Catalytic reduction of nitroarenes under aqueous conditions using magnetically reusable Co3O4 nanoparticles

Biogenic synthesis of magnetically separable Co3O4 nanoparticles (Co3O4@PH NPs) has been reported using aqueous extract of Parthenium hysterophorus (PH) leaves as inexpensive and sustainable stabilizer as well as capping agent. Co3O4@PH NPs were further characterized by various analytical techniques viz. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), UV-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM) etc. XRD studies revealed the cubic spinel structure and HRTEM analysis indicated the spherical shape of the prepared Co3O4@PH NPs with an average size of 1.9 nm. The functional groups responsible for capping and stabilizing NPs identified were indicated by the FTIR analysis. The VSM analysis showed that the nanoparticles were super-magnetic in nature. Furthermore, synthesized NPs were explored for the catalytic reduction of substituted nitroarenes to corresponding amines tolerating various functionalities under mild conditions in aqueous media. The developed catalyst was heterogeneous in nature, magnetically separable and showed recyclability (up to 5 cycles) without any significant loss in catalytic activity. The green synthesis, gram scale reactions (1 g scale), high isolated yields (80-90 %), high TON/TOF values, and applicability for the complex molecules showed the utility of the developed method for sustainable transformations. A comparison of current method was also done with the existing biogenic nanoparticle-based catalytic systems for the reduction of nitro compounds.