STUDIES ON INORGANIC ION EXCHANGERS AND CHELATE ION EXCHANGERS AND THEIR APPLICATIONS IN THE STUDY OF POLLUTION

SUMMARY THESIS

SUBMITTED FOR THE AWARD OF THE DEGREE OF

iSottor of $t|i[os;oplip IN

CHEMISTRY

BY

MAN/SHA BHARDWAJ

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

AUGARH (INDIA)

2000

v .^^"i.^--i.

\'k( ' ^ -, i [ Ace. No \j

SUMMARY

SUMMARY

The thesis entitled "Studies on inorganic ion exchangers and

chelate ion exchangers and their applications in the study of pollution"

comprises of five chapters. Chapter I is general introduction covering

the background of the work presented in this thesis. The emphasis has

been given on the importance of the ion exchange as an analytical

technique. To cover the matter in a concise manner the description has

been presented in tabular form wherever possible. The survey of the

literature has been made on the basis of recent available journals and

chemical abstracts. Certain fundamental points of importance are

mentioned.

The second chapter entitled "Sorption equilibria of some

transitional metal ions on a chelating ion exchange resin, Duolite ES

467" describes the thermodynamic sorption equilibrium studies of

Nickel (II), Cadmium (II), Cobalt (II) and Iron (III). The sorption

equilibrium studies were performed by batch process, shaking for a

period of 6 hrs. Sorption isotherms were obtained by Plottig x/m vs

Ce. These plots show the variation of sorption with the increasing

temperature revealing a very complex behaviour. The plots between

Ce/(x/m) vs Ce show that sorption of metal ions obeys Langmuir

equation. Langmuir constants 'K' and 'b' are also evaluated.

Equilibrium constants for sorption were obtained and various

thermodynamic parameters viz. AH", AS", AG" were evaluated.

The third chapter deals with the "Redox studies on hydrazine

sulphate sorbed Duolite ES 467". The most important advantage of

such materials for redox studies over dissolved redox reagents is the

insolubility of the redox exchanger in the medium. Therefore, the

solution is free from contamination of any redox material or its

products. Dilute acidic, dilute basic and neutral solutions can be safely

used for the redox studies on hydrazine sulphate sorbed Duolite ES

467. The successful reductions of Fe (III), V (V), Mo (VI), Cr (VI),

Sb (V), As (V) and Ce (IV) have been achieved on this material by

batch process. The reduction of only those substances is possible

whose redox potentials are higher than that of hydrazine sulphate

which is incorporated in the exchanger. The rate of reduction has been

studied for vanadium and found that equilibrium was reached in 20

minutes.

The fourth chapter describes the " Electron Exchange Studies on

Stannic Molybdate". Stannic molybdate has been reported for the

detection of ferrous ions in our laboratories. It has been used as an

electron exchanger in the present work. The electron exchangers are

insoluble in the medium thereby making it free from any

contamination. They can also be regenerated readily. Stannic

molybdate has been used for the quantitative oxidation of Fe (II), Sn

(II), ascorbic acid, thioglycolic acid, hydrazine and hydroquinone by

batch process. The rate of oxidation has been studied for Sn (II) and

found that equilibrium was reached in ninty minutes.

3

The chapter fifth deals with Chromatography of Organo-

phosphate pesticides on hydrated stannic oxide layers. TLC is highly

sensitive and selective technique used for the analysis of all types of

samples and analytes responsible for environmental pollution.

Hydrated stannic oxide coated glass plates were used for the TLC of

seven organophosphate pesticides in forty solvent systems and Rp

va'ues were calculated. On the basis of the difference in Rp values, the

separations were tried and those achieved are also reported. The Rp

were related to the polarity of different solvents used, and the possible

interaction of these compounds with hydrated stannic oxide. It was

observed that monocrotophos was strongly retained on the hydrated

stannic oxide layers. The other organophosphate pesticides showed

none or a weaker retention effect.

STUDIES ON INORGANIC ION EXCHANGERS AND CHELATE ION EXCHANGERS AND THEIR APPLICATIONS IN THE STUDY OF POLLUTION

r I THESrS

SUBMITTED FOR THE AWARD OF THE DEGREE OF

Boctor of ^l)tIo!e(Qpl)p IN

CHEMISTRY

BY

MANISHA BHARDWAJ

DEPARTMENT OF CHEMISTRY AUGARH MUSLIM UNIVERSITY

AUGARH (INDIA)

2000

Dedicated To My

Loving Parents

%. % f. fiawai PROFESSOR

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

AUGARH-202002 INDIA

Phon«Off. : 400515 * "0""- Res.: 403144

Diittd.l3.:Pl-.^PPp

Certificate

This is to certify that the work embodied in this Thesis entitled

"Studies On Inorganic Ion Exchangers and Chelate Ion Exchangers

And Their Applications In The Study of Pollution" is original work

carried out by Miss Manisha Bhardwaj under my supervision and is

suitable for submission for the award ofPh.D. degjve in Chemistry of

this University.

(PROE J.P RAWAT)

ACKNOWLEDGEMENT

It is a priviledge to express my sensibility and gratitude to my

sage supervisor. Prof. J.P. Rawat, for his inestimable guidance,

precious suggestions, constructive criticism and constant

encouragement. His pertinacious efforts, humanity and honesty made

this work progressive. He introduced me to the realms of Scientific

knowledge and was always a source of insipiration during the entire

course of this work.

I am grateful to Prof. S.Z. Qureshi, Chairman, Department of

Chemistry, for providing research facilities.

I also take this opportunity to thank my colleagues and friends

Dr. Uzma, Mr. Manish, Mr. P. V. Singh, Deepa, Ritu, Nupur and IJzma

who have been spurring me to get a smooth success throughout the

tenure of this work.

With due reverences, I am cordially enthusiastic to thank my all

loving family members. Their continuous endeavour, strive, prudence

and blessings made the lucrative triumph in my academic pursuit and

blooming future.

I am thankful to Mr Pradeep Kumar, Aldus Computer Typing

Centre, Aligarh, for word processing in time.

At last, I believe that whatever I achieved in my academic career

is the result of God's blessings.

(MANISHA BHARDWAJ)

CONTENTS

Page No.

List of Publications I

List of Tables 11

List of Figures IV

Chapter - /

Introduction 1 References 26

Chapter - / /

Sorption equilibria of some transitional metal ions on a chelating ion exhange resin, Duolite ES 467

Introduction 40 Experimental 41 Results 43 Discussion 47 References 103

Chapter - III

Redox studies on hydrazine sulphate sorbed Duolite ES 467

Introduction 105 Experimental 106 Results 107 Discussion 113 References 117

Page No.

Chapter - IV

Electron exchange studies on Stannic Molybdate

Introduction Experimental Results Discussion References

119 120

120 121 129

Chapter - V

Thin layer chromatographic behaviour of Organo-phosphate pesticides on hydrated Stannic oxide layers

Introduction 130 Experimental 131 Results 132 Discussion J 33 References 143

LIST OF PUBLICATIONS

1. "Sorption equilibria of some transitional metal ions on chelating

ion-exchange resin, Duolite ES 467".

Adsorption Science and Technology (In Press).

2. "Thin layer Chromatographic behaviour of Organophosphate

pesticides on hydrated stannic oxide layers".

Oriental Journal of Chemistry (In Press).

3. Electron exchange studies on stannic molybdate

(communicated).

II

LIST OF TABLES

Tables Page No.

