Green synthesis of reduced graphene oxide anchored Fe3O4‐Pd hetero‐nanostructure: An efficient, magnetically separable and reusable catalyst for Beckmann rearrangement of aldoximes to amides

Abstract

The multifaceted Fe3O4‐Pd@rGO nanocomposite (NC) has been synthesized successfully by a biogenic method using Ocimum tenuiflorum leaf extract. The preparation of graphene oxide (GO) was done by the well‐known modified Hummer method. The as‐synthesized Fe3O4‐Pd@rGO NC was extensively characterized by various analytical techniques, namely, Fourier transform infrared (FTIR), X‐ray diffraction (XRD), field emission scanning electron microscopy‐energy‐dispersive X‐ray spectroscopy (FESEM‐EDX), high‐resolution transmission electron microscopy (HRTEM), inductively coupled plasma‐atomic emission spectrometry (ICP‐AES), X‐ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM) and Brunauer–Emmett–Teller (BET) surface area analysis. The absence of peak corresponding to υ(CO) at 1732 cm−1 in the FTIR spectrum of Fe3O4‐Pd@rGO enumerates the reduction of GO to reduced graphene oxide (rGO) during Fe3O4‐Pd nanoparticle (NP) synthesis with O. tenuiflorum leaf extract. The XRD pattern reveals the existence of rGO, cubic‐phased spinel‐structured Fe3O4 along with the formation of metallic Pd NP without any impurities. The FESEM image designates the spherical and flake‐like morphology of the NC. The crystallite size of the NC was calculated employing the Debye–Scherrer equation and was found to be 3.45 nm corresponding to the (220) plane. The average particle size of Fe3O4‐Pd NPs as estimated from the particle size distribution curve was ascertained as 3.03 nm. The utmost saturation magnetization value of the NC as evaluated by VSM study has appeared at 0.6219 emu g−1 having coercivity value of 335.1 Oe and remanent magnetization value of 0.0767 emu g−1, suggesting the existence of a ferromagnetic material in the synthesized NC. It was a stable and highly efficient catalyst for Beckmann rearrangement of aldoximes using in an environment‐friendly medium. It afforded up to 99% isolated yield of the preferred products under acid‐free condition, avoiding the use of any harsh chemicals that will be beneficial for future industrial applications. Finally, the magnetic component of the NC allowed for easy recovery of the catalyst, thereby eliminating the chance of leaching of metal atoms, and was reusable till six successive cycles without apparent loss of its catalytic performance.