Room-temperature synthesis of bimetallic Co-Zn based zeolitic imidazolate frameworks in water for enhanced CO2 and H2 uptakes

A simple methodology was explored to access highly robust bimetallic Co-Zn based zeolitic imidazolate frameworks at room temperature. By tuning the content of Co and Zn precursors, CoZn-ZIF-8 frameworks with varying Co : Zn (25-90% of Co2+ as confirmed by ICP-AES results) were synthesized. Electron micrographs and powder X-ray diffraction (PXRD) patterns confirmed the formation of bimetallic CoZn-ZIF-8 frameworks of 150-300 nm size, where Zn atoms were partially replaced by Co atoms. The as-synthesized CoZn-ZIF-8 frameworks displayed a tuned pore size, pore volume and surface area, with the highest surface area (enhanced by similar to 40% compared to Zn-ZIF-8) and pore volume (enhanced by similar to 33% compared to Zn-ZIF-8) for Co75Zn25-ZIF-8. The as-synthesized CoZn-ZIF-8 frameworks also displayed enhanced CO2 and H2 uptakes at 298 K and 77 K, respectively, at 1 bar. Noteworthy enhancement of similar to 30% in the CO2 and similar to 23% in the H2 uptake was displayed by Co75Zn25-ZIF-8 frameworks as compared to Zn-ZIF-8 under analogous conditions.