Layered Double Hydroxide Adsorbents for Pharmaceutical Removal

Abstract

Layered double hydroxides (LDHs) are synthetic clays with high adsorption capacity that favors the efficient removal of pharmaceutical compounds from aqueous media. These materials consist of positively charged layered structures formed by metal cations and hydroxyl groups and stabilized by interlayer anions. This structure gives LDHs a high specific surface area and ion exchange capacity that promote the selective capture of pollutants present in water. Furthermore, LDHs have been assembled with diverse materials, such as metal nanoparticles or organic compounds, yielding LDH hybrids with improved adsorption capacity. Adsorption onto LDH-based materials mainly involves electrostatic interactions and newly formed hydrogen bonds between the functional groups of drugs, especially neutral and anionic, and the layers of LDHs. Due to this mechanism, the adsorption efficiency depends on factors such as the pH of the medium and both the chemical nature and the concentration of the drugs. This chapter provides an overview of LDH-based adsorbent synthesis approaches for the removal of pharmaceutical pollutants from water, their adsorption mechanisms, the adsorbent recovery processes, and the main factors that affect the efficiency of removal. Some challenges faced by LDH-based adsorbents to achieve the sustainable treatment of drug-contaminated wastewater are presented as well.