xiii

CHAPTER-1 INTRODUCTION

Water the wonder liquid, which is the basis of life contains various salts

dissolved in varied concentrations. The salts dissociate in water to form positively

charged cations and negatively charged anions. The ionic impurities can seriously

affect the quality of water system and lead to serious health hazards in human beings.

The dissolved salts of calcium and magnesium form scaly deposits inside the boilers

in the industry and thus affect the overall steam production. As per the World Health

Organization report 97.5% water present on the earth is salty and can be used after

proper treatment. Remaining 2.5% is fresh water, of which about 70% is present in

the polar region in the form of glaciers. Almost 1% of total quantity of water is

available for ready use on the surface of the earth (Snoeyink and Jenkins, 1980).

Population explosion, extensive industrialization and advancement in

agricultural techniques have led to the degradation of aquatic environment due to the

discharge of non-degradable and hazardous material into the aquatic system. The

water contaminated with toxic pollutants and pathogenic microorganisms is hazardous

to health (Gupta and Gupta, 1997). The toxic heavy metals are the common

constituents present in polluted water. If the concentrations of these metals exceeds

the permissible limits then it leads to serious health hazards in living beings (Nabi et

al., 2007). The polluted water is not suitable for drinking, irrigation and also for the

industrial processes (Velmurugun et al., 2011). The major pollutants present in

polluted water are mainly of organic and inorganic origin. Water is mainly

contaminated by the industrial effluents comprising of heavy metals, synthetic dyes,

phenols, buffers, bleaching agents, water softeners, surfactants, acids, alkalis,

detergents, pesticides and other inorganic and organic substances (Reid and Green,

1996; Srivastava and Tyagi, 1995). Heavy metal contamination is the most polluting

and highly dangerous due to high water and soil persistence, ecotoxicological effects

and bioaccumulation in plants and animals (Chern and Wu, 2001).

1.1. Heavy metals

Minerals in the form of micronutrients and macronutrients are essential for the

normal functioning of human body. The metal ions such as Zn2+, Mg2+, Mn2+, Fe2+,

2

Cu2+, Mo3+, Co2+, K+, Na+ etc. play a very important role in the body metabolism.

Whereas, heavy metals such as mercury, lead, cadmium, aluminum, chromium and

arsenic can prove to be highly dangerous when consumed through untreated water. A

large amount of work has been carried out for the removal of toxic heavy metal ions

from the industrial waste and hazardous nuclear waste.

Heavy metal pollution is one of the most important environmental problems

today. The wastewater generated from many industries such as iron and steel industry,

non-ferrous metal industry, mining and mineral processing, car manufacturing, metal

plating, tanning, battery, glassware, ceramics, electroplating, paints, textile,

photography etc. contain a number of heavy metals which have significant noxious

effects on human beings and climate. The amount and number of heavy metals

present in wastewater are related directly to the effluents of the industry (Hossain et

al., 2005).

The concentration of heavy metals above the permissible limits in waste water

causes carcinogenic and mutagenic effects to human beings. Heavy metal ions such as

Cr (VI), Cu (II), Ni (II), Pb (II), Mn (II), Hg (II), Cd (II) etc. form complexes with

organic substances in the environment, thereby increasing their mobility in the biota

and manifest lethal effects (Parab et al., 2006). Toxic effects of some heavy metals are

discussed as follows:

1.1.1. Cadmium

The cadmium is introduced into the water system from different sources such

as metal plating, cadmium-nickel batteries, mining, phosphate fertilizers, smelting,

alloy industries and sewage sludge. Cadmium once absorbed by an organism remains

resident for many years and when dispersed in the soil persists for a long time. The

most hazardous effect of cadmium may be due to its long half-life period in the

human body, which accumulates in the kidney leading to renal disfunction, whereas a

high exposure can lead to lung cancer. Cadmium may also produce bone defects in

humans and animals. In addition, the metal is also linked to high blood pressure and

myocardium in animals. A normal human being takes an estimated 0.15 µg of

cadmium from air and 1 µg from water. 2-4 µg of cadmium are inhaled on smoking a

3

packet of twenty cigarettes, although it may vary. The inhalation of cadmium causes

choking, bronchitis and damage to renal tissues (Demirbas, 2004). During the refining

of zinc, cadmium is produced as a byproduct. Cadmium has been used as pigments

and stabilizers for PVC. Phosphate fertilizers, detergents and refined petroleum

products contain cadmium as an impurity.

1.1.2. Chromium

Chromium is required in traces for the normal functioning of our body mainly

for the digestion of food. The main sources of chromium include yeast, meats, cheese,

molasses, spices, whole grain breads, cereals, fresh fruits and vegetables. Chromium

is an important constituent of metal alloys and pigments for paints, cement, paper,

rubber and used in many industrial processes such as tanning of leather, metal works

and plating process. A large amount of chemical agents are used in the tanning

industries for the transforming of animal hide into leather and produce a large volume

of residual water containing chromium(IV). In India, tannery is the one of the oldest

and fastest growing industry, increasing the environment pollution level (Bansal et al.,

2009). Due to the high reactivity and hazardous nature of chromium (IV), it has been

included in the priority list of Comprehensive Environmental Response,

Compensation and Liability Act (CERCLA) (Gupta et al., 2011). A short term

exposure to chromium causes skin irritation, ulcers, high cholesterol levels, thereby

increasing the risk of coronary artery disease. Deficiency of chromium may affect the

eyes causing glaucoma. Generally, both trivalent and hexavalent form of chromium is

found in contaminated water. The toxicity of chromium is mainly due to chromium

(VI) form, which is easily absorbed by the lungs, intestine and skin. Chromium

compounds when inhaled affect the respiratory tract causing lung cancer, nasal,

epigastric pain, hemorrhage, ulcer, kidney damage and a sinus cancer (IARC

Monographs, 1982). The adverse effect of chromium on the health depends upon the

dose, exposure period and specific compounds. The exposure of skin to chromium

causes irritant and allergic dermatitis which is identified by symptoms like dryness,

erythema, fissuring, papules, scaling and swelling of the skin. This is commonly seen

on the fingers, knuckles and forearms. The United States Environment Protection

4

Agency (USEPA) has fixed the tolerance limits for drinking and inland surface water

as 0.05 and 0.1 mg/L, respectively (Moussavi and Barikbin, 2010).

