A review of heavy metals' removal from aqueous matrices by Metal-Organic Frameworks (MOFs): State-of-the art and recent advances

Surface water and groundwater contamination by heavy metals is a global serious concern, which despite its well-known character, still lacks a decisive application to tackle its harmful side-effects. Among the various existing methods, due to its simplicity of the process and efficiency in removing heavy metals, adsorption is widely used in wastewater treatment. Recently, a new class of materials, metal-organic frameworks (MOFs), synthesized through hydrothermal or heating methods, sonochemistry, microwaves, and chemical ways, has been used as an effective adsorbent to remove toxic heavy metals from aqueous solutions, due to their unique properties such as their high chemical stability, high surface area, structural design, and reusability. In this review, we evaluated the various MOFs (including plain and modified MOFs, magnetic MOFs composites, etc.) for potential applications in the removal of the selected heavy metals. The values reported for the adsorption capacity of the selected heavy metal onto MOFs are in range of a few to several hundred mg/g. The mechanisms associated with these processes, i.e., physical and chemical adsorption, are discussed in detail; we assess the recent works of MOFs application in heavy metals removal, explain in-depth the physico-chemical processes governing adsorption, analyze the MOF categories and critically compare them with the existing technologies available. Overall, this review aims to gather the available knowledge on heavy metals' adsorption by MOFs and act as a guide for the development of either new MOFs or further applications of adsorption.