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CHAPTER 1

INTRODUCTION

1.1 COMPOSITES

Composite materials are prepared from two or more constituent

materials with significantly different properties when compared with the

property of its individual components. Matrix and reinforcement are two main

categories of constituent materials. The matrix material surrounds and

supports the reinforcement materials by maintaining their relative positions.

The reinforcements impart special mechanical and physical properties and

hence enhance the matrix properties. A synergism produces material

properties unavailable from the individual constituent materials, while the

wide variety of matrix and strengthening materials allow the designer of the

product or structure to choose an optimum combination.

1.1.1 Activated Carbon (Matrix)

Matrix is defined as materials which can bind together the

reinforcing fibers of a composite. Advanced composites use specially

formulated polymers, ceramics, and carbons as matrix.

There are several allotropes of carbon, among which the best

known are graphite, diamond and amorphous carbon. Activated carbon is a

low crystalline form of carbon which has high surface area and its types are

shown in Figure 1.1. Hence activated carbon is an effective adsorbent

primarily due to its extensive porosity and very large available surface area.

Figure 1.2 reveals important techniques such as carbonization, oxidation and

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chemical activation involved in activation of normal carbon for increasing

porosity and also the porous structure of activated carbon is shown in Figures

1.3 & 1.4.

Figure 1.1 Classification of activated Carbon Based on their Physical

Characteristics

Figure 1.2 Types of Process of Activation of Carbon Containing raw

material using Physical (a and b) and Chemical Activation (c)

Activated carbon

(1) Powder activated carbon (PAC)(2) Granular activated carbon (GAC)(3) Extruded activated carbon (4) Bead activated carbon (5) Impregnated carbon(6) Polymer coated carbon

Pyrolysis of carbon containing material in presence of inert atmosphere at 600-900 oC(a) Carbonization

Calcination of Carbon containing raw material in presence of oxygen atmosphere in the range of 300 - 400 oC

(b) Oxidation

Raw material is impregnated with certainchemicals such as KOH, NaOH, H3PO4,CaCl2 and ZnCl2 etc., and it is calcined atlower temperature. It is preferred overphysical activation owing to the lowertemperature and shorter time for activatingmaterial.

(c) Chemicalactivation

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Figure 1.3 Diagram of Porous Structure of Activated Carbon

Figure 1.4 Diagram of Structure of Activated Carbon

Generally, some hazardous organic pollutants like phenol, synthetic

dyes etc., are removed from aqueous medium by the process of oxidation,

precipitation, ion exchange and solvent extraction. However, in water

treatment, the most widely used technique is adsorption onto pores of

activated carbon. Activated carbon is widely used as adsorbent for the removal

of a wide range of pollutants because of its high adsorption capacity, fast

adsorption kinetics and ease of regeneration. Activated carbon is a complex

and heterogeneous material made of wood, coconut shells, coal, etc with

unique adsorptive characteristics mainly influenced by the porous structure,

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surface area and chemical structure of the surface (Jung et al 2001). Many

researchers have tried to produce activated carbon for removal of various

pollutants using renewable and cheaper precursors which were mainly

industrial and agricultural byproducts, such as coconut shell (Radhika and

Palanivelu 2006), sugar beet bagasee (Onal et al 2007), molasses (Legrouri

et al 2005), waste apricot (Basar 2006), rubberwood sawdust (Prakash kumar

2006), rice straw (Wang et al 2007), bamboo (Hameed 2007), rattan sawdust

(Hameed 2007), oil palm fibre (Tan et al 2007) and coconut husk (Tan et al

2008). Activated carbon offers an attractive and inexpensive option for the

removal of organic and inorganic contaminants from water (Pignon et al 2000

and Lua et al 2001). Due to its high surface area and porous structure, it can

efficiently adsorb gases and compounds dispersed or dissolved in liquids

(Matson and Mark 1971). The adsorption of several organic contaminants in

water, such as pesticides, phenols and chlorophenols, has recently been

reported (Baup et al 2000, Garner et al 2001, Martin and Font 2001, Jung

2001, Denizili, 2001, Aksu and Yener 2001, Daifullah 1998). Moreover,

activated carbon can easily be functionalised and used as an efficient

adsorbent for heavy metal cationic contaminants (Shim et al 2001).

1.1.2 Nano- Reinforcements and their Types

In the common view, a composite material is composed of

reinforcement (fibers, particles, flakes, fillers) embedded in a matrix

(polymers, metals, ceramics). The matrix holds the reinforcement to form the

desired shape, while the reinforcement improves the overall mechanical

properties of the matrix. When designed properly, the new combined material

exhibits better strength than would each individual material.

Reinforcing material provides the strength that makes the

composite what it is. They also serve certain additional properties such as

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resistance to heat or conduction, resistance to corrosion and provide rigidity.

Reinforcement can be made to perform all or one of these functions as per the

requirements. In other words, a reinforcement that embellishes the matrix

strength must be stronger and stiffer than the matrix and capable of changing

failure mechanism to the advantage of the composite. Reinforcing materials

and its types are shown in Figure 1.5.

Figure 1.5 Types of Reinforcements in Composite Materials

Nowadays, nano metal oxides are used as reinforcements to

improve the physical properties and its applications in the various

technologies. For example, metal oxides such as -Fe2O3 (Oliveira et al 2002),

NiO (Yuan et al 2005), MnO2 (Ko and Kim 2009) and RuO2 (Ramani et al

2001) etc.,

1.1.2.1 Iron oxide nanoparticles

Iron oxide nanoparticles ranges from 1 to 100 nm in diameter and

various types of iron oxides and oxyhydroxides nanoparticles are shown in

Figure 1.6 Magnetite (Fe3O4 -Fe2O3) are the two main

oxides among all iron oxides. They have attracted extensive interest of the

current researches due to their superparamagnetic properties and their potential

applications in many fields. Though the oxides of Co and Ni are also highly

magnetic in nature, they are avoided due to their toxic in nature.

Reinforcements

FlakesMetal oxides

FibresCarbon materials

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1.1.2.1.1 Basic structure

Magnetite, Fe3O4 is a ferromagnetic mineral containing both

Fe(II)/Fe(III) and it is black in color. In stoichiometric magnetite of

Fe(II)/Fe(III) is 0.5 but non-stoichiometric is formed often in magnetite due to

the cation deficient Fe (III) layer. The crystal structure of magnetite is inverse

spinel with a unit cell consisting of 32 oxygen atoms in a face-centered cubic

structure and a unit cell edge length of 0.839 nm. Moreover, Fe(II) and half of

the Fe(III) ions occupy octahedral sites and the other Fe(III) half occupies

tetrahedral sites. Because Fe(II) mostly prefers to occupy octahedral sites due

to high CFSE, while the Fe(III) has a CFSE=0 in both octahedral and

tetrahedral sites. The crystal form of magnetite includes both octahedron and

rhombodecahedron and the specific surface area ranges from 4 100 m2/g

(Cornell and Schwertmann 2003).

