Comparison and interpretation of isotherm models for the adsorption of dyes, proteins, antibiotics, pesticides and heavy metal ions on different nanomaterials and non-nano materials—a comprehensive review

Adsorption is most commonly applied in water treatment, gas purification/separation, catalysis, etc. It is a very simple and inexpensive technique. However, the performance depends on the type of adsorbent and its dosage. Researchers across the world keep seeking low-cost and more effective adsorbents. As a result, millions of research publications on adsorption have been published yearly. Most of these publications report the synthesis of new adsorbents from various sources and their application in the remediation of several inorganic and organic pollutants from water bodies. Researchers attempt to fit their experimental results with various isotherm models to understand the adsorption mechanism. Some researchers fit data into linear isotherm models, while others add non-linear isotherm models for estimating the isotherm parameters. The fit of isotherm models differs for various adsorbents and contaminants. The present paper is comprehensive review compiling information on isotherm models that explain the intrinsic mechanisms of adsorptive removal of pollutants such as antibiotics, dyes, proteins, pesticides and heavy metal ions. Furthermore, a detailed characteristic property of numerous cationic dyes, anionic dyes, proteins, antibiotics, pesticides and heavy metal ions was also discussed. It is observed that based on the literature reviewed, it was found that the adsorption equilibrium data of cationic dyes and anionic dyes were well defined with the Langmuir model. Additionally, in the case of the adsorption of proteins, antibiotics and heavy metal ions, the Langmuir model is well matched among all applications.