Synthesis and structural analysis of a ZIF-9/GO composite for green catalytic C–C bond formation and N-formylation: a spectroscopic study

Abstract

We report a new synthetic approach for a ZIF-9/GO composite material at room temperature and its comprehensive characterization using a variety of techniques, including PXRD, FT-IR, Raman, UV-vis, DRS, TGA, SEM, FE-SEM, EDX, TEM, ICP-MS, XPS, and BET. The material exhibited a moderate surface area and good thermal stability, as indicated by BET and TGA results. DRS revealed a band gap of 3.4 eV, which indicates slight semiconductor nature of the material. The crystalline nature of the ZIF-9/GO composite was confirmed by PXRD. The ZIF-9/GO composite exhibited excellent catalytic efficiency as a heterogeneous catalyst in Knoevenagel condensation and N-formylation, achieving yields of up to 98% under green reaction conditions with a wide range of substrate tolerance. The E-factor (0.10) and atom economy (91.7%) values were very close to ideal green chemistry parameters. In situ and UV-vis studies revealed reaction intermediates. The practical utility of this protocol was demonstrated by the gram scale synthesis of the value-added compounds 2-imino-2H-1-benzopyran-3-carbonitrile and paracetamol. Single-crystal XRD analysis of three of the compounds confirmed their structural integrity. The catalyst was easily separated via filtration and reused for up to six catalytic cycles without significant loss of activity, which is a crucial component of green synthesis, and hot-filtration experiments confirmed its heterogeneity. The probable mechanisms for both reactions are also well presented.