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The Langmuir adsorption model deviates significantly in many cases, primarily because it fails to account for the surface roughness of the adsorbent. Rough inhomogeneous surfaces have multiple site types available for adsorption, with some parameters varying from site to site, such as the heat of adsorption.
The langmuir (symbol: L) is a unit of exposure (or dosage) to a surface (e.g. of a crystal) and is used in ultra-high vacuum (UHV) surface physics to study the adsorption of gases. It is a practical unit, and is not dimensionally homogeneous, and so is used only in this field. It is named after American physicist Irving Langmuir.
The Hertz–Knudsen equation describes the non-dissociative adsorption of a gas molecule on a surface by expressing the variation of the number of molecules impacting on the surfaces per unit of time as a function of the pressure of the gas and other parameters which characterise both the gas phase molecule and the surface: [1] [2]
The Langmuir model of adsorption [2] assumes . The maximum coverage is one adsorbate molecule per substrate site. Independent and equivalent adsorption sites. This model is the simplest useful approximation that still retains the dependence of the adsorption rate on the coverage, and in the simplest case, precursor states are not considered.
The following reactions follow an Langmuir–Rideal mechanism: [4] C 2 H 4 + 1 / 2 O 2 (adsorbed) → (CH 2 CH 2)O The dissociative adsorption of oxygen is also possible, which leads to secondary products carbon dioxide and water. CO 2 + H 2 (ads.) → H 2 O + CO; 2 NH 3 + 1 + 1 / 2 O 2 (ads.) → N 2 + 3H 2 O on a platinum catalyst
While the Langmuir model assumes that the energy of adsorption remains constant with surface occupancy, the Freundlich equation is derived with the assumption that the heat of adsorption continually decrease as the binding sites are occupied. [16] The choice of the model based on best fitting of the data is a common misconception. [15]
3.3 Chemical phosphorus removal and carbon ... treatment demonstrated the model's incorporation of the Langmuir isotherm to simulate powdered activated carbon ...
Molecular model. Ball-and-stick model; ... Phosphorus Allotropes of phosphorus; ... Langmuir adsorption model; Freundlich equation;