Does chemisorption or physisorption depend on isotherm models? please add references too.
thanks in advance
Dear friend Ayushi Mishra
Hey there! Now, let's dive into the realm of adsorption and isotherm models. I am ready to unravel the mysteries for you.
Isotherm models are mathematical representations that describe the relationship between the amount of adsorbate (gas or solute) adsorbed on the surface of a solid adsorbent at a particular temperature and pressure. They are fundamental tools in understanding adsorption processes.
Now, how do isotherm models give insights into chemisorption or physisorption?
1. **Langmuir Isotherm Model:**
- **Chemisorption:** It assumes a monolayer adsorption where molecules are held by chemical bonds. If the experimental data fits the Langmuir model, it suggests chemisorption.
- **Physisorption:** Deviations from the Langmuir model may indicate multilayer adsorption or interactions inconsistent with chemical bonding, suggesting physisorption.
2. **Freundlich Isotherm Model:**
- **Chemisorption:** The Freundlich model suggests a heterogeneous surface with varied adsorption energies. Deviations from this model may indicate a more uniform adsorption energy distribution, characteristic of chemisorption.
- **Physisorption:** A fit to the Freundlich model indicates a heterogeneous surface with varying adsorption energies, typical of physisorption.
3. **BET Isotherm Model:**
- **Chemisorption:** The BET model is often applied to monolayer adsorption on a homogeneous surface. Deviations might suggest chemisorption.
- **Physisorption:** Good fits to the BET model typically indicate multilayer adsorption, common in physisorption.
It's crucial to note that isotherm models provide insights into the mechanism of adsorption, but they are not definitive proof. Real-world systems can exhibit deviations due to complexities.
References:
- Brunauer, S., Emmett, P. H., & Teller, E. (1938). Adsorption of Gases in Multimolecular Layers. Journal of the American Chemical Society, 60(2), 309–319.
- Freundlich, H. (1906). Über die Adsorption in Lösungen. Zeitschrift für Physikalische Chemie, 57, 385–470.
- 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.
Remember, I am here to illuminate, but always cross-check with the latest research for the most accurate information!
Kaushik Shandilya
Thank you so much, sir
you have poured all the knowledge of adsorption isotherms and mechanisms.
Just an addition.....
Aside the the three models mentioned before ( Langmuir, Freundlich and BET), there are other models that have been applied in adsorption systems, such as the Redlich–Peterson (R–P) (1959) model, the Sips model (Sips, 1948), the Temkin model (Temkin and Pyzhev, 1940) e.t.c, and are all used to provide more understanding about adsorption mechanism. The isotherm data of the adsorption isotherm which depends on the adsorbed species, adsorbate, adsorbent, and various physical properties of the solution including pH, ionic strength, and temperature (Yan et al., 2017) are fitted into various above mentioned models in order to examine the adsorption behaviour of the materials used (adsorbate and adsorbent).
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