We report a green synthesis of magnetically separable hybrid metal nanobiomaterial as water dispersible and recyclable catalysts. The hybrid nanobiomaterial was prepared in a three-step process. The magnetic nanoparticles were initially synthesized by biomineralization process and coated with chitosan followed by binding and reduction of metal ions, which led to the formation of a magnetically separable hybrid nanobiomaterial (Fe3O4@Ch-MNPs, M = Au, Pd). The chemical composition, morphology, thermal stability, and magnetic behavior of the hybrid nanobiomaterial were characterized with zeta potential, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and field emission scanning electron microscopy (FESEM) analysis. The FESEM measurement demonstrated formation of highly dispersed Au and PdNPs on the surface of nanobiomaterial, while thermogravimetric and VSM analyses indicated high thermal stability and superparamagnetic behavior of the hybrid nanobiomaterial. The X-ray photoelectron spectroscopy studies revealed formation of pure metallic nanoparticles on the surface of the hybrid nanobiomaterial. The as-synthesized hybrid nanobiomaterial were tested for several model reactions such as photocatalytic reduction of dye, hydrogenation of p-nitrophenol, and Suzuki coupling reaction at ambient temperature and in aqueous solution. The catalytic efficiencies varied with the type of MNPs, and Fe3O4@Ch-PdNPs exhibited superior catalytic activities in all chemical reactions. In addition the hybrid nanobiomaterial demonstrated excellent recyclability and reusability without significant loss of catalytic activities. Furthermore, the leaching of metal ions was not detected during catalytic reaction confirming high stability and low environmental impact of the as-synthesized hybrid nanobiomaterial. We believe that our result will help to synthesize easily separable hybrid nanobiomaterial as a heterogeneous catalyst through a cost-effective and eco-benign synthetic route for the development of environmental sustainable nanotechnology.

Increasing demand of noble-metal nanoparticles (MNPs) in catalysis research urges the development of a nontoxic, clean, and environmentally friendly methodology for the production of MNPs on solid surface. Herein we have developed a facile approach for biosynthesis of MNPs (Pd, Pt, and Ag) on the surface of Rhizopous oryzae mycelia through in situ reduction process without using any toxic chemicals. The size and shape of the biosynthesized MNPs varied among the MNPs, and "flower"-like branched nanoparticles were obtained in case of Pd and Pt, while Ag produced spheroidal nanoparticles. The cell-surface proteins of the mycelia acted as protecting, reducing, and shape-directing agent to control the size and shape of the synthesized MNPs. Proteins of 78, 62, and 55 kDa were bound on the MNPs surfaces and played a significant role in determining the morphology of the MNPs. The catalytic efficiency varied among the MNPs, and Pd nanoflower exhibited superior catalytic activities in both hydrogenation and Suzuki coupling reactions. Surface composition, concentration, and intracellular localization of MNPs determine the catalytic activity of the biosynthesized MNPs. The nanocatalyst could be easily separated and reused multiple times without significant loss in activity (95% average conversion). Overall, the understanding of this complex biomineralization mechanism and catalytic behavior at the nano−bio interface has provided an alternative for the synthesis of supported metal nanocatalyst to improve the environmental sustainability.

In this article, we reported the synthesis of thermoresponsive palladium nanoparticles, stabilized by polymer‐tagged N‐heterocyclic carbenes (NHCs), using two different approaches. In one case, the nanoparticles were synthesized from the NHC–palladium complex, while in other cases, palladium nanoparticles and NHC were synthesized simultaneously for the in situ cappings of the nanomaterial. While the thermoresponsive nature of the nanomaterials was observed in both cases, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) analyses showed distinct characteristics in the thermal behavior of those materials. High‐resolution transmission electron microscopic (HRTEM) and scanning electron microscopic studies separately revealed temperature‐dependent aggregation in both cases although separate patterns were observed when the nanomaterials were synthesized using different approaches. Finally, both the nanomaterials were successfully used as a recyclable catalyst for Suzuki reactions in an aqueous medium, with slightly different catalytic activity, plausibly due to variations in the size of the nanoparticles.