Adsorption Theories: Langmuir V yb v Adsorbate Va volume of gas adsorbed at pressure P: Assumptions homogeneous surface (all adsorption tically identical) Adsorbent monolayer adsorption(no multilayer adsorption) no interaction between adsorbed \ Nao Adsorption Theories: BET Va= volume of gas adsorbed at pressure P, V volum P Modification of Langmuir Adsorbat isotherm Both monolayer and multilayer adsorption . Adsorbent14 http://nano.materials.drexel.edu Adsorption Theories: Langmuir Adsorption Theories: Langmuir Adsorbate Adsorbent Assumptions: ¾ homogeneous surface (all adsorption sites energetically identical) ¾ monolayer adsorption (no multilayer adsorption) ¾ no interaction between adsorbed molecules pressure of adsorbate. empirical constant; and volume of gas required to form monolayer; volume of gas adsorbed at pressure ; where 1 = = = = = + P b V V P V P V V b P m a a m m http://nano.materials.drexel.edu Adsorption Theories: BET Adsorption Theories: BET relative pressure of adsorbate. C BET constant (related to energy of adsorption of 1st layer); and volume of gas required to form monolayer; volume of gas adsorbed at pressure ; where 1 ( 1) ( ) = = = = ⎟ ⎠ ⎞ ⎜ ⎝ − ⎛ = + − o m a o m m o a P P V V P P P V C C V P P V C P ¾ Modification of Langmuir isotherm ¾ Both monolayer and multilayer adsorption Adsorbate Adsorbent