多糖凝胶的孔径和化学结构对单壁碳纳米管流动性和选择性分离的影响

基于凝胶柱色谱分离技术研究了单分散的单壁碳纳米管(SWCNTs)在不同化学结构多孔多糖凝胶中的流动特性以及对金属型(m-)/半导体型(s-)SWCNTs分离的影响.通过比较SWCNTs在一系列不同孔径的葡聚糖Sephacryl凝胶中的流动行为,发现减小孔径尺寸能够增强s-SWCNTs与凝胶之间的吸附作用力,使大直径的m-SWCNTs快速地流过凝胶颗粒,而选择性地保留了小直径的s-SWCNTs.进一步发现多糖凝胶化学结构比孔径尺寸在SWCNTs的m/s分离中起着更重要的作用.当基于葡聚糖结构的Sephacryl凝胶中的氨基结构被琼脂糖结构所取代时,如Superdex 200和Sepharose 2B凝胶会增强它们与SWCNTs之间的作用力,使SWCNTs的保留时间延长,降低了s-SWCNTs的选择性和纯度.此外,即使拥有与Sephacryl S100类似的孔径范围,当Sephacryl凝胶中的氨基被疏水环氧丙烷基团取代时,葡聚糖凝胶Sephadex G100与SWCNTs的作用力很弱,导致所有SWCNTs快速流动,无法实现SWCNTs的m/s分离.因而,我们认为凝胶孔径和化学结构共同影响并调控了SWCNTs的m/s分离的选择性、纯度以及分离效率.     

多糖凝胶的孔径和化学结构对单壁碳纳米管流动性和选择性分离的影响

基于凝胶柱色谱分离技术研究了单分散的单壁碳纳米管（SWCNTs）在不同化学结构多孔多糖凝胶中的流动特性以及对金属型（m-）/半导体型（s-）SWCNTs 分离的影响. 通过比较SWCNTs 在一系列不同孔径的葡聚糖Sephacryl 凝胶中的流动行为,发现减小孔径尺寸能够增强s-SWCNTs 与凝胶之间的吸附作用力,使大直径的m-SWCNTs 快速地流过凝胶颗粒,而选择性地保留了小直径的s-SWCNTs. 进一步发现多糖凝胶化学结构比孔径尺寸在SWCNTs 的m/s 分离中起着更重要的作用. 当基于葡聚糖结构的Sephacryl 凝胶中的氨基结构被琼脂糖结构所取代时,如Superdex 200 和Sepharose 2B凝胶会增强它们与SWCNTs 之间的作用力,使SWCNTs 的保留时间延长,降低了s-SWCNTs 的选择性和纯度. 此外,即使拥有与Sephacryl S100类似的孔径范围,当Sephacryl 凝胶中的氨基被疏水环氧丙烷基团取代时,葡聚糖凝胶Sephadex G100 与SWCNTs 的作用力很弱,导致所有SWCNTs 快速流动,无法实现SWCNTs 的m/s 分离. 因而,我们认为凝胶孔径和化学结构共同影响并调控了SWCNTs的m/s分离的选择性、纯度以及分离效率.     

单壁碳纳米管的电子速度及有效质量

利用单壁碳纳米管(SWCNTs)能量色散关系, 计算了最低导带的电子速度和有效质量, 重点讨论了SWCNTs中最低导带电子速度和有效质量与波矢及管径大小的关系. 结果表明, 半导体型锯齿SWCNTs的电子速度和有效质量与其结构参量(管径)有直接的关系. 各种椅型SWCNTs(金属型)和金属型锯齿SWCNTs最低导带电子速度和有效质量随波矢的变化规律分别相同, 各种半导体型锯齿SWCNTs最低导带电子速度和有效质量随波矢的变化规律则有明显差别. 这意味着在低偏压下, 不同管径的椅型SWCNTs和金属型锯齿SWCNTs输运性能相同, 而各种不同管径半导体型锯齿SWCNTs输运性能有明显差别.     

单一导电属性及手性单壁碳纳米管的分离技术

综述了基于生长后处理策略下单一导电属性及手性单壁碳纳米管(SWCNTs)分离技术的研究进展, 阐述了SWCNTs 的选择性分离原理, 并比较了不同分离技术在分离纯度、效率、成本以及可规模化等方面的优缺点, 为SWCNTs 分离技术的发展及应用提供了方向性指导.     

