Ni-Mo双金属氧化物催化剂CVD法大量制备成束多壁纳米碳管

采用溶胶凝胶法合成的Ni-Mo双金属氧化物催化剂,用CVD法催化裂解甲烷从而大量制备高质量高纯度的成束多壁纳米碳管.实验结果表明,该催化剂具有很高的活性和催化效率.反应2 h后,制备的多壁纳米碳管的量可达到初始催化剂量的80倍以上.碳管的直径较均匀,在10～20 nm之间.随着反应时间的延长,制备的纳米碳管石墨化程度增加,反应1 h后,粗产品中纳米碳管的含量就超过了97％. 简单放大后,单炉每克催化剂可以在0.5 h内制得40 g以上多壁纳米碳管.     

催化剂载体对CVD法制备碳纳米管的影响

用DTA、TEM和XRD方法研究了碳氢化合物催化裂解制备碳纳米管(CNTs)反应中催化剂载体的影响。实验结果表明:当以金属Co作为活性组分时,对于催化剂Co/Al₂O₃,在最佳反应温度(650℃)条件下,碳纳米管粗产品的产率为457g/100g·cat,明显高于以Co/SiO₂作载体时的产率131g/100g·cat,且碳纳米管直径小,直径分布范围窄(10nm～20nm)。但在空气气氛中的DTA结果表明,在催化剂Co/SiO₂上生成的碳纳米管的抗氧化能力较在催化剂Co/Al₂O₃上生成的碳纳米管强。通过TEM和XRD方法进一步研究发现:反应过程中,催化剂Co/Al₂O₃中的Co微晶粒度随反应温度升高(从650℃到750℃)而增大(从15.8nm到16.7nm)的速率小于催化剂Co/SiO₂中的Co微晶粒度随反应温度升高而增大(从11.0nm到13.4nm)的速率;相应地,在催化剂Co/Al₂O₃上生成的碳纳米管的(外)直径随反应温度升高而增大的速率(从10～20nm到20～25nm)亦小于在催化剂Co/SiO₂上生成的碳纳米管的(外)直径随反应温度升高而增大的速率(从10～30nm到30～50nm)。     

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).     

载气对注入CVD法制备碳纳米管和碳纳米纤维的影响

采用注入化学蒸气沉积法,在石英管壁上制备得到了定向的多壁纳米碳管和纳米碳纤维.在相同的反应体系中,采用不同的载气,得到的碳材料的形态有较大不同.经SEM, TEM及Raman等证实,采用氩气和氮气作为载气时,得到了内部填充铁的碳纳米纤维,而且具有较好的类石墨晶体结构;用氢气作为载气时得到了中空的碳纳米管.通过控制氢气和惰性气体的比例,改变了碳纳米管的直径分布.     

高Co含量的Co-Mo系列催化剂甲烷裂解制备单壁纳米碳管

制备了高Co含量的Co-Mo／γ-A12O3系列催化剂，发现此类催化剂可以在温和的反应温度下制备高质量的单壁纳米碳管．讨论了Mo组分的作用．认为Mo分散、稳定金属颗粒，促进了SWNTs的生长．同时，Mo组分的升华决定了单壁纳米碳管的生长和管径分布．这为可控地制备单壁纳米碳管提供了依据．     

载气气氛对Co/MgMoO4催化剂CVD法高效合成碳纳米材料的影响

High yield and quality mutli-walled carbon nanotube (MWNT) bundles and carbon nanofibers were synthesized by catalytic decomposition of methane over Co/MgMoO₄ catalyst at 1 000 ℃. TEM studies showed that the products were mainly carbon nanofibers without carrier gas and were all MWNT bundles with hydrogen or nitrogen as carrier gas. Thermal gravimetric analyses (TGA) on the raw product indicated that the purity of MWNT was higher than 95wt%. The growth mechanism of carbon nanofibers and MWNTs was also discussed.     

基于纳米材料、聚电解质制备高性能乙醇生物传感器

以明胶包埋法作为乙醇氧化酶(AOX)的酶固定化方法,在比较多壁纳米碳管(MWCNTs)、纳米金、纳米氧化铁3种纳米材料的基础上,选择加入增效最明显的多壁纳米碳管提高灵敏度,在电极表面自组装聚丙烯胺盐酸盐/聚磺化乙烯硫酸盐(PAA/PVS)膜提高抗干扰性,制备出一种高灵敏度抗干扰性电流型乙醇生物传感器(Pt/(PAA/PVS)2PAA-MWCNTs/AOX)。本传感器灵敏度为1.04μA/(mmol/L),在2.5×10-5~2.5×10-3mol/L浓度范围内呈良好线性关系,线性方程为:I(μA)=0.2199 1.0400C(乙醇,mmol/L),r=0.9939;检出限为2.5×10-5mol/L;RSD<5%,稳定性好、抗干扰能力强。     

超声分散法制备Sn-Cd纳米微粒

用超声分散法制备了Sn-Cd纳米微粒,用XRD和TG/DTA研究了样品的晶型与结构,用TEM观察了样品的形貌,考察了超声功率对纳米颗粒粒径的影响,并在四球机上研究了样品的摩擦学性能.     

