多壁碳纳米管的改性及其储氢性能研究

考察了空气处理、混酸处理、H₂O₂处理和等离子体活化等化学改性和多种活性金属修饰对碳纳米管储氢性能的影响,采用TPD-H₂评价装置测试了不同样品吸附的氢气在程序升温后的脱附情况,用峰面积和氢气的校正因子计算出样品吸附氢气的体积,从而计算出碳纳米管的储氢容量.实验结果表明,化学改性和金属修饰均能明显提高碳纳米管的储氢性能,其中经过混合酸和H₂O₂化学处理并负载质量分数为20%Ni的碳纳米管,在常温常压下的氢气储存的质量分数达到2.55%,比未做任何处理的碳纳米管的储氢容量提高了7倍.     

用分子动力学模拟水合物储氢

用分子动力学(MD)模拟方法系统研究了结构Ⅰ型(SⅠ)和结构H型(SH)氢气水合物中氢气的占据情况并确定了氢气水合物的稳定结构: SⅠ水合物氢气分子数小胞中为2, 大胞中为3; SH水合物氢气分子数小胞中为2, 中胞中为2, 大胞中为11. 分析了稳定情况下水合物各胞腔内氢气分子之间的径向分布函数(RDF), 得出了氢气分子在各胞腔内的稳定位置. 由稳定位置得到了稳定结构下氢气水合物的储氢质量分数: SⅠ为5.085%, SH为6.467%. 与实验对比得出结论: SH水合物稳定结构下的储氢能力最强.     

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.     

定向多壁碳纳米管电化学储氢研究

利用恒流充放电、循环伏安曲线(CV)和电化学阻抗技术(EIS)等方法对定向多壁碳纳米管(AMWCNTs)储氢的电化学行为及其储氢机制进行了探讨.研究表明,定向AMWCNTs-Cu电极有较高的电化学储氢性能,其储氢容量在1500mA/g的电流密度下可以达到1162mA·h/g.定向AMWCNTs的电化学储氢能力强与其空间结构有关,而铜粉的加入有利于提高碳纳米管的电催化反应表面积和电极电化学反应活性,有利于氢在碳纳米管中扩散,从而提高了碳纳米管电极材料的储氢量.     

碳纳米管固相微萃取涂层吸附性能研究

利用空气氧化和稀酸回流纯化单壁碳纳米管,用高分辨透射电镜、拉曼光谱对碳纳米管进行了表征.在分子模拟中,非极性氢气、甲烷分子采用单点Lennard-Jones球形分子模型,流体分子与C原子之间相互作用采用虚拟原子模型.以液氮温度下碳纳米管对氮气的吸附等温线实验数据为依据,利用巨正则蒙特卡罗方法模拟得到了碳纳米管的孔径分布,主要集中在6nm.计算了常温常压下碳纳米管中甲烷及氢气的吸附等温线,298K及0.1MPa压力下,氢气的吸附量达到0.015%(质量分数),甲烷在样品中的吸附量可以达到0.5%(质量分数).模拟研究结果表明碳纳米管可以用作固相微萃取涂层材料.     

述评碳纳米管储氢研究*

碳纳米管因被认为可能是氢能的主要载体而备受关注,但几年来的文献报道不尽一致.本文评述了关于单壁和多壁碳纳米管对氢气的吸附实验和模拟计算研究结果,探讨了碳纳米管作为储氢材料的可行性.     

DNA共价修饰单壁碳纳米管电极的制备及与VB6 相互作用的研究

利用单壁碳纳米管(SWNTs)上的羧基与DNA末端的氨基形成酰胺共价键从而共价修饰SWNTs,制备了新型DNA共价修饰SWNTs电极.傅立叶红外光谱表明DNA共价结合在SWNTs上,用扫描电镜(SEM)表征了SWNTs、DNA共价修饰的SWNTs的结构与形貌.循环伏安法(CV)研究了DNA修饰SWNTs电极的电化学特性,通过改变扫描速率,发现DNA修饰电极的过程属于扩散控制过程.维生素B6(VB6)与SWNTs上DNA的相互作用研究结果表明:DNA分子共价修饰在SWNTs上后仍具有生物活性,且能够与其他生物分子发生相互作用.     

氢气在碳纳米管基材料上的吸附-脱附特性

利用高压容积法测定多壁碳纳米管(MWCNTs)及钾盐修饰的相应体系(K＋-MWCNTs)的储氢容量,并用程序升温脱附(TPD)方法表征研究氢气在MWCNTs基材料上的吸附-脱附特性.结果表明,在经纯化MWCNTs上,室温、9.0 MPa实验条件下氢的储量可达1.51％（质量分数）;K＋盐对MWCNTs的修饰对增加其储氢容量并无促进效应,但相应化学吸附氢物种的脱附温度有所升高;K＋的修饰也改变了MWCNTs表面原有的疏水性质.在低于723 K的温度下,H2/MWCNTs体系的脱附产物几乎全为氢气;773 K以上高温脱附产物不仅含H2,也含有CH4、C2H4、C2H2等C1/C2烃混合物;H2/K＋-MWCNTs储氢试样的脱附产物除占主体量的H2及少量C1/C2烃混合物外,还含水汽,其量与吸附质H2源水汽含量密切相关.H2在碳纳米管基材料上吸附兼具非解离 (即分子态) 和解离(即原子态)两种形式.     