1.1.3. Lead

Lead has been introduced into the environment from both natural and

anthropogenic sources. The exposure of lead to living organisms can occur through

drinking water, food, air, soil and dust from old paintings containing lead. The main

sources of lead pollution are various industrial processes such as battery

manufacturing, ammonium manufacturing, metal plating and finishing, ceramic and

glass industries, pigments, lead compounds etc. The Environmental Protection

Agency (EPA) has recommended the permissible limit 0.05mg/L for lead (II) in

wastewater (Kumar, 2009).

Lead is a highly toxic metal having wide range of biological effects on human

body. The magnitude of effects depends upon the level and duration of exposure.

Lead mainly affects the nervous system of humans. The toxic effect of lead is more

pronounced in the developing foetus and infants. Prolonged exposure of lead or its

salt can cause problems in the synthesis of hemoglobin, effects the kidneys, digestive

tract, nervous system, joints and reproductive system. High level of exposure may

cause the damage to the brain and kidneys in humans and lead to death. Lead

poisoning may also cause weakness in fingers, wrists and increase in the blood

pressure in the middle aged and older people, may also causes anemia. Even a very

low level of lead exposure leads to permanently reduce of the cognitive capacity of

children.

1.1.4. Nickel

Nickel occurs in nature in two oxidation states specifically Ni (0) and Ni (II).

Among these two forms Ni (II) has toxic effects on environment. The various

industries like non-ferrous metal processing, nickel plating, electroplating, coins and

jewellery making, battery and accumulator manufacturing etc. are the main sources of

nickel level in natural water. Though human body requires small amount of nickel to

produce the red blood cells. However, it becomes slightly toxic at higher

concentration. No health problem is observed in short duration exposure to nickel, but

5

exposure for long duration causes cancer of lungs, bone, heart and liver. Severe effect

of nickel poisoning causes dizziness, headache, chest pain, vomiting and sickness,

rapid respiration and cyanosis (Demirbas et al., 2002).

1.1.5. Mercury

The major sources of mercury to the environment are the degassing of earth’s

crust, volcanic activity, biological processes, evaporation from natural bodies of

water, combustion of fossil fuels, mining of metals etc. Mercury has a long

atmospheric lifetime and is present in unreactive gaseous state. Mercury present in

water is converted into methylmercury by some microorganisms, which has high toxic

effect, causing neurotoxicological disorders. This form of mercury bioaccumulated is

over a million fold and concentrates in living animals like fish and shell fish. Through

food chain mercury has been introduced into the human body. ‘Minamata’a disease is

caused by mercury which results in weakness in muscles, hearing and vision power,

mental retardation and paralysis. High level exposure of mercury affects the brain,

heart, kidneys, lungs and immune system of the humans. Less common exposure to

mercury causes breathing problems (Namasivayam and Perasamy, 1993). Higher

concentration of methylmercury in the blood stream affects the development of

nervous system and reduces the thinking and learning ability of unborn and young

children.

1.1.6. Iron

Human body commonly absorbs iron from plants and animal products. Iron is

the essential part of the haemoglobin present in blood. Inhalation of fumes or dust of

iron oxide in high concentration may cause the siderosis and enhance the probability

of lung cancer. Iron deficiency in human beings leads to anaemia. However, overdose

of iron causes a severe problem of respiration, pulse rates, drowsiness, congestion of

blood vessels and hypertension (Shukla et al., 2005).

1.1.7. Zinc

Zinc has been introduced in water bodies from the industrial wastewater which

contains a large amount of zinc. Although zinc is a trace element and required for

6

biological functioning of human body, high dose of zinc causes eminent health

problems such as decrease in the sense of taste and smell, loss of appetite, renal

damage, slow wound healing, vomiting and skin sores. Excess concentrations of zinc

in human body harm the pancreas and imbalance the protein metabolism. Exposure to

oxide and chloride of zinc causes pneumonitis and respiratory disorders (Arshad et al.,

2008).

1.1.8. Cobalt

Cobalt is extensively spread in the environment and most of the population is

exposed to cobalt through breathing, drinking water and eating food. Cobalt is

essential for human body and health. However high concentration of cobalt harms the

human health. Excess exposure of cobalt may causes asthma and pneumonia problem.

Over dose of cobalt resulted in several problems in human body such as vomiting,

nausea, vision, heart and thyroid (Lauwerys and Lison, 1994).

1.1.9. Manganese

Manganese is an essential trace element for human health (Leach and Harris,

1997). The humans are exposed to manganese generally through the ingestion of food.

Although it is the least toxic element but at high concentration it is toxic to health. At

high concentration it generates several problems in human body such as growth

retardation, fever, muscular fatigue and eye blindness. Exposure of manganese for

long duration causes impotency in man. Prolonged inhalation of dust and fumes of

manganese compounds harms the nervous system and causes permanent disability.

Mn (II) form of manganese is more toxic than Mn (III) form (Kumar, 2009).

1.2. Organic pollutants

1.2.1. Organic dyes

Colour adds a lot of spice to our lives. More than ten thousand dyes are

available on a large scale and seven lakh tons of dyes have been produced annually

(Zolinger, 1987). The largest consumption of dyes takes place in the textile industry.

A large amount of synthetic discharge is sent in to the water system as it is unable to

bind with the substrate (Weber and Adams, 1995).

7

Dyes are mostly water soluble thus can be easily transported through sewers

and rivers. They may undergo degradation to form products which are highly toxic

and carcinogenic to human beings (Rindle and Troll, 1975). Therefore, these dyes are

a probable health hazards to living organisms. It is hence imperative to protect our

environment from such toxic pollutants. Every year around 106 Kg of dyes are

discharged into the water systems (Hameed and Ahmad, 2009; Velmurugan et al.,

2011). Further, statistics revealed that 2% of the dyes annually are discharged from

manufacturing operations while 10% is discharged from textile units (Robinson et al.,

2001). The effluent contaminated with dyes has fluctuating pH, high demand of

oxygen, non- biodegradable nature and stable towards oxidizing agents (Crinic, 2006;

Ozcan et al., 2005). Dyes are coloured aromatic organic compounds which have a

strong affinity towards the substrate. Some dyes are bonded to the substrate by

physical forces while other dyes are bonded chemically. The dyes are broadly

classified into two types on the basis of their nature.

On the basis of the sources from which they are obtained, the dyes are mainly

classified into two groups as;

1. Natural dyes

2. Synthetic dyes.

1.2.1.1. Natural dyes

The natural dyes are mainly obtained from animals and plants. Today, many of

these traditional dyes are rarely used. Each of these dyes are named according to their

specific colour. Natural dyes are usually negatively charged and the positively

charged dyes rarely exist. The most commonly used natural dye is hematein (natural

black 1), obtained from the heartwood of a tree and requires a mordant to bond with

the substrate. Another common natural dye is Saffron (natural yellow- 6) obtained

from the stigmata of a plant called ‘Crocus sativus’, used without mordant. It is

commonly used as colour and spice for food rather than a dye, due to its high cost.

8

1.2.1.2. Synthetic dyes

These dyes are derived from organic or inorganic compounds. On the basis of

general dye chemistry synthetic dyes are classified into different types as follows:

Group Application

Direct Cotton, cellulosic and blends

Vat dyes Cotton, cellulosic and blends

Sulphur dyes Cotton, cellulosic fibers

Organic pigments Cotton, cellulosic, blended fibers, paper

Reactive dyes Cellulosic fibers and fabric

Dispersed dyes Synthetic fibers

Acid dyes Wool, silk, synthetic fibers, leather

Azoic dyes Printing inks and pigments

Basic dyes Silk, wool, cotten

Oxidation dyes Hair

Developed dyes Cellulosic fibers and fabric

Mordant dyes Cellulosic fibers and fabric, silk. wool

Optical or fluorescent

brighteners

Synthetic fibers, leather, cotton, sports

goods

Solvent dyes Wood staining, solvent inks, waxes,

colouring oils

Recently, organic dyes have been of great concern to the scientists due to their

high solubility in water and nonbiodegradable nature. Apart from health hazards, dyes

also inhibit the growth of some aquatic plants which are required for self-purification

9

by preventing sunlight, thus prohibiting photosynthesis (Gurham, 1965). The

complicated aromatic structure of the dyes and the presence of heavy metals in their

structure enhances their mutagenic or carcinogenic toxicity (McGeorge et al., 1985).

Chromosomal defects and respiratory toxicity are also caused by dyes.

Epidemiological studies have revealed that the workers working in the dye industry

are more prone to bladder tumors. Some of the adverse effects of synthetic dyes are

listed below:

1. Methylene blue has caused the following disorders to living being such as

Nausea, vomiting, sweating, mental disorders and haemoglobinemia (Bulut and

Aydın, 2006).

2. Lung tumors, local sarcomas, fibrosarcomas, hepatomas, liver tumors and

bladder papilloma are caused by methyl orange dye.

3. Azo Dyes cause poisoning of blood, skin sensitization reaction

These dyes have electron-withdrawing groups, which create an electron deficiency

and get reduced to certain compounds which are also carcinogenic and leading to

chronic toxicity (Brown and DeVito, 1993).

1.2.2. Phenols

Phenols are enter into the aquatic environment from effluents of different

industries such as phenol manufacturing, pharmaceuticals, paint, dyeing, textiles,

automotive, construction etc. (Fleeger et al., 2003; Mukherjee et al., 1991, Abo-Hegab

et al., 1990). The phenols cause some serious effects to the human health such as

irritation on skin and eyes, irregular breathing, muscle weakness, loss of coordination

and coma (Calabrese and Kenyon, 1991). Phenolic compounds cause carcinogenic,

immunotoxic, hematological and physiological effects to the living organism (Tsutsui

et al., 1997; Taysse et al., 1995). Therefore, phenol pollution indicates a threat to the

human health and natural environment (Hori et al., 2006). Polyphenols have an

adverse effect on health if its level increased to a certain limit (Halliwell, 2007). Thus

due to adverse effect to living being their detection and separation is of important

concern to the environmentalists.

10

1.2.3. Other organic pollutants

The effluents from different industries may contain a large number of other

organic compounds which are toxic to the living organisms. Some of these are as

follows:

1. Halogenated aliphatic compounds bromochloroethane, dibromoethane,

tetreachloromethane, chloroform, bromoform, trichloroethylene,

tetrachloroethylene, halogenated ethers.

2. Halogenated aromatic compounds (chlorobenzene, dichlorobenzene,

chlorotoluene and chloroxylene).

3. Aromatic hydrocarbons (benzene, toluene, xylene, biphenyls and polycyclic

aromatic hydrocarbons).

4. Apart from the above the effluent also contains aldehydes, esters, ketones,

polychlorinated biphenyls, alicyclic hydrocarbons, insecticides, nematicides,

rodenticides, algicides and herbicides (Chen and Zhao, 2009; Snoeyink and

Jenkins,1980).

Pollutants are the chemicals which when present above a certain permissible

limit in the environment may be toxic. Many methods have been suggested for the

removal of pollutants from waste water. But researchers have been looking for cost

effective methods for the treatment of polluted water.

Various methods have been adopted for the removal of pollutants from water.

Among these ion exchange process has been the most widely and efficiently used for

the removal of impurities present in aqueous phase.

1.3. Methods for the removal of pollutants

Due to lack of proper effluent disposal system in the industries the dangerous

organic and inorganic pollutants are discharged into the nearby water bodies which

finally seep into the drinking water sources. These pollutants if present beyond a

certain acceptable limit in water, affect the quality of the water. Therefore, most of the

countries have made strict environmental rules and regulations in order to safeguard

11

the health of their citizens. It has made compulsory for the industries to ensure safe

pollutant levels in wastewater prior to its discharge into the natural water bodies

(McKay et al., 1982).

The treatment processes depend upon the nature of the pollutants and the

extent of their harmful effects. A number of methods have been used for the removal

of organic and inorganic pollutants from waste water which include biological,

chemical and physical methods (Zollinger, 1987).

1.3.1. Biological methods

Biological methods involve different kinds of microorganisms such as

bacteria, yeasts, algae and fungi capable of accumulating and degrading different

pollutants. Fungal decolorisation, microbial degradation and bioremediation are some

of the commonly used biological methods for the degradation of pollutants present in

water. These methods have been considered as the most economical although they

have their own limitations. All the organic molecules cannot be degraded by

biological method, firstly due to their complex structures and synthetic origin (Hasan,

2008) and secondly, biological treatment requires a large land area (Robinson et al.,

2001).

1.3.2. Chemical methods

Chemical oxidation, photochemical degradation, ozonation, irradiation,

electrochemical processes, coagulation combined with flocculation and filtration,

precipitation-flocculation, electroflotation, chemisorption are some of the commonly

used chemical methods for the treatment of effluents (Srinivasan et al., 2009). One of

the major drawbacks of the chemical methods is that they are often expensive and

extensive use of chemicals may lead to further pollution. Recently, advanced

oxidation processes with the generation of hydroxyl radicals have been explained for

the treatment of pollutants present in water. These radicals are powerful oxidizing

agents and have successfully resulted in the degradation of pollutants. This treatment

is most effective among the other available chemical methods for the removal of

organic and inorganic pollutants from water system.

12

1.3.3. Physical methods

Physical methods such as dialysis, electrodialysis, ultrafiltration,

nanofiltration, reverse osmosis, ion exchange, solvent extraction, adsorption,

magnetic separation etc. have been largely used for the treatment of effluents. Some

of these methods are not practically feasible due to high costs and inability to meet the

strict regulatory requirements. Moreover these methods may also generate certain

harmful products which are difficult to treat (Nicolet and Rot, 1991). The ion

exchange, precipitation and reverse osmosis are widely used but have certain

limitations due to their complexity and high costs (Faur-Brasquet et al., 2002). During

reverse osmosis the organic pollutants and dyes present in the effluent clog the

semipermeable membrane and suppress the rate of osmosis.

1.4. Commonly used pollution remediation techniques

1.4.1. Adsorption

The term ‘adsorption’ was used for the first time by H. Kayser in 1881 (Gupta

et al., 2009; Kumar and Gayathri, 2009). The process of accumulation of a molecular

species on the surface of a solid or a liquid is known as adsorption. Adsorption

comprises of two components the adsorbats and the adsorbent. The substance which is

adsorbed is called as the adsorbate and the one that adsorbs it, is the adsorbent. In

1903, Tswett isolated chlorophyll from other pigments using silica as adsorbent. This

technique involved the selective adsorption of one component from the mixture and is

called as solid liquid adsorption chromatography.

When compared to the other physical methods for the removal of heavy metals

and dyes, adsorption is the most preferred method due the following reasons:

1. High efficiency, fast and easy operation.

2. Low costs and wide availability.

3. Adsorbent can be easily recovered and reused.

4. Environment friendly as no sludge is produced.

13

It has been recorded that the effluent produced after adsorption may be of a superior

quality (Unuabonah et al., 2008; Nandi et al., 2009). The application of adsorption in

pollution remediation has been widely recognized worldwide.

1.4.2. Photocatalysis

Reactions which occur in the presence of sunlight are known as a

photochemical reaction. Most of the photochemical reactions take place by a free

radical mechanism. When light is used as a catalyst to increase the rate of a

photochemical reaction, the process is known as photocatalysis. Light has a lot of

energy and is able to break chemical bonds. When light breaks the chemical bonds

free radicals are formed. A free radical is an atom or an ion that takes up electrons

from other molecules or atoms and initiates the chemical reactions. The water system

consists of a wide range of organic pollutants, from sources such as industrial

effluents, agricultural overflow and chemical wastes (Muszkat et al., 1994; Cohen et

al., 1986). After the discovery of photo-induced splitting of water on TiO2 electrodes

in the year 1972, the researchers have started intensive studies in photocatalysis

(Fujishima and Honda, 1972). Photocatalysed degradation of a large variety of

organic pollutants under different reaction conditions has been reported worldwide.

On the basis of the state of the photocatalyst, it can be classified in to two categories

as:

1.4.2.1. Homogeneous photocatalysis

In this type of photocatalysis, both reactants and photocatalysts are present in

same phase. Ozone and photo- Fenton system (Fe+ and Fe+/H2O2) types of reactions

are mostly used in homogeneous photocatalysis process. During this process the

hydroxyle ( •OH) radical, a reactive species has been produced by ozone and used for

different purposes.

O3 + hν → O2 + O (1D)

O (1D) + H2O → •OH + •OH

O (1D) + H2O → H2O2

H2O2+ hν → •OH + •OH

14

The following mechanism of photo-Fenton process has been reported (Peternel et al.,

2007).

Fe2++ H2O2 → •OH + Fe3+ + OH-

Fe3++H2O2→Fe2++ 2•OH + H+

Fe2++ •OH →Fe3+ + OH-

Under UV radiations both the reagents produce the hydroxyl radicals through the

photolysis of H2O2 and reduction of Fe3+ ions.

