多壁碳纳米管/水纳米流体的蓄冷特性研究

目的 探究多壁碳纳米管的浓度、管径以及超声声强对纳米流体的蓄冷特性和换热性能的影响规律。方法 将 5~12 nm、10~20 nm、20~30 nm 3种不同管径的多壁碳纳米管和质量分数为0.05%~0.2%的多壁碳纳米管分别制备成不同的纳米流体样品,并搭建试验台对样品进行蓄冷实验。结果 在质量分数从0.05%变为0.2%时,纳米流体的平均过冷度减小了0.7 ℃,管径由20~30 nm变至5~12 nm时,平均过冷度下降了64.3%;1级超声声强使传热能力提高了5.3%,而4级超声声强使传热能力提高了7.8%。结论 研究表明,多壁碳纳米管浓度的增加及管径的减小,可使纳米流体的换热能力增大,过冷度减小,超声声强对多壁碳纳米管/水纳米流体有强化传热作用。     

超短多壁碳纳米管组装管的制备研究

以质量分数为10％的过氧化氢溶液为氧化剂,1mol／L的硫酸为酸性介质,常温下放置48h,即可以简单地将冗长团聚的多壁碳纳米管切割成超短碳纳米管的组装管。碳纳米管组装管的长度为50～800nm,超短碳纳米管的长度为8～15nm。碳纳米管被切短后没有引入取代官能团。     

Fe-Mo/Al_2O_3催化剂催化分解甲烷制备碳纳米管:温度对碳管结构的影响

利用化学气相沉积法,以Fe-Mo/Al_2O_3为催化剂,催化分解甲烷气体制备碳纳米管(CNTs).研究了温度,反应时间和气体流速对碳纳米管结构的影响.结果显示:温度是影响碳纳米管壁厚的关键参数.低温导致壁厚为2 nm～7 nm的多壁碳纳米管(MWCNTs)的生成.相对地,高温有利于双壁碳纳米管(DWCNTs)的生长,而更高的温度促使单壁碳纳米管(SWCNTs)的产生.进一步升高温度,得到了壁厚为3 nm～15 nm的MWCNTs和大的炭颗粒.     

多壁碳纳米管在硫酸溶液中的γ辐射剪切

在硫酸溶液中系统地研究了γ辐射法剪切多壁碳纳米管,以及影响碳管长度的反应条件,详细讨论了多壁碳纳米管的剪切机理.采用透射电子显微镜(TEM)、傅立叶变换红外光谱(FT-IR)、紫外可见分光光度计(UV-Vis)和Raman光谱对短多壁碳纳米管进行了分析与表征,分析了多壁碳纳米管浓度与其对UV270nm吸光度的关系,得出了多壁碳纳米管质量浓度与其对UV270nm吸光度的线性回归方程.结果表明,γ辐射和硫酸氧化作用在剪切多壁碳纳米管的过程中存在协同效应.随着辐射剂量和酸浓度的增加,剪切后的碳管长度不断缩短.当辐射剂量增加到200kGy、酸浓度为5mol/L时,短多壁碳纳米管长度为200～300nm.辐射剪切的方法在碳纳米管外侧及末端引进C-OH、-COOH等官能团,从而对MWNTs的石墨型结构造成微弱损伤.另外,制备的短多壁碳管在水中可以均匀分散2周而不出现沉淀.     

多壁碳纳米管的分散性研究

以多壁碳纳米管为原料,添加十二烷基苯磺酸钠进行表面活化,并溶于乙醇中,用超声震荡法分散多壁碳纳米管,采用扫描电镜（SEM）对其进行粒子表征。结果表明,运用超声振荡法分散的多壁碳纳米管分散情况良好,碳纳米管直径在30--50nm之间,能够达到较好的分散效果。     

水分散多壁碳纳米管紫外光谱特征及其应用

研究了多壁碳纳米管水分散体系的紫外光谱特征及其影响因素,并将其应用于碳纳米管对环境污染物五氯苯酚的吸附过程。结果表明:水分散多壁碳纳米管的主吸收带在190~250nm;最大吸收峰位于190~207nm,且随碳纳米管管外径的增加向短波方向偏移;抽滤次数n影响水分散体系中碳纳米管的浓度及其紫外光谱强度,n≥4时吸收强度趋于稳定低值。紫外光谱法研究碳纳米管吸附五氯苯酚的体系中,选用232nm作为测定波长可得到良好的线性关系且避免碳纳米管背景浓度的干扰。     

