Bi2S3/BiOCl复合光催化剂的水热合成及其高活性

采用一种简便的水热法在433 K的温度下成功合成了具有不同Bi2S3质量分数的Bi2S3/BiOCl复合光催化剂,利用各种技术对其进行了表征.在紫外光照射下,以甲基橙水溶液的光催化降解为模型反应,评价了Bi2S3/BiOCl复合光催化剂的活性.研究结果表明:与纯Bi2S3和纯BiOCl相比,Bi2S3/BiOCl样品明显具有更高的光催化性能,尤其当Bi2S3在Bi2SJBiOCl中的质量分数为26.5％时,Bi2 SJBiOCl复合催化剂的光催化活性与商业P25(TiO2)的活性非常接近,而这种商业P25在紫外光照射下是公认的高效光催化剂.这种明显提高的光催化活性主要归功于光生电子和空穴在Bi2S3和BiOCl形成异质结界面上的有效转移,降低了电子-空穴对的复合.     

Z型光催化材料的研究进展

与植物光合作用相似, Z型光催化材料体系是由电子传输介质、光还原剂和光氧化剂组成的双光子体系, 其应用于光催化反应具有很大的优势: 借助双光子激发过程, 在不同光催化剂上分别完成氧化反应和还原反应, 有效促进了光生电荷的分离和迁移. Z型反应体系中的光催化剂只需分别满足各自的光激发过程和对应的半反应, 为光催化材料的选择和设计提供了很大的空间. 光催化还原位点和氧化位点分别在两个光催化半导体上, 还原和氧化过程相互分离, 可以有效抑制逆反应的发生. 同时, 催化材料光还原剂中的光生空穴被来自光氧化剂中的光生电子复合, 光催化体系的稳定性随之增强. Z型光催化材料体系, 表现出了宽光谱响应, 高稳定性, 高光生载流子的分离效率, 强氧化还原能力, 具有广阔的应用前景.     

Ag/K_4Nb_6O_(17)异质结催化剂的制备、光谱分析及光催化性能研究

采用低温水热法成功制备了层状的K4Nb6O17半导体光催化材料。考虑到水热合成的K4Nb6O17表面多羟基(Nb—OH)和端氧(Nb O,Nb—O-)的特点,采用Ag(en)2+配合物前驱体法制备了高度均匀分散的Ag/K4Nb6O17异质结光催化剂,光催化性能评价结果表明,半导体K4Nb6O17表面负载极少量的Ag,其光催化降解甲基橙活性便得到大幅度提高,Ag的最佳负载量为0.5 at%。综合XRD,FTIR,UV-VisDRS,XRF和TEM表征结果,对Ag/K4Nb6O17异质结光催化剂的作用机制进行了较详细地阐述并获得如下结论:(1)K4Nb6O17提供了降解有机染料分子的电子和空穴;(2)K4Nb6O17纳米晶上Ag粒子作为光生电子接受器,促进了金属-半导体界面上电荷的转移,有效地分离了光生电子-空穴对,提高了光催化活性。     

石墨烯/BiOI纳米复合物电子结构和光学性质的第一性原理模拟计算

光催化材料在解决能源短缺和环境污染等问题方面具有广泛的应用前景,本文通过构建BiOI纳米薄膜并将其与石墨烯复合起来,得到具有较高的比表面积和良好的光催化活性的纳米复合物光催化材料.采用基于密度泛函理论的第一性原理方法分别计算了单层和双层BiOI纳米片及其与石墨烯复合结构的电子结构和光学性质,并考虑了BiOI中的Bi,O,I三种空位缺陷对电子结构和光学特性的影响.计算结果表明,由于BiOI和石墨烯之间的相互作用,在石墨烯和BiOI界面处自发发生电荷转移,形成电子-空穴对,且石墨烯衬底可有效提高BiOI对可见光的光吸收,提高其光催化活性.对空位缺陷的计算表明,Bi空位缺陷可促进石墨烯和BiOI之间的电荷转移,形成更多的层间电子-空穴对;相反,O和I空位缺陷则抑制层间电荷转移,减少电子-空穴对的生成.     

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...     

Synthesis and Photocatalytic Activity of One-dimensional ZnO-Zn2SnO4 Mixed Oxide Nanowires

采用简单的热蒸发方法得到具有不同尺寸的混合ZnO-Zn2SnO4 (ZnO-ZTO)纳米线,并对纳米线进行结构和成分分析,试验还以甲基橙溶液为处理对象考察了ZnO-ZTO纳米线的光催化活性.结果表明ZnO-ZTO 混合纳米线的光催化性较纯ZnO、纯Zn2SnO4纳米线有较大提高; 光催化剂浓度对光降解效率有很大影响, 与纯ZnO、纯Zn2SnO4纳米线相比,少量的ZnO-ZTO纳米线即达到较高的光催化效率;并且光催化活性随着纳米线直径的减小而增加. 实验表明异质结的存在能够加快电子空穴的分离,提高光催化活     

Bi2S3/BiOCl复合光催化剂的水热合成及其高活性

采用一种简便的水热法在433 K的温度下成功合成了具有不同Bi₂S₃质量分数的Bi₂S₃/BiOCl复合光催化剂,利用各种技术对其进行了表征.在紫外光照射下,以甲基橙水溶液的光催化降解为模型反应,评价了Bi₂S₃/BiOCl复合光催化剂的活性.研究结果表明:与纯Bi₂S₃和纯BiOCl相比,Bi₂S₃/BiOCl样品明显具有更高的光催化性能,尤其当Bi₂S₃在Bi₂S₃/BiOCl中的质量分数为26.5%时,Bi₂S₃/BiOCl复合催化剂的光催化活性与商业P25(TiO₂)的活性非常接近,而这种商业P25在紫外光照射下是公认的高效光催化剂.这种明显提高的光催化活性主要归功于光生电子和空穴在Bi₂S₃和BiOCl形成异质结界面上的有效转移,降低了电子-空穴对的复合.     

钙钛矿铁电半导体的光催化研究现状及其展望

钙钛矿材料可以分为ABO_3氧化物和或I)卤化物两大类,它们都具有丰富的物理性质和优异的光电性能,比如铁电性和光催化性能.本文介绍了和等铁电半导体光催化材料和异质结的制备方法,总结了它们在光电催化方面的研究进展.目前研究者已经针对氧化物光催化材料做了各种研究,包括:降低吸光层铁电材料的带隙,制备铁电/窄带半导体吸光层异质结,制备比表面积很大的纳米片、纳米棒或者其他纳米结构,以便吸收更多可见光;让铁电极化及其退极化场垂直于光催化工作电极表面,通过铁电/半导体异质结能带弯曲提供内电场,通过外电场进行光电催化,从而通过内、外电场高效分离光生-电子空穴对;通过光催化或者光电催化降解染料、分解水制氢、将CO2转换为燃料;通过铁电、热释电和压电协同效应提高催化效应和能量转换效率等卤素钙钛矿具有优异的半导体性质,其铁电性可能是引起超长的少数载流子寿命和载流子扩散长度的原因.通过优化光催化多层膜结构并添加防止电解液渗透的封装层可以避免被电解液分解,从而制备了具有很高能量转换效率的光电催化结构.最后,我们分析和比较了这些钙钛矿铁电半导体在光电催化领域面临的挑战,并展望了其应用前景.     

基于电子顺磁共振的锌卟啉敏化TiO2光催化性机理的研究

为了研究锌卟啉/TiO₂复合光催化剂的光催化效率及电子转移问题, 本文采用溶胶凝胶法制备了锌卟啉/TiO₂的混合光催化材料, 并利用紫外可见光谱、电子顺磁共振谱对锌卟啉/TiO₂复合光催化剂进行了表征与分析. 采用溶胶凝胶法制备了锌卟啉-TiO₂的混合光催化材料, 通过比较纯P25型TiO₂和掺入质量比分别为0.2%, 0.5%, 0.9%锌卟啉敏化剂的锌卟啉/TiO₂混合光催化材料的紫外可见光谱图可知, 加入适量锌卟啉敏化剂可提高TiO₂对甲基橙溶液的降解效率, 过多的掺入锌卟啉敏化剂会导致TiO₂表面被敏化剂覆盖, 从而影响了其对光子的吸收, 降低TiO₂的光催化效率, 降低TiO₂的光降解率, 甚至低于纯TiO₂的光降解率. 应用电子顺磁共振技术对锌卟啉敏化TiO₂光催化剂的光催化机理进行了合理的解释, 当使用紫外可见光源对粉末样品进行辐照时, 锌卟啉受光辐照产生的激发态电子促进具有强氧化性的Ti³⁺和超氧根自由基的生成, 从而有效的促进了光生空穴-电子对的分离, 提高了TiO₂的光催化性能.     

铁镧复合氧化物纳米米微粒的制备及其光催化性能

以溶胶-凝胶法制备了纳米铁镧复合氧化物.通过了XRD、TG-DTA等手段,对该氧化物进行了分析.研究了焙烧温度、光催化剂的用量、光照等因素对催化剂光催化降解活性染料的影响.并用红外光谱分析方法验证光催化降解效果.结果表明在适当的用量和700C焙烧并在紫外光照射下铁镧复合氧化物对活性翠蓝KGL和活性B-GFF黑有较强的光催化降解活性.     

Introduction to the Performance and Mechanism of Various Photocatalytic Materials Compounded with Carbon Dots

With their unique optical and electronic properties, carbon dots (CDs) are showing great momentum in many fields such as biosensing, imaging, drug delivery, and photocatalysis. Due to their efficient light harvesting, extraordinary upconversion photoluminescence, and excellent photoinduced electron transfer capabilities, the combination of CDs with photocatalytic materials will promote light absorption resulting in increased generation of electron-hole pairs and faster photogenerated electron transfer, effectively suppressing the rate of electron-hole pair complexation and thus improving photocatalytic activity. In this paper, the mechanism of CDs photocatalysis and various photocatalytic materials such as TiO₂, Bi-based, CdS, and g-C₃N₄ complexed with CDs are reviewed. It is hoped that research into CDs in the field of photocatalysis will be advanced and that CDs will be used more widely in environmental and energy applications.     

In-Situ and In-Operando Experiments

How do we learn about the electronic and atomic characteristics of novel materials for efficient solar energy conversion (photovoltaics and water-splitting), energy storage (Li-ion batteries and multivalent-ion batteries), and efficient catalytic activity and selectivity in catalysis? The fundamental scientific problems that we plan to understand and ultimately control are: (1) efficient absorption-induced electron-hole pair formation and its separation at the complex interfaces; (2) bandgap, band levels, and band structure of earth abundant materials that are of crucial importance in electrochemical and photocatalytic applications.     

First-principles study of the electronic and optical properties of the （Y,N）-codoped anatase TiO2 photocatalyst

First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures,formation energies,and electronic and optical properties of Y-doped,N-doped,and(Y,N)-codoped TiO 2.The calculated results show that Y and N codoping leads to lattice distortion,easier separation of photogenerated electron-hole pairs and band gap narrowing.The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping,which enhances visible-light photocatalytic activity.     

First-principles study of the electronic and optical properties of the (Y, N)-codoped anatase TiO2 photocatalyst

First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures, formation energies, and electronic and optical properties of Y-doped, N-doped, and (Y, N)-codoped TiO₂. The calculated results show that Y and N codoping leads to lattice distortion, easier separation of photogenerated electron-hole pairs and band gap narrowing. The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping, which enhances visible-light photocatalytic activity.     

铁电相变中极化与介电性的随机场效应

基于随机场Ising模型描述的有序无序相变中偶极子在电场作用下的反转运动, 研究了有序无序相变过程中电场与极化强度的关系. 认为tanh(x) 的函数关系与位移型二阶铁电相变极化强度随电场变化的实验结果完全相同. 由此得出基本结论: 偶极子的集体转向造成了极化强度的增大并等同于内电场的增加. 通过区分光学模和偶极子对介电隔离率的贡献, 考虑偶极子极化对介电常数复数形式的频率色散关系, 发现从高斯分布的居里温度可以导出二阶铁电相变过程中介电常数与温度和频率的色散关系. 关键词： 铁电相变 极化强度 随机场     

Study of Depolarization Field Influence on Ferroelectric Films Within Transverse Ising Model

An improved transverse Ising model is proposed by taking the depolarization field effect into account. Within the framework of mean-field theory we investigate the behavior of the ferroelectric thin film. Our results show that the influence of the depolarization field is to flatten the spontaneous polarization profile and make the films more homogeneous, which is consistent with Ginzburg-Landau theory. This fact shows that this model can be taken as an effective model to deal with the ferroelectric film and can be further extended to refer to quantum effect. The competition between quantum effect and depolarization field induces some interesting phenomena on ferroelectric thin films.     

Coexistence of the relaxor-like and ferroelectric behavior in K1-xLixTaO3

ABSTRACT

The results of low-temperature linear and nonlinear susceptibilities, polarization measurements and the dc electric field dependence of the dielectric properties of the lithium-doped potassium tantalate K_1-xLi_xTaO₃, x = 0.034 (KLT-3.4%Li) solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition is of the first-order type with temperature hysteresis. This transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. Clusters of Li⁺ ions produce a relaxor-like behavior and random electric field. This field reduces the depolarization field and allows off-center motions of Ta ions and an appearance of spontaneous polarization.     

Effect of electromechanical boundary conditions on the properties of epitaxial ferroelectric thin films

The effects of internal stresses and depolarization fields on the properties of epitaxial ferroelectric perovskite thin films are discussed by employing the dynamic Ginzburg-Landau equation (DGLE). The numerical solution for BaTiO₃ film shows that internal stress and the depolarization field have the most effects on ferroelectric properties such as polarization, Curie temperature and susceptibility. With the increase of the thickness of the film, the polarization of epitaxial ferroelectric thin film is enhanced rapidly under high internal compressively stress. With the thickness exceeding the critical thickness for dislocation formation, the polarization increases slowly and even weakens due to relaxed internal stresses and a weak electrical boundary condition. This indicates that the effects of mechanical and electrical boundary conditions both diminish for ferroelectric thick films. Consequently, our thermodynamic method is a full scale model that can predict the properties of ferroelectric perovskite films in a wide range of film thickness.     

37BiScO_3-63PbTiO_3铁电陶瓷的极化翻转行为研究

在正弦电场E=E0sin(2πft)加载下,通过改变电场E0(5—55kV/cm)和频率f(0.1—100Hz),测量了37BiScO3-63PbTiO3铁电陶瓷材料的电滞回线.数据拟合结果表明:在低电场和高电场阶段,剩余极化强度Pr的对数和矫顽场强Ec的对数都与电场强度E0的对数存在线性关系,而介于高电场与低电场之间则无线性关系存在,这种三阶段行为有别于现有的两阶段行为.这可归结于铁电陶瓷在不同的电场作用下铁电极化机理的不同.