Ag作催化剂制备的GaN的形貌及其性能

用化学气相沉积法(CVD)在Si(100)衬底上以Ag纳米颗粒为催化剂制备了微纳米结构的GaN,原料是熔融态的金属Ga和气态的NH3。采用X射线衍射仪(XRD)、透射电镜(TEM)、X-ray能谱仪(EDS)、场发射扫描电子显微镜(SEM)、光致发光能谱(PL)和霍尔效应测试对样品进行了结构、成分、形貌和发光、电学性能分析。结果表明:生成的自组装GaN为六方纤锌矿的类似小梯子的微纳米单晶结构,且在不同的温度下,GaN的发光性能和电学性能也有所不同,相对于强的紫外发光峰,其它杂质发光峰很微弱,且均呈p型导电。对本实验所得到的GaN微纳米结构的可能形成机理进行了探讨。     

单壁碳纳米管短管的制备

分别通过控制CVD生长时间的方法和在混合的硝酸硫酸中超声氧化碳纳米管的化学剪裁法制备了单壁碳纳米管短管.两种方法都能将大多数碳纳米管的长度控制在500 nm以下.拉曼光谱结果表明: 在化学剪裁过程中,单壁碳纳米管部分被破坏产生无定形碳杂质;用控制CVD反应时间得到的单壁碳纳米管短管样品比长时间反应得到的长管样品杂质少,且不存在后处理时碳纳米管的破损问题,其纯度比化学剪裁法得到的产品纯度高.     

CVD synthesis of spiral carbon nanotubes over asymmetric catalytic particles

The influence of asymmetric catalytic particles prepared by various methods was investigated on the growth of spiral carbon nanotubes using the CVD method. Asymmetric particles were prepared by either milling or crystallization from oversaturated solution onto the surface of catalyst support or catalyst impregnation at pH 8–9. As-prepared catalysts were tested in the decomposition of acetylene. Carbon deposit, thus carbon nanotubes and spirals were observed by transmission electron microscopy the activity was characterized by carbon yield.     

纳米CaCO3负载过渡金属CVD法制备多壁碳纳米管的研究

以纳米碳酸钙粉体为载体,用浸渍法制备了可用于化学气相沉积(CVD)法制备碳纳米管的高产率催化剂.应用FESEM,HRTEM,TEM,XRD和激光拉曼谱对产物进行了表征.结果表明,由于纳米碳酸钙具有较大的比表面积,可高密度地承载催化剂活性组分.在碳纳米管生长初期,处于缓慢分解状态的纳米碳酸钙才能有效地起到载体作用,且反应温度为700～750℃时,碳纳米管的产率较高.Fe-Co双金属催化剂在700℃,催化生长60min后,可增重10倍,而且产物中无定形碳含量极少.纳米碳酸钙载体易于提纯,用质量分数为30%的硝酸超声提纯粗产品1h,可使纯度提高到97%,且不破坏碳纳米管结构.     

Electrical and Optical Studies of Hydrogen Bonded Ferroelectric Liquid Crystals Dispersed with MWCNT

Two hydrogen bonded ferroelectric liquid crystals (HBFLC) are dispersed with multi-walled carbon nanotubes (MWCNT) for achieving better thermal and electrical performance. Interesting feature of the present communication is the enhancement in the enthalpy value pertaining to isotropic-nematic transition in MWCNT doped liquid crystals compare to its pure counter parts. Dielectric relaxations studies are carried out in the pure and the MWCNT doped systems. It is observed that doping of MWCNT elevated the activation energies considerably. Optical shuttering action in one of the complex dispersed with MWCNT are discussed.     

Application of Thermogravimetry and Differential Thermal Analysis in Catalytic CVD Synthesis of Carbon Nanotubes

Multi-walled carbon nanotubes (MW-CNTs) were prepared by chemical vapor deposition (CVD) method with the decomposition of acetylene over Co/SiO2 catalyst. TG-DTA technique was used together with TEM and XRD to study the effect of reaction temperature on the composition, graphitized extent, and diameter distribution of the produced raw CNTs based on their oxidization resistance. During the decomposition, the micro-crystallite of the active constituent (Co/SiO2) were growing up as the reaction temperature rising. This in turn resulted in an increase of the diameter distribution range of produced MW-CNTs. The average diameter increased from 20~30 nm (650℃) to 30~50 nm (750℃). XRD results also showed the graphitized extent of MW-CNTs was enhanced meanwhile the spacing between the layers (d002) decreased from 3.45 (650℃) to 3.32 (850℃) with the reaction temperature raised. TG-DTA data showed that the exothermic peak of the amorphous carbon was below 380℃and its content would decrease as temperature increasing. In summary, for CVD production of CNTs using acetylene gas on Co/SiO2 catalyst, low temperature (about 650℃) favored producing thinner MW-CNTs with the diameter from 20 to 30 nm while higher temperature (about 850℃) is favored thicker MW-CNTs (diameter from 70 to 100 nm).     

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.     

CVD Growth of Carbon Nanotubes and Nanofibers: Big Length and Constant Diameter

Summary: We report mass production of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with relatively high length and aspect ratio. We synthesized carbon nanomaterials by chemical vapor deposition (CVD) of methane as the feeding gas on Fe/Mo nanoparticles that use alumina-aerogel support. Alumina-aerogel-supported Fe/Mo catalyst was prepared using sol-gel. Drying step performed using rotary evaporation and freeze-drying. CVD was performed using a quartz tube furnace. Samples were analyzed using scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Raman spectroscopy.     

Control of the Properties of Carbon Nanotubes Synthesized by CVD for Application in Electrochemical Biosensors

Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical properties open attractive possibilities in many application areas. These properties depend on the process conditions during synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors. Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source and Ni–Al₂O₃–SiO₂ as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass, temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been determined by analytical techniques. Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are the characterization techniques employed in this work.