NANOCHEMISTRY

Nanomaterials Some important terms materials having size between 1 – 100 nm

Deals with synthesis and characterization of materials at nano scale. Nanochemistry Deals with synthesis and characterization of materials at nano scale.

Nanotechnology The study of design, production, characterization and application of nano materials

Classification of Nanomaterials - Based of dimensions 1D – It has only one parameter either length (or) breadth (or) height Eg. Film, sheet, surface coatings 2D – it has only length and breadth Eg.nano tube, nanowire

3D – it has all parameter of length, breadth and height Eg. Nanoparticles, nanoprecipitates, nanocluster, nanocolloids

Nanorods

Nanowires

D/W nanorods and nanowires distinguished on the basis of aspect ratio. length of nanomaterial Aspect ratio = width of nanomaterial

Nanorod aspect ratio = 1 to 20 and material being 10-100 nm Nanorod aspect ratio = 1 to 20 and material being 10-100 nm. Nanowire aspect ratio greater than 20 and material being 10-100 nm.

Synthesis of Nanomaterials (Small to big method) (Big to small method)

(Small to big method) (Big to small method)

Bottom-up nanofabrication Small to big method: atoms or molecules nanoparticle Eg. Chemical vapour deposition, sol-gel process, chemical reduction

Top-down nanofabrication Larger structures nanoparticles Eg. Lithography, ball milling

Characterizing Tools - Nanomaterials SEM (scanning electron microscope) TEM (Transmission electron microscope) STM (scanning tunneling microscope) AFM (Atomic force microscope)

Reduced Melting Point   Eg) M.Pt. of Bulk Gold is 1064oC M.Pt. of nano Gold is 300oC.

Melting Point The melting point decreases dramatically as the particle size gets below 5 nm Source: Nanoscale Materials in Chemistry, Wiley, 2001

2. Optical properties Nano particles show different optical properties from that of bulk materials

Band gap The band gap is increases with reducing the size of the particles

ii) Cadmium sulphide (CdS) in bulk appears as red, but 6nm CdS is orange, 4nm CdS shows yellow and 2nm size appears as white.  

Optical Properties Example: Zinc Oxide (ZnO) Bulk ZnO particles Block UV light Scatter visible light Appear white Nano ZnO particles don’t scatter visible light Appear clear Application to sunscreen Nanoscale ZnO sunscreen is clear “Traditional” ZnO sunscreen is white Zinc oxide nanoparticles

optical absorption peak of nano particles

Magnetic Properties: Ferro magnetic behaviour (Uniform orientation) of bulk changes to super paramagnetism (Random orientation).

4. Mechanical Properties:   Nanomaterials are having high flexibility. Flexibility is measured by Young’s modulus. Their Young’s modulus is 10 times greater than that of steel. iv) Due to less defects in nano materials, the mechanical strength is improved.

Increased Internal Perfection

Electrical properties Conductivity decreases with reduced dimension due to increased surface scattering and decreased delocalization.  

6. Chemical Properties: water resistance, chemical resistance and corrosion resistance are improved. Increased total surface area Increased number of atoms on the surface Increased catalytic activity

a) For converting Nickel oxide to nickel So, they are acting as very good catalyst compared with their bulk materials. Eg) CNT a) For converting Nickel oxide to nickel b) For converting Aluminum chloride to Aluminium 1 x 10-5 7.5 x 10-6 5 x 10-6 2.5 x 10-6 1 x 10-6 Reaction rate

Bulk Nickel 12 reactive sides 9 x 4 = 36 Reactive sides Nano nickel particles 1 2 3 12 11 10 Ni Ni Ni 4 5 6 1 After size reduction 4 Ni Ni Ni Ni 2 3 Ni Ni Ni 9 8 7 12 reactive sides 9 x 4 = 36 Reactive sides

7. Surface properties The total surface area (or) the number of surface atom increases with reducing size of the particles

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