碳纳米管12～18GHz电磁波衰减实验研究

用电磁波穿透方法实验研究了长度为2μm和15μm,直径分别为30,60,100nm 6种碳纳米管12~18GHz电磁波衰减特性.实验结果表明:直径为30nm时长度15μm碳纳米管的衰减能力大于长度2μm的;直径为60nm时长度2μm碳纳米管衰减能力大于长度15μm的;直径为100nm时长度15μm纳米管的电磁波衰减能力大于长度为2μm的.在长度相同的情况下,不同直径碳纳米管的电磁波衰减能力为:60nm>100nm>30nm.电磁波衰减效果最好的是φ 60nm×2μm的碳纳米管;最差的是φ 30nm×2μm的碳纳米管.6种碳纳米管的电磁波衰减能力为:φ 60nm×2μm>φ 60nm×15μm>φ 100nm×15>μmφ 100nm×2μm>φ 30nm×15μm>φ 30nm×2μm.     

碳纳米管8～12 GHz 电磁波衰减实验研究

用电磁波穿透方法实验研究了长度为2μm 和15μm , 直径分别为30 、60 和100 nm 的6 种碳纳米管8～12 GHz 电磁波衰减特性。结果表明, 直径为30 nm 时, 长度为15μm 的碳纳米管的电磁波衰减能力大于长度2μm的; 直径分别为60 nm 和100 nm 时, 长度为2μm 的碳纳米管的电磁波衰减能力均大于长度为15μm 的。在长度相同的情况下, 不同直径碳纳米管的电磁波衰减能力为: 60 nm > 100 nm > 30 nm。6 种碳纳米管的电磁波衰减能力为: Ф60 nm ×2μm > Ф60 nm ×15μm > Ф100 nm ×2μm > Ф100 nm ×15μm > Ф30 nm ×15μm > Ф30 nm ×2μm。实验还发现长径比较小的碳纳米管的电磁波衰减能力明显好于长径比较大的磁纳米管的电磁波衰减能力;但碳纳米管长径比与电磁波衰减能力之间并不存在简单的线性关系。      

催化化学气相沉积法制备螺旋形多壁碳纳米管(英文)

以乙炔为碳源、FeMo/MgO催化剂为模板,采用催化化学沉积法制备了螺旋状多壁碳纳米管(hs-MWC-NTs)。其中FeMo/MgO模板,由作为发泡和助燃剂的柠檬酸燃烧而制成。FeMo/MgO催化剂的XRD谱图揭示其具有微晶的通性。应用SEM、TEM和Raman光谱剖析了合成的炭材料。SEM和TEM观察表明获得了hs-MWC-NTs;Raman光谱的D峰和G峰确认了所获碳纳米管(CNTs)的结晶状态。结果表明:此法乃是合成直径10nm～20nm螺旋形多壁碳纳米管的最容易和简便方法。     

多壁碳纳米管负载镁掺杂氧化锌纳米颗粒的研究

利用醋酸锌和醋酸镁为原料,无水乙醇为溶剂,草酸为沉淀剂,通过共沉淀法和后续热处理实现多壁碳纳米管表面负载镁掺杂氧化锌纳米颗粒,并使用X射线衍射仪、扫描电子显微镜、透射电子显微镜和紫外吸收光度计研究复合材料的形貌和光学性能。电子显微镜结果表明,在450℃热处理下,多壁碳纳米管表面能够均匀地负载镁掺杂氧化锌纳米颗粒,其颗粒粒径大约为10～20nm。紫外吸收光谱结果说明,镁掺杂显著地提高多壁碳纳米管/氧化锌复合材料的紫外吸收性能,而且其紫外吸收峰向短波方向蓝移达22nm。     

Production of empty and iron-filled multiwalled carbon nanotubes from iron–phthalocyanine polymer and their electromagnetic properties

A facile production of multiwalled carbon nanotubes (MCNTs) using iron-phthalocyanine polymer as the only carbon source with two kinds of metallic catalysts (Fe(CO)₅ and nano-iron) has been compared here. SEM, TEM and XRD were employed to figure the detailed structures of the carbon nanotubes. Consequently, catalyst played a key role in the formation of MCNTs: nano-iron resulted in iron-filled CNTs while Fe(CO)₅ led to empty CNTs. Both of these two CNTs were long and straight, with ~100 nm in diameter and several tens of micrometers in length. Moreover, dielectric and magnetic properties were carried to further study synthesized carbon nanotubes. The results showed that the empty MCNTs had better dielectric properties than iron-filled MCNTs although the iron-filled CNTs exhibited the magnetic saturation of ~3.5 emu/g and coercive force of ~594.0 Oe, which is much higher than empty MCNTs.     

