The ability of uranium to undergo nuclear fission has been exploited primarily to manufacture nuclear weapons and to generate nuclear power. Outside of its nuclear physics, uranium also exhibits rich chemistry, and it forms various compounds with other elements. Among the uranium-bearing compounds, those with a uranium oxidation state of +6 are most common and a particular structural unit, uranyl UO(2)(2+) is usually involved in these hexavalent uranium compounds. Apart from forming solids with inorganic ions, the uranyl unit also bonds to organic molecules to generate uranyl-organic coordination materials. If appropriate reaction conditions are employed, uranyl-organic extended structures (1-D chains, 2-D layers, and 3-D frameworks) can be obtained. Research on uranyl-organic compounds with extended structures allows for the exploration of their rich structural chemistry, and such studies also point to potential applications such as in materials that could facilitate nuclear waste disposal. In this Account, we describe the structural features of uranyl-organic compounds and efforts to synthesize uranyl-organic compounds with desired structures. We address strategies to construct 3-D uranyl-organic frameworks through rational selection of organic ligands and the incorporation of heteroatoms. The UO(2)(2+) species with inactive U═O double bonds usually form bipyramidal polyhedral structures with ligands coordinated at the equatorial positions, and these polyhedra act as primary building units (PBUs) for the construction of uranyl-organic compounds. The geometry of the uranyl ions and the steric arrangements and functionalities of organic ligands can be exploited in the the design of uranyl--organic extended structures, We also focus on the investigation of the promising physicochemical properties of uranyl-organic compounds. Uranyl-organic materials with an extended structure may exhibit attractive properties, such as photoluminescence, photocatalysis, photocurrent, and photovoltaic responses. In particular, the intriguing, visible-light photocatalytic activities of uranyl-organic compounds are potentially applicable in decomposition of organic pollutants and in water-splitting with the irradiation of solar light. We ascribe the photochemical properties of uranyl-organic compounds to the electronic transitions within the U═O bonds, which may be affected by the presence of organic ligands.

Lithium-ion batteries are regarded as promising energy storage devices for next-generation electric and hybrid electric vehicles. In order to meet the demands of electric vehicles, considerable efforts have been devoted to the development of advanced electrode materials for lithium-ion batteries with high energy and power densities. Although significant progress has been recently made in the development of novel electrode materials, some critical issues comprising low electronic conductivity, low ionic diffusion efficiency, and large structural variation have to be addressed before the practical application of these materials. Surface and interface engineering is essential to improve the electrochemical performance of electrode materials for lithium-ion batteries. This article reviews the recent progress in surface and interface engineering of electrode materials including the increase in contact interface by decreasing the particle size or introducing porous or hierarchical structures and surface modification or functionalization by metal nanoparticles, metal oxides, carbon materials, polymers, and other ionic and electronic conductive species.

Mesoporous titania and titania nanotubes, with high surface-to-volume ratios, have recently been reported to demonstrate improved properties compared to colloids, films and other forms of titania in applications such as photocatalysts, [1,2] gas sensors, [3] photovoltaic cells [4][5][6] and rechargeable lithium batteries. [7][8][9][10] Therefore, particular attention has been paid to the preparation of titania nanotubes, or arrays of tubes, and many methods have been developed including the hydrothermal treatment of TiO 2 nanoparticles with alkali solution, [8][9][10][11][12][13] anodization of titanium foil, [14,15] deposition of sol-gels within templates, [16][17][18] hydrolysis of TiF 4 under acidic conditions, [19] sonication of titania particles in aqueous NaOH solution, [20] and surfactant-assisted templating methods. [21,22] Materials with mesoporous structures possess an extraordinarily high surface area. The synthesis of titania nanotubes, with mesoporous walls and hence high surface areas, will be invaluable for all applications employing the wide bandgap semiconductor. Therefore, there is a requirement for the development of a facile and reproducible way to prepare titania nanotubes with well-defined mesoporous wall structures. We have previously shown that one-dimensional mesoporous silica nanotubes and nanowires can be fabricated inside the pores of anodic aluminum oxide (AAO) membranes.[23] Recently, Chae et al. reported the preparation of titania nanofibres with wormhole-like mesoporous structure using AAO as a 'hard template'. [24] Even though mesoporous SiO 2 nanotubes and titania nanofibres have been prepared, the fabrications of TiO 2 nanotubes with well ordered mesopores are still a challenge because of the complexity of sol-gel chemistry. Herein, we report the preparation of titania nanotubes with mesoporous walls within AAO membranes and their application in a high rate rechargeable lithium battery. Well-aligned titania nanotube arrays were fabricated via a drying process utilizing supercritical CO 2 after the dissolution of the membranes. These mesoporous titania nanotubes, with a 3-dimensional (3D) network structure, were investigated as the electrode material of a rechargeable lithium battery. The structure of the mesoporous nanotubes was specifically designed to allow efficient transport of both lithium ions and electrons, which are necessary for a high rate rechargeable battery. The experimental results obtained proved that the mesoporous nanotube structure plays an important role in the efficiency of the high rate performance of the battery. Scanning electron microscope (SEM) images of the titania nanotubes annealed at 150°C are shown in Figure 1. Well-defined nanotubes are observed occupying most of the pores of the AAO. The size and uniformity of the nanotubes fabricated by this templating method are closely related to the pore size and quality of the alumina membranes employed.[17] Nanotubes prepared within a 0.2 lm Whatman AAO membrane have an outer diameter of approximately 200 nm...

