Effective removal of heavy metal-lead and inorganic salts by microporous carbon derived from Zeolitic Imidazolate Framework-67 electrode using capacitive deionization

The available fresh water resources have been polluted by rapid industrialization and urbanization. Several techniques have been developed and practiced for the treatment of wastewater, including physical, thermal, chemical, membrane-based and electrochemical techniques. Still the efficient and effective technique for the wastewater treatment is challenging for researchers over the years. The capacitive deionization (CDI) is an environmentally friendly technology for water purification (desalination) with substantial scope, which works on the principle of electrical double layer (EDL). In this case, salt ions are electrostatically adsorbed on the surface of electrode material. Porous carbon with optimized pore size, hierarchal pore structure and high surface area is preferred for CDI. Herein, we report the detailed study of microporous carbon derived from Zeolitic Imidazolate Framework-67 (PC-ZIF-67) and its application as electrode material in CDI. This setup has been utilized for the removal of monovalent cations (Na+ and K+) and divalent cation (Ca2+) along with heavy metal- lead (Pb2+) from water. The PC-ZIF-67 exhibits typical truncated cubic morphology with microporosity and high gravimetric surface area of 532 m2/g. The as-synthesized PC-ZIF-67 offers salt adsorption capacity (SAC) of 28.1, 30.6, 50.9 mg/g for the removal of Na+, K+ and Ca2+, respectively. Moreover, PC-ZIF-67 shows SAC of 117.2 mg/g for the removal of Pb2+, which is higher than other saline cations. The mechanism of Pb2+ removal is attributed to the electrostatic and pi- pi interaction between the surface of PC-ZIF-67 and Pb2+. Further, the material displays good cyclic stability during the removal of each cation, retaining 90% of SAC after ten adsorption-desorption cycles. The selectivity of cations is studied by mixed salt electrosorption experiment revealing that there is higher selectivity of PC-ZIF-67 electrode towards divalent cations as compared to monovalent cations. The SAC values have been validated by matching with theoretical adsorption model isotherms. This work promotes future utilization of MOF-derived porous carbon for the effective removal of dissolved Na+, K+, Ca2+ and Pb2+ from aqueous source using CDI.