Preparation of high-yield multi-walled carbon nanotubes by catalytic decomposition of mixture of natural gas and propylene and their electrothermal properties

Abstract

Multi-walled carbon nanotubes (MWNTs) with high-yield were prepared by pyrolysis of mixture of natural gas (NG) and propylene (C₃H₆) over Fe-Ni/Al₂O₃-MgO catalyst. For C₃H₆/NG flow rate ratio ranging from 0 to 0.33, the carbon yield was increased from 903% to 4400%. The synthesized MWNTs after purification were dispersed by ball milling method and mixed with waterborne polyurethane to fabricate the electrothermal film. The mass fraction of CNT filler in the cured electrothermal film was controlled at 50%. The coating after drying was ca. 6?μm and the coating’s volume resistivity was 0.053 Ω·cm. The time-dependent temperature curves indicated that the heating rate of the electrothermal film was very fast under different low voltage and the steady-state temperatures were achieved within 100?s. The steady-state temperature reached 47.9?°C, 76.8?°C, and 102.8?°C, respectively at 10?V, 15?V, and 18?V.     

Influence of Mo or Cu doping in Fe/MgO catalyst for synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of methane

A series of mono-, bi- or tri-metallic Fe–Mo-Cu/MgO catalysts with the same metal loading of 6 wt% were prepared by impregnation method and used as catalysts for synthesis single-walled carbon nanotubes (SWCNTs) via methane decomposition. XRD, H₂-TPR, and nitrogen physisorption techniques were used to characterize the freshly calcined catalysts, while HRTEM, Raman spectroscopy and TGA were employed to investigate the morphology and microstructure of the SWCNTs product. The obtained results indicated that the introduction of Mo or Cu in the Fe/MgO catalyst enhanced the catalytic growth activity. TEM images showed that both bundles and isolated SWCNTs were obtained over Mo containing catalysts, whereas only SWCNTs bundles were grown over the Fe-Cu/MgO catalyst. The obtained SWCNTs having a diameter of around 0.9–2.4 nm. Raman analysis illustrated that all promoted catalysts produced high quality of SWCNTs compared to the unpromoted Fe/MgO catalyst.     

催化剂对乙醇催化燃烧法制备碳纳米纤维的影响

分别以硝酸铁、硝酸钴、硝酸镍以及氯化铁、氯化钴、氯化镍作为催化剂先体，利用乙醇催化燃烧法制备了碳纳米纤维。利用扫描电子显微术、透射电子显微术和X射线能量分散谱术对样品进行了表征。讨论了不同种类的催化剂先体对产物形貌和生长机制的影响。     

不同氧化体系处理对多壁碳纳米管的影响

采用3种氧化体系(H2SO4/H2O2,H2SO4/K2Cr2O7,H2SO4/HNO3)对多壁碳纳米管(MWC-NTs)进行处理,通过红外光谱、拉曼光谱、热失重、滴定分析、Zeta电位激光粒度分析仪、透射电镜对氧化前后的样品进行表征.结果表明,氧化处理未明显破坏MWCNTs的管状结构,并在表面引入羧基官能团,滴定分析...     

多壁碳纳米管的表面功能化及分散性研究

多壁碳纳米管(MWCNTs)分别经混合、强酸氧化浸泡和酰氯化处理后,再与9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)的衍生物(DHDOPO)进行接枝反应得到表面功能化的MWCNTs。利用傅里叶变换红外光谱仪(FT-IR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、热重分析仪(TGA)、紫外-可见分光光度仪(UV-Vis)和沉降实验等分别表征改性前后MWCNTs的结构和表面形态,估算DHDOPO在MWCNTs表面的相对接枝率,研究改性前后MWCNTs在乙醇中的分散性。结果表明,MWCNTs经混合强酸氧化后表面出现羧基;DHDOPO在MWCNTs上的相对接枝率为51%;混合强酸氧化和表面接枝DHDOPO的MWCNTs在无水乙醇中具有良好的分散性。     

Role of catalysts in the surface synthesis of single-walled carbon nanotubes

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.      

