The versatility of montmorillonite in water remediation using adsorption: Current studies and challenges in drug removal

The persistence of contaminants such as pharmaceutical products including antibiotics, anti-inflammatory agents, hormones, and many other substances in aquatic environments has significantly increased demand for new remediation alternatives. One such alternative is adsorption using ecologically safe, abundant, and low-cost adsorbent materials such as clay minerals. Montmorillonite is one of the most researched clay minerals for this purpose as its unique physicochemical properties (i.e., cation exchange capacity, intercalation, and adsorption) facilitate the efficient removal of different contaminants, including pharmaceutical compounds. In addition, the incorporation of organic and/or inorganic compounds in modification reactions may alter the hydrophobicity and hydrophilicity of the montmorillonite surface. The production of new active sites on clay minerals improves its affinity to specific chemical species and may even provide a degree of selectivity for adsorptive processes. This review discusses the structural and experimental factors that control the mechanisms and performance of drug adsorption by natural or modified montmorillonite under simulated or real conditions. Adsorptions conducted in batch and column experiments using the clay mineral are presented, and their challenges are discussed. Research to date has demonstrated that montmorillonite-based adsorbents are versatile materials showing promise for drug adsorption.