Stepwise Growth of Copper-Based Coordination Polymer on α-MnO2 Nanorods for Sustainable Reduction of Nitroarenes

Abstract

Metal oxide/coordination polymer composites have gained great attraction due to their synergistic effects to increase their efficiency in various fields. In this work, a Cu-based coordination polymer (Cu-CP) was grown on the surface of α-MnO2 nanorods via stepwise assembly of benzene-1,4-dicarboxylic acid (H2BDC) as a ligand and a Cu(II) ion as a metal center. Comprehensive characterization techniques confirmed the successful growth of Cu-CP on the surface of α-MnO2 without affecting the morphology of pristine α-MnO2 nanorods. The obtained nanocomposite (α-MnO2/Cu-CP) revealed outstanding activity in the catalytic reduction of nitroarenes to aminoarenes under mild reaction conditions and afforded wide substrate applicability (more than 99% for nitrobenzene and 70–99% for other substituted nitroarenes during 1 h at room temperature). Importantly, α-MnO2/Cu-CP served as a better catalyst than bare α-MnO2 and Cu-CP due to the synergistic effects between building components. In addition, α-MnO2/Cu-CP was easily separable by centrifugation and its catalytic activity remained unaffected over five cycles. The use of water as a sustainable and green solvent and non-toxic and inexpensive metals used for the synthesis of the catalyst along with easy recovery and stability of the catalyst make the present protocol economical and sustainable. The time-dependent reduction kinetics followed pseudo-first-order kinetics with respect to the substrates.