H2O + hν → HO• + HO•

Fe3+ + H2O + hν → Fe3+ + HO• + H+

The effectiveness of the process depends upon the concentration of reagents,

pH of solution and intensity of the radiations. These reactions are more efficient and

occur under a light of low sensitivity, thus saving the high cost of UV lamps and

electrical energy. These reactions are more efficient at lower pH values.

1.4.2.2. Heterogeneous photcatalysis

In heterogenous catalysis the reactants, products and catalyst are present in a

different phase. Heterogeneous photocatalysis includes a large variety of reactions

such as:

1. Oxidation.

2. Dehydrogenation.

3. Hydrogen transfer.

4. 18O2-16O2 and deuterium-alkane isotopic exchange.

5. Metal deposition.

6. Water detoxification.

7. Gaseous pollutant removal.

The transition metal oxides and semiconductors have been used as the most

common heterogeneous photocatalysts. Metal oxides have a wide range of electronic

states and semiconductors possess a void energy region where no energy levels are

available for the recombination of an electron and hole produced by photo activation.

15

In the semiconductor the band gap extends from the top of the filled valence

band to the bottom of the vacant conduction band (Linz et al., 2006). When the

semiconductor absorbs energy in the form of a photon, greater than the band gap of the

material, an electron is excited from the valence band to the conduction band, it results

in the generation of positive hole in the valence band. There is a possibility that the

excited electron and hole recombine and release the energy gained from the excitation

of the electron in the form of heat. This recombination is not desired as it may lead to

inefficient photocatalysis. Thus due to the generation of positive holes and electrons,

oxidation-reductions occurs on the surface of semiconductors. The positive holes react

with the moisture present on the surface and produce hydroxyl radicals.

UV( 400 nm)λ

valence band

conduction band

Energy(eV)

Redox potential(V)

adsorption

adsorption

reduction

oxidation

e-

e-

e-

h+

Eg

Transition metal oxide

Sun

Fig.1.1. Heterogeneous photocatalysis

1.4.3. Ion exchange method

Ion exchange may be defined as a reversible process in which an interchange

of one type of ion on insoluble matrix with another type of ion of the same charge in a

solution present around the solid (Boyd et al., 1947; Bauman and Eichhorn, 1947;

Applezweig and Ann., 1948). This reaction is being used for the softening of water,

purification of chemicals or separation of matter especially the removal of toxic metal

ions from contaminated water. A common type of ion exchange reaction is shown in

following equation:

16

XA + B(aq) XB + A(aq)__ ___

Where A and B are the exchangeable ions and X is the matrix of the ion

exchanger. Bar represents the exchanger phase and (aq) indicates the aqueous phase.

The ion exchange involves the sorption, elution, regeneration processes.

In the past two decades the synthetic inorganic ion exchangers have been used

more extensively due to their high selectivity for certain metals, good kinetics of

sorption, greater stability to heat and ionizing radiation. The inorganic ion exchangers

such as insoluble oxides, crystalline silicates, salts of polybasic acids and multivalent

metals have been studied for many applications. Following properties should be

determined to characterize a new material as ion exchanger.

1. Ion exchange capacity

2. Chemical and thermal stability

3. Composition and pH - titration

4. Chemical composition.

1.4.4. Progressive development of ion exchangers

The ability to use and reuse the ion exchange material enhances its utility.

Evidence of the ion exchange process was found in the Holy Bible, which mentioned

that through ion exchange process ‘Mosses’ succeeded in preparing drinking water

from brackish water (Exodus). The discovery of ion exchangers is dated back to 1400

B.C and 330 B.C. Aristotle found that sea water loses some of its contents when

percolated through sand (Aristotle, 330 B.C). A technique was described by Francis

Bacon and Hales in 1663 for removing salts from sea water by filtration and

desalination.

The first information leading to the discovery of the ion exchange principle

came up in the first half of the nineteenth century which was based on the work done

on soil chemistry. In 1819, Gazzeri explained the retention of dissolved fertilizer

particles in clay. Although a lot of observations and information had been collected by

the middle of nineteenth century but the exact principle of the ion exchange was yet

not known.

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Thompson in 1845 and Way in 1850 had observed the phenomenon of ion

exchange first time in soil (Thompson and Roy, 1850; Way, 1850). The ion

exchangers were used to exchange the malefic ions with the beneficial ones. They

observed that an ion exchange process takes place in the soil. When the soil was

treated with ammonium salts, the ammonium ions were exchanged by the equivalent

amount of calcium and magnesium ions present in the soil. The agro chemist Way

explained the process observed by the Thomson using the following exchange

mechanism:

Ca-Soil + (NH4)2SO4 NH4-Soil + CaSO4

Later the reversible ion exchange mechanism was established by Eichorn in

1850 and took place due to the presence of zeolites in soil (Breck, 1974). The ion

exchange materials such as clays, zeolites, humic acids, gluconites, some mineral

species and coals are extensively spread in nature (Clearfield and Stynes, 1964). The

natural inorganic ion exchangers are mainly of three types: zeolites, oxides and clay

minerals. Naturally occurring zeolites have been contaminated by some different

impurities like other minerals, metals and other zeolites. Therefore, these zeolites

were not used for various commercial applications, which need purity and uniformity.

Further development in the field of naturally occurring substances resulted in the

synthesis of zeolites from sodium aluminate and sodium silicate (Mattson,1928;

Wiegner, 1931; Vanselow, 1932). The sulphonated coals were used for the synthesis

of synthetic organic exchangers (Walton, 1943). Historical evidence suggested that

the major development in the field of ion exchangers occurred in the middle of the

20th century.

