Composition Dependence of Structural, Optical, Magnetic and Photodegradation Properties of Nanocrystalline NiO/CuO Heterostructured Powders

Nanocrystalline NiO/CuO solid solutions and heterostructured powders are prepared by a sol-gel auto combustion method. Herein, the NiO/CuO compounds at various molar ratio, including 100/0, 97.5/2.5, 95/5, 92.5/7.5, 90/10, 80/20, 50/50, 20/80, 10/90, 5/95 and 0/100, are investigated. The structures, morphologies, optical, and magnetic properties of all samples are explored. The detailed structures of the NiO/CuO system are deduced from Rietveld refinements of X-ray diffraction (XRD) data and the combination of experimental and simulation studies of X-ray absorption spectroscopy (XAS) spectra. It is found that a small addition of CuO in NiO enhances the formation of rock salt CuxNi1-xO solid solutions with 0 <= x <= 0.1. The NiO/CuO composites with CuO mole fractions (m) of 20% <= m <= 95% are affirmed by the coexistence of NiO rock salt and CuO tenorite phases. The composites rich in CuO exhibit strong adsorption in the visible and ultraviolet spectral regions, while the absorption of composites rich in NiO is absent in certain regions of visible and infrared light. In addition, the superparamagnetism of NiO can be tuned to ferromagnetism by a small addition of CuO. The photocatalytic degradation efficiencies of rhodamine B, methylene blue, methyl orange, and methyl red over NiO/CuO reach 92%-97% within a period of 150 min under sunlight irradiation.