N-doped P25 TiO2–amorphous Al2O3 composites: One-step solution combustion preparation and enhanced visible-light photocatalytic activity

Abstract Nitrogen-doped Degussa P25 TiO 2 –amorphous Al 2 O 3 composites were prepared via facile solution combustion. The composites were characterised using X-ray diffraction, high-resolution transmission microscopy, scanning electron microscopy, nitrogen adsorption–desorption measurements, X-ray photoelectron spectroscopy, UV–vis light-diffusion reflectance spectrometry (DRS), zeta-potential measurements, and photoluminescence spectroscopy. The DRS results showed that TiO 2 and amorphous Al 2 O 3 exhibited absorption in the UV region. However, the Al 2 O 3 /TiO 2 composite exhibited visible-light absorption, which was attributed to N-doping during high-temperature combustion and to alterations in the electronic structure of Ti species induced by the addition of Al. The optimal molar ratio of TiO 2 to Al 2 O 3 was 1.5:1, and this composite exhibited a large specific surface area of 152 m 2 /g, surface positive charges, and enhanced photocatalytic activity. These characteristics enhanced the degradation rate of anionic methylene orange, which was 43.6 times greater than that of pure P25 TiO 2 . The high visible-light photocatalytic activity was attributed to synthetic effects between amorphous Al 2 O 3 and TiO 2 , low recombination efficiency of photo-excited electrons and holes, N-doping, and a large specific surface area. Experiments that involved radical scavengers indicated that OH and O 2 − were the main reactive species. A potential photocatalytic mechanism was also proposed.