Harms and Rumpler in 1903, synthesized the first aluminum based zeolite to

purify the beet syrup. In 1913, the first synthetic zeolites were marketed by the

Permutit Company in America. Later in 1935, sulphonated coals were manufactured

on a large scale for the softening of water. Considering the size of molecules

absorbable quickly or not considerably at room temperature or above, Barrer in 1945

categorized zeolites in to different types (Barrer, 1945; Sherman, 1999).

As early as 1950, Milloton and Breck discovered the commercially important

zeolites. Easily available raw materials were utilized to synthesize these zeolites at

18

lower temperature and pressure. The synthetic zeolites were considered to be better

than the natural zeolites due to their large pore size which made them applicable for

processes involving larger molecules. More over a larger pore volume increased their

capacity. Synthetic zeolite was used for the first time as an adsorbent to remove the

oxygen impurity from argon at a Union Carbide plant in the year 1953 (Milton, 1968).

These zeolites were further introduced as hydrocarbon conversion catalysts in 1959.

Later in the 1980s and 1990s the aluminosilicate zeolites had undergone a quick

transformation from its original structure to microporous silica polymorphs and

microporous aluminophosphate based polymorphs and metallo- silicate compositions

(Flanigen, 1991).

1.4.4.1. Inorganic ion exchangers

A zeolite is an aluminosilicate with a network structure having cavities

occupied by large ions and water molecules which have substantial movement,

facilitating ion exchange. The name zeolite originated from the Greek words ‘Zein’

and ‘Lithos’ which literally means ‘boiling rock’. There are over fifty natural and

more than hundred synthetic zeolites. In the beginning of the 20th century the zeolites

(natural and synthetic) have been used for water softening (Singh and Singh, 2004).

Though they were extensively used, they had a low ion exchange capacity and

stability. The zeolites such as clinoptilolite, a natural zeolite existed which is still used

in nuclear industry due to its high affinity for metals like cesium.

Follin and Bell for the first time explored the applications of the synthetic

zeolite for the separation and collection of ammonia from urine (Folin and Bell,

1917). In the year 1905, Gans from Germany developed the commercial applications

of synthetic sodium aluminosilicate ion exchanger for softening of water and treating

sugar solution (Gans, 1905). However, the natural and synthetic aluminosilicates ion

exchanger was not used extensively due to their limitations in several industrial

applications. This gave the awareness to the researchers to progress in the

development of ion exchange resins. The effective improvement in separation,

recovery and catalysis of synthetic ion exchange resins was done by the former I.G.

Farben industries in Germany and manufacturers in U.S.A. and U.K. In spite of its

lower ion exchange capacity than the synthetic zeolites, the material was found to be

more suitable for industrial purposes due to its better physical stability. Though

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natural and synthetic zeolites are available in the same quantity, the synthetic zeolites

are more preferred due to variable phase purity and chemical properties.

Synthetic ion exchangers have been prepared with the desired properties

according to our convenience. The major advantage of the synthetic ion exchangers is

that they can be made with large variety of chemical properties and pore sizes. They

are also stable at high temperatures. Synthetic zeolites were the first synthetic

inorganic materials to be prepared. They are alumino-silicate based materials which

can be prepared as microcrystalline powders, pellets or beads. The major limitations

of synthetic ion exchangers are their high costs and limited chemical stability at

extreme pH ranges.

1.4.4.2. Organic ion exchangers or resins

With the passage of time to fulfill the demands of the industries, an organic

ion exchanger was developed initially by Adom and Holms in 1935 (Adams and

Holmes, 1935), from crushed phonographs records. These are insoluble cross-linked,

high molecular weight, long chain polymers with a microporous structure. The

functional groups attached to the chain are responsible for the exchange of ions of

similar charge from the surrounding medium. These ion exchangers are also known as

ion exchange resins. The resins are formed by a number of hydrocarbon chains with a

cross linked network. The properties of organic resins such as mechanical stability,

movement of mobile ions, swelling ability, width of the matrix etc. depend upon the

extent of cross linking. The organic ion exchanger with large extent of overlapping

increased the hardness, mechanical strength decreases the swelling in solvent.

Although the percentage of swelling depends upon various factors such as polarity of

the solvent, extent of cross linking, exchange capacity, solvation tendency of fixed ion

groups, magnitude of solvation of counter ions, concentration of surrounding solution

and magnitude of ionic dissociation of functional groups.

These organic ion exchangers have high ion exchange capacity, chemical

stability and uniformity. The maximum number of exchanges per unit of the resin

may be due to the presence of specific number of mobile ion sites in the resins. They

are extensively used for the removal of toxic heavy metals like lead, mercury and

chromium from various industrial processes. The organic resins are not stable in

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organic solvents at elevated temperature. The organic ion exchange resins have

proved to be reliable and effective for processing liquid radioactive waste.

Depending upon the nature of exchange ion the materials can be classified into

the following types:

a) Cation exchangers

b) Anion exchangers

a) Cation exchangers

Cation exchangers are high molecular weight, crossed linked polymers

containing sulphonic, carboxylic, phenolic groups etc. as integral parts of the

polymeric lattice and an equivalent number of anions such as chloride, hydroxyl,

sulphate ions etc.

M-X+ + Y+ ↔ M-Y+ + X+

A commonly used cation exchanger has been prepared by copolymerization of

styrene and divinyl benzene followed by sulphonation. The resulting structure is a

vast sponge like network with negatively charged sulphonate ions attached firmly to

the frame work. These fixed negative ions are balanced by an equivalent number of

cations (H+ or Na+).

b) Anion exchangers

Anion exchangers are cross linked high molecular weight polymers containing

quaternary ammonium groups in the integral part of the resin and an equivalent

number of anion such as chloride, hydroxide, sulphate etc. These exchangers are

formed by the condensation of aromatic or aliphatic amines, aldehydes and

dihaloparaffins.

M+X- + Y- ↔ M+Y- + X+

The widely used anion exchangers have been prepared by the

copolymerization of polystyrene and divinly benzene, followed by chloromethylation

and interaction with bases such as primary, secondary or tertiary amines.

