GAS PHYSISORPTION: THE BASIC TOOL
TO CHARACTERIZE ADSORBENTS
Jean Rouquerol, Sandrine Bourelly, Françoise Rouquerol,
Philip Llewellyn and Renaud Denoyel
LCP, CNRS-Université de Provence, site MADIREL, Centre de St Jérôme,
13397 Marseille Cedex, FRANCE E-mail: jean.rouquerol@univ-provence.fr
We shall focus here our attention on the use of physisorption at the gas/solid interface and see what kind of information can be drawn from the three basic approaches listed hereafter.
1/ Information provided by the adsorption-desorption isotherm. As adsorption proceeds, the successive parts of the adsorption isotherm provide information about:
a) The heterogeneity and/or the microporosity of the adsorbing surface: t-plot, α- plot, HK method, (DFT)
b) The surface area, from the content of a statistical monolayer: BET equation
c) The mesopores: BJH method, (DFT) |
2/ Information provided by the use of various probes, i.e. different adsorbable species. Two major parameters of the adsorbable molecule can indeed be selected and controlled:
a) Its electrical properties (polar, dipolar, quadrupolar), which will make it interact differently with the solid surface. This is quite helpful to distinguish between surface heterogeneities and micropores
b) Its geometrical properties: its size (more or less bulky) and shape (linear, flat, spherical etc…). This allows for instance to distinguish between slit-shaped and cylindrical micropores. |
3/ Information provided by the curves of differential enthalpy of adsorption, which are basically needed to follow and understand the adsorption mechanism. As the adsorption proceeds, they provide information about:
a) The presence of heterogeneities and/or micropores.
b) The energetical homogeneity of the surface, which provides a clear “signature” in the shape of the calorimetric curve
c) The phase changes, taking place in the adsorbed layer |
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