Adsorption energy and pore-size distributions of activated carbons calculated using Hill's model

An integral equation derived using a statistical physics treatment by considering the adsorption energy distribution (AED) was used to model the adsorption of ethylene and ethane on resorcinol-formaldehyde-based activated carbon xerogels. Hill's model was taken as a local adsorption isotherm. This model was based on a grand canonical ensemble. Then a relationship between the energetic and the structural heterogeneities is used to determine the pore-size distribution (PSD) function. The AED and PSD obtained illustrate the greater affinity of activated carbon for adsorption of ethylene compared to ethane. In addition, this method was applied to determine the PSD of the British Drug House (BDH) activated carbon. The behaviour of the obtained PSDs at different temperatures was examined and related to the adsorption capacity of BDH activated carbon towards ethane, methane and nitrogen.Scopus2-s2.0-8492834888

Modeling and Thermodynamic Study of Water Vapor Desorption Isotherms of Orange Peel and Leaves using Statistical Physics Treatment

The shelf life and safety of food products is related to the water content, in particular to the water activity (aw). This is important to predict the physical, chemical and biological processes that take place during food storage. Analytical expression for modeling water desorption isotherms of food is developed using the grand canonical ensemble in statistical physics. The model is further applied to fit and interpret the desorption isotherms of water vapor on the orange peel and leaves at three different temperatures. In the developed model we introduce essentially six parameters such as the number of adsorbed water molecules per site, the number of adsorbed layers, the energy of desorption and receptor sites density. We interpret the results of fitting then we apply the model to calculate thermodynamic functions which govern the desorption mechanism such as internal energy and entropy

Contribution à l'étude de la gustation des molécules sucrées à travers un processus d'adsorption. Modélisation par la physique statistique

L'adsorption des molécules sucrées sur les sites récepteurs du goût est une étape déterminante dans le mécanisme de la perception de la saveur sucrée. Naturellement, l adsorption se situe à la périphérie dans ce mécanisme. Nous avons réalisé des courbes de réponse psychophysique à l'aide d'un dispositif approprié nommé SMURF pour quatre molécules sucrées: le saccharose, le fructose, le glucose et le maltitol. Par l'intermédiaire de l'ensemble grand canonique un traitement de physique statistique a été utilisé pour le développement des expressions analytiques de la réponse gustative en terme d'adsorption. La modélisation nous a permis d'adopter le modèle double couche pour l'interprétation du phénomène d'adsorption. Les valeurs du nombre de molécules par site trouvées nous ont permis de déterminer le type d'ancrage pour chaque molécule selon la géométrie: un ancrage parallèle et un ancrage perpendiculaire. Nous avons trouvé une corrélation entre le pouvoir sucrant d'une part et l'énergie d'adsorption, la réponse maximale, la solubilité et le taux d'occupation à la concentration seuil d'autre part. En parallèle nous avons réalisé des isothermes d'adsorption du saccharose à l'aide d'une microbalance à quartz (QCM) sur trois couches minces de porphyrine, de calixarène et d'or. La modélisation de ces isothermes par le modèle de BET modifié nous a permis de caractériser l'adsorption à l'aide des paramètres physicochimiques du modèle. Nous avons montré que les nombres de molécules par site et les énergies d'adsorption sont proches de celles de la gustation. Le saccharose présente donc le même comportement sur ces supports que dans le mécanisme de perception du goûtAdsorption of sweet molecules on gustatory receptor sites is a determining step in the mechanism of taste chemoreception. Obviously adsorption is a peripheral event. A SMURF device (Sensory Measuring Unit for Recording Flux) is used to obtain experimental psychophysical curves relative to four sweeteners: sucrose, fructose, glucose and maltitol. Through the grand canonical ensemble a treatment of statistical physics is used to develop analytic expressions of the gustatory response in terms of adsorption. The modeling allowed selecting of the double layer model which is used to interpret the adsorption phenomenon. The variation of the number of adsorbed molecules per site permitted proposing of two types of anchorage of a sweet molecule to the adsorbent surface: the first consists in a parallel anchorage and the second is a perpendicular anchorage. We found out a relationship between sweetness potency of molecules and the physical parameters of the model. Hence, a correlation was found between sweetness potency on the one hand and the maximum response, the solubility, and the occupation rate at threshold concentration on the other. In parallel we carried out using a Quartz Crystal Microbalance (QCM) adsorption isotherms of sucrose on three thin layers of porphyrin, calixarene and gold. The modeling of the isotherms by the modified BET model allowed characterization of the adsorption using physicochemical parameters of the model. We showed that the number of molecules per site and the adsorption energies are similar to those of taste. So the sucrose presents the same behavior on these supports as in taste chemoreceptionREIMS-BU Sciences (514542101) / SudocSudocFranceF

