金纳米粒子组装体的连续离散型纳米结构控制

采用柠檬酸钠还原氯金酸的方法,制备出粒径均一的金纳米粒子(AuNPs),通过加入二水合双(对-磺酰苯基)苯基膦化二钾盐(BSPP),增强了AuNPs体系的分散性与稳定性.选用直径为15和40nm的AuNPs,用不同序列巯基修饰的单链DNA连接到其表面,通过DNA链的杂交,形成不同结构的金纳米粒子组装体.通过改变加入DNA延长连接单元的比例,可以控制金纳米粒子组装体具有连续离散型的1∶1,2∶1和3∶1纳米结构.     

Nanostructured heterogeneous catalysts for electrochemical reduction of CO2

Electrochemical reduction of CO₂ provides a sustainable solution to address the intermittent renewable electricity storage while recycling CO₂ to produce fuels and chemicals. Highly efficient catalytic materials and reaction systems are required to drive this process economically. This Review highlights the new trends in advancing the electrochemical reduction of CO₂ by developing and designing nanostructured heterogeneous catalysts. The activity, selectivity and reaction mechanism are significantly affected by the nano effects in nanostructured heterogeneous catalysts. In the future, energy efficiency and current density in electrochemical reduction of CO₂ need to be further improved to meet the requirements for practical applications.     

Effect of the dielectric-constant mismatch and magnetic field on the binding energy of hydrogenic impurities in a spherical quantum dot

Within the effective mass approximation and variational method the effect of dielectric constant mismatch between the size-quantized semiconductor sphere, coating and surrounding environment on impurity binding energy in both the absence and presence of a magnetic field is considered. The dependences of the binding energy of a hydrogenic on-center impurity on the sphere and coating radii, alloy concentration, dielectric-constant mismatch, and magnetic field intensity are found for the GaAs–Ga_1−xAl_xAs–AlAs (or vacuum) system.     

Unusual features of the dispersion force in layered and striated nanostructures

A discussion is presented on some physics behind the unusually long ranged dispersion forces recently predicted between one-dimensional and nanolayered structures with a zero electronic energy gap, such as metallic nanotubes and graphitic structures. The various results for these systems, previously obtained via a variety of formalisms, are here re-derived systematically from a single approach.     

银催化合成Tb(BO2)3纳米棒

采用固相反应银作催化剂成功合成出棒状结构的稀土硼酸盐Tb(BO₂)₃发光材料. 利用X射线衍射和区域电子衍射研究了产物的结构特性,在700 oC煅烧时,Tb(BO₂)₃纳米棒具有良好晶形. 透射电镜分析表明,Tb(BO₂)₃纳米棒直径为100～200 nm,厚度为30～50 nm,长约3 μm. 基于Ag纳米颗粒附在Tb(BO₂)₃纳米棒的顶端和中部的事实,探讨了Tb(BO₂)₃纳米棒的生长机理. 荧光光谱研究表明,在369 nm紫外光激发下,Tb(BO₂)₃能发出Tb³⁺的特征绿色荧光,发射主峰位于546 nm,归属于⁵D₄→⁷F₅跃迁. 同时,也探讨了煅烧温度对产物的结构、形貌以及发光性质的影响.     

Syntheses and characterization of Sr(OH)2 and SrCO3 nanostructures by ultrasonic method

The Sr(OH)₂ and SrCO₃ nanostructures were synthesized by reaction of strontium(II) acetate and sodium hydroxide or tetramethylammonium hydroxide (TMAH) via ultrasonic method. Reaction conditions, such as the concentration of the Sr²⁺ ion, aging time, power of the ultrasonic device and alkali salts show important roles in the size, morphology and growth process of the final products. The pure crystalline SrCO₃ were obtained by heating of product at 400 °C. The Sr(OH)₂ and SrCO₃ nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermal gravimetric (TG), differential thermal analyses (DTA) and the infrared spectroscopy (IR).     

