Carbonyl-rich porous organic polymers for cobalt adsorption from water

Abstract

Transition metals such as cobalt are necessary for various clean-energy technologies, notably electric-vehicle batteries. Global demand for these metals is therefore projected to increase exponentially in coming decades. Metal-ion adsorption from water offers many advantages over mining, as adsorption processes are energy-efficient and compatible with diverse water sources. Porous organic polymers are promising adsorbents: Their covalent nature provides thermal and chemical stability, while their porosity leads to high adsorption capacity. Here, we synthesized a series of amide-linked porous organic polymers denoted TMC-TAPM through the polymerization of a tri-functional acyl chloride monomer with a tetra-functional amine monomer, and we studied the resulting materials for cobalt capture from aqueous solution. By controlling monomer stoichiometry during synthesis, we obtained materials with varying amounts of carbonyl or amino groups. The materials with increasing carbonyl content showed increasing cobalt adsorption capacities, with measured adsorption capacities up to 50 mg Co g⁻¹. Cobalt adsorption capacity was observed to plateau past a certain stoichiometric ratio, indicating an optimal monomer stoichiometry of 1.5-fold excess acyl chlorides relative to amines. The captured cobalt could be desorbed to yield a re-activated adsorbent capable of repeated adsorption cycles, without loss in performance. These results provide design rules for the synthesis of robust, high-capacity transition metal adsorbents.