1.1 Certain oxides, inorganic ion exchangers and 11 ion exchange resins used as adsorbents.

1.2 Redox ion exchangers and their redox 18 capacity.

2.1 Effect of equilibrium time on the sorption of 44 Nickel (II) and Cadmium (II) by Duolite ES467.

2.2 Effect of equilibrium time on the sorption of 45 Cobalt (II) and Iron (II) by Duolite ES467.

2.3 Sorption of Nickel (II) on Duolite ES467 48 (0.2 gm) at 20«C.

2.4 Sorption of Cadmium (II) on Duolite ES467 49 (0.2 gm) at 20*'C.

2.5 Sorption of Cobalt (II) on Duolite ES467 50 (0.2 gm) at 20»C.

2.6 Sorption of Iron (III) on Duolite ES467 51 (0.2 gm) at 20»C.

2.7 Sorption of Nickel (II) on Duolite ES467 52 (0.2 gm) at s e c .

2.8 Sorption of Cadmium (II) on Duolite ES467 53 (0.2 gm) at 30"C.

2.9 Sorption of Cobalt (II) on Duolite ES467 54 (0.2 gm) at 300C.

2.10 Sorption of Iron (III) on Duolite ES467 55 (0.2 gm) at 30"C.

2.11 Sorption of Nickel (II) on Duolite ES467 56 (0.2 gm) at 40»C.

2.12 Sorption of Cadmium (II) on Duolite ES467 57 (0.2 gm) at 40»C.

m

Tables P«ge No.

2.13 Sorption of Cobalt (II) on Duolitc ES467 58 (0.2 gm) at 40°C.

2.14 Sorption of Iron (III) on Duolitc ES467 59 (0.2 gm) at 40»C.

2.15 Sorption of Nickel (II) on Duolite ES467 ^0 (0.2 gm) at 50»C.

2.16 Sorption of Cadmium (11) on Duolite ES467 61 (0.2 gm) at 50»C.

2.17 Sorption of Cobalt (II) on Duolite ES467 ^2 (0.2 gm) at 50°C.

2.18 Sorption of Iron (III) on Duolite ES467 63 (0.2 gm) at 50»C.

2.19 Values of Cs and In Cs/Ce for Nickel (II) on 69 Duolite ES467 at 20«C.

2.20 Values of Cs and In Cs/Ce for Cadmium (II) 70 on Duolite ES467 at lO^C.

12\ Values of Cs and In Cs/Ce for Cobalt (II) on 71 Duolite ES467 at 20«C.

2.22 Values of Cs and In Cs/Ce for Iron (III) on 72 Duolite ES467 at 20°C.

2.23 Values of Cs and In Cs/Ce for Nickel (II) on 73 Duolite ES467 at 30°C.

2.24 Values of Cs and In Cs/Ce for Cadmium (II) 74 on Duolite ES467 at 30"C.

2.25 Values of Cs and In Cs/Ce for Cobalt (II) on 75 Duolite ES467 at SCC.

2.26 Values of Cs and In Cs/Ce for Iron (III) on 76 Duolite ES467 at 30°C.

2.27 Values of Cs and In Cs/Ce for Nickel (II) on 77 Duolite ES467 at 40»C.

IV

Tables P*ge No.

2.28 Values of Cs and In Cs/Ce for Cadmium (II) 78 on Duolite ES467 at 40"C.

2.29 Values of Cs and In Cs/Ce for Cobalt (II) on 79 Duolite ES467 at 40*'C.

2.30 Values of Cs and In Cs/Ce for Iron (III) on 80 Duolite ES467 at 40»C.

2.31 Values of Cs and In Cs/Ce for Nickel (II) on 81 Duolite ES467 at 50»C.

2.32 Values of Cs and In Cs/Ce for Cadmium (II) 82 on Duolite ES467 at 50»C.

2.33 Values of Cs and In Cs/Ce for Cobalt (II) on 83 Duolite ES467 at 50"C.

2.34 Values of Cs and In Cs/Ce for Iron (III) on 84 Duolite ES467 at 50»C.

2.35 Langmuir constants K and b at 20»C, 30"C, 85 40«»C and SO C.

2.36 Various thermodynamic parameters for the 86 sorption of metal ions on Duolite ES467.

3.1 Dissolution of Hydrazine sulphate. 107

3.2 Reduction of Fe(III) to Fe(II). 108

3.3 Reduction of V(V) to V(IV). 109

3.4 Reduction of Mo(VI) to Mo(V). 109

3.5 Reduction of Sb(V) to Sb(III). 110

3.6 Reduction of Cr(VI) to Cr(III). 110

3.7 Reduction of Ce(IV) to Ce(III). 111

3.8 Reduction of As(V) to As(III). 111

3.9 Maximum redox capacity for some reducible 112 substances.

3.10 Rate of reduction of Vanadium (V) to 113 Vanadium (IV).

V

Tables Page No.

3.11 Standard redox potential of some redox 116 couples.

4.1 Oxidation of Tin (II) to Tin (IV). 122

4.2 Oxidation of Iron (II) to Iron (III). 122

4.3 Oxidation of Hydrazine to Ammonia. 123

4.4 Oxidation of Thioglycolic acid to 123 Dithioglycolic acid.

4.5 Oxidation of Hydroquinone to Quinone. 124

4.6 Oxidation of Ascorbic acid to Deascorbic acid. 124

4.7 Rate of Oxidation of Sn(II) to Sn(IV). 125

4.8 Standard potentials of some redox couples. 128

5.1 Rp values of organophosphate pesticides with 134 the composition of the mobile phases studied on hydrated stannic oxide plates.

5.2 Rp values of organophosphate pesticides on 137 silica gel G plates.

5.3 Separations achieved using different solvent 139 systems on hydrated stannic oxide gel as coating material on TLC plates.

YI

LIST OF FIGURES

Figures P«ge No.

2.1 Time dependence of sorption of some 46 transitional metal ions on Duolite ES467.

2.2 Sorption isotherms of Nickel (II) on Duolite 64 ES467.

2.3 Sorption isotherms of Cadmium (II) on Duolite 65 ES467.

2.4 Sorption isotherms of Cobalt (II) on Duolite 66 ES467.

2.5 Sorption isotherms of Iron (III) on Duolite 67 ES467.

2.6 Effect of temperature on sorption of some 68 transitional metal ions on Duolite ES467.

2.7 Langmuir isotherm for Nickel (II) on Duolite 88 ES467.

2.8 Langmuir isotherm for Cadmium (II) on 89 Duolite ES467.

2.9 Langmuir isotherm for Cobalt (II) on Duolite 90 ES467.

2.10 Langmuir isotherm for Iron (III) on Duolite 91 ES467.

2.11 Plots of In/Ce vs Ce of Nickel (II) on Duolite 92 ES467.

2.12 Plots of In Cs/Ce vs Ce of Cadmium (II) on 93 Duolite ES467.

2.13 Plots of In Cs/Ce vs Ce of Cobalt (II) on 94 Duolite ES467.

2.14 Plots of In Cs/Ce vs Ce of Iron (III) on 95 Duolite ES467.

VII

Figures Page No.

2.15 Determination of enthalpy of sorption of 96 different transitional metal ions on Duolite ES467.

3.1 Rate of Reduction of Vanadium (V) to 114 Vanadium (IV).

4.1 Rate of Oxidation of Sn(II) to Sn(IV). 126

Chapter -1

INTRODUCTION

INTRODUCTION

Ion exchange, from the day of its discovery has added a shining

spark in the field of analytical chemistry. It is widely used in

inorganic, organic and biochemical separations. In laboratories ion

exchangers are being used as an important tool to solve new problems.

