NANOCHEMISTRY

BOOKS ON NANOTEHNOLOGY

S.NO. TITLE AUTHOR1. Nanotechnology: Basic Science and Emerging

TechnologiesMick Wilson

2. Nanotechnology (AIP-Press) Gregory L. Timp

3. Unleashing the Potentials of Nanotechnology Torres Clivia M Sotomayor

4. Nanocomposite Science and Technology Braun Paul V

5. Materials and Processes for Surface and Interface Engineering

Pauleau Yves

6. A Journey into the Nanoworld Balzani Vincenzo

7. Nanotechnology and Life Jones Richard A L

8. Nanosystems: Molecular Machinery, Manufacuring and Computation

K. Eric Drexler

CONTENTS

• Introduction• Principle• Methods of preparation• Properties• Techniques• Application Areas

Nanoscience

A discipline concerning with making, manipulating and imaging materials having at least one spatial dimension in the size range 1–100 nm

Nanotechnology

A device or machine, product or process based upon individual or multiple integrated nanoscale components

Nanochemistry

Utilization of synthetic chemistry to make nanoscale building blocks of different:

• Size and shape• Composition • Surface structure• Charge • Functionality.

Hierarchical Assembly• Feature of self-assembly, where primary building blocks

associate into more complex secondary structures that are integrated into the next size level in the hierarchy. This organizational scheme continues until the highest level in the hierarchy is reached.

• Characteristic of many self-assembling biological structures.

Few basic types

• Nano powder/crystals• Nanotubes• Nanowires• Nanocomposites etc.

Nano powder/crystals• Crystals of nanometer dimensions.• Typical dimensions of 1 to 50 nanometers (nm),

intermediate in size between molecules and bulk materials.

• Exhibit intermediate properties.• Applications as:o Biochemical tagso As laser and optical componentso For the preparation of display deviceso For chemical catalysis.

Nanotubes• Hollow carbon tubes of nanometer dimensions.• Constitute a new form of carbon, configurationally equivalent to a

graphite sheet rolled into a hollow tube.• May be synthesized, with sizes ranging from a few microns to a few

nanometers and with thicknesses of many carbon layers down to single-walled structures.

• The unique structure of these nanotubes gives them advantageous behavior relative to properties, such as electrical and thermal conductivity, strength, stiffness and toughness.

Nanowires

• Very small rods of atoms.• Solid, dense structures, much like a

conventional wire. • Offer the potential for creating very small IC

components.

Nanocomposites• Comprise a large variety of systems composed of dissimilar

components that are mixed at the nanometer scale.

• Can be one-, two-, or three-dimensional; organic or inorganic; crystalline or amorphous.

• Behavior is dependent on not only the properties of the components, but also morphology and interactions between the individual components, which can give rise to novel properties not exhibited by the parent materials.

• Size reduction from microcomposites to nanocomposites yields an increase in surface area that is important in applications, such as mechanically reinforced components, nonlinear optics, batteries, sensors and catalysts.

Methods of Preparation

• By synthesis strategy• By nature of process• By medium of synthesis

1. By synthesis strategy

a. Bottom-Up Strategy: By the agglomeration of atoms or particles.

b. Top-Down Strategy: (Attrition; like- erosion)• By breaking the larger particles to the nano size. • Generally done by high energy ball milling.

2. By nature of process

a. Physical methods:• Only the size of the particles can be reduced mechanically.• Physical properties will be changed.• No change in chemical properties.• Just the increase in chemical reactivity due to

increase in surface area.

b. Chemical methods:• Chemical properties get change according to the chemical

route adapted.

3. By medium of synthesis

(i) Gas phase synthesis(ii) Liquid phase synthesis(iii)Solid phase synthesis

(i) Gas phase synthesis

• Nano particles are formed as a result of reactions among gaseous molecules, gas molecule condensation or decomposition.

(ii) Liquid phase synthesis:most widely used technique

• Precipitation in homogeneous medium.

• Routes:a. Chemical precipitationb. Hydro/solvo-thermal synthesis (Thermal hydrolysis)c. Sol-gel synthesisd. Micro-emulsion synthesis or synthesis in reverse micelles

a. Chemical precipitation• Fast chemical reaction is required to obtain a high degree of

super-saturation of the product to favor homogeneous nucleation.

Methodology

Scheme of precipitation process.

Reactant A Reactant B

Supersaturated solution

Nucleation

Crystal growth

Nuclei

Nanoparticles

Mixing

Primary processes

Super-saturation is a state of a solution that contains more of the dissolved material that could be dissolved by the solvent under normal circumstances.

b. Hydrothermal synthesis (Thermal hydrolysis)

• Aqueous solutions of metal salts or gels are treated at elevated temperatures (100-300˚C) and pressures above 1 atm.

