Carbon nanotubes (CNTs) From preparation to applications Ali Ahmadpour Department of Chemical Engineering & Nanotechnology center Ferdowsi University of Mashhad
Contents Introduction CNT Properties Preparation methods Applications Conclusions 2
World of Carbon Materials Amorphous Graphite Diamond Fullerene Carbon nanotube 3
Fullerenes 1985 Robert F. Curl Jr. Richard E. Smalley Sir Harold W. Kroto In 1991 during the preparation of Fullerenes by Arc vaporization method, Iijima changed the current from AC to DC and CNTs was found. 4
Nanotubes Nanotubes are flat sheets of interlinked carbon atoms which are rolled into cylinders with a few nanometer diameter. Because tubes are hollow, gases can pass through as well as between them. So a mass of carbon nanotubes is rather like porous graphite. 5
CNT Structures Single wall (SWNT) Double-wall (DWNT) Multi-wall (MWNT) 6
Cont. Carbon nanotubes are considered to be the building blocks of future nanoscale electronic and mechanical devices. SWNT is seamless, with either open or capped ends. The diameter of is 0.7-2 nm (100,000 times thinner than a human hair). Length ~ microns Diameter ~ 1-30 nm Interlayer distance ~ 0.34nm 7
Structures of SWNTs 8
Different Indexed CNTs a) Armchair b) Zigzag c) Chiral C h = na 1 + ma 2 d t = C h / π n: Column m: Row
Cont. All the parameters governing the structure of a SWNT can be uniquely determined by knowing the n and m values. The nanotubes of type (n,n), are commonly called armchair nanotubes because of the \_/ \_/ shape, perpendicular to the tube axis, and have a symmetry along the axis with a short unit cell (0.25 nm) that can be repeated to make the entire section of a long nanotube. Another type of nanotube (n,0) is known as zigzag nanotube, because of the \/ \/ shape perpendicular to the axis and as well as the short unit cell (0.43 nm) along the axis. All the remaining nanotubes are known as chiral or helical nanotubes and have longer unit cell sizes along the tube axis. 10
Three distinct types of nanotube structures Schematic models for SWNTs with the nanotube axis normal to the chiral vector which, in turn, is along: (a) the θ = 30 direction [an armchair (n, n) nanotube], (b) the θ = 0 direction [a zigzag (n, 0) nanotube], and (c) a general θ direction, with 0 < θ < 30 [a chiral (n,m) nanotube]. 11
CNTs يك اليه گرافيت را در نظر بگيريد. اتمهايي را كه در يك رديف قرار گرفتهاند با ) n,m ( كه نشاندهندة مختصات يك نقطه در صفحه است مكانيابي ميكنيم. به طوري كه مختصات n مربوط به ستون اتمها و مختصات m مربوط به رديف اتمها باشد. يك نانولوله مانند صفحة گرافيتي است كه به شكل لوله درآمده باشد. بسته به اينكه چگونه دو سر صفحه گرافيتي به يكديگر متصل شده باشند انواع مختلفي از نانولوله ها را خواهيم داشت. 12
Structural parameters for CNTs 13
Structure of different types of carbon nanotubes (a) (2, 2), (b) (10, 10), (c) (5, 0), and (d) (5, 2). 14
Chirality CNTs could be either semiconducting or metallic depending on their geometrical characteristics, namely their diameter and the orientation of their hexagons with respect to the nanotube axis (chiral angle). CNT exhibits extraordinary mechanical properties: Young s modulus over 1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa. 15
Properties Electrical Electrical conductivity (metallic) Semi-conductivity Mechanical The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network. High tensile strength (Young modulus) Strength to weight ratio 500 times > Al; similar improvements over steel and titanium; 10 times more than graphite/ epoxy. Maximum strain 10-30% higher than any material. Low weight High flexibility 16
Cont. Thermal High thermal conductivity ~ 3000 W/m.K in the axial direction with small values in the radial direction. Chemical reactivity Chemical reactivity of a CNT is comparable with a graphene sheet, enhanced as a direct result of the curvature of the CNT surface. Small nanotube diameter results in increased reactivity. Optical activity Optical activity of chiral nanotubes disappears if the nanotubes become larger. 17
Cont.. Storage Gas storage (hydrogen, methane, ) Gas separation Waste water treatment, air pollution control Energy storage 18
Cont... Flexibility 19
Preparation Processes Electric Arc-Discharge o o High current are passed through 2 opposing graphite electrodes in an inert atmosphere (He). Carbon atoms evaporate from the anode (3000 C) and grow on the cathode. Product: Mainly MWNTs [SWNTs by using electrode impregnated with metals (Co, Ni, Fe, )] Laser Ablation (Vaporization) o o An intense laser pulse ablate a carbon target containing metals. Target is heated in a furnace (1200 C) and inert atmosphere. Product: Mainly ropes of SWNTs Chemical Vapor Deposition (CVD) o o o Thermal decomposition (500-1000 C) of hydrocarbons (CH 4 ) in the presence of a catalyst containing transition metals (Fe, Mo, ). Product: SWNTs and MWNTs Large-scale production of nanotubes 20
Cont. High-pressure CO conversion (HiPCO) Plasma CVD Microwave CVD Electrochemical 21
Iijima DC( amorphous( CNTS( 22
CNT Fabrication Carbon Arc or Arc Discharge 23
Inert tube Quartz tube Target Argon flow Laser beam Witness plates 1473 K. 24
CNT Fabrication Laser Ablation or Pulsed Laser Vaporization (PLV) 25
PLV ( b arc-discharge ( a SWNT TEM 26
Quartz tube Gas inlet Quartz boat Oven 720 Gas outlet Sample 27
CNT Fabrication Chemical Vapor Deposition (CVD) 28