琼脂糖凝胶电泳法分离金属性和半导体性单壁碳纳米管

琼脂糖凝胶电泳(AGE)是实现金属性单壁碳纳米管(m-SWCNTs)和半导体性单壁碳纳米管(s-SWCNTs)低成本、规模化分离的有效技术之一。本研究利用琼脂糖凝胶电泳分离单壁碳纳米管。通过紫外-可见-近红外吸收光谱和拉曼光谱对色谱带进行分段表征,发现电泳中迁移的最快的部分m-SWCNTs含量最高。考察了琼脂糖的浓度对SWCNTs中m-SWCNTs分离的影响。结果表明:高的琼脂糖浓度有利于m-SWC-NTs的富集,可以通过扩大电荷密度带来的迁移速率的差异来使SWCNTs中的m-SWCNTs得到更有效的分离。     

琼脂糖性质对凝胶电泳法分离金属性和半导体性单壁碳纳米管的影响

利用琼脂糖凝胶电泳分离单壁碳纳米管(SWCNTs)技术, 考察了MB, Agarose, Agarose B和LRU 4种琼脂糖对SWCNTs分离效率的影响. 紫外-可见-近红外(UV-Vis-NIR)吸收光谱研究结果表明, 不同的琼脂糖对SWCNTs中s-SWCNTs的分离效率影响较小, 而对m-SWCNTs的分离效率影响较大. 分析4种琼脂糖凝胶的凝胶强度和凝胶网孔尺寸等发现, 影响SWCNTs中m-SWCNTs分离效率的主要因素是琼脂糖的凝胶强度和琼脂糖凝胶形成的网孔尺寸, 小的凝胶网孔尺寸有利于m-SWCNTs富集, 高凝胶强度则不利于其富集.     

单壁碳纳米管在胆酸类表面活性剂中的分散及手性碳管(6,5)的双水相分离方法

选用牛磺脱氧胆酸钠和脱氧胆酸钠等6种胆酸类表面活性剂,考察其对单壁碳纳米管(SWCNTs)的分散能力.紫外-可见-近红外吸收光谱测试结果表明,在超声功率为225 W,超声时间1 h的分散条件下,胆酸类表面活性剂均能对SWCNTs均匀分散,均可作为SWCNTs的分散剂.在相同条件下,质量分数为2%的牛磺脱氧胆酸钠对SWCNTs的分散能力最强,脱氧胆酸钠对SWCNTs的分散能力最弱.此外,还采用聚乙二醇/葡聚糖双水相系统对SWCNTs分散液进行了萃取分离,获得了纯度较高的手性SWCNTs(6,5).所筛选的SWCNTs分散剂及采用的双水相分离方法为单一手性SWCNTs的分离提供了一定的技术参考.     

基于溶液法的单壁碳纳米管手性分离

本文综述了基于溶液法分离策略,利用表面活性剂、生物分子、共轭聚合物分子在溶液中分散或选择性分散单壁碳纳米管(SWCNTs),结合各种分离技术获得单一手性SWCNTs的研究进展.阐述了不同体系中SWCNTs手性分离的原理,综合比较了不同分离技术的优缺点.单一手性SWCNTs分离技术的不断进展有助于推动单壁碳纳米管的进一步研究与应用.     

多壁碳纳米管与溴的相互作用及导电机理

通过溴蒸气的吸附, 提高多壁碳纳米管(MWNT)的本征导电性能, 加溴多壁碳纳米管的电导率提高了3倍. X光电子能谱、近红外光谱、紫外光谱、拉曼光谱表明多壁碳纳米管与溴之间存在共轭作用, 这种作用导致多壁碳纳米管上的π电子向溴偏移, 产生空穴载流子. 利用半导体能带图, 提出加溴多壁碳纳米管微观体系模型来研究溴对多壁碳纳米管的作用及导电机理.     

非共价方法分离金属型和半导体型单壁碳纳米管

目前商品化生产的单壁碳纳米管(SWNTs)都是金属型和半导体型碳管的混合物,极大地限制了其在微电子等领域的研究和应用。非共价分离方法既能保持SWNTs特有的电子结构又可实现可逆分离,是目前研究最多的分离方法。本文在介绍SWNTs的结构与导电性能关系的基础上,概述了金属型和半导体型SWNTs的表征原理和方法,并对各种非共价分离SWNTs的方法进行了综述和比较。     

Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization

The efficient and controllable synthesis, the detailed characterization, and the chemical postfunctionalization of polycarboxylated single-walled carbon nanotubes SWCNT(COOH)(n) are reported. This innovative covalent sidewall functionalization method is characterized by (a) the preservation of the integrity of the entire σ-framework of SWCNTs; (b) the possibility of achieving very high degrees of addition; (c) control of the functionalization degrees by the variation of the reaction conditions (reaction time, ultrasonic treatment, pressure); (d) the identification of conditions for the selective functionalization of semiconducting carbon nanotubes, leaving unfunctionalized metallic tubes behind; (e) the proof that the introduced carboxylic acid functionalities can serve as versatile anchor points for the coupling to functional molecules; and (f) the application of a subsequent thermal degradation step of the functionalized semiconducting tubes leaving behind intact metallic SWCNTs. Functional derivatives have been characterized in detail by means of Raman, UV-vis/nIR, IR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry, atomic force microscopy, and zeta-potential measurements.     

