金属卤化物钙钛矿光催化材料研究进展

发展绿色、环保、可持续的化学过程是当今环境、能源、化学学科面临的重大挑战。太阳能驱动光催化实现化学燃料制备、降解环境污染物、高附加值产物转化是解决目前面临的能源和环境问题的一条有效途径。近年来,金属卤化物钙钛矿材料作为一种新型高效的光催化材料受到了广泛关注。本文系统地阐述了金属卤化物钙钛矿材料在光催化析氢、光催化CO₂还原和光催化有机物转化中的研究进展,讨论了金属卤化物钙钛矿的光催化作用机理和面临的困难,最后对金属卤化物钙钛矿光催化材料的发展方向进行了分析和展望。     

拓展光催化材料光谱响应的研究进展

光催化技术在解决能源短缺和环境污染问题方面有重要的应用前景,引起了人们的广泛关注。宽光谱响应和高量子效率是实现光催化材料大规模应用的前提。本文介绍了近年来紫外、可见和近红外光催化方面的最新进展,阐述了拓展光响应范围和促进载流子分离的有效途径,总结了光催化材料发展所面临的问题,并对其发展趋势进行了展望。     

Z型InN/SnS2范德华异质结增强光催化水分解

寻找高效的光催化剂分解水制氢是解决能源危机和环境问题的有效途径之一.基于第一性原理,对InN/SnS₂异质结的几何结构、电子结构和光催化水分解性能进行研究.结果表明InN/SnS₂异质结是具有的Ⅱ型能带排列半导体材料可以有效地分离电子空穴对.在光激发下,较小的带隙以及合适的内建电场使得光生载流子迁移路径成“Z”字型,这保留了InN/SnS₂异质结强氧化还原能力.光生电子在InN的导带底累积并发生析氢反应,而积累在SnS₂上的光生空穴使析氧反应自发发生.它们的带边位置都跨越了水的氧化还原电位,证明能够实现水的完全分解.因此,InN/SnS₂异质结有希望成为高效光解水催化剂.     

铁电材料光催化活性的研究进展

光催化技术被认为是最有前景的环境污染处理技术,这就使得光催化剂材料备受瞩目.近年来,铁电材料作为新型光催化剂材料受到人们越来越多的关注,其原因在于铁电材料特有的自发极化有望解决催化反应过程中的电子-空穴对复合问题,进而提高光催化活性.本文从两个方面对铁电极化如何影响光催化进行综述:一方面,从铁电极化入手归纳总结其对电子-空穴对分离的影响,进而更深入地从极化引发的退极化场和能带弯曲两个部分来阐述具体的影响机理;另一方面,为了消除静电屏蔽,分别从温度、应力(应变)、电场三个外场因素调控极化入手,归纳总结外场调控极化对电子-空穴对分离的影响,进而影响光催化活性.最后对该领域今后的发展前景进行了展望.     

全功能型有机光折变材料的研究进展

本文综述了全功能型光折变聚合物和小分子材料的研究进展，并详细汇 总了这种材料的热特性，光电和电光特性，及光折变特性参数。基于对材料从分子水平上的设计思想，阐述了这种光折变材料的发展思路。     

二氧化钛负载光纤型光催化反应器的研究进展

详解了纳米二氧化钛光催化降解有机污染物的反应机理,综述了为了提高光催化效率,在光纤型光催化反应器的设计、改进、研制及应用方面所做的工作,同时讨论了光催化剂负载技术和光催化剂重复利用问题。最后,简述了近年来光纤型光催化反应器在国内外的研究进展,针对目前光催化反应器存在的技术瓶颈,对该项技术未来的发展进行了简要分析并提出了改进建议。     

钙钛矿太阳能电池中电子传输材料的研究进展

有机-无机杂化的卤素钙钛矿材料在2009年首次应用在光伏器件中, 而后有关此类型太阳能电池的报道数量呈井喷式增长. 至2014年5月钙钛矿电池光电转化效率已接近20%, 已超过有机及染料敏化太阳能电池的效率, 且有望达到单晶硅太阳能的水平, 成为光伏发电领域中的希望之星. 在钙钛矿电池中, 电子传输材料与吸收层的电子选择性接触对提高光电转化效率起到重要作用, 尤其在正置结构器件中, 电子传输层的介观结构直接影响钙钛矿的生长情况. 同时, 电子传输层的化学性质及其界面也会对电池的稳定性和寿命产生影响. 本文总结了电子传输材料在该类电池中的研究现状和热点, 并按材料的化学组分不同, 将电子传输材料分为三类: 金属氧化物、有机小分子和复合材料, 详细地介绍了电子传输材料在钙钛矿太阳能电池中的作用和近来的最新进展.     

二维光催化材料的电子结构调控与应用研究进展(特邀)

首先综述了基于二维光催化剂的电子结构调控方式,包括厚度调节、元素掺杂、缺陷工程和异质结的设计等.其次,由于半导体异质结在减少光生电子空穴复合速度方面具有独特的优势,着重介绍了由二维材料与其它不同维数的半导体界面组成的异质结的研究进展.最后介绍了新型二维光催化材料在析氢、CO2还原、固氮和污染物降解等方面的应用.总结文献...     

