Showing posts with label Chemistry. Show all posts
Showing posts with label Chemistry. Show all posts

Wednesday, 9 October 2019

Important Applications of Microbiology:

October 09, 2019 0
Important Applications of Microbiology:
Microbiology and pharmaceutical research

Some of the considerable applications of microbiology are as discussed below:
Microbiology is one the main branches of applied sciences. It exceptional applications in the field of medical microbiology, soil microbiology, food microbiology, water and wastewater microbiology, extraction of metals, microbial technology, industrial microbiology and environmental microbiology containing applications of microorganisms as biosensors are discussed as fellow:
1.                Systematic study of Microorganism:
It give us the information about various types of microorganisms which enables us to reveal their structural and functional aspects, identifying and differentiating them, their classifications, naming, essential needs regarding their nutrition, to isolate and purify them as pathogens of plant and human, to develop phylogenetic relationships (relationships of various developmental stages during the evolution of an organism) and to interpret the origin of life itself.
systematic study of microorganisms

2.               Microorganisms as a source of food:
Besides edible fungi such as mushrooms, microorganisms are also now used in the production of single cell protein in the form of bacteria, cyanobacteria, yeasts, and fungi as animal feed or human food. Japan, Mexico, Taiwan, Thailand, Israel, and America produces algal microbes on large scale. Various microbe synthesizing products are now utilized as human food such as cellulose or lignocellulose. Animal feed are also based on different microbial products.

3.              Fermented Food Products:
 Microorganisms are utilized in the manufacture of a large number of fermented foods such as sourdough bread, leavened bread, flavours and fermented milk products. The fermented milk products include cheese, yoghurt and many other products.
Fermentation by microorganisms
4.              Fermented Vegetables:
 The important fermented vegetables are sauerkraut that is obtained from cabbage and Kimchi obtained from fermented vegetables in Korea.
Various fermented vegetables

5.              Fermented meats and Fermented Fish:
Fermented fish and fermented meats are utilized in various parts of the world because of their increasing retentivity, otherwise the fish and meats are extremely perishable.
6.              Fermentation and Beverage Products:
Beer, rice wine, tempeh, vinegar, soya sauce too are fermented products.
7.               Preservation of Food:
Microbiology has been playing vital role in preservation of food by appertization and pasteurization that is commercially sterile food and by heat processing, prevention of spoilage of canned food, irradiation, aspectic packaging, ionizing radiation, UV radiation, high pressure processing that is low temperature storage, pascalization and chemical preservation ( esters, organic acids, sulphur dioxide and nitrites).
Food microbiology gives the tools for prevention of food borne illness caused by bacterial and non-bacterial agents. The food borne illness agents among the nematodes and helminthes are Platyhelminthes that are tapeworms and liver flukes and roundworms such as Trichinella spiralis. Among the protozoa, the agents that are causing food borne diseases are Entamoeba histolytica and Giardia lamblia.
Various Food Preserves

8.              Microbial Diseases:
Microorganisms are the leading cause of several diseases which are spreading worldwide and causing serious health issues. Microbiology provides a number of tools for the treatment and control of such diseases.
Cholera vector illustration

9.              Industrial Microbiology:
Various products obtained from microbial metabolism after microbial processing of raw material have been produced on industrial scale. These include high value drugs, chemicals, fuels and electricity.
Microbiology in different industrial processes

10.        Microbes as a Source of Enery:
Several substrates can be utilized as a source of energy such as methanogenic bacteria are source of biogas. The methanococcus and methanobacterium produce methane gas by utilizing CO2 as an electron acceptor. In japan, for the faster production of methane gas, a new specie of methanobacterium has been evolved that is M. cadomensis 23 strain. Ethanol can also be utilized for the manufacture of gasohol by mixing 20 percent ethanol and 80 percent gasoline.
11.           Degradation of cellulose and lignin:
Trichoderina reesei can be utilized degrading cellulose because it is producing extracellular cellulase. The white rot fungus Sporotrichum pulverulentum which is a cellulase negative organism, whoever a mutant of it has been produced which can degrade wood and kraft lignocellulase actively. Now biological pulp has been produced in the absence of any chemical treatment for delignification
12.         Mining and Extraction of Metals:
Pyrite (FeS2) and chalcopyrite (CuFeS2)  can be degraded by utilizing Thiobacillus ferroxidants and a combination of Thiobacillus organoparpus and Leptospirillium ferroxidants. Iron and sulphur can be oxidized by using archaeal species S.brierlevi and Sulfolobus acidocaldarius that depends on CO2 or other simple organic compounds for energy. These archeobacterial specie can also degrade chalcopyrite (CuFeS2) and Pyrite (FeS2).
Metal extraction process

