Delayed Doublet Emission in a Cerium(III) Complex.

Doublet emission from open-shell molecules has demonstrated its research and application value in recent years. However, understandings of the photoluminescence mechanism of open-shell molecules are far less than that of closed-shell molecules, leading to challenges in molecular design of efficient doublet emission systems. Here we report a cerium(III) 4-(9H-carbozol-9-yl)phenyl-tris(pyrazolyl)borate complex Ce(CzPhTp)3 with a new luminescence mechanism of delayed doublet emission, which also represents the first example with metal-centered delayed photoluminescence. The energy gap between the doublet and triplet excited states of Ce(CzPhTp)3 is reduced by the management of the inner and outer coordination spheres, thereby promoting efficient energy transfer between the two excited states and activating the delayed emission. The photoluminescence mechanism discovered may provide a new way for the design of efficient doublet emission and bring insights into rational molecular design and energy level regulation in open-shell molecules.

Platinum-based heterogeneous nanomaterials via wet-chemistry approaches toward electrocatalytic applications.

The heterogeneously structured nanomaterials usually exhibit enhanced catalytic properties in comparison with each one of the constituent materials due to the synergistic effect among their different domains. Within the last decade, the development of wet-chemistry methods leads to the blossom of research in materials with heterogeneous nanostructures, which creates great opportunities also a tremendous challenge to apply these materials for highly efficient energy conversion. We herein would systematically introduce the latest research developments in Pt-based nanomaterials with heterogeneous structures, e.g. core-shell, hollow interiors, stellated/dendritic morphologies, dimeric, or composite construction, and their potential applications as electrocatalysts toward direct methanol fuel cell reactions, including methanol oxidation reaction and oxygen reduction reaction in acidic conditions, aiming at the summarization of the fundamentals and technical approaches in synthesis, fabrication and processing of heterogeneous nanomaterials so as to provide the readers a systematic and coherent picture of the filed. This review will focus on the intrinsic relationship between the catalytic properties and the physical or/and chemical effects in the heterogeneous nanomaterials, providing for technical bases for effectively developing novel electrocatalyts with low cost, enhanced activity and high selectivity.

Exploring metal nanoclusters for lithium-oxygen batteries.

α-MnO2 nanowires modified with dispersed poly(3,4-ethylenedioxythiophene)-protected Au and Ag nanoclusters (Au-MnO2 and Ag-MnO2) were used for the first time as hybrid oxygen electrocatalysts for nonaqueous lithium-oxygen batteries. The Au-MnO2 and Ag-MnO2 hybrid catalysts surpassed the performance of pristine α-MnO2 nanowires in full-cell tests in the following order: Au-MnO2 > Ag-MnO2 > pristine α-MnO2. Specifically, cells with the Au-MnO2 catalyst could reduce the discharge/charge overpotentials at 100 mA g(-1) to 0.23/1.02 V and deliver discharge/charge capacities of 5784/5020 mAh g(-1). They could also be cycled for at least 60 times at the depth of discharge of 1000 mAh g(-1). The good full cell performance demonstrated the effectiveness of Au/Ag nanoclusters in promoting oxygen electrocatalysis on α-MnO2; forming discharge products with more reactive morphologies. It is therefore worthwhile to explore the use of Au and Ag nanoclusters in other catalyst systems for oxygen electrocatalysis in nonaqueous solutions.

Oxide-on-metal as an inverted design of oxygen electrocatalysts for non-aqueous Li-O2 batteries.

A wheat-like Ag-Mn3O4 composite consisting of a Ag core and Mn3O4 shell was found to be as active as the state-of-the-art Pt-Au/C catalyst for oxygen electrocatalysis in non-aqueous Li-O2 batteries.

A kinetics study on promising hydrogen storage properties of Mg-based thin films at room temperature.

Pd-Mg-Pd thin films with variable thickness of Mg layers were prepared. Their optical and electrical changes in both gasochromic and chemochromic processes were compared to investigate the kinetics of Mg-based thin films at room temperature. Hydrogen absorption and desorption kinetics of Pd-Mg-Pd thin films were strongly dependent on the thickness of the Mg layer. Especially, when the thickness was lowered to 60 nm, a MgH2 layer formed immediately after exposure to H2 at room temperature, while a Mg layer was rapidly generated during hydrogen desorption in ambient air. By means of optical and electrical resistance measurements, we found that the diffusion process contributed significantly to hydrogen absorption and desorption. The remarkable absorption and desorption kinetics at room temperature reported here suggested promising applications in Mg-based energy-efficient devices and hydrogen sensors.

