Space-Confined Metal Ion Strategy for Carbon Materials Derived from Cobalt Benzimidazole Frameworks with High Desalination Performance in Simulated Seawater

Various metal ions with different valence states (Mg²⁺, Al³⁺, Ca²⁺, Ti⁴⁺, Mn²⁺, Fe³⁺, Ni²⁺, Zn²⁺, Pb²⁺, Ba²⁺, Ce⁴⁺) are successfully confined in quasi-microcube shaped cobalt benzimidazole frameworks using a space-confined synthesis strategy. More importantly, a series of derived carbon materials that confine metal ions are obtained by high-temperature pyrolysis. Interestingly, the derived carbon materials exhibited electric double-layer and pseudocapacitance properties because of the presence of metal ions with various valence states. Moreover, the presence of additional metal ions within carbon materials may create new phases, which can accelerate Na⁺ insertion/extraction and thus increase electrochemical adsorption. Density functional theory results showed that carbon materials in which Ti ions are confined exhibit enhanced insertion/extraction of Na⁺ resulting from the presence of the characteristic anatase crystalline phases of TiO₂. The Ti-containing materials have an impressive desalination capacity (62.8 mg g⁻¹) in capacitive deionization (CDI) applications with high cycling stability. This work provides a facile synthetic strategy for the confinement of metal ions in metal–organic frameworks and thus supports the further development of derived carbon materials for seawater desalination by CDI.