Ni, Co and Ni–Co codoping induced modification in shape, optical band gap and enhanced photocatalytic activity of CeO2 nanostructures for photodegradation of methylene blue dye under visible light irradiation

Abstract

A simple method has been used to synthesize uneven sizes and shapes of CeO₂ nanostructures by Ni, Co and Ni–Co codoping without using any surfactant. All the samples were further characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) spectroscopy measurements. The Ni–Co codoped CeO₂ nanostructures show broad absorption in the visible range (450–800 nm) as compared to undoped, Ni and Co doped CeO₂ nanostructures. The broad absorption feature (visible range) has made it a suitable material for obtaining enhanced photocatalytic activity under visible light irradiation. Further, Ni–Co codoping reduces the value of the optical band gap of CeO₂ nanostructures sharply from 3.46 to 2.5 eV. The recombination rate of photo-induced electrons and holes for Ni–Co codoped CeO₂ nanostructures is significantly reduced. A more realistic mechanism for superior photocatalytic activity of the Ni–Co codoped CeO₂ nanostructures is also proposed. In the CeO₂ matrix, the Ni and Co ion sites may act as electron and hole trap centers, which essentially improve the separation efficiency of the photo-induced electrons and holes in the Ni–Co codoped CeO₂ nanostructures.