Surface characteristics and electronic structure of photocatalytic reactions on TiO_2 and doped TiO_2 nanoparticles

摘要

A molecular approach to understand the photocatalytic degradation of small organic molecules adsorbed from the gas phase on anatase, rutile and doped TiO_2 nanoparticles is presented. Using in situ Fourier transform infrared (FTIR) spectroscopy and mass spectrometry the rate determining steps for the photocatalytic degradation of formic acid, acetone and propane are unraveled. Key intermediates are identified and correlated to structural properties of the TiO_2 nanoparticles. Specifically, stable bridging bidentate carboxylate (R-CO_2) and (bi)carbonate species forms preferentially on rutile particles, and are proposed to inhibit the total photodegradation efficiency. In particular, the concentration of R-CO_2 is found to decrease with increasing size of the anatase particles, and may at least partly explain why Degussa P25 is a good photocatalyst. Means to avoid R-CO_2 site-blocking is discussed. Improved solar light efficiencies are difficulty to achieve in cation doped TiO_2 despite higher visible light absorption and stronger adsorbate-surface interactions.