Synthesis and Growth of Flower-Like Zn-Doped CdSe Microstructures

Hexagonal phase flower-like Zn-doped CdSe (Cd_1-xZn_xSe, x = 0.3) semiconductor microstructures from the solid air-stable precursor have been achieved in the mixed solution of ethylenediamine (en) and ethylene glycol (EG) at 180°C for 12 hours. Characterized by powder x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrum (EDS), and UV-vis absorption spectroscopy, it can be seen that the as-synthesized Cd_0.7Zn_0.3Se is hexagonal phase, and each flower-like Cd_0.7Zn_0.3Se microstructure is made up of many Cd_0.7Zn_0.3Se nanoflakes. From the UV-vis absorption spectrum of the product, it was observed that the optical band gap energies of flower-like Cd_0.7Zn_0.3Se microstructures shift toward shorter wavelengths compared with CdSe.     

硫化锌镉固溶体光催化分解水产氢研究现状

硫化锌镉（Cd_1-xZn_xS,0 < x < 1）固溶体因其优异的活性、可调谐的能带结构在光催化分解水制氢领域备受关注,但其较快的光生电荷复合速率和光腐蚀仍阻碍了其进一步应用。因此,研究者们针对其固有缺陷进行了大量改性工作。我们首先简述了光催化反应热力学与动力学特征,随后详细综述了近年来Cd_1-xZn_xS在光解水制氢领域的研究进展,包括其结构调控、异质结构建、杂原子掺杂等方面,简要分析了Cd_1-xZn_xS光催化分解水所面临的挑战和问题,并对近期研究进行了展望。     

New strategy for band-gap tuning in semiconductor nanocrystals

In the last decade, the main efforts have focused on the preparation of different sized binary II–VI group semiconductor nanocrystals to obtain different color-emitting luminescence. However, the tuning of physical and chemical properties by changing the particle size could cause problems in many applications, in particular if unstable small particles are used. Recent advances have led to the exploration of tunable optical properties by changing their constituent stoichiometries in ternary alloy nanocrystals. High-quality Zn _x Cd_1?x Se alloy nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals or embryonic CdSe nuclei. With increasing Zn content, a composition-tunable emission across the whole visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. High-quality alloy Zn _x Cd_1?x S nanocrystals have been obtained by the conucleation and co-growth of the constituents through the reaction of a mixture of CdO- and ZnO-oleic acid complexes with sulfur at elevated temperatures. The obtained Zn _x Cd_1?x S alloy nanocrystals possess superior optical properties with photoluminescence quantum yields of 25–50%, especially the extremely narrow emission spectral width (fwhm=14 nm).     

Photocatalytic hydrogen generation using glucose as electron donor over Pt/Cd x Zn1−x S solid solutions

Cd _x Zn_1?x S solid solution photocatalysts were prepared by a hydrothermal process. The photocatalysts were characterized by X-ray diffraction (XRD), UV–vis diffusive reflectance spectroscopy (DRS), and transmission electron microscope (TEM) measurements. Using glucose as an electron donor, photocatalytic hydrogen generation over Pt/Cd _x Zn_1?x S was investigated. The results show that glucose not only improves the efficiency of photocatalytic hydrogen generation but prevents photocorrosion of Cd _x Zn_1?x S. Glucose was degraded effectively with the hydrogen generation. The factors which affect photocatalytic hydrogen generation, such as composition and structure of Cd _x Zn_1?x S solid solutions, irradiation time, initial concentration of the glucose, and concentration of NaOH were studied.     

Formation of solid solutions in the CdSe–PbSe system under the action of high pressures and temperatures

A method was proposed for producing solid solutions in the CdSe–PbSe systems, which is based on heat and high pressure treatment. X-ray powder diffraction analysis showed the formation of substitutional solid solutions Cd_xPb_1–xSe with the NaCl structure, which contained 20, 40, 60, and 80 mol % cadmium selenide. The solid solutions were characterized by scanning electron microscopy, impedance spectroscopy, gas pycnometry, and Raman spectroscopy.     

Chemical dissolution of CdTe and Cd1-x ZnxTe solid solution single crystals in bromine etchants of the H2O2-HBr-ethylene glycol system

Equal-etching-rate surfaces for single-crystalline CdTe and Cd_1-x Zn _x Te solid solution samples in etching mixtures of the H₂O₂-HBr-ethylene glycol (EG) system are mapped under reproducible hydrodynamic conditions using simplex design. The dissolution rate laws for these materials are studied, and the concentration boundaries of existence for polishing and nonpolishing solutions are determined. The increasing zinc concentration in the Cd_1-x Zn_xTe solid solution increases the etching rates, while the concentration boundaries of the polishing solutions in the diagram do not change significantly.     

