Objective
Surface topography predetermines the surface properties of adsorbents both under natural conditions (retention and exchange of nutriment and of pollutants in soils and ground water) and in applied technology (catalysis, adsorption, chromatography, membranes, polyphased materials, cosmetics, medicines).
However, up to now the potential relief remains the most hidden property of surfaces. As result of superposition of pair potentials of superficial atoms with a probe molecule (e.g. that of argon or nitrogen) Van der Waals relief, which expresses a potential at a level of optimal distance between the molecule and the surface, presents a "mountainous" function with a multitude of valleys ("traps") in neighbourhood of which localisation of adsorbed molecules takes place. A statistical distribution of the potential minima with respect to their depths (an energy distribution) is reflected in all thermodynamic functions of adsorbed films. Thus, by solving some inverse problems one can find the energy distributions in which resolved peaks can be referred to certain spatial combinations of superficial atoms. During eight decades, this problem has attracted significant creative forces in different countries of the world. However, till now it remains one of the unsolved fundamental problems of physical chemistry of the twentieth century.
The project aims to bring together a variety of complementary techniques targeted on its solution:
i) High-resolution adsorption techniques for measurement of argon and nitrogen adsorption isotherms and differential heats at low temperature (78 K) (France);
ii) controlled-rate thermal desorption (CRTD) of water at constant pressure (France);
iii) precise calorimetry of gases' and vapours' adsorption at room temperature (Uzbekistan, Ukraine);
iv) adsorption chromatography (Ukraine);
v) spectroscopic techniques such as FTIR, Raman, EXAFS (France);
vi) Monte Carlo simulation (United Kingdom);
vii) semi-analytic statistical models of adsorption (Russia);
viii) stable algorithms for solution of inverse problems (Kazakhstan, France).
Synthetic and natural oxides such as rutile, silica, alumina and phyllosilicates will be used as model adsorbents.
The analytical models of adsorption (Russia, Kazakhstan) will be tested and modified by comparison with results of Monte Carlo calculations (United Kingdom). These rapid methods will then be applied to solve the inverse problems on low-temperature adsorption isotherms and heats of argon and nitrogen adsorption (France, Kazakhstan, Russia). The determined surface topographical fragments under study will be chemically identified by CRTD and adsorption calorimetry of water at room temperature (Uzbekistan, Ukraine) and by spectroscopic methods (France). Status of adsorbed water molecules will be derived from independent CRTD and differential calorimetry measurements (France, Kazakhstan, Russia, Uzbekistan, Ukraine). Information about water adsorption will also be used to interpret argon and nitrogen adsorption results on hydroxylated surfaces.
The final result of the project will be elaboration of a new tool for evaluation of topography and energetic heterogeneity of solid surfaces. It will result in a global experimental/thermodynamic strategy to analyse, compare and understand the surface properties of heterogeneous adsorbents.
Topic(s)
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54 501 Vandoeuvre-les-Nancy
France