High yield synthesis of multi-walled carbon nanotubed from CaCO3 supported iron (III) nitrate catalyst

VIETNAM NATIONAL UNIVERSITY HANOI COLLEGE OF TECHNOLOGY Nguyen Duc Dung HIGH YIELD SYNTHESIS OF MULTI-WALLED CARBON NANOTUBES FROM CaCO3 SUPPORTED IRON (III) NITRATE CATALYST MASTER THESIS Hanoi - 2006 VIETNAM NATIONAL UNIVERSITY HANOI COLLEGE OF TECHNOLOGY Nguyen Duc Dung HIGH YIELD SYNTHESIS OF MULTI-WALLED CARBON NANOTUBES FROM CaCO3 SUPPORTED IRON (III) NITRATE CATALYST Speciality: Nano Materials and Devices MASTER THESIS Advisor: Dr Phan Ngoc Minh Hanoi - 2006 Content Abbreviations Preface and target of the work Chapter Introduction to carbon nanotubes material 1.1 Brief history of carbon canotubes 1.2 Geometry of carbon nanotubes 1.3 Syntheses of carbon canotubes 13 1.3.1 Arc discharge 13 1.3.2 Laser ablation 14 1.3.3 Chemical vapor deposition 15 1.4 Growth mechanism of carbon nanotubes 19 1.5 Purification 20 1.5.1 Oxidization 21 1.5.2 Acid treatment 21 1.5.3 Micro filtration 21 1.6 Physical properties 22 1.6.1 Electronic properties 22 1.6.2 Mechanical properties 25 1.7 Application of carbon nanotubes 27 1.7.1 Energy storage 27 1.7.2 Composite materials 29 Chapter Experimental and investigation methods 31 2.1 Experimental 31 2.1.1 Description of the CVD system for growing carbon nanotubes 31 2.1.2 Synthesis of carbon nanotubes 31 2.2 Investigation methods 35 2.2.1 Electron microscope 35 2.2.2 Raman spectroscopy of carbon nanotubes 38 2.2.3 Xray diffraction of carbon nanotubes 41 2.2.4 Thermogravimetric analysis 42 Chapter Results and discussion 43 3.1 Catalytic Fe nanoparticles in the CNTs growth process 43 3.1.1 Effect of supported iron salts on the CVD products 43 3.1.2 Formation of catalytic Fe nanoparticles nucleating CNTs 47 3.2 Effect of growth temperature 53 3.2.1 CNTs perfomance 53 3.2.2 Structural characteristics of CNTs 54 3.3 Optimal procedure for large-scale synthesis of MWCNTs 59 Conclusion 62 References 63 Abbreviations CCVD Catalytic Chemical Vapor Deposition CFs Carbon Fibers CNTs Carbon Nanotubes CVD Chemical Vapor Deposition DrTGA Differential Thermo-Gravimetric Ananlysis ECDL Electro-Chemical Double Layer EDX Energy Dispersive X-ray spectroscopy FTIR Fourier Transform Infrared HRTEM High Resolution Transmission Electron microscope MWCNTs Multi-Walled Carbon Nanotubes PECVD Plasma Enhanced Chemical Vapor Deposition SCCM Standard Cubic Centimeters per Minute SEM Scanning Electron Microscope STEM Scanning Transmission Electron Microscope STM Scanning Tunneling Microscope SWCNTs Single-Walled Carbon Nanotubes TEM Transmission Electron microscope TGA Thermo-Gravimetric Analysis XRD X-Ray Diffraction Preface and target of the work Carbon nanotubes were identified for the first time in 1991 by Sumio Iijima at the NEC Research Laboratory By using high resolution transmission electron microscope (HRTEM) he clearly observed the tiny tubes called multi-walled carbon nanotubes (MWCNTs) in the soot made from by-product obtained in the synthesis of fullerenes The MWCNTs comprise carbon atoms arranged in a graphitic structure rolled up to form concentric cylinders [38] Two years later, single-walled carbon nanotubes (SWCNTs) were synthesized by adding metal particles to the carbon electrodes [9, 36] Their small diameter (of the order of a nanometer) and their long length (of the order of microns) lead to aspect ratios so large that the carbon nanotubes possibly reach to ideal one-dimensional (1D) systems Depending on the chirality of their atomic structure, they can be excellent metals or semiconductors with a band gap that is inversely proportional to their diameter Theoretical and experimental results have shown extremely high elastic modulus, greater than TPa and strengths 10100 times higher than strongest steel [77] In addition to exceptional mechanical properties, they also possess superior thermal properties: thermally stable up to 2800oC in vacuum, thermal