Metal–organic frameworks HKUST-1 as porous matrix for encapsulation of basic ionic liquid catalyst: effect of chemical behaviour of ionic liquid in solvent

Abstract

Ionic liquid hybrid MOFs composite materials, copper-based metal–organic frameworks HKUST-1 as porous matrix was used to encapsulate amino-functionalized basic ionic liquid (ABIL) catalyst by post-synthetic modification strategy under different solvents such as H2O, ethanol and N,N-dimethylformamide. A series of characterization techniques such as PXRD, SEM, N2 physical adsorption–desorption, ICP-OES, element analysis, FT-IR, DRS UV–Vis, XPS and TGA were employed to probe the textural properties, surface characteristics, variations in coordination environment of metal center and thermal stability of as-synthesized catalysts. Furthermore, the Knoevenagel condensation of benzaldehyde and malononitrile was used as a probe reaction to evaluate their catalytic performances. It was interesting to find that the chemical behaviour of ABIL dissolved in these solvent had a profound impact on synthesis of catalysts and their catalytic performances. In the weak alkaline and neutral environment, ABIL can be dissolved as molecular state and be well confined inside HKUST-1 nanocavities via Cu–NH2 coordination bond. In particular, the alkalinity of ABIL dissolved ethanol solvent was the optimal environment for encapsulation of ABIL organocatalyst, and the as-synthesized heterogeneous catalyst demonstrated favourable structural property and excellent catalytic performance.