Solution combustion synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl2O4 nanopowders

Abstract Mixed amorphous and crystalline MgAl 2 O 4 nanopowders with visible light-induced photocatalytic activity were prepared via a simple solution combustion method using glycine and urea as fuel mixtures. The obtained samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, Brunauer–Emmett–Teller (BET) surface area, thermogravimetry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV–Vis diffuse reflection spectrum. The results showed that the combustion was almost complete, the crystallinity and crystallite size of MgAl 2 O 4 increased with the increase of fuels, and there was N atoms doped in the catalysts. The MgAl 2 O 4 containing amorphism had photo-absorption ability in visible light region. The photocatalytic results for degradation of methylene blue (MB) indicated that the combustion-synthesized samples had photocatalytic activity, whereas the annealed well crystalline MgAl 2 O 4 nanopowders had none. The MgAl 2 O 4 sample containing about 45.6% crystalline and 55.4% amorphous materials showed the highest photocatalytic activity, with a 99.5% MB removal in 100 min under visible light irradiation. The fluorescence spectra verified that the greater the formation rate of OH radicals, the higher the photocatalytic activity achieved.