conductivity about twice as high as diamond [16] The above properties make carbon nanotubes (CNTs) the object of widespread studies in both basic science and technology They can be applied in many fields: fabrication of nano sized electronic devices, energy storage equipments, field emission display, nano probes, nano composites, There are many methods (mentioned in detail in section 1.3) for synthesizing carbon nanotubes having different performance from diverse material sources The arc discharge method relates to connecting two graphite rods to a power supply, placing them millimeters apart, and vaporizing carbon by a hot plasma Its product can be SWCNTs and MWCNTs with few structural defects Tubes tend to be short with random sizes and directions This method can produce large scale production of CNTs but its typical yield of about 30% is not high Laser ablation method was firstly used in 1996 by Smalley at al using intense laser pulses blasting graphite to form primarily SWCNTs The diameters of SWCNTs can be controlled in a large range by varying the reaction temperature Although the yield of laser ablation method can reach to 70%, it has never been candidate for large-scale production because of requiring expensive lasers and the limitation of a laser spot area Emerging as the best method for industrial production of CNTs is chemical vapor deposition (CVD) Carbon feedstocks are hydrocarbons in gaseous and liquid phases, alcohol, etc., decomposed at 600-1200oC into carbon atoms recombining to nanotubes over metal nanoparticles Carbon nanotubes produced by CVD having the yield probably up to 100% are usually long MWCNTs with quite high defects Thus, the investigation of suitable technologies to synthesize large-scale production of carbon nanotubes with high yield and purity to reduce cost satisfying for industrial demands is an opening solution until now The most common and optimal method for large-scale production of CNTs is catalytic chemical vapor deposition (CCVD) (discussed in section 1.3.3) In the CCVD process, catalyst supports are the essential ingredients such as, MgO, Al2O3, SiO2, CaCO3 etc., due to their high surface area for CCVD reaction The choice of CaCO3 as catalyst support was reported in Ref [18] The advantages of this technique are:  CaCO3 support is easily dissolved in a dilute acid, thus the CNTs purification is a one-step procedure, simple and harmless to CNTs structure  CaCO3 and Fe salts from which catalysts synthesized are available in market and low cost  This is the simplest CVD method for large scale production of CNTs By supplying catalysts and collecting CVD product continuously, the production yield is significantly increased With the aim of large scale and low cost production and the idea using CaCO3 support, this thesis investigates the technological aspects that relate to synthesis of carbon nanotubes We develop a simple method for making catalyst only by grinding CaCO3 and Fe salts, therefore, neglect the impregnating and drying steps, that reduce stages in CNTs synthesis The addition of H2 gas in CVD process is believed not only to form Fe nanoparticles enhancing catalytic activity but also to improve the CNTs yield By varying growth temperature, another role of CaCO3 as the factor contributing to the formation of Fe nanoparticles necessary to the CNTs growth is studied in this thesis Furthermore, Fe salt radicals are found significant to the creation of Fe nanoparticles on the support (CaCO3 or CaO) At last, the more dilute acid (HCl 10%) is used for purification process The arrangement of the thesis: In addition to the “Preface and target of the work” and “Conclusion” parts the thesis is organized into three chapters as follow: Chapter shows an overview of carbon nanotubes material, the CNTs synthesizing methods and ability in industrial applications Chapter lists the experimental process for synthesis of carbon nanotubes This chapter also