Preparation and investigation of magnetic properties of MnNiTi-substituted strontium hexaferrite nanoparticles

A series of M-type strontium hexaferrite powders with substitution of Mn²⁺, Ni²⁺ and Ti⁴⁺ ions for Fe³⁺ ions according to the formula SrFe₉(Mn_0.5−xNi_xTi_0.5)₃O₁₉, where x ranges from 0 to 0.5 with a step of 0.1, has been prepared via the conventional ceramic method. In order to get nanoparticles, the obtained powders were milled in a high energy SPEX mill for 1 h. XRD investigations of the unmilled and milled powders show that the prepared samples are all single phase hexaferrite. Lattice parameters and mean crystallite sizes of the powders were determined from the XRD data and Scherrer’s formula. Transmission electron microscope (TEM) was used to analyze their structures. Room temperature magnetizations and coercivities of the samples in a magnetic field of 15 kOe have been determined from the hysteresis loops. It was found that magnetizations of the milled samples were smaller than the magnetization of the unmilled samples. This decrease, based on core-shell model, has been attributed to the presence of a magnetically dead layer on the particles’ surface of the milled powders. In addition, the magnetizations of the milled samples decrease with the increase in x value. This decrease has been discussed according to site occupation of the substituted cations on the sublattices. The discussion also supports the increase of lattice parameters and the decrease of Curie temperature as x increases.     

Chemical reactions in cracks of aluminum crystals: Generation of hydrogen from water

Pure hydrogen is generated from water molecules which are dissociated by specific aluminum particles called activated Al powder. Reaction mechanism of Al atoms with H₂O molecules is investigated in micro-cracks of Al crystals. It becomes obvious that hydrogen atoms exist in Al crystal mainly in states of AlH₃ hydrides. It is concluded that virgin walls of micro-cracks right after the creation provide virtually Al radical atoms of (Al−) or (Al=) with one or two free bonds, which react with H₂O molecules via surface diffusion resulting in producing AlH₃ and eventually in producing H₂. The production of H₂ seems to be a result of micro-tribochemical reactions in cracks, which are produced by mechanical crushing of Al crystals in water; tips of cracks as stress-focused points play a major role to create AlH_3. Peculiar environments of nano-spaces in micro-cracks surrounded by reactive atoms enable us to realize unusual chemical reactions at low temperatures as exemplified in the present paper.     

飞秒激光诱导硒化锌晶体表面自组织生长纳米结构

 以250 kHz高重复频率钛宝石飞秒激光聚焦到硒化锌晶体表面,利用扫描电子显微镜观测飞秒激光辐照后晶体的表面结构。发现线偏振激光辐照的区域形成了自组织周期性纳米结构,其周期为160 nm左右,并且可以通过改变激光的偏振方向调节纳米光栅结构的取向;当晶体相对于激光光束以10 mm/s速度移动,经激光扫描后,在晶体表面形成了长程类布拉格光栅。当飞秒激光光束为圆偏振光时,辐照区域形成均匀的纳米颗粒。     

Nanostructured BiVO4 Derived from Bi-MOF for Enhanced Visible-light Photodegradation

BiVO4,a promising visible-light responding photocatalyst,has aroused extensive research interest because of inexpensiveness and excellent chemical stability.However,its main drawback is the poor photoinduced charge-transfer dynamics.Building nanostructures is an effective way to tackle this problem.Herein,we put forward a new method to prepare nanostructured BiVO4 from Bi-based metal-organic frameworks[Bi-MOF(CAU-17)]precursor.The as-prepared material has a rod-like morphology inherited from the Bi-MOF sacrificial template and consists of small nanoparticle as building blocks.Compared with its counterparts prepared by conventional methods,MOF-derived nanostructured BiVO4 shows better light absorption ability,narrower bandgap,and improved electrical conductivity as well as reduced recombination.Consequently,BiVO4 nanostructure demonstrates high photocatalytic activity under visible light towards the degradation of methylene blue.Methylene blue can be degraded up to 90%within 30 min with a reaction rate constant of 0.058 min-1.Moreover,the cycling stability of the catalyst is excellent to withstand unchanged degradation efficiency for at least 5 cycles.