纳米晶氧化锌微球的制备

通过醋酸锌在一缩二乙二醇中热醇解反应制备了纳米晶ZnO微球,探讨了在醋酸锌热醇解法制备过程中升温速率对醇解反应温度和ZnO微球粒径分布的影响.在此基础上采用种子法制备了ZnO微球,考察了种子液加入量和反应时间对ZnO微球粒径分布的影响,并尝试使用SJN-30硅溶胶和SiO2微球乳液为种子液制备核-壳结构ZnO复合微球.     

Study on growth and photoluminescence of zinc telluride crystals synthesized by hydrothermal method

Zinc telluride powders were synthesized in sodium hydroxide solution by hydrothermal method by changing the growth temperature and time. The powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and micro-Raman spectroscopy, respectively. The results indicate that zinc telluride crystallizes in zinc blende structure and their sizes were increased with the increase in temperature and time, and oxygen easily is incorporated into zinc telluride crystals. The photoluminescence of the powders were investigated at room temperature. The photoluminescence spectra exhibit the emission peaks related to complex defects containing zinc vacancies and impurities and excitons bound to isoelectronic oxygen traps at about 556 and 703 nm, respectively. The growth of zinc telluride crystals and the relation of the photoluminescence with the growth conditions were analyzed.     

Preparation of ZnO nanoparticles by thermal decomposition of zinc alginate

A new method to produce zinc oxide nanocrystals is presented. The method is based on the thermal decomposition of zinc alginate gels. The gels were produced in the form of beads by ionic gelation between a zinc solution and sodium alginate. The wet beads were heated at 800 and 450 °C for 24 h and the products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission electron microscopy (TEM) and micro-Raman spectroscopy. XRD analysis showed that all obtained samples are of wurtzite structure. TEM analysis combined with electron diffraction also showed the presence of single crystals indexed as ZnO hexagonal phase. Crystal size was determined by measuring individual crystals from SEM pictures. It was found that heating temperature and the kind of zinc agent influence the crystal size. Raman scattering revealed the existence of defects in the structure of nanoparticles whose cringing was discussed in the context of recent studies in this field.     

弛豫铁电单晶及织构陶瓷的研究进展

综述了近年来弛豫铁电单晶和织构陶瓷的制备及其介电、压电性能的研究进展。弛豫铁电单晶的制备方法主要有高温溶液法、布里奇曼法和固态再结晶法，尺寸可达40mm以上，(001)切片压电常数d33最大可达3000pC／N，k3达到0.93，但是成分不均匀仍是影响晶体压电性能的一个主要因素。织构陶瓷的制备方法主要为固态再结晶法(TGG法和RTGG法)，其耗时短、成本低，压电性能可达到单晶的60％～80％，介电常数甚至可以超过部分单晶，是一个新的发展方向。     

Growth of single crystals of some complex salts in silica gels

Single crystals of ammonium nickel sulphate, potassium nickel sulphate, ammonium alum and potassium alum are grown in sodium-metasilicate gels. The method of gel preparation and growth procedure are described. Both single diffusion and double diffusion methods are used. Studies on nucleation and characterisation of crystals are also reported. Crystals grown are illustrated.     

纳米氧化锌的制备工艺研究

以均匀沉淀法作为纳米氧化锌的制备方法,通过单因素实验和正交实验,系统地分析了溶液水解反应温度、水解反应时间、原料摩尔配比、煅烧温度等对氧化锌粉体产率和粒径的影响。结果表明,最佳工艺是:以直接混合的方式混合原料液,聚乙二醇-400作表面活性剂,反应温度90℃,原料摩尔配比c(尿素)/c(硝酸锌)=3:1,反应时间5.5h,前驱体碱式碳酸锌的最佳煅烧温度为500℃。通过所制得纳米氧化锌的XRD、SEM的粒径分析,证明了所制得的纳米氧化锌晶形为六方晶相,纯度大于99.9%、平均粒径约为68nm,产率为89.6%。     

