Magnetically separable silica@Fe3O4 core–shell supported nano-structured copper(II) composites as a versatile catalyst for the reduction of nitroarenes in aqueous medium at room temperature

• Novel magnetically separable silica@Fe3O4 core–shell supported nano-structured copper(II) catalyst synthesized by grafting method.
• Characterizations and application of organic–inorganic hybrid catalyst.
• Efficient method for the degradation of various organic nitro-analogues in aqueous medium at room temperature.
• Catalyst shows high activity and selectivity for concurrent nine reactions.

In this paper, the fabrication of a highly efficient magnetically separable organic–inorganic hybrid nanocatalyst has been reported by covalently immobilizing the copper(II) acetylacetonate complex over amine functionalized silica@magnetite nanoparticles. The prepared nanocatalyst was characterized by electron microscopy techniques (SEM and TEM with EDS), X-ray diffraction (XRD), vibrational sampling magnetometer (VSM), Fourier transform infrared spectroscopy (FT-IR) and atomic absorption spectroscopy (AAS) techniques. The catalytic performance of the resulting nano-composites was examined for the degradation of various organic nitro-analogues in aqueous medium at room temperature using sodium-borohydride as the source of hydrogen. This nano-catalytic system selectively reduces the nitro group even in presence of other sensitive functional groups. To achieve the best catalytic efficacy, various parameters such as catalyst loading, reaction time, effect of various bases and solvents etc. were optimized. The reaction kinetics for the reduction of o-nitroaniline to benzenediamine was studied by UV–vis spectroscopy, and its apparent rate constant was determined and compared with different copper nanocatalysts. The identification of organic residues and purity of the obtained products was analysed by GC–MS. The acquisition of this nanocatalyst has been demonstrated by employing the catalyst in hot filtration and reusability test, and the results obtained from the tests show negligible metal leaching. The nano-catalytic system can be efficiently recovered using simple magnet and reused for multiple cycles without appreciable loss in its catalytic activity. In addition, the stability of the recycled catalyst has been proved by SEM and VSM techniques. It is noteworthy that the key-features like mild reaction conditions, simple work-up procedure, high turnover frequency (TOF), no use of toxic organic solvents, ease in recovery and reusability of the catalyst makes the present protocol more fascinating from an environmental and economic point of view.

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