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.

Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen‐ and oxygen‐containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H2SO4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X‐ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea‐ and melamine‐treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 Å. On the other hand, pores between 5 Å and 6 Å are most effective in a double‐layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic‐N‐oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen.

We developed two-step solution-phase reactions to form hybrid materials of Mn 3 O 4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn 3 O 4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn 3 O 4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn 3 O 4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn 3 O 4 nanoparticles grown atop. The Mn 3 O 4 /RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Owing to wide-ranging industrial applications and fundamental importance, tailored synthesis of well-faceted single crystals of anatase TiO(2) with high percentage of reactive facets has attracted much research interest. In this work, high-quality anatase TiO(2) single-crystal nanosheets mainly dominated by {001} facets have been prepared by using a water-2-propanol solvothermal synthetic route. The synergistic functions of 2-propanol and HF on the growth of anatase TiO(2) single-crystal nanosheets were studied by first-principle theoretical calculations, revealing that the addition of 2-propanol can strengthen the stabilization effect associated with fluorine adsorption over (001) surface and thus stimulate its preferred growth. By measuring the (*)OH species with terephthalic acid scavenger, the as-prepared anatase TiO(2) single-crystal nanosheets having 64% {001} facets show superior photoreactivity (more than 5 times), compared to P25 as a benchmarking material.

Flexible energy storage devices 1Ϫ3 have many potential applications in portable electronic devices, 4Ϫ6 including roll-up display, electronic paper, stretchable integrated circuits, and wearable systems for personal multimedia, computing, or medical devices. Flexible supercapacitors are available with large power density, moderate energy density, good operational safety, and long cycling life and hence are highly desirable as a modern energy storage system. 7 A freestanding binder-free electrode with favorable mechanical strength and large capacitance is a vital component of a flexible supercapacitor. Although transition metal oxides and conducting polymers have been widely studied as supercapacitor electrode materials, only carbon-based materials have shown favorable flexibility and hence been promising as freestanding soft electrodes. Papers, films, and/or clothes made from carbon nanotubes/fibers have been demonstrated to be suitable as freestanding electrodes.2,8Ϫ13 Nevertheless, the less active surface of carbon materials always prevents them from high capacitance performance. The incorporation of an electrochemically active second phase in a carbonbased freestanding electrode can dramatically enhance the electrode capacitance.14 Graphene is an intriguing twodimensional carbon material and has attracted much research attention due to several breakthroughs in fundamental research and promising practical applications. 15Ϫ30Chemical modified graphene exhibits enormous active edges and oxygen functional groups. It has extraordinary electrochemical and mechanical properties comparable to or even better than carbon nanotubes. 21,26,27 Flexible papers with graphene sheet or graphene oxide sheet as sole building block have already been fabricated by flow-directed assembly. 16,25,31,32 Graphene paper presents excellent tensile modulus up to 35 GPa and room temperature electrical conductivity of 7200 S m Ϫ1. 25 These intriguing characteristics enable graphene paper as a freestanding electrode. Various conducting polymers have been widely studied as electrode materials for supercapacitors because of their high capacitance, easy production, and low cost. However, poor conductivity and weak flexibility of conducting polymers limit them from usage in high-performance flexible supercapacitors. It has been confirmed that graphene can enhance not only the electric conductivity of silica 18 but especially the mechanical strength of polymer composites. 21 This work is aimed to prepare graphene-conducting polymer composite paper as a flexible electrode combining the advantages of graphene paper (high