Samples are commonly prepared by heating them under vacuum or under a gas stream to remove impurities. The samples are then analyzed by measuring the volume of adsorbed gas, for example nitrogen, at specific pressures and at low temperatures, for example at 77K in liquid nitrogen.
The surface area is a measure of the exposed surface of a solid sample on a molecular scale. The BET theory is the most used model to determine the area but the results can also be obtained according to the Langmuir model.
To measure pore size by gas adsorption, isotherms are recorded in the range from low pressures to saturation pressure. The pressure range is determined by the pore size range to be measured: microporous materials are measured by isotherms in the pressure range 0.00001-0.1 torr, while mesoporous materials typically in a pressure range 1 – 760 torr.
The methods available for measuring micropore distribution include: Density Functional Theory (DFT), MP-Method, Dubinin Plots (Dubinin-Radushkevich D-R, Dubinin-Astakov D-A) and Horvath-Kawazoe (H-K). Methods available for Mesopores include: Barrett method, Joyner and Halenda (BJH) and Density Functional Theory (DFT).