碳纳米管复合聚对氨基吡啶修饰电极伏安法同时测定硝基酚异构体的研究

利用导电聚合物的分子识别性和碳纳米管奇特的物理化学性质, 制备了碳纳米管复合聚对氨基吡啶(SWNTs/POAP)修饰电极, 研究了邻、间、对硝基酚异构体同时在该电极上的电化学响应. 实验结果表明, 邻、间、对硝基酚异构体在SWNTs/POAP纳米电极界面具有不同的构象, 其氧化峰电位能够完全分开, 并能显著地提高电化学测定的灵敏度. 文中的SWNTs/POAP纳米电极制备简单方便, 可用于硝基酚位置异构体的同时电化学量测.     

碳纳米管的电化学贮氢性能研究

研究了碳纳米管电极的电化学性能 ,其电化学储氢量达到 2 0 0mAh·g 1且具有高的电化学活性和良好的循环寿命 .采用循环伏安法研究了氢在碳纳米管电极上吸附 /氧化机理 .     

Separation of Semiconducting Single‐Walled Carbon Nanotubes by Using a Long‐Alkyl‐Chain Benzenediazonium Compound

We designed and synthesized 4‐dodecyloxybenzenediazonium tetrafluoroborate ( 1 ), which preferentially reacts with metallic single‐walled carbon nanotubes (SWNTs) by kinetic control. We first determined the suitable experimental conditions for the preferential reaction of 1 with individually dissolved SWNTs by monitoring the decrease in absorbance for the metallic SWNT in the range of 400–650 nm in the absorption spectrum of the SWNTs. The reacted SWNTs were thoroughly rinsed with THF to obtain THF‐insoluble SWNTs. The Raman spectrum of the THF‐insoluble SWNTs showed a strong peak near 180 cm^?1, which corresponds to a semiconducting breathing band. The metallic breathing bands (≈220 cm^?1) and Breit–Wingner–Fano (BWF) modes (1520 cm^?1) corresponding to the metallic SWNTs were much weaker than those of the pristine SWNTs. We also confirmed that metallic peaks in the range of 400–650 nm in the absorption spectrum of THF‐insoluble SWNTs that were individually dissolved in an aqueous micelle of sodium cholate were almost nondetectable. All the results indicate that the THF‐insoluble SWNTs are semiconducting.     

Surface area measurement of functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes have been functionalized and the specific surface areas of the functionalized nanotubes measured. Contrary to expectations, functionalization leads to a decrease in specific surface area compared to that of the unfunctionalized nanotubes. Treatment with a concentrated 1:1 nitric/sulfuric acid mixture followed by high-temperature baking at 1000 degrees C was found to increase the specific surface area of the nanotubes. For the unfunctionalized SWNTs, this treatment increases the specific surface area (SSA) by 20%. In the case of SWNTs functionalized by n-butyl groups the increase in the SSA was nearly 2-fold with the value increasing from 410 (drying at 110 degrees C) to 770 m2/gm (acid and bake treatment followed by drying at 110 degrees C). For the ozonized SWNTs, the SSA increases more than 3-fold from 381 (drying at 110 degrees C) to 1068 m2/gm (acid and bake treatment followed by drying at 110 degrees C). SEM images indicate that the nanotubes rebundle in the solid state with an average bundle size of 10-30 nm. AFM studies show that the ozonized tubes have been cut to short bundles after ozonolysis. Hydrogen uptake studies carried out on the baked ozonized tubes led to a 3 wt % hydrogen uptake at 77 K and 30 bar.     

Pd/SWNTs负载型催化剂的制备及其催化性能

利用单壁碳纳米管(SWNTs)自身的还原性, 将PdCl2溶液中的Pd2+直接还原成金属Pd负载在SWNTs表面上, 制备了具有良好催化性能的Pd/SWNTs负载型催化剂. 通过透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)和热重分析(TG)对Pd/SWNTs 进行了表征, 并利用Suzuki反应对Pd/SWNTs的催化性能进行了测试. 实验结果表明, 用SWNTs与12 mmol·L-1的PdCl2的水溶液直接作用, 得到Pd/SWNTs催化材料的Pd负载量达到14.13%(w, 质量分数), 颗粒分散均匀, 粒径小(2 nm左右), 与SWNTs结合紧密; 用经过H2还原的Pd/SWNTs作催化剂, 在90 ℃下进行Suzuki反应, 30 min后反应就基本完成, 其联苯的产率达到98.10%, 催化活性较高, 可望广泛用于有机合成反应.     

单壁碳纳米管自还原法制备负载Pt催化剂及其催化性能

金属Pt是良好的催化加氢、脱氢催化剂, 利用单壁碳纳米管(SWNTs)自身的还原性, 将K2PtCl6溶液中的Pt直接还原并负载在SWNTs表面上, 制备了具有良好催化性能的SWNTs/Pt负载型催化剂. 通过TEM, XPS和TG对材料进行了表征, 研究了K2PtCl6浓度及溶剂对Pt负载量、粒径的影响, 并测试了SWNTs/Pt的催化性能. 实验结果表明, SWNTs负载的Pt颗粒小, 分散均匀, 负载量高, 与SWNTs结合紧密, 催化性能好, 是催化加氢和脱氢反应的良好催化剂.     

