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

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. <i>In situ</i> 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-2<i>H</i>-1-benzopyran-3-carbonitrile and paracetamol. Single-crystal XRD analysis of three of the compounds confirmed their structural integrity. The catalyst was easily separated <i>via</i> 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.