-Fe2O3, is isostructural with

-Al2O3. Three-dimensional framework is built up in its structure

with trigonally distorted octahedral FeO6, linked to thirteen neighbours by one

-Fe2O3 structure, Fe(III) ions are in

octahedral coordination with oxygen atoms in hexagonal closest-packing and

also it can be explained as the stacking of sheets of octahedral coordinated

Fe(III) ions between two closely packed layers of oxygen. Since iron is in Fe+3

state, two Fe(III) ions are bonded with only oxygen atom and hence only two

of the three available oxygen octahedrons are occupied. This arrangement

makes the compound neutral with no charge excess or deficit. The Fe-O sheets

are held together by strong covalent bonds. The crystal system of hematite is

hexagonal, but they appear in a wide variety of forms. The specific surface

area ranges form 10-90 m2/g (Cornell and Schwertmann 2003).

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Figure 1.6 Sixteen known iron Oxides and Oxyhydroxides

FeO, Wurtzite crystallizes in the NaCl structure containing four

formula units in cubic unit cells. The large O2- anions form a close packed fcc

sub-lattice with the small Fe(II) cations located in the interstitial sites. All

Fe(II) are octahedrally coordinated to oxygen. Bond length between Fe and O

is 2.16 Å (Cornell and Schwertmann 2003). -FeO(OH) exhibits an

orthorhombic symmetry, space group Pnma (No 62). Crystal parameters are: a,

b and c are 9.95, 3.01 and 4.62 Å respectively. The specific surface area

ranges from 8 to 200 m2/g (Cornell and Schwertmann 2003).

1.1.2.1.2 Magnetic Properties

Due to its 4 unpaired electrons in 3d shell, an iron atom has strong

magnetic moment. Unpaired electrons of Fe2+ and Fe3+ in 3d shell are 4 and 5

respectively. Hence, when crystals are formed from iron, such as Fe2+ and Fe3+

Iron oxides and oxyhydroxides nanoparticles

Oxides:1. iron(II) oxide (FeO)2. iron(II, III) oxide (Fe3O4)3. iorn(III) oxide (Fe2O3)4. hematite ( -Fe2O3)5. beta phase ( -Fe2O3)6. gamma phase, ( -Fe2O3)7.epsilon phase, ( -Fe2O3)

Hydroxides:1. iron(II) hydroxide (Fe(OH)2)2. iron(II) hydroxide (Fe(OH)2)Oxide/hydroxide: 1. goethite ( -FeOOH)2. akaganeite ( -FeOOH)3. lepidocrocite ( -FeOOH)4. feroxyhyte ( -FeOOH)5. ferrihydrite (Fe5HO8.4H2O approx.),

or 5Fe2O3.9H2O,better recast as FeOOH.0.4H2O

6. high-pressure FeOOH7. schwertmannite

(ideally Fe8O8(OH)6)(SO)nH2O)

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ions, they can be in ferromagnetic, antiferromagnetic or ferrimagnetic state. In

the paramagnetic state, all the magnetic moments are randomly oriented, and

hence the crystal has a zero net magnetic moment. These crystals have a small

net magnetic moment when an external magnetic field is applied, and the

magnetic moment is zero when the field is removed. In a ferromagetnic

crystal, all the magnetic moments are aligned even without an external

magnetic field. In a ferrimagnetic crystal, two types of atoms with different

magnetic moments are aligned in an antiparallel fashion, and the antiparallel

moments have different magnitudes. Both magnetite and maghemite iron

oxides are ferrimagnetic. When an external magnetic field is applied to

ferromagnetic material, the magnetization (Ms) increases with the strength of

the magnetic field (H) and approaches saturation. Over some range of fields,

the magnetization has hysteresis because there is more than one stable

magnetic state for each field. Therefore, a remenent magnetization will be

present even after the removal of external magnetic field. A single domain

magnetic material that has no hysteresis loop is said to be superparamagentic

in nature. The order of magnetic moments in ferromagnetic, antiferromagnetic

and ferrimagnetic materials decreases with increasing temperature. Both

magnetite and maghemite nanoparticles are super-paramagentic at room

temperature. This superparamagnetic behaviour of iron oxide nanoparticles

can be attributed to their size. When the size gets small enough (<20 nm),

thermal fluctuation can change the direction of magnetization of the entire

crystal.

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Figure 1.7 Important Techniques for Synthesis of Iron Oxide

1.1.2.1.3 Synthesis methods

Essential techniques for synthesis of Iron oxide nanoparticles are

shown in Figure 1.7. Chemical precipitation method is probably the simplest

and most efficient pathway to obtain iron oxide particles. Iron oxides

(FeOOH, Fe3O4 -Fe2O3) are usually prepared by addition of alkali to iron

salt solutions such as sulphate, chloride etc., and keeping suspensions for

ageing. The main advantage of this method is large quantity of nanoparticles

can be synthesized with a particle size controlling phenomenon, which would

not be good when compared with other techniques like thermal decomposition

and hydrothermal synthesis. Pure goethite was prepared using iron(III) nitrate

and 10 M sodium hydroxide solutions under controlled conditions. NaOH was

added to Fe(III) solution until pH of 12-12.5 is reached. Transition metals such

as Cu, Ni and Co were doped with goethites by mixing respective sulphate

solution with iron(III) nitrate prior to alkali addition. On the heating the

Ce(IV)/Fe(III) samples to 400 oC, goethite was entirely transformed to

hematite, while the CeO2 was only partially. Nanostructures of CeO2- -Fe2O3

oxides were retained even on calcinations upto 800 oC (Mohapatra et al 2003,

Mohapatra et al 2005a, Mohapatra et al 2005b, Sahoo et al 2009).

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The first attempt of controlled preparation of super-paramagnetic

iron oxide particles using alkaline precipitation of Fe(II) and Fe(III) chlorides

was performed by Massart (1981). For rapid synthesis of homogeneous

-Fe2O3 nanoparticles, a wide range of monomeric species, such as amino

acids, R-hydroxyacids (citric, tartaric, and gluconic acids) (Fauconnier et al

1996) hydroxamate (arginine hydroxamate) (Fauconnier et al 1999),

dimercaptosuccinic acid (DMSA) (Fauconnier et al 1997) and phosphoryl

choline (Denizot et al 1999) were used. Bee et al (1995) reported that addition

of excess amount of citrate ions in the Massart process allowed a decrease in

the diameter of citrate-coated nanoparticles from 8 to 3 nm and with the same

procedure by adding NaCl as an extra electrolyte, the size of the nanoparticles

could be reduced below 7 nm (Massart et al 1995 and Cabuil et al 1995).

Jolivet et al (1994) and Babes et al (1999) studied the influence of ratio of

Fe(II)/ Fe(III) and different parameters including solvent medium respectively,

on the composition, size, morphology and magnetic properties of co-

precipitated nano-scale particles. The dependence of mean size of magnetite

particles upon the acidity and the ionic strength of the precipitation medium

have been reported (jiang et al 2004 and jolivet, 2000). The higher pH and

ionic strength, the smaller the particle size and size distribution width will be,

because these parameters determine the chemical composition of the crystal

surface and consequently the electrostatic surface charge of the particles

(Tartaj et al 2006).

