水热法制备二氧化钛纳米管-石墨烯复合光催化剂及其光催化性能

采用水热法制备了二氧化钛纳米管-石墨烯的复合光催化剂。利用X射线衍射仪、扫描电镜、透射电镜和拉曼光谱仪对复合材料进行了表征与分析,并对其光催化性能进行了测试。结果显示,同纯二氧化钛纳米管相比,二氧化钛纳米管-石墨烯的光催化性能较高。石墨烯与二氧化钛纳米管复合,充当电子受体,载流子迁移率得到提高,从而提升了光催化性能。     

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.     

NiO/TiO2复合纳米管的水热制备及光催化性能

采用水热法,制得了管径约为10～15nm、管长约为10～300nm、管壁上附着NiO纳米颗粒的TiO_2纳米管复合光催化剂(NiO/TiO_2).采用X射线衍射、透射电子显微镜、扫描电镜、X射线光电子能谱及紫外-可见漫反射光谱等技术对催化剂进行了表征;以甲基橙为模拟污染物,评价了纳米管的光催化活性.结果表明:NiO晶粒与TiO_2晶粒结合形成p-n异质结,有效地促进了光生电子和空穴的分离;NiO对可见光有强烈的吸收,使复合TiO_2纳米管在整个可见光区域均有很好的光吸收;以上两点使NiO/TiO_2纳米管可见光下的光催化活性大幅提升,500℃煅烧后纳米管对甲基橙1h分解比由纯TiO_2纳米管的7.0%提升至NiO/TiO_2纳米管的95.6%.     

PbSe/TiO2同轴异质结纳米管的制备及光催化性能

通过溶液法合成了PbSe/TiO2复合纳米管,并对其进行了微观形貌、晶体结构等的表征。结果表明,制得的样品是由PbSe和TiO2两种材料构成的复合材料,致密、均匀的TiO2薄膜包覆在PbSe纳米管表面。以氙灯为模拟光源,通过对甲基橙的降解研究了PbSe/TiO2复合纳米管的光催化性能。结果显示,PbSe与TiO2之间形成的异质结使PbSe/TiO2复合纳米管具有较高的光催化性能,比纯PbSe纳米管的催化降解率提高了约4.5倍。另外,对PbSe/TiO2复合纳米管光催化稳定性也进行了研究。     

纳米复合材料TiO2-ZrO2光催化降解可溶性染料的研究

采用溶胶-凝胶方法将光催化剂TiO2和ZrO2复合,再经700℃灼烧5h后获得了纳米复合光催化材料TiO2-ZrO2.该材料经XRD检测具有光催化活性良好的晶型结构.TEM测定结果显示产物的平均粒径约为20nm.通过对可溶性染料刚果红等的光催化降解实验证明,该复合材料具有较高的光催化活性.     

N-F共掺杂锐钛矿二氧化钛(101)面纳米管的第一性原理研究

共掺杂是提高二氧化钛纳米管可见光催化性能的一种有效方式. 采用基于密度泛函理论的第一性原理方法, 研究了N单掺杂、F单掺杂及N-F共掺杂二氧化钛纳米管的原子结构、电子性质和光学性质. 计算结果表明, 相比N单掺杂和F单掺杂, N-F共掺杂二氧化钛纳米管的形成能更低, 掺杂后的体系热力学稳定性更好. 此外, 相比未掺杂时的带隙, N-F共掺杂后体系的带隙变化最多, 减少了0.557 eV, 而这主要源于价带顶附近的杂质能级的贡献. 此外, 通过分析掺杂后的光催化活性发现, N-F共掺杂时纳米管的还原性和氧化性都有所降低, 但并没有丧失活性, 并且光吸收谱表明, 共掺杂体系的红移现象最为明显. 因此, N-F共掺杂可有效提高二氧化钛纳米管可见光的光催化性能.     

超亲水性SiO2-TiO2纳米颗粒阵列结构的制备与性能研究

用分子自组装的方法在玻璃衬底上分别制备了TiO₂纳米颗粒层和SiO₂-TiO₂复合纳米颗粒阵列结构. 其中,SiO₂ 纳米颗粒层用旋涂法制备,得到密排阵列结构,而TiO₂纳米颗粒层则用浸渍提拉法制备. 文章分析了TiO₂纳米颗粒层和SiO₂-TiO₂复合纳米颗粒阵列结构的理论粗糙度,并通过扫描电子显微镜研究了它们的微观结构,用接触角 关键词： 自清洁 表面粗糙度 光催化 分子自组装     

