Controllable deposition of titanium dioxides onto carbon nanotubes in aqueous solutions

Within the field of nanotechnology, nano-scale composites have significant potential in the development of advanced materials for functional applications. Here, composites based on carbon nanotubes and titanium dioxides have been prepared with titanyl sulfate using a chemical bath deposition method at or near room temperature. Two kinds of titanium dioxide depositions corresponding to rutile and anatase were sheathed on carbon nanotubes evenly by adjusting the precursor concentration and temperature. Possible composite mechanisms are discussed. Compared with original tubes, the specific surface areas have been improved nearly four times and the content ratio of mesostructures has also been increased after deposition processes.     

Boltzman transport simulation of single-walled carbon nanotubes

This works treats electronic transport in SWNTs in the Boltzmann Transport equation (BTE) formalism. The BTE is solved self-consistently with the Poisson equation and iterated in time using an upwinding finite-difference scheme until a steady-state is reached. Phonon scattering is included in the relaxation time approximation. Current-voltage characteristics of small diameter metallic nanotubes are explored with lengths ranging from 50 nm up to one micron. Current-voltage results show saturation at high bias near the value of 25 μA. Resistance of the tubes is shown to scale linearity with their length in the low bias regime with a slope of 80 kΩ/μm.     

One-dimensional screening effects in bulk-modulated carbon nanotube transistors

We report density-functional theory (DFT), atomistic simulations of the screening properties of carbon nanotube (CNT) field-effect transistors (FETs). Our attention has been focused on recently demonstrated [1, 2] bulk-modulated CNTFETs. Our calculations have been intended to explore, at an atomistic level, the effect of the one-dimensional screening properties on the physical mechanisms which govern the channel conductance modulation in these new devices. We find that in order to correctly describe charge response mechanisms in a small-diameter nanotube, a calculation including electron-electron interaction effects is necessary. Many-body effects tied to the attractive nature of the exchange interaction can produce an unconventional charge response which manifests itself in a negative quantum capacitance.     

A simple method to fabricate high-performance carbon nanotube field emitters

A simple new method to fabricate carbon nanotube field emitters was developed. Single wall carbon nanotubes with high graphitization were attached on Sn or Ni layered glass substrate in-situ in arc-discharge chamber. Post heat treatments below the deformation temperature of soda-lime glass guaranteed a good mechanical adhesion and electrical contact of the nanotubes. The morphology of the metal electrode layers was examined with the heat treatment temperatures to optimize the heat treatments. The emitters formed on Sn layers showed lower turn-on voltage and higher current density than those formed on Ni layers. A good field emission performance was realized in an emitter where nanotubes were deposited on Sn layer of the thickness 100 nm and annealed at 300^∘C. The current density was 2.5 mA/cm² at 3.5 V/μm. The emitter structure was maintained stable for 8 h.     

Basis-set choice for DFT/NEGF simulations of carbon nanotubes

We investigate the effect of the choice of the basis set on the results of ab initio (density functional theory/non-equilibrium Green’s function) calculations of the bandgap of semiconducting carbon nanotubes, and near-zero-bias conductance of metallic carbon nanotubes. Both ideal and deformed carbon nanotubes are studied, as well as nanotubes with an adsorbed biomolecule. The results show that the near-zero-bias conductance of armchair nanotubes can be calculated accurately with a minimal basis set, with the exception of the (2,2) tube, where a polarized basis set is necessary to accurately predict the metallic behaviour of this tube. For zigzag tubes, a double-zeta polarized basis set is in general required for accuracy in bandgap and near-zero-bias conductance calculations.     

碳纳米管对铅酸电池负极性能影响的研究

本文研究了不同类型及不同含量的碳纳米管添加于铅酸蓄电池负极后,对极板表面形貌及电池性能的影响。实验表明,碳纳米管可促进活性物质均匀分布,并可形成有效的三维导电网络;3种碳纳米管均可提高电池性能,电池初容量最多可提高6.8%。在低温-15℃下容量最多可提高20.7%。并可有效地提高电池的容量保持率。     