The dependence of ionic strength of the reaction solution on the

formation of magnetite by using 1 M aqueous NaCl solution which has created

iron oxide nanoparticles 1.5 nm smaller than those formed without NaCl was

investigated. Additionally, these smaller nanoparticles possess lower

saturation magnetization (63emu/g) than those prepared in NaCl-free solution.

Additionally, many factors may influence the size such as mixing rate of

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substrate, elevated reaction temperature (Sun and Zeng 2002) and nitrogen gas

atmosphere (Gupta and wells 2004 and Kim et al 2001).

The synthesis of metal oxide by sol-gel process has proven to be an

extremely versatile method, since it allows the formation of a large variety of

metal oxides at relatively low temperature via the processing of metal salt or

metal alkoxide precursors. The structure and composition of nano-oxides

prepared by sol-gel technique depend on the preparation condition, the nature

of the precursors, the ion source and pH. The sol-gel method involves the

synthesis of iron oxide materials from condensed ferric hydroxide gels,

obtained from FeCl3 solution in NaOH. After ageing for 8 days at 100 oC,

monodispers -Fe2O3 were formed (Sugimoto and Sakata 1992

and Sugimoto et al 1993) and this reaction takes place in two-step phase

transformation from precipitated Fe(OH)3 gel to a FeOOH and finally to

-Fe2O3 (Sugimoto and Sakata 1992). FeOOH was successfully prepared by

ageing of sol using Fe(III) salt and alkali solution (Pascal et al 1999). Plate

like hematite particles of about 5-

basic Fe(III) salt solution in the presence of either EDTA or KNO3 or

triethanolamine and hydrazine or hydrogen peroxide (Ozaki et al 1990). FeCl2

is used to synthesis of poly disperse magnetite microcrystals by KNO3/alkali

solution and spindle-type of colloidal hematite by phosphate/hypophosphate

have been reported (Ozaki et al 1984). These hematite particles can be

converted to maghemite with similar size and shape by heating under H2 gas

flow followed by re-oxidation with air (Ozaki and Matijevic 1985).

Hydrothermal technique is defined as any heterogeneous reaction in

the presence of aqueous solvents or mineralizers under high pressure and

temperature. Changing of pH during synthesis can play a vital role in

hydrothermal synthesis. In the range pH 8.0-10.0, 10.5-10.8 and 0.8-2.6, the

products were goethite/hematite, pure goethite and pure hematite respectively

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(Christensena et al 1968). In neutral and weakly alkaline medium at 150±20 o -Fe2O3 -FeOOH and this temperature

was suggested to be the upper temperature for the formation of the -FeOOH

minerals. However, the transformation is also strongly pH dependent so that

the transformation temperature increased by 25 K per pH unit (Robins 1967).

Christensena et al (2007) reported that the rate of crystallization of amorphous

Fe(III) hydroxide -Fe2O3 -FeOOH was made at hydrothermal

conditions using neutron powder diffraction. Ultrasonic-assisted hydrothermal

involves preparing goethite in flower like structures using Fe nano-powders at

85 oC (Chen et al 1998).

Hydrothermal synthesis of Fe3O4 particles has been reported

successfully by Zheng et al (2006). The hydrothermal synthesis of size

controlled Fe3O4 nanoparticles was carried out by Mizutani et al (2010) using

the starting solution containing lactate and sulfate ions at various

concentrations in order to control the particle size. The particle size was

controlled by means of the co-existence effects of lactate and sulfate ions.

Depending on their concentration, the particle size could be varied from 9.5 to

38.6 nm. Sun et al (2009) also reported the synthesis of size-controlled

magnetite nanoparticles in the range of 4-16 nm using ferric chloride with

glucose and gluconic acid. In this technique, sucrose was used for the

formation of nanoscale and coated magnetite instead of the much larger

hematite. Moreover sucrose acts as a bifunctional agent as it decomposes into

reducing species that help to form magnetite by the change of Fe3+ to Fe2+ ion

and it acts as the source of a capping agent to alter the surface properties and

enable the formation of nanoparticles. By adjusting the temperature in

hydrothermal synthesis, Dong et al (2009) have reported a selective synthesis

-Fe2O3 (at 150 o -FeOOH nanorods (at 200 oC) using ferrous

sulphate and H2O2.

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Supramolecular surfactant-controlled method for the synthesis of

mesostructured iron oxides has acquired more importance in recent scenario,

which uses neutral or charged template molecules. Hexa-decylsulfonic acid

mixed at room temperature with an aqueous solution of FeCl2 yielded a

hexagonal structured iron oxide with a d-spacing of 3.75 nm (Ciesla et al

- Fe2O3 have been synthesized (Liu et al 2006)

using different surfactant i.e., polyisobutylene (L113B) or surfactant Span80.

Deliyanni et al (2006) reported a hybrid nano crystalline surfactant modified

-FeOOH) sorbent which was prepared by using FeCl3 and

hexadecyltrimethylammonium bromide (cationic surfactant).

A microemulsion is a stable isotropic dispersion of two immiscible

liquids consisting of nanosized domains of one or both liquids in the other

stabilized by an interfacial film of surface-active molecules. Microemulsion

may be categorized further as oil-in-water (o/w) or water-in-oil (w/o),

depending on the dispersed and continous phase. Water in oil is more popular

for synthesizing many kinds of nanoparticles. The water and oil are mixed

with an amphiphillic surfactant which lowers the surface tension between

water and oil, making the solution transparent. The water nanodroplets act as

nanoreactors for synthesizing nanoparticles. The shape of the water pool is

spherical. The size of the nanoparticles depends on the size of the water pool

to a great extent. Thus, the size of the spherical nanoparticles can be tailored

and tuned by changing the size of the water pool. Microemulsion and inverse

micelles route can be employed for obtaining the shape and size controlled

iron oxide nanoparticles. Geng et al -FeOOH nanorods at

room temperature by using Pluronic triblock copolymer P123, poly

(ethyleneoxide)-block-poly(propyleneoxide)-block-poly(ethyleneoxide)

(EO20PO70EO20, Mav = 5800) -FeOOH

nanorods depends on the surfactant and high basic condition.

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Electrons act as reactant in electrochemical method and it is an

environmental friendly process with no pollution. However, platinum, which

is expensive, is used as an electrode and cannot be reused in aqueous solution.

The electrochemical synthesis of -Fe2O3 nanoparticles of about 20 nm in non-

aqueous medium was reported by Zhang et al (2007). Electrochemical

deposition under oxidizing conditions has been used to prepare nanowires of

by Kahn and Petrikowski (2000). Pascel et al (1999) have prepared 3-8 nm

maghemite particles by electrochemical method from an iron electrode in an

aqueous solution of dimethylformamide and cationic surfactants and in this

technique, current density controlled the particle size.

An aerosol technology, such as spray and laser pyrolysis, is

attractive because they are the continous chemical processes that allows high

rate production (Veintemillas-Verdaguer et al 2004). Maghemite particles with

size ranging from 5 to 60 nm and with different shapes have been obtained

using different iron precursor salts in alcoholic solution (Veintemillas-

Verdaguer et al 2001 and Veintemillas-Verdaguer et al 2002). Laser pyrolysis

can be used to reduce the reaction volume. Laser heats the gaseous mixture of

iron precursor and a flowing mixture of gas produces small, narrow size and

aggregated nanoparticles. This technique was performed in maghemite

synthesis with particle sizes less than 10 nm (Morales et al 2003).