Rapid and accurate determination of the constituents of a sample or

contaminants of alloys with multicomponents, phannaceuticals,

biological substances and fission products of radioactive elements has

become possible by the use of ion exchangers. The use of ion

exchangers on large scale may provide mankind with pure water and

may be useftil for the concentration and extraction of important metals

and raw materials which are becoming more and more difficult to

produce.

The ion exchange materials have found a number of important

analytical applications. The analytical applications of ion exchange

continues to increase at an exponential rate. Ion exchange has found

its application in :-

1. Water pollution control (purification of water)

2. Removal of interfering ions

3. Recovery of precious metals

4. Water softening

5. Preparation of deionized water

6. Separation of metal ions

7. Determination of total salt content of a solution

8. Separation of organic and biologically important substances

9. Concentration of trace constituents

10. Specific spot tests

11. Location of end point in titrations

12. Gas chromatography, electrophoresis and solid state separations

13. Preparation of ion selective electrodes, and

14. Preparation of ion exchanger fuel cells.

The most important application of ion exchangers is purification

of water. The water pollution is increasing at alarming rate due to

increase in industrialization and urbanization. Ion exchange

technology is useful in removing the toxic species, when present in

ionic form. The great simplicity of the technique makes ion exchange

very attractive and an inexpensive tool. Purification on large scale can

be made by passing the sample solution through the ion exchanger bed

which takes up certain materials in preference to others.

The removal of interfering ions by replacement with an

innocuous ion is another application of ion exchange. This technique

can also be utilized for the recovery of useful elements in traces from

dilute solution. By this technique, elements present in ionic form are

exchanged by an equivalent amount of counter ion present in

exchanger and subsequently eluted from the exchanger by suitable

electrolytic reagents. Thus, trace amount of an ion is isolated from a

large volume of aqueous solution into a small volume of the eluent.

This is an important step in determination of trace metals in water or

in recovery of precious metals. This technique has also been used for

the isolation and identification of the new trans-uranic elements (1,2)

and for the isotopes enrichment (3,4).

Ion exchange being a separation technique finds its use in water

analysis to concentrate the trace quantities and separate one substance

from another. Ion exchange is advantageous for the separation of metal

ions with similar properties for which specific methods are not

available. Ion exchangers have been used to separate rare earth

elements (5-7) now-a-days. Taylor and Urey have performed partial

separation of lithium isotopes (8). Ion exchange columns now provide

pure rare earth compounds on commercial scale. It has also been used

for the separation of organic and biologically important substances

such as aminoacids (9,10), nucleic acids (11), proteins (12), alcohols

(13), carbohydrates and their derivatives (14), glycols (15), ethers

(16), phenols (17), amines (18) and hydrocarbons (19) have been

separated on ion exchange columns.

Ion exchangers are useful in gas chromatography, solid state

separations, electrophoresis, location of end point in titrations etc.

Papers impregnated with ion exchangers are used for paper

chromatographic separations.

Ion exchange has established itself as one of the most powerful

techniquesin the field of water analysis thus proving its worth in water

'pollution control.

Gans (20) recognized the practical utility of the ion exchange

phenomenon for water softening using natural and synthetic zeolites

and clays. In 1931 Kullgren (21) observed that sulphite cellulose

works as an ion exchangers for the determination of copper. An

interesting discovery began in 1935, when Adams and Holmes

discovered that crushed phonograph records exhibit ion exchange

properties. This led them to the synthesis of organic ion exchange

resins (22) which exhibited an improved properties over the previously

known ion exchangers. These organic ion exchangers have been used

both in laboratory and on industrial scale for separations, recoveries of

metals, purification of water, concentration of electrolytes and

elucidating the mechanism of many chemical reactions (23).

The application of organic ion exchangers also suffers from

certain limitations i.e. they decompose at elevated temperatures in

aqueous systems and under the influence of ionizing radiations. This

led to a revived interest in inorganic based exchangers. Apart from

their far improved temperature resistance and complete immunity to

ionizing radiation the inorganic ion exchangers possess a rigid

molecular framework. This stiffness of structure leads to enhanced

selectivity for the separation of ions on the basis of their pore size.

They can also be used as ionic or molecular sieves. Being resistant to

high temperatures they can be satisfactorily used in reactor technology.

Inorganic ion exchangers selectivity have also been utilized for the

preparation of ion selective electrodes which have now become an

impoTtant tool for solving various analytical problems.

Systematic and fundamental studies on inorganic ion exchangers

commenced in 1943 with ^ e discovery of insoluble compound.

Zirconium phosphate, and its application to the separation of Uranium

and Plutonium from fission products (24). The earlier work through

1964 has been excellently summarized in a monograph of Amphlett

(25) entitled "Inorganic ion exchangers", which has become a classic

and has stimulated impetus for subsequent research in the field.

Representative type of inorganic ion exchangers have been reviewed

by Ito and Abe (26). A set of reviews by Pekarek and Vesely (27,28),

summarizes relevant work done till 1970. The theoretical aspects of

ion exchange in the inorganic ion exchangers have been described by

Marinsky (29) who has described pioneering work in this field.

Marinsky (30) and Walton (31) have edited the reviews on the

applications of inorganic ion exchangers. The synthesis and

applications of inoiganic ion exchangers have been reviewed by

Walton (32-36), Clearfield (37), Qureshi and Varshney (38).

The utility of the ion exchange materials can be developed on

the basis of following studies :

1. Distribution of counter ions between the exchanger and solution

phases.

2. Thermodynamics

3. Kinetics and

4. Analytical applications.

The incorporation of bi or polydentate ligands on the ion

exchanger matrix gives a new class of exchangers, known as chelate

ion exchangers. A number of chelating ion exchangers have been

synthesised to encourage the applications of ion exechange to a

broader range of separation and for the recovery of certain metal ions

selectivity. The chelating ion exchangers may provide a convenient

technique for the analytical concentrations of many of the more

interesting trace elements from natural waters and collection of toxic

elements from industrial waste water. The selectivity of the most

complexing agents predominantly depends on their ability to form

chelates with certain metal ions.

Thermodynamics is an appropriate means of describing the

theoretical behaviour of sorption ion exchange equilibria. The attempts

have been made to correlate the activities with some measurable

quantities, with the thermodynamic equations. The earliest approaches

were based on semiempirical or empirical equations to fit in the

experimental results. Probably the first quantitative formulation of ion

exchange equilibria was made by Cans (39). For this purpose he used

the law of mass action in its simplest form, without involving

the concept of activity coefficient. This concept was extended

by Kielland (40). The formula did not involve the concept of activity

coefficient. Gaines and Thomas (41) gave a general treatment using an

expression for the calculation of thermodynamic equlibrium constant

which is a suitable choice for this purpose. However, Gregor was able

to relate selectivity to hydrated ionic volumes in his semi-quantitative

model. Rigid structure, negligible swelling pressure and a differential

selectivity have made the study simple on inorganic exchangers. The

thermodynamic studies of alkali metals on ferric antimonate (42,43),

niobium arsenate (44), zirconium triethylamine (45), thorium

tetracyclohexylamine (46) were made in our laboratories.

Solid-liquid interactions which can be measured in terms of

sorption have always been of interest for many workers because of the

diversity of the phenomena involved and immense application in

chemistry and related sciences.

Adsorption is one of the most fascinating areas of chemistry.

Since, the molecules on the surface have a different environment from

those in the bulk of the material, hence, surface energy is different

from the energy of the bulk.

