School for PhD June 8-12, 2015 Luigi PASQUA Science and Technologies at UNICAL Luigi PASQUA DEPARTMENT of ENVIRONMENTAL and CHEMICAL ENGINEERING

Nitrogen Gas Adsorption Gas adsorption on a surface is a phenomenon based on weak interactions, such as London or Van der Waals forces, in which gas molecules condense on the surface of a solid. It is possible to have evidence of adsorption if a solid (free of adsorbed molecules) is placed in a closed volume at atmospheric pressure.

The pressure decreases until equilibrium is reached, and this pressure is lower than atmospheric pressure because some of the gas molecules have been adsorbed from the surface of the solid. The amount of adsorbed gas can be determined, if the volumes of the recipient and the solid are known, by the fall in pressure (according to the gas law) or by gravimetric estimation of the weight increase per unit mass of solid.

Adsorption can generally be described in terms of n, the amount of gas adsorbed (in moles per gram of solid) as a function of pressure, p, of the vapour, the temperature, T, and the kind of adsorptive. The material in the adsorbed state is called the adsorbate, while that present in one or other (or both) of the bulk phases and capable of being adsorbed may be distinguished as the adsorptive.

In some cases of chemisorptions, adsorptive and adsorbate may be chemically different species (e.g., in dissociative adsorption). When adsorption occurs (or may occur) at the interface between a fluid phase and a solid, the solid is usually called the adsorbent; for gas-liquid interfaces it may be in some case, but not in all, useful to call the liquid phase the adsorbent.

Thus: nadsorbate= f (T, p, adsorbate, solid) (1) For a particular solid, for a given gas at a fixed temperature, adsorption is a function of pressure: n = f (p)T, adsorbate, {solid) (2) Alternatively, if the temperature is below the critical temperature of the gas, the equation becomes: n = f (p/p0) T, adsorbate, solid (3) wherep/p0 is the relative pressure and p0 is the saturation vapour pressure of the adsorptive.

Equations 2 and 3 represent the adsorption isotherms, and thus are expressions of the amount of adsorbed gas on a solid at a given temperature as a function of pressure or relative pressure. Most isotherms that result from physical adsorption will fall into one of five classes in the original classification system as proposed by Brunauer, Deming, Deming and Teller (BDDT). These are presented in the following Figure

Representation of the five different type of adsorption isotherms I to V in the classification proposed by Brunauer, Deming, Deming and Teller.

Kelvin equation

Post synthetic grafting

-Si-OH + HO-Si- Si-O-Si Surface properties of calcined and surfactant-extracted mesoporous materials -Si-OH + HO-Si- Si-O-Si

by Luigi Pasqua 'Update on Silica-based Mesoporous Materials for Biomedical Applications' discusses the details of synthesis and modification strategies by reviewing the open literature. The discussion concerning the potential of mesoporous silica in modern biomedical applications will be related to a critical analysis in the field of material science.