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1.4.4.3. Hybrid ion exchangers

In spite of the good utility in diverse fields and properties such as excellent

thermal stability, resistivity towards radiation fields and selectivity for ionic

species,the inorganic ion exchangers have some limitations (Khan and Alam, 2003;

Amphlett, 1964; Clearifield, 1984; Alberti et al., 1995). The basic constraints allied

with the inorganic ionexchangers were their low mechanical and chemical stability.

Moreover, they have been obtained in the form of fine powder which made them

unsuitable for column process (Khan et al., 2003). As compared to the organic ion

exchangers they have lower mechanical and chemical strength which is attributed to

their inorganic nature. The serious drawback of inorganic ion exchanger is its non-

reproducibility (Siddiquiet al., 2007). However, the organic ionexchangers have not

been used as an alternative due to their low pollutant removal capacity at high

temperature and less stability in high radiation field (Niwas et al., 1999).

To overcome the limitations associated with organic and inorganic ion

exchangers, hybrid ion exchangers have been introduced with conjugate properties.

The composite ion exchangers have overcome the drawbacks associated with both

organic and inorganic ion exchangers and hence are preferred. The combination of

organic and inorganic exchangers leads to the formation of a composite material

which shows improved granulometric properties, better suited for column operation.

A composite material comprises of two or more components having different physical

properties. The hybrid materials formed exhibit entirely different and superior

properties from its original components and thus enhancing its applications in

different fields (Mark et al., 1995; Judeinstein and Sanchez, 1996; Sanchez et al.,

2001; Chujo and Opin., 1996). The organic- inorganic ion exchange hybrid materials

are the most advanced composite materials which will incorporate a large variety of

applications in the near future (Lacy Costello et al., 1996; Mittal et al., 2006; Oriakhi

et al.,1999; Sampath and Lev, 1997; Collinson, 1999; Khan et al., 2005; Raman and

Brinker, 1995; Levy et al., 1997; Levy and Esquivias, 1995; Stein et al., 1996;

Sanchez et al., 2001). The composite materials are providing a wide range of

fascinating properties due to their multifunctional nature such as mechanical,

chemical, optical activity, catalytic activity, environment stability and good selectivity

for heavy metals (Coetzee et al., 1991; Chen and Alexander, 1997; Iqbal and Rafiquee

(2010); Vatutsina et al., 2007; Nabi et al., 2010; Arrad and Sasson, 1989). By using

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various methods for the combination of organic monomers into inorganic precipitates,

several composite ion exchangers have been formed earlier (Nilchi et al., 2006); Yang

and Clearfield, 1987; Clearfield, 1991; Alberti et al., 1995).

Researchers have developed some exceptionally good composite ion exchange

materials which have found importance in environmental analysis (Khan et al., 2003;

Khan and Alam, 2003; Varshney et al., 2001; Niwas et al., 1999).

Macroscopic composite materials have been the very conventional composite

materials which have shaped our world during the past. One such material is the

adobe, a mixture of clay and straw and has been used to make bricks and wall in dry

areas which reinforced the concrete and is an effective structural composite material.

One step forward in the development of the ion exchangers was the discovery of

nanocomposite materials which were undoubtedly better than the composite ion

exchangers. Nanoparticles have drawn a lot of attention from scientists and

researchers due to their wide applications in various fields such as medicine, optics

and electronics (Feng et al., 2006). They form a bridge between bulk material and

atomic or molecular structure. They have been produced by different methods such as

physical, chemical and biological. Nanocomposite material is more effective due to

greater surface area and volume ratio of nanoparticles compared to bulk particles

(Khan and Khan, 2010). Nanocomposite materials incorporate a large variety of

systems such as one dimensional, two dimensional, three dimensional, semicrystalline

or crystalline mixed at nanometer scale. In these composite materials nano or

molecular domain sized particals of inorganic ion exchange materials are embedded

into an organic polymer (Nabi et al., 2010). The latest research survey in the field of

polymer based hybrid nanocomposites revealed that these materials exhibit superior

mechanical and electrical properties. Their origin is dated back to the 1970’s where

the sol-gel method was used to synthesize homogeneous dispersions of small sized

inorganic particals into a polymer substrate. These were the first generation

nanocomposites, which were followed by the second generation nanocomposite in the

1980’s. Later in the 1990’s a new form of nanocomposite material was synthesized by

reinforcing polymeric materials with nanofibers such as carbon nanotubes.

Thus in view of above discussion the present study has been attempted with

objectives as discussed below:

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1.4.5. Chromatography for the separation of organic pollutants

Chromatography is an analytical technique used for separating compounds on

the basis of differences in affinity for a stationary and mobile phase. The components

present in the mixture have different partition coefficients which result in the variable

retention on the stationary phase and leads to the separation of components. The

retention time of the sample was calculated on the basis of the differences in the rates

of movements along the medium (IUPAC, 1993). In the beginning of the 20th century

chromatography was mainly used for the separation of plant pigments, which are

coloured and hence the term chromatography. With the passage of time advanced

chromatographic techniques were developed with wide range of applications. The

chromatographic techniques are classified into different categories such as: Column

chromatography (CC), Paper chromatography (PC), Thin layer chromatography

(TLC), Gas liquid chromatography (GLC), Gas solid chromatography (GSC), High

performance chromatography (HPLC), Ion exchange chromatography (IEC), Fast

protein liquid chromatography (FPLC), Reversed-phase chromatography (RPC) and

chiral chromatography (CC) (Still et al. 1978). Out of these techniques, thin layer

chromatography (TLC) has been used effectively in the laboratory for the separation

of organic mixture. Compared to paper chromatography, thin layer chromatography

using a thin layer of adsorbent has a faster run, better separation and selection of

different adsorbents. Thin layer chromatography was used effectively for the isolation

and analysis of inorganic pollutants present in real and synthetic environmental

samples (Mohammad et al., 1993). The inorganic ion exchanger as adsorbent in the

thin layer chromatography has effectively facilitated the separation of metal ions,

anions, phenols and organic acids (Gupta and Dassani, 2013; Nabi et al., 2000; Nabi

et al., 2003; Ghoulipour and Husain, 2006; Nabi et al., 1985; Gaur and Joshi, 2013).