硝酸溶液中制备不同粒度级别黑索今的方法

文章报道了一种生结晶制备不同粒度级别黑索今的方法。探讨了硝酸溶液中ＲＤＸ晶核形成，晶体缺陷与ＲＤＸ晶体酸度之间的关系；研究了结晶温度，搅拌速度，稀释速度等工艺条件对ＲＤＸ晶体粒度，形状及酸度的影响。     

Control of cathodic potential for deposition of ZnO by constant-current electrochemical method

For the preparation of functional films and crystals, the electrochemical deposition method has advantages of large-area deposition at low temperature and high efficiency in terms of the raw materials used. However, crystallization through electrochemical processes is not currently well understood. To apply the electrochemical deposition method, it is necessary to better understand the crystallization and the growth mechanism. To investigate the mechanism, it is essential to ensure the reproducibility of the growth process. We focused on cathodic potential as a parameter that affects the reproducibility of the galvanostatic method. The repeatability of cathodic potentials during deposition was drastically improved by optimizing the mask pattern on the electrode and the pre-treatment conditions. As the result, the cathodic potential was able to be controlled by the current density. Furthermore, nucleation and grain growth of ZnO crystals by the galvanostatic electrochemical method are discussed in association with the change of cathodic potential. Changes in grain size at various cathodic currents are also discussed.     

Colloid stable sorbents for cesium removal: preparation and application of latex particles functionalized with transition metals ferrocyanides

In this paper we suggest a principally new approach to preparation of colloid stable selective sorbents for cesium uptake using immobilization of transition metals (cobalt, nickel, and copper) ferrocyanides in nanosized carboxylic latex emulsions. The effects of ferrocyanide composition, pH, and media salinity on the sorption properties of the colloid stable sorbents toward cesium ions were studied in solutions containing up to 200 g/L of sodium nitrate or potassium chloride. The sorption capacities of the colloid sorbents based on mixed potassium/transition metals ferrocyanides were in the range 1.3-1.5 mol Cs/mol ferrocyanide with the highest value found for the copper ferrocyanide. It was shown that the obtained colloid-stable sorbents were capable to penetrate through bulk materials without filtration that made them applicable for decontamination of solids, e.g. soils, zeolites, spent ion-exchange resins contaminated with cesium radionuclides. After decontamination of liquid or solid radioactive wastes the colloid-stable sorbents can be easily separated from solutions by precipitation with cationic flocculants providing localization of radionuclides in a small volume of the precipitates formed.     

Effect of peptization of an inorganic sorbent on its sorption characteristics

A series of samples of Termoxid-35 inorganic sorbent (nickel ferrocyanide applied onto zirconium hydroxide granules) were prepared. The samples have similar chemical composition but differ in the degree of peptization in aqueous solutions. Kinetic curves of ¹³⁷Cs sorption from aqueous solution demonstrate relationship between the sorbent tendency to peptization and its sorption properties. With an increase in the peptizability of the sorbent, its sorption-selective properties become considerably worse. The sorbent preparation process should involve treatment procedures allowing preparation of the peptization-resistant material.     

Effects of morphology on NO2 detection in air at room temperature with phthalocyanine thin films

Lead phthalocyanine films freshly deposited on alumina and glass were found to consist of disordered phases and fine particles with mean diameter below 0.2m. Following annealing at 300 ° C, a transition to a crystalline form is obtained. The crystal size in the films annealed at 300 ° C or above is affected by the nature of the substrate, ambient atmosphere and annealing time. Following an optimized preparation procedure, the films exhibit response times of less than 20 sec and recovery times of the order of several minutes, independently of N0₂ concentration or exposure time, at room temperature. They consist of fine crystals with mean diameters of the order of 0.2m and amorphous phases are not observed. For zinc, copper, cobalt and nickel phthalocyanine films, some improvements in the response and recovery times are achieved by annealing but not sufficient to allow No₂ detection at room temperature. For films of these phthalocyanines, fine crystals of the type formed in leadphthalocyanine films were not produced in the conductive paths when the films were annealed at 300 ° C in air.     

