Langmuir isotherm is good enough when the adsorbate surface can be saturated (doesnt matter if by a gas or liquid) with a monolayer (and no more!). If you are dealing with multilayer adsorption, then Langmuir is not good.
Langmuir isotherm is good enough when the adsorbate surface can be saturated (doesnt matter if by a gas or liquid) with a monolayer (and no more!). If you are dealing with multilayer adsorption, then Langmuir is not good.
Langmuir isotherm is the classic isotherm of a reaction leading to formation of a 1:1 stoichiometry complex, e.g., between a sorption site and a molecule or ion. If you will consider just formation of complexes in solutions, e.g., H-bonding, charge transfer and any other 1:1 complex (with a stoichiometry of 1:1), you will end up with the model relating the bound and free concentrations which is absolutely identical to adsorption Langmuir isotherm wherenever you wish to use it. This 1:1 complex formation approach is very effective for very many liquid and liquid-solid systems. It will make problems when stoichiometry differs from 1:1 (like, as mentioned, in multilayer adsorption), or when there are lateral or even cooperative interactions. To see clearly the links, there may be no a formal difference between binding of a molecule to one site at macromolecule (biopolymer like proteins, or DNA) dissolved in a liquid or a site interaction between this molecule and clay particle suspended in the same solution. . However, when the Langmuir model is "working", there may be problems in understanding the meaning of parameters. For example, if it is about molecules, the Langmuir affinity cannot be related directly to adsorption heat, as it sometimes done, specifically, in text books and in references to gas phase adsortion. Also, when doing measurements at different temperatures, and the Langmuir maximal capacity becomes temperature-dependent, it is "red light". In a Langmuir model (or a 1;1 stoichiometry complex formation model), the maximal capacity should not depend on temperature. If it happened with the calculated model parameters, then, perhaps, all the model needs to be reformulated. After all, if the temperature effects were examined, the best way is to check whether isosteric heat is loading-dependent, and it will help to decide whether the Langmuir model is physically sounding. Finally, if it is about ion adsorption, one should be especially careful in interpretation of the data. If it is about ion exchange, then, the exchange isotherm is close to the Langmuir model but in the general case it is not the same; but, at some experimental conditions they cannot be distinguished. If it is any "specific" adsorption of an ion, then, the issue of electrostatic contribition, the co-adsorption of counter-ions etc has to be evaluated. This means the Langmuir afffinity may become too empirical,
Langmuir isotherm is the classic isotherm of a reaction leading to formation of a 1:1 stoichiometry complex, e.g., between a sorption site and a molecule or ion. If you will consider just formation of complexes in solutions, e.g., H-bonding, charge transfer and any other 1:1 complex (with a stoichiometry of 1:1), you will end up with the model relating the bound and free concentrations which is absolutely identical to adsorption Langmuir isotherm wherenever you wish to use it. This 1:1 complex formation approach is very effective for very many liquid and liquid-solid systems. It will make problems when stoichiometry differs from 1:1 (like, as mentioned, in multilayer adsorption), or when there are lateral or even cooperative interactions. To see clearly the links, there may be no a formal difference between binding of a molecule to one site at macromolecule (biopolymer like proteins, or DNA) dissolved in a liquid or a site interaction between this molecule and clay particle suspended in the same solution. . However, when the Langmuir model is "working", there may be problems in understanding the meaning of parameters. For example, if it is about molecules, the Langmuir affinity cannot be related directly to adsorption heat, as it sometimes done, specifically, in text books and in references to gas phase adsortion. Also, when doing measurements at different temperatures, and the Langmuir maximal capacity becomes temperature-dependent, it is "red light". In a Langmuir model (or a 1;1 stoichiometry complex formation model), the maximal capacity should not depend on temperature. If it happened with the calculated model parameters, then, perhaps, all the model needs to be reformulated. After all, if the temperature effects were examined, the best way is to check whether isosteric heat is loading-dependent, and it will help to decide whether the Langmuir model is physically sounding. Finally, if it is about ion adsorption, one should be especially careful in interpretation of the data. If it is about ion exchange, then, the exchange isotherm is close to the Langmuir model but in the general case it is not the same; but, at some experimental conditions they cannot be distinguished. If it is any "specific" adsorption of an ion, then, the issue of electrostatic contribition, the co-adsorption of counter-ions etc has to be evaluated. This means the Langmuir afffinity may become too empirical,
Fernando Vallejos-Burgos how to determine whether the adsorption is multilayer or monolayer? Thank you
Fernando Vallejos-Burgos how to determine whether the adsorption is multilayer or monolayer? Thank you
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for better understanding you can refer any physical chemistry books or publications
for better understanding you can refer any physical chemistry books or publications
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Langmuir isotherm is good enough when the adsorbate surface can be saturated (doesnt matter if by a gas or liquid) with a monolayer (and no more!).