Crafting Core/Graded Shell–Shell Quantum Dots with Suppressed Re‐absorption and Tunable Stokes Shift as High Optical Gain Materials

The key to utilizing quantum dots (QDs) as lasing media is to effectively reduce non‐radiative processes, such as Auger recombination and surface trapping. A robust strategy to craft a set of CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS core/graded shell–shell QDs with suppressed re‐absorption, reduced Auger recombination rate, and tunable Stokes shift is presented. In sharp contrast to conventional CdSe/ZnS QDs, which have a large energy level mismatch between CdSe and ZnS and thus show strong re‐absorption and a constrained Stokes shift, the as‐synthesized CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS QDs exhibited the suppressed re‐absorption of CdSe core and tunable Stokes shift as a direct consequence of the delocalization of the electron wavefunction over the entire QD. Such Stokes shift‐engineered QDs with suppressed re‐absorption may represent an important class of building blocks for use in lasers, light emitting diodes, solar concentrators, and parity‐time symmetry materials and devices.     

Photocatalytic production of hydrogen in systems based on Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S/Ni<Superscript>0</Superscript> nanostructures

A relation was established between the composition of Cd _x Zn_1–x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd _x Zn_1–x S nanoparticles in the release of hydrogen from solutions of Na₂SO₃, their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni⁰ nanoparticles photodeposited on the surface of Cd _x Zn_1–x S are effective cocatalysts for the release of hydrogen. It was found that Zn^II additions in photocatalytic systems based on Cd _x Zn_1–x S/Ni⁰ nanostructures have a promoting action on the release of hydrogen from water–ethanol mixtures. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 8–16, January-February, 2009.     

Photocatalytic hydrogen production using Me/Cd<Subscript>0.3</Subscript>Zn<Subscript>0.7</Subscript>S (Me = Au,Pt, Pd) catalysts: Transformation of the metallic catalyst under the action of the reaction medium

The activity and stability of Me/Cd_0.3Zn_0.7S (Me = Au, Pt, Pd) photocatalysts in the course of hydrogen production from water under the action of visible radiation have been investigated. The mechanism of activation and deactivation of the catalysts have been elucidated for the first time using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. An increase in the hydrogen evolution rate is observed for all of the catalysts at the early stages of testing. The highest hydrogen evolution rate, 5.4 μmol/min, is afforded by the 1%Pt/Cd_0.3Zn_0.7S catalyst. The activity of the Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S catalysts becomes constant 7.5–9 h after the beginning of the photocatalytic test, while in the case of Pd/Cd_0.3Zn_0.7S the hydrogen evolution rate increases over the initial 6 h and then decreases. These specific features of the catalysts likely correlate with the initial state of the metals on the support surface. In particular, supported palladium is in the form of PdO, while gold and platinum are in the metallic state. The Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S photocatalysts are activated due to metal encapsulation; the 1%Pd/Cd_0.3Zn_0.7S catalyst, due to the partial reduction of PdO to PdO _x . The 1%Pd/Cd_0.3Zn_0.7S catalyst is deactivated because of the aggregation of nanoparticles of the cadmium sulfide–zinc sulfide solid solution.     

Phase diagrams in the quaternary systems M1−xCuxCr2X4 with M = Cd,Mn, and X = S,Se

The phase diagrams of the spinel systems Cd_1?xCu_xCr₂S₄, Cd_1?xCu_xCr₂Se₄, and Mn_1?xCu_xCr₂S₄ have been studied on the basis of X-ray powder photographs of quenched samples and high-temperature X-ray diffraction patterns. At room temperature the mutual solid solubilities of the metallic copper and the semiconducting cadmium and manganese spinels are only small (x < 0.05 and >0.95). The interchangeability, however, increases largely with increasing temperature. Complete series of mixed crystals, as in the Zn_1?xCu_xCr₂X₄ (X = S, Se) systems, however, are not formed. The solid solutions with x > 0.07 and <0.95, x > 0.095 and <0.90, and x > 0.36 and <0.87, respectively, formed at higher temperatures cannot be quenched to room temperature without decomposition. The unit cell dimensions of the spinel solid solutions studied obviously do not obey Vegard's rule.     

Near‐Infrared‐Emitting CdxHg1−xSe Nanorods Fabricated by Ion Exchange in an Aqueous Medium

Whereas CdSe nanorods that are grown in organic solution have a hexagonal wurtzite structure, which is the limiting case for exchange, HgSe is more commonly encountered as a cubic zinc blende system. An exchange process was performed at room temperature and at atmospheric pressure in an aqueous environment after phase transfer of the original CdSe nanorods, which reinforced the tendency for the endpoint of HgSe to be cubic. Consequently, we observed that under ambient conditions, the exchange process terminated with an average composition of only Cd_0.9Hg_0.1Se. Following the changes during the process by optical spectroscopy and high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), we observed that the Hg²⁺ ions diffused into the rods to a point limited by the formation of stacking faults due to the different lattice structures of the two limiting cases of zinc blende and wurtzite. HAADF‐STEM and energy dispersive spectroscopy analyses also confirmed that the Hg substitution did not occur uniformly throughout the individual nanorods, as Hg‐poor and Hg‐rich regions coexist around the stacking faults. The formation of near‐infrared‐emitting alloyed Cd_xHg_1?xSe nanorods in an aqueous medium highlights the subtle dependence of the ion‐exchange process on the differences in the crystal structures of the two endpoint lattices.     

