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Synchronous illumination X-ray photoelectron spectroscopy (SIXPS) was employed for the first time to directly identify the photogenerated charge separation and transfer on anatase TiO2 single-crystals with selectively etched 001 facets. More specifically, for the TiO2 crystals with intact 001 and 101 facets, most of photogenerated charge carriers rapidly recombined, and no evident electron-hole separation was detected. With selectively etching on 001 facets, high efficient charge separation via hole transfer to titanium and electron to oxygen was clearly observed. However, when the 001 facets were completely etched into a hollow structure, the recombination for photogenerated electron-hole pairs would dominate again. These demonstrations clearly reveal that the appropriate corrosion on 001 facets could facilitate more efficient electron-hole separation and transfer. As expected, the optimized TiO2 microcrystals with etched 001 facets could achieve a hydrogen generation rate of 74. 3 μmol/h/g, which is nearly 7 times higher than the intact-TiO2 crystals.
Liu et al. (Mon,) studied this question.