If you are dealing with multilayer adsorption, then Langmuir is not good.
Langmuir isotherm is good enough when the adsorbate surface can be saturated (doesnt matter if by a gas or liquid) with a monolayer (and no more!).
If you are dealing with multilayer adsorption, then Langmuir is not good.
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Thanks Fernando
Thanks Fernando
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Langmuir isotherm is the classic isotherm of a reaction leading to formation of a 1:1 stoichiometry complex, e.g., between a sorption site and a molecule or ion. If you will consider just formation of complexes in solutions, e.g., H-bonding, charge transfer and any other 1:1 complex (with a stoichiometry of 1:1), you will end up with the model relating the bound and free concentrations which is absolutely identical to adsorption Langmuir isotherm wherenever you wish to use it. This 1:1 complex formation approach is very effective for very many liquid and liquid-solid systems. It will make problems when stoichiometry differs from 1:1 (like, as mentioned, in multilayer adsorption), or when there are lateral or even cooperative interactions. To see clearly the links, there may be no a formal difference between binding of a molecule to one site at macromolecule (biopolymer like proteins, or DNA) dissolved in a liquid or a site interaction between this molecule and clay particle suspended in the same solution. .
However, when the Langmuir model is "working", there may be problems in understanding the meaning of parameters. For example, if it is about molecules, the Langmuir affinity cannot be related directly to adsorption heat, as it sometimes done, specifically, in text books and in references to gas phase adsortion. Also, when doing measurements at different temperatures, and the Langmuir maximal capacity becomes temperature-dependent, it is "red light". In a Langmuir model (or a 1;1 stoichiometry complex formation model), the maximal capacity should not depend on temperature. If it happened with the calculated model parameters, then, perhaps, all the model needs to be reformulated. After all, if the temperature effects were examined, the best way is to check whether isosteric heat is loading-dependent, and it will help to decide whether the Langmuir model is physically sounding. Finally, if it is about ion adsorption, one should be especially careful in interpretation of the data. If it is about ion exchange, then, the exchange isotherm is close to the Langmuir model but in the general case it is not the same; but, at some experimental conditions they cannot be distinguished. If it is any "specific" adsorption of an ion, then, the issue of electrostatic contribition, the co-adsorption of counter-ions etc has to be evaluated. This means the Langmuir afffinity may become too empirical,
Langmuir isotherm is the classic isotherm of a reaction leading to formation of a 1:1 stoichiometry complex, e.g., between a sorption site and a molecule or ion. If you will consider just formation of complexes in solutions, e.g., H-bonding, charge transfer and any other 1:1 complex (with a stoichiometry of 1:1), you will end up with the model relating the bound and free concentrations which is absolutely identical to adsorption Langmuir isotherm wherenever you wish to use it. This 1:1 complex formation approach is very effective for very many liquid and liquid-solid systems. It will make problems when stoichiometry differs from 1:1 (like, as mentioned, in multilayer adsorption), or when there are lateral or even cooperative interactions. To see clearly the links, there may be no a formal difference between binding of a molecule to one site at macromolecule (biopolymer like proteins, or DNA) dissolved in a liquid or a site interaction between this molecule and clay particle suspended in the same solution. .
However, when the Langmuir model is "working", there may be problems in understanding the meaning of parameters. For example, if it is about molecules, the Langmuir affinity cannot be related directly to adsorption heat, as it sometimes done, specifically, in text books and in references to gas phase adsortion. Also, when doing measurements at different temperatures, and the Langmuir maximal capacity becomes temperature-dependent, it is "red light". In a Langmuir model (or a 1;1 stoichiometry complex formation model), the maximal capacity should not depend on temperature. If it happened with the calculated model parameters, then, perhaps, all the model needs to be reformulated. After all, if the temperature effects were examined, the best way is to check whether isosteric heat is loading-dependent, and it will help to decide whether the Langmuir model is physically sounding. Finally, if it is about ion adsorption, one should be especially careful in interpretation of the data. If it is about ion exchange, then, the exchange isotherm is close to the Langmuir model but in the general case it is not the same; but, at some experimental conditions they cannot be distinguished. If it is any "specific" adsorption of an ion, then, the issue of electrostatic contribition, the co-adsorption of counter-ions etc has to be evaluated. This means the Langmuir afffinity may become too empirical,
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