扶手椅型单壁碳纳米管的理论研究

用半经验的AM1和PM3 方法,对不同长度的扶手椅型单壁碳纳米管(3,3)进行了理论研究.讨论了其几何结构、前线轨道的分布情况和红外光谱.结果表明:碳纳米管中的六边形不再像石墨中的六边形,而是发生了变形;从碳纳米管的中间到两端,各层碳原子在前线轨道中的轨道系数的平方和呈现规律性衰减的锯齿状变化;用AM1方法计算得扶手椅型单壁碳纳米管(3,3)的红外特征吸收波数约在1290～1645cm^-1之间.     

异型碳纳米管储氢性能的分子动力学模拟研究

采用分子动力学(MD)方法对三种理想的Y型碳纳米管[记为Y(4,4), Y(6,6), Y(10,0)]和三种L型碳纳米管[记为L(9,0), L(6,6), L(10,0)]之储氢性能进行了模拟研究, 并与相应的直线型碳纳米管的储氢能力进行了比较, 同时考察了温度、碳纳米管的直径和螺旋性以及缺陷的位置和大小对异型碳纳米管储氢性能的影响. 结果表明, 在室温和低温条件下, 异型碳纳米管的储氢量高于直线型碳纳米管的储氢量, 且其储氢量大小随温度的降低和碳管直径的增大而增加, 椅式碳纳米管的储氢性能优于齿式碳纳米管, 而缺陷的位置和大小对异型碳管之储氢性能的影响则因碳管的形貌和直径的大小不同而存在差异.     

扶手椅形单壁碳纳米管环氧异构体的理论研究

用半经验AM1方法对不同直径的单壁碳纳米管(3,3)/C₄₂H₁₂,(4,4)/C₅₆H₁₆,(5,5)/C₇₀H₂₀和(6,6)/C₈₄H₂₄本体及其环氧衍生物进行了理论研究.结果表明,对于直径较大的(5,5)C₇₀H₂₀和(6,6)/C₈₄H₂₄单壁碳纳米管,可以得到4种不同的环氧化异构体.而直径较小的单壁碳纳米管(3,3)/C₄₂H₁₂和(4,4)/C₅₆H₁₆,只能得到3种异构体.讨论了这些异构体的生成热(H_f)、离子势、电子亲和能、最低非占据轨道和最高占据轨道的能级差E_g等参数及其与单壁碳纳米管直径的关系,并排列了这些异构体的稳定性次序.同时,用POAV程序分析了单壁碳纳米管中sp²碳原子轨道的再次杂化和张力的大小.     

在不同激发波长下的单壁碳纳米管的拉曼光谱研究

采用直流电弧法制备单壁碳纳米管样品,用457.5和632.8nm两种不同的激发光分别测得单壁碳纳米管的正常拉曼光谱和共振拉曼光谱.通过理论分析得到了单壁碳纳米管的直径分布,进一步推测了其类型及结构参数;对单壁碳纳米管的正切拉伸模的成分进行了归属.在632.8nm激发波长下得到了IG/ID值随激光功率变化的曲线,认为在2.5mW时,单壁碳纳米管缺陷的结构可能发生了改变.在用457.5nm波长激发的单壁碳纳米管的拉曼光谱中,首次发现了1421cm-1的拉曼谱峰.     

有限长Y型碳纳米管结构和性质的第一性原理研究

采用密度泛函理论的GGA/PW91方法对有限长Y型碳纳米管的结构和性质进行了研究. 研究结果表明, 由于缺陷环的影响, Y型碳纳米管与直型管的性质明显不同, 而且, Y型碳纳米管的结构和性质与分支管长度存在一定的关系. 当分支管长度大于1 nm 时, Y型碳纳米管的结构、能隙和电学性质均出现周期性振荡变化的趋势.     

自组装半导体碳纳米管薄膜的光电特性

采用自组装的方法制备99%高纯度半导体碳纳米管平行阵列条带,以金属钯和钪为非对称接触电极制备碳纳米管(CNT)薄膜晶体管(TFTs)器件.主要研究不同沟道长度碳纳米管薄膜晶体管器件的电输运特性和红外光电响应特性,分析了其中的载流子输运和光生载流子分离的物理机制.我们发现薄膜晶体管器件的电学性能和光电性能依赖于器件沟道长度(L)和碳纳米管的平均长度(LCNT).当沟道长度小于碳纳米管的平均长度时,器件开关比最低;当沟道长度超过碳纳米管平均长度时,随着沟道长度的增加,器件开关比增加,光电流减小.相关研究结果为高纯碳纳米管薄膜晶体管器件在红外光探测器方面的进一步应用提供参考依据.     

