Anatase TiO2 single crystals with a large percentage of reactive facets

Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied(1-13). 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 applications(14-17). Most available anatase TiO2 crystals are dominated by the thermodynamically stable {101} facets ( more than 94 per cent, according to the Wulff construction(10)), rather than the much more reactive {001} facets(8-13,18-20). 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-