The sonochemical method has been used to generate novel

materials with unusual properties. Highly mono dispersive nanoparticles have

been synthesized via chemical ultrasound. Sonochemical synthesis route have

been used for preparing nanosized hallow hematite, pure magnetite and

amorphous nanoscopic iron oxide successfully by Bang and Suslick (2007),

Vijaykumar et al (2000) and Pinkas et al (2008) respectively.

Superparamagnetic iron oxide nanoparticles (SPIO) having high

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magnetization with crystallinity (Kim et al 2005) and nanoparticles of Fe,

Fe3O4 and Fe2O3 have been prepared using a sonochemical method.

Figure 1.8 Applications of Iron Oxide Nanoparticles in Various

Fields

1.1.2.1.4 Applications

Iron oxides nanoparticles are of considerable interest due to their

wide range of applications in various fields and are shown in Figure 1.8. A

brief literature survey of application of various forms of nano iron oxides in

the above fields is discussed below.

Since prehistoric times, hematite and other iron oxides are used as

natural red ceramic pigments. Iron oxides such as magnetite, hematite,

maghemite and goethite are commonly used as pigments for black, red, brown

and yellow colours respectively. Predominantly natural iron oxides are used in

primers for steel constructions and cars that reduce corrosion problems. By

reducing the particle size to nano range, transparent iron oxide pigments can

be obtained. In the year 1992, science news have published that the

transparency of iron oxide increases 3-10 times when the nano-size ranges

Iron oxide nanoparticles

1. Colouring and coating material,2. Catalyst3. Gas sensing material4. Adsorbent material5. Electromagnetic material6. Biological application

Used

as

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from 2-10 nm. Thermal stability of red can extend up to 300 oC while the

yellow, black, green and brown can withstand upto 160 oC only. These oxides

are strong absorbers of ultraviolet radiation and mostly used in automotive

paints, wood finishes, construction paints, industrial coatings, plastic, nylon,

rubber and print ink (Sreeram et al 2006).

These oxides have been found to be good candidates as cheap and

efficient catalysts, especially in environmental catalysis. Miyata et al (1978)

studied the catalytic activity of several iron oxides and oxide hydroxides of

various particle sizes for the reduction of 4-nitro toluene using hydrazine

-FeOOH was the most effective

catalyst. From the literature, nanosize iron oxide is more efficient than micro-

size iron oxide (Walker et al 1988 and Li et al 2003) for the oxidation of CO

and the oxidative pyrolysis of biomass (Li et al 2003) or biomass model

compounds (shin et al 2004). These effects could be derived from the high

activity of nano-particles that have high BET surface area and more

coordination of unsaturated sites on the surfaces. Chemical and electronic

properties, such as phase changes, OH content, band gap etc., could also

contribute to their high reactivity. Catalytic activity of nano sized Au/Fe2O3 at

low temperatures on a CO oxidation reaction was investigated (Hutchings et al

2006). Sohn and Lim (2006) reported the dehydration of isopropyl alcohol and

dealkylation of cumene with the iron oxide related catalyst. Hence many

research work have been carried out in the catalysis field using iron oxide

related materials such as iron oxide/TiO2 for cyclohexane oxidation (Perkas et

al -pinene oxide isomerization (Neri et al 2004), o-cresol photo-

degradation (Pal et al 2001) and formation of dimethyl ether from methanol

(Wang and Ro 2006).

Many research articles have discussed the gas sensing behaviour of

various iron oxides using hydrocarbon gases, CO and alcohol (Lee and Choi

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1990, Peng and Chai 1993, Siroky et al 1994, Tianshu et al 1996, Tao et al

1999, Lim et al 2001, Neri et al 2006). Sensitivity has been investigated for

iron oxide after doping with Pd, Sn, Ti, Zn etc (Kanai et al 1992, Neri et al,

2002, Reddy et al, 2002, Vasiliev 1992, Tan et al 2003). Chitosan based iron

oxide nanocomposite have been used for glucose biosensor and urea sensor

(Kaushik et al 2008; Kaushik et al 2009). Abolanle et al (2010) have reported

that iron oxide particles were used for sensing toxic biological drug like

dopamine.

Iron oxides have relatively high surface area and surface charge,

therefore, often regulate free metal and organic matter concentrations in soil or

water through adsorption reactions (Barrow et al 1989, Manceau et al 2000,

Randall et al 2001). Many toxic cations (Co, Zn, Pb, Cd, Cs, U, Sr etc.) and

anions like AsO43-, CrO4

2-, PO43-, CO3

2- etc., are removed by using various

phases of iron oxide (Benjamin and Leckie 1981, Todorovic et al 1992, Ding

et al 2000, Zhou et al 2001, Luengo et al 2006, Mohapatra et al 2006). The

adsorption properties of the iron oxide is due to combination of both surface

complexation by inner or outer sphere bonding with adsorbate and ion

exchange by Vander Wall forces. Nanoparticles have high surface area to

volume ratio, which enhances the interaction with several kinds of chemical

species, both gaseous and aqueous (Hiemstra et al 2004). Metal ion adsorption

process depends on the size of the metal oxide because nano-metal oxide has

more efficient for binding it and so iron oxide nanoparticles are good magnetic

adsorbent, which is used in adsorption of metal ions from industrial wastes or

natural water streams. Moreover, magnetic separation has been shown to be a

useful solid-solid phase separation technique. Formation of large aggregates in

magnetic materials is a problem due to interaction with each other. However,

when its size will be reduced to nano range, they become superparamagnetic.

When field is applied, the particles acquire certain magnetization but, because

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of the high thermal energy, the long range order is lost when the field is

removed, and the particles have no remanent magnetization (Uheia et al 2006).

This makes magnetic nanoparticles as excellent candidates for combining

metal binding and selective adsorption properties with ease of phase

separation. Current studies have been reported on removal of dipositive

cations of Pb, Cd, Cu and Zn by nano structured doped goethite (Mohapatra et

al 2009), ferrihydrite (Mohapatra et al 2011a) and akaganeite (Mohapatra et al

2010a) synthesized using different precipitation techniques. Nano goethite

(Mohapatra et al 2010b), nano powders of mixed metal iron oxides

(Mohapatra et al 2011b) and nano Al/Fe mixed and pure oxides (Sujana et al

2009 and Sujana et al 2010) have been reported to be good adsorbents for the

removal of fluoride from aqueous solutions and contaminated ground water.

Cu, Ni and Co doped nano goethites were found to be quite effective for

arsenic removal from aqueous solutions (Mohapatra et al 2006).

