A copper bromide-decorated magnetic oyster shell biosupport as a sustainable catalyst for heterogeneous synthesis of imidazo[1,2- <i>a</i> ]pyridines in glycerol

Oyster shells (OSs) are a kind of biomineralized material derived from renewable resources, comprising calcium carbonate (>95 wt%) as the main component, organic moieties, and trace elements, which are often discarded haphazardly as waste. Due to their notable properties, OSs have been widely employed as templates or precursors in the synthesis of different functional nanomaterials. The acidic hydrolysis of the matrix proteins present in the OS structure produces an acid-cured OS powder (AOS) containing coordination sites -COOH and -NH₂, which can be used as a bed to immobilize catalytic metal species. In this context, we focused on utilizing acid-pretreated waste OS to stabilize copper bromide, which was subsequently combined with magnetite nanoparticles. The copper bromide-supported magnetic AOS was well characterized using various analyses, such as FT-IR, XRD, FE-SEM, EDX elemental mapping, TEM, ICP-OES, TGA, BET, and VSM. Then, the Cu-incorporated magnetic catalyst was successfully applied for the synthesis of a variety of imidazo[1,2-<i>a</i>]pyridine derivatives in glycerol as a green and sustainable medium. The synergistic effect of metallic Lewis acid and hydrogen bonding between the precursors and glycerol led to the production of desirable products in high yields. Furthermore, the catalyst can be easily synthesized and recovered.