Can a material with a lower percentage removal have the maximum adsorption capacity (qm) when comparing two materials using Langmuir isotherm? If so, what are the causes of the highest adsorption capacity?
Yes, a material with a lower percentage removal can still have a higher maximum adsorption capacity (qmq_mqm) when comparing two materials using the Langmuir isotherm. The percentage removal is related to how effectively a material removes a contaminant from the solution at a given concentration and under specific conditions, while qmq_mqm represents the theoretical maximum amount of adsorbate that a material can adsorb per unit mass of adsorbent when the surface is fully covered.
This discrepancy can occur due to several reasons:
Initial Concentration and Conditions: The percentage removal depends on the initial concentration of the adsorbate and how close the system is to equilibrium. A material might have lower percentage removal at a given concentration because it hasn't reached its full adsorption potential at those conditions, but it may still have a higher qmq_mqm if it can adsorb more at saturation.
Adsorbent Surface Characteristics: A material might have a lower percentage removal if it adsorbs slowly or if it has limited active sites at lower concentrations. However, it can have a higher maximum capacity due to larger surface area, better pore structure, or stronger binding sites for adsorbates.
Binding Affinity (Langmuir Constant bbb): The Langmuir constant bbb, related to the affinity between the adsorbate and the adsorbent, also plays a role. A material with a lower bbb might show slower or less adsorption at lower concentrations, leading to lower percentage removal, but still have a high qmq_mqm because it can eventually adsorb more as concentration increases.