Adsorption is of two types : physical and chemical called as

"Physiosorption" and "Chemisorption" respectively. In physiosorption

the molecules are adsorbed to a solid surface essentially by physical

forces, while in chemisorption, the molecule forms the chemical bonds

with the solid surface. In physiosorption there is a Vanderwaal's

interaction (for instance dispersion or polar interaction) between the

surface and adsorbed molecule. These are weak types of interactions

and the amount of energy released when the molecule is physiosorbed

is of order of 25 KJ mol' i.e. the enthalpy of condensation. This

energy can be absorbed by the vibration of the lattice and is dissipated

as heat. A molecule bouncing across the surface will loose its kinetic

energy and stick to the surface resulting in the rise in temperature of

the system i.e. heat is evolved. In chemisorption, the molecules stick

to the surface, as a result of the formation of chemical bonds, usually

covalent bonds and tend to find the site that increases their

coordination number with the temperature. Thus the energy of

attachment is in the range of 40 to 200 KJ mol~'.

For a spontaneous process, AG should be negative. As the

species is adsorbed, there is reduction in its translational freedom. So,

AS is also negative. Hence, AH must be negative if AG = AH - TAS is

to be negative and a negative AH corresponds to the exothermic

process. But sometimes the adsorbate dissociates at high temperature,

thus leading to breaking of bonds -and high translational mobility on

the surface, in that case enthalpy is small and positive. f . i '

Plotting of adsorption isotherms is the most convenient way of

studying and understanding the nature of adsorption taking place in a

particular system. The isotherms are obtained by plotting the amount

adsorbed against the equilibrium concentration at any instant at a

particular temperature. Different models for adsorption isotherm,

applicable to both gases and liquids, are available in literature. Two of

the most common models are however being discussed in brief as

follows :-

1. Langmuir Model

Langmuir proposed

Ce 1 1 1 ^ — = — — + — . Ce Xm K b b

Where Ce is the equilibrium concentration and Xm is the

amount adsorbed per specified amount of adsorbent. K is the

e(|uilibrium constant and b is the amount of adsorbate required to foim

a monolayer. Hence a plot of Ce/Xm vs Ce should be a straight line,

with a slope equal to 1/b and intercept equal to (1/K) . (1/b).

2. Freundlich Model

According to this model

Xm = K.Ce'/"

In Xm = In K + 1/n.lnCe.

where all the terms have usual significance and n is an empirical

constant, thus a plot of In Xm Vs In Ce should give a straight line

with a slope equal to 1/n and intercept gives the value of InK.

This model deals with the multilayer adsorption of the

substance on the adsorbent. Alumina, silica, cellulose and carbon are

most commonly studied adsorbents. They are mainly used for the

adsorption of phenols, organic acids, hydrocarbons, alcohols, dyes.

10

pesticides and pollutants etc. Literature survey reveals that even

inorganic ion exchanger^and organic synthetic resins have also been

used for many adsorption studies Table 1.1.

In addition to the materials mentioned so far, a number of other

types of exchangers have been developed, e.g. "electron ion

exchangers" and "redox ion exchangers". The electron ion exchangers

are solid oxidizing and reducing agents. They are, as a rule, resins

with a cross linked hydrocarbon matrix. They contain the species such

as quinone/hydroquinone, forming a redox couple which can be

reversibly oxidised or reduced. They can be regenerated by a suitable

reducing (or oxidising) agent after having been oxidised (or reduced)

by a substrate.

Redox ion exchangers are conventional ion exchange resins

containing reversible oxidation-reduction couples such as Fe- ' /Fe^V,

Cu^VCu or methylene blue etc (97-98). These redox couples are held

by the ion exchange resins (eg Dowex-50, cation exchange resin)

either as a counter ion or by sorption or complex formation. Duolite

S-10 is a commercial redox ion exchanger.

The behaviour of redox ion exchangers and electron ion

exchangers is similiar to that of the soluble oxidation-reduction

couples. The redox potential of a couple is little affected by

incorporation of the couple into a resin (100,101). In its reduced form

the redox ion exchanger can reduce the couples having a higher

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17

standard redox potential, whereas in its oxidised form it can oxidise

the couples having a lower redox potential. Standard redox potentials

of some of the most common redox couples are given by Latimer

(102).

The redox ion exchangers possess some advantages over

dissolved oxidizing or reducing agents. The most important advantage

is their insolubility and hence they can be easily separated from the

solution containing a substrate being oxidised or reduced, No

contamination of the solution by these exchangers occur as only

electrons and protons are transferred between the exchanger and

solution phases. The only possible change in solution, except for the

redox reaction of the substrate,is a change in pH. Another advantage is

that they can be easily regenerated after use by a suitable reducing or

oxidising agent.

Redox ion exchangers and electron ion exchangers are

characterized by their redox capacity, redox potential and rate of the

reaction. The redox capacity is the amount of a substrate being

oxidised or reduced by a specified amount of the exchanger and is

expressed in terms of the milliequivalents per gram of dry resin. The

reaction rate determines the time required for the redox process under

a given set of conditions. The standard redox potential indicates,

which subtrate can be reduced or oxidised. Some important redox ion

exchangers are listed in Table 1.2.

IB

Table 1.2 : Redox Ion Exchangers And Their Redox Capacity.

S.No. Name of the Redox Redox Capacity References ion exchanger (meq/g)

1. 2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

Zirconium phosphoiodate

Hydrazine sulphate sorbed zinc silicate

Polystyrene based redox resin

Phosphonic acid type redox resin

Phosphomolybdo-vanadic acid

Tetra chloro-hydroquinone

Tetra chloroquinone

p-benzoquinone melomine copolymer

Zirconium molybdovanadate

Alkali and Nickel ferrocynide

Phospho tungstovanadic acid

Active carbon

Zeolite alumino silicate

Zirconium peroxide metatungstate

Molybdenum benzoinoximate

Redox polyampholytes based on poly (aminoquinones)

Zirconium silico molybdate

-

-

-

-

0.318

-

-

4.00

0.520

-

-

-

-

-

-

"

~

103 104

105

105

106

107

108

109

110

111

112

113

114

115

116

117

118

19

Chromatography is an analytical method based on differences in

the partition coefficient of substances distributed between stationary

and mobile phases, usually a great surface area and a moving fluid

phase. Thin layer chromatography (TLC) together with paper

chromatography comprise "planar" or "flat-bed" chromatography is the

simplest of all of the widely used chromatographic methods to

perform.

The history of liquid chromatography dates back to the first

description of chromatography by Michael Tswett (119) in early

1900's, who separated components of plant pigments by passing their

solutions through columns of solid adsorbents. Stahl (120,121),

Kirchner (122) and Pelick et al (123) have reviewed the history of

TLC. TLC is a relatively new discipline and chromatography

historians usually date the advent of modem TLC from 1958. The

review of Pelick et al. tabulated significant early developments in TLC

and provide4 translations of classical TLC studies by Izmailov and

Schraiber and by Stahl. In 1938, Izmailov and Schraiber separated

certain medicinal compounds on unbound alumina spread on glass

plates. Since they applied drops of solvent to the plate containing the

sample and sorbent layer, their procedure was called "drop

chromatography". Meinhard and Hall in 1949 used a binder to adhere

alumina to microscope slides, and these layers were used in the

separation of certain inorganic ions using drop chromatography.

20

In the early 1950's Kirchner and colleagues (124) at the U.S.

Department of Agriculture developed TLC as we know it today. They

used sorbent held on glass plates with the aid of a binder and plates

which were developed with conventional ascending procedures used in

paper chromatography. Kirchner coined the term "Chromostrips" for

his layers. Stahl introduced the term "Thin layer chromatography

(TLC)" in the late 1950's. His major contributions were the

standardization of materials, procedures and nomenclature and the

description of selective solvent systems for resolution of important

compound classes.