Bulk electrical properties of single-walled carbon nanotubes immobilized by dielectrophoresis: evidence of metallic or semiconductor behavior

We report the electrical characterization of single-walled carbon nanotubes (SWCNTs) trapped between two electrodes by dielectrophoresis (DEP). At high frequency, SWCNTs collected by DEP are expected to be of metallic type. Indeed current-voltage (I-V) measurements for devices made at 10 MHz show high values of conductivity and exhibit metallic behavior with linear and symmetric electrical features attributed to ohmic conduction. At low frequency, SWCNTs attracted by DEP are expected to be of semiconducting nature. Devices made at 10 kHz behave as semiconductors and demonstrate nonlinear and rectifying electrical characteristics with conductivities many orders of magnitude below the sample resulting from high-frequency immobilization of SWCNTs. Conducting atomic force microscopy (C-AFM) and current density calculation results are presented to reinforce results obtained by I-V measurements which clearly show type separation of SWCNTs after DEP experiments.     

Discovery of surfactants for metal/semiconductor separation of single-wall carbon nanotubes via high-throughput screening

We report novel surfactants that can be used for the separation of metallic (M) and semiconducting (S) single-wall carbon nanotubes (SWCNTs). Among the M/S separation methods using surfactants in an aqueous solution, sodium dodecyl sulfate plays a key role in density gradient ultracentrifugation (DGU) and agarose gel separations. In this study, we screened 100 surfactants for M/S separation using a high-throughput screening system. We identified five surfactants, which could be used for both DGU and agarose gel separations, suggesting that the basic principle of these separations is common. These surfactants have relatively low dispersibilities, which is likely due to their common structural features, i.e., straight alkyl tails and charged head groups, and appeared to enable M- and S-SWCNTs to be distinguished and separated. These surfactants should stimulate research in this field and extend the application of electrically homogeneous SWCNTs not only for electronics but also for biology and medicine.     

Nerve agents interacting with single wall carbon nanotubes: Density functional calculations

First-principles calculations based on density functional theory (DFT) method are used to investigate the adsorption properties of nerve agent DMMP on typical zigzag (semiconducting) and armchair (metallic) single wall carbon nanotubes (SWCNTs). The adsorption energies for DMMP molecule on different adsorption sites on SWCNTs are obtained. The results indicate that DMMP is weakly bound to the outer surface of both the considered SWCNTs and the obtained adsorption energy values and binding distances are typical for the physisorption. We find that DMMP adsorptive capability of metallic CNTs is about twofold that of semiconducting one. The adsorption of DMMP on the higher chiral angle nanotubes was also investigated and the results indicate that nanotube’s chirality increases the adsorption capability of the tube but however the adsorption characteristic is typical for the physisorption. Furthermore, co-adsorption of two DMMP molecules on the SWCNTs as a single-layer/bi-layer of adsorbed molecules as well as the adsorption of one DMMP molecule on the CNT bundles consisting of three SWCNTs has also been examined. The obtained results reveal that for both the considered systems the binding energy was increased for the DMMP adsorption but it’s still typical for the physisorption, consistent with the recent experimental result. The study of the electronic structures and charge analysis indicate that no significant hybridization between the respective orbital takes place and the small interaction obtained quantitatively in terms of binding energies.     

Characterisation of Nanohybrids of Porphyrins with Metallic and Semiconducting Carbon Nanotubes by EPR and Optical Spectroscopy

Single‐walled carbon nanotubes (SWCNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of cobalt(II)OEP, adsorbed on the nanotube walls by π–π‐stacking, demonstrates that the CNTs act as electron acceptors. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Moreover, molecular oxygen is shown to bind selectively to nanohybrids with semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99 % of the porphyrins are interacting with the CNTs. Due to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red‐shifted compared to the free porphyrin absorption. In addition a quasi‐complete quenching of the porphyrin fluorescence is also observed.     

Theoretical investigation of the stability,electronic and magnetic properties of thiolated single‐wall carbon nanotubes

The addition of SH and OH groups to single‐wall carbon nanotubes (SWCNTs) was investigated employing first principles calculations. In the case of the semiconducting (10, 0) SWCNT the SWCNT‐SH binding energy is weak, 2–4 kcal/mol. However, for the metallic (5, 5) SWCNT it is larger, 7–9 kcal/mol. Thus metallic SWCNTs seem to be more reactive to SH than the semiconducting ones. Indeed, the (6, 6) SWCNT is more reactive to SH than the (10, 0) SWCNT, by 2–3 kcal/mol, something that can be explained only considering the electronic structure of the tube, because the (6, 6) has a larger diameter. The binding energies are larger for the addition of the OH group, 25 and 30 kcal/mol for the (10, 0) and (5, 5) SWCNTs, respectively. When a single OH or SH group is attached to the metallic SWCNTs, we observe important changes in the DOS at the Fermi level. However, when multiple SH groups are attached, the changes in the electronic and magnetic properties depend on the position of the SH groups. The small binding energy found for the SH addition indicates that the successful functionalization of SWCNTs with SH, SCH₃, and S(CH₂)_nSH groups is mostly due to the presence of defects created after acid treatment and to a minor extent by the metallic tubes present in the samples. Perfect semiconducting SWCNTs showed very low reactivity against the SH group. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009