超细镍粉的制备及还原生长机理研究

以联氨为还原剂,在硫酸镍水溶液中控制液相还原反应条件制备了超细镍粉,并讨论了超细镍粉的还原生长机理.通过实验分析了工艺参数对还原反应的影响,采用X射线衍射(XRD),扫描电镜(SEM),比表面积测定等分析手段对超细镍粉进行表征,结果表明:超细镍粉的形核和生长独立进行;温度、Ni2+浓度和pH值调控着溶液中镍离子的释放并...     

液相法制备纳米镍粉研究进展

详细介绍了液相法制备纳米镍粉的研究进展,并对液相法制备纳米镍粉的一些影响因素进行了探讨,例如反应物和还原剂的浓度、温度、表面活性剂等。对比分析了一些制备方法的特点,同时简单地介绍了纳米镍粉的应用前景和发展趋势。     

Sorption of cesium on finely dispersed composite ferrocyanide sorbents

Sorption of microamounts of cesium on finely dispersed composite ferrocyanide sorbents was studied. The sorbents were prepared by precipitation of nickel potassium ferrocyanide in the presence of various mineral supports (chalk, wollastonite, bentonite, clinoptilolite, diatomite, biosilica). The distribution coefficient (K _d) of ¹³⁷Cs on composite ferrocyanide sorbents is considerably higher than on nickel potassium ferrocyanide without support. The K _d values on the composite sorbents increase by a factor of 25–110 when separating the solid phase with a paper filter and by a factor of 4.3–8.2 when using a microfiltration membrane. Considerable increase in K _d of ¹³⁷Cs on composite sorbents is attributed to the formation of a nickel potassium ferrocyanide phase firmly fixed on the support surface and resistant to peptization. Composite ferrocyanide sorbents were tested for the ¹³⁷Cs recovery from a simulated NPP bottom residue in the pH range 8.5–12.0. On the composite sorbents, K _d of ¹³⁷Cs is 2.5–3.0 times higher than on the nickel ferrocyanide precipitate throughout the examined pH range. The composite sorbent based on biosilica and nickel potassium ferrocyanide was tested for treatment of real liquid radioactive waste with a total salt content of 22.0 g dm⁻³ to remove ¹³⁷Cs. The decontamination factor as high as 5190 was attained owing to simultaneous use of the finely dispersed composite ferrocyanide sorbent and an ultrafiltration ceramic membrane.     

Preconcentration and separation of copper, nickel and zinc in aqueous samples by flame atomic absorption spectrometry after column solid-phase extraction onto MWCNTs impregnated with D2EHPA-TOPO mixture

A solid phase extraction method has been developed for the determination of copper, nickel and zinc ions in natural water samples. This method is based on the adsorption of copper, nickel and zinc on multiwalled carbon nanotubes (MWCNTs) impregnated with di-(2-ethyl hexyl phosphoric acid) (D2EHPA) and tri-n-octyl phosphine oxide (TOPO). The influence of parameters such as pH of the aqueous solution, amount of adsorbent, flow rates of the sample and eluent, matrix effects and D2EHPA-TOPO concentration have been investigated. Desorption studies have been carried out with 2 mol L(-1) HNO(3). The copper, nickel and zinc concentrations were determined by flame atomic absorption spectrometry. The results indicated that the maximum adsorption of copper, nickel and zinc is at pH 5.0 with 500 mg of MWCNTs. The detection limits by three sigma were 50 μg L(-1) for copper, 40 μg L(-1) for nickel and 60 μg L(-1) zinc. The highest enrichment factors were found to be 25. The adsorption capacity of MWCNTs-D2EHPA-TOPO was found to be 4.90 mg g(-1) for copper, 4.78 mg g(-1) for nickel and 4.82 mg g(-1) for zinc. The developed method was applied for the determination of copper, nickel and zinc in electroplating wastewater and real water sample with satisfactory results (R.S.D.'s <10%).     

Some aspects of nanocrystalline nickel and zinc ferrites processed using microemulsion technique

Abstract

Nanocrystalline nickel and zinc ferrites synthesised using a microemulsion technique were characterised by high resolution transmission electron microscopy and vibrating sample magnetometry. A narrow and uniform distribution of crystals of size range 5-8 nm, distinguished by a clear lack of saturation magnetisation at 9 kOe, were obtained. Also, no coercivity or remanence was observed.     