Self-consistent ion transport simulation in carbon nanotube channels

We propose a method to self-consistently deal with polarisation effects in Monte Carlo particle simulations of charge transport. The systems of interest were membrane structures with a narrow (4–8 Å) carbon nanotube (CNT) channel in an aqueous environment. Due to computational limitations for Molecular Dynamics (MD) simulations, we extended the Transport Monte Carlo known from semiconductor simulations to ionic transport in water as a background medium. This method has been used successfully to compute transport rates of ions in biological channels but polarization effects on protein walls cannot be easily included self-consistently, due to the complexity of the structure. Since CNTs have a regular structure, it is practical to employ a self-consistent scheme that accounts for the charge redistribution on the channel wall when an external bias is applied or when the electrical field of a passing ion is screened out. Previous work has shown that this is necessary and the computationally efficient tight-binding (TB) approach developed there [1] is combined with transport Monte Carlo simulations in this work.     

水热法制备PEMFC用Pt/CNT电催化剂

首次使用水热法制备用于质子交换膜燃料电池(PEMFC)的Pt/CNT。首先使用HNO3-H2O2体系对纳米碳管(CNT)进行预处理并用红外线(IR)光谱进行表征,结果表明,预处理过程打开了CNT端口并去除了大量杂质。在水热法实验中,反应温度和时间是决定铂颗粒大小的重要因素。样品的X射线衍射仪(XRD)和透射电子显微镜法(TEM)分析表明:最优的反应条件是在140℃反应1.5h,此时铂颗粒的平均尺寸小于1.94nm,并且有着狭窄的粒径分布;催化剂中Pt的质量百分含量为40%。该水热法使用常规试剂H2PtCl6·2H2O和HCHO溶液,操作简单,是一个制备Pt/CNT催化剂较好的方法。     

Issues in the modeling of carbon nanotube FETs: Structure, gate thickness, and azimuthal asymmetry

Factors affecting the modeling of practical carbon nanotube field-effect transistors are addressed, namely: non-coaxial geometries such as the double-planar gate, and the semi-cylindrical gate; the thickness of the gate metalization; the azimuthal variation of the potential and the current. The p-i-n device is used to illustrate the importance of these factors.     

Electrical and dielectric properties of barium titanate – polydimethylsiloxane nanocomposite with 0-3 connectivity modified with carbon nanotube (CNT)

Abstract

This study explored the preparation and electrical properties of 0–3 barium titanate/polydimethylsiloxane nanocomposites by dispersing barium titanate nanoparticles (BaTiO₃; BT) into the polydimethylsiloxane (PDMS) matrix phase. The effect of barium titanate nanoparticles on electrical properties has been investigated systematically, and the relative permittivity of nanocomposites was found to increase significantly with increasing barium titanate content. Different theoretical models were used to predict the dielectric constant of these composites and compare their experimental value with the theoretical value in order to find an appropriate equation. The result indicated that the dielectric properties of composites are influenced not only by relative permittivity of the components but also dependence on interactions between ceramics and polymers. Furthermore, the preparation and dielectric properties of BT/PDMS nanocomposites modified with carbon nanotube (CNT) were also studied. The dielectric results demonstrate that adding CNT can enhance the relative permittivity of the BT/PDMS composite via improvement of dispersion and distribution of the BT nanoparticles in the PDMS matrix phase. Moreover, the electrical outputs from the BT/PDMS/CNT nanocomposites generator were measured under periodic knocking. The nanocomposites innovatively expand the feasibility of self-powered energy systems for smart sensor and energy harvesting applications.     

The role of carbon capture and storage in the race to carbon neutrality

Research and observable climate impacts point almost unequivocally to the need for a larger and faster climate mitigation effort that includes capturing and permanently storing CO₂ both from large sources and from the atmosphere directly. Carbon capture and storage technologies are mature and available, with considerable real-world experience, but their deployment is still limited. We examine why this is so and suggest viable path forward.     

Electron beam evaporated carbon nanotube dispersed SnO2 thin film gas sensor

Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO₂powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO₂thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO₂layer. Experimental results indicate that the sensitivity to ethanol of SnO₂thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250–300^∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced by CNT protrusion.     