Magnetic iron oxide nanoparticles have been studied for many

years for their application as magnetic storage media and ferro-fluids. From

-Fe2O3, a ferromagnetic material is widely used as magnetic

storage media in audio and video recording, magneto-optical devices (Goya et

al 2003 and Kawanishi et al 1997), magnetic refrigeration (Mcmichael et al

1992) where as -Fe2O3 in nano-size is a potential candidate as photo anode

for possible photo-electrochemical cells (Prosini et al 2002 and Wang et al

2004a). Recently studies have been reported on Fe-based nano-compounds, as

positive cathode materials for Li-ion batteries due to the low-cost and non-

toxicity (Lindgren et al 2002, Wang et al 2004b, Liu et al 2009). A novel

-

of iron oxide-based nanotube arrays including hematite and magnetite was

reported by Liu et al (2010). By introducing glucose into the precursor

solution, they obtained carbon/hematite composite nanotube arrays on large-

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area flexible alloy substrate, with large number of pores and uniform carbon

distribution with nanoscale in the nanotube walls. These materials have good

cyclic performance upto 150 times (659 mA h g-1) and outstanding rate

capability.

Biomedical applications of iron based magnetic nanoparticles

(MNPs) are classified according to their application inside (in vivo) or outside

(in vitro) the body. In vivo applications could be further separated in

therapeutic (hyperthermia and drug targeting) and diagnostic applications

(nuclear magnetic resonance (NMR) imaging), while for in vitro applications,

the main use is in diagnostic (separation/selection and magneto-relaxometry).

Aqueous magnetic fluids composed of small magnetic particles about 5-20 nm

covered with biocompatible functionalized shells are well known for their use

in hyperthermia, as immuno assays, and for transportation of drugs to the

places of diseases (Reimer and Weissleder 1996, Bonnemain 1998, Rogers et

al 1999 Babincova et al 2001, Wang et al 2001, Arbab et al 2003, Pankhurst et

al 2003). Ferrofluids are magnetic suspensions which can interact with an

external magnetic field and be positioned to a specific area, facilitating

magnetic resonance imaging for medical diagnosis and AC magnetic field-

assisted cancer therapy. Such a magnetic suspension has been prepared by a

proper surface coating of magnetite nanoparticles and was dispersed into

suitable solvents, forming homogeneous suspensions, called ferrofluids

(Babincova et al 2001). Several iron oxide based cell labeling techniques have

been developed including conjugation with antigen-specific internalizing

monocolonal antibody, modification of USPIO (Ultra small super

paramagnetic iron oxide) or MION (mono crystalline iron oxide nanoparticles)

with tat-proteins facilitating the incorporation into the cells (Hafeli et al 1997,

Josephson et al 1999, Lewin et al 2000, Bulte et al 2001). Active research

work is continuing in finding suitable biomedical applications of versatile iron

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oxides in the nano scale both for drug release and drug delivery (Kubo et al

2001, Frank et al 2003, Gonzales et al 2005, Cengeli et al 2006, Aslam et al

2007, Naka et al 2008, Piao et al 2008, Guo et al 2009, Mahmoudi et al 2009;

Zheng et al 2009, Tran et al 2010). Engineered fluorescent superparamagnetic

iron oxide nanoparticles (SPIONs) were coated with polyvinyl alcohol (PVA)

functionalized with a fluorescent reporter molecule and were administered to

the microglia cell culture containing immune cells of the nervous system.

Mahmoudi et al (2009) prepared iron oxide NPs with a cross-linked poly

(ethylene glycol)-co-fumarate (PEGF) coating. The cross-linked PEGF coating

reduced the burst release by 21 % in comparison with the noncross-linked

tamoxifen loaded particles. Mono-disperse SPIONs with a mesoporous

structure were prepared via simple solvothermal method by Guo et al (2009)

for studying loading and release behaviour of anticancer drug, (Doxorubicin,

Dox). The release behaviour of Dox indicated that these SPIONs had a high

drug loading capacity and favourable release kinetics for this drug. Similar

studies have been carried out for targeted delivery applications (Kubo et al

2001, Gonzales et al 2005). Most of polymeric coatings in SPIONs are

selected from hydrogel categories. Permeability, temperature sensitivity, pH

sensitivity, osmolarity sensitivity, surface functionality, swelling,

biodegradability, and surface biorecognition sites are recognized as major

factors for controlled drug release applications of hydrogels. Tran et al (2010)

reported that magnetic nanoparticles have been used to treat bone diseases

(such as osteoporosis and infection) by using surface modified magnetic

nanoparticles.

21

1.1.2.2 Manganese oxide nanoparticles

1.1.2.2.1 Basic structure and magnetic properties

Hausmannite Mn3O4 is known to have a normal spinel structure

with tetragonal distortion elongated along the c-axis due to Jahn-Teller effect

on the Mn3+ ion. Manganese ions occupy the octahedral B-site (Mn3+) and

tetrahedral A-site (Mn2+) corresponding to a normal spinel structure. There are

32 oxygen and 24 cations in the unit cell (Fritsch et al 1998). Bulk Mn3O4

exhibits a tetragonal Jahn-Teller distortion at the Mn3+ site at high temperature

to the I41/amd space group (Regmi et al 2009).

Ozkaya et al., (2008) reported the superparamagnetic nature of

Mn3O4 nanoparticle at room temperature, with no apparent saturation

magnetization, and hysteresis in the region of measured field strength, and

they also exhibit relatively large coercivity below the ferromagnetic transition

temperature. Below the transition, marked differences are observed in

temperature dependence of magnetization, hysteresis loop shape, and type of

the samples from the bulk values. These nanoparticles are considered as single

magnetic domains with random orientations of magnetic moments and thermal

fluctuations of anisotropic axes. These results are attributed to the smaller size

(increase in surface to volume ratio) of the samples, which cause an increase

of effective magnetic surface anisotropy.

The magnetic measurements were carried out on the Mn3O4

prepared using manganese acetate precursor in sodium hydroxide under

ultrasonic irradiation (Bastami and Entezari 2012). These measurements as a

function of temperature and field strength showed a reduction in ferrimagnetic

temperature (Tc = 40 K) as compared to those reported for the bulk (Tc = 43

K). The superparamagnetic behavior was observed at room temperature with

22

no saturation magnetization and hysteresis in the region of measured field

strength.

1.1.2.2.2 Synthesis methods

Mn3O4 nanoparticles were successfully prepared by a novel

oxidation-precipitation method based on oxidation of manganese sulfate and

hydrolyzing with NaOH and concentrated ammonia (Ozkaya et al 2008).

