Influence of doping with Co, Cu and Ni on the morphological and structural parameters and functional properties of ZnO nanoobjects

Abstract

Recently, ZnO nanoobjects (nanoparticles, nanosheets, nanorods, nanoflowers, etc.) have been extensively studied due to their unique dielectric, optical and photocatalytic properties. Appearing on a nanoscale, these properties make ZnO nanoobjects a promising material in optoelectronics, photocatalytic degradation of cyclic pollutants in wastewater and other applications. Introducing 3d elements into the ZnO lattice not only results in appearing additional levels in the band gap, but also significantly impacts the process of nanoobject formation. While many works were devoted to the former issue, the latter has not been fully studied yet, which determined the direction of this work.In this context, we obtained undoped and Cu-, Co- and Ni-doped ZnO nanoobjects by the precipitation method. To study morphological and structural parameters of the samples obtained, they were characterised by a set of methods (XRD, SEM, FTIR, AES-ICP, SSA, XPS, Raman and absorbance spectroscopy). The developed approach was used in order to evaluate the amount of oxygen vacancies and defects in (un)doped ZnO from XPS and Raman spectra. As for functional properties, impedance spectroscopy as well as photoluminescence and photocatalytic activity studies were conducted.In this work, it was discovered that crystallite sizes become greater for doped ZnO nanoobjects and their values depend on the dopant hydroxo complex equilibrium constants. Doping changes a shape of nanoobjects: ZnO, Cu–ZnO and Ni–ZnO are nanosheets of different thickness, but Co–ZnO has a shape of nanoflowers. Oxygen vacancy and defect amount also changes in case of doped samples. As for functional properties, doping leads to an increase of photoluminescence, reduces ZnO nanoobjects’ dielectric losses and enhance photodegradation velocity of methylene blue.The results of the comprehensive study reveal the possibility of changing morphological, structural and consequently, functional parameters of ZnO nanoobjects by varying the chemical nature of the dopant. This leads to new opportunities in developing materials with desired properties.