Physicochemical and thermodynamic investigation of hydrogen absorption and desorption in LaNi3.8Al1.0Mn0.2 using the statistical physics modeling

In the present work, experimental absorption and desorption isotherms of hydrogen in LaNi3.8Al1.0Mn0.2 metal at two temperatures (T = 433 K, 453 K) have been fitted using a monolayer model with two energies treated by statistical physics formalism by means of the grand canonical ensemble. Six parameters of the model are adjusted, namely the numbers of hydrogen atoms per site nα and nβ, the receptor site densities Nmα and Nmβ, and the energetic parameters Pα and Pβ. The behaviors of these parameters are discussed in relationship with temperature of absorption/desorption process. Then, a dynamic investigation of the simultaneous evolution with pressure of the two α and β phases in the absorption and desorption phenomena using the adjustment parameters. Thanks to the energetic parameters, we calculated the sorption energies which are typically ranged between 276.107 and 310.711 kJ/mol for absorption process and between 277.01 and 310.9 kJ/mol for desorption process comparable to usual chemical bond energies. The calculated thermodynamic parameters such as entropy, Gibbs free energy and internal energy from experimental data showed that the absorption/desorption of hydrogen in LaNi3.8Al1.0Mn0.2 alloy was feasible, spontaneous and exothermic in nature. Keywords: Absorption-desorption isotherms, Statistical physics model, Metal hydride, Thermodynamic potential function

Investigation of Adsorption Process of Hydrogen on Fe-Ti: Theoretical Simulation and Interpretation of Isotherms with Statistical Physics Treatment

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Study of the effect of variation in temperature and pH on the adsorption process of natural Gardenia yellow dye into TiO2 mesoporous for dye sensitized solar cells using the statistical physics formalism: Physicochemical and thermodynamic investigation

International audienceIn this paper, three adsorption isotherms of natural yellow Gardenia dye, at three different temperatures and at three pH values, were fitted by models established through statistical physics treatment. A double-layer model with two energies is able to give good fitting of these experimental data. Four physicochemical parameters are involved in the fitting of the experimental adsorption isotherms such as the number of adsorbed dye molecules per site n, the density of receptor sites Nm and the two energetic parameters C1 and C2. From the numerical simulation, the number of molecules per site showed that the adsorbate molecules have two anchorage positions parallel and nonparallel respectively when pH and temperature vary. The variation of the adsorbed quantity at saturation with temperature shows the exothermic nature of aggregation process of the natural Gardenia yellow dye. In the case of variation of pH, the acidic conditions are more favorable for the adsorption process. The numerical values of the calculated adsorption energies have revealed that the Gardenia yellow dye is physisorbed onto TiO2 mesoporous. A new method based on Kelvin equation in liquid phase has been developed to determine the pore size distribution (PSD) of TiO2 mesoporous in comparison with other experimental measurements. The result of PSD shows a significant effect of the variation with temperature and with pH values on the morphology of pore size structure. Finally, the calculated thermodynamic functions such as entropy, free enthalpy and internal energy exhibited that the system evolved spontaneously

Modeling of adsorption isotherms of dye N719 on titanium oxide using the grand canonical ensemble in statistical physics for dye sensitized solar cells

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Energetic investigation of the adsorption process of CH4, C 2H6 and N2 on activated carbon: Numerical and statistical physics treatment

The adsorption energy distribution (AED) function of a commercial activated carbon (BDH-activated carbon) was investigated. For this purpose, the integral equation is derived by using a purely analytical statistical physics treatment. The description of the heterogeneity of the adsorbent is significantly clarified by defining the parameter N?m(E). This parameter represents the energetic density of the spatial density of the effectively occupied sites. To solve the integral equation, a numerical method was used based on an adequate algorithm. The Langmuir model was adopted as a local adsorption isotherm. This model is developed by using the grand canonical ensemble, which allows defining the physico-chemical parameters involved in the adsorption process. The AED function is estimated by a normal Gaussian function. This method is applied to the adsorption isotherms of nitrogen, methane and ethane at different temperatures. The development of the AED using a statistical physics treatment provides an explanation of the gas molecules behaviour during the adsorption process and gives new physical interpretations at microscopic levels.Scopus2-s2.0-8488711346