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As the photo-dissociation product of methanol on the TiO2 (110) surface, the diffusion and desorption processes of formaldehyde (HCHO) were investigated by using scanning tunneling microscope (STM) and density functional theory (DFT). The molecular-level images revealed the HCHO molecules could diffuse and desorb on the surface at 80 K under UV laser irradiation. The diffusion was found to be mediated by hydrogen adatoms nearby, which were produced from photodissociation of methanol. Diffusion of HCHO was significantly decreased when there was only one H adatom near the HCHO molecule. Furthermore, single HCHO molecule adsorbed on the bare TiO2(110) surface was quite stable, little photo-desorption was observed during laser irradiation. The mechanism of hydroxyl groups assisted diffusion of formaldehyde was also investigated using theoretical calculations.

Photocatalytic dissociation of ethanol molecules on the rutile TiO2(110) surface after UV irradiation has been investigated by scanning tunneling microscope at 80 K. Most of the ethanol molecules adsorb molecularly at Ti sites, similar to the case of methanol. After UV irradiation, two different protrusions of products were observed, one of them has been identified by the technique of tip manipulation, which was likely composed of an acetaldehyde in the middle and two bridge-bonded hydroxyls on both neighbored oxygen sites. Multi-time irradiation experiments have also been performed to further understand the relationship between the two protrusions and the process of ethanol photocatalytic dissociation. These results provide detailed insights into the photocatalysis of ethanol on rutile TiO2(110), which would help us to understand how phtotocatalytic reactions of ethnaol proceed at the fundamental level.

The electronic structure of methanol/TiO2(110) interface has been studied by photoemission spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy (2PPE) is associated with the photocatalyzed dissociation of methanol at fivefold coordinated Ti sites (Ti5c) on TiO2(110) surface [Chemical Science 1, 575 (2010)]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently suggest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive characterization of the excited states on methanol/TiO2(110) interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.

the kinetics and dynamics of photocatalyzed dissociation of ethanol on tio2(110) surface have been studied using the time-dependent and time-resolved femtosecond two-photon photoemission spectroscopy respectively, in order to unravel the photochemical properties of ethanol on this prototypical metal oxide surface. by monitoring the time evolution of the photoinduced excited state which is associated with the photocatalyzed dissociation of ethanol on ti-5c sites of tio2(110), the fractal-like kinetics of this surface photocatalytic reaction has been obtained. the measured photocatalytic dissociation rate on reduced tio2(110) is faster than that on the oxidized surface. this is attributed to the larger defect density on the reduced surface which lowers the reaction barrier of the photocatalytic reaction at least methodologically. possible reasons associated with the defect electrons for the acceleration have been discussed. by performing the interferometric two-pulse correlation on ethanol/tio2(110) interface, the ultrafast electron dynamics of the excited state has been measured. the analyzed lifetime (24 fs) of the excited state is similar to that on methanol/tio2(110). the appearance of the excited state provides a channel to mediate the electron transfer between the tio2 substrate and its environment. therefore studying its ultrafast electron dynamics may lead to the understanding of the microscopic mechanism of photocatalysis and photoelectrochemical energy conversion on tio2.