what could be the reasons I am getting negative intercept negative qmax (maximum adsorption capacity) and negative KL (Langmuir constant) values? many of the researchers said that it can be possible when the Langmuir model is not applicable. but I am not getting any reference.
if anyone has reported a negative qmax value in any article please provide references.
Thanks in advance
The Langmuir isotherm model is widely used to describe adsorption behavior, especially for monolayer adsorption onto a homogeneous surface. However, there are cases where the Langmuir model may not be applicable, and negative values for the intercept, qmax, and KL can indicate that the model is not appropriate for your data. To address this issue, you may want to explore alternative adsorption models that better suit your experimental data. The Freundlich isotherm, or other models may be more appropriate depending on the characteristics of your system. Here you can find how to fit these models, hope it shall help: https://youtu.be/d6nSIZ0_qiY?si=KYcpaTD4d5BETsQb
Dear Ayushi, This result may be correlated with the linearization of the Langmuir model, which I have encountered before. I recommend utilizing the non-linear Langmuir model to analyze your data, employing the Origin software for its ease and speed. If the fitting has a weak correlation with the empirical value, characterized by a low R2 value and a significant discrepancy between the experimental and estimated qmax. The model has been considered inapplicable. However, if the modeling resulted in a high R2 value indicating a significant correlation between the experimental and predicted q max, it suggests that the failure in linear fitting occurred due to the linearization of the Langmuir equation. In many cases, non-linear fitting yields more desirable results when compared to the linearized equation. Good luck
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