• Size and shape of nanoparticles can be controlled by changing the conditions of the solutions:– pH– Concentration– Solvent and process conditions (temperature,

duration, etc.).

Hydrothermal synthesis is a technique of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin.

It is a method of synthesis of single crystals.

The crystal growth is performed an autoclave.

At the hotter end the nutrient solute dissolves, while at the cooler end it is deposited on a seed crystal, growing the desired crystal.

Possible advantages The ability to create crystalline phases.

Materials which have a high vapor pressure near their melting points can also be grown by the hydrothermal method.

The method is also particularly suitable for the growth of large good-quality crystals while maintaining good control over their composition.

Disadvantages of the method include the need of expensive autoclaves, and the impossibility of observing the crystal as it grows.

c. Sol- Gel synthesis• Process involves the alkoxide hydrolysis and a condensation reaction.

M(OR)x + yH-OH → M(OR)x-y(OH)y + yROH

• Partially hydrolysed species are then linked to form M-O-M bonds by condensation via dehydration or dealcoholation.-M-OH + HO-M- → -M-O-M- + H2O -M-OH + RO-M- → -M-O-M- + ROH

• So, the process involving hydrolysis, polymerization, nucleation and growth condenses the molecular units together into small clusters called sols, eventually leading to the formation of an insoluble three dimensional network, the gel.

• The sol-gel process is a wet-chemical technique

• starting from a chemical solution, which acts as the precursor for an integrated

network (or gel) of either discrete particles or network polymers.

• Typical precursors are metal alkoxides and metal chlorides, which

undergo hydrolysis and polycondensation reactions to form either a network

"elastic solid" or colloidal suspension

• Formation of a metal oxide involves connecting the metal centers with oxo (M-O-

M) or hydroxo (M-OH-M) bridges to generate metal-oxo or metal-hydroxo

polymers in solution.

• The sol evolves toward the formation of a gel-like diphasic system containing both

a liquid phase and solid phase whose morphologies range from discrete particles

to continuous polymer networks.

• In the case of the colloid, a significant amount of fluid may need to be

removed initially for the gel-like properties to be recognized.

• The most simple method is to allow time for sedimentation to occur, and

then pour off the remaining liquid. Centrifugation can also be used to

accelerate the process of phase separation.

• Removal of the remaining liquid (solvent) phase requires a drying process.

• The rate at which the solvent can be removed is ultimately determined by

the distribution of porosity in the gel.

• The sol-gel approach is a cheap and low-temperature technique that

allows for the fine control of the product’s chemical composition.

d. Micro-emulsion synthesis• Microemulsions: Thermodynamically stable, optically clear

dispersions of two immiscible liquids, such as water and oil.

• They are formed, when a surfactant lowers the oil/water interfacial

tension allowing thermal motions to spontaneously disperse the two

immiscible phases.

• Reverse micelles are molecular self assemblies from surfactants which

have a spherical shape with a hydrophillic core and a hydrophobic tail

on the sphere surface.

• Most popular method to prepare Nano-sized inorganic particles as

oxides.

(iii) Solid phase synthesis

• Nanoparticles are formed directly from solids or semisolids (viscous liquids).

• It belongs to top-down approach.

i) Mechanical Milling:– Mechanical forces, involved in high energy ball milling, are used

to break bulk material down to bring it to nano-level.

ii) Mechano-chemical method:– Involves the physical reduction in the material size as well as the

milling energy is used to initiate the chemical reaction between the materials that are being milled.

Properties• Surface area: Large.

• Reactivity: High due to the unsaturated bonds on their pristine surfaces.

• Basic properties: Properties of materials change as:- their size approaches the nanoscale.- percentage of atoms at the surface of a material becomes significant.

Example- Gold nanoparticles melt at much lower temperatures (~300 °C for 2.5 nm size) than the gold slabs (1064°C).

• Optical properties: Often possess unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. Example- Gold nanoparticles appear deep red to black in solution.

Techniques

• Scanning tunneling microscope (STM)• Atomic force microscope (AFM)• Scanning electron microscopy (SEM)• Transmission electron microscopy (TEM)• X-ray diffraction (XRD), etc.

Application Areas• Medicine• Diagnosis• Drug delivery• Tissue engineering• Environment• Catalysis• Filtration• Energy• Computers• Aerospace• Refineries• Vehicle manufacturing• Food packaging• Optics• Textiles• Cosmetics