High quantum efficiency of photocatalytic water oxidation over the TiO2/MMO nanocomposite under visible-light irradiation

The titanium dioxide/ZnAl-layered double hydroxide (TiO2/ZnAI-LDH) nanocomposite was first prepared using the co-precipitation method, and the TiO2/metal mixed oxide (TiO2/MMO) was then fabricated by annealing the TiO2/ZnAl-LDH nanocomposite at 430 degrees C. The obtained materials were characterized by means of techniques, such as field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-visible diffuse reflectance spectroscopy (DRS), and N-2 adsorption-desorption (BET). Photocatalytic activities of the TiO2/MMO nanocomposite was evaluated for O-2 generation from aqueous solutions in the presence of AgNO3 (1 mmol) as the sacrificial agent at neutral pH and room temperature under visible-light irradiation. It is found that photocatalytic activity of the TiO2/MMO sample was better than that of the TiO2/ZnAl-LDH sample, which could be attributed to the reduction in bandgap energy, low electron-hole recombination, and high surface area. An O-2 generation rate of 371 pmol/(g h) was achieved over 20 mg of the TiO2/MMO nanocomposite photocatalyst, and the quantum efficiency for O-2 generation was 84% at 400 nm. Such a quantum efficiency was the highest value obtained over the TiO2/MMO sample under visible-light illumination. This study presents a novel approach for water oxidation using the visible-light-responsive TiO2/MMO nanocomposite photocatalyst, which might be applied as a promising candidate in solar energy conversion and environmental science for highly efficient O-2 generation. (C) 2019 Elsevier B.V. All rights reserved.