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

Abstract

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.

The Role of Aggregation on Energy Transfer in Layered Rare-Earth Hydroxide/Naphthalene Diimide Hybrid Materials

“…In these systems, a two-step mechanism has been proposed to explain the formation of aggregates: (i) rapid adsorption, where unstable aggregates could be formed in zones such as the electric double layer surrounding the particles, and (ii) rearrangement of initially formed species, which is a slow process and can take several hours. 29,30 Importantly, the LYH not only acted as a host matrix for the photoactive NDI-SO 3 molecules but also served as an energy transfer bridge that connected the host layers and the organic chromophores. The energy transfer pathway for LYH/NDI-SO 3 luminescence involved the following steps: (i) the LYH host absorbed the UV-light via Y 3+ -induced increased absorption cross-section; (ii) energy transfer to NDI-SO 3 species.…”

“…It is plausible that the aggregation of NDI-SO 3 in the surface of LYH follows a similar mechanism reported for other organic dyes adsorbed on layered materials. In these systems, a two-step mechanism has been proposed to explain the formation of aggregates: (i) rapid adsorption, where unstable aggregates could be formed in zones such as the electric double layer surrounding the particles, and (ii) rearrangement of initially formed species, which is a slow process and can take several hours. , …”

Effect of Violet Laser Irradiation on the Optical Properties of Polyvinyl Alcohol/Methyl Orange Composite Thick Films: A Model for Medical Applications

“…Dyes are characterized as organic compounds designed to color substrates through absorption, adsorption, reaction, or deposition with a certain level of permanence [6]. Methyl orange, an organic dye with the chemical formula (CH 2 CH[CH 2 CH(CH 3 ) 2 ]) n , is one such compound [7,8]. This dye is represented in Figure 2 below [9].…”