Phase-transfer based size refining of metal nanoparticles from arbitrary particle size distributions.

The size-dependent phase-transfer property of metal nanoparticles is used to develop a simple experimental procedure that can effectively refine the particle size from colloidal solutions prepared by wet-chemistry. The protocol calls for firstly the mixing of the metal hydrosol with an ethanol solution of dodecylamine, and then the extraction of the dodecylamine-stabilized metal nanoparticles into toluene. This method offers an effective approach to prepare metal nanoparticles with narrow size distribution from an arbitrary particle size distribution.

Hollow and cage-bell structured nanomaterials of noble metals.

Mastery of the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the synthesis of metal nanomaterials with hollow interiors or cage-bell structures based on the inside-out diffusion of Ag in core-shell structured nanoparticles. It begins with the synthesis of core-shell Ag-M or core-shell-shell M(A)-Ag-M(B) nanoparticles in an organic solvent. Ag is then extracted from the core or the inner shell by bis(p-sulfonatophenyl)phenylphosphane, which binds strongly with Ag(I)/Ag(0) to allow the complete removal of Ag in 24-48 h, leaving behind an organosol of hollow or cage-bell structured metal nanomaterials. Because of their relatively lower densities, which usually translate to a higher surface area than their solid counterparts, the hollow and cage-bell structured metal nanomaterials are especially relevant to catalysis. For example, cage-bell structured Pt-Ru nanoparticles were found to display outstanding methanol tolerance for the cathode reaction of direct methanol fuel cells (DMFCs) as a result of the differential diffusion of methanol and oxygen in the cage-bell structure.

The bis(p-sulfonatophenyl)phenylphosphine-assisted synthesis and phase transfer of ultrafine gold nanoclusters.

Gold nanoclusters (Au NCs) have attracted intensive attention for their molecular-like properties such as luminescence and unique charging behavior. A facile route has been developed for the preparation of ultrafine Au NCs at room temperature. Bis(p-sulfonatophenyl)phenylphosphine dihydrate dipotassium was used to stabilize the Au NCs obtained by NaBH(4) reduction of HAuCl(4) at pH of ∼12 and facilitated the phase transfer of Au NCs from aqueous phase to an organic medium based on electrostatic interaction. From the analyses of TEM, HRTEM, and XRD patterns, the formation of fcc structured Au NCs dominated by {200} facets was identified. The Au NCs transferred into toluene could be used as seeds for the formation of core-shell Au@Ag(2)S nanoparticles, providing for a promising strategy for the metal doping in semiconductor nanocrystals.

Plasma-assisted approaches in inorganic nanostructure fabrication.

Plasma is a unique medium for chemical reactions and materials preparations, which also finds its application in the current tide of nanostructure fabrication. Although plasma-assisted approaches have been long used in thin-film deposition and the top-down scheme of micro-/nanofabrication, fabrication of zero- and one-dimensional inorganic nanostructures through the bottom-up scheme is a relatively new focus of plasma application. In this article, recent plasma-assisted techniques in inorganic zero- and one-dimensional nanostructure fabrication are reviewed, which includes four categories of plasma-assisted approaches: plasma-enhanced chemical vapor deposition, thermal plasma sintering with liquid/solid feeding, thermal plasma evaporation and condensation, and plasma treatment of solids. The special effects and the advantages of plasmas on nanostructure fabrication are illustrated with examples, emphasizing on the understandings and ideas for controlling the growth, structure, and properties during plasma-assisted fabrications. This Review provides insight into the utilization of the special properties of plasmas in nanostructure fabrication.

The synthesis and hydrogen storage properties of pure nanostructured Mg2FeH6.

In this work, pure nanostructured Mg(2)FeH(6) is successfully synthesized by sintering of a mixture of 2Mg + Fe nanoparticles. The successful preparation of pure Mg(2)FeH(6) can be attributed to the small particle sizes of Mg and Fe nanoparticles prepared by hydrogen plasma-metal reaction (HPMR), which benefits the synthesis. The hydrogen storage properties of Mg(2)FeH(6) and the synthesis mechanism of the Mg-Fe-H system are studied. The sample desorbs 5.0 wt% of hydrogen rapidly in 6 min under an initial hydrogen pressure of approximately 100 Pa at 623 K. The enthalpy and entropy of the reaction are deduced from the equilibrium plateau pressures of the desorption isotherms. The obtained Mg(2)FeH(6) shows favorable hydrogen storage properties due to the specific nanostructure of the materials.