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

Abstract

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 ∼40% compared to Zn-ZIF-8) and pore volume (enhanced by ∼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 ∼30% in the CO₂ and ∼23% in the H₂ uptake was displayed by Co₇₅Zn₂₅-ZIF-8 frameworks as compared to Zn-ZIF-8 under analogous conditions.