Copper ions-coordinated galacturonic acid-modified UiO-66-NH2 as a nanocatalyst for the eco-friendly synthesis of pyrroles and polyhydroquinolines

In this study, a novel metal-organic framework (MOF) nanocatalyst was prepared by modifying UiO-66-NH2 with galacturonic acid (UiO-Galacturonic). Then, copper ions were coordinated to the galacturonic acid ligands on the surface of UiO-66-NH2, yielding a novel acidic nanocatalyst (UiO-Galacturonic/Cu). The presence of hydroxyl groups on the galacturonic acid ligand and pores and surface moieties of UiO-66-NH2 can improve the nanocatalyst’s reactivity, dispersibility, metal coordination, and hydrogen-bonding ability. TGA, FT-IR, TEM, XRD, BET, t-plot, ICP, SEM, EDS, and elemental analysis confirmed the formation of UiO-Galacturonic and UiO-Galacturonic/Cu nanocatalysts. The catalytic efficiency of the nanocatalyst (UiO-Galacturonic), with the ability to form hydrogen bonds, in the synthesis of pyrroles with high yield (84–98%), under mild conditions (20–30 min, room temperature), as well as the acidic nanocatalyst (UiO-Galacturonic/Cu) in the synthesis of polyhydroquinolines with high yield (86–97%) under mild conditions (15–20 min, room temperature), was investigated. After separation by centrifugation, this catalyst can be reused for up to five consecutive cycles without significant loss in activity.