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Adsorption Theory (Langmuir Isotherm)

🔬 Natural Sciences By CampusDown Wiki Editorial Team Last updated
Quick answer: adsorption is the accumulation of gas or dissolved substances on a solid surface. Langmuir's theory assumes a single layer of identical sites and relates surface coverage to pressure or concentration as θ = KP/(1+KP).
Contents
  1. 1. Types of adsorption
  2. 2. The Langmuir isotherm
  3. 3. Other isotherms
  4. 4. Applications
  5. 5. References

Types of adsorption

  • Physisorption: weak van der Waals attraction, low heat of adsorption (roughly 20-40 kJ/mol), multilayers possible, reversible.
  • Chemisorption: chemical bonds with the surface, high heat, monolayer, selective. Catalysis in the Haber-Bosch process is a classic case.

Adsorption is accumulation on a surface, distinct from absorption into the bulk.

The Langmuir isotherm

Irving Langmuir (1918) assumed (1) a fixed number of energetically identical sites, (2) one molecule per site forming a monolayer, and (3) no interaction between adsorbed molecules. Setting adsorption and desorption rates equal gives coverage θ = KP/(1+KP): proportional to pressure at low pressure, approaching saturation (1) at high pressure. In solution, q = qmaxKC/(1+KC); plotting C/q against C gives a straight line from which the maximum capacity is found.

Other isotherms

  • Freundlich: q = K C1/n, an empirical fit for heterogeneous surfaces
  • BET (1938): multilayer physisorption, used to measure surface area by nitrogen adsorption

Applications

Activated carbon water treatment, zeolite gas separation, heterogeneous catalysis and heavy-metal removal by materials such as chitosan (alongside chelation) are analyzed by fitting data to Langmuir and Freundlich equations.

References

  1. Langmuir, I. (1918). The adsorption of gases on plane surfaces of glass, mica and platinum. Journal of the American Chemical Society, 40(9), 1361-1403.
  2. Brunauer, S., Emmett, P. H., & Teller, E. (1938). Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 60(2), 309-319.
  3. Freundlich, H. (1906). Über die Adsorption in Lösungen. Zeitschrift für Physikalische Chemie, 57, 385-470.
  4. Atkins, P., & de Paula, J. (2014). Physical Chemistry (10th ed.). Oxford University Press.

Reports and materials that use this theory (Korean)

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ChelationChelation explained: one ligand binding a metal ion at several sites like a claw to form a ring-shaped complex. Coordinate bonds and ligands, EDTA, the entropy-driven chelate effect, heme and chlorophyll, heavy-metal detoxification and water treatment.🔬 Natural SciencesHaber-Bosch ProcessThe Haber-Bosch process explained: the industrial synthesis of ammonia from nitrogen and hydrogen. Equation and heat of reaction, temperature, pressure and iron catalyst, the Le Chatelier compromise, its role in fertilizer and population growth, and environmental costs.🔬 Natural SciencesDeacetylationDeacetylation explained: removal of an acetyl group (CH₃CO−) from a molecule. Converting chitin to chitosan with concentrated alkali, degree of deacetylation and its effects, and histone deacetylases (HDACs) in gene regulation.🔬 Natural SciencesAluminum Passivation (Oxide Layer)Aluminum passivation explained: the thin, dense aluminum oxide (Al₂O₃) film on aluminum surfaces. Why a reactive metal resists corrosion, passivation in concentrated nitric acid, anodizing, and breakdown by chloride ions, gallium and mercury.🔬 Natural Sciences

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This article was last updated on October 15, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.