CO Cooling water Furnace Cold CO + Fe (CO)5 Hot co 200-1-10 SWNT Fe(CO) 5 CO 800 Fe(CO) 5 29
CNT Fabrication High-pressure CO conversion (HiPCO) Method is similar to CVD Carbon source is carbon monoxide Catalytic particles are generated in-situ Thermal decomposition of iron pentacarbonyl in a reactor heated to 800-1200 C High pressure to speed up the growth (~10 atm) Bulk production of SWNTs 30
Growth mechanism 31
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SWNT bundle 33
Cont. 34
Applications Diodes and transistors for computing CNT quantum wire interconnects Capacitors Data Storage Field emitters for instrumentation Flat panel displays Oscillators CNT based microscopy: AFM, STM Nanotube sensors: force, pressure, chemical Biosensors 35
Molecular gears, motors, actuators Batteries, Fuel Cells: H 2, Li storage Nanoscale reactors, ion channels Biomedical Lab on a chip Drug delivery DNA sequencing Cont. Artificial muscles, bone replacement, bionic eye, ear... coatings for prosthetics and surgical implants 36
Cont.. Gene therapy Nano-pipet Nano-capsule Nano-tweezer Use in composite materials Oil absorbent Catalyst support CNT ceramics CNT based plastic packaging Co Fe Ni Fe/Ni Ni/Co Si wafer Catalyst Layers W Ti Ta Ir Cr 37
Light elements 38
Nanocomposites 39
CNT based Sensor Gas molecules Pt contact Pt contact Nanotube s Sio2 + + + + + + + + + + MWNT based chemical sensor 40
Gas Sensors Gas detection instruments are increasingly needed for industrial health and safety, environmental monitoring (detection of NO 2 and CO) and process control. The worldwide revenue of the gas sensors will exceed $2.5B by 2010. 41
Biosensors CNT, though inert, can be functionalized at the tip with a probe molecule to be used as a sensor for food industry, medical and research purposes. Schematic diagram of the CNT array biosensor 42
Hydrogen storage 43
Hydrogen storage with electrochemical charge-discharge cycles CNT H 2 O xe (CNT charge xh ) xoh 44
Fuel cells 45
SWCNTs in H 2 fuel cells 46
AFM with CNT tip 47
CNT Applications in Food industries Functionalized CNT: When CNT is attached by organic functional groups, it can be dissolved into solution. This will increase processability of CNT for device fabrication. Polymer-CNT Gas Sensor: vapor/gas sensor based on carbon nanotube and polymer nanocomposites. Biosensors: Novel applications which makes possible the reversibility of some redox-enzymes reactions, which are irreversible at common electrodes. 48
Cont. Biological application: For protein crystallization and bioreactors. Membrane synthesis using CNTs: For detection and separation of enzymes, antibodies, proteins, vitamins, minerals, and DNA. Conductive membrane: More separation of aromas and nutritious from food substances. 49
CNTs Find New Applications as Heat Sensors for Hot Chilli Peppers HPLC, which is currently used, requires bulky, expensive equipment and detailed analysis of the capsaicinoids. In the new method, the capsaicinoids are adsorbed onto MWCNT electrodes. The current change is measured as the capsaicinoids are oxidised by an electrochemical reaction, and this reading can be translated into Scoville units. The technique is called adsorptive stripping voltammetry (ASV), and is a relatively simple electrochemical method. 50
Environmental applications of CNTs CNTs are just the thing for cleaning up poisonous pollutants. These tiny tubes mop up dioxins, the hazardous and persistent by-products of a wide range of industrial processes that contaminate the air, soil, water and, thence, the food chain. CNTs attract much more dioxin than activated carbon, currently used to clean up incinerator gases. 51
Purification of air and water Another environmental catalysis includes photocatalysis for air and water purification and for heavy metal removal. The Base is CNT and active material is nanostructured TiO 2. Environmentally toxic materials such as volatile organic compounds and heavy metal compounds become harmless by oxidation or reduction processes. 52
Ethanol production inside CNTs CNTs are increasingly recognized as promising materials for catalysis, catalyst additives or supports. Researchers in China used CNTs loaded with rhodium (Rh) nanoparticles as reactors to convert a gas mixture of CO and H 2 into ethanol (nanosized CNT reaction vessel). 53
CNT Market Global CNT production capacity is ~ 2.5 tons per day. Bayer is planning to produce about 3,000 tons CNTs by 2012. The price of MWCNTs has fallen from tens of thousands of dollars in just few years ago to hundreds of dollars per kg. Recent market analyses forecast sales of all nanotubes to reach 1-2 billion dollars annually within the next four to seven years. In terms of dollar value, electronics devices will be the largest end-use category, although composite materials may account for greater volumes. These volumes are expected to approach several thousand metric tons per year. 54
Conclusions CNTs have attracted much attention due to their remarkable properties. These materials will have a significant contribution to the new science fields. Complete experimental characterization of CNTs is not an easy task, as there are several parameters affecting the type and structure of CNTs. Theoretical methods of characterization is necessary to have better control over the CNT preparation step. Future advancement of nanotube science and technology requires much research works. 55