Chemical interaction of CdTe and Cd1? x Zn x single crystals with aqueous H2O2 + HBr + Citric acid solutions

The chemical etching of single crystals of CdTe and Cd_1−x Zn _x Te solid solutions in bromine-evolving aqueous H₂O₂ + HBr + citric acid solutions is considered. Simplex design of experiments is used to construct the projections of etching rate isosurfaces and to map the polishing and nonpolishing composition regions. Dissolution in the polishing etchants is diffusion-controlled. As the zinc content of Cd_1−x Zn _x Te is raised, the etching rate increases; the boundaries of the polishing region do not change to any significant extent. The polish composition and the dynamic chemical polishing conditions are optimized for the semiconductors examined. Original Russian Text ? Z.F. Tomashik, I.I. Gnativ, V.N. Tomashik, I.B. Stratiichuk, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1234–1238.     

Optical damping constants in narrow gap semiconductors

Optical damping constants due to free carriers of HgSe, Zn _x Hg_1–x and Cd _x Hg_1–x Se were estimated from far infrared reflection spectra at 5 and 10 K. The damping mechanism was explained by the Drude type scattering below plasma frequency and by doubly ionized impurity scattering in the higher frequency range.     

Determination of the stoichiometry of semiconductor systems of the type CdvHg1?vSe and CdxHg1?xTe by X-ray fluorescence spectrometry

Summary Semiconductors of the composition Cd _v Hg_1–v Se and Cd _x Hg_1–x Te are gaining growing industrial interest. The energy gap between the bands of such systems depends significantly on the magnitude of the mole fractions v and x. X-ray fluorescence analysis of acid solutions of these crystals is a simple and precise procedure to determine the stoichiometry. Sample preparation, calibration series and results are discussed.

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Bestimmung der Stöchiometrie von Halbleitersystemen des Typs Cd_vHg_1–vSe und Cd_xHg_1–xTe, durch Röntgenfluorescenz-Spektrometrie

Zusammenfassung Halbleiter der Typen Cd _v Hg_1–v Se und Cd _x Hg_1–x Te gewinnen zunehmend industrielles Interesse. Der Energieabstand der Bänder in solchen Systemen hängt entscheidend von der Größe der Molenbrüche v und x ab. Ein einfaches und sicheres Analysenverfahren zur Ermittlung der Stöchiometrie ist die Röntgenfluorescenzanalyse von sauren Lösungen dieser Kristalle. Die Probenvorbereitung, Eichreihen und Resultate werden diskutiert.

Delegated to Central Institute of Analytical Chemistry, Nuclear Research Establishment (KFA), Jülich, FRG.     

Enhanced Photocatalytic Hydrogen‐Production Performance of Graphene–ZnxCd1−xS Composites by Using an Organic S Source

In response to the increasing concerns over energy and environmental sustainability, photocatalytic water‐splitting technology has attracted broad attention for its application in directly converting solar energy to valuable hydrogen (H₂) energy. In this study, high‐efficiency visible‐light‐driven photocatalytic H₂ production without the assistance of precious‐metal cocatalysts was achieved on graphene–Zn_xCd_1?xS composites with controlled compositions. The graphene‐Zn_xCd_1?xS composites were for the first time fabricated by a one‐step hydrothermal method with thiourea as an organic S source. It was found that thiourea facilitates heterogeneous nucleation of Zn_xCd_1?xS and in situ growth of Zn_xCd_1?xS nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and Zn_xCd_1?xS nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H₂ production. The highest H₂‐production rate of 1.06 mmol h^?1 g^?1 was achieved on a graphene–Zn_0.5Cd_0.5S composite photocatalyst with a graphene content of 0.5 wt %, and the apparent quantum efficiency was 19.8 % at 420 nm. In comparison, the graphene–Zn_xCd_1?xS composite photocatalyst prepared by using an inorganic S source such as Na₂S exhibited much lower activity for photocatalytic H₂ production. In this case, homogeneous nucleation of Zn_xCd_1?xS becomes predominant and results in insufficient and loose contact with the graphene backbone through weak van der Waals forces and a large particle size. This study highlights the significance of the choice of S source in the design and fabrication of advanced graphene‐based sulfide photocatalytic materials with enhanced activity for photocatalytic H₂ production.     

