Hibiscus Rosasinensis L. aqueous extract-assisted valorization of lignin: preparation of Pd NPs@Fe3O4-lignin for Cr(VI) reduction and Suzuki-Miyaura coupling reaction in eco-friendly media

Lignin as the second most abundant renewable natural polymer can be broadly used in different fields owing to several properties, such as biodegradability, high thermal stability and etc. Respect to these properties, lignin can be used as a significant support for catalytic systems [1]. These catalytic systems were found to be efficient towards different reactions such as coupling reactions including Suzuki-Miyaura as a powerful tool for C-C bond formation and the production of bioactive organic molecules [2].Among the heavy metals in water, Cr(VI) is one of the most toxic substances produced during industrial processes [3]. Despite the high solubility of Cr(VI), removing it from wastewater is one of the most important challenges in wastewater treatment. Cr(III) has low toxicity and forms insoluble hydroxides. Therefore, reduction to Cr(III) is the simple approach to remove Cr(VI).Hibiscus Rosasinensis L. extract mediated biosynthesis of Pd nanoparticles (NPs) and their deposition on the magnetic calcium lignosulfonate, as a simple and eco-friendly process for the preparation of Pd NPs@Fe3O4-lignin, is reported. The Pd NPs@Fe3O4-lignin was characterized by TEM, XRD, EDS, FE-SEM, FT-IR, VSM, and UV-Vis. The Pd NPs@Fe3O4-lignin was employed as exceptional catalysts in the catalytic reduction of Cr(VI) to Cr(III) and Suzuki-Miyaura reaction between PhB(OH)2 and substituted aryl halides in EtOH:H2O as well as under ligand-free conditions in the presence of K2CO3 with satisfactory product yields. Regeneration of the Pd NPs@Fe3O4-lignin was carried out by a magnet after the preparation of biphenyls. Catalytic efficiency retention was achieved after seven cycles.

کلیدواژه ها:

Hibiscus Rosasinensis L. ، Bio-waste ، Pd NPs@Fe3O4-lignin