Current Inorganic Chemistry (Discontinued) - Volume 2, Issue 2, 2012

Titanium dioxide (TiO2) is the most intensely investigated photocatalyst and until today the only one that has already been commercialized and that is involved in many applications such as self-cleaning materials, dye-sensitized solar cells, as well as water and air purification. Consequently, an exponential growth of research activities concerning the nanoscience and nanotechnology of TiO2 has been observed during the last decades. These raising research activities have recently lead to the synthesis of nanosized TiO2 single crystals with well-defined shapes and with specific exposed surfaces. Thus, the present review will focus mainly on the synthesis of these nanomaterials. The thermodynamic stability, the transition between different TiO2 polymorphs, and the surface properties of these polymorphs are presented with the aim to utilize these informations for a better understanding of the mechanism of the formation of shape-defined TiO2 nanomaterials and their various applications in photocatalysis.

Photocatalysts hold great potential for using sunlight to drive oxidations. Among photocatalysts, TiO2 is one of the most promising due to the strong oxidizing potential of the valence band; the strong oxidizing potential results in mineralization of a wide range of pollutants found in water. Developing a practical material requires improving the photo catalyst in two ways: narrowing the band gap and improving the quantum efficiency. Progress for improving TiO2 is hampered by apparently inconsistent literature reports for the effect of doping on efficiency. The basic source of the apparent inconsistencies is that charge transfer occurs at the catalyst surface and is thus affected by seemingly small differences in catalyst generation. This report contains results from 2.4 nm diameter particles; the small size results in improved consistency enabling comparison of modified and unmodified particles. Results suggest that batch-to-batch variation in grain boundaries and defects are a source of the apparent inconsistencies in the literature. The specific results reported here for iron doping support a model in which low-level iron doping enhances efficiency by acting as an electron transfer agent to molecular oxygen. Iron doping also modifies surface adsorption of methanol, the test molecule, and water. This contribution concludes with suggestions for future directions in developing iron-doped TiO2 photocatalysts.

Sunlight has a great potential to replace current fossil fuels due to its abundance and environmental merit. Considering the solar energy conversion, metal oxides are extensively studied in dye- sensitized solar cell (DSSC) and solar fuel because of its many advantages, such as chemical stability, suitable band gap structures, and abundance on the Earth. Therefore, it is very important to present an overview of the metal oxides in the solar energy conversion, especially in DSSC and water splitting. The major difference of the present review from other reviews in solar energy conversion is that it mainly focuses on the introduction of binary and ternary metal oxides in solar energy conversion, especially in DSSC and water splitting. The basic principle, new approaches for improved efficiency, and current existing problems in both DSSC and water splitting were discussed in detail. In water splitting part of this review, several methods aimed at producing hydrogen and oxygen, and approaches for visible-light band gap engineering of binary and ternary metal oxides were explained. This review provides important scientific information to the solar energy community and opens up new possibilities in the field.

One alternative of low-cost solar cells is to develop new photovoltaic cells based on hybrid organic and inorganic materials. The certified efficiency record achieved from this type of devices has been frequently broken during the past decades. Now the maximum energy conversion efficiency has already reached above 11%. The inorganic materials, especially nanostructured materials, play a crucial role in these photovoltaic devices in that they can be used as electrodes, as well as in some cases as photoactive materials. This paper focuses on the most recent developments observed in the applications of inorganic materials in the hybrid solar cells (HSCs), mainly on dye-sensitized solar cells and polymer/ inorganic HSCs. This underscores the opportunity of realizing practical applications of these HSC devices.

Hydrogen is considered to be a next generation of energy carrier due to its environmentally friendly and renewable characteristics. Among many techniques for hydrogen production, photocatalytic water splitting using semiconductor materials is a promising pathway where abundant solar light is utilized. From the prospect of solar light utilization, development of efficient visible-light-driven photocatalysts is critically needed. In recent years, nanostructured sulfides with a suitable band structure have attracted extensive attention because their properties remarkably distinguish from those of their bulk counterparts. In this minireview, emphasis is placed on recent research progress towards the design, preparation, and modification of nanostructured sulfides for photocatalytic splitting of water into hydrogen. These sulfides are classified into three categories: 1) CdS-based nanostructures; 2) ZnS-based nanostructures; and 3) other nanostructured sulfides. Their excellent performances in photocatalytic hydrogen production are discussed in detail by correlating with the features of relevant nanostructures.

