Gold nanoparticles, Magnetic nanoparticles - Method of synthesis

Synthesis of nano materials, gold nanoparticles, magnetic nanoparticles, method of synthesis

Gold nanoparticles

• Gold nanoparticles are emerging as promising agents for cancer therapy

• These are beneficial in diagnosis of cancer due to their photo physical property and optical property

• Unlike conventional cancer treatment, the golden nanoparticle approach uses no toxic chemicals and no radiation, reducing the risk of unpleasant side effects.

• Golden nanoparticles occur as cluster of gold atoms up to 100nm in diameter.

• Nanogold has unusual visible properties as the particles are small enough to scatter visible light.

Types of Gold Nanoparticles

1. Nanorods

2. Nanoshells

3. Nanocages

 

Synthesis of Gold Nanoparticles

1. Turkevich Method

2. Brust Method

3. Martin Method

1. Turkevich Method

• Small amounts of chlorauric acid is reacted with small amounts of sodium citrate solution. The colloidal gold will form because the citrate ions act as both a reducing agent, and a capping agent.

• Thereby monodisperse gold nanospheres are produced.

• The size of the nano spheres can be controlled by varying the citrate/gold ratio.

• The major limitations of this method are the low yield and the restriction of using wate as the solvent.

2. Brust Method

• This method used to produced gold nanoparticles in organic liquid that are normally not miscible with water like toluene).

• It involves the reaction of a chlorauric acid solution with tetraoctyleammonium bromide (TOAB) solution in toluene and sodium borohydride as anti-coagulant and a reducing agent, respectively.

3. Martin Method

• ‘Naked’ gold nanoparticles are produced in water by reducing HAuCl₄ with NaBH₄. Even without any other stabilizer like citrate, gold nanoparticles are stably dispersed.

• The key is to stabilize HAuCl₄ and NaBH₄ in aqueous stock solution with HCl and NaOH for >3 month and >3 hours respectively.

Magnetic nanoparticles

• Magnetic nanoparticles (MNPs) are the type of nano particles that can be easily tracked, manipulated and targeted by external magnetic field.

• It has been the focus of the research these days due to its properties which could increase the potential use of nanomaterial based catalysis, data storage and optical fibers.

• Elements like Fe, Co, Ni and their oxides can form MNPs. Iron oxide NPs are commonly used due to its high electrical resistivity, chemical stability, mechanical hardness, magnetic properties in RF region.

Synthesis of Magnetic Nanoparticle

1. Co-precipitation method

2. Micro emulsion method

3. Chemical vapour deposition method

4. Thermal decomposition method

5. Solvothermal method/Hydrothermal

6. Microwave assisted method

1. Co-precipitation method

• Co-precipitation is the most useful and proper method for controlled sizes Magnetic Nanoparticles synthesis method.

• In this method, MNPs are prepared from aqueous salt solutions, by the addition of a base under an inert atmosphere at room temperatures or at high temperature.

• The trouble with the synthesis of Nanoparticles by this method is the tendency of particles to agglomerate because of the extremely small size which have high surface area and surface energy.

 

2. Micro emulsion method

• Microemulsion is the thermodynamically stable isotropic dispersal of two immiscible water and oil phases in the presence of a surfactant.

• The surfactant molecules can form a monolayer at the interface between the oil and water, with the hydrophilic head groups in the aqueous phase and the hydrophobic tails of the surfactant molecules dissolved in the oil phase.

• This method has series of advantages over other methods namely use of simple equipment, controlled sized nanoparticles synthesis, particle with crystalline structure and high surface area and simple experiment conditions.

• Particles produced by the microemulsion method are smaller in size and are higher in saturation magnetization.

 

3. Chemical vapor decomposition method

• In vapor decomposition method, The vapor phase mixture is thermodynamically unstable than the generation of solid material.

• This method has wonderful flexible in production of wide range of materials.

 

4. Thermal decomposition method

• The decomposition of metal precursors in the presence of hot organic

• surfactants has yielded improved samples with good size control, narrow size distribution, good crystallinity of individual and dispersible Nanoparticles.

• Nanoparticles with high level monodispersity and size controlled particles can be produced by high temperature decomposition of organic surfactants.

• The nanoparticles produced by this method are crystalline in nature and can be dispersed in Organic solvents.

• The size of the nanoparticles produced in this method varied with reaction temperature and time.

 

5. Hydrothermal method:

• This method is also known as solvothermal method. This technique is one of the most successful ways to grow crystals of many different materials.

• The hydrothermal method contains various wet-chemical technologies of crystallizing material in a sealed container, from aqueous solution at the high temperature and at high vapor pressure.

• Despite the best method to produce monodisperse Nanocrystals, the method fails to produce nanoparticles smaller than 10nm size.

• The residence time had a more significant impact on the average particle size than the precursor concentration. Monodisperse particles were produced at short residence times.

 

6. Sol-gel method:

• This method is one of the most important methods for the preparation of Inorganic Oxides.

• This method is based on the hydroxylation and condensation of molecular precursor in solution.

• It is a wet chemical method involving both physical and chemical processes like drying, hydrolysis, polymerization etc..

• The name "sol-gel" is given to the process due to the distinctive increase in viscosity in a certain stage of the process producing a sol of nanoparticles.

• This method has an advantage to produce homogenous powders with good control of particle size. The nanostructures can be varied by changing the experimental conditions.

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