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Anatase TiO2 single crystals with a large percentage of reactive facets

Abstract

Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied1,2,3,4,5,6,7,8,9,10,11,12,13. Unfortunately, surfaces with high reactivity usually diminish rapidly during the crystal growth process as a result of the minimization of surface energy. A typical example is titanium dioxide (TiO2), which has promising energy and environmental applications14,15,16,17. Most available anatase TiO2 crystals are dominated by the thermodynamically stable {101} facets (more than 94 per cent, according to the Wulff construction10), rather than the much more reactive {001} facets8,9,10,11,12,13,18,19,20. Here we demonstrate that for fluorine-terminated surfaces this relative stability is reversed: {001} is energetically preferable to {101}. We explored this effect systematically for a range of non-metallic adsorbate atoms by first-principle quantum chemical calculations. On the basis of theoretical predictions, we have synthesized uniform anatase TiO2 single crystals with a high percentage (47 per cent) of {001} facets using hydrofluoric acid as a morphology controlling agent. Moreover, the fluorated surface of anatase single crystals can easily be cleaned using heat treatment to render a fluorine-free surface without altering the crystal structure and morphology.

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Figure 1: Slab models and calculated surface energies of anatase TiO 2 (001) and (101) surfaces.
Figure 2: SEM images and statistical data for the size and truncation degree of anatase single crystals.
Figure 3: Crystalline phase determination.
Figure 4: Confirmation of the spatial distribution of F atoms in anatase single crystals.

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Acknowledgements

This work was supported by the Australian Research Council. H.G.Y. wishes to express his gratitude to the National University of Singapore, where the preliminary experimental work was carried out. The authors acknowledge Qiu Hong Hu for her help with statistical analysis.

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Correspondence to Shi Zhang Qiao or Gao Qing Lu.

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Supplementray Information

The file contains Supplementary Notes and Supplementary Figures S1-S8 with legends. The Supplementary Information is divided into two parts: Calculation Section and Experiment Section. Calculation Section contains structural models, computational methods, reliability of methods, extensive test based on (4x4) slab models, stabilization mechanism of fluorine atoms, and additional references. Experiment Section has 5 additional figures (Figure S4-S8 with legends). (PDF 4965 kb)

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Yang, H., Sun, C., Qiao, S. et al. Anatase TiO2 single crystals with a large percentage of reactive facets. Nature 453, 638–641 (2008). https://doi.org/10.1038/nature06964

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