13.         Recombinant DNA and genetic recombination:
Manufacturing and manipulating genetic material in vitro that is genetic engineering has produced extremely wonderful products such as Recombinant DNA. The genetic recombination is the process of joining DNA from various sources. Different microorganisms have been used to isolate several number of restriction enzymes and restriction endonucleases that have the abilities to cleave or cut double stranded DNA leaving staggered ends.
DNA cutting and manipulation

14.         Hybridoma and preparation of monoclonal antibodies:
A cell which is made by combining antibody-producing B cell with a cancer cell is called as Hybridoma. The resulting hybridoma cells or myeloma contain properties of both parent cells immortality and can also secrete considerable amount of a single specific type of antibody. This phenomenon was discovered by Kohler
15.           Harvesting DNA biotechnology for various public health engineering programmes:
These programmes include manufacturing of an antiviral protein that is interferon prepared by specific animal cells in response to a viral infection, production of somatotrophin that is a human growth hormone, production of human insulin and production of several other vaccines and hormones
The vaccines for diphtheria, cholera, tetanus, viral hepatitis type A and type B, pertussis, influenza, plague, mumps, measles (rubella) poliomyelitis, rabies, typhoid, typhus, rubbela,  and yellow fever have been prepared so far.
16.         Microbes as Biofertilizers:
Microbial technology of nitrogen fixation exploiting symbiotic
Microbial technology involves the nitrogen fixation by symbiotic microoganisms having association with higher or lower plants and nonsymbiotic or asymbiotic relationship that involves the nitrogen fixation by microorganisms independently. The main enzymes that are responsible of converting molecular nitrogen to ammonia involves nitrogenases.
17.          Making smarter and faster computers:
The Archaeobacterium Halobacterium halobium are growing in nature in solar evaporation ponds that have excessive concentration of salts. These salty ponds are present around San Francisco Bay located on the Western coast of USA.
It has been investigated that when the cell of Halobactrium halobium is broken down, it fragments into two main fractions which are red and purple in colour. The purple fraction plays important role in manufacturing computer chips. The protein which is responsible for purple colour is referred to as bactriorhodopsin.
Robert Birge at Syracuse University’s Centre of Molecular Electronics has grown Halobacerium halobium in 5-litre batches and has extracted the protein bacteriorhodopsin from the cells and developed the computer chips which are made up of a thin layer of bacteriorhodopsin.
The chips that are prepared from bacterial sources have the capacity to store more information as compared to conventional silicon chips and can process the information as fast as human brain. These chips must be stored at -4°C.
DNA chip: DNA micro-array


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Saturday, 14 September 2019

SILICONES AND THEIR IMPORTANT INDUSTRIAL APPLICATIONS

September 14, 2019 0
SILICONES AND THEIR IMPORTANT INDUSTRIAL APPLICATIONS
   

1.  Introduction

Silicones are inorganic synthetic polymers with alternate silicon and oxygen atoms, having organic groups attached to silicon atom. The silicones was given that name due to their resemblance with ketones by kipping in 1901 having the brut formula R2SiO. These are actually known as plydialkylsiloxanes having formula
  R
  I
(Si - O -) n
  I
  R

2.  Industrial applications of Silicones

The quality of life is protected and improved by silicone products. From aviation to textile, the quality of everything is enhanced by silicone and they makes the rout for new products. The important industrial applications of silicones are discussed below:

2.1.    Health Care

Silicone made medical infant care products and applications provides the highest quality standards to fulfil the demand of health care professionals, families and patients. They have resistant to bacteria and can be sterilized easily. They are inert and do not irritate the body.
Silicone tubing in various medical devices like drug delivery systems and heart pacemaker helps to minimize the risk of infections. Silicone boost lubricants facilitate the insertion of devices and needles. They can be used externally, intravenously or internally and not trigger allergic reactions and unwelcome by-products. Silicones help to soften and smooth medications that can be applied without having greasy residue and helpful in forming a seal for protecting the wounds during healing process.
Silicones can most likely approximate the uniformity of skin and offer extraordinary cushion and consolation in prosthetics.

2.2.        Aviation and Aerospace

Silicones are used in various aspects of spacecraft and aircraft assembly and maintenance due their extraordinary ability to withstand extreme stress and temperature conditions. Silicones are used as sealants and adhesives for protecting and sealing various elements such as windows, doors, hydraulic switches, fuel tanks, leading electrical devices and engine gaskets etc.

2.3.    Construction

Silicone sealants, coatings and adhesives improves the working of construction materials and makes them to work last longer. Diverse materials can be bonded by silicone adhesives such as glass, concrete, steel, granite and plastics. This provides innovative engineering and architecture such as curved and suspended structures and dramatic glass facades. Silicone sealants make the material stay affixed and protects them from earth quake and movement from wind by absorbing stress.

2.4.    Electronics

Silicones have provide advancement in telecommunication, technology and macro and micro-electronics and electrical power distribution.
Highly sensitive materials such as circuits and microprocessors to semiconductors are protected by sealing and bonding them. They provide protection to electronic equipments from moisture, heat, salt, corrosion, and movements in appliances, cars, and airplanes. Silicones provide electronic and technological innovations.

2.5.    Household Products

The cookware and bakeware which are made of silicone rubber are more convenient, sturdy, long lasting and easy to use. The non-stick and flexible surface is facile to clean and does not drift any odour or flavour to food. The baking mats, muffin molds and cake pans made of silicone do not affect the quality of food product.
The household polishes and cleaners made of silicone are ideal for countertops and floors. They increase the shine, their spreading is facile and have no chemical reaction with surface materials.
Silicones are used in fabric softeners to preserve the “newness” due to their softening properties. They are also used as anti-foaming agents in detergents.

2.6.    Paints and Coatings

With the advancement in silicone technology, exterior coatings and paints have become last longer and can stand up to salts, pollution, sun and age better than ever. The silicone paints provide extraordinary adhesion, stain, chemical and weather resistance and better chemical dispersion. Advance silicone based paints help to keep the exterior coatings of bridges, houses and railway cars flexible so that they remain unaffected from freeze and thaw cycles chalking, blistering, cracking and peeling. Silicone coatings on oil-rig, highway and road surfaces remain unaffected from corrosion, acid rain and salt spray.

2.7.        Paper and Film

Silicones extraordinary foam controlling ability provides advancement in paper and pulp processing and make the production easier on larger scales. Silicones also have huge market as paper release agents. Silicones provide pressure sensitive adhesives. They are resistant to temperature and humidity and are good for using in extreme environments such as in hot engine compartments of a vehical or tapes that need to adhere to outer surface.

2.8.    Personal Care Products

Versatile silicones provide various exceptional qualities that are associated with personal care products, silky smoothness, luxuriant texture, luster and smooth applications.
The personal care products made of silicones are non-irritating and non-stinging. For example, silicones minimizes the tacky feel and white residue of antiperspirants in deodorants.
Silicones provide long lasting make-up and also retain its luster and colour. Hair conditioners and shampoos containing silicone have better shine and stronger SPF and have improved wetting and spreading qualities of sunscreens, lotions and cleansers

2.9.    Restoration

Silicones facile to restore historical buildings landmarks and buildings without changing the original integrity and appearance of the material. Sealants and adhesives made of silicones srengthen the “weatherability” and natural strength of the structure and joints. They are water repellent and allow "breathability" to natural materials eg. porous limestone and porous soapstone. Silicone coatings  have uniformity and do not have the risk of streaking or straining.

2.10. Sealants and Adhesives

Silicones are perfect for affixing materials and are utilized in construction, expansion, connection and for moving joints. Silicone rubber keeps the material in place and the joints are able to absorb the shifting and movement from temperature and humidity fluctuations and various other environmental factors.
In the home, sealants made of silicone rubber are used in kitchens and bathrooms to prevent damage from bacteria build-up and moisture.
Structural glazes made of silicone rubber secure the long term appearance of facade and quality. They can either be manufactured with material or can be applied on the finished surface and these industrial and commercial structure can withstand exposure to extreme conditions. Silicone rubber glazing protects and insulates glass panels in cars and facades from UV radiation.

