Controversial Issues Related to Dye Adsorption on Clay Minerals: A Critical Review

This critical review points out the most serious and problematic issues to be found in the literature on the adsorption of dyes on clay minerals. The introduction draws attention to the fundamental problems, namely the insufficient characterization of adsorbents, the influence of impurities on the adsorption of dyes, and the choice of inappropriate models for the description of the very complex systems that clay minerals and their systems represent. This paper discusses the main processes accompanying adsorption in colloidal systems of clay minerals. The relationship between the stability of the colloidal systems and the adsorption of dye molecules is analyzed. The usual methodological procedures for determining and evaluating the adsorption of dyes are critically reviewed. A brief overview and examples of modified clay minerals and complex systems for the adsorption of organic dyes are summarized. This review is a guide for avoiding some faults in characterizing the adsorption of organic dyes on clay minerals, to improve the procedure for determining adsorption, to evaluate results correctly, and to find an appropriate theoretical interpretation. The main message of this article is a critical analysis of the current state of the research in this field, but at the same time, it is a guide on how to avoid the most common problems and mistakes.

Automated summary

This critical review examines the literature on the adsorption of dyes on clay minerals and identifies the most serious issues. Insufficient characterization of adsorbents, the influence of impurities, and inappropriate models are highlighted as fundamental problems. The paper discusses the main processes accompanying adsorption in colloidal systems and analyzes the relationship between system stability and dye adsorption. Methodological procedures for determining and evaluating adsorption are critically reviewed. A summary of modified clay minerals and complex systems for the adsorption of organic dyes is provided. The review serves as a guide for improving characterization, determining adsorption, evaluating results, and interpreting data accurately.