Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied. 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. Most available anatase TiO(2) crystals are dominated by the thermodynamically stable {101} facets (more than 94 per cent, according to the Wulff construction), rather than the much more reactive {001} facets. 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 TiO(2) 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.

Design and morphological control of crystal facets is a commonly employed strategy to optimize the performance of various crystalline catalysts from noble metals to semiconductors. [1][2][3][4][5][6][7][8] The basis of this strategy is that surface atomic configuration and coordination, which inherently determine their heterogeneous reactivity, can be finely tuned by morphological control.[3] The conventional understanding of the surface atomic structure of a crystal is that facets with a higher percentage of undercoordinated atoms are usually more reactive in heterogeneous reactions. For instance, {001} facets of anatase TiO 2 , which is one of the most important photocatalysts, [9][10][11][12][13][14][15][16][17] are considered to be more reactive than {101}. We have now discovered, by investigating a set of anatase crystals with predominant {001}, {101}, or {010} facets, that, contrary to conventional understanding, clean {001} exhibits lower reactivity than {101} in photooxidation reactions for OH radical generation and photoreduction reactions for hydrogen evolution. Furthermore, the {010} facets showed the highest photoreactivity. However, these three facets had similar photoreactivity when partially terminated with fluorine. We concluded that a cooperative mechanism of surface atomic structure (the density of undercoordinated Ti atoms) and surface electronic structure (the power of photoexcited charge carriers) is the determining factor for photoreactivity. The findings of this work open up new opportunities for maximizing photoreactivity through morphological control of photocatalysts.The predicted shape of anatase crystals under equilibrium conditions is a slightly truncated tetragonal bipyramid, enclosed by a majority of {101} and a minority of {001} facets.[18] In contrast to {101} facets with only 50 % fivecoordinate Ti (Ti 5c ) atoms, {001} facets with 100 % Ti 5c atoms were once considered more reactive in heterogeneous reactions. [19][20][21][22] A breakthrough by Yang et al. in understanding and controlling crystal facets dramatically increased the ratio of {001} to {101} in anatase, as illustrated in Figure 1 a. [8] Other important low-index facets, namely {010} facets, which also have 100 % Ti 5c atoms, may be dominant in the elongated truncated tetragonal bipyramids with appropriate surface chemistry, as predicted by Barnard and Curtiss [23] (see the right panel in Figure 1 a), and which was realized recently. [24,25]

Electronic structure intrinsically controls the light absorbance, redox potential, charge-carrier mobility, and consequently, photoreactivity of semiconductor photocatalysts. The conventional approach of modifying the electronic structure of a semiconductor photocatalyst for a wider absorption range by anion doping operates at the cost of reduced redox potentials and/or charge-carrier mobility, so that its photoreactivity is usually limited and some important reactions may not occur at all. Here, we report sulfur-doped graphitic C(3)N(4) (C(3)N(4-x)S(x)) with a unique electronic structure that displays an increased valence bandwidth in combination with an elevated conduction band minimum and a slightly reduced absorbance. The C(3)N(4-x)S(x) shows a photoreactivity of H(2) evolution 7.2 and 8.0 times higher than C(3)N(4) under lambda > 300 and 420 nm, respectively. More strikingly, the complete oxidation process of phenol under lambda > 400 nm can occur for sulfur-doped C(3)N(4), which is impossible for C(3)N(4) even under lambda > 300 nm. The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of C(3)N(4-x)S(x). The results acquired may shed light on general doping strategies for designing potentially efficient photocatalysts.

New opportunities for the conversion of glycerol into value-added chemicals have emerged in recent years as a result of glycerol's unique structure, properties, bioavailability, and renewability. Glycerol is currently produced in large amounts during the transesterification of fatty acids into biodiesel and as such represents a useful by-product. This paper provides a comprehensive review and critical analysis on the different reaction pathways for catalytic conversion of glycerol into commodity chemicals, including selective oxidation, selective hydrogenolysis, selective dehydration, pyrolysis and gasification, steam reforming, thermal reduction into syngas, selective transesterification, selective etherification, oligomerization and polymerization, and conversion of glycerol into glycerol carbonate.