Synthesis, characterization and properties of carbon nanotubes microspheres from pyrolysis of polypropylene and maleated polypropylene

Microspheres assembled from carbon nanotubes (MCNTs), with the diameters ranging from 5.5 to 7.5 μm, were synthesized by means of pyrolysis of polypropylene and maleated polypropylene in an autoclave. The characterization of structure and morphology was carried out by X-ray diffractometer (XRD), field-emission scanning electron microscopy (FESEM), (high resolution) transmission electron microscope [(HR)TEM)], selected-area electron diffraction (SAED) and Raman spectrum. As a typical morphology, the possible growth process of MCNTs was also investigated and discussed. The results of nitrogen adsorption-desorption indicate that the Brunauer-Emett-Teller (BET) surface area (140.6 m²/g) of the MCNTs obtained at 600 °C is about twice as that (74.5 m²/g) of carbon nanotubes obtained at 700 °C. The results of catalytic experiment show that MCNTs based catalyst has higher catalytic activity than the carbon nanotubes based catalyst for the preparation of methanol and dimethoxy-ethane by oxidation of dimethyl ether.     

碳纳米管吸附腐植酸的动力学、热力学及机理研究

针对天然水中腐植酸(HA)类溶解性有机物去除问题, 采用多壁碳纳米管为吸附剂, 在不同的pH值、吸附剂量、初始HA浓度下进行吸附动力学实验, 用准二级速率方程拟合了动力学数据, 其线性相关度在0.99以上, 拟合得到的平衡吸附量为27mg/g,与实验结果(25.5 mg/g)基本一致. 在25~50℃下进行了碳纳米管吸附腐植酸的等温吸附实验, 以Langmuir模型拟合的平衡吸附量为29.7mg/g, 与实验结果相近. 用Clapeyron-Clausius与Gibbs- Helmholtz方程计算的自由能(Δ G)、焓(Δ H)、熵(Δ S)皆为负值, 说明碳纳米管对腐植酸的吸附为放热熵减过程. 碳纳米管的表面、管间隙、管内腔及管束之间形成的束聚孔为其有效吸附点位, 腐植酸与碳纳米管间的π-π作用也是吸附的主要原因之一.     

Ag纳米晶颗粒/碳纳米管复合材料的制备与结构研究

利用热蒸发方法在多壁碳纳米管表面沉积Ag纳米颗粒,XRD结果显示,Ag纳米颗粒以晶体形态存在,同时透射电镜分析结果表明,Ag纳米晶颗粒引起碳纳米管横截面形变,从而形成Ag纳米晶颗粒/碳纳米管异质复合材料,这些纳米异质复合材料相互连接,形成网络化分布的结构.     

MnO2对多壁碳纳米管的包覆与表面改性研究

利用高锰酸钾(KMnO4)在分散有多壁碳纳米管的硝酸溶液作用下分解,控制反应条件,在多壁碳纳米管上原位生成并包覆了颗粒状和丝状两种不同形貌的MnO3.通过XPS对反应产物进行了验证,利用TEM对碳纳米管包覆前后的形貌进行了表征,并对反应机理进行了初步探讨.     

Carbon dioxide as a carbon source for synthesis of carbon nanotubes by chemical vapor deposition

Carbon dioxide was successfully used as carbon source in the synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over Fe/CaO catalyst. The product was evaluated using both transmission electron microscopy (TEM) and Raman spectroscopy. Crooked and branching structures of multi-walled carbon nanotubes (MCNTs) with diameters of around 50 nm were observed on the TEM micrographs. Raman spectrum results show that the nanotubes have small defects, which is in agreement with the results of TEM. The influence of reaction variable such as furnace temperature and types of support media was also studied and the reaction mechanism was then discussed in this paper.     

A Study on the Wear Resistance of Nano-Material/E51

Epoxy resin modified by nanometric γ-alumina or multi-walled carbon nanotubes (MCNTs) was prepared with solution mixingmethod, and the wear resistance of the composite was studied. The results show that when an optimum amount of nanometricalumina or MCNTs is filled in epikote51 (E51), the wear resistance of the composite will increase. When 8 wt pct nanometricγ-alumina is filled in E51, the wear resistance of the composite increases to 230%. When 10% MCNTs is filled in E51, thewear resistance of the composite increases to 226%. When nanometric alumina is filled in, the wear resistance of modifiedepikote51 will increase as the cure temperature is heightened.     

