Surfactant-aided sol–gel synthesis of mesoporous-assembled TiO2–NiO mixed oxide nanocrystals and their photocatalytic azo dye degradation activity

Abstract

In this work, the mesoporous-assembled TiO2–NiO mixed oxide nanocrystals were successfully synthesized by a sol–gel process with the aid of a structure-directing surfactant under mild conditions. The photocatalytic activity of the synthesized mixed oxide nanocrystals for degradation of Methyl Orange (MO) azo dye used as a model wastewater contaminant was investigated under UV light irradiation. The synthesized mixed oxide nanocrystals were systematically characterized by TG-DTA, N2 adsorption–desorption analysis, SEM-EDX, XRD, and UV–visible spectroscopy. The photocatalytic activity results showed that the incorporation of NiO phase with a suitable content into the TiO2–NiO mixed oxide increased the photocatalytic MO degradation efficiency. It was found that the mesoporous-assembled Ti75–Ni25 mixed oxide nanocrystal (with 75mol % TiO2 and 25mol % NiO) provided a maximum MO degradation efficiency as compared to the other investigated nanocrystals as well as the commercial P-25 TiO2 powder. The induced n–p junction at the interfacial contact between the TiO2 and NiO phases in the Ti75–Ni25 mixed oxide nanocrystal is supposed to efficiently prevent the electron–hole recombination upon the UV light excitation and consequently enhance its photocatalytic degradation activity.