Photocatalytic water splitting is a promising approach to produce clean and renewable hydrogen energy by using energy. Efficiency of photocatalytic water splitting can be improved by loading cocatalyst on the surface of the photocatalyst. We reviewed different kinds of cocatalysts applied in photocatalysis, and introduced the loading technic, coreshell structure and co-loading in detail.

The olivine-structured lithium ion phosphate (LiFePO4) is one of the most competitive candidates of cathode materials for the sustainable lithium ion battery (LIB) systems. However, the major drawback of olivine-structured LiFePO4 is the poor intrinsic electronic and lithium ion conductivities arising from the lack of mixed valency and the onedimensional lithium ion diffusion, which influence its high electrochemical performance, especially high rate capability. Nano-structured LiFePO4 materials offer a potential solution to enhance surface-to-volume ratio and reduce transport length for mobile charges, but they have high interfacial energy, aggregate easily and need more agglutinant in electrode, which seriously impact the electrochemical performance and practical applications of LiFePO4. Furthermore they continue to experience limitations as energy and power requirements escalate with the evolution of technology. Recently, three-dimensional (3D) porous LiFePO4 architectures have been widely designed and studied. This has led to increased interest in the development of cathode materials and processing capabilities necessary to enable high-performance, nextgeneration LIB system that can deliver large amounts of energy at high rates. In this review, we focus on 3D porous LiFePO4 architectures for high power LIBs, summarize and discuss its structure, synthesis, electrochemical behaviors, mechanism, and the problems encountered in its application. The major goal is to highlight the recent progress of 3D porous LiFePO4 architectures with high rate capability, high energy density and application.

Metal nanoparticles (NPs) as high surface area heterogeneous catalysts are important in catalysis areas. Ionic liquids (ILs) have proven to be suitable media for the synthesis and stabilization of metal NPs. In addition, ILs can also act as additive to modified the physicochemical properties of metal NPs, including the size, shape and catalytic performance. This review summarizes recently reported various ILs which are applied to generate metal NPs by reduction or decomposition of metal precursor. Then, the interaction of the metal NP surfaces with the functionalized or nonfunctionalized IL has been discussed. Finally, the application of the ILs/metal NPs system in catalytic hydrogenation is reviewed with particular attention.

Technetium and rhenium congener metals have wide applications in radiopharmacy. Techentium-99m is an ideal γ-emitting diagnostic radionuclide and Re-186, Re-188 are β-emitting isotopes applied in radiotherapy. Organometallic complexes of the fac-[ReI/TcI(CO)3]-type have suitable properties for radiopharmaceutical applications and high in vivo stability. In this review, general aspects of radiopharmaceutical design with technetium and rhenium are covered. Emphasis is given on the ligands designed for the fac-[ReI/TcI(CO)3] core. Examples of targeted fac-[ReI/TcI(CO)3]-type and ReIII/TcIII(NS3)(CNR)-type complexes in various radiopharmaceutical applications are presented in the last section.

Polycrystalline new Na6Pb4(SO4)6Cl2:(Ce3+; Ce3+ →Dy3+; Ce3+ →Tb3+ and Eu2+ →Dy3+) halosulphate inorganic phosphors were synthesized by solid state diffusion method. The effects of Dy3+ and Tb3+co-doping on the photoluminescence (PL) characteristics of the phosphors have been studied. In Na6Pb4(SO4)6Cl2, Ce3+ emission is observed at 340 nm due to 5d → 4f transition of Ce3+ ion. A strong PL emission of Dy3+ ions is observed at 475 and 575 nm in Na6Pb4(SO4)6Cl2: Ce, Dy phosphor, while Tb3+ green color emission is also observed at 550 nm in Ce3+ → Tb3+ energy transfer. The host is also suitable for sufficient Eu2+ →Dy3+ energy transfer. This paper reports that Na6Pb4(SO4)6Cl2 inorganic material is most suitable for photoluminescence phenomena and energy transfer mechanism.