Olmos et al (2005) reported that the Mn3O4 is used as catalyst to limit the

emission of NOx and CO, which provides a powerful method of controlling air

pollution. Mn3O4 powder is used for selective oxidation and reduction of

nitrobenzene (Grootendorst et al 1995 and Baldi 1998) and in rechargeable

lithium batteries (Sanchez 1996 and Thackeray et al 1983). Moreover,

hausmanite nanoparticles have corrosion-inhibiting pigment of

epoxypolyamide and epoxy-ester gassed primers (Wang et al 2002, Zhang et

al 2004, Weixin et al 1999) as top coating and used as electrochromic

materials for anodic coloration (Torresi and Gorenstein 1992). Mn3O4

nanoparticles have been successfully obtained via a facile hydrothermal

treatment, in which newly prepared amorphous MnO2 nanoparticles with its

mother-solution are directly used as precursor. This work firstly shows that

MnO2 can be transferred into monodisperse Mn3O4 polyhedron nanoparticles

with 60-80 nm via a suitable hydrothermal process, and reveals MnOOH

nanorods is an important intermediate. During the formation of Mn3O4

nanoparticles, the crystal phase growth and shape change are reasonably

illuminated by a dissolution-recrystallization mechanism. The as-prepared

Mn3O4 nanoparticles show super-paramagnetic character due to the small size

effect (Zhang et al 2010). Mn3O4 nanostructural materials with different shape

and size have been prepared by various methods. From the literature,

polyhedral nanocrystals were prepared by a microwave-assisted solution-

based method (Yang et al 2006), tetragonal nanoparticles were synthesized

23

using a mild solution method (Wang et al 2007), hexagonal nanoplates were

synthesized via a solvent-assisted hydrothermal oxidation process (Ahmed

et al 2010), thin films were prepared by novel chemical successive ionic layer

adsorption and reaction method (Dubal et al 2010). Mn3O4 nanorods have

been prepared successfully using surfactant (C18H29NaO3S) and alkaline

solution based on self-catalysed solution-liquid-solid mechanism. These

nanorods appear as very smooth, straight and perfect geometrical shape, with

100 nm to a few micrometers of length and 10-30 nm range of diameter and

this result depends on dripping speed of alkali solution (Chen et al 2005). The

hierarchical structure of Mn3O4 with radiated spherulitic nanorods was

prepared via a simple solution-based coordinated route in the presence of

macrocycle polyamine, hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene

(CT) with the assistance of thiourea as an additive (Wu et al 2007). Mn3O4

polyhedral nanocrystals was prepared by a microwave-assisted solution-based

method using manganese acetate and (CH2)6N4 at 80 oC (Yang et al 2006).

Mn3O4 nanocrystals were synthesized by one-pot pathway, using surfactants

such as CTAB, PVP and P123 as structure-directing agents and manganese

sulfate hydrate as metal precursor. The size and shape of the nano-crystals

were easily controlled by varying the synthetic parameters. The change of

reaction temperature from the range of 75-80 oC and 85-150 oC yields

amorphous nature and octahedral nanocrystals respectively and its application

were studied in the degradation of methylene blue (Zhang et al 2010).

1.1.2.2.3 Applications

It is a well-accepted concept that the chemical and physical

properties of nano-structured materials strongly depends on their shape and

size. Therefore, nanometer-sized Mn3O4, with notably increased surface area

and greatly reduced size are expected to display better performance in these

aspects of application. Manganese oxides and oxy-hydroxides have been paid

24

more attentions as important multifunctional and extensive utilized-prospects

materials. Manganese oxides nano-materials show excellent supercapacitive

charteristics with high values of specific capacitance, catalysis and magnetic

properties (Zhang et al 2008, Subramanian et al 2005, Cui et al 2005).

Manganese oxides have been the focus of researchers due to their novel

chemical/physical properties and potential applications in the areas of

catalysis, electrochemistry and magnetic materials. Among them, hausmannite

Mn3O4 is known to be a good electrochemical material, high density magnetic

storage medium, catalyst, ion-exhange, adsorbent etc., (Bernard et al 1993,

De vries et al 2002, Yamashita et al 2002), efficient catalyst for the

decomposition of waste gas (Yamashita et al 1996), the oxidation of methane

and carbon monoxide (Stobhe et al 1999), the selective reduction of

nitrobenzene (Grootendorst et al 1995) and the oxyhydrogenation of alcohols

(Baldi et al 1998). Recent reports have indicated that nanostructural

hausmannite has the potential for capacitor electrode materials (Dubal et al

and Jiang et al 2010). Gao et al (2011) reported the synthesis of sponge like

nanosized Mn3O4 particles using manganese acetate tetrahydrate and NH4OH

as a high-capacity anode material for rechargeable lithium batteries.

1.2 ACTIVATED CARBON/METAL OXIDE

NANOCOMPOSITES

Nano composites are multiphase solid materials in which one of the

phases has one, two or three dimensions of less than 100 nm. Carbon - metal

oxide nano composites containing porous carbon embedded with nano metal

oxides have markedly improved electrical, thermal, optical, chemical,

electrochemical and catalytic properties from that of the component materials.

Generally, size limits for these effects have been proposed, <5 nm for catalytic

activity, <20 nm for making a hard magnetic material soft, <50 nm for

25

refractive index changes and <100 nm for achieving superparamagnetism,

mechanical strengthening or restricting matrix dislocation movement.

Simple precipitation method is preferred for synthesis of AC/iron

oxide magnetic composites by a suspension of activated carbon in a 400 ml

solution of FeCl3 and FeSO4 at 70 oC and NaOH solution is added dropwise to

precipitate the iron oxide (Oliveira et al 2002 and Castro et al 2009).

AC/Fe3O4 nanocomposite was synthesized by co-precipitation of Fe2+ and Fe3+

salts in the presence of N2 gas and by mixing of magnetite nanoparticles with a

mixture of AC/cellulose solution under stirring for 1 h and it was poured into

coagulation bath containing NaCl solution with continous stirring. After 12 h

of ageing, 5 ml of epichlorohydrin was slowly added into the above mixture

with stirring for 45 min, and then it was raised to 75 oC with stirring for

another 150 min to get wet m-cell/ Fe3O4/ACs (H-Y Zhu et al 2011). Synthesis

of activated carbon/iron oxide nanocomposite by mixing the modified

activated carbon and Fe(III) solution and 3M NaOH was used to maintain pH

9 (Liang et al 2011). CuFe2O4/activated carbon magnetic nanocomposite were

prepared by a coprecipitation method after suspension of ACs in Cu(II)

chloride and Fe(II) chloride solution and using NaOH for adjusting pH to

around 10 (Zhang et al 2007). Activated carbon/Fe3O4 nanocomposite has

been prepared by suspending AC in iron (III) nitrate/HNO3 solution with

constant stirring at 100 oC for 8h. Then dried sample was heated in muffle

furnace at 600 oC for 1 h in the presence of nitrogen atmosphere to form Fe3O4

nanoparticles in carbon matrix (Do et al 2011). Coating of benzene vapour

using during calcination period which improves the stability of the AC/iron

oxide nanocomposite and it has been prepared by impregnation of activated

carbon in aqueous iron (III) solution, followed by drying and calcination under

argon atmosphere. During calcination, iron particles are formed in the pores of

26

the carbon, which is then coated with a carbon layer formed by CVD using

benzene as carbon precursor (Schwickardi et al 2006).

Birnessite-type MnO2/activated carbon nanocomposites have been

synthesized by directly reducing with activated carbon in an aqueous solution.

Author discussed the morphology of MnO2 grown on activated carbon, that

can be tailored by changing the reaction ratio of activated carbon and grown

(Zhang et al 2012). Tsumura et al (2012) have reported the preparation of

spinel-type manganese oxide/porus carbon (Mn3O4) nanocomposite powders

simply by the thermal decomposition of manganese gluconate dehydrate under

inert gas atmosphere.