2.11.Textiles and Leather

Silicones have dramatically alter the fabrics of all kind. They are used as finishes to retain the texture, shape and resistance to abrasion. They are used to achieve brilliance and uniformity of colour. They are used for water proofing the raingear and leather shoes and seal out goggles and diving masks from water.
Silicones enable new routes for designing sportswear having lightweight, water repellent, durable and high performing and also allows the fabric to maintain “breathability”.
Silicones maintain the colour and quality of dry-cleaned clothes because they are inert and do not interact with the fabric. Home fabric softeners made of silicones helps in preserving the textiles due to their softening properties and their elasticity also maintains the smooth wrinkles.

2.12.Rubber

From cake pans to keypads and from tubing to tires, silicone rubber is essential in various sophisticated synthetic and production processes.
The formulation and manufacturing of silicone rubber is easy and essentially applicable to most trades and accessible in varying hardness and colour. Silicone rubber has a variety of formulation for molding, curing and manufacturing, it facilitates business streamline their processing and ensures the consistent quality production. Silicone rubber when used with right technology, provides advance design opportunities and synthetic solutions.
Silicone rubber can be easily cured and molded to create materials, including electronic and automotive sealants and gaskets, cables, tires, food molds, industrial molds, artistic replications, play and toy equipment, molds, bakeware and reproduction.

2.13.Transportation

In high-performance automobiles, planes, ocean vessels spacecraft and planes, silicones give strength, durability and adhesion.
The service life of cars, boats and planes can be extended by using silicones coatings and adhesives. Exteriors become more resistant to wind, rain, abrasion, salt, chemicals and ultraviolet radiations. The joints coated with silicones are last longer and their maintenance and repair is less costly.
Silicones are now used in a wide range of car parts including: engine gaskets, headlamps, airbags, ignition cables, hydraulic bearings, radiator seals and shock absorbers, ventilation flaps and spark plug boots.
Silicone rubbers offers superior traction and long bear life to tires and silicone release coatings offer the tire manufacturers in getting the tires out of their manufacturing molds.

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Thursday, 12 September 2019

CARBIDES, THEIR TYPES, SYNTHESIS AND INDUSTRIAL APPLICATIONS

September 12, 2019 0
CARBIDES, THEIR TYPES, SYNTHESIS AND INDUSTRIAL APPLICATIONS

1. Carbides

The compounds which are made of carbon and more electropositive elements are called carbides. In carbides, carbon is usually combined with metallic and semi-metallic  elements such as calcium carbide, tungsten carbide, iron carbide etc.

2. Types of Carbides:

Carbides are classified on the basis of chemical composition, chemical bonds, physical composition, method of manufacture and on the basis of their applications.

2.1. Saline Carbides

The saline word refers to salt-like. These carbides are composed of high electropositive element such as alkali matels, alkaline earth metals have mixed with carbon. Isolated carbon centers are present in these carbides such as “C4-” in the metanides, “C34-” in the sesquicarbide and “C22-” in the acetylides

i) Methanid

Methanides get their name from the property of formation of methane gas when treated with water. Aluminium carbide (Al4C3) and beryllium carbide (Be2C) are important methanides.                            
Al4C3 + 12H2O → 3CH4 + 4Al(OH)3

ii) Acetylides

Acetylides are salt like carbides with C22- anion. There is triple bond between two carbon atoms in C22- anion. The elements which form acetylides include alkali metals, alkaline earth metals and lanthanoids having formula M2C3. Actinides form acetylides with the stoichiometry MC2 and M2C3. Acetylides get their from the property of acetylene formation when treated with water.
CaC2 + 2H2O → C2H2 + Ca(OH)2

iii) Sesquicarbides

Sesquicarbides contain C34- anion , which produces methylacetylene
(propyne) on hydrolysis:

2.2. Covalent Carbides

Covalent carbides are those carbides which have less electronegativity difference between carbon and the combining atom. The elements of group IVA form covalent carbides such as boron and silicon. Silicon carbide exists in two crystalline forms having resemblance with the structure of diamond. Whereas the structure of boron carbide (B4C) is very unusual and forms icosahedral boron units connected by carbon atom. Both boron carbide and silicon carbide also called caborundum are refractory and hard material and have important industrial applications.

2.3. Interstitial Carbides

The transition metals having atomic radius nearly greater than 0.135nm form interstitial carbides. The elements of group IVB, VB and VI and 4th, 5th, and 6th fall in this category. These transition metals have interstices which act as host lattice for small atoms like carbon. According to arrangement of metal atom, interstitial carbides may have 1:1 or 2:1 stoichiometry. In 1:1 stoichiometrty, there is cubic closed packing having octahedral interstices filled with carbon  eg. rock salt structure. While in 2:1 stoichiometry, there is hexagonal close packing in which octahedral interstices are directly opposite to the layers of metal atom.

