What is adsorption capacity (qe)?

qe is the equilibrium adsorption capacity — the mass of adsorbate (e.g., mg) retained per unit mass of dry adsorbent (e.g., g) at a given equilibrium concentration. Units are typically mg/g.

When should I use the Langmuir model?

Use the Langmuir model when adsorption is monolayer and occurs on a homogeneous surface with a finite number of identical sites. It predicts a maximum saturation capacity (Qmax).

When should I use the Freundlich model?

The Freundlich model suits heterogeneous surfaces and multilayer adsorption. It is empirical and does not predict a saturation limit, making it useful over a wide concentration range.

What is the separation factor RL?

RL = 1 / (1 + KL * C0) indicates isotherm favorability. RL 1 means unfavorable.

What units should I use?

The tool uses mg/L for concentration and mg/g for capacity, which are the most common units in water treatment literature. Ensure your isotherm constants were determined in the same unit system.

What does 1/n mean in the Freundlich model?

1/n (the heterogeneity factor) describes isotherm shape. Values between 0 and 1 indicate favorable adsorption; values greater than 1 suggest cooperative adsorption or complex behavior.

Adsorption Capacity Calculator

Calculate the equilibrium adsorption capacity (qe) of a material using the Langmuir or Freundlich isotherm equations.

Isotherm Parameters

Isotherm Model

Langmuir Freundlich

Equilibrium Concentration, C_e (mg/L)

Maximum Adsorption Capacity, Q_max (mg/g)

Langmuir Constant, K_L (L/mg)

Initial Concentration, C₀ (mg/L) — for R_L

Result

Enter parameters and click Calculate.

Formula Used

q_e = (Q_max × K_L × C_e) / (1 + K_L × C_e)

R_L = 1 / (1 + K_L × C₀)

R_L Interpretation (Langmuir)

R_L range	Isotherm type
R_L = 0	Irreversible
0 < R_L < 1	Favorable
R_L = 1	Linear
R_L > 1	Unfavorable

Summary

This tool computes the equilibrium adsorption capacity (qe) of an adsorbent material based on either the Langmuir or Freundlich isotherm model. Enter the equilibrium concentration and the isotherm constants for your system to get the amount of adsorbate retained per unit mass of adsorbent. Useful for designing water treatment, air purification, and separation processes.

How it works

Select the isotherm model: Langmuir or Freundlich.
Enter the equilibrium concentration (Ce) in mg/L.
For Langmuir, provide the maximum adsorption capacity (Qmax) and the Langmuir constant (KL).
For Freundlich, provide the Freundlich constant (KF) and the heterogeneity factor (1/n).
Click Calculate to get qe (mg/g), the amount adsorbed per gram of adsorbent.
Use the separation factor RL (Langmuir only) to assess isotherm favorability.

Use cases

Evaluate adsorbent performance for heavy metal removal from wastewater.
Compare Langmuir and Freundlich fits for experimental sorption data.
Design activated carbon filters for water and air treatment systems.
Estimate loading capacity of ion-exchange resins.
Academic coursework in environmental and chemical engineering.
Predict breakthrough capacity in packed-bed adsorption columns.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu