CARBON NANO TUBES (CNTs) Definition: When number of graphite sheets are rolled like a cylinder is called CNT.

Structure: In CNT, all the carbon atoms are covalently bonded (tetrahedral). But, the sheet lattices of graphite are held by Vanderwalls forces.

Two types of CNT: Single walled (SWCNT) If a nanotube has a single cylinder of graphite sheet, it is called SWCNT. diameter is 1-2 nm and length is 0.2-100 µm.

Types of SWCT a) arm chair form b) Zigzag model c) Chiral model

Explanation Zig-Zag = Rolling of graphene sheet in vertical direction w.r.t. tube axis Arm chair = Rolling of graphene sheet in horizotal direction direction w.r.t. tube axis Chiral = Rolling of graphene sheet in diagonal

Properties of CNT:   CNT possess only very few defects in the structure which is the main reason for their desirable and enhanced qualities. 1. Mechanical property:    Flexibility is measured by Young’s modulus. CNT Young’s modulus is 5-10 times greater than that of steel. Tensile strength of CNTs are 50 -100 times stronger than steel 

2. Electrical property: This depends on diameter, number of walls and chirality of the nanomaterial.

3. Density CNT have density of 1.33 – 1.44 g.cm-3 while Al has 2.7g.cm-3. It means that CNTs have density ½ to that of Al

4. Thermal property: 10 times greater than steel. 5. Kinetic property: In MWCNT, during movement, there will be no friction between inner and outer walls. This is due to the graphite structure.

6. Vibrational property: a) A1g mode: This is symmetrical mode. The vibration is uniform throughout the inner plane and outer plane. A1g

b). E2g mode: This is asymmetrical mode b) E2g mode: This is asymmetrical mode. As the vibrations are competing in and out, they are lying between elliptical and spherical shape. E2g

Differences b/w molecules, nanomaterials and bulk materials

Synthesis of nanomaterials Chemical Vapour Deposition (CVD) Gas Phase Method Liquid Phase Methods Solid Phase Methods Thermolysis Chemical Precipitation Hydrothermal synthesis Solvothermal synthesis Electrodeposition Laser Ablation Chemical Vapour Deposition (CVD)

SYNTHESIS OF NANO PARTICLES: Bottom up method – Soft method – Chemical method – Small to big method: This method involves building up of materials from the bottom, by atom by atom, molecule by molecule or cluster by cluster. There are five important techniques under this method. No Type Example 1 Precipitation BaSO4 Nano particles, Mo Nano partilces 2 Thermolysis Li Nano clusters 3 Hydro thermal method Iron oxide Nano particles 4 Solvo thermal method ZnO, ZrO2 nano clusters 5 Vapour Liquid Solid (VSL) technique Si nano wire

Eg Precipitation by Displacement reaction: 1) BaSO4 nano particle production In presence of Sodium hexa meta phosphate (stabilizing agent), Ba(NO3)2 + Na2SO4  BaSO4 + 2 NaNO3 Barium nitrate (Nano precipitate)

Eg 2) Precipitation by reduction reaction: Mo Nano particle production   MoCl3 + 3 Na B Et3 H  Mo (Nano) + 3 NaCl + 3 B Et3 + 1.5 H2 (Tri ethoxy boron hydride) reducing agent

Thermolysis At High temperature and in the presence of stabilising agents, metal precursors are decomposed to form nanomaterials. This is known as thermolysis.

Requirements vacuum chamber Precursor inert gas (Ar / He) Temperature cold finger scrapper

Lithium azide (LiN3) at 370oC, decomposes to N2 and Li. 2LiN3  2 Li + 3 N2

Hydrothermal synthesis [OR] Thermal Hydrolysis Requirements: auto clave temperature - 300 – 400 oC pressure - 1 atm Advantages: Easy to control the size and shape. Disadvantages: Expensive autoclaves – safety problems – could not monitor the reaction.

elementary nano product is known as seed The precursor is known as nutrient.

Example: nano Iron oxide production 2000C FeCl3 + 3 H2O  Fe (OH)3 + 3 HCl Fe(OH)3 + Ethanol + Ethylene oxide  α Fe2O3 (50 nm)

Vapour Liquid Solid Technique (VLS technique)

Example: Synthesis of silicon nano wire Requirements furnace silicon substrate Gold nanoparticles as catalyst Silane ( SiH4 )

Solvothermal analysis Requirements non aqueous solution like Xylene, Ethylene diamine, Cyclo hexane, propanol high temperature ( 100 – 1000 oC) higher pressure. ( 1- 10000 atm).

S.No Content Nano ZnO production Nano ZrO2 production 1 Precursor Zinc acetate di hydrate Zirconium oxy chloride 2 Solvent Propanol Hexane 3 Stabilising agent Sodium Hydroxide Ammonium hydroxide 4 Capping agent ( to stop the growth) Do decane thiol

Top down methods(or) Physical / hard / big to small methods It involves conversion of larger particles to small nano scale particles. No Method Example 1 Laser Ablation SWCNT 2 Chemical Vapour Deposition CNT 3 Carbon arc method 4 Electrodeposition Ni, Cu, Co Nano rods, nano wires, nano sheets

i) It is used to prepare SWCNT Laser ablation method: i) It is used to prepare SWCNT ii) Components of Laser ablation set-up: S.No Component Purpose 1 Furnace To heat the set-up at 1200oC 2 Fused Silica Window Through this, laser beam is sent 3 Graphite target Contains the precursor 4 Laser source Produces Nd-YAG ( Neodymium-Yttrium-Aluminium – Garnet) or CO2 laser bem 5 Inert gas inlet To send Helium or Neon inert gas 6 Copper collector At cooler end, it collects the nano particle

Example Acetylene 1100 oC CNT (Condensed over the catalyst) Ni / Co / Fe + MgO

3. Carbon arc method: Two graphite electrodes of 10 -20 μm dia are taken, connected externally. At high pressure, when 20 -25V AC current is passed, CNT is produced.

Cathode (-) Anode (+) Cu2+

Porous Alumina Templates: To fabricate nanotubes

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