2.4. Intermediate Carbides

The intermediate carbides are formed by transition metals having size smaller than 0.135 nm and carbon atoms are not accommodated in interstices without distortion of crystal lattice. The elements of group VIIB and VIIIB form intermediate carbides.They have multiple stoichiometry and are more complex than interstitial carbides.

3. Synthesis of Carbides

Carbides can be prepared by various synthetic routes. Some of them are given below:
  •  Solid combustion synthesis which involves direct combination of the elements at elevated temperature.
  • Carbo-thermal reduction of metal oxide.
  •  Vapour phase synthesis
  • Pyrolyses of metal-organic compounds
  • Sol-gel route
  •  Laser-induced reactions
  • Plasma-chemical synthesis

Only one of them will be discussed here.

3.1. Vapor-Phase Synthesis

In vapour phase synthesis, metal chlorides are combined with carbon containing gases eg. methane or benzene.
Ti + CH4 → TiC + 2H2
ZrCl4 + CH4 → ZrC + 4HCl
With chlorides, the reaction is carried out in the gas phase above .600°C. Nanopowders can be obtained by using this rout because transition metal halogenides are highly volatile and can also be used to deposit the solid substrate by carbide layer.
Gas phase reactions are also developed to prepare SiC:
CH4 + SiH4 → SiC + 4H2
SiCl4 + CH4 → SiC + 4HCl (26)
7SiCl4 + C7H8 + 10H2 → 7SiC + 28HCl
3SiH4 + C3H 8→ 3SiC + 10H2
The advantage of this method is the synthesis of high purity nanopowders having potential control over shape, size and crystal structure in addition to control of reaction rates. However the yield obtained by this method is not appropriate.

4. Important Industrial Applications of Carbides:

Carbides have special physical and structural properties due to which they have special industrial applications. These are
  • High resistance to abrasion and have hard steel grades.
  • Resistance towards deflection: Carbides have nearly three times more elasticity modulus comparing to steel bars of same grade and thus resistance towards deflection
These are properties which make these carbide chemicals very effective in extreme temperature and pressure conditions such as in drilling and machine tool bits. Carbide balls are also used as milling agents due to their hardness in Attritor mills. Some Specific carbide chemicals include;
Due to these properties, carbide chemicals are very effective in extreme pressure and temperature conditions and are used as:
·         As milling agents in Attritor mills due to hardness of carbide balls
·         In drilling and machine tool bits such as tantalum carbide which has extreme degree of stability and resistance.
·         As heated spray to protect vulnerable metal surfaces such as chromium carbide powder.
·         To produce hard coatings eg. plasma spraying and to require high surface area in solar panels and fuel cells such as hafnium carbide powder.
·         In the manufacture of grinding wheels, sand papers, cutting tools and as refractory lining such as silicon carbide
·         For decorative purposes due to resemblance with gold and as non-toxic covering of medical equipments such as carbon titanium nitride powder.
·         For electrical and radio purposes.
·         To manufacture special tools and hard gears for mining and oil exploration sectors such as tungsten carbide powder.

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Wednesday, 11 September 2019

NANOMATERIALS, THEIR PROPERTIES, SYNTHESIS AND APPLICATION

September 11, 2019 0

NANOMATERIALS, THEIR PROPERTIES, SYNTHESIS AND APPLICATION

1    INTRODUCTION TO NANOMATERIALS

Nanomaterials are those materials in which one dimension is atleast less than 100 nanometers. The diameter of human hair is 100,000 times larger than a nanopartical. Because of their size nanomaterials have unique magnetic, optical, electrical and other properties. Due these properties nanomaterials have potential applications in medicine, electronics and other fields.

Fig.1: Nanomaterials ( carbon nanotubes)

  •  Evolution of science and nanomaterials

Nanotechnology and nano-science are dependent upon nanoparticals. Nanotechnology and nano- science has been evolved as a vast area of development and research activity. It can revolutionize the methods of creating products and materials and broad range of functionalities can be retrieved. It has significant commercial value which will be increased in future.

