I am working on paper about the adsorption of some water pollution by plant waste, and I have a problem concerning the models of isotherm(Langmuir,Freundlich and Temkin)(its calculations to be exact), I need to know how to calculate and how to choose which model will be chosen.thank you
You plot a linear straignt line for:
Freundlich: Ln qe versus Ln Ce
Langmuir: Ce/qe versus Ce
Temkin: qe versus Ln Ce
The high R2 (correlation coefficient) value indicates which the model describe well the adsorption.
Use the linear form of these isotherms and make plots as Chemini said
You can use CAVS - adsorption evaluation to perform all regressions (Kinetcis, Isotherm and Fixed-bed).
The program uses non-linear regression, which is far more better than linear regression, and the equations are ready to be use.
The software is FREE to be used.
check the software here: http://bit.ly/CAVS_tutorials
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Please contact me for further details
From the experiments, for any initial concentration, after the equilibrium time, we get equilibrium concentration (ce). Then find the value of qe.
Then the Langmuir isotherm model is solved by plotting Ce/qe on y-axis and Ce on x-axis. The slope will give the value of 1/qm and intercept will give 1/(kl *qm).
In the Freundlich model, we plot log qe on y-axis and log Ce on x-axis. The slope will give 1/n where n is adsorption intensity and intercept will give log kf, where kf is model constant.
1. First determine the kinetic parameters of all methods
2. Then, for each technique, calculate the calculated value
3. Then compare all of them according to the measured data
4. Using the criteria for choosing models, determine which model (Langmuir, Freundlich and Temkin) is better
Mustafa Raqeeb Mohammed, I recommend the use of non-linear regression method as this gives a more accurate result with lesser associated errors compared to the linear regression method. You only need your experimental Ce and Qe to use with the Non-linear Equations of these Models. MS Excel SOLVER is an add-on in MS Excel that can help in Non-linear regression analysis.
Read through this paper.
@ Anwana Ukpong, Dear how can we calculate isotherm constants from nonlinear Freundlich or Langmuir
There is software such as Statistica, Origin, MathLab etc. which have a built-in Marquardt procedure and then there is no problem with determining the parameters of isotherms using the nonlinear method. Excel does not provide such possibilities, but you can implement graphical methods here, and present datapoints in non-linearly transformed coordinate systems Ce/qe vs Ce (Langmuir), lnqe vs lnCe (Freundlich) or q vs lnCe (Tiemkin) and fit a straight line to them.
These videos can answer your questions: https://www.youtube.com/channel/UC5MiS3nMoji95OZ7uE1V8qw/playlists?view=50&sort=dd&shelf_id=6
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