When you say linear behavior, I understand you mean constant (or nearly constant), right? If this is the case, the surface could be already saturated at concentrations as low as 100 mg/L, so you see no change for larger concentrations.

Have you tried lower concentration ranges, say lower than 100 mg/L?

Hello,

What is the adsorbent nature, what is its specific surface area? Did you do the effect of the pH on the adsorption?

I think nonlinear fitting is good.

If you need any questions

You can send me an email

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Here is my article, it contains 4 activated carbons, where different concentrations have been used due to various specific surface area of each activated carbon

https://kwnsfk27.r.eu-west-1.awstrack.me/L0/https:%2F%2Fauthors.elsevier.com%2Fa%2F1jo6Q_WRZ3VRp/1/010201920979dffe-8aba31f2-8f62-4e0d-9240-ca80c55002a3-000000/hlgRYS9VD8uWdBMNgiyfsJZZUh8=392

Forgive me, I changed the part of the question regarding the linear behavior. Actually, what I meant to say is that within the studied initial concentration range (100-1000 mg/L), my material is able to completely remove the adsorbate up to near the maximum concentration, meaning that most points are on the y-axis, as the equilibrium concentration (x-axis) approaches zero.

What about the removal percentage? Is it going down continuously?

If so, keep increasing the concentration and see what is going on.

What is the specific surface area of your adsorbent?

Megherbi Hamza the removal percentage starts to slightly decline at the last two concentrations (900 and 1000 mg/L). As for the material, it is biochar. I have not yet analyzed surface area, porosity, pore volume, or pore diameter. So, in order to fit the experimental data to the nonlinear isotherm models, is it enough to keep increasing the initial concentration?

To help you well, could you please send a picture of your graph.

Because I am working on the same type of adsorbent.

I will try my best to find the solution for you.

Dear,

I don't know exactly why did you get the negative R2 value for any model. Could you please mention reason for selecting the initial concentrations over 100 ppm for your adsorbent? Also, whether you fitted linear or non linear? W e can't ensure as such without the details of the operations you carried out during the experiment and fitting.

Dear, Dharma Raj Kandel

I chose an initial concentration range between 100-1000 mg/L because my material was able to completely remove the adsorbate up to initial concentrations of 800 mg/L. After this concentration, it still adsorbs, but slightly decreases. Therefore, any concentration below 800 mg/L is fully removed. As for the isotherm models, I chose to model using the nonlinear equations of all models. However, none of the models converged, as most of the points are at zero or very close to zero with respect to the equilibrium concentration.

Dear Yago Neco Teixeira Please check the parameters very carefully while fitting with equation of corresponding isotherm. Did you get negative values R2 in all isotherms model? Negative R2 means data is fitted, so could you share the screenshot of your excel sheet and graph?

Dharma Raj Kandel Megherbi Hamza Fernando Hernández Ramírez

These are the results I have been obtaining for the study of isotherms. Initial concentration range ranging between 100-1000 mg/L.

Hi

Two isotherm models exist. Mono and multi-layer may be your adsorption method, and it's possible your absorber was a multilayer adsorber. The Sips and Temkin model was suggested for your fitting.

Hi

Two isotherm models exist. Mono and multi-layer may be your adsorption method, and it's possible your absorber was a multi-layer adsorbent. The Sips and Temkin models were suggested for your fitting.