soft chemical processes

Soft Chemical Processes

Presented By_ To_

Sanjeeb Limbu (Reg.No:14305019) Dr.A.Vadivel Murugan Sir

M.Tech.-Nanoscience & Technology Associate Professor(CNST)

Centre for Nanoscience and Technology

Methods For The Preparation of Nano-particle:

Chemical precipitation and co-precipitation

Matel nanocrystels synthesis by polyol and

borohydride reduction methods

Sol-Gel synthesis

Micro emulsions synthesis

Normal and Reverse micelles Formation

Hydrothermal

Solvothermal


Chemical Precipitation:

Precipitation is a process that involves the formation of a precipitate when a solid is formed during a chemical reaction or diffusion. The precipitation usually settles at the bottom and the liquid layer on the top of it is called as supernatant.

Eg: AgNO3(aq) +KCl (aq) AgCl (solid) + KNO3 (aq)

(white ppt)

Cd2+Cl2+Na2S 2- CdS +2NaCl

(bright yellow ppt)


Chemical co-precipitation:

It is most facile and easy method to synthesize Fe3O4(Fe2+/3+)compound under inert/ambient condition. The type of compound iron co-ppt depends on the type of salts used.

Eg: Fe3+Cl3+Fe2+Cl2 Fe3O4+2NaCl

Zn2+Cl2+Fe3+Cl3 Zn2+Fe23+O4

8-

(Zinc Ferrite)

NaOH


Co-Precipitation Methods For Nanoparticle System:


Matel nanocrystals synthesis by polyol (Alcohol Reduction) :

A polyol is an alcohol containing multiple hydroxyl group In two polyol has a special meaning food science and polymer chemistry.

The general mechanism of metal reduction in glycol(polyol) can be represent by the following reaction.

CH2OH CH2OH CH2OH CH2OH

CHOH CHOH + H2 CHOH +H2 C=O + H2

CH2OH CHO CH2OH CH2OH


Borohydride Reduction :

Borohydride reduction known since the 1950s,was one of the subjects of investigation under the Manhattan Project.

The basic reaction involves the hydrolysis of the borohydride accompanied by the evaluation of hydrogen.

BH4

- + 2H2O BO-

2+ 4H

2

Pt4++4e- Pto

H2PtCl

6 [Pt4+Cl6-]2-+2H+

Nanocrystels of variety of metals have been made by borohydride reduction


Sol-Gel Synthesis :

The sol-gel process is a wet-chemical technique that uses either a chemical solution (sol short for solution) or colloidal particles (sol for nanoscale particle) to produce an integrated network (gel). Metal Alkoxides (M(OR')n) and metal chlorides are typical precursors. They undergo hydrolysis and polycondensation reactions to form a colloid, a system composed of nanoparticles dispersed in a solvent. The sol evolves then towards the formation of an inorganic continuous network containing a liquid phase (gel).

Formation of a metal oxide involves connecting the metal centers with oxo

Metal (M-O-M) or hydroxo (M-OH-M) bridges, therefore generating metal-oxo or metal-hydroxo polymers in solution.

After a drying process, the liquid phase is removed from the gel. Then, a thermal treatment (calcination) may be performed in order to favor further polycondensation and enhance mechanical properties.


Example: TiO2 nanoparticle-mediated mesoporous film by sol-gel processing

Alkoxide

+H2O Stabilizer

Nanodisperse Oxide Sol (Particulate or Polymeric)

-H2O

Gel

Xerogel

Porous TiO2

-H2O

T > 400 ºC -H2O

-Stabilizer

SEM image of TiO2 Centre for Nanoscience and Technology

Applications:

It can be used in ceramics manufacturing processes, as an investment casting material, or as a means of producing very thin films of metal oxides for various purposes. Sol-gel derived materials have diverse applications in optics, electronics, energy, space, biosensors, medicine (e.g. controlled drug release) and separation (e.g. chromatography) technology. One of the more important applications of sol-gel processing is to carry out zeolite synthesis. Other elements (metals, metal oxides) can be easily incorporated into the final product and the silicalite sol formed by this method is very stable. Other products fabricated with this process include various ceramic membranes for microfiltration, ultra filtration, nanofiltration, and reverse osmosis.


Microemulsion synthesis :

The microemulsion concept was introduced as early as 1940s by Hoar and Schulman who generated a clear single phase solution by titrating a milky emulsion with hexanol.

Schulman and co-worker (1959) subsequently coined the term microemulsion

The micro emulsion definition provided by Danielson and Lindeman in 1981 will be used as the point of reference

Micro emulsions are clear,transparent,thermodynamically stable dispersion of oil and water, stabilised by an interfacial film of surfactant frequently in combination with a co-surfactant.

Diameter 10-200 nm

Three types of micro emulsions are most likely to be formed depending on the composition-

i) O/W-Microemulsion

ii) W/O-Microemulsion iii) Bio/Continuous Microemulsion

Normal and Reverse Micelle formation :

Hydrothermal Synthesis :

Hydrothermal synthesis can be defined as a method of synthesis of single

crystal that depends on the solubility of minerals in hot water under high pressure.

Hydrothermal synthesis usually refer to heterogeneous reaction in aqueous media above 100°C

The use of Hydrothermal method in preparing metals on metal oxides has become a recent trend. This is because the resultant powder needs no more high temperature calcinations and thus can avoid the nano-particles from reclusturing and from being contaminated.


Hydrothermal Method

1. Precipitating!!

2. Pouring! !

3. Autoclave ! !

4. Heating ! !

5. Keeping ! !

6. Cooling! ! and Drying ! !

6. Obtained Powder ! !

6. SEM Image ! !

Solvothermal Synthesis :

A “Solvothermal reaction can be defined as a chemical reaction (or a

transformation) between precursors in a solvent (in a close system) at a temperature higher than the boiling temperature of this solvent and under high pressure”

The term « Solvothermal» was proposed at the beginning of the during the development of non-aqueous solvents.

Main types of chemical reactions involved in Solvothermal processes

Oxidation/Reduction,Hydrolysis,Thermolysis,Complexation,Metathesis


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