Guangtian Zou

Synthesis of Cu2O nanoframes and nanocages by selective oxidative etching at room temperature.

In recent years, hollow-structure particles (HSPs) have been widely studied due to their unique structures and potential applications. One successful synthetic strategy involves direct construction of HSPs from functional building blocks by processes such as the Kirkendall effect, acid etching, coordination-polymer self-template-directed growth, and solid-state thermal decomposition process for the preparation of Cu7S4, [2] Fe2O3, [3] ZnO, and MnO2 [5] HSPs. However, all of the reported HSPs require further heator acid-treatment processes, which have disadvantages such as increased costs and environmental pollution. Therefore, it remains a great challenge to develop a simple, mild (at room temperature), and environmentally friendly method for the one-pot synthesis of HSPs with well-defined shape. Cu2O is a typical p-type direct band gap semiconductor with a band gap of 2.17 eV and has potential applications in solar-energy conversion, electrode materials, sensors, and catalysts. Considerable effort has been devoted to obtaining hollow Cu2O structure by employing techniques such as hydrothermal synthesis, microemulsions, template synthesis, and acid etching. Qi and co-workers prepared octahedral Cu2O nanocages by Pd-catalytic reduction of an alkaline copper tartrate complex with glucose followed by a catalytic oxidation process. More recently, truncated rhombic dodecahedral Cu2O nanoframes and nanocages were synthesized by particle aggregation and acid etching. In both synthetic processes, expensive and acidic or toxic solvents were used. Here we report a cheap and green synthetic route for Cu2O nanoframes and nanocages with single-crystal walls. In our synthetic strategy, polyhedral Cu2O particles were first prepared by adding a weak reducing agent (glucose) to a solution of copper citrate complex with polyvinylpyrrolidone (PVP) as capping agent, and then Cu2O nanoframes and nanocages were obtained in situ by oxidative etching at room temperature. Perfect Cu2O nanoframes were taken from the reaction mixture after the solution was exposed to air for 16 days at room temperature. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) images provided insight into the nanostructure and morphology of the Cu2O nanoframes. As shown in Figure 1A, the Cu2O nanoframes are

Reactions of xenon with iron and nickel are predicted in the Earth's inner core.

Studies of the Earths atmosphere have shown that more than 90% of xenon (Xe) is depleted compared with its abundance in chondritic meteorites. This long-standing missing Xe paradox has become the subject of considerable interest and several models for a Xe reservoir have been proposed. Whether the missing Xe is hiding in the Earths core has remained a long unanswered question. The key to address this issue lies in the reactivity of Xe with iron (Fe, the main constituent of the Earths core), which has been denied by earlier studies. Here we report on the first evidence of the chemical reaction of Xe and Fe at the conditions of the Earths core, predicted through first-principles calculations and unbiased structure searching techniques. We find that Xe and Fe form a stable, inter-metallic compound of XeFe3, adopting a Cu3Au-type face-centered cubic structure above 183 GPa and at 4470 K. As the result of a Xe ->Fe charge transfer, Xe loses its chemical inertness by opening up the filled 5p electron shell and functioning as a 5p-like element, whilst Fe is unusually negatively charged, acting as an oxidant rather than a reductant as usual. Our work establishes that the Earths core is a natural reservoir for Xe storage, and possibly provides the key to unlocking the missing Xe paradox.

Nitrogen-rich carbon nitride hollow vessels: synthesis, characterization, and their properties.

Bulk quantities of nitrogen-rich graphitic carbon nitride are synthesized via a facile reactive pyrolysis process with a mixture of melamine and cyanuric chloride as the molecular precursors. Scanning electron microscopy and transmission electron microscopy studies show that micrometer-sized hollow vessels with high aspect ratios have been successfully elaborated without the designed addition of any catalyst or template. The composition of the prepared carbon nitride determined by combustion method is C(3)N(4.91)H(1.00)O(0.22), with the N/C ratio to be 1.64, indicating a high nitrogen content. X-ray diffraction pattern reveals the regular stacking of graphene CN(x) monolayers along the (002) direction with the presence of turbostratic ordering of C and N atoms in the a-b basal planes. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy investigations provide further evidence for graphite-like sp(2)-bonded building blocks based on both triazine and heptazine ring units bridged by 3-fold coordinated nitrogen atoms. The optical properties of the sample are investigated by UV-vis absorption and photoluminescence spectroscopy, which show features characteristic of pi-pi* and n-pi* electronic transitions involving lone pairs of nitrogen atoms. Thermogravimetric analysis curves of the synthesized graphitic carbon nitride hollow vessels show typical weight loss steps related to the volatilization of triazine and heptazine structural units.

Origin of hardness in WB4 and its implications for ReB4, TaB4, MoB4, TcB4, and OsB4

First-principles calculations were performed on the superhard material, WB4 (Vicker hardness exceeding 46GPa), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar B2 dimer along the z-axis and a xy planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (TMB4, TM=Re, Mo, Ta, Os, and Tc) within the WB4 structure are potential superhard materials.

