Liquid N2 quenching induced oxygen defects and surface distortion in TiO2 and the effect on the photocatalysis of methylene blue and acetone

In the current research, TiO2 materials pre-annealed at high temperatures were subject to fast super-cold quenching in liquid N2, with the effect on their structures and photocatalytic properties being studied. Although the liquid N2 quenching did not change the crystalline structure, morphologies, and specific surface area of TiO2 materials, some local disorders and lattice distortion were caused on the TiO2 surfaces. It has been revealed that the quenching process led to a change in surface structure of anatase that is greater than rutile. Clear experimental proofs showed that more oxygen defects were introduced in anatase than in rutile. It was interesting to see that the quenching induced oxygen defects had different effects on the photocatalysis under aqueous and gaseous conditions. For the aqueous photocatalysis of methylene blue, the oxygen defects led to a decrease in the photocatalysis over anatase, while led to an increase over rutile. By contrast, the acetone gaseous photocatalysis over anatase TiO2 could be increased by ~2 times by the quenching induced oxygen defects, and independent on the quenching or not, rutile TiO2 almost inactive to gaseous acetone.