Quantitative TLC, introduced by Kirchner et al in 1954 (124),

described an elution method for direct measurement of bands

separated by means of electrophoresis and was later used on paper

chromatograms. Densitometry in TLC was initially reported in the mid

1960's by Dallas et al. (125) using the Joyce Loebl Chromascan and

by Genest (126) and Thomas et al. (127) using the Photovolt

densitometer. A symposium on quantitative TLC held in 1968 in Great

Britain led to the 1"' book published on this topic (128).

High performance TLC plates (129) were produced

commercially in the mid-1970's and provided impetus for the

improvements in practice and instrumentation that occured in the late

1970's and 1980's and led to the methods termed "High-performance

thin layer Chromatography (HPTLC)" (130) and "instrumental

21

HPTLC" (131), centrifugally accelerated preparative-layer

chromatography (132) and forced-flow techniques in TLC

(overpressured layer chromatography, OPLC) (133) were introduced in

the late 1970's.

TLC is highly sensitive, selective, quantitative, rapid and

automated technique for analysis of all types of samples and analytes

and for preparative separations. The biennial review by Sherma (134)

of advances in theory, practice and applications of TLC is

indispensable.

TLC involves the concurrent processing of multiple samples and

standards on an open layer developed by a mobile phase. Development

is performed, usually without pressure, in a variety of modes,

including simple one dimensional, multiple, circular and

multidimensional. Paper chromatography, which was invented by

Consden, Gordon and Martin in 1944, is fundamentally very similar to

TLC, differing mainly in the nature of the stationary phase. Paper

chromatography has lost favour compared to TLC because the latter is

faster, more efficient and allows more versatility in the choice of

stationary and mobile phases.

HPTLC layers are smaller, contain sorbent with a smaller, more

uniform particle size, are thinner and are developed for a shorter

distance compared to TLC layers. These factors lead to faster

separations, reduced zone diffusion better separation efficiency, lower

22

detection limits and less solvent consumption. However, smaller

sample, more exact spotting techniques are required.

Column liquid chromatography involves the elution under

pressure of sequential samples in a closed, "On-line" system, with

dynamic detection of solutes, usually by UV adsorption.

TLC is most versatile and flexible chromatographic method. It

is rapid because precoated layers are usually used as received without

preparation. Even though it is not fully automated like HPLC, TLC

has the highest sample throughout, because upto 30, individual

samples and standards can be applied to a single plate and separated at

the same time. Modem computer-controlled scanning instruments and

automated sample applicators and developers allow accuracy and

precision in quantification that rival HPLC and GC. There is a wide

choice of layers, developing solvents (acidic, basic, completely

aqueous, aqueous organic) and detection methods. Every sample is

separated on a fresh layer, so that carry over and cross contamination

of samples and sorbent regeneration procedures are avoided. Mobile

phase consumption is low, minimizing the costs of solvents and waste

disposal because layers are normally not reused, sample preparation

methods are less demanding and less pure samples can be applied. The

wide choice of detection reagents leads to unsurpassed specificity in

TLC, and all components in every sample including irreversibly

sorbed substances, can be detected visually. There is no need to rely

23

on peaks drawn by a recorder or to worry about sample components

possibly remaining uneluted on a column. Being an "off line" method,

the various steps of the procedure are carried out independently. This

allows zones to be scanned repeatedly with different parameters that

are optimum for individual sample components.

The beginning of inorganic chromatography may be attributed to

the work of Runge on paper chromatography (135), and Beyerinck on

thin layers of gelatin (136). Planar chromatography has found wide

use in forensic chemistry, identification of drug samples. Since years,

TLC technique has been applied in the analysis of organic and

inorganic substances and for the analysis of pharmaceutical, biological

and environmental samples (137). In addition to the analysis of

aminoacids, bases, steroids, pesticides, toxins and inorganics, TLC and

HPTLC technique is also applicable in drug formulations,

pharmaceutical preparation and in analysis of Lipid.

The ion exchange property of the adsorbent plays a more

prominent role than its simple adsorption behaviour. The analytical

capabilities of synthetic inorganic ion exchangers as thin layer

materials in TLC had been reviewed by Sherma and Fried (138). For

the sake of convenience, inorganic ion exchangers are classified into

four categories, and all of them find their use in TLC :

(a). Thin layer of hydrated oxide.

(b). Thin layer of insoluble metal salts of polybasic acids.

24

(c). Thin layer of heteropoly acid salts.

(d). Thin layer of metal ferrocyanide.

For the first time, zirconium oxide was used for the separation

of metal ions by Zabin and Rollins (139). Berger et al. (140, 141)

used zirconium oxide for the study of ferrocyanide, sulfocyanide and

ferricynide. Terpenes were separated on the layers of zirconium oxide

by Kirchner et al. (142). Ortho-para and meta amino phenols were

separated by TLC on titanium oxide layers by Grace (143). Alberti et

al. (144) studied the movement of cations on the titanium phosphate

layer. The movement of cations was also studied on the layers of

zirconium hypophosphate and cerium phosphate by Keonig and Deniiel

(145) and Keonig and Gray (146) respectively. The movement of 47

metal ions on stannic arsenate layers was studied by Sherma et al.

(147). Qureshi et al. (148) reported 20 binary separations of metal

ions on non refluxed stannic arsenate layers. Amino acids were

separated on stannic tungstate layers by Nabi et al. (149). Rawat et al.

(150, 151) used zinc silicate as a adsorbent for paper chromatographic

separations of phenols and amines respectively. Chromatography of

some metal ions on ligand combined ion exchange papers was studied

by Rawat and Chitra (152). TLC method (153) was developed for

quantitative separation of Hg(II) from several metal ions on

lanthanum antimonate layers. TLC behaviour of 28 phenolic

compounds was studied on stannic tungstate layers (154). Tin

vanadopyrophosphate layers was used for the anlaysis of amino acids

25

by HPLC method (155). Layers of lanthanum silicate were used to

study the behaviour of 28 metal ions by Husain et al. (156).

Zhengquan et al. (157) studied TLC application of Ce metaphosphate

layer in the separation of 10 metal ions. TLC behaviour of 30 cations

using Ce(Ill) silicate was studied by Husain et al. (158) Kawamura

and co-workers (159) have analysed various alkali metals on layers of

zinc ferrocyanide. Recently inorganic ion exchanger layers have been

used as adsorbent for studying the behaviour of pesticides by TLC

method. Qureshi et al. (160) used zirconium phosphate layer for the

separation of carbamate pesticides and related compounds.

In the present work sorption equilibria of transitional metal ions

[Nickel (II), Cadmium (II), Cobalt (II) and Iron (III)] on Duolite ES

467 at 20 to 50°C have been studied and various thermodynamic

parameters, such as standard free energy (AG°), standard enthalpy

(AH°) and standard entropy (AS°) changes are evaluated. The

application of inorganic ion exchanger, stannic molybdate as an

electron exchanger have been carried out by studying its redox

property. A new redox exchange material has been prepared by

immobilising hydrazine sulphate on Duolite ES 467. The successful

reduction of certain metal ions has been studied. The application of

the inorganic ion exchanger stannic oxide, have been extended to the

thin layer chromatographic separations of organophosphate pesticides

(chloropyriphos, methyl demeton, dimecron, dimethoate, malathion,

monocrotophos, quinolphos) which are responsible for environmental

pollution.

26

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Chapter - / /

SORPTION EQUILIBRIA OF SOME TRANSITIONAL METAL IONS ON A CHELATING ION EXHANGE RESIN,

DUOLITE ES 467

INTRODUCTION

Ion exchangers especially chelating and ligand ion exchangers

have received attention during the past decade due to their definite and

specific selectivity towards certain ions or groups of ions. In analytical

as well as in preparative inorganic chemistry there exists a need for

chelating and ligand polymers that combine the ease of operation of

conventional ion exchangers and the selectivity of organic analytical

reagents. The selectivity of most organic reagents for metals resides

predominantly in their ability to form chelates with certain cations.

