Thickness-dependent exciton relaxation dynamics of few-layer rhenium diselenide

Rhenium diselenide(ReSe_(2))has gathered much attention due to its low symmetry of lattice structure,which makes it possess in-plane anisotropic optical,electrical as well as excitonic properties and further enables ReSe_(2)have an important application in optoelectronic devices.Here,we report the thickness-dependent exciton relaxation dynamics of mechanically exfoliated few-layer ReSe_(2)flakes by using time-resolved pump–probe transient transmission spectroscopies.The results reveal two thickness-dependent relaxation processes of the excitons.The fast one correlates with the exciton formation(i.e.,the conversion of hot carriers to excitons),while the slow one is attributed to the exciton recombination dominated by defect-assisted exciton trapping besides photon emission channel.The decrease of scattering probability caused by defects leads to the increase of fast lifetime with thickness,and the increase of slow lifetime with thickness is related to the trap-mediated exciton depopulation induced by surface defects.Polarization-dependent transient spectroscopy indicates the isotropic exciton dynamics in the two-dimensional(2D)plane.These results are insightful for better understanding of excitonic dynamics of ReSe_(2)materials and its application in future optoelectronic and electronic devices.

Preparation of ultrafine rhenium powders by CVD hydrogen reduction of volatile rhenium oxides

A novel CVD process for the preparation of ultrafine rhenium powders was investigated using ammonium perrhenate as starting materials. In the process, volatile rhenium oxides, such as ReO4 and Re2O7, were vaporized under a controlled oxidizing atmosphere via the pyrolysis of ammonium perrhenate, and carried into reduction zone by carrier gas, and there reduced into rhenium powders by hydrogen gas. Thermodynamic calculations indicated that Re207 could be prevented from further decomposition through controlling the oxygen partial pressure higher than 10 1.248 Pa in the pyrolysis of ammonium perrhenate. This result was further validated via DSC-TGA analysis of ammonium perrhenate. The typical rhenium powders prepared by the CVD method proposed show irregular polyhedron morphology with particle size in the range of 100-800 nm and a Ds0 of 308 nm. The specific surface area and oxygen content were measured to be 4.37 m^2/g and 0.45%, respectively.

Adsorption of Rhenium（Ⅶ） with Anion Exchange Resin D318

The adsorption and mechanism of Re(Ⅶ)on resin D318 were studied using chemical methods and IR spectrometry.At pH 5.2,the static and dynamic saturation adsorption capacities were 351.4 and 366.5 mg·g-1,respectively.The adsorption behavior obeyed the Freundlich empirical equation and the adsorption rate constant k298 was 6.37×10-4s-1.The desorption percentage was up to 99.7%when 2.0 mol·L-1KSCN was used for dynamic desorption.

Roasting oxidation behaviors of ReS_2 and MoS_2 in powdery rhenium-bearing, low-grade molybdenum concentrate

The oxidation roasting process of molybdenum concentrate has significant advantages in industrial applications.However,utilization of low-grade mineral has many problems because it is more complex than the standard concentrate.In this study,the oxidation behaviors of powdery rhenium-bearing low-grade molybdenum concentrate were investigated through thermodynamic calculation,roasting experiments,thermogravimetric analysis,and phase analysis.The results obtained show that oxidation of MoS2 begins at 450℃,and MoO3 reacts with metal-oxide forming molybdate at 600℃.Finally,MoO3 can be dissolved in ammonia with a maximum content of approximately 80%.The volatile speed of Re was considerably slower than the oxidation speed of MoS2 because the nonvolatile products ReO2 and ReO3 were generated in reactions among MoS2,SO2,and Re2O7.The final volatilization rate of Re was almost 70%.This study determined the problems related to the roasting of low-grade molybdenum concentrate,which lays the scientific foundations for subsequent enhancement of molybdenum and rhenium extraction.