1.2.1 Adsorption Properties

Olievera et al (2002) reported as-prepared AC/iron oxide magnetic

adsorbent used for removal of volatile organic compounds such as chloroform,

phenol, chlorobenzene, and drimaren red dye from aqueous solution onto the

composites. The adsorption capacity of AC/iron oxide was tested using

atrazine compound which is a selective triazine herbicide used to control

weeds in various crops and in agricultural areas. The main iron oxide actually

-FeOOH). Impregnation of iron

oxide can reduce the surface area of composite, and this change could not

affect the adsorption behaviour. They also indicate that the efficiency of the

oxidation reaction is related with the iron content (Castro et al 2009).

MnFe2O4/activated carbon magnetic composite has been prepared by co-

precipitation method. The results showed that the composites had good

magnetic properties and used for removal of tetracycline successfully by Shao

et al (2012). Zhu et al (2009) reported a nano-zero valent iron is an effective

adsorbent for arsenic removal from drinking water. Panneerselvam et al

(2011) reported synthesis of Fe3O4 impregnated onto tea waste and its

27

application in the removal of Ni(II) form aqueous solution. Carbon/Fe3O4 core

shell composite has been prepared by hydrothermal synthesis. Ethylene glycol

and ferric chloride were mixed and stirred for period of time until FeCl3 get

completely dissolved and then sodium acetate solution was added to get

transparent solution. Then the mixture was transferred to a Teflon autoclave at

200 oC and heated for 8-16 h. The as-prepared magnetic composite materials

were used for the removal of organic dyes such as methylene blue and cresol

red (Zhang et al 2011).

1.2.2 Electrochemical Properties

Activated carbon with high volumetric capacitance is prepared

from apricot shell by optimizing the carbonization temperature prior to NaOH

activation in order to balance the porosity and density. The carbonization

temperature has a marked effect on both the pore structure and the

electrochemical performances of ACs. Xu et al (2010) concluded that, as the

carbonization temperature increases, the specific surface area and gravimetric

capacitance of the carbon decrease, while the apparent electrode density

increases. Moderate carbonization at 500 oC results in not only high

gravimetric capacitance (339 F/g) but also high apparent electrode density

(0.504 g/cm-3), and hence a highest volumetric capacitance of 171 F/cm-3 in 6

M KOH aqueous electrolyte is obtained. Qu et al (2002) reported the

influences of activated carbon structure and surface groups on the performance

of a supercapacitor application as follow: (a) the specific capacitance of an

activated carbon relies on the crystal orientation of its surface. The higher

percentage of edge orientation results of the higher double layer capacitance

and favours the stronger bonding of surface functional groups and (b) surface

functional groups may be electrochemically reactive in certain potential range.

Activated carbon/polyaniline nanocomposites have been prepared using

different electrochemical methods: single-step potentiostatic polymerization,

28

multistep potentiostatic polymerization, and potentiodynamic polymerization

with the anodic potential limits being fixed at either 0.75 or 1 V (vs Ag/AgCl).

The synthetic conditions were found to strongly affect the electrochemical

behaviour of the samples and high capacitance was achieved by the

potentiostatic polymerization methods. This benefit is attributed to the

enhanced electron delocalization along the polymer chains in the composite

resulting from the influence of the activated carbon, as evidenced by the FTIR.

(Martinez et al 2008). Nian et al reported that oxidation through HNO3

treatment enhanced the electrochemical capacitance of PAN-based activated

carbon fabric electrodes in H2SO4 solution. The capacitance enhancement can

be attributed to the increase in the crowd of the CO-desorbing complexes,

while the CO2-desorbing complexes show a negative effect in double layer

formation. CV results showed that the presence of the CO-desorbing

complexes significantly enhanced the double-layer formation and thus the

capacitance. This indicates that due to the local changes of electronic charge

density, a proton adsorbed by a carbonyl or quinone-type site facilitates an

excess specific double layer capacitance. The overall capacitance was found to

increase more than 40% (from 120 to 170 F/g). The capacitors prepared in the

present work exhibit excellent capacitance stability with a coulombic

efficiency of 99.5 % over 100 cycles. Huang et al (2007) reported nickel

hydroxide/AC composite electrode for use in an electrochemical capacitor was

prepared by a simple chemical precipitation method. Specific capacitance of

nickel hydroxide (6 wt. %)/AC composite electrode is 314.5 F/g and for pure

activated carbon (255.1 F/g) and it exhibits a stable cyclic life in the potential

range of 0 1.0 V.

Stable colloidal suspension of Fe3O4/starch nanocomposite was

prepared by a facile and aqueous-based chemical precipitation method and its

thin film nature were subsequently formed upon carbonization of the starch

29

component by heat treatment under controlled conditions. A specific

capacitance of 124 F/g was achieved for the magnetite/carbon nanocomposite

thin films as compared to that of 82 F/g for pure magnetite thin films in

Na2SO4 aqueous electrolyte (Pang et al 2011). A nanocomposite of goethite

-FeOOH) nanorods and reduced graphene oxide (RGO) using a solution

method and as-prepared goethite nanorods have an average length of 200 nm

and a diameter of 30 nm and are densely attached on both sides of the RGO

sheets. The CV results showed that goethite/RGO composites have a high

electrochemical capacitance of 165.5 F/g with an excellent recycling

capability making the material a promising candidate for electrochemical

capacitors. (Shou et al 2012). A solution combustion method have been

adopted to prepare single and mixed metal oxide/carbon composites like

Fe2O3/carbon, Fe2O3-SnO2/carbon, Fe2O3-ZnO/carbon using dextrose as

precursor and fuel. CV results showed that the specific electrochemical double

layer capacitances are: Fe2O3/carbon, 255 F/g; Fe2O3-SnO2/carbon, 78.6 F/g;

Fe2O3-ZnO/carbon, 122 F/g respectively (Jayalakshmi and Balasubramanian

2009). Lian et al (2010) reported Fe3O4-graphene nanocomposite was prepared

by a gas/liquid interface reaction and electrochemical tests show that the

Fe3O4-22.7 wt% graphene nanocomposite exhibits much higher capacity

retention with a large reversible specific capacity of 1048 mAh/g (99% of the

initial reversible specific capacity) at the 90th cycle in comparison with that of

the bare Fe3O4 nanoparticles (only 226 mAh/g at the 34th cycle). The enhanced

cycling performance can be attributed to the fact that the Fe3O4 nanoparticles,

and the Fe3O4-graphene nanocomposite can provide buffering spaces against

the volume changes of Fe3O4 nanoparticles during electrochemical cycling.