NixCo3-xO4表面修饰对CdSe/TiO2纳米管阵列光电化学氧化水活性的影响

利用氨挥发诱导法在CdSe/TiO2纳米管阵列表面负载一层NixCo3-xO4。采用SEM、XRD、XPS、UV-Vis对样品进行表征,通过线性扫描伏安法测定光阳极的释氧电势来评价其光电水氧化活性。结果表明:表面NixCo3-xO4是尖晶石结构;相对于CdSe/TiO2纳米管阵列光阳极,NixCo3-xO4/CdSe/TiO2光阳极能将光电氧化水的过电势降低430 mV。Ni离子的引入使得NixCo3-xO4表面富含三价阳离子(Ni3+,Co3+),从而促进CdSe/TiO2光阳极光电水氧化的进行。     

Electrochemical and mechanochemical formation of solid solutions of potassium copper(II)/zinc(II) hexacyanocobaltate(III)/hexacyanoferrate(III) KCu x Zn1-x [hcc] x [hcf]1-x

Electrochemical reduction/oxidation cycles of immobilised powder mixtures of KCu[hcc] and KZn[hcf] as well as their mechanical milling lead to the formation of a quaternary solid solution (mixed crystals) with Cu²⁺ and Zn²⁺ on the nitrogen coordinated sites and Fe³⁺ and Co³⁺ on the carbon coordinated sites. The reaction products were studied by the X-ray diffractometry and voltammetric techniques. The formation of solid solutions of the general formula KCu_xZn_1-x[hcc]_x[hcf]_1-x is the first example of an electrochemical and mechanochemical reaction leading to mixed hexacyanometalates.Dedicated to Professor Dr. G. Horányi on the occasion of his 70th birthday.     

ZnxCd1-xS纳米线的可控合成及其可调的光学性质

采用简单的气相沉积法,合成了不同组成的Zn_xCd_1-xS (0< x <1)纳米线. 利用扫描电子显微镜、透射电子显微镜和电子能谱研究了所制得的纳米线的表面形貌和组成. 该方法以Au为催化剂,简单控制起始物质的相对用量和沉积温度,可以获得可控的Zn/Cd 比例. X射线衍射结果表明所制得的Zn_xCd_1-xS纳米线具有纤维锌矿的单晶结构. 根据制得纳米线的表面形貌讨论了纳米线可能的生长机理为“底部生长”机理. 利用拉曼光谱和光致发光光谱研究了Zn_xCd_1-xS纳米线的光学性质,其纵向光学(LO)声子的拉曼位移频率随着组成的变化在ZnS和CdS的拉曼位移频率之间连续变化. 光致发光光谱中同时存在带边发光和缺陷发光. Zn_xCd_1-xS纳米线的带间跃迁的频率可随着组成的调节而调节,纳米线的禁带宽度介于ZnS (3.63 eV)和CdS (2.41 eV)的禁带宽度之间.     

SbxZn1-xO1+x/2及其壳聚糖复配物的制备和抗菌性能

采用溶胶-凝胶法制备了SbxZn1-xO1+x/2及其壳聚糖的复配物,通过X-射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等表征了样品的物相结构、组成和微观形貌。以大肠杆菌、白色念珠菌和金黄色葡萄球菌为测试菌种,研究了样品的抗菌性能。结果表明,SbxZn1-xO1+x/2的抗菌活性优于纯ZnO,其中x=0.05的样品活性最好;复配物的抗菌活性明显优于单一组分,当Sb0.05Zn0.95O1.025和壳聚糖质量比mSZ/mCS=2时,样品抗菌性能最佳。     

Template‐Free Preparation of Volvox‐like CdxZn1−xS Nanospheres with Cubic Phase for Efficient Photocatalytic Hydrogen Production

Volvox‐like Cd_xZn_1?xS solid solutions with a cubic zinc blend structure were synthesized through a template‐free ethylene glycol process. Cd(Ac)₂ ? 2 H₂O, Zn(Ac)₂ ? 2 H₂O, and thiourea are used as the starting materials and dissolved in ethylene glycol. These reaction precursors and solvent not only contributed to control over the formation of the volvox‐like spherical geometry, but also exerted vigorous domination for existence of cubic‐phase Cd_xZn_1?xS nanostructures. As‐prepared volvox‐like Cd_xZn_1?xS nanospheres have a diameter of around 100 nm with extensional shells. These samples show excellent photocatalytic H₂ evolution activity from water splitting under visible‐light irradiation without any cocatalyst or scaffolding, owing to their tunable band gap, cubic zinc blend structure, and unique hierarchical porous structure with a high surface area (as high as 95.2 m² g^?1).