Organorhenium(Ⅶ) oxides

Methyltrioxorhenium (MTO) and its derivatives were utilized as catalysts for a broad variety of organic reactions after the discovery of an easy synthetic access way to this class of compounds. Among the numerous characterization techniques, 17O-NMR spectroscopy and vibrational spectroscopy were exemplary discussed. The immobilization of MTO and its derivatives is of significant current interest as is the synthesis of chiral derivatives.

A Study of the Rhenium-Osmium Geochronometry of Molybdenites

This study deals with the first application of the isotope dilution - inductively coupled plasma mass spectrometry in the rhenium-osmium geochronometry in China. The chemical separation procedure included decomposition of samples by means of alkali fusion, extraction of rhenium by acetone and extraction of osmium by distillation. The recovery of both elements in the entire process was more than 90% . The blanks of analyses were 0.07 ng for rhenium and 0.01 ng for 187Os. The mineralization ages of molybdenites from four molybdenum deposits in China were determined by using this method, with a precision (2σ)of about ±3% . These results agree satisfactorily with their geological backgrounds. The Re-Os method can directly determine ages of metal deposits and reflect the true ages more reliably than other dating methods that only determine the ages of country rocks from which mineralization ages are inferred. As many hydrothermal sulphide deposits usually contain molybdenites, this method has bright prospects of wide application.

Synthesis,characterization,photoluminescence and electroluminescence properties of new 1,3,4-oxadiazole-containing rhenium(I)complex Re(CO)_3(Bphen)(PTOP)

A new 1,3,4-oxadiazole-contanining rhenium（I） complex, with the formula [Re（CO）a（Bphen）（PTOP）], （Bphen = bathophe- nardine, PTOP = 4-（5-p-tolyl-1,3, 4-oxadiazd-2-yl） pyridine）, is synthesized and characterized by elemental analysis, IR, 1H NMR, UV-vis and luminescence spectroscopy. The double-layer electroluminescence devices based on the Re（l） complex have been fabricated by spin-coating technique. The turn-on voltage, maximum efficiency, and brightness for green emission obtained from the devices are 9 V, 2.1 cd/A and 165 cd/m^2, respectively.

Separation of rhenium from electric-oxidation leaching solution of molybdenite

The separation of rhenium from molybdenum in aqueous solution has always been a problem in hydrometallurgy. The separation of rhenium from the electro-oxidation leachate of molybdenite and its mechanism were investigated. The results show that pH of the leachate significantly affects adsorption rate compared with other experimental parameters. When temperature is 30℃, pH=8, and adsorbing time is 1 h, adsorption rates of rhenium and molybdenum are 93.46% and 3.57%, respectively, and separation factor of D301 resin for rhenium and molybdenum is 169.56. In addition, the separation factor is higher when the initial molybdenum concentration in model solution is increased. The saturated adsorption capacity of D301 resin for molybdenum and rhenium calculated based on simulated results are 4.263 3 mmol/g and 4.235 5 mmol/g, respectively. D301 resin is an effective separation material of rhenium from electric-oxidation leachate of molybdenite. The adsorption kinetics results also show that the adsorption of rhenium is easier than that of molybdenum, and the adsorption process of D301 for rhenium and molybdenum may be controlled by liquid film diffusion.

Role of support nature (γ-Al_2O_3 and SiO_2-Al_2O_3) on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re2O7/γ-Al2O3 and Re2O7/SiO2-Al2O3 catalysts. Both NH3 temperature-programmed desorption （NH3-TPD） and H2 temperature-programmed reduction （H2-TPR） results showed that Re2O7/SiO2-Al2O3 exhibited stronger acidity and weaker metal-support interaction than Re2O7/γ-Al2O3. At 35 60℃, isomerization free metathesis was observed only over Re2O7/γ-Al2O3, suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re2O7/SiO2-Al2O3, hydrido-rhenium species （[Re]-H） were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.

