction energy. Among the various equations tested, the Hill-de Boer equation accounting for BET-postulated multilayer formation describes well the adsorption isotherms of all adsorbates. On average, the adsorbate-adsorbate interaction energy in the adsorbed phase is less than that in the bulk phase, suggesting that the distance between adsorbed molecules in the first layer of the adsorbed phase is slightly less than the equilibrium distance between two adsorbate molecules in the bulk phase. This suggests that the first layer is in a compressed state, which is due to the attraction of the adsorbent surface. The monolayer concentration as determined from the fitting of the Hill-de Boer equation with experimental data is slightly larger than the values calculated from the molecular projection area, suggesting that molecules can be oriented such that a larger number of molecules can be accommodated on the carbon black surface. This further supports the shorter distance between adsorbate molecules in the adsorbed phase.

Surface heterogeneity of carbon–silica adsorbents studied on the basis of the complex adsorption investigations

Silica-gel (SG) Si-60 was coated by pyrolytic coke using CVD from methylene chloride. The porous structure of carbon–silica adsorbents (carbosils) was analyzed on the basis of nitrogen adsorption isotherms at 77 K. It has been shown that carbosils are mesoporous adsorbents with complete absence of micropores. Total pore volume and surface area decrease during the carbon deposition on silica surface. Heterogeneity of surface of carbosil samples was estimated by adsorption energy distribution (AEDs) calculated from adsorption isotherms of nitrogen at 77 K and hexane, cyclohexane, benzene and chloroform adsorption isotherms at 473 and 483 K. AEDs were obtained by solving Adsorption Integral Equation with Hill-de Boer kernel function. N2 AEDs show that distribution of silica active surface sites responsible for N2 adsorption at 77 K is not altered during the carbon deposition. However, coke deposition leads to improving of polar–apolar surface composition, resulting in increase of adsorption of apolar (hexane) and decrease of adsorption of polar (chlorophorm) substances. The main changes observed in AEDs are connected with decreasing of silica accessible area at stable carbon structure during CVD of carbon.

The Adsorption of Anionic Surfactants by Iron(III) and Aluminium Hydroxides

The adsorption of sodium dodecyl sulphate and sulphanol NP-3 by iron(III) and aluminium hydroxides was studied. The applicability of the Langmuir, Freundlich and Hill–de Boer adsorption equations for the description of the adsorption isotherms obtained experimentally was verified. Values of various parameters characterising the adsorption of the anionic surfactants investigated by iron(III) and aluminium hydroxides have been calculated. These allowed assumptions to be made about the adsorption mechanism. The possibility of using air as an adsorbent for anionic surfactants was studied.

Adsorption of Ethoxylated Alkyl Phenols on Silica Gel from Aqueous Micellar Solutions

Adsorption of ethoxylated nonylphenols (Neonols) from their micellar solutions on coarse-pore KSK silica gel was studied under static conditions. The energy of adsorption interaction between micelles and silica gel surface was determined using the Hill–de Boer isotherm. For the initial parts of the isotherms (from 1 to 6 CMC1), it was equal to –15.8kT. The study of coadsorption of Neonols with dye methylene blue showed that the micellar adsorption layer is fragmentary and that the amount of the adsorbed surfactant is dependent on the conditions of the adsorption layer formation.

Dubinin"s theory and its contribution to adsorption science

Dubinin"s theory for the volume filling of micropores (TVFM), originally developed for the adsorption of single vapours by microporous solids such as activated carbons and zeolites, has gradually been extended to other areas. They include immersion calorimetry, the adsorption of water vapour and of mixtures, as well as adsorption from aqueous solutions. Recent studies in the field of adsorption from aqueous solutions, by activated carbons, suggest that the principle of temperature invariance is fulfilled and in the case of phenolic compounds a modified DRK equation can be used to predict the adsorption equilibrium over a certain range of temperatures. Computer modelling of CO2 adsorption by carbons at 273 K leads to micropore distributions, which are in good agreement with those derived from other techniques. It also appears that the model isotherms in single slit-shaped micropores can be fitted to the Hill-de Boer isotherm, in agreement with mathematical studies of the origin of the Dubinin—Astakhov equation.

