Lignin-Induced Click Synthesis of Au, Ag, Pd, and Iron Oxide Nanoparticles and Their Nanocomposites in Aqueous Bulk and at the Solid–Liquid Interface

Application of lignin in green click synthesis of Au, Ag, Pd, Au–Ag bimetallic, Au–Ag–Pd trimetallic, and Fe3O4–Au–Ag–Pd nanocomposite nanoparticles (NPs) in aqueous bulk as well as at the solid–liquid interface was developed. Crossed-linked lignols of aqueous solubilized lignin or adsorbed at the solid–liquid interface acted as potential electron donors in click reduction of the metal center that depended on the oxidation state, molecular geometry, and oxidizing ability of electron-deficient species. Click reduction occurred in aqueous bulk and at the solid–liquid interface, which was a rapid and thermodynamically driven reaction at room temperature and did not depend on reaction conditions such as pH and temperature. Quantitative information was drawn by using UV–visible, DLS, and IR studies, whereas the elemental composition of different kinds of lignin-stabilized nanomaterials was determined by using TEM, FESEM, and XPS analyses. Au–Ag–Pd trimetallic NPs produced in aqueous bulk or at the solid–liquid interface because of the click reduction were homogenously mixed at the solid–liquid interface but retained the core–shell in aqueous bulk. Lignin-stabilized Fe3O4–Au–Ag–Pd nanocomposite NPs were highly responsive to the external magnetic field. They proved to be excellent vehicles for quick and rapid extraction of KMnO4 from contaminated water, which was highly specific and sustainable.