introduces investigation methods mainly used during this thesis Chapter indicates the effect of Fe content in catalysts The formation of Fe nanoparticles necessary to CNTs growth is studied The structural characteristics of the CNTs depend on the growth temperature are characterized The optimal chemical vapor deposition process is established for the aim of large-scale production of carbon nanotubes It is confirmed that by using the presented technique we can produce 97.9 % purity, 78.6 % yield CNTs with mass of 50 grams/day Chapter Introduction to carbon nanotubes material 1.1 Brief history of carbon nanotubes In 1970‟s and 1980‟s, small diameter carbon filaments were produced through the synthesis of carbon fibers by the decomposition of hydrocarbons at high temperature in the presence of transition metal catalyst nanoparticles [57, 78] However, there was not any detailed systematic study on such small filaments until the observation of carbon nanotubes by Iijima in 1991 [38] These tubes (called multiwall carbon nanotubes) contained at least two layers, often many more, and ranged in outer diameter from about nm to 30 nm with both closed ends A new class of carbon nanotubes with only single layer was discovered in 1993 [9, 36] These single-walled nanotubes with diameters typically in the range 12 nm are generally narrower than the multiwalled nanotubes, and tend to be curved rather than straight Since these pioneering works, the study of carbon nanotubes has developed rapidly Fig 1.1: Multi-walled CNTs observed in 1991 [38] 1.2 Geometry of carbon nanotubes The structure of carbon nanotubes has been characterized by High Resolution Transmission Electron Microscope (HRTEM) and Scanning Tunneling Microscope (STM) These techniques directly confirmed that the carbon nanotubes are cylinders derived from the honeycomb lattice representing a single atomic layer of crystalline graphite (a graphen sheet) Most important structures are single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) A SWCNT is considered as a cylinder with only one wrapped graphene sheet Multi walled carbon nanotubes (MWCNTs) are similar to a set of concentric SWNTs The structure of a single walled carbon nanotube is explained in terms of its 1D unit cell, defined by the vectors Ch and T in Fig 1.2a [20] The circumference of any carbon nanotube is expressed in terms of the chiral vector Ch = nâ1 + mâ2 which connects two crystallographically equivalent sites on a 2D graphene sheet (see Fig 1.2a) The construction in Fig 1.2a depends uniquely on the pair of integers (n, m) which specify the chiral vector Fig 1.2a shows the chiral angle θ between the chiral vector and the “zigzag” direction (θ = 0) and the unit vectors â1 and â2 of the hexagonal honeycomb lattice of the graphene sheet Three distinct types of carbon nanotube structures can be generated by rolling up the graphene sheet into a cylinder as discribe below and shown in Fig 1.3 The zigzag and armchair nanotubes, respectively, correspond to chiral angles of θ = and 30o, and chiral nanotubes correspond to < θ < 30o The intersection of the  vector OB (which is normal to Ch) with the first lattice point determines the fundamental one dimension (1D) translation vector T The unit cell of the 1D lattice is the rectangle defined by the vectors Ch and T (Fig 1.2a) ... NATIONAL UNIVERSITY HANOI COLLEGE OF TECHNOLOGY Nguyen Duc Dung HIGH YIELD SYNTHESIS OF MULTI-WALLED CARBON NANOTUBES FROM CaCO3 SUPPORTED IRON (III) NITRATE CATALYST Speciality: Nano Materials... Abbreviations Preface and target of the work Chapter Introduction to carbon nanotubes material 1.1 Brief history of carbon canotubes 1.2 Geometry of carbon nanotubes 1.3 Syntheses of carbon canotubes 13 1.3.1... filaments were produced through the synthesis of carbon fibers by the decomposition of hydrocarbons at high temperature in the presence of transition metal catalyst nanoparticles [57, 78] However,