Non-equilibrium Green’s function (NEGF) simulation of metallic carbon nanotubes including vacancy defects

The electronic behavior of metallic carbon nanotubes under the influence of externally applied electric fields is investigated using the Non-Equilibrium Green’s function method self consistently coupled with three-dimensional (3D) electrostatics. A nearest neighbor tight binding model based on a single pz orbital for constructing the device Hamiltonian is used. The 3D Poisson equation is solved using the Finite Element Method. Carbon nanotubes exhibit a very weak metallic behavior, and external electric fields can alter the electrostatic potential of the tubes significantly. A single vacancy defect in the channel of a metallic carbon nanotube can decrease its conductance by a factor of two. More than one vacancy can further decrease the conductance.     

纳米碳管的研究与发展

综述了纳米碳管的最新研究方法及工艺技术,给出了应用领域及前景。     

碳纳米管填充的高介电常数聚合物基复合电介质材料

介绍了碳纳米管电性能及其功能化改性、以及利用碳纳米管掺杂聚合物制备柔性高介电常数复合材料的研究现状,发现化学气相沉积法得到的多壁碳纳米管(MWNT)在化学处理前后形成的聚合物基复合材料具有明显不同的分散特性和介电性能.相对于微米级球形导电颗粒填充的复合材料,一维尺度碳纳米管填充的复合材料具有明显低得多的渗流阈值,低渗流阈值可以明显保持聚合物基体优良的机械性能.期望在这一领域从工程电介质的角度做深入的研究工作,以发现碳纳米管在聚合物基复合材料领域所表现出的新特性、新现象.     

纳米碳管在锂离子电池中的应用

纳米碳管(CNTs)作为锂离子电池负极活性材料,表现出很高的初始容量,但在后续的稳定循环中的容量表现却并未超越石墨负极。CNTs具有特殊的电子导电性,作为电极材料导电剂制作成锂离子电池,可以改善电池性能,提升电池循环寿命。在高倍率电池中,其作用则更加显著。     

碳纳米管在电池工业中的潜在应用

介绍了碳纳米管的结构,叙述了碳纳米管在电池领域的潜在应用.碳纳米管是一种极具发展前途的贮氢材料,它具有较高的贮氢量,能够反复进行吸贮氢和释放氢的可逆过程;作为锂离子电极材料,碳纳米管具有高于石墨的嵌锂容量和良好的循环性能;在碳纳米管上沉积贵金属制成燃料电池的催化剂能减少贵金属的用量,降低催化剂的颗粒尺寸和提高催化剂的性能.     

碳纳米管改性碳纤维增强复合材料结构电容器

以碳纤维/环氧树脂/碳纳米管复合材料为电极,聚对苯二甲酸乙二醇酯膜为隔膜,利用真空袋固化成型制备了结构电容器,用场发射扫描电镜观察碳纳米管在环氧树脂中的分散情况,用恒流充放电法、三点短梁弯曲法研究了结构电容器的综合性能;结果表明,加入碳纳米管可使结构电容器的电容提高77.8％,层间剪切强度提高27.7％,综合性能效率在碳纳米管含量为0.5％时达到最高值0.636.     

磁性纳米材料在分离和检测中的应用研究进展

磁性纳米材料应用于生物、环境等众多领域近年来受到了广泛关注。磁性纳米粒子经过适当的表面修饰,可高度选择性地结合目标分子,在解决目标物的快速分离检测及高特异性的选择性分离检测方面具有优势。本文介绍了磁性纳米粒子在分离(包括水处理中的离子吸附分离、水处理中有机物吸附分离、膜分离、生物分离和其他分离)及分析检测(包括水体检测、生物监测、食品安全检测)中的应用,对多功能磁性纳米粒子的构建及其在分离及分析检测领域中的应用具有指导意义。     

Preparation of P doped TiO2 nanotubes and its photocatalytic activity

Using tetrabutyl titanate as the titanium precursor, H₃PO₄ as the source of phosphorus, P-doped TiO₂ nanoparticles HPT were prepared by hydrothermal method. Then P-doped nanotubes ETNT and DTNT were prepared by two-step hydrothermal and calcination method by taking titanate nanotubes (TNT) TiO₂ as raw materials. The resulting materials were characterized by XRD, TEM, DRS and N₂ adsorption. The photocatalytic degradation of phenol experiments showed that the P-doped nanotubes, especially the DTNT photocatalyst exhibited higher degradation efficiency than the others. Hydroxyl radicals (?OH) have been confirmed to be the active species during the photo-catalytic oxidation reaction.