Removal of heavy metals by covalent organic frameworks (COFs): A review on its mechanism and adsorption properties

Covalent organic frameworks (COFs) have demonstrated a great potential in the removal of heavy metals due to its high adsorption capacity, large surface area, tunable porosity, porous structure, and recyclability. These features give COFs advantages over traditional adsorbents. The occurrence of heavy metals in surface and groundwater above the maximum acceptable limit poses a great threat not only for human health but also for the environment. The elimination of these large amounts of heavy metals serves as a significant challenge. Hence, this review complies the recent investigations on COFs as a superior material in the removal of heavy metals from water considering various environmental parameters as well as the recycling process using different regeneration agents. The selectivity and sensitivity of COFs and COF-based materials were elucidated. Moreover, the different adsorption mechanisms of heavy metals by COF-based materials are critically discussed. The chemical structures and functional groups play a significant role in enhancing the removal efficiency of heavy metals. In addition, personal insights based on the interaction mechanism of COFs and various functional groups into future research prospects. We believe that this review paper can motivate more researchers to use COFs for water remediation.