碳纳米管负载金属氮化物催化剂的制备及其性能研究

采用等体积浸渍法结合程序升温还原技术制备出一系列负载型过渡金属氮化物催化剂。利用XRD、BET、TPR等表征手段,结合氨分解制氢反应,研究了它们的表面性质和反应性能。发现改性碳纳米管负载的氮化钴催化剂具有较大的比表面积,对氨分解制氢反应的催化活性最高。新鲜态CoNx/CNTs催化剂的比表面积可达151.85m2/g,在650℃时氨转化率为80.3%,850℃达到完全转化。     

含碳纳米管导电剂改善LiCoO2电极电化学性能

采用多壁碳纳米管(MWCNTs)和片状石墨(FNG)的复合物作导电剂来改善LiCoO2电极的电化学性能,并用恒电流充放电和扫描电子显微镜(SEM)对这种含MWCNTs的LiCoO2电极进行了研究.结果表明,复合物导电剂提高了LiCoO2电极的电化学性能.MWCNTs/FNG质量比为5的复合物(FNGMWCNTs)作导电剂,LiCoO2电极的0.2C首次放电容量约为154.2mAh/g.和单纯的MWCNTs作导电剂相比,FNGMWCNTs作导电剂,LiCoO2电极有好的倍率放电性能,在3C倍率放电电压更高,放电比容量更高.原因可能如下:首先,MWCNTs、FNG和LiCoO2颗粒三者实现了均匀的分散;其次,MWCNTs把多个孤立的FNG联系起来,形成了更为有效的导电通道.     

超声频率对碳纳米管结构及其负载PtRu催化剂催化活性的影响

在浓硝酸和浓硫酸混合液中,采用频率分别为25、40、60和80kHz的超声波对碳纳米管(CNTs)进行官能团化处理,运用X射线衍射(XRD)、傅立叶红外(FT-IR)、热重分析(TG)等手段,考察了超声处理对碳纳米管晶相结构、表面基团、含氧基团含量的影响.以不同超声频率处理的碳纳米管作为载体,制备了一系列碳纳米管负载PtRu催化剂,并用X射线衍射技术对催化剂的晶体结构进行了表征.采用循环伏安法(CV)测试了催化剂对甲醇电氧化反应的催化活性.结果表明,采用超声频率为60Hz处理的碳纳米管具有较高的含氧基团含量,用其作为载体制备的PtRu/CNTs60催化剂具有最佳的甲醇电氧化催化活性.     

不同官能化碳纳米管对MWCNTs-碳纤维/环氧树脂复合材料力学性能的影响

为研究加入不同官能化碳纳米管对环氧树脂力学性能的影响,通过对羧基化多壁碳纳米管(MWCNTsCOOH)进行化学处理,得到表面接枝乙二胺的碳纳米管(MWCNTs-EDA)。分别将MWCNTs-COOH和MWCNTs-EDA分散在环氧树脂中,通过热熔法制备环氧树脂中含有碳纳米管的T700碳纤维预浸料,并热压成准各向同性复合材料层合板。结果表明:MWCNTs-EDA在环氧树脂中的分散性优于MWCNTs-COOH,MWCNTsEDA本身具有固化反应活性,加入后对基体的交联密度影响较小。与MWCNTs-COOH相比,MWCNTs-EDA可以有效改善环氧树脂及碳纤维/环氧树脂复合材料的力学性能。当MWCNTs-EDA含量为1.0wt%时,MWCNTs-碳纤维/环氧树脂准各向同性复合材料层合板的压缩性能、弯曲性能和冲击后压缩强度分别提高了14.7%、40.9%和20.6%。     

碳纳米管磁化氢等离子体薄膜的微波吸收特性

为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3～30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合.     

