MAl₂O₄ (M=Ba, Mg) photocatalytic activity dependence on annealing atmosphere

Aluminate spinel type ${{\rm MAl}_2}{{\rm O}_4}$MAl₂O₄ (M=Ba or Mg) materials prepared using the combustion synthesis method were annealed either in an air or carbon atmosphere. The materials were characterized using X-ray diffraction, scanning electron microscopy, diffuse reflectance spectra, electrochemical impedance spectroscopy, and photoluminescence (PL) measurements. Their photocatalytic activity was evaluated for the dye degradation and hydrogen evolution. Methylene blue (15 ppm) was completely degraded using the air-annealed barium aluminate after 90 min, while a maximum hydrogen generation rate of $97 . 0 \;{\rm\unicode{x00B5}{\rm mol}\cdot{\rm h}^{ - 1}\cdot{\rm g}^{ - 1}}$97.0µmol⋅h^-1⋅g^-1 was achieved using the carbon-annealed magnesium aluminate. The results suggest that air-annealed photocatalysts are suitable for oxidation-dependent reactions, while carbon annealing may enhance reduction-dependent reactions.