TiO_2/石墨烯/Ag复合结构SERS实验

基于氧化物半导体的光催化特性,能够降解有机物分子,使表面增强拉曼散射基底得以重复使用。提出了银纳米颗粒有效修饰覆盖有石墨烯的二氧化钛纳米棒阵列(TiO_2/石墨烯/Ag)复合结构作为表面增强拉曼散射基底,并对其进行了实验研究。利用水热法制备了二氧化钛纳米棒阵列;采用湿法转移石墨烯和光照还原方法制备了TiO_2/石墨烯/Ag复合结构。用罗丹明6G(R6G)分子作为探测分子,结果表明:随着紫外光照沉积时间增加,探针分子的拉曼信号先增强后减弱;计算得到最大增强因子值约为2.6×106。此外,还对TiO_2/石墨烯/Ag复合结构的紫外自清洁特性进行了初步实验,结果表明,紫外光照射20min后,其拉曼强度下降到42.3%,具有一定的紫外清洁效果。     

界面自组装的金/氧化石墨烯复合材料的表面增强拉曼散射行为研究

采用Frens法制备金纳米粒子溶胶,通过界面自组装技术在掺磷的非晶碳衬底表面构筑三维的金/氧化石墨烯/金复合结构.以罗丹明B为探针分子,考察金/氧化石墨烯/金复合材料的表面增强拉曼散射活性.结果表明,由于氧化石墨烯的化学增强和金纳米粒子的电磁场增强的协同作用,在该三维复合材料上获得了很强的罗丹明B拉曼信号.所设计的三维金/氧化石墨烯/金复合材料在生物分析、环境监测、疾病防控、食品安全等领域具有潜在的应用价值.     

纳米结构表面形貌成型机理及其对石墨烯拉曼光谱的影响

通过真空热蒸镀和高温退火法制备的金属纳米复结构SERS基底因其具有良好的灵敏度,稳定性和均匀性而广泛应用于各种检测领域。石墨烯具有优良的光学特性,化学惰性以及荧光猝灭效应,自被发现以后一直是光学微纳器件中的一大热门材料。石墨烯还可以有效分离探针分子与基底,优化拉曼光谱质量,因此广泛应用于SERS研究领域。同时石墨烯可以有效隔绝金属纳米结构与空气的直接接触防止金属纳米结构被氧化而失效,也可以催化氧化银的脱氧反应提升SERS基底的稳定性。在石墨烯/金属纳米复合结构SERS基底在制备过程中,受到金属膜的种类、厚度参数、气体种类、退火时间、温度和气压等因素的影响,制备的金属纳米结构形貌存在很大差异。石墨烯的拉曼光谱会因为应力和掺杂导致其拉曼特征峰出现不同程度的增强,移动以及展宽。（1）采用真空热蒸镀法和高温退火法制备石墨烯/银纳米复合结构SERS基底,建立了金属纳米颗粒成型机理的模型,从孔洞形成、孔洞生长、金属纳米岛形成三个阶段分析了金属纳米粒子的成型过程,实验沉积5,10,15以及20 nm的银薄膜,退火后银纳米结构的覆盖率分别为~35.1%,~24.4%,~30%以及~96.0%,在沉积银薄膜样品上使用湿法转移石墨烯,退火处理后发现石墨烯阻止了银纳米岛的形成过程;（2）理论分析了银薄膜厚度、石墨烯覆盖对复合结构的几何形貌、拉曼增强特性的影响,石墨烯由于其具有较高的杨氏模量和表面张力,可以有效抑制退火过程中银薄膜向纳米粒子转变的过程,从而实现对复合结构表面形貌的调控;（3）实验研究了银纳米粒结构形貌对石墨烯拉曼光谱的影响,并理论分析了蒸镀不同银薄膜厚度的样品对石墨烯的拉曼光谱增强,移动以及展宽影响的具体原因。     

Optical Response From Functionalized Atomically Thin Nanomaterials

Chemical functionalization of atomically thin nanostructures presents a promising strategy to create new hybrid nanomaterials with remarkable and externally controllable properties. Here, we review our research in the field of theoretical modeling of carbon nanotubes, graphene, and transition metal dichalcogenides located in molecular dipole fields. In particular, we provide a microscopic view on the change of the optical response of these technologically promising nanomaterials due to the presence of photo‐active spiropyran molecules. The feature article presents a review of recent theoretical work providing microscopic view on the optical response of chemically functionalized carbon nanotubes, graphene, and monolayered transition metal dichalcogenides. In particular, we propose a novel sensor mechanism based on the molecule‐induced activation of dark excitons. This results in a pronounced additional peak presenting an unambiguous optical fingerprint for the attached molecules.     

Geometrically induced π-band splitting in graphene superlattices

According to band folding analyses, the graphene superlattices can be differed by whether the Dirac points are folded to Γ point or not. In previous studies, the inversion symmetry preserved defects open bandgap in the former superlattices while they cannot in the latter ones. In this paper, by using density functional theory with generalized gradient approximation, we have carefully studied the electronic properties of the latter graphene superlattices, in which the defects would induce π-band splitting to get the π_a1–π_a2 and π_z1–π_z2 band sets. Based on our detailed studies, such splitting could be attributed to the geometrically induced bond-symmetry breaking. In addition, these band sets could be shifted toward each other by the methodology of strain engineering. A bandgap would be opened once the band sets start to overlap. Then,its gap width could be continuously enlarged by enhancing strain until reaching the maximum value determined by the defect density. These studies contribute to the bandstructure engineering of graphene-based nanomaterials, which would be interesting to call for further investigations on both theory and experiment.     

Free-carrier generation in aggregates of single-wall carbon nanotubes by photoexcitation in the ultraviolet regime

We present evidence for the generation of free carriers in aggregated single-wall carbon nanotubes by photoexcitation in the energetic range of the π→π(*) transition associated with the M saddle point of the graphene lattice. The underlying broad absorption culminating at 4.3 eV can be fit well with a Fano line shape that describes strong coupling of a saddle-point exciton to an underlying free electron-hole pair continuum. Moreover, it is demonstrated that transitions in this energetic region autoionize into the continuum by detecting features unique to the presence of free charges in the transient transmission spectra of the continuum-embedded second sub-band exciton, S(2).     

Oxidation degree dependent adsorption of ssDNA onto graphene-based surface

DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology, and attracts a great deal of interest. However, it is still unclear how the oxidation degree of the graphene-based surface affects the adsorption process of single-strand DNA(ss DNA). In this paper, based on the molecular dynamics simulations, we find that ss DNA molecule is absorbed on the GO surface in the most stable state with the oxidation degree around 15%. The microscopic mechanism is attributed to the van Der Walls and the electrostatic interactions between the ss DNA molecule and the graphene-based surface, which is accompanied with the π–π stacking and hydrogen bond formation. The number of π–π stacking between ss DNA and GO reaches the maximum value when the oxidation degree is around 15% among all the GO surfaces. Our simulation results also reveal the coexistence of stretched and curved configurations as well as the adsorption orientation of ss DNA on the GO surface. Furthermore, it is found that the absorbed ss DNA molecules are more likely to move on the graphene-based surface of low oxidation degree, especially on pristine graphene. Our work provides the physics picture of ss DNA's physisorption dynamics onto graphene-based surface and it is helpful in designing DNA/GO nanomaterials.     

Phase-and spin-dependent manipulation of leakage of Majorana mode into double quantum dot

We present a phase-and spin-dependent manipulation of leakage of a Majorana mode into a double quantum dot. We study the density of states(DOS) to show the effect of phase change factor on the Majorana leakage into(out) of a double quantum dot. The DOS is derived from the Green's function of the quantum dot by the equation of motion method, and exhibits a formant structure when φ = 0, 2π and a resonance shape when φ = 0.5π and 1.5π. Also, it changes more strongly under the spin-polarized coefficient than the non-polarized lead. Such a theoretical model can be modified to explore the spin-dependent effect in the hybrid Majorana quantum dot system.     

聚酰亚胺/功能化石墨烯复合材料力学性能及玻璃化转变温度的分子动力学模拟

应用分子模拟方法,建立了聚酰亚胺(polyimide,PI),石墨烯及羧基、氨基、羟基功能化石墨烯模型,探究了聚酰亚胺和石墨烯,聚酰亚胺和功能化石墨烯共混后复合材料的力学性能和玻璃化转变温度(T_g).研究结果表明,羧基修饰的石墨烯与PI复合后材料力学性能增加显著,其杨氏模量和剪切模量分别为4.946 GPa和1.816 GPa.不同官能团修饰的石墨烯引入PI后材料的T_g均有不同程度下降;未修饰的石墨烯与PI复合后,其T_g(559.30 K)较纯PI的T_g(663.57 K)降幅最大;而羧基修饰的石墨烯与PI复合后T_g(601.61 K)降幅最小.计算比较了PI/石墨烯复合材料体系密度、溶解度参数、相互作用能、弹性系数和氢键平均密度,研究发现羧基修饰石墨烯/PI复合材料的密度为1.396 g·cm~(-3),溶解度参数为23.51 J~(1/2)·cm~(-3/2),其相互作用能与氢键平均密度最大,弹性系数显示羧基修饰石墨烯与PI组成的复合材料内部最均匀.计算结果表明,羧基功能化石墨烯可以大幅度提高PI的力学性能,增强石墨烯与PI之间的相互作用可以减少复合材料T_g的降幅程度.此基体间相互作用的研究方法可以作为预测聚合物基纳米复合材料结构与性能的有效工具,以期为材料的设计与应用提供理论指导.     

Steered coherence and entanglement in the Heisenberg XX chain under twisted boundary conditions

We study steered coherence(SC) and entanglement in a three-spin Heisenberg XX model under twisted boundary conditions and show that their strengths can be significantly enhanced by tuning the twist angle. The optimal twist angle θ_(opt) for achieving the maximum l_1 norm of SC is π in the region of weak field B and decreases gradually from π to 0 when B increases after a critical value, while for the relative entropy of SC, θ_(opt) equals π in the weak field region and 0 otherwise.The entanglement and the critical temperature above which the entanglement vanishes can also be significantly enhanced by tuning the twist angle from 0 to π.     

Facile fabrication of highly flexible,porous PEDOT: PSS/SWCNTs films for thermoelectric applications

High-performance organic composite thermoelectric(TE)materials are considered as a promising alternative for harvesting heat energy.Herein,composite films of poly(3,4-ethyienedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotubes(PEDOT:PSS/SWCNTs)were fabricated by utilizing a convenient solution mixing method.Thereafter,the as-prepared hybrid films were treated using sulfuric acid(H₂SO₄)to further optimize the TE performance.Film morphological studies revealed that the sulfuric acid treated PEDOT:PSS/SWCNTs composite samples all possessed porous structures.Due to the successful fabrication of highly conductive networks,the porous nano-architecture also exhibited much more excellent TE properties when compared with the dense structure of the pristine samples.For the post-treated sample,a high power factor of 156.43μW·m^-1·K^-2can be achieved by adjusting the content of CNTs,which is approximately 3 orders of magnitude higher than that of the corresponding untreated samples(0.23μW·m^-1·K^-2).Besides,the obtained films also showed excellent mechanical flexibility,owing to the porous nanostructure and the strong p–p interactions between the two components.This work indicates that the H₂SO₄ treatment could be a promising strategy for fabricating highly-flexible and porous PEDOT:PSS/SWCNTs films with high TE performances.     

TiO$lt;sub$gt;2$lt;/sub$gt;纳米管电子结构和光学性质的第一性原理研究

运用基于密度泛函理论的第一性原理方法, 系统研究了小尺寸锐钛矿相(n,0)型TiO₂纳米管(D<16 Å)的几何构型、电子结构和光学性质. 结果表明: 随着管径增大, 体系单位TiO₂分子的形成能降低, 体系趋于稳定; 在管径14 Å左右, (n,0)型TiO₂纳米管会发生一次构型的转变. 能带分析显示, TiO₂纳米管的电子态比较局域化, 小管径下(D<14 Å)其导电性更好; 随着构型的转变, TiO₂纳米管由直接带隙转变为间接带隙, 并且带隙值随着管径的增大而增大, 这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果. 两种效应的竞争, 使得TiO₂纳米管的介电函数虚部ε₂ (ω)谱的峰值位置随管径增大既可能红移也可能蓝移, 管径大于9 Å (即(8, 0)管)之后, TiO₂纳米管的光吸收会出现明显的增强. 关键词： 2纳米管')" href="#">TiO₂纳米管 第一性原理 电子结构 光学性质     

Round-robin differential quadrature phase-shift quantum key distribution

Recently,a round-robin differential phase-shift(RRDPS) protocol was proposed[Nature 509,475(2014)],in which the amount of leakage is bounded without monitoring the signal disturbance.Introducing states of the phase-encoded Bennett-Brassard 1984 protocol(PE-BB84) to the RRDPS,this paper presents another quantum key distribution protocol called round-robin differential quadrature phase-shift(RRDQPS) quantum key distribution.Regarding a train of many pulses as a single packet,the sender modulates the phase of each pulse by one of {0,π/2,π,3π/2},then the receiver measures each packet with a Mach-Zehnder interferometer having a phase basis of 0 or π/2.The RRDQPS protocol can be implemented with essential similar hardware to the PE-BB84,so it has great compatibility with the current quantum system.Here we analyze the security of the RRDQPS protocol against the intercept-resend attack and the beam-splitting attack.Results show that the proposed protocol inherits the advantages arising from the simplicity of the RRDPS protocol and is more robust against these attacks than the original protocol.