Porous photocatalytically active ZnO films obtained from ethylcellulose modified solutions by spray pyrolysis

Nanocrystalline porous ZnO films are deposited onto alumina foil substrates by polymer-modified spray pyrolysis of zinc nitrate and zinc acetate solutions. The dependence of the concentration of added ethylcellulose and the type of zinc precursor on both the photocatalytic properties and films morphologies is investigated. It is established that the addition of ethylcellulose as a modifier in the spray solution leads to the formation of a porous structure with crystallites sizes about 15 nm, when zinc acetate is used as precursor. These films show better photocatalytic activity for degradation of Malachite Green (MG) dye than the films obtained from zinc nitrate modified solution. The zinc nitrate films exhibit weaker activity for degradation of MG regardless of their smaller crystallite size (8–12 nm). This can be explained with their lower porosity than that of polymer-modified zinc acetate films. It is established that 450 °C is the limit temperature of treatment for the preparation of ZnO films with good photocatalytic activities. This photocatalytic activity in films shows a drop in the comparison to the films treated at lower temperature, due to decreasing of the pore number and deterioration of the surface morphology.     

Graphene Single Crystals: Size and Morphology Engineering

Recently developed chemical vapor deposition (CVD) is considered as an effective way to large‐area and high‐quality graphene preparation due to its ultra‐low cost, high controllability, and high scalability. However, CVD‐grown graphene film is polycrystalline, and composed of numerous grains separated by grain boundaries, which are detrimental to graphene‐based electronics. Intensive investigations have been inspired on the controlled growth of graphene single crystals with the absence of intrinsic defects. As the two most concerned parameters, the size and morphology serve critical roles in affecting properties and understanding the growth mechanism of graphene crystals. Therefore, a precise tuning of the size and morphology will be of great significance in scale‐up graphene production and wide applications. Here, recent advances in the synthesis of graphene single crystals on both metals and dielectric substrates by the CVD method are discussed. The review mainly covers the size and morphology engineering of graphene single crystals. Furthermore, recent progress in the growth mechanism and device applications of graphene single crystals are presented. Finally, the opportunities and challenges are discussed.     

Source-material dependent growth limitations in unseeded dissociative sublimation of ZnSe

It has been found that besides temperature conditions, source-material composition (phase purity, impurity concentration and non-stoichiometry) dominates the quality of ZnSe crystals due to mass transport limitations and fluctuations. Therefore, without definite pretreatment, commercially supplied ZnSe source material is unsuitable for the physical vapour growth of ZnSe in closed systems. In this work the results of various characterization methods have been closely related to the optimal source preparation. For characterization of the non-stoichiometry of crystals, a qualitative relation between colour and zinc vacancy concentration has been established.     

Enhanced optoelectronic,thermal, mechanical and third order nonlinear optical properties of dichlorobis(thiourea)zinc(II) crystal: an effect of Phenol red dye

For the first time the growth of dichlorobis (thiourea) zinc(II) (ZTC) monocrystal in presence of Phenol red dye of considerably good size (~13 mm?×?5 mm) has been achieved from aqueous solution using slow evaporation solution technique at room temperature. The solubility was calculated at different temperatures. The crystal structure was confirmed through X-ray diffraction analysis. The crystallinity of the dyed crystals has been enhanced revealed by Powder X-ray diffraction study. The presence of dye was inveterate by FT-IR and FT-Raman spectroscopic studies. The scanning electron microscopy analyses show that the grown crystals with dye are better than pure. Diffused reflectance was measured and optical band gap was calculated found to be enhanced from 4.5 to 4.65 eV for dyed crystals. The enhancement in the PL intensity has been observed in the dyed crystals. DSC study shows that the thermal stability has been remarkably enhanced from 163?°C (pure) to 203?°C (dyed) and various other thermal parameters are calculated. The surface study shows that the grown crystals with dye possess less dislocation than pure. Mechanical strength of the dyed crystal is found to be remarkably enhanced. Third-order nonlinear optical susceptibility (χ3) of PRZTC was found to be 2 times higher than pure. All results suggest that the properties of ZTC crystals grown in presence of dye are enhanced and can be considered as better contender in various nonlinear devices.