3.      Classification of Nanomaterials:

The size of nanomaterials is extremely small with at least one dimension of 100 nm or smaller. Common types of nanomaterials are
Ø  Zero Dimensional eg. gold, palladium with size 1-50nm
Ø  One Dimensional eg. surface films.
Ø  Two Dimensional eg. strands or fibres
Ø  Three Dimensional eg. particles
Nanomaterials can exist as nanotubes, quantum dots, dendrimers and fullerenes.
Nanomaterials have been characterized by an ultra fine grain size to 50 nm. Nanomaterials can be adopted into different modulations which are defined by Richard W. Siegel as zero dimension (cluster assemblies and filaments, atomic clusters), one dimension (multilayers), two dimension (buried layers or ultrafine-grained overlayers), and three dimension (equiaxed nanometer sized grains)

4.     Causes of so much interest in nanomaterials

Nanomaterials have got significant importance in recent years because of their extra-ordinary electrical, mechanical, magnetic and optical properties. Some useful examples are as follows:
Ø  Nanophase ceramics are of special interest due to their extended ductility at elevated temperatures in comparison to the coarse-grained ceramics.
Ø  Different non-linear optical properties have been achieved by using nanostructured semiconductor. Quantum confinement effects have also been achieved by using nanostructured semiconductors which may results special properties, like the luminescence effect in silicon powders and  infrared optoelectronic devices by using silicon germanium quantum dots . Nanostructured semiconductors also have applications in solar cells as window layers.
Ø  Various gas tight materials, porous coatings and dense parts have been produced by using nanosized metallic powders.
Ø  Magnetic nanocomposites are now widely using for mechanical
force transfer (ferrofluids), magnetic refrigeration and for high density information storage.
Ø  Nanostructured metal clusters particular impact in catalytic applications. They have also been used as precursors for novel type of heterogeneous catalysts and also offer substantial utilization including selectivity, activity and lifetime in electrocatalysis and chemical transformations. Nanoscale metal particles having chiral modifiers on their surface have been used in Enantioselective catalysis.
Ø   Nanostructured metal-oxide thin films have been received much attention for the realization of gas sensors (NOx, CO2, CO, CH4 and aromatic hydrocarbons) with greater selectivity and sensitivity. Nanostructured metal-oxide eg. MnO have found uses for rechargeable batteries for consumer goods and cars.
Ø   Polymer based composites with a major percentage of inorganic particles having a high dielectric constant are important materials for photonic band gap structure.

5.      SYNTHESIS AND PROCESSING OF NANOMATERIAL

Two basic synthetic approaches can be used for naomaterial synthesis, i.e. either
Ø  top down approach’ in which bulk solid is dissociate into smaller particals until their constituents of only a few aroms.
Ø  bottom up approach’ in which atoms are assembled together.
Fig.2: Schematic representation of synthetic methods of nanomaterials

It is a field of interdisciplinary work confining chemistry, physics and engineering including medicine 

6.     Methods of creating nanostructures:

There are many various methods  of synthesizing nanostructures. Some of them are given below:

Mechanical grinding:

Mechanical grinding is done by ‘top down’ method of creating nanomaterials. In this method coarser-grained structure is decomposed by severe plastic deformation. This is one of the best method for creating nanocrystalline materials and it is relatively simple and inexpensive method and materials of all classes can be synthesized by this method The major advantage often quoted is the possibility for easily scaling up to tonnage quantities of
material for various applications. But it has two major problems
1. Contamination may occur from milling media and atmosphere
2. Powder consolidation may occur without coarsening microcrystalline material
Therefore this method is dismissed for some material due to above mentioned problems.
Fig.3: Schematic illustration of principle of mechanical milling

 Wet Chemical Synthesis of Nanomaterials

In principle the wet chemical synthesis of nanomaterials can be classified into two major groups:
1. The top down approach: where single crystals are chiseled in an aqueous solution for creating nanomaterials, For example, electrochemical etching is used for synthesizing porous silicon.
2. The bottom up approach: which consists of precipitation, sol-gel method etc. where a colloidal solution is formed by mixing the materials of desired precursors in a controlled fashion.