Comparative electrochemistry of haemoglobin on the long and ball milling shortened carbon nanotubes

Short multi-walled carbon nanotubes (S-MWCNTs) were obtained by ball milling method and employed as a supporting matrix to explore a novel immobilisation and biosensing platform of redox proteins such as haemoglobin (Hb). Compared to long MWCNTs, the shortened MWCNTs-based biosensor did not show better electrocatalytic activity, which was contrary to previous theoretical expectations. The electron transfer rate constants of Hb on long and short MWCNTs modified electrodes in phosphate buffer solution were 1.08 and 0.95?s^?1, respectively. The lower electron transfer rate between haemoglobin and the electrode can be attributed to their larger resistive properties, which were confirmed by cyclic voltammetry and AC impedance.     

Fabrication of a room temperature hydrogen sensor based on thin film of single-walled carbon nanotubes doped with palladium nanoparticles

A new sensor for the detection of hydrogen at parts per million (ppm) levels was fabricated by coating a thin film of palladium-doped activated single-walled carbon nanotube on the inner wall of a glass tube. The response of the sensor was based on the changes in the impedance of the sensor upon the adsorption of hydrogen molecules. The linear dynamic range of the sensor was from 1 to 50?ppm. The relative standard deviation of six replicate analyses of 5?ppm of H₂ was 2.1% and the limit of detection was 0.73?ppm for H₂ species. Humidity, methane and hydrogen sulphide did not have any serious effect on hydrogen recognition. Also, no interfering effect was observed when 20-fold excess (mass/mass) of carbon dioxide or carbon monoxide was present with hydrogen.     

高分散度非晶态NiB／CNTs催化剂制备及其催化加氢性能

利用苯胺、曲拉通分别对氨气热处理的碳纳米管进一步功能化，修饰碳纳米管表面，促进碳纳米管分散。采用超声波辅助的浸渍-化学还原法制备非晶态NiB／CNTs合金催化剂，平均粒径为14nm、10nm的非晶态NiB颗粒均匀分布在苯胺、曲拉通处理的碳纳米管表面。苯胺、曲拉通功能化处理使催化剂的Ni负载量分别提高了10．4％、14．6％，同时提高了催化剂的乙炔加氢活性和乙烯选择性。将苯胺和曲拉通的处理效果比较，发现无论是NiB颗粒的分散度还是催化剂的加氢性能，曲拉通处理的效果明显优于苯胺。     

载气在CVD法制备纳米碳管工艺中的作用

纳米碳管是性能优异的具有准一维特征的纳米材料,CVD法是制备纳米碳管的典型工艺之一。本文以乙炔气体为原料气体、循环失效后的贮氢电极舍金材料作为反应催化剂,研究了在相同反应条件下,CVD法制备纳米碳管过程中载气对纳米碳管形貌和产率的影响。通过对产物TEM观察和TG分析发现,虽然载气不直接参与合成反应但对产物产率和形貌有很大的影响,氢气作为载气可以获得形貌和热稳定性更好的纳米碳管。     

载气种类对单壁碳纳米管管径的影响研究

单壁碳纳米管的管径对其性能、特别是储氢性能有极其重要的影响,但至今未见制备过程中系统控制单壁碳纳米管管径的报道.本文分别以氦气、氮气和氩气为载气,采用催化裂解法制备了不同直径范围的单壁碳纳米管.HRTEM和Raman光谱分析表明,以氦气、氩气为载气制得的碳管直径分布范围相对较窄,平均直径分别约为1.6和5.0nm.以氮气为载气时碳管直径分布相对较宽,约为2.0～4.5nm.氮气与碳反应生成氮化碳可能是导致单壁碳纳米管直径分布相对较宽的主要原因.分别以氦气、氮气和氩气为载气制得的单壁碳纳米管,在273K,15MPa时质量储氢分数依次为4.21%、6.30%和8.05%.     