Multiwalled Carbon Nanotubes Modified Electrode as a Sensor for Adsorptive Stripping Voltammetric Determination of Hydrochlorothiazide

The study of electrochemical behavior and determination of hydrochlorothiazide, a thiazide diuretic and antihypertensive drug, on multiwalled carbon nanotubes (MCNTs) modified glassy carbon electrode (GCE) is described by adsorptive stripping voltammetry in open circuit potential. The cyclic voltammetric results indicate that MCNTs remarkably enhance the oxidation of hydrochlorothiazide in wide pH range of 2.0–9.5, which is leading to considerable improvement of anodic peak current for hydrochlorothiazide, and allow the development of a highly sensitive voltammetric sensor for determination of hydrochlorothiazide in pharmaceutical and urine samples. Electrochemical studies by alpha-Fe$_{2}$O $_{3}$ nanoparticles modified carbon paste electrode show these oxides have no electrocatalytic effect for hydrochlorothiazide oxidation and support iron oxide impurities in the MCNTs are not active sites in sensing of hydrochlorothiazide. Under optimized conditions, the oxidation peak have two linear dynamic range of 2.0–20.0 nM and 0.2–100.0 $mu$M with experimental detection limit of 0.8 nM and a precision of $≪hbox{4}hbox{%}$ (RSD for 8 analysis).      

Designing of carbon nanotube/polymer composites using melt recirculation approach: Effect of aspect ratio on mechanical,electrical and EMI shielding response

The paper describes the effect of aspect ratio of multiwall carbon nanotubes (MCNTs) on the electrical, mechanical and electromagnetic properties of polypropylene random copolymer (PPC). Long and short MCNTs with aspect ratio of ~ 1356–1937 and ~ 158 respectively were melt-blended with PPC in a micro twin screw extruder with melt recirculation that allow the formation of composites having ~ 15 wt.% MCNTs. The good dispersion was confirmed by scanning electron microscopy and observation of electrical conductivity at low percolation threshold (0.45 and 1.07 wt.% for l- & s-MCNT/PPC composite respectively) and improvement of modulus and strength. The 15 wt.% l-MCNTs and s-MCNT loaded composites show 52% and 60% improvement in modulus respectively and 20% & 18% improvement in strength over neat PPC. The electromagnetic interference (EMI) shielding response (in 8.2–12.4 GHz frequency range) revealed that l-MCNT based PPC composites display better shielding at lower loading (up to 4 wt.%) while s-MCNT show better attenuation at higher loadings. The realization shielding effectiveness value of − 27 dB (> 99% attenuation) respectively for l-MCNT composites: and − 37 dB (> 99.9% attenuation) for s-MCNTs composites at 15 wt.% reflect their potential for making light weight and structurally strong EMI shields.     

Pt-Pd alloy nanoparticle-decorated carbon nanotubes: a durable and methanol tolerant oxygen reduction electrocatalyst

We describe the decoration of multiwalled carbon nanotubes (MCNTs) with Pt-Pd alloy nanoelectrocatalysts of three different compositions and their electrocatalytic performance toward the oxygen reduction reaction (ORR). The decoration of the MCNTs involves polymer-assisted impregnation of metal precursors [Formula: see text] and [Formula: see text] and the subsequent reduction of the impregnated precursors by a modified polyol route. The composition of the catalyst was controlled by tuning the molar ratio of the precursors during their impregnation. Electron probe microscopic analysis shows that the catalysts have compositions of Pt(46)Pd(54,) Pt(64)Pd(36) and Pt(28)Pd(72). The Pt(46)Pd(54) and Pt(64)Pd(36) catalysts have truncated octahedral and icosahedral shapes with a size ranging from 8 to 10?nm. On the other hand, the catalyst of Pt(28)Pd(72) composition has a spherical/quasispherical shape with a size distribution of 1-2?nm. The XPS measurement confirms the signature of metallic Pt and Pd. The Pt(46)Pd(54) catalyst has a pronounced electrocatalytic activity toward the ORR with a specific and mass activity of 378 [Formula: see text] and [Formula: see text], respectively at 0.8?V. Moreover, the Pt(46)Pd(54) nanoelectrocatalyst is highly durable and it retains its initial catalytic activity even after 1000 extensive cycles. Interestingly, this catalyst has a very high tolerance toward methanol and it does not favor the oxidation of methanol in the potential window of 0.1-1.4?V. The electrocatalytic activity of the alloy electrocatalyst is compared with commercially available Pt black and MCNT-supported spherical Pt nanoparticles. The catalytic activity of the Pt(46)Pd(54) nanoelectrocatalyst is higher than the other catalysts. The Pt(46)Pd(54) catalyst outperforms the electrocatalytic activity of all other catalysts.