Imine-based covalent organic framework gels for efficient removal of Fe2+ from contaminated water

Abstract

The presence of high concentrations of metal ions in water distribution systems and industrial plants gives rise to the appearance of deposits responsible for incrustation and corrosion events. In this context, the search for new approaches to remove these contaminants from water using more efficient techniques has gained substantial importance over the last decades. Covalent Organic Frameworks (COFs) have emerged as a new class of porous crystalline materials with distinctive properties based on the reticular chemistry principle, making them very promising for this purpose. Specifically, they are characterized by their permanent porosity, excellent water stability, and tailored design for specific applications on demand. In this study, we present two imine-based COFs, TAPB-PDA-COF and TAPB-DHTA-COF, obtained at room temperature, as a sustainable alternative for the removal of Fe²⁺ from water as a previous step to reverse osmosis in the water treatment process. The two imine-based COFs were directly obtained as gels and easily activated under argon flow to xerogels. The materials showed remarkable adsorption uptakes at neutral pH towards Fe²⁺ within 5 minutes of contact. Additionally, the COF xerogels exhibited maximum adsorption capacity values in the range of other porous reported materials. Finally, the gels were successfully processed into COF@Polysulfone composite beads, paving the way for the obtention of COFs into macroscopic products easily removable from any media, leaving no residues, and easily incorporated into the water treatment process. These COF composite beads are excellent candidates for large-scale preparation and easy commercialization.