Preparation of mesoporous alumina with large pore size and their supported rhenium oxide catalysts in metathesis of 1-butene and 2-butene to propene

Mesoporous γ-aluminas with large pore size （up to 19 nm, denoted as MAI9） are prepared from dispersed pseudo-boehmite using pluronic P123 as template. It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size （5 nm）. At 60 ℃ and atmospheric pressure with WHSV = 1 h^-1, the similar stable conversions of butene （ca. 55%） for all the 13 wt% Re207/alumina catalysts were obtained near the chemical equilibrium, and the stable working life-spans of Re2OT/MA19 were far longer than that of Re2O7/A1203, being about 70 h and 20 h, respectively.

Synthesis of Two Novel Rhenium(I) Bipyridyl Photosensitive Dyes

Two novel rhenium(I) 2, 2'-bipyridyl complexes, [(4,4'-di-COOEt-bipy) Re(CO)3 (NCCH3)PF6] and [(4,4'-di-COOEt-bipy) Re (CO)3 (NCS)], a model complex [(4,4'-di- COOEt-bipy) Re (CO)3 (pyridine)PF6], were synthesized. Their ground stat?electronic spectra and emission spectra were measured in acetonitrile. The MLCT absorption maximum of the complex exhibited a considerable red shift as the ligand changed from pyridine to CNCH3, or SCN.

Geochemistry of Rhenium and Other Trace Elements in Molybdenite,Sar Cheshmeh Porphyry Cu-Mo Deposit,Iran

LA-ICP-MS analysis of molybdenite from the Sar Cheshmeh porphyry Cu-Mo deposit(PCD),Iran,shows moderate concentration of Re(average~207 ppm)and low concentration of chalcogenides(average of Pb+Te+Bi,~31 ppm)as well as metalloids(average of As+Sb+Ge,~4.5 ppm).The early-formed quartz–molybdenites associated with potassic alteration are characterized by moderately low concentration of Re(21–215 ppm with an average of 83 ppm),whereas the transitional quartz–molybdenite veins related to the sericitic stage of mineralization contain more Re(62–465 ppm,with an average of 207 ppm).In contrast,the late-formed quartz–molybdenite veins associated with phyllic alteration show the highest concentration of Re(up to 1273 ppm with an average of 395 ppm).Gradual increase in Re content of molybdenites deposited throughout the evolution of the porphyry system is probably related to elevated fO_(2) and acidic conditions of the ore fluids governing the transitional and late stage of mineralization,when compared to the moderately low fO_(2) and basic conditions of the ore fluids precipitating the low-Re molybdenites associated with potassic alteration.The mixed mantle/crustal source of the ore-related magma and its fractionated composition in Sar Cheshmeh are consistent with magmatic conditions for the formation of Mo-rich and Re-poor PCDs in the world.

The Electro-Physical Properties of Rhenium Chalcogenides＇ Thin Films

The electro-physical properties of thin layers of rhenium chalcogenides＇ alloys, their dynamical and static ampere-voltaic characteristics were investigated. During the investigation of static and dynamical ampere-voltaic characteristics of rectifying contact of aluminium and rhenium chalcogenides＇ alloys the switching effects were found.

High-pressure Raman study of osmium and rhenium up to 200 GPa and pressure dependent elastic shear modulus C_(44)

High-pressure Raman scattering from hexagonal close-packed(HCP) metals Os and Re have been extended up to 200 GPa, and the pressure-dependent shear modulus C_(44)has been deduced from the Raman-active mode E_(28), which is generated from the adjacent vibration of atoms in hexagonal planes, providing the valuable information about the elastic properties for HCP metals under high pressure. Combined with the available data of HCP metals from previous works,a further study indicates that the C_(44)/C_(44)ratio would be close to a constant value, 0.01, with increasing atomic number of metals. The results obtained from high-pressure Raman scattering will allow us to probe the elastic anisotropy of the HCP metals at very high pressure.

