Prospects of layered double hydroxide (LDH)-based adsorbents for the remediation of environmental inorganic pollutants from wastewater: a critical review

Abstract

Heavy metal pollution is extremely deleterious and has emerged as a major environmental concern, posing a hazardous threat to humans and aquatic organisms. It is increasing at an alarming rate owing to significant contributions from natural and anthropogenic activities, which include mining operations, spraying pesticides, land filling, rock abrasion, volcanic eruptions, and fossil fuel combustion. Heavy metals are potentially toxic even at low concentrations and can induce hepatotoxicity, nephrotoxicity, neurotoxicity, carcinogenicity, genotoxicity, and cardiovascular toxicity. Thus, the removal of heavy metals is critical from an environmental perspective. Recently, various efficient adsorbents have been developed for the treatment of heavy metal contaminants, among which LDHs have received great interest owing to their outstanding features such as structural flexibility, biocompatibility, reusability, simple synthesis, low cost, high adsorption efficiency as well as rheological and swelling properties. This review presents an extensive summary of LDH-based adsorbents reported in the literature in the last ten years for heavy metal remediation. Herein, we systematically explore the recent advancements in aspects such as sources of heavy metals, toxicological effects, functionalization strategies, application of LDH-based hybrids in metal detoxification, influencing factors, and machine learning approaches. Moreover, this review highlights pivotal parameters such as isotherms, kinetics, thermodynamics, adsorption capacity, adsorption mechanisms, and optimised experimental values. Finally, we discuss the future perspectives in this promising field. This work will provide valuable insights to new researchers for further exploring the potential of LDH-based adsorbents in heavy metal remediation.