氯过氧化物酶修饰电极对一氯二甲酮的催化氯化

通过将氯过氧化物酶溶液(Chloroperoxidase, CPO)与Nafion分散的单壁碳纳米管分散液混合后直接滴涂到玻碳电极表面制得修饰电极. 这个固定了氯过氧化物酶的碳纳米管修饰玻碳电极, 在pH=5.0的磷酸缓冲溶液中测得的循环伏安曲线上有一对准可逆的氧化还原电流峰, 经过与裸电极和没有固定氯过氧化物酶的碳纳米管修饰电极上测得的循环伏安行为对比后确认, 碳纳米管对氯过氧化物酶与电极之间的电子传递反应具有很好的促进作用. 利用该修饰电极能催化一氯二甲酮氯化为二氯二甲酮, 无需添加过氧化氢作为反应启动剂, 紫外光谱的测试结果表明, 每摩尔氯过氧化物酶可催化氯化4.0×105 mol 的一氯二甲酮, 表现出很高的催化效率.     

Dispersion and separation of small-diameter single-walled carbon nanotubes

The dispersion of small-diameter single-walled carbon nanotubes (SWNTs) produced by the CoMoCAT method in tetrahydrofuran (THF) with the use of amine was studied. The absorption, photoluminescence, and Raman spectroscopies showed that the dispersion and centrifugation process leads to an effective separation of metallic SWNTs from semiconducting SWNTs. Since this method is simple and convenient, it is highly applicable to an industrial utilization for widespread applications of SWNTs.     

Studies of bromine modified single-walled carbon nanotubes using photoelectron spectroscopy and density-functional theory

Many applications based on single-walled carbon nanotubes (SWNTs) require chemical modification of carbon nanotube to optimize the functionalities of the device. In this contribution we discuss the properties of SWNTs immersed in a hydrobromic acid (HBr) solution. Changes of atomic and electronic structures of bromine modified SWNTs were investigated using photoelectron spectroscopy (PES). Spectra of SWNTs before and after immersion in the HBr solution exhibit different features. To understand the mechanism of interaction between SWNTs and bromine, we performed density-functional theory calculations to reveal the structural changes, adsorption energy and chemical bonding information of SWNTs interacting with bromine. In addition, based on the Gelius model, from the molecular orbitals (MOs), we calculated ultraviolet photoelectron spectra (UPS) of SWNTs with and without functionalizing and compared them with the experiment. The present study is a first step in the understanding of the functionalization mechanism of carbon nanotubes.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

Purity assessment of single-wall carbon nanotubes, using optical absorption spectroscopy

A demand currently exists for a method of assessing the purity of single-wall carbon nanotubes (SWNTs), which will allow for meaningful material comparisons. An established metric and protocol will enable accurate and reproducible purity claims to be substantiated. In the present work, the ability to accurately quantify the mass fraction of SWNTs in the carbonaceous portion of a given sample is demonstrated, using optical absorption spectroscopy on both laser and arc discharge-generated SWNT-N,N-dimethylacetamide (DMA) dispersions. Verification of purity assessment protocols is based upon constructed sample sets comprising designed mass fractions of purified SWNTs and representative carbonaceous synthesis byproducts. Application of a previously reported method based on a ratio of the areal absorbance from linear subtractions of the second interband electronic transitions of semiconducting SWNTs ((S)E(22)) has shown a severe overestimation of SWNT purity (average error >24%). Instead, the development of a nonlinear pi-plasmon model, which considers overlap of electronic transitions and peak broadening, has dramatically improved the purity assessment accuracy (average error <7%), derived from a strong correlation to the constructed sample sets. This approach has enabled corroboration of rapid assessment procedures, such as absorbance peak maxima ratio and Beer's law analysis, directed at purification monitoring and synthesis sample screening. Specifically, a simple protocol for purity assessment of laser and arc-discharge SWNTs has been established that can be extended to other synthetic types (i.e. CVD, HiPco, etc.) and diameter distributions.     

Electrochemical absorption and oxidation of hydrogen on palladium alloys with platinum, gold and rhodium

Thin layers of Pd and its alloys with Pt, Au and Rh were prepared by electrodeposition on a Au substrate. Hydrogen electrosorption by the obtained electrodes was studied in 0.5 M H(2)SO(4) solution using cyclic voltammetry and chronoamperometry. The influence of the alloying process on selected thermodynamic (the amount of absorbed hydrogen, the stability of the β-phase, the extent of the absorption/desorption hysteresis) and kinetic aspects (the rate of hydrogen absorption and absorbed hydrogen oxidation) of hydrogen absorption and desorption was examined. It was found that the addition of the non-absorbing elements to Pd results in faster kinetics of the hydrogen electrosorption process and a smaller absorption/desorption hysteresis.