 Sol-gel process

The sol-gel method forms the basis of evolution of inorganic network by forming colloidal suspension (sol) and by forming continuous liquid phase (gel) through gelation of sol. Usually metals or metalloids having reactive ligands are used as precursors to synthesize these colloids. Dispersible oxide is formed by processing the starting material and then forming the sol in water or dilute acid. Gel is formed by removal of water from sol and the particle shape and size is controlled by sol/gel transition. The oxide is produced by calcination of sol.
Sol-gel processing involves the hydrolysis and condensing the alkoxide-based precursors eg. tetraethyl orthosilicate (TEOS). The reaction is as fellows:
H2O + MOR  → ROH + MOH (hydrolysis)
ROM + MOH → ROH + M-O-M (condensation)
where MOR refers to metal alkoxide
Sol-gel method of creating nanomaterials is much popular among chemists and is extensively employed to synthesize oxide materials. The sol-gel method can be descibed by a series of steps.
Fig.4: Schematic illustration of sol-gel process

1. Preparation of various rational solutions of the solvated metal precursor or alkoxide.
2. Gelation results from the plycondensation reaction of an oxide- or alcohol- bridged network (gel) resulting in a considerable increase in the solution’s viscosity.
3. The next step is aging of the gel referred as Syneresis which is done by polycondensation reactions and continue for gel transforms into a solid mass, followed by contracting the gel network and exclusion of solvent from gel pores. Ostwald ripening and phase transformations may happen contemporary with syneresis. The process of gel aging may occur in 7 days or more and is essential to prevent the cracks in gels.
4. Aging is followed by drying of the gel, which is done by removing the water and volatile liquids from the gel network. This process consists of four definite steps: (i) the rate period, (ii) the hypercritical point, (iii) the first falling rate period, (iv) the second falling rate period.
5. Dehydration, which is followed by removal of surface- bound M-OH groups and preventing the gel from rehydration. This is done by calcination of monolith accompanied at temperatures exceed from 8000C.
6. The last step is decomposition and densification of the gels accompanied at high temperatures exceed from 8000C
The main advantage of this process is preparing the non-metallic inorganic materials like ceramic materials, glasses, glass ceramics at very low temperature in comparison to high temperature process which involves the firing ceramics or melting glass.

 Flame assisted ultrasonic spray pyrolysis

This process involves the nebulization of precursors and then flame is used for burning the unwanted components to obtain required material such as ZrO2 has been prepared by this process using precursor of Zr(CH2CH2O)4
The main idea of  this process is low pressure combustion flame synthesis which extends the pressure range for using in gas phase synthesis and thus minimize the agglomeration. Low pressure flames have been considerably utilized by aerosol scientists for studying the particle formation in the flame.

7.     Properties of Nanomaterials:

Nanomaterials have intermediate structural characteristics between atoms and bulk materials. They exhibit properties significantly different from atom and bulk material. This is mainly due to
Ø  Large surface area to volume ratio
Ø  High surface energy
Ø  Reduced imperfections
Ø  Spatial confinement
Some of the extra-ordinary important properties of nanomaterials are given below:

Optical properties

One of the most interesting and useful features of nanomaterials is their optical properties. The important applications of optical properties of nanomaterials consists of optical detector, sensor, laser, maging, display, phosphor, solar cell, photoelectrochemistry, photocatalysis and biomedicine.
Their optical properties mainly based on features such as size, surface, shape, and other different characteristics which includes interaction and doping with the surrounding environment or nanostructures. Similarly, shape can have considerable influence on optical characteristics of metal nanostructures. Fig. () differentiates between the optical properties of semiconductor nanoparticles and metals. A simple change in size of CdSe semiconductor nanomaterial can alter the opticals properties of nanomaterials. The optical properties of nanomaterials can be changed dramatically by adding an anisotropy to the nanomaterials such as growth of nanorods.

 Electrical Properties

Electrical properties of nanomaterials include electrical conductivity in nanorods and nantubes, photoconductivity of nanorods, carbon nanotubes, electrical conductivity of nanocomposites. One fascinating method which can be adopted to exhibit the steps in conductance is measurement of the electrical current at a constant applied voltage and the mechanical thinning of a nanowire.

   Mechanical Properties

“Mechanical Properties of Nanomaterials” deals with ceramic and bulk metallic materials, effect of porosity, effect of grain size, filled polymer composites, superplasticity, particlefilled polymers, carbon nanotube-based composites, polymer-based nanocomposites filled with platelets. Because of their mechanical properties, nanomaterials have achieved much industrial importance.
The mechanical properties of nanomaterials can be greatly improved by filling polymers with nanorods or nanoparticles and nanotubes. These properties are significantly depend upon the type of filler and the method of filling. Composite which consists of a polymer matrix and defoliated phyllosilicates show exceptional mechanical and thermal properties.

