Mechanism Of Photogenerated Carriers In Nonmetal Doped TiO₂ Revealed By Time-resolved IR Spectroscopy

Revealing the electronic structure of the photocatalysts is fundamental to fully understand the photocatalytic process.The alteration of electronic structure is closely related to the trapped states（localized states）in the band gap.In this thesis,we choose the photogenerated carriers which are from the trapped states as the jumping-off point,and some basic physical and chemical properties of nonmetal doped titanium dioxide photocatalytic materials were studied by the time-resovled infrared absorption spectroscopy.The two main points are as follows:（1）We first characterized the boron doped Ti O₂ by transient infrared absorption-energy excitation scanning spectroscopy.And we found that the B-free surface Ti O₂ can do better in H2 generation during the photocatalytic water splitting,but is not good for O₂ generation.While,we modified the boron from core to surface by heating,the photocatalytic water splitting performance was reversed,that is,O₂ generation of B-containing surface Ti O₂ is better than B-free surface Ti O₂,while H2 generation is weak than the B-free one.In term of the results which are from IR absorption spectra,there are lots of deep trapped levels above the VB in the B-free surface Ti O₂,which decreased the oxidation power of photogenerated holes.B-containing surface,however,no such trapped states level can be found,so the holes here possess much stronger oxidation power.On the other hand,the boron on the surface may act as the electrons acceptor,which prevents the reaction between electrons and protons,leading to poor hydrogen generation.（2）The behavior of photogenerated carriers in the nonmetal nitrogen doped titanium dioxide samples was studied preliminarily by transient infrared absorption spectroscopy.It was found that with the increase of nitrogen concentration,both of the absorption range of the visible light and the absorption coefficient of the sample were increased,but the recombination of photogenerated carriers were increased as well because of the recombination center.In the B/N-Ti O₂（red Ti O₂）samples,the absorption of visible light has been achieved successfully,even in the 525 nm,there were still a large number of photogenerated carriers and they were retaining long lifetime.Under this excitation condition,the number of photogenerated carriers produced by undoped Ti O₂ or B-Ti O₂ or N-Ti O₂ was all less than red Ti O₂,and the lifetime is short than red Ti O₂ as well.