Long‐Lasting Non‐hydrogenated Dark Titanium Dioxide: Medium Vacuum Anneal for Enhanced Visible Activity of Modified Multiphase Photocatalysts

Multiphase TiO2 was stably modified by vacuum treatment for a dramatic improvement in visible‐light absorption and photocatalytic reactivity. The samples were made of rutile‐brookite, bare or N doped, and were grown on reduced graphene oxide. The stable introduction of Ti3+ species and oxygen vacancies resulting in mitigated electron–hole recombination was identified as the main responsible factor, along with a change in surface charges. Anneal appeal: Thermal annealing in medium vacuum (TAMV) results in stable TiO2 that shows irreversible strong visible absorption and enhanced activity for the degradation of 4‐nitrophenol. The introduction of Ti3+ and oxygen vacancies is believed to mitigate electron–hole recombination, and this, in combination with a change in surface charges, is thought to contribute to the enhanced stability. EPR=electron paramagnetic resonance.