自组装半导体碳纳米管薄膜的光电特性

采用自组装的方法制备99%高纯度半导体碳纳米管平行阵列条带,以金属钯和钪为非对称接触电极制备碳纳米管（CNT）薄膜晶体管（TFTs）器件. 主要研究不同沟道长度碳纳米管薄膜晶体管器件的电输运特性和红外光电响应特性,分析了其中的载流子输运和光生载流子分离的物理机制. 我们发现薄膜晶体管器件的电学性能和光电性能依赖于器件沟道长度（L）和碳纳米管的平均长度（L_CNT）. 当沟道长度小于碳纳米管的平均长度时,器件开关比最低;当沟道长度超过碳纳米管平均长度时,随着沟道长度的增加,器件开关比增加,光电流减小.相关研究结果为高纯碳纳米管薄膜晶体管器件在红外光探测器方面的进一步应用提供参考依据.     

CVD法制备碳纳米管的TG-DTA研究--温度对CVD法制备碳纳米管的影响

基于碳纳米管粗产品中无定形碳和不同直径碳纳米管对氧的反应活性的差异,通过差热-热重(TG-DTA)方法,结合透射电镜(TEM)和X射线衍射(XRD)的测试结果,研究了合成温度对以乙炔气体为碳源,用CVD法制备碳纳米管的石墨化程度、碳纳米管直径以及直径分布的影响.结果表明:反应中,由于催化剂Co/SiO2中活性组分(Co)微晶随合成温度的升高而增大,导致所制备的碳纳米管的直径增大,从20～30 nm(650℃)增加到30～50nm(750℃).碳纳米管的石墨化程度随着反应温度的升高而增加.XRD实验结果还表明,当合成温度从650℃增加到850℃时,2θ值从25.8°增加到26.8°,(002)晶面的层间距从3.45 A减小到3.32 A,即随着合成温度的升高,碳纳米管(002)晶面的层间距减小.通过DTA放热峰的峰温和半峰宽的分析得出,无定形碳的放热峰峰温Tp＜380℃,其含量随着温度的升高而减小.碳纳米管的DTA放热峰的峰温Tp随着碳纳米管的直径和石墨化的程度的增加而升高,半峰宽随着碳纳米管的直径的分布范围增大而增宽.低温(650℃)有利于生成直径小且均匀的多层碳纳米管(20～30nm),而高温(大于750℃)则有利于生成直径大的多层碳纳米管(大于30～50 nm).     

磺化碳纳米管改性聚苯胺复合材料的合成与超级电容特性

运用重氮化技术制备了水溶性磺化碳纳米管,在此基础上,以不同直径的磺化碳纳米管(1～2 nm,<8 nm,10～20 nm,30～50 nm)为载体,采用原位氧化聚合方法合成了一系列磺化碳纳米管改性聚苯胺复合材料.红外和紫外-可见光谱分析表明,聚苯胺与磺化碳纳米管之间存在π-π相互作用,并形成了电荷转移复合物;且随着碳纳...     

含氟聚合物修饰碳纳米管及其聚氨酯复合疏水膜的研究

利用羟基碳纳米管上的羟基与2-溴异丁基酰溴之间的简单反应, 在碳纳米管上引入了含溴ATRP引发剂, 并进一步引发含氟丙烯酸酯的ATRP聚合, 从而在碳纳米管表面接枝上了低表面能的含氟聚合物. 红外光谱(FT-IR)、热重分析(TGA)和透射电镜(TEM)的研究结果表明碳纳米管与含氟聚合物之间为化学键连接. 以此低表面能聚合物包裹的碳纳米管作为填充粒子, 采用溶液浇铸方法制备了聚氨酯/碳纳米管复合膜, 并利用溶剂四氢呋喃(THF)刻蚀表面获得了不同碳纳米管裸露程度的复合膜材料. 静态接触角测试结果表明, 无论是羟基碳纳米管还是低表面能修饰的碳纳米管均可提高其复合膜的疏水性能, 且其疏水性能随碳纳米管含量的增加而增加; 相同含量时, 含氟聚合物接枝后的碳纳米管使复合膜具有更佳的疏水性能, 膜表面经溶剂刻蚀后可显著提高其疏水性能. 采用扫描电子显微镜(SEM)研究了加入碳纳米管和溶剂刻蚀对聚合物表面微观结构以及材料表面疏水性能的影响. 上述结果表明: 利用接枝聚合物可改变碳纳米管本身的疏水性能, 并可进一步制备新型的具有表面疏水性能的聚合物纳米复合材料.     

Study on Diameter Controlled Growth of Carbon Nanotubes by LaAl1-xFexO3 Catalysts

A series of LaAl1-xFexO3 catalysts prepared with lanthanum nitrate, aluminium nitrate and iron nitrate was investigated in catalytical syntheses of carbon nanotubes with high yields and purity. The properties of carbon nanotubes prepared by the method of CVD(chemical vapor deposition) with n-hexane as the carbon resource were studied and it was shown that the diameter of carbon nanotubes can be controlled by the molar ratio of iron to aluminum in the catalysts and that the diameter of carbon nanotubes changes a little with the decrease of the iron content in the catalysts. From the TEM pictures of carbon nanotubes, it can be found that the LaAl1-xFexO3 catalysts have a significant influence on the wall thickness of the carbon nanotubes, whereas they have little influence on the inner diameter of the carbon nanotubes.     

