## 3 Environmental Applications of Organoclays
### Water Pollution  
According to Sustainable Development Goal 6, clean water and sanitation are priorities for everyone in the 21 st century. Over the past two decades, many researchers have worked on clay-based adsorption materials for removing contaminants from water systems. There are many reports which are regarding the applicability of clay for water and wastewater treatment. [PERSON] [44] published a report on clay and clay-based composites for removing organic, inorganic, and bio-based contaminants from drinking water. In that report, the author has reviewed natural clay and its application for heavy metal removals, such as Cd\({}^{2+}\), Cr\({}^{3+}\), Cu\({}^{2+}\), Zn\({}^{2+}\), Se\({}^{2+}\), Ni\({}^{2+}\), Fe\({}^{3+}\), Pb\({}^{2+}\), U\({}^{4+}\), Co\({}^{2+}\), etc. The author also considered its application for inorganic contaminants, fluoride and nitrates, and organic compounds, such as dichloroacetic acid, carbon tetrachloride, phenol, humidity and O-dichlorobenzene, algae removal, atrazine, sulfentrazome, imazaquin and alachlor, naphthalene and phenolic derivative, salicylic acid, carbamazepine, etc., and pathogens. [PERSON] et al., 2019 [45], reported a review on clay minerals being used as an adsorption material to remove heavy metals from the water system. In this review, they focused specifically on the removal of water and wastewater contaminants. At the same time, [PERSON] [46] published a report on the use of organoclay in the environment. [PERSON] and [PERSON] [47] published a review highlighting the applicability of gemini-surfactant-modified clay to combating water pollution. All of these investigations concluded that clay is suitable for heavy metal and organoclay contaminants. In addition, high surface area and CEC clays, such as montmorillonite clay, played a dominant role. In the 2020-2023 period, clay-based reviews were published by [PERSON] et al. [48], [PERSON] et al. [49], [PERSON] et al. [50], [PERSON] [51], and [PERSON] [52]; they focused on the implementation of wastewater treatment technologies using clay as a composite with a polymeric material, a flocculating material, or other nanomaterials. So many works on this water pollution related to clay materials have been reported and reviewed. Therefore, in this segment, we have focused on the chronology of research over the last 10 years and placed the emphasis on pollutants and their efficiency. Table 3 focuses on the applicability of clay and organoclay for removing solid pollutants. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Clay** & **Modifier** & **Methodology** & **Application** & **Efficiency** & **Reference** \\ \hline \multicolumn{6}{c}{2013} \\ Bentonite (Sigma & Hexadecyltrimethylammonium & Cation exchange & Dye Removal & 99.5\% & [53] \\ Aldrich) & bromide & & & & \\ \hline \multicolumn{6}{c}{benzylhexadecyldine} \\ Bentonite (Vietnam) & benzylstearyldimethylammonium & Cation exchange & Phenol Removal & 0.92 mmol g\({}^{-1}\) & \\ \multicolumn{6}{c}{chloride} \\ dimethylidioctadecylammonium & & & 0.64 mmol g\({}^{-1}\) & \\ \multicolumn{6}{c}{bromide} \\ Na- & Dodecyltrimethylammonium & & & \\ montmorillonite (Sigma & bromide & & \\ (Sigma & Didodecyldimethylammonium & & \\ Aldrich) & bromide & & \\ \hline \multicolumn{6}{c}{Dodecyltrimethyl ammonium} \\ \multicolumn{6}{c}{bromide} \\ Ca- & \multicolumn{6}{c}{Hexadecyltrimethyl ammonium} \\ montmorillonite (Arizona) & & & & \\ \multicolumn{6}{c}{bromide} \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of the application of natural clay and its modified clay in the removal of water pollutants and their efficiency.