Preparative methods for nanomaterials by SOLVOLTHERMAL METHOD

PRADEEP JAISWALMSC PART -1 (2015-16)SEM -1PAPER-2ROLL NO. 6

CONTENTS :• Basic defination.• Classification of

preparative method.• Advantages and

disadvantages of chemical method.

• Solvothermal :i. Principle.ii. Method.iii. Synthesis Set up.iv. Working.v. E.g. Preparation of

chromium dioxide.vi. Advantages and

disadvantages .vii. Reference's.

Defination's :

• Nano :Greek word meaning dwarf or very small.• Nanomaterials : Nanomaterial thus the tiny particles of material that

have size in the range of 1nm to 100nm.• Nano science :It is the study of phenomena and manipulation of material

at atomic ,molecular and macro-molecular scales where properties differ significantly forom those at larger scale.• Nanotechnology: The design, characterization, production, and

application of structures and devices by controlling shape and size at the nanometer scale.• SOLVOTHERMAL METHOD :It refers to conducting the reaction in a

closed vessel ,in which the solvent has a possibility to achieve its supercritical state.

Classification of methods of preparations:Preparative

methods

Physical

mechanical

vapour

Chemical

Chemical vapour deposition

Biological

Bio membranes

DNA , Enzymes

Hybrid

Micro emulsion

Advantages of Chemical methods : • These are low temperature techniques• They involve less instrumentation,

therefore less expensive and are simple• Nanomaterials of different sizes and

shapes can be obtained• Nanomaterials are obtained in the

form of liquid can be easily converted to dry powder.

Disadvantages of Chemical methods :

• It dose not solve the problem of

chemical in homogenetic and temperature in the reaction.

Solvothermal :• This involves heating of the reactants in a close vessel called Autoclave.• An autoclave is usually constructed from thick stainless steel to withstood the high press

and is fitted with a safety wall. It may be liner with Teflon (Non-reactive material). • When autoclave is heated the pressure increases and the water remains liquid above its

normal boiling temperature of 373K which is called “Superheated water”. • These condition in which the pressure is raised above atmospheric pressure and

temperature above the boiling temperature are known as ‘Hydrothermal condition’.

Principle :

Solvothermal :

• Solvothermal method is very similar to hydrothermal method.• Solvothermal synthesis is a method for preparing a

variety of materials such as metals, semiconductors, ceramics and polymers. • Solvothermal processes can be described as a

reaction or a transformation of precursor in presence of a solvent in a close system and at a temperature higher than the boiling temperature of the solvent.• Zinc oxide is an example of a II–VI compound that

can be prepared solvothermally and will exhibit quantum dot effects.

Methods :

Solvothermal synthesis setup: • 1 STAINLESS STEE AUTODAVE

• 2 PRECURSOR SOLUTION

• 3 TEFLON LINER

• 4 STAINLESS LID

• 5 SPRING

Working of Solvothermal method :• Water act as reacting medium

which exists in liquid and vapour state.

• Vessel is heated one end and other end kept lower temperature hence there is temperature gradient

• Product carry from hot end to cool end by the process of convenction of heat.

• Material finally deposited at cool end .

• Since reaction is carried at much lower temperature the product is nano size.

E.g. Preparation of chromium dioxide (CrO2) particles by Solvothermal method :• The CrO2 is very important compound because of its magnetic properties

and used in audio tapes which contains the Cr in the unusual oxidation state of +4.• It is prepared by oxidation of Cr (III) oxide i.e. Cr2O3 which is the stable

oxide of chromium under normal condition.• Cr2O3 and CrO3 are placed in an autoclave in a water and heated to 623k.

Oxygen is produced during reaction because autoclave sealed, partial pressure of O2 is developed.

CrO3 = CrO2 + 1/2O2

Cr2O3 + CrO3 = 3CrO2

• Advantages of Solvothermal synthesis

Easy and precise control of the size, shape distribution, crystalline of the final product through adjusting the parameters such as reaction temperature, reaction time, solvent type, surfactant type, precursor type and the like.• Disadvantages of Solvothermal synthesis :

The need of expensive autoclaves Safety issues during the reaction process Impossibility of observing the reaction process

• Sulabha K. Kulkarni, Nanotechnology-Principles and Practices, Capital Publishing Co., (2007).

• Lesley Smart and Elaine Moore, Solid state Chemistry – An Introduction, 3rd edition, Taylor and Francis (2005).

• M. A. Shah and Tokeer Ahmad, Principles of nanoscience and nanotechnology, Narosa Publishing House (2010).

• Edited by C. N. R. Rao, Achim Müller, Anthony K. Cheetham, The Chemistry of Nanomaterials: Synthesis, Properties and Applications, Volume 1, Wiley-VCH (2004).

References: