Gas Sorption Analysis (GSA) Oleh: Gani Purwiandono

Introduction  When a gas or vapour phase is brought into contact with a solid, part of it is taken up and remains on the outside attached to the surface.  In physisorption (physical adsorption), there is a weak Van der Waals attraction between the adsorbate and the solid surface.  Useful tool to characterize porous materials allowing for the determination of specific surface area, pore size distribution and porosity.

Brunauer, Emmett and Teller (BET), most common method used to describe specific surface area: the BET equation : W= weight of gas adsorbed P/P 0 =relative pressure Wm = weight of adsorbate as monolayer C = BET constant BET equation requires a linear plot of 1/[W(P/P 0 )-1] against P/P 0 Slope (s) Intercept (i) Wm (weight of monolayer)

Total Surface area (S t ) can then be derived N = Avagadro’s number (6.023x10 23 ) M = Molecular weight of Adsorbate A cs = Adsorbate cross sectional area (16.2Å 2 for Nitrogen) Specific Surface Area (S) is defined as the ratio between the total surface area of a solid and its mass (sample weight). Unit (m 2 /g) Isotherm types described by Brunauer, Deming and Teller

Kurva Distribusi Ukuran Pori BJH

X Ray Flourescense (XRF)

X-ray fluorescence (XRF) analysis is a powerful analytical tool for the spectrochemical determination of almost all the elements present in a sample. XRF radiation is induced when photons of sufficiently high energy, emitted from an X-ray source, impinge on a material. These primary X-rays undergo interaction processes with the analyte atoms. High-energy photons induce ionization of inner shell electrons by the photoelectric effect and thus electron vacancies in inner shells (K, L, M, ) are created. The prompt transition of outer shell electrons into these vacancies within some 100 fs can cause the emission of characteristic fluorescence radiation.

Energy-dispersive XRF

Wavelength-dispersive XRF

J. Anal. Chem. 2014, 86, 10892−10899 J. Anal. Chem. 2014, 86, 8253−8260

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