Fast Water Relaxation through One‐Dimensional Channels by Rapid Energy Transfer

Water in carbon nanotubes is surrounded by hydrophobic carbon surfaces and shows anomalous structural and fast transport properties. However, the dynamics of water in hydrophobic nanospaces is only phenomenologically understood. In this study, water dynamics in hydrophobic carbon nanotubes is evaluated based on water relaxation using nuclear magnetic resonance spectroscopy and molecular dynamics simulations. Extremely fast relaxation (0.001 s) of water confined in carbon nanotubes of 1 nm in diameter on average is observed; the relaxation times of water confined in carbon nanotubes with an average diameter of 2 nm (0.40 s) is similar to that of bulk water (0.44 s). The extremely fast relaxation time of water confined in carbon nanotubes with an average diameter of 1 nm is a result of frequent energy transfer between water and carbon surfaces. Water relaxation in carbon nanotubes of average diameter 2 nm is slow because of the limited number of collisions between water molecules. The dynamics of interfacial water can therefore be controlled by varying the size of the hydrophobic nanospace.     

Constrained iron catalysts for single-walled carbon nanotube growth

The diameter of single walled carbon nanotubes (SWNTs) determines the electronic properties of the nanotube. The diameter of carbon nanotubes is dictated by the diameter of the catalyst particle. Here we describe the use of iron nanoparticles synthesized within the Dps protein cage as catalysts for the growth of single-walled carbon nanotubes. The discrete iron particles synthesized within the Dps protein cages when used as catalyst particles gives rise to single-walled carbon nanotubes with a limited diameter distribution.     

过渡金属氧化物和金属负载型沸石催化剂上合成 纳米碳管及其表征

采用气相催化沉积法催化合成纳米碳管,比较了不同金属氧化物和金属负载型沸石催化剂以及不同分子筛载体对合成纳米碳管的影响,并用TEM,XRD表征其形貌和结晶度,用DTA-TG考察了纳米碳管的热和稳定性。实验结果表明纳米碳管的形成除了与金属种类有关外,还直接与催化剂的颗粒大小和分散状态有关。粒径在20nm左右的不规则形状的纳米粒子是形成纳米碳管的活性组分,非负载和负载型的催化剂均表明活性组分的粒径与纳米碳管的管径有一定的对应关系。化学提纯后能得到高纯度的纳米碳管;其管壁具有较好的石墨化结构,在空气中的热稳定性大于400℃,而在氮气中能维持到1200℃以上。     

多壁碳纳米管的制备及改性处理

用自制的镍 硅二元气凝胶作催化剂,合成了多壁碳纳米管.甲烷在680℃催化裂解120min,再升温至800℃继续裂解20min,得到多壁碳纳米管.TEM、HRTEM和Raman光谱分析表明,所得多壁碳纳米管与高定向石墨具有相似的层状结构,其管径分布均匀,约15～30nm左右,长径比大,管端封闭,并含有金属催化剂粒子;采用不同方法改性处理,发现经过稀硝酸浸泡和空气氧化处理后,能去除碳管中金属催化剂,同时碳纳米管管长变短,端帽开口,能有效利用内表面,比表面积增大.     

单壁碳纳米管的CVD合成及管径分布

甲烷在以活性氧化铝为载体的Fe、Co、Ni、Ru等催化剂上于850 ℃分解并生成直径为0.8～5 nm的单壁碳纳米管.预先将催化剂在1100 ℃焙烧,能够减少产物中无定形碳的生成.拉曼光谱结果表明,由该法制备的碳纳米管的管径分布主要受温度的影响,较低温度有利于较小直径的单壁碳纳米管的生成和较好的管径选择性.     

Structural and electronic characteristics of perhydrogenated carbon nanotubes

The structural and electronic characteristics of fully hydrogenated armchair and zigzag carbon nanotubes have been determined by quantum chemical methods. With use of line group symmetries, the structures of nanotubes up to 10 nm in diameter could be optimized by periodic B3LYP calculations. “In–out” isomerism is shown to significantly stabilize perhydrogenated carbon nanotubes, the energetically most favorable structures being those with 1/3–1/2 of the carbon atoms endo-hydrogenated. In favored nanotubes the ratio of endo- to exo-hydrogens is 1:1, the stabilities increasing as a function of the diameter of the nanotube. The calculated band gaps indicate that the perhydrogenated carbon nanotubes are insulators.     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.     

Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.     

Synthesis of alumina nanotubes using carbon nanotubes as templates

Alumina nanotubes have been fabricated using carbon nanotubes (CNTs) as templates at 1473 K. The Al₂O₃ nanotubes are polycrystals. They are less than 100 nm in outer diameter and tens of nanometer in inner diameter, which is close to the outer diameters of the templates. Under certain conditions, AlN and Al₂O₃ nanowires can also be fabricated in this reaction system. Discussions on the growth mechanisms of these nanotubes and nanowires are presented.