New synthesis route of Cu-CuO-Ni nano-heterostructures for hydrogenation and chromium reduction reactions

A simple one-pot aqueous phase chemical reduction has been used for the successful synthesis of flower-like Cu-CuO-Ni heterostructures. X-ray diffraction analysis and X-ray photoelectron spectroscopy confirms the presence of metallic copper, nickel and monoclinic copper oxide (CuO) in the sample with traces of Cu(OH)₂. Scanning electron microscope images confirms the flower like morphology of the Cu-CuO-Ni nanoheterostructures. For the first time, Cu-CuO-Ni nanocrystals were employed as a new heterogeneous efficient nanocatalyst for the hydrogenation reduction of 4-nitrophenol (4-NP) and reduction of chromium (VI) (Cr) to chromium (III). The synthesized Cu-CuO-Ni nanocrystals showed highest catalytic properties with an activity factor of 0.0088 s^-1 mg^-1for reduction of 4-nitrophenol and 0.057 min^-1for chromium reduction reaction. The XRD and XPS analysis of the catalytically recycled samples suggests the higher catalytic stability of Cu-CuO-Ni nanocrystals. In comparison to the bare CuO and CuO- Ni nanocrystals the maximum catalytic activity was shown by Cu-CuO-Ni nanocrystals. The improved catalytic activity was found to be due to the combined effect of morphological and compositional differences. The commendable catalytic efficiency along with the facile synthetic approach and the use of low-cost copper and nickel significantly reduces the cost of the catalytic process. The stability of the Cu-CuO-Ni catalyst system for the chromium reduction reactions was monitored by conducting recyclability test for three times. Therefore, the developed Cu-CuO-Ni nanocatalyst offers significant applications in waste water treatment systems and other industrial applications.