This leads to the formation of organic polymers that contain ligand or

chelate forming groups as exchanging functions. The selectivity

behaviour of these resins is based on the different stabilities of metal

complexes on the resins at appropriate pH-values. The influence of

complex formation on ion exchange sorption equilibria and on the

distribution of metal ions between the liquid and resin phases has

extensively been studied (1-5).

Ion exchange resins having chelating groups i.e. having electron

donor groups are more in use due to the demanded selectivity and

sufficient mechanical and chemical stability especially towards acids

and bases.

Duolite ES 467 is a macroporous weakly acidic polystyrene resin

containing a chelating functionality due to the presence of amino

41

phosphonic group. This group present in the resin forms complexes

with metallic ions. It differs from other chelating resins containing

amino acetate groups by its tendency to form stable complexes even in

the presence of other cations. Duolite ES 467 forms more stable

complexes with the metallic cations of low atomic mass.

The adsorption studies of metal ions on some ion exchange resins

have been reported on Duolite A 101 and Duolite C-264 (6), KRP 5P,

KRF 2P & SF 5 (7,8), Dowex A 1 (9), NKA 9 resin (10), Amberlite

IRA 68 (11).

The present work summarizes the sorption behaviour of some

metal ions on Duolite ES 467. Effect of temperature is studied and the

thermodynamic parameters AG°, AH° and AS° are evaluated.

EXPERIMENTAL

Materials

Synthetic Duolite ES 467 in hydrogen form was a Rohm & Hass Co.

product (U.S.A.). Reagent grade metal salts of four different metals were used

which were standarised by titrating against EDTA solution (12).

Apparatus

An electrical temperature controlled SICO shaker was used for

shaking.

42

Procedure

Hydrogen form of the exchanger was washed with deionized

water to remove all the excess of acid. It was then dried at 40°C. The

dried product of a constant mesh size (0.5-0.25 mm) 35-60 sieve mesh

no. (U.S. Standard) was used for further experimental work.

Surface Area

The surface area (A) of the exchanger was determined by the

method proposed by Dyal and Hendricks (13). This method is applied

only for the estimation of external surface area. For this purpose , 2gnr

of the exchanger was takep in a small aluminium box and placed in a

dessicator over 250 gnr PjOj. The weight of the dried exchanger was

measured. The exchangeer was then wetted with ethylene glycol added

from a pipette dropwise and placed in a dessicator at 25±1°C to

evaporate excess of ethylence glycol. This exchanger was weighed

several times till a constant weight was observed. Surface area was then

calculated from the equation.

(W^-W,) Surface Area (A) = (1)

W, X 0.00031

Where W, and W2 are weights ( g ^ of the dried exchanger and

exchanger wetted with ethylene glycol, respectively, and 0.00031 is the

Dyal and Hendricks value for the grams of ethylene glycol required to

form a monolayer on one m^ surface area of the exchanger.

43

Effect of Time

The effect of time on the sorption of metal ions by the exchanger

was determined by batch process by taking 0.2 gm exchanger with 20

ml of aqueous metal nitrate solution containing 0.09 mmoles/20ml metal

ion in stoppered conical flask. The flasks were shaken for different time

intervals in a temperature controlled SICO shaker at 25±1°C. The

amount of metal ions left was determined in the supernatant solution

titrimetrically by EDTA titration using PAN indicator.

Eqilibrium Studies

For equilibrium studies 0.2 gnli of the exchanger in H" form was

taken in different stoppered conical flasks containing varying amounts

of pure metal nitrate solution and the volume adjusted to 20 ml with

distilled water. The flasks were shaken thoroughly in a temperature

controlled shaker for 6 hrs at a desired temperature. Experiments show

that equilibrium was attained within this period. The corresponding

original solution and the metal ion left unexchanged were determined

by titrating with EDTA solution using the recommended procedure (12).

RESULTS

The results of the effect of equilibrium time on the sorption of

metal ions [Nickel (II), Cadmium (II), Cobalt (II), Iron (III)] on Duolite

ES467 are presented in Table 2.1 to 2.2, and plotted in figure 2.1. The

44

g

u e 08

I

e '•5 Cu e

e e « E

a

« ^ vo

U e . Q

= E 3

E •a ei

U

/ — N 1 — ^m

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u 2 S -S E 3 :•= H .s §• £ u

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• o o « n o « n o o o o

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46

25

Fig. 2.1

50 75 100 Time(min.)

125 150

Time dependence of sorprion of some transitional metal ions on Duolite ES467.

47

sorption isotherms of metal ions on Duolite ES467 at four different

temperatures are plotted in figure 2.2 to 2.5, and the results are given in

Table 2.3-2.18. The plots for Langmuir isotherms, Ce/(x/m) vs Ce are

presented in Figure 2.7 to 2.10, and the values of Langmuir constants

'K' and 'b' are given in Table 2.35.

The plots of hi Cs/Ce Vs Cs for the metal ions are presented in Figures

2.11 to 2.14 and these values are given in Table 2.19 to 2.34. The diermodynamic

equilibrium constant, Ko, obtained from these plots are given in Table 2.36. The

entiialpy change was evaluated from the plots of In Ko Vs 1/T and is presented

in Figure 2.15. The free energy change and entropy change are calculated by

using appropriate equations. The values of various thermodynamic parameters

are summarized in Table 2.36.

DISCUSSION

Duolite ES 467 is a macroporous weakly acidic polystyrene resin

containing a chelating functionality due to the presence of

aminophosphonic group. Its structure is:

O II

R - CHj - HN - CH2 - P - OH

OH

and it forms complex with a metal ion M as follows

4b

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M

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< ft.

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< -fi

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2 •• « O >M^ »• E — 0

U

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1 ^ J "© E S

1

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0 10 20 30 40

Ce X l O " 3 ( m m o l e s / m i )

Fig. 2.3 Sorption isotherms of Cadmium (II) on Duolite ES467.

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Fig. 2.4

10 20 30 40 Ce X 10"^ (mmoles/ml)

Sorption isotherms of Cobalt (II) on Duolite ES467.

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Fig. 2.5

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Sorption isotherms of Iron (III) on Duolite ES467.

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^ 1 - ^

^ • v — " '

b»

100

I O

X

0 10 20 30 4 0

Ce XlO'^(mmoles/ml)

Fig. 2.7 Langmuir isotherm for Nickel (II) on Duolin ES467.

b9

0 10 20 30 40 Ce X 10'^ (mmoles/ml)

Fig. 2.8 Langmuir isotherm for Cadmium (II) on Duolite ES467.

90

100 h

I

o

0>

u

10 20 30 40

Ce X I0~^(mmoies/ml)

Fig. 2.9 Langmuir isotherm for Cobalt (II) on Duolite ES467.

91

100 -

b K

9t yxjmr^

' / ^ ' > ^ # /

-f f. , . 1

o20'*C • 30* 0 X iiO C i 50'*C

1 i 1 1 1 0 10 ?0 30 40

CeXlO*3(mmoles /ml)

Fig. 2.10 Langmuir isotherm for Iron (III) on Duolite ES467.

92

3.00 4 0 0 5 0 0 6.00 7.00

CsXlO^ (mmoles/Qin)

Fig. 2.11 Plots of In/Ce vs Ce of Nickel (II) on Duolite ES467.

