Nanostructured mesoporous NiO as an efficient photocatalyst for degradation of methylene blue: Structure, properties and performance

Abstract

Nanostructured NiO with an average crystallite size ∼2–3 nm is synthesized through a two step process. X-ray diffraction analysis reveals high value of microstrain indicating the presence of large concentration of point defects. Sample is found to be mesoporous with a high specific surface area of 187.27 m2/g. Raman and Infrared spectra shows the presence of surface modes and forbidden vibrations respectively due to the small size and broken symmetry. Ni 2p and O 1s X-ray photoelectron spectra confirms the presence of large percentage of Ni2+ vacancies. UV–visible absorption spectra show efficient absorption in both ultraviolet and visible regions, while, Photoluminescence emission spectra show two emission bands characteristic of O2− vacancies. DC electrical conductivity studies reveal the semiconducting nature of the sample. The sample is found to be an efficient photocatalyst for the degradation of methylene blue in water with a pseudo first order rate constant of k=1.97×10−2 min−1. It is proposed that the high surface area, efficient absorption in the ultraviolet and visible regions and presence of Ni2+ and O2− vacancies leads to the efficient photocatalytic activity.