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Detecting the Photoactivity of the Rutile TiO2(100)-(1 × 1) Surface by Methanol

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journal contribution
posted on 14.04.2020, 17:03 by Fangliang Li, Xiao Chen, Qing Guo, Dongxu Dai, Xueming Yang
We utilize methanol (CH3OH) photolysis as a probe to identify the photoactivity of rutile (R)-TiO2(100) using the temperature-programmed desorption (TPD) method. Experimental results show that part of CH3OH molecules are likely to adsorb on the surface in the dissociative form. During the TPD process, dissociated methoxy groups (CH3O) at the five-coordinated Ti4+ (Ti5c) sites disproportionate to produce CH3OH and formaldehyde (CH2O) at 675 K. In addition, dissociated H atoms react with CH3OH or dissociated CH3O groups to form H2O on the Ti5c sites and CH3O on the bridging oxygen sites (Ob). Photocatalytic products, such as CH2O and a tiny amount of methyl format (HCOOCH3), have been detected under 355 nm light irradiation. Compared with CH3OH chemistry on the R-TiO2(110) surface, R-TiO2(100) has a much better thermal activity for CH3OH dissociation. However, the photoactivity of R-TiO2(100) for CH3OH photolysis is slightly inferior to that of R-TiO2(110). Two sources may be probably attributed to the discrepancy. One may be due to the dissociated H atoms on the Ob sites, which may act as electron-trapping sites to (electrostatically) attract and neutralize photoexcited holes, thus suppressing the hole-mediated CH3OH photolysis. The other may come from the difference between TiO2 surface structures, which affects the energy barriers of elementary steps in CH3OH photolysis. Our findings provide insightful understanding of the thermal and photocatalytic reactions of CH3OH on the R-TiO2(100) surface.