Temperature dependence of the Raman spectra of single-wall carbon nanotubes

Raman spectra of single-wall carbon nanotubes (SWCNTs) were measured at different temperatures by varying the incident laser power. The elevated temperature of the SWCNTs and multiwall carbon nanotubes (MWCNTs) is confirmed to be due to the presence of impurities, defects, and disorder. The temperature coefficient of the frequency of the C–C stretching mode E2g (GM) and that of the radial breathing mode in the SWCNT were determined to be ∼−0.038 and ∼−0.013 cm−1/K, respectively. It is found that the temperature coefficient of the GM in the SWCNT is larger than that of the MWCNT, highly oriented pyrolytic graphite, and the graphite. This is attributed to the structural characteristic of the SWCNT—a single tubular carbon sheet with smaller diameter.

Large-Scale Synthesis and Microwave Absorption Enhancement of Actinomorphic Tubular ZnO/CoFe2O4 Nanocomposites

Actinomorphic tubular ZnO/CoFe(2)O(4) nanocomposites were fabricated in large scale via a simple solution method at low temperature. The phase structures, morphologies, particle size, shell thickness, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The as-synthesized nanocomposites were uniformly dispersed into the phenolic resin then the mixture was pasted on metal plate with the area of 200 mm x 200 mm as the microwave absorption test plate. The test of microwave absorption was carried out by the radar-absorbing materials (RAM) reflectivity far field radar cross-section (RCS) method. The range of microwave absorption is from 2 to 18 Hz and the best microwave absorption reach to 28.2 dB at 8.5 Hz. The results indicate that the composites are of excellence with respect to microwave absorption.

Facile Synthesis of Tin Oxide Nanoflowers: A Potential High-Capacity Lithium-Ion-Storage Material

A facile and reproducible approach was reported to synthesize nanoparticle-attached SnO nanoflowers via decomposition of an intermediate product Sn6O4(OH)4. Sn6O4(OH)4 formed after introducing water into the traditional nonaqueous reaction, and then decomposed to SnO nanoflowers with the help of free metal cations, such as Sn2+, Fe2+, and Mn2+. This free cation-induced formation process was found independent of the nature of the surface ligand. It was demonstrated further that the as-prepared SnO nanoflowers could be utilized as good anode materials for lithium ion rechargeable batteries with a high capacity of around 800 mA h g(-1), close to the theoretical value (875 mA h g(-1)).

High-pressure crystal structures and superconductivity of Stannane (SnH4)

There is great interest in the exploration of hydrogen-rich compounds upon strong compression where they can become superconductors. Stannane (SnH4) has been proposed to be a potential high-temperature superconductor under pressure, but its high-pressure crystal structures, fundamental for the understanding of superconductivity, remain unsolved. Using an ab initio evolutionary algorithm for crystal structure prediction, we propose the existence of two unique high-pressure metallic phases having space groups Ama2 and P63/mmc, which both contain hexagonal layers of Sn atoms and semimolecular (perhydride) H2 units. Enthalpy calculations reveal that the Ama2 and P63/mmc structures are stable at 96–180 GPa and above 180 GPa, respectively, while below 96 GPa SnH4 is unstable with respect to elemental decomposition. The application of the Allen-Dynes modified McMillan equation reveals high superconducting temperatures of 15–22 K for the Ama2 phase at 120 GPa and 52–62 K for the P63/mmc phase at 200 GPa.

Facile fabrication of faceted copper nanocrystals with high catalytic activity for p-nitrophenol reduction

This article reports a reproducible and facile approach to synthesize faceted copper nanocrystals (Cu NCs) using an inexpensive copper oxide as a precursor. By simply prolonging the reaction time, Cu cubes and polyhedrons were successfully produced, and the mean size could be effectively controlled in the range of 9 to 21 nm. The catalytic activities of the Cu cubes and polyhedrons were investigated by photometrically monitoring the reduction of p-nitrophenol by an excess of NaBH4. The kinetics of the reduction reaction at different temperatures were investigated to determine the activation parameters. Our investigations indicate that Cu nanocubes exhibit higher catalytic activity than Cu polyhedrons, which can be ascribed to three features: the higher surface-to-volume ratio, the higher surface energy of the {100} facet, and the lower redox potential. In addition, these catalysts can be easily recycled with a slight decrease of the catalytic activities, and are stable in the air. Therefore, this facile route provides a useful platform for the fabrication of Cu catalysts which have the potential to replace noble metals for certain catalytic applications.

Spiral chain O4 form of dense oxygen

Oxygen is in many ways a unique element: It is the only known diatomic molecular magnet, and it exhibits an unusual O8 cluster in its high-pressure solid phase. Pressure-induced molecular dissociation as one of the fundamental problems in physical sciences has been reported from theoretical or experimental studies of diatomic solids H2, N2, F2, Cl2, Br2, and I2 but remains elusive for molecular oxygen. We report here the prediction of the dissociation of molecular oxygen into a polymeric spiral chain O4 structure (space group I41/acd, θ-O4) above 1.92-TPa pressure using the particle-swarm search method. The θ-O4 phase has a similar structure as the high-pressure phase III of sulfur. The molecular bonding in the insulating ε-O8 phase or the isostructural superconducting ζ-O8 phase remains remarkably stable over a large pressure range of 0.008–1.92 TPa. The pressure-induced softening of a transverse acoustic phonon mode at the zone boundary V point of O8 phase might be the ultimate driving force for the formation of θ-O4. Stabilization of θ-O4 turns oxygen from a superconductor into an insulator by opening a wide band gap (approximately 5.9 eV) that originates from the sp3-like hybridized orbitals of oxygen and the localization of valence electrons.