93

3.00 A.00 5.00 6.00 7.00 8 0 0 9.00 CsXlO^(mmotes/gm)

Fig. 2.12 Plots of In Cs/Ce vs Ce of Cadmium (II) on Duolite ES467.

94

2.00 3.00 AOO 5.00 600 800 CsXiO (mmoles/gm)

Fig. 2.13 Plots of In Cs/Ce vs Ce of Cobalt (II) on Duolite ES467.

9b

2.00 3.00 4.00 5.00 6.00 7.00 CsX 10^ (m moles/gn^)

8.00

Fig. 2.14 Plots of In Cs/Ce vs t e of Iron (III) on Duolite ES467.

96

3.2 3.3 I /TXIO^

Fig. 2.15 Determination of enthalpy of sorption of different transitional metal ions on Duolite ES467.

97

R-CH^-NH

The results of the effect of equilibrium time on the sorption of metal ions

[Ni(II), Cd(II), Co(II), Fe(III)] on Duolite ES 467 (H ^ foim). Table 2.1 and 2.2,

and Figure 2.1, shows that the soq)tion increases with the increase in time of

equilibrium for certain time, after that it becomes constant at one hour for Ni(II)

and Co(II) and one and quarter hours for Cd(II) and Fe(III). Therefore these

periods were chosen for all sorption studies of corresponding metal ions on

Duolite ES 467 (H^ form).

Sorption of metal ions on Duolite ES467 was studied by batch

process in the concentrarion range 0.09-0.90 mmole/20 ml at 20°, 30°,

40° and 50°C. The sorption isotherms were plotted between the amount

of metal ion sorbed per gram exchange (mmoles/gm) and the amount of

metal ions in equilibrium solution (mmoles/ml). The isotherms (Figure

2.2 to 2.5) show that sorption of Cd(II) was higher than the other metal

ions studied. LM^A^/

The sorption isotherms (plots of x/m vs Ce) at 20°-50°C also

reveal the fact that the sorption of each metal ion increases as

temperature increases from 20° to 40°C and start decreasing on further

9b

increase in temperature to 50°C. These results are further confirmed

by the plot of x/m vs temperature (Figure 2.6) showing that sorption

increases from 20 to 40°C and decreases on further increase of

temperature to 50°C, showing that the sorption of metal ions is governed

by chemisorption phenomenon.

The plots for Langmuir isotherms, Ce/(x/m) vs Ce (Figure 2.7 to

2.10), shows that the sorption behaviour of metal ions on Duolite ES

467 is in close agreement with the linear form of Langmuir equation

(14).

Ce 1 Ce = + * (2)

x/m Kb b

where K and b are constants which represent the binding energy

coefficient and sorption maxima respectively. The plots of Ce/(x/m)

against Ce (Figure 2.7 to 2.10) gave the curves that are very close to

straight lines. These curves are modified in the form of straight lines

and extrapolated tangentially to calculate Langmuir constants, 'K' and

'b' from the intercepts and slopes of these plots respectively. The values

of Langmuir constants 'K' and 'b' for metal ions are reported in Table

2.35, indicating higher values of Langmuir constants for cadmium than

for other metal ions.

The thermodynamic equilibrium constant, Ko, obtained from

these plots are given in Table 2.36. The thermodynamic equilibrium

100

solution approached zero, the activity coefficient approached unity.

Equation (3) may then be written as

lim Cs Cs >o = Ko (6)

Ce

The values of Ko were obtained by plotting In Cs/Ce vs Cs and

extrapolating to zero Cs (Figure 2.11-2.14 ).

From the values of thermodynamic equilibrium constant, free

energy changes (AG°) during the sorption were calculated from the

relationship (18).

AG° =-RTlnKo (7)

where R is the universal gas constant and T the absolute

temperature.

The standard enthalpy change (AH°) was calculated by using the

integrated form of the Vant Hoff equation.

/ K, \ AH" A 1 .

where Kj and K2 are the thermodynamic equilibrium constants at

temperatures T, and Tj respectively.

The enthalpy change (AH°) value was evaluated from the plots of

In Ko versus 1/T (Figure 2.15) and the entropy changes (AS°) were

calculated from AH° and AG° values using the equation

101

AH° - AG° AS° = (9)

The values of thermodynamic equilibrium constants, free energy

changes, enthalpy changes and entropy changes at 20°, 30°, 40° and

50°C for the sorption of metal ions on Duolite ES 467 are reported in

Table 2.36. These results show higher value of Ko from 20° to 40°C and

the value of Ko decrease at 50°C. The values of K^ were higher for

cadmium ions than that of other metal ions confirming that sorption of

cadmium ion by Duolite ES467 was higher at all temperatures.

The results (Table 2.36) show negative values of AG° for the

sorption of metal ions on Duolite ES 467 at all temperatures. The higher

values of standard free energy (AG^ ) at 40^C followed by those at 30^

and 20''C might be due to the existence of weak attractive forces at

higher temperature. It is clear from these resuhs that overall enthalpy

change AH° of the system is negative which indicates, that the sorption

of metal ions on Duolite ES 467 is exothermic and the product is

energetically stable with a high binding of metal ion to the exchange

site. The resuhs of Table 2.36 shows that negative values of AG°

confirm that the sorption process has a natural tendency to proceed

spontaneously. The entropy of the system changes with temperature.

The lowest value of entropy is observed at 20°C and highest at 40°C.

However, at 50^C a slight decrease in entropy is observed. The positive

value of AS* suggests an increased, randomness at the solid/solution

102

interface during the sorption process. The sorbed solvent molecules

displaced by the adsorbate species gain more translational entropy than

that lost by the adsorbate ions, thus allowing for the increasing extent

of randomness of the system. The negative value of entropy change for

FeCIII) suggests that there was reduction in translational freedom when

the solute was sorbed.

103

REFERENCES

1. J.P. Rawat and K.P.S. Muktawat, / Inorg. Nucl. Chem., 43, 2121

(1981).

2. A. Masaaki, A. Takaaki and K. Hiryuki, Fugimota Satsui Nippon

Kagaku. Kaishi, 8, 1310 (1984).

3. A.A. Khan and R.P. Singh, Colloids Surfs., 24(1), 33 (1987).

4. J.P. Rawat, A. Ahmad and A. Agrawal, Colloids and Surface,

46,239 (1990).

5. C. Heonles, J. Suk Kim, M. Yulsuch and W. Lee, Anal. Chim.

Acta, 339 (3), 303(1997).

6. A. El-Hourch, S. Belcadi and M. Rumeau, Analusis, 14(8), 401

(1986).

7. S.N. Gadzhiev, A. Yu Leikin, A.N. Amelin and S.V. Kertman, Zh

Fiz. Khim., 60(11), 2848 (1986) .

8. A.N. Amelin, S.N. Gadzhiev, S.V. Kertman and A. Yu Leikin, Zh.

Fiz. Khim., 60(11), 2859 (1986).

9. J.N. Mathur and RK. Khopkar, Solvent Extr Ion. Exch., 3(5),

753 (1985).

10. He Xingcun and J. Yimin, Guijinshu. 18(4), 35 (1997).

11. J. Ruey-Shin and S. Lih-Dong, Ind. Eng Chem. Res., 37(2), 555

(1998).

12. C.N. Reilley, R.W. Schmid and F.S. Sadek, J. Chem. Education,

35, 555 (1959).

104

13. R.S. Dyal and S.B. Hendricks, Trans 4th Inter. Congs. Soil Set,

1, 71(1950).

14. I. Langmuir, J. Am. Chem. Soe., 40, 1361 (1918).

15. Y. Fu, R.S. Hansomand and F.E. Bartell, J. Phy. Chem., 52, 374

(1948).