Tensile properties of tungsten-rhenium wires with nanofibrous structure

In this study, the mechanical properties of tungsten-rhenium wires with nanofibrous microstructure were investigated at both room temperature(RT) and 800?C. The strengthening mechanism associated to the nanofibrous microstructure was discussed. The results showed that the tungsten-rhenium wires with nanofibrous grains exhibited a very high tensile strength reaching values of 3.5 GPa and 4.4 GPa for the coarse(grains diameter of 240 nm) and fine(grains diameter of 80 nm) wires, respectively. With increasing the temperature from RT to 800?C, the tensile strength decreased slightly but still held high values(1.8 GPa and 3.8 GPa). All the fracture surfaces exhibited apparent necking and characteristics of spear-edge shaped fracture surface, indicating excellent ductility of the wires. A model of the strengthening mechanism of these tungsten-rhenium wires was proposed.

The Electrodeposition of Rhenium in Alkaline and Acidic Elektrolytes

The investigation of electrodeposition of rhenium in alkaline and acidic electrolytes was carried out, polarization curves were obtained by electrochemically and cyclically potentiodynamic methods. By the investigation of rhenium concentration, sulphuric acid, alkali, ammonium sulphate, temperature and acidity of solution, it was found that reaming velocity was an optimal regime and electrolyte composition for an obtaining of high quality rhenium deposits from an alkaline electrolyte and acidic electrolyte. It was defined that the process of electrodeposition of rhenium in alkaline electrolyte is accompanied by chemical polarization and the electrodeposition of rhenium in acidic electrolyte goes gradually with the formation of intermediate films of sediments,

Determination of rhenium and osmium by ICP-MS for galena and sphalerite

Digestion with aqua regia in a Carius tube and separation of Re with anion exchange resin is commonly employed for Re–Os dating of molybdenite and pyrite.However, the recovery of Re is extremely low when this routine anion exchange method is applied to galena,causing difficulty in Re–Os dating of galena. In this study,we investigated the mechanism of Re loss during sample preparation and tested a revised procedure for Re–Os dating of galena and sphalerite.

Chloroform Aided Extraction Spectrophotometric Determination of Rhenium Using Thiocyanate Complexing Agent

A new technique is developed for quantitative determination of rhenium in aqueous media containing molybdenum, iron and copper ions. The method seems easier and more accurate than the traditional ones. It consists of the formation of rhenium thiocyanate complex, which is extracted with chloroform at the presence of hydrochloric acid. This complex is a highly visible light absorbent that can easily be detected with the aid of a spectrophotometer. The maximum absorbance (λmax) observed for this complex was in the visible range of 430-435 nm. The experimental results showed that in a concentration range from 0.5-8 mg/L, the absorbance behavior of the rhenium thiocyanate complex is followed to the Beer-Lambert law.

First-principles calculations of lattice stability of technetium and rhenium

Lattice constants, total energies and densities of state of technetium(Tc) and rhenium(Re) with different crystalline structures were calculated with the GGA+PBE function, ultra-soft pseudo-potential and plane wave method in first-principles. The results were compared with those of projector augmented wave(PAW) method in first-principles and experimental data. The lattice stability results prove that HCP phase is the most stable phase, which agrees well with those of PAW method in first-principles and CALPHAD method. Further analyses of densities of state also give the same result of lattice stability for HCP-, FCC-, BCC-Tc and Re. Analyses of atomic populations show that the lattice stability of technetium and rhenium is probably related to the electrons in p and d state.

Studies of a Series of Novel Rhenium（Ⅰ） Bipyridyl Dyes for Solar Cells

A series of novel rhenium(I) 2,2'-bipyridyl complexes [fac-Re(4,4'-di-COOEt-bpy) -(CO)3(Xpy)PF6], where bpy is 2,2'-bipyridine, py is pyridine and X is 3-methyl, 3-hydroxy, or 3-amino, were synthesized, their photophysical and electrochemical properties were studied. The Re(II/I) oxidation potentials decreased as the X group becomes more electron donating from H to 3-methyl, 3-hydroxy, or 3-amino, which might be a very convenient ways for adjusting the electron transfer driving force.