Zwitterionic ionic liquids modulating two-dimensional hierarchically porous zeolitic imidazolate framework composites.

ABSTRACT

HYPOTHESIS: Two-dimensional hierarchically porous zeolitic imidazolate frameworks (H-ZIFs) show great promising applications in catalysis, gas separation, energy storage and sensing. Herein, a facile ionic-liquid-modulation approach is proposed for constructing H-ZIFs nanosheets with tunable thickness. EXPERIMENTS Sulfo-functionalized zwitterionic ionic liquids (SFIL) have been designed as monodentate ligands to direct the formation of microporous nanosheets (ZIF-SFIL) in aqueous solution. Anions of SFIL have been tuned to modulate the coordination environment, enabling the control of the structure, thickness and pores of the nanosheets. FINDINGS: SFIL is demonstrated to pre-coordinate with Zn(II) to induce micropores with high specific surface areas (up to 1176 m2·g-1) and accelerate the nucleation of crystals. The BF4- anion serves as a competitive ligand to partially replace SFIL to cause structural defects, thus yielding hierarchically porous ZIF-SFIL nanosheets with high specific surface areas (270-466 m2·g-1) and variable thicknesses (from ca. 58 nm to ca. 455 nm). Benefiting from the versatile designability and multifunctionality of ionic liquids, the strategy in this work offers a facile approach for designing and constructing multifunctional materials with hierarchical pores.