厚高阶光学非线性介质Z扫描的变分法分析

利用变分法对具有五阶光学非线性介质的Z扫描特性进行了研究。通过比较，发现当介质在具有较大的五阶非线性系数或较大光强的情况下，五阶非线性项的作用是不可忽略的。这对光限制器的设计和Z扫描实验都具有一定的指导意义。     

微波吸收法研究(ZnCd)S∶Cu发光材料光生载流子的衰减过程

采用微波吸收法,测量了(ZnCd)S∶Cu及ZnS∶Mn,Cu粉末材料受到超短脉冲激光激发后,其自由电子和浅束缚电子的衰减过程。发现Cd2+的浓度对导带电子和浅束缚电子的寿命影响较小,而Cu+的浓度对导带电子和浅束缚电子的寿命有明显的影响,提高激活剂掺杂浓度会使自由电子的寿命大大缩短。     

Transition from the Kondo effect to a Coulomb blockade in an electron shuttle

We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle.Employing the equation of motion method for the nonequilibrium Green’s function,we show that the oscillation of the dot,i.e.,the time-dependent coupling between the dot’s electron and the reservoirs,can destroy the Kondo effect.With the increase in the oscillation frequency of the dot,the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern.Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states.Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices.     

电子叠层衍射成像技术的突破及应用

像差校正透射电子显微镜是材料微观结构和物态高分辨率表征最常用的工具之一,极大地推动了相关学科的发展。近年来,电子显微学领域一个新的突破是电子叠层衍射成像技术。它突破了常规成像技术分辨率的极限,实现了原子晶格振动决定的终极分辨率,并且能够实现纳米尺度电磁物态的高精度成像。文章主要简述了电子叠层衍射成像技术的发展历程、原理和最新进展,最后讨论其应用前景和未来展望。     

Design and application of a new control system for tokamak ECRH power supply

The biggest challenge of designing and building tokamak electron cyclotron resonance heating (ECRH) pulse step modulation (PSM) power supply is satisfying its required output voltage rising time to be less than 100?µs while suppressing the voltage overshoot to be no more than 1%. To fulfill the two requirements, a new control strategy with startup time in microsecond range is proposed in this paper, and a new control system to realize the control strategy is introduced. The control system was built and tested on 60?kV/50?A ECRH power supply. The experimental results indicate that the control system can restrain the overshoot effectively, increase response speed, and obviously improve the dynamic characteristics of the PSM power supply system. Thus, the proposed control system helps the PSM power supply to meet the design specifications.     

Symmetry of the charge-ordered phases in Pr0.5Ca0.5MnO3

The crystallographic symmetry of the charge-ordered Pr_0.5Ca_0.5MnO₃ manganite is studied at ～98?K using convergent beam electron diffraction technique. These studies have revealed appearance of two different type of charge-ordered phases in different domains of the same grain. These correspond to be monoclinic and triclinic phases. These studies reveal that the symmetry of the charge-ordered phase is highly sensitive to the local strain conditions.     

Electron spin resonance study of the Ba-doping manganite Nd0.5Sr0.5MnO3

We have performed magnetization measurements and electron spin resonance （ESR） on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 （x = 0.1）. Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K （～ Tc） and 185 K （～ TN）, the system coexists of the paramagnetic phase and the ferromagnetic （FM） phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic （AFM） phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2＋ ions for the smaller Sr^2＋ ions.     

Effect of nanocrystalline particles on the magnetic properties of Z-type hexaferrites

In order to improve the magnetic properties of Z-type hexaferrites such as high initial permeability and high-quality factor, the nanocrystalline hexaferrite particles (NHPs) with the same chemical composition were introduced. The influence of NHPs on the densification, microstructures and magnetic properties of the ceramics prepared by a combined method was investigated. The results show that these NHPs, which spread around the micron-sized hexaferrite particles (MHPs), enhance the densification by increasing the inter-diffusion of the particles due to the increase of contact area; simultaneously, the grain growth in the direction of c-plane is dominant. Due to the special microstructure, high sintering density, and no addition sintering aids with different chemical composition, relatively high initial permeability and Q-factor than those of the samples with 1.0 wt% Bi₂O₃ were obtained in the samples with proper nanocrystalline particles sintered at 900 °C.     

取代基效应对对称共价有机框架光催化性质的影响

对称共价有机框架(COF)光催化剂通常存在电荷分离效率低和光激发态寿命短的问题. 通过密度泛函理论和含时密度泛函理论计算,本文发现了用一个或两个取代基(N或NH₂)在具有代表性的对称共价有机框架(N₀-COF)的连接单元内进行部分取代可得到具有电荷分离特征的共价有机框架(N₁-COF、N₂-COF、(NH₂)₁-N₀-COF和(NH₂)₂-N₀-COF). 此外,还发现N₀-COF的最高占据晶体轨道和最低未占据晶体轨道的能级位置可通过取代远离或靠近真空能级,这取决于取代基的吸电子或给电子特性. 因此,本文提出了通过精心选择具有吸电子或给电子效应的取代基,并在对称共价有机框架的连接单元内进行部分取代,所获得的共价有机框架可具有高效的电荷分离以及驱动特定光催化反应的合适最高占据晶体轨道和最低未占据晶体轨道能级位置. 该规则可用于进一步提升许多具有对称性的共价有机框架的光催化性能.     

Effect of MgO additive on the high-frequency properties of Z-type hexaferrites

MgO was introduced into low-temperature sintered Z-type hexaferrites in order to improve their high-frequency electromagnetic properties. In the doped samples the major Z-type phase coexists with a small amount of W-type magnetoplumbite phase. The addition of MgO causes a decrease of the average grain size and an increase of the magnetocrystalline anisotropy (K₁) and the saturation magnetization (M_s) with the increment of K₁ being larger than that of M_s. These factors result in a reduce of the initial permeability. Also, the samples with MgO additive exhibit higher Q-factor and dc resistivity. Furthermore, the introduction of MgO can decrease the dielectric constant and improve the dielectric loss tangent of the samples by reducing the electronic transition in octahedral site (B-site) between Fe²⁺ and Fe³⁺ ions.