   Magnetic properties

Some materials are non-magnetic at bulk but becomes magnetic at nano size such as bulk Pt and gold are non-magnetic but becomes magnetic at nano size. The surface atoms of nanomaterials are different from bulk atoms due to modifying by interaction with other chemical specie which is done by capping the nanomaterial.
This fact allows us to alter the physical properties of nanomaterials by capping them with suitable molecules. This phenomenon makes it possible to convert non-ferromagnetic bulk material into ferromagnetic at nano size.

8.     Important Applications of nanomaterials

Nanomaterials having vast range of applications in the field of fuel cells, electronics, batteries, food industry, medicines, and agriculture etc. It is obvious that nanomaterials cleave their conventional counterparts due to their superior physical, chemical and mechanical properties and of their extraordinary formability.

 Fuel cells:

A fuel cell is an electrochemical cell which converts the chemical energy into electrical energy. The working of fuel cell depends upon the electrodes. By modifying the physical structure and by utilizing the more active electro catalyst, the working of fuel cell electrode can be optimized.

 Carbon nanotubes - Microbial fuel cell

Microbial fuel cell is an instrument in which bacteria absorb water-soluble waste such as starch, sugar and alcohols and generate electricity in addition to clean water.
Carbon nanotubes can be used to built microbial fuel cells due to their good mechanical properties, chemical stability and high surface area. Because of high electrode surface area for growth medium and three dimensional architectures, bacteria can easily grow, proliferate and become immobilized. Carbon nanotubes and multi walled carbon nanotubes offers biocompatibility for various eukaryotic cells.
Fig.5: Schematic diagram of microbial fuel cell

       Catalysis

Nanomaterial counterparts have higher surface area, nano-catalysts offers extraordinary surface activity.
Nano-aluminium provides such high reaction rates that it is used as a solid-fuel in rocket propulsion. Furthermore surface activity assists catalyst accelerating or retarding reaction rates and are used in operating rate-controlling steps.

      Phosphors for High-Definition TV

The size of the pixel determine the resolution of  a monitor, a television. The material which is used for the formation of pixels are phosphors which shows fluorescence when a beam of electrons strike with them inside cathode ray tube. By reducing the size of phosphors, the resolution can be improved. The resolution of televisions and monitors can be greatly improved by using nanocrystalline zinc sulphide, cadmium sulphide, zinc sulphide and lead telluride. The utilization of nanophosphors help greatly in reducing the cost of personal computers and high definition televisions.

      Computer Chips of Next-Generation:

The microelectronics industry now emphasizes miniaturization in which size of circuits such as resistors, transistors and capacitors are reduced. However there are many technological limitations in addition to advancements such as poor dissipation of several amount of heat produced by these microprocessors and short mean time to failures etc.. These barriers can be greatly solved by nanomaterials providing high purity material having durable, long-lasting interconnections between dfferent components of microprocessors and having better thermal conductivity.

    Junctionless transistors by nanowires:

The tiny size of transistors reduces the sizes of electronic devices but it is very challenging to alter the doping concentration of a material over distances smaller than 10nm. Now researchers have successfully make the junctionless transistors which have ideal electrical properties. It could comparatively work faster and utilize less power than conventional transistors. The devices are made of a silicon nanowire in which flow of current is controlled by a silicon gate which is partitioned from nanowire by thin insulating layer. The whole silicon nanowire is n-doped, which makes it excellent conductor. The silicon gate is p-doped which can deplete the number of electrons in nanowire region under gate. It operates at faster rate and utilizes less energy and free from current leakage.

Fig.6: Schematic diagram of microbial fuel cell


Elimination of Pollutants


The grain boundaries of nanomaterials are larger than their grain size. So nanomaterials are extremely active in terms of their physical, chemical and mechanical properties. Because of their potential chemical activity, nanomaterials are using as catalysts for reacting with toxic and noxious gases such as oxides of nitrogen and carbon monoxide in catalytic converters of automobiles and other power generation equipments for prevention of environmental pollution.

  Sun-screen lotion

Skin-burns and cancer are the leading effects of prolonged UV exposure. Nano-TiO2 are used to prepare sun-screen lotions which provides potential sun protection factor without stickiness. They protect the skin without penetrating into the skin. Moreover, they have transparency, thus natural skin colour is retained.

      Sensors

Sensors are the highly active substances which can response to a minute change in specie’s concentration which have to be detected. Sensors having engineered monolayers of nanomaterials on their surfaces have specific functionality and are used in sensing.

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