A simple adsorption model for ionic surfactants

In the past, few theoretical attempts have been made to describe quantitatively the adsorption of ionic surfactants at liquid interfaces. Well-known adsorption isotherms due to Frumkin or Hill–de Boer cannot respond to the specific electrostatic and geometric properties of the surfactant molecules. Our approach is based on a combination of the Gouy–Chapman theory with a modified Frumkin isotherm. The modification implies that the system is free to choose an optimal head group area and an optimal arrangement of the surfactant molecules in the interface as a function of bulk concentration. Interaction energies between neighbouring adsorbed surfactant molecules and between surfactant and water molecules are taken into consideration. The minimum of the Gibbs free energy of the system is equivalent to a minimal interfacial tension. Thus, the thermodynamically stable isotherm can be obtained as the lower envelope of the family of σ versus ln c isotherms resulting from different choices of the model parameters, including the area per molecule. According to the Gibbs equation, the Γ versus ln c adsorption isotherm is obtained as the derivative of this envelope. By variation of the model parameters, the envelope of the calculated adsorption isotherms can be fitted to experimental data of the interfacial tension versus bulk concentration. A computer program is used to calculate the σ versus c and the Γ versus ln c curves as well as to fit the parameters.

Determination of the Porous Structure of Activated Carbons Using the IAE Concept. Influence of the Local Adsorption Model

In this paper we study a method for the determination of the micropore volume distribution function of activated carbons. This method is based on the Integral Adsorption Equation concept (IAE). The micropore volume distribution function is assumed to be a Gaussian of which the parameters are unknown. These parameters are determined using adsorption isotherms of carbon dioxide on a given activated carbon (F30/470 CHEMVIRON CARBON) at 278, 288, 298, 303, 308, 318 and 328 K and for pressures up to 100 kPa. Several local adsorption models are used (Langmuir, Volmer, Fowler-Guggenheim, Hill-de Boer). The influence of the choice of the local model on the pore volume distribution function is discussed. The physical validity of this function and the performances of the different models are presented. It appears that the effect of the temperature on the adsorption isotherms is difficult to model over a wide range of relative pressure. The Hill-de Boer and the Langmuir local models are the most efficient (average errors respectively equal to 3.53% and 2.80% in the studied range of temperature and pressure). They provide the most meaningful parameters for the pore volume distribution function.

Determination of the micropore volume distribution function of activated carbons by gas adsorption

A new method for the determination of the micropore volume distribution function of activated carbons is presented. It is based on the treatment of pure gas adsorption isotherms by a theoretical model derived from the Hill-de Boer theory. Adsorption data (isotherms and heat curves) for carbon dioxide, ethane and ethylene on activated carbon (F30/470 CHEMVIRON CARBON) have been provided by a thermobalance coupled to a calorimeter (TG-DSC 111 SETARAM) at different temperatures (233, 273, 303 and 323 K) for pressures up to 100 kPa. Adsorption isotherms of carbon dioxide and ethane at 303 and 323 K have been used for the determination of the micropore volume distribution function of the activated carbon of interest. The knowledge of its structure has then allowed the simulation of adsorption isotherms and heats for the same adsorbates at the same temperatures as those experimentally studied. Similar calculations have been conducted for ethylene. Whatever the adsorbate (carbon dioxide and ethane used for the determination of the micropore volume distribution function or ethylene), the mean deviation between experimental and calculated isotherms does not exceed 4% at quasicritical and supercritical temperatures (303 and 323 K). In the same temperature conditions, discrepancies between calculation and experiment reach about 10% for adsorption heats. For both isotherms and heats, large discrepancies appear at low temperature (233 and 273 K). This method allows the determination of the micropore volume distribution function of activated carbons. The validity of the results is insured using several isotherms of several adsorbates and taking into account the calorimetric effect of the phenomenon. That is the reason why this method can also be seen as a new possible model for pure gas adsorption data prediction. This paper also presents a brief summary of the state of the art in this field.

Intracrystalline diffusion of benzene in silicalite: effect of structural heterogeneity

The sorption kinetics of benzene in silicalite have been measured gravimetrically using large silicalite crystals of sizes 350 µm × 105 µm × 105 µm and 270 µm × 70 µm × 70 µm in the temperature range 283–343 K. Experiments were performed under conditions that ensured isothermal operation with intracrystalline diffusion control. An analytical expression for the Darken's correction factor (δ In P/δ In a) was derived based on the Hill–de-Boer equation and was used to determine the variation of corrected diffusivity with concentration. The transport diffusivity varied significantly with the adsorbed-phase concentration but the corrected diffusivity was found to be essentially independent of the concentration. However, at temperatures below the surface transition temperature, a maximum in corrected diffusivity was observed at an adsorbed-phase concentration of four molecules per unit cell (uc). This maximum is the direct result of the type IV isotherm exhibited by the silicalite–benzene system below the surface transition temperature. It is proposed that the increase in corrected diffusivity at the critical adsorbed-phase concentration of 4 molecules uc–1 arises from reorientation of benzene molecules resulting in a much more efficient packing in the pore channel system.

Argon and nitrogen adsorption on graphite at high temperatures

Nitrogen and argon adsorption on two graphites differing in their surface homogeneity was studied in a wide range of temperatures (77.5 K up to 183.2 K). The experimentally determined entropy of the adsorbed phase and isoteric heat of adsorption were analyzed. The Hill-de Boer adsorption isotherm was employed to calculate the apparent two-dimensional critical temperature. The behaviour of the adsorbed film was analyzed to explain the influence exerted upon it by temperature and surface homogenity.

The inception of condensation of water vapor on smooth solid substrates

The critical supersaturation for the inception of condensation of water vapor on smooth solid substrates can be predicted theoretically by the nucleation theory and determined experimentally. By equating these theoretical and experimental values, one is able to find the empirical correlations among the coefficient k a in the Hill-de Boer adsorption isotherm, the contact angle θ, and the equilibrium fraction of coverage F e and film pressure π e under saturated vapor, which are all different ways of expressing the affinity between the condensing matter and the solid substrate. The condensate clusters on the substrate grow by direct addition of the vapor molecules and by the addition of the adsorbed vapor molecules through two-dimensional migration. The result of this work shows that the latter route of cluster growth is far more important than the former except in the extreme cases of θ ≐ 0 and θ ≐ π. The ratio of contributions of these two routes has a maximum at θ ≐ 51.8°, where the ratio of the vapor-condensate-solid interline length to the vapor-condensate interfacial area is a maximum.

Apparent bidimensional critical temperature as a graphite surface homogeneity criterion

Nitrogen adsorption isotherms at 77.7 K, over graphites with different surface homogeneity, are analyzed. Three of the samples exhibited the transition from a fluid to a bidimensional solid before the monolayer was completed. The apparent bidimensional critical temperature, deduced from the Hillde Boer equation (applied to experimental isotherms), is proposed as a criterion for surface homogeneity. The calculated values range from 61 K for the most homogeneous surface to 36 K for the less homogeneous one. The estimated degrees of homogeneity are in agreement with previous experimental evidence and the surface characteristics of these samples.

Calculation of adsorption equilibria for the binary gaseous mixtures on a heterogeneous surface

The prediction method for the adsorption equilibria of binary gaseous mixtures on a heterogeneous surface using only experimental isotherms of pure components is presented. The experimental isotherms were analysed by Ross and Olivier's model isotherms. The heterogeneous surface of the adsorbent was considered as the ensemble of the 1000 homogeneous patches of the different adsorption energies which distribute in a Gaussian form. The equilibrium coefficient was obtained for each patch and for each component. These coefficients for component 1 were numbered consecutively from 1 to 1000 in the order of the adsorption energy, and each coefficient was combined to the coefficient of the corresponding number of component 2, one by one. The adsorption equilibrium was calculated by Hill-de Boer equation for mixtures for 1000 combinations of the equilibrium coefficient of components 1 and 2. The amount adsorbed of each component could be obtained as the average value over the 1000 combinations. The results agreed with the experimental data for the mixtures of ethylene and ethane, and ethylene and propylene on a carbon molecular sieve at 30°C (20, 50 and 100 mmHg) and at 30°C (20 and 50 mmHg), respectively.

The double layer properties of electrolytes with large cations: tetraalkylammonium perchlorates in CH 3CN at a Hg electrode

An analytical extension of the unequal size GCS model (URGCS) is presented considering different dielectric constants in the Stern layers and adsorption. Within this model ionic adsorption is treated by Langmuir or Hill-De Boer isotherms. The distance of the adsorption plane from the surface can be varied. A comparison of the calculated differential capacity and concentration dependence of the potential of zero charge with the measurements is given. Characteristic features due to different sizes and to adsorption are discussed.