Thermal catalytic mechanism for the metal ions(Cu, in, Pd and Pt) modified TiO2 on degradation of HCHO

Four metal ions (M: Pt, Pd, Cu and In) modified TiO2 (TiO2-M) thermal catalysts were prepared. The metal ions exist on the surface of TiO2 as O-M-O and/or O-M-Cl species. TiO2–Pd and TiO2–Pt samples exhibit much better thermal catalytic activity than TiO2, TiO2–Cu and TiO2–In. Due to the efficient thermal excited electrons transfer from the valence band to the conduction band through quasi-continuous energy levels of Pd or Pt species, the TiO2–Pd and TiO2–Pt catalysts exhibited significant thermal catalytic activity for degradation of HCHO. Furthermore, the relationship between band structure and redox ability of thermal charge carriers for TiO2-M, as well as the generation ability of ROS (reactive oxygen species, for instance, O2− and·OH) in thermal catalysis system are investigated systematically. This work revealed that the quasi-continuous energy level in the band gap of semiconductors is one of the key factors to achieve efficient thermal catalytic performance over thermal-functional materials.