Recently, increasing research efforts have been focused on

alternative low cost transition-metal oxide MnO2 because of its high energy

density, environmental compatibility and natural abundance (Chang and Tsai

30

2003). However, MnO2 shows a low capacitance without conductive additives

due to its intrinsically poor electrical conductivity (Lee et al 2001). Some

studies have shown the benefits of using CNTs as conducting supports to

improve the specific capacitance of MnO2. The specific capacitance based on

MnO2 is reported in the range of 150-790 F/g (Zhang et al 2008), where MnO2

particles are deposited on the outer surface of CNTs. Since the pseudo

capacitive MnO2 stores charge by virtue of the circulation between

Mn(IV)/Mn(III) species (Pang et al 2000), the pseudocapacitance can be

further increased by modifying the redox couple composition of manganese

oxides. Composite electrodes consisting of Mn-Co oxide and high electrical

conductive carbon nanofibers (vapor grown carbon nanofiber, VGCF)

(CoMnO2/VGCF) were prepared by thermally decomposing manganese and

cobalt nitrates directly onto the pore of a porous nickel foam substrate as a

current collector to form manganese and cobalt oxides. Their supercapacitive

properties were investigated using cyclic voltammetry in 1M KOH aqueous

solution. The CoMnO2/VGCF electrodes exhibited high specific capacitance

value of 630 F/g at 5 mV/s and excellent capacitance retention of 95 % after

104 cycles. (Kim et al 2009). Spinel-type Mn3O4/C nanocomposite powders

have been prepared by thermal decomposition of manganese gluconate

dehydrate under argon atmosphere and its electrochemical properties in 1M

KOH were studied by Tsumura et al (2012). The nanocomposite powders

prepared at 800 oC exhibit a high specific capacitance calculated from cyclic

voltammogram of 350 and 600 F/g at a sweep rate of 1 and 0.1 mV/s,

respectively. The influence of the heating temperature on the structure and the

electrochemical properties of nanocomposite powders are also discussed.

Zhang et al (2011) reported hausmannite (Mn3O4) polyhedral nanocrystals

have been successfully synthesized by simple solution based thermolysis route

using a 3D hydrogen-bonded polymer as precursor. The as-prepared

nanocrystals have good electrochemical specific capacitance of 178 F/g in a

31

potential range from - 0.1 to 0.8 V vs SCE in a 0.5 M sodium sulphate solution

at a current density of 0.2 A/g. Luo et al (2013) reported coke powder

activated carbon/Mn3O4 nanocomposite electrode (CPAC/Mn3O4), which was

prepared by Sol-Gel method using (CPAC/Mn3O4), as a precursor. The results

obtained from electrochemical measurement shows that the electrode

possesses better electrochemical performance with a manganese content of 20

wt % in precursor. The specific capacitance of CPAC/Mn3O4 nanocomposite

electrode is 277 F/g at a calcining temperature of 500oC for 3 hours.

Co2SnO4/ACs electrode materials were synthesized by co-precipitation

method. CV results showed 285.3 F/g at the current density of 5 mA cm-2 and

it exhibited excellent long-term stability and, even after 1000 cycles (He et al

2012). Ko et al reported the specific capacitance of the MnO2/A-CNT

composite electrode at scan rates of 10 and 100 mv/s, were found to be 250

and 184 F/g, respectively, and compared to 215 and 138 F/g, respectively, for

the MnO2/CNT. Because activation process improvise the capacitance and

cyclic performance, due to the improvement of the accumulated stress during

charge/discharge cycling. Zhang et al (2012) reported the synthesis of

birnessite-type MnO2/ACs nanocomposites by directly reducing KMnO4 with

activated carbon in an aqueous solution for supercapacitance application.

1.3 ACID YELLOW 17 DYE

Nowadays India and China have become the largest synthetic dyes

producing countries. Most of the dyes are used in textile processing, in which

the degree of fixation of dyes to fabrics is never complete, and 10-15 % of the

used dyes enter the environment through wastes, resulting in dye-containing

effluents. If the effluents are not properly treated, these dyes may pose

aesthetic problem, for the presence of dyes even at a very low concentration

and reduce photosynthetic action within ecosystem, also their breakdown

products may be toxic and even carcinogenic to aquatic life. It is known that

32

dyes are stable to light, heat and oxidizing agents, and are usually biologically

non-degradable (Gupta and Suhas 2009, Aksu 2005 and Ozer et al 2005).

The colours in wastewater usually have azo groups and aromatic

structures which are harmful for humans and ecosystem due to their toxicity

and stability. They can also decrease the transparency of water and influence

photosynthesis activity which hinders the microbial activities of submerged

organisms (Ligini et al 1993, Wang et al 1998 and Oh et al 2004). Nowadays

the major techniques for treating dye wastewater are adsorption process and

biological treatment (Zhou et al 2008).

Of the dyes, water soluble reactive and acid dyes are the most

problematic, as they tend to pass through conventional treatment systems

unaffected, hence, their removal is also great importance (Aksu et al 2005).

Acid yellow 17 dye (AYD 17), a monoazo dye, is widely used in dyeing wool,

silk, cotton, leather, paper and hot stamping foil. Also it is a common additive

found in ordinary household products such as shampoo, bubble bath, shower

gel, liquid soap, multi-purpose cleanser, dishwashing liquid and alcohol based

perfumes. As regulations associated with dyestuff are being tightened,

associated industries are facing difficulties in finding economically viable

water treatment solutions (Lackey et al 2006).

1.3.1 Removal of Acid Dyes using Various Adsorbents

During the past years, a number of wastewater treatment methods

have been reported and attempted for the removal of pollutants from dye-

containing wastewaters, such as coagulation, flocculation, adsorption,

membrane separation and advanced oxidation (Crini et al 2008). Gupta et al

(2011) reported the synthesis of a mesorporus carbon developed from waste

tire rubber and used as an adsorbent for the removal and recovery of a

33

hazardous azo dye, acid blue 113. Muthuvel et al (2012) reported that Fe

encapsulated montmorillonite K10 clay has been prepared by solid state

dispersion method and it was applied for photodegradation of AYD 17 in the

presence of H2O2 under UV light. Moreover, the solid hetero-Fenton catalyst

with 26 % ferric nitrate is found to be most efficient in the degradation of

AYD 17 and also feasible for this hetero-Fenton process over a wide range of

pH 3-7. Removal of AYD 17 using various low cost adsorbents such as non-

living aerobic granular sludge (Gao et al 2010) and calcined alunite (Ozcar

and Sengil 2002) were reported.

1.4 OBJECTIVE OF THE PRESENT WORK

The literature survey indicates that nanocomposites used for specific

applications, are synthesized by various techniques which involve complex

procedure. Further, synthesis of metal carboxylates have been reported

profusively and many metal carboxylates are also reported to produce metal

oxides in micro and nanoscale depending their structure and owing to the

fueling nature of carbons, on simple decomposition. Amalgamating these

ideas, it was intended to synthesize nanocomposites of carbon dispersed with

nanometal oxides via simple route.

The objectives of this work are:

1. Selection of suitable Iron and manganese carboyxlates and study of

their thermal decomposition temperature at which oxides are

formed.

2. Preparation of the carboxylates by the reaction of metal nitrate with

the respective carboxylic acid.

3. Synthesis of nanocomposites.

34

4. Characterization of metal carboxylats and nanocomposites by FTIR,

PXRD, SEM, TEM and VSM.

5. Application of composites in dye removal.

6. Application of composites in capacitance studies.

Based on these objectives, this research work was performed and the

results obtained are discussed in the following chapters.