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[ICQM]

[School of Physics]

[Peking University]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fill the pressure gap of photocatalysis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The initial process of heterogenerous photocatalysis is the generation of electron-hole pair in the semiconductor, like TiO2. The enlarge section of the figure shows the excitation of an electron from the valence band to the conduction band by absorbing a photon with energy equal to or greater than the band gap of the semiconductor. Upon excitation, the fate of the separated electron and hole can follow several pathways: bulk recombination, surface recombination, and survivals transporting to the surface. Surface electrons can reduce the acceptors, like reducing H2O to H2, and surface holes can oxidize the donor, like oxidizing CH3OH to CO2. Cited from Yates et al. Photocatalysis on TiO2 surfaces –principles, mechanisms, and selected results. Chem. Rev., 95, 735-758(1995)

 

 

 

 

 

 

 

 

 

 

 

 

 

Model research of photocatalysis is normally in UHV condition, far from the real conditions(~ 1bar), which is called “pressure gap”. Gibbs free energy is dependent on the pressure. From the left equations, we can find that the difference of Gibbs free energy is about 0.3-0.4eV from UHV to real conditions, which is huge for a chemical reaction, and can completely invert a reaction direction. Surface SFG is a photon-in & photon-out method, not limited by the gas phase pressure. But the infrared light is attenuated by the gas absorption, which limits the application of broadband-IR SFG.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We have designed a mini high-pressure chamber with a short light path from the window to the single crystal sample.