Uniform porous silicon hollow nano-spheres are prepared without any sacrificial templates through a magnesio-thermic reduction of mesoporous silica hollow nanospheres and surface modified by the following in situ chemical polymerization of polypyrrole. The porous hollow structure and polypyrrole coating contribute significantly to the excellent structure stability and high electrochemical performance of the nanocomposite.

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Effective conversion of methane to a mixture of more valuable hydrocarbons and hydrogen under mild conditions is a great scientific and practical challenge. [1][2][3][4][5][6][7] Up to date, the thermal routes for activation of the strong CÀH bond (104 kcal mol À1 ) in methane require high temperatures and multistep processes, and therefore they are energy-consuming and inefficient. [8,9] Compared to methods powered by thermal energy, [10][11][12][13][14] techniques that use photonic energy have substantial advantages, such as the capacity to minimize coking at room temperature. A promising approach to methane conversion is the direct non-oxidative coupling of methane (NOCM) to form ethane and hydrogen powered by photons [Equation (1)]. [15,16] 2 CH 4The produced ethane can in turn be conveniently converted to liquid fuels or ethene through metathesis and dehydrogenation, respectively. [17] Furthermore, this NOCM reaction is the best way to produce clean H 2 energy from fossil fuels because methane has the highest H/C ratio among all hydrocarbons. However, the methane conversion using photocatalysts previously reported for the NOCM reaction is very low (less than 4 % upon UV irradiation for 90 hours).[18] More importantly, the wavelength of the light used in the photocatalytic systems previously reported for NOCM needs to be shorter than 270 nm, which is beyond the region of the solar spectrum (wavelength l > 290 nm) reaching the surface of the Earth. To achieve a substantial yield and to exploit solar energy effectively, the development of photocatalytic systems with a distinctly higher activity, higher selectivity, and lower photon energy threshold is desired.Herein, we report a Zn + -modified ZSM-5 zeolite catalyst which exhibits superior photocatalytic activity for selective C À H activation of an alkane molecule and methane conversion both upon high-pressure irradiation of a mercury lamp and sunlight irradiation at room temperature. An optimized catalyst converts 24 % of methane upon irradiation for 8 hours by a high-pressure mercury lamp with a selectivity larger than 99 % for ethane and hydrogen products. Mechanistic studies suggest a two-stage photoexcitation process, which lowers the energy threshold (l < 390 nm) needed to power our photocatalytic system relative to that (l < 270 nm) required by previously reported systems.Interactions of zeolites with metal vapors are an effective approach for the preparation of metal-containing zeolites. [19,20] Using this approach, we have synthesized a zincmodified ZSM-5 catalyst with a Brunauer-Emmett-Teller (BET) surface area of 362 m 2 g À1 through a solid-vapor reaction between a dehydrated HZSM-5 zeolite (protonated ZSM-5 with a Si/Al ratio of the framework of 14.8) and metallic zinc vapor. During the reaction, the protons of the Brønsted acidic sites (OH groups bridging Al and Si atoms of the framework) in the zeolite are reduced by zinc atoms to form H 2 molecules (as detected by gas chromatography, GC), whereas the zinc atoms undergo two different oxidation r...

Exploiting useful contacts: The exceptional catalytic performance of a photocatalyst composed of Pd nanoparticles and mesoporous carbon nitride for the dehydrogenation of formic acid in water at room temperature to produce H2 gas (see picture) is due to enhanced electron enrichment of the Pd nanoparticles through charge transfer at the interface of the Mott–Schottky contact.