Heterogeneity of the Glass Fiber Surface from Inverse Gas Chromatography

Physicochemical aspects of mucosa surface

An insight into adsorption thermodynamics of molecular probes onto the mucin surface of porcine intestinal is given by the aid of IGC based on chromatographic retention time.

Time-resolved chromatographic analysis and mechanisms in adsorption and catalysis

The main object of this review is the study of fundamentals of adsorption and heterogeneous catalysis, a benefit for the understanding of adsorptive and catalytic properties. This work aims to define and record, with the utmost accuracy, the phenomena and the possible reactions. A new methodology for the study of the adsorption is presented, which is a version of the well-known inverse gas chromatography. This reversed-flow inverse gas chromatography (RF-IGC) is technically very simple, and it is combined with a mathematical analysis that gives the possibility for the estimation of various physicochemical parameters related to adsorbent or catalyst characterization, under conditions compatible with the operation of real adsorbents and catalysts. On this base, this methodology has been successfully applied to the study of the impact of air pollutants, volatile organic and/or inorganic, on many solids such as marbles, ceramics, oxide-pigments of works of art, building materials, authentic statues of the Greek Archaeological Museums. Moreover, this methodology proved to be a powerful tool for studying the topography of active sites of heterogeneous surfaces in the nano-scale domain. Thus, some very important local quantities for the surface chemistry have been determined experimentally for many solids including thin films. These physicochemical local quantities (among which adsorption energy and entropy, surface diffusion coefficient, probability density function) have been determined from the experimental pairs of height of extra chromatographic peaks and time by a nonlinear least-squares method, through personal computer programs written in GW BASIC and lately in FORTRAN. Through the time-resolved analysis the surface characterization of the examined materials took place. In addition, the kinetic constants responsible for adsorption/desorption and surface chemical reactions have also been calculated. Thus, important answers have been provided to the following essential questions: (1) Can RF-IGC define the gnostic regions of adsorption/desorption, surface diffusion, surface reaction? Yes, irrefutably and undeniably. (2) Can RF-IGC deal with issues of catalysis, the existence of more than one reaction? Certainly yes. Indeed, it is impressive to observe the reactions "on line". (3) Can RF-IGC identify peaks of products and reactants simultaneously? Certainly yes. (4) Can RF-IGC be applied to thin films in a nano-scale domain? The answer is "definitely yes". (5) Can it kinetically follow the above? Yes, again.

Determination of adsorption entropies on solid surfaces by reversed-flow gas chromatography

The reversed-flow gas chromatography (RF-GC) method has been applied to measure the time separation of adsorption entropies and their probability density functions, when acetic and formic acid vapors, responsible for artifacts degradation inside museums, are adsorbed on various heterogeneous surfaces. The solid materials studied were Penteli marble and solid metals (lead, copper and iron), which are commonly used for the construction of the artifacts. Physicochemical measurements were performed at various temperatures in the range 353-473 K, the surface coverage theta being also calculated over time. A new mathematical model, based on well known equations was used in order to extract the above quantities.

Time distribution of adsorption entropy of gases on heterogeneous surfaces by reversed-flow gas chromatography

The reversed-flow gas chromatography (RF-GC) technique has been applied to measure the adsorption entropy over time, when gaseous pentane is adsorbed on the surface of two solids (gamma-alumina and a silica supported rhodium catalyst) at 393.15 and 413.15K, respectively. Utilizing experimental chromatographic data, this novel methodology also permits the simultaneous measurement of the local adsorption energy, epsilon, local equilibrium adsorbed concentration, c(s)(*), and local adsorption isotherm, theta(p, T, epsilon) in a time resolved way. In contrast with other inverse gas chromatographic methods, which determine the standard entropy at zero surface coverage, the present method operates over a wide range of surface coverage taking into account not only the adsorbate-adsorbent interaction, but also the adsorbate-adsorbate interaction. One of the most interesting observations of the present work is the fact that the interaction of n-pentane is spontaneous on the Rh/SiO(2) catalyst for a very short time interval compared to that on gamma-Al(2)O(3). This can explain the different kinetic behavior of each particular gas-solid system, and it can be attributed to the fact that large amounts of n-C(5)H(12) are present on the active sites of the Rh/SiO(2) catalyst compared to those on gamma-Al(2)O(3), as the local equilibrium adsorbed concentration values, c(s)(*), indicate.

Cosorption effect in gas chromatography: flow fluctuations caused by adsorbing carrier gases

Adsorbing carrier gases have a number of advantages in analytical and preparative gas chromatography, such as clearer detector signals and higher column efficiencies. This work shows that adsorbing carrier gases also may be useful because they cause the mobile phase flow rate to become unsteady after injecting a small amount of sample. This work shows that a 100 microL sample of helium can liberate enough carbon dioxide carrier gas from a zeolite 5A packed column at 373 K, that the departure from the steady-state flow rate had an upper lobe area of 586 microL of carrier gas. This was confirmed by coupling a modified Langmuir kinetic model with the Ergun equation.

Determination of isotherms by gas–solid chromatography

This literature review of the fundamental developments in gas-solid adsorption isotherms includes articles published from 1933 until now. Analytical and numerical methods used for calculating the adsorption energy distribution function, as a quantitative measure of surface heterogeneity, are included. Special attention is paid to inverse gas chromatography (IGC) and more precisely to a new version of IGC known as reversed-flow gas chromatography (RF-IGC or RF-GC). RF-GC is presented as a quick, precise and effective method to investigate physicochemical properties of different kinds of adsorbents, through adsorption isotherms and related energetic parameter determinations. Advantages of the RF-GC method over traditional chromatographic methods are discussed.

Introduction into the characterisation of porous materials by inverse gas chromatography

Modern methods for the characterisation of porous materials are probably as numerous and divers as applications of porous solids. In recent years interest has grown in a deeper understanding of surface phenomena beyond the usual description of surface area and adsorption isotherm. This has lead to an introduction of more sophisticated approaches, which allow for a study of thermodynamic and kinetic information. One technique, which has been shown to be very valuable is inverse gas chromatography (IGC). Due to its increasing application in industry it is the intention of this short review to introduce the principals as well as the more common applications of IGC. The methods and parameters to be discussed include isotherm determination, the measurement of surface and free energy as well as the calculation of acid-base parameters. Further, the determination of the surface heterogeneity and heat of sorption is shown. The measurement and calculation of diffusion parameters is also briefly described. It is also the intention of this paper to discuss experimental aspects and common misconceptions.

Surface heterogeneity and surface area from linear inverse gas chromatography. Application to glass fibers

A new method of measuring surface heterogeneity of non-porous adsorbents by inverse gas chromatography (IGC) is developed. In contrast with the methods described in the literature which are based on nonlinear chromatography (thermodynamics of adsorption) this method is based on linear chromatography (kinetics of adsorption). The mass balance equation of linear chromatography with axial diffusion term and the Langmuir kinetic equation on an open (non-porous) heterogeneous surface are solved by the method of Laplace transforms. The expressions for four semi-invariants of an elution profile are obtained. These are linear combinations of the moments of the distribution of sites in residence time of adsorbed molecule with coefficients determined from elution profile of non-adsorbing gas. Four semi-invariants of elution profiles of benzene and methane on a column packed with E-glass fiber were determined experimentally at temperatures around 100 degrees C. The mean, the standard deviation of the normal distribution in adsorption energy as well as the sticking coefficient and pre-exponential factor of the Frenkel equation are determined for benzene on E-glass. A method of the specific surface determination from linear IGC is proposed.