The common compounds generally found in the natural products are phenols.

So it is a matter of great interest to separate and investigate the different phenolic

compounds occurring in plant materials like tea, cocoa and grapes. The composition

and status of a few phenolic compounds were investigated during tea fungus

fermentation. Catechin and epicatechin were the main phenolic compounds detected

in green tea and quercetin in black tea (Malbasa et al., 2004). Silica gel G thin layer

plate was used for the detection and separation of different phenolic acids present in a

mixture (Schmidtlein and Herrmann, 1975; Sumere et al., 1965).

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Phenols and phenolic compounds are the omnipresent pollutants which occur

in waste water from the effluent of industries like oil refineries, leather, paint,

pharmaceuticals, textile, wood, steel etc (Fleeger et al., 2003; Mukherjee et al., 1990;

Mukherjee et al., 1991).Using different absorbents, phenolic compounds have been

separated by applying thin-layer chromatography (Katyal and Sharma, 1980). Several

compounds of substituted benzoic acid were separated and analyzed by using a

mobile phase of α- cyclodextrin solution (Hinze and Armstrong, 1980). Nabi in 1985

have used the semicrystalline stannic tungstate ion exchange material for the

separation of different phenols in various solvent systems. They also performed the

quaternary separations of phenols using n-butanol-formic acids system (Nabi et al.,

1985).The different adsorbents which have been used for the preparation of the thin

layer in thin layer chromatography TLC as follow:

1.4.5.1. Activated carbon

Activated carbon has been considered as good adsorbent material due to its

highly porous nature which provides a large surface area for adsorption. The large

interparticulate surface area and high level of microporosity makes it an excellent and

versatile adsorbent. For the removal of pollutants the major applications of activated

carbon includes purification, detoxification, decolourisation, dechlorination and

deodorization of substances. Activated carbon has been widely used in industrial and

environmental areas (Babel and Kurniawan, 2004). The quality of activated carbon

produced depends upon the method employed for their activation. Activated carbon is

usually produced from coal, wood, bone etc. by carbonization followed by activation.

The degree of activation considerably alters the characteristics of the produced

carbons (Yang et al., 2011). Different types of pollutants such as metal ions, phenols,

dyes, pesticides, chlorinated hydrocarbons, detergents, organic compounds etc. have

been removed by using activated carbon as the adsorbent materials. Inspite of its high

efficiency and good applicability, its use is avoided sometimes due to higher cost.

1.4.5.2. Clays

Clay has been a commonly used household material in rural area. Its evidence

has been found in the early civilization. Its high availability, low cost and good

absorption make it a competent adsorbent material for the removal of pollutants. Clay

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mainly consists of oxides of metals such as Si, Al, Fe, Ca and Mg. Clay carries a net

negative charge on the structure which is responsible for its adsorption capacity

(Arfaoui et al., 2008).

1.4.5.3. Silica gel

Silica gel is a white coloured amorphous solid, commonly found in nature in

the form of quartz (Otto W. Florkeet al., 2008). Silica is a complex and abundant

material which occurs in various minerals and is considered as an effective adsorbent

material. It has been used in many industries for the drying of gases, liquids and the

purification of hydrocarbons. Silica gel consists of a closed network of spherical

colloidal silica particles. The silica gel has a surface area which ranges between 300

and 850 m2/g with pore diameter ranging from 22 to 150 Å (Shivaji, 2010). Silica gel

is used for the adsorption of more polar organic and inorganic compounds.

1.4.5.4.Fly ash

It mainly consists of silica in two forms theamorphous and crystalline. Fly ash

is generated as a residue during the combustion of coal. It is used in the cement

industry, for the synthesis of geopolymers, zeolites and also in waste water treatment

(Mall et al., 2006).

1.4.5.5. Ion exchangers

Ion exchange process is defined as the exchange of ions of like charge

between solution and a highly insoluble material in contact with it. The solid material

must contain ions of its own, for the exchange to proceed rapidly and extensively. The

solid should have an open, permeable molecular structure so that the ions and solvent

can move freely in and out. All ion exchangers have several common properties such

as they are insoluble in water and organic solvents. They contain counter ions that

will be exchanged with other ions in the surrounding solution without any physical

change in the material. Ion exchangers have played a significant role in the growth

and development of mankind. The ion exchangers have been extensively used for

water treatment, pollution control, antibiotic purification and separation of

radioisotopes (Nabi et al., 2011; Liang and Hsu, 1993).

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1.4.6. Objectives

On the basis of literature survey no work has been reported so far on the

objectives of the present work. Due to wide analytical applications of hybrid ion

exchange material in different fields, the current research work has been attempted

with following objectives:

7. To synthesize styrene, cellulose acetate based organic-inorganic hybrid ion-

exchangers.

8. To characterize the synthesized hybrid ion-exchangers using scanning electron

microscopy (SEM), transmission electron microscopy (TEM), X-ray

diffractrometer (XRD), Fourier transform infrared spectroscopy (FTIR), thermo

gravimetric analysis (TGA/DTA), UV-visible spectrophotometer etc.

9. To determine the ion exchange capacity, pH titration, chemical stability, thermal

stability, chemical composition, distribution coefficient and elution studies of

synthesized ion exchangers.

10. To separate the metal ions and organic molecules by column and thin layer

chromatography.

11. To study the antimicrobial activities of nanocomposite ion exchangers.

12. To study the photocatalytic activities for the degradation of organic pollutants.