DBSA二次掺杂聚苯胺接枝多壁碳纳米管复合材料的结构与性能研究

多壁碳纳米管(MWNTs)经对苯二胺功能化后,通过原位聚合及去掺杂和二次掺杂反应,首次制备了能在N_甲基吡咯烷酮(NMP)中稳定溶解的十二烷基苯磺酸(DBSA)二次掺杂聚苯胺接枝MWNTs(PANI-g-MWNTs)复合材料.研究表明:复合材料中PANI与p-MWNTs通过酰胺键连接,形成以p-MWNTs为核、DBSA 二次掺杂PANI为壳的纳米复合结构;当复合材料溶解在NMP中时,借助DBSA二次掺杂PANI的溶解性和p-MWNTs与PANI间的连接作用,使其在NMP中获得35.56mg/mL的溶解度和近1个月的稳定性;该复合材料的热稳定性在300～500℃明显提高,其室温电导率较DBSA二次掺杂PANI提高近两个数量级.     

氟化多壁碳纳米管作正极对锂/氟电池性能的影响

通过对多壁碳纳米管(MWCNTs)进行氟化改性,获得氟碳原子比分别为0.28(CF0.28),0.56(CF0.56),0.78(CF0.78)的氟化多壁碳纳米管。将氟化多壁碳纳米管作正极活性物质涂覆于铝箔,金属锂片为对极,组装成锂/氟化多壁碳纳米管(Li/CFx)一次纽扣电池。采用热重分析(TGA)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、X射线光电子能谱分析(XPS)进行结构和性能表征,通过恒流放电检测电池的电化学性能。结果表明:活性物质为CF0.78的正极电极的电化学性能最佳,在电流密度为39mA/g时放电比容量达724mAh/g,同时出现了稳定的放电平台。在0.05C放电倍率时,3种电极的活性物质利用率分别达到73.4%,89.6%,92.9%。相比0.05C,2C放电倍率下的放电比容量衰减率分别为68.8%,34.1%,39.6%,表明提高氟化程度,能够降低放电比容量衰减率,虽CF0.78相对CF0.56的放电化容量衰减率有所上升,但在相同放电倍率时,其放电曲线稳定性是最好的。     

MWCNTs/多孔ZnO纳米材料的制备及室温NO气敏性研究

为开发室温气敏传感器材料,以Zn(NO3)2.6H2O为锌源、尿素为沉淀剂,在制备水合碱式碳酸锌(Zn4CO3(OH)6.H2O)的过程中加入羧基化的MWCNTs(MWCNT-COOH),焙烧制备了MWCNTs/ZnO复合材料.采用XRD,SEM和TEM等对其进行了分析.结果表明:复合材料中MWCNTs分散均匀,ZnO呈多孔纳米片状,纳米片由多个尺寸在10～20 nm的ZnO颗粒组成;在室温、空气湿度为50%的氛围中测试复合材料对NO的气敏响应发现,复合材料对体积浓度1×10-4的NO气敏响应灵敏度大约是MWCNT-COOH的3倍,明显高于MWCNT-COOH;对比加入不同量MWCNT-COOH制备的3种复合材料对NO的气敏性可知,加入200 mg MWCNT-COOH所制备的复合材料对低浓度(体积浓度≤50×10-6)的NO气体表现出较高的灵敏度.     

气体种类对CVD法制备碳纳米管的影响研究

以甲烷(CH4)和丙烷(C3H6)为碳源气,以纳米级NiO/SiO2气凝胶为催化剂,采用化学气相沉积法(CVD),在合适的工艺条件下,制备出碳纳米管.通过XRD、TEM、BET吸附等手段对制得的碳纳米管进行了表征,考察气体种类对碳纳米管的影响.结果表明:采用两种碳源气制备的碳纳米管,其形貌和结构均有所不同.由CH4制备的碳纳米管长径比大,管壁光滑,形貌规整;而由C3H6制备的碳纳米管,产物中有少量无定形物,且管壁不光滑,有折点出现.