16. K. Kodera and Y. Onishi, Bull. Chem. Soc. Jpn., 32, 356 (1959).

17. R.A. Robinson and R.H. Stokes, "Electrolyte Solution",

Butterworths, London (1959).

18. RW. Atkins, Physical Chemistry, Oxford University Press,

London (1983).

Chapter - / / /

REDOX STUDIES ON HYDRAZINE SULPHATE SORBED

DUOLITE ES 467

INTRODUCTION

The redox exchangers may be considered as solid oxidizing or

reducing agents. They contain the species forming a redox couple and

after having oxidised (or reduced) a substrate the redox exchangers

can be regenerated by a suitable oxidizing or reducing agent. The most

important advantage of redox exchangers over dissolved oxidizing or

reducing agent is their insolubility and hence a redox exchanger can

be easily separated from the solution containing a substrate being

oxidised or reduced. The solution is free from contamination of a

redox agent or its product. Only electrons are transferred between the

exchangers and the only possible change in the solution, except for the

redox reaction of the substrate, is a change in pH. Another advantage

of electron exchangers is that they can be easily regenerated (oxidised

or reduced) after use. The redox ion exchangers which contain the

redox couple in the exchanger phase also behave in a way similar to

electron exchangers. The few synthetic inorganic ion exchangers have

been used as electron ion exchangers (1-5) and as redox ion

exchangers (6-12).

In this chapter, the studies on a redox exchange material are

reported. The material has been prepared by the sorption of a reducing

agent, hydrazine sulphate, on Duolite ES467. The successful reduction

of Fe(III), V(V), Mo(VI), Ce(IV), Cr(VI), Sb(V) and As(V), have been

achieved quantitatively using the above redox exchange material.

10b

EXPERIMENTAL

Reagents

Synthetic Duolite ES467 in H" form was a Rohm & Hass co-

product (USA), Hydrazine Sulphate (Merck) was used. All the other

reagents were of analytical grade.

Apparatus

An electrical temperature controlled shaker (SICO) was used for

shaking.

Procedure

H^ form of exchanger was washed with deionized water to

remove all the excess of acid. It was then dried at 40°C. The dried

product of mesh size (0.5-0.2 mm) 35-60 sieve mesh no. (U.S.

Standard) was used for further experimental work.

Hydrazine Sulphate Uptake

The capacity of Duolite ES467 to take up hydrazine sulphate

from its aqueous solution was estimated by shaking a predetermined

quantity of hydrazine sulphate solution with one gram of the

exchanger for six hours in a temperature controlled shaker at a desired

temperature. Amount of hydrazine sulphate remaining in the supemate

was then determined by titration against 0.05M KBrO^ solution using

indigo as indicator (13). The amount of hydrazine sulphate taken

107

initially minus the amount found finally after shaking with the

exchanger gave the total amount of the reducing agent taken up by the

exchanger.

RESULTS

Chemical Stability

1 0.5 gm of the hydrazine sulphate sorbed Duolite ES467 was

shaken with the appropriate solvent for six hours at 40°C in a

temperature controlled shaker. The amount of hydrazine sulphate

released into the solution was determined in the supernatant liquid in

the manner mentioned above. The results are summarized in Table 3.1.

Table 3.1 : Dissolution of Hydrazine Sulphate

S.No.

1.

2.

3. 4.

5.

6. 7.

Solvent

Deionized water

1 MHCl

2MHC1

1 M H2SO4

2 M H2SO4

1 M NH4OH

1 M NaOH

Redox Studies

Hydrazine Sulphate Released (meq)

0.00

0.02

0.06

0.01

0.04

0.0

0.01

Reduction of some reducible ions possessing higher redox

potentials than hydrazine/NHj couple have been carried out by batch

10b

process. Reduction of Fe(III), Mo(VI), V(V), Ce(IV), Cr(VI), Sb(V)

and As(V) to their respective lower oxidation states were performed

by taking the weighed amount of exchanger in stoppered conical flasks

and shaking thoroughly with their solutions in a temperature controlled

shaker for six hours. Mo(V) and Fe(II) obtained were determined by

titrating with a standard solution of KMnO^ (14, 15). V(V)(16),

Ce(VI) (17), Fe(III) (18), Sb(V) (19), Cr(VI) (20) and As(V) (21) were

determined iodometrically before and after reduction. The amount

initially taken minus the amount fmally found gave the total amount

reduced by the exchanger.

(a) Reduction of Fe(III) to Fe(II)

Results of reduction of Fe(III) to Fe(II) is given in Table 3.2.

Table 3.2 : Reduction of Fe (III) to Fe(II)

Amount of / Exchanger (gdi)

..0 f /

1.0

I.O

1.0

1.0

Fe(ni) Taken (meq)

0.105

0.165

0.210

0.260

0.315

Fe(II)

found (meq)

0.095

0.145

0.200

0.220

0.300

(b) Reduction of V(V) to V(IV)

Results of reduction of V(V) to V(IV) are given in Table 3.3.

109

Table 3.3 : Reduction of V(V) to V(IV)

Amount of exchanger (gm)

1.0

1.0

1.0

V(V) taken (meq)

0.062

0.124

0.186

V(IV) found (meq)

0.062

0.122

0.180

1.0 0.248 0.238

1.0 0.370 0.310

(c) Reduction of Mo(VI) to Mo(V)

Results of reduction of Mo(yi) to Mo(V) are presented in Table 3.4.

Table 3.4 : Reduction of Mo(VI) to Mo(V)

Amount of exchanger (gm)

1.0

1.0

1.0

1.0

1.0

Mo(VI) taken (meq)

0.075

0.150

0.250

0.300

0.330

Mo(V) found (meq)

0.065

0.150

0.235

0.275

0.310

(d) Reduction of Sb(V) to Sb(III)

Results of reduction of Sb(V) to Sb(III) are presented in

Table 3.5.

110

Table 3.5 : Reduction of Sb(V) to Sb(III)

Amount of Sb(V) Sb(III) exchanger (gm) taken (meq) found (meq)

1.0 0.065 0.065

1.0 0.130 0.126

1.0 0.195 0.187

1.0 0.254 0.240

I.O 0.375 0.306

(e) Reduction of Cr(VI) to Cr(III)

Results of reduction of Cr(VI) to Cr(III) are given in Table 3.6.

Table 3.6 : Reduction of Cr(VI) to Cr(III)

Amount of exchanger (gm)

1.0

1.0

1.0

1.0

1.0

Cr(VI) taken (meq)

0.05

0.15

0.20

0.25

0.31

Cr(III) found (meq)

0.05

0.132

0.198

0.242

0.306

(f) Reduction of Ce(IV) to Ce(III)

Results of reduction of Ce(IV) to Ce(III) are presented in Table 3.7 :

I l l

Table 3.7 : Reduction of Ce(IV) to Ce (III)

Amount of exchanger (gm)

1.0

1.0

1.0

1.0

1.0

Ce(IV) taken (meq)

0.038

0.114

0.152

0.190

0.228

Ce(lII) found (meq)

0.038

0.104

0.143

0.178

0.203

(g) Reduction of As(V) to As(IIl)

Results of reduction of As(V) to As(III) are given in Table 3.8.

Table 3.8 : Reduction of As(V) to As(III)

Amount of exchanger (gm)

1.0

1.0

1.0

1.0

1.0

As(V) taken (meq)

0.160

0.205

0.235

0.310

0.355

As(III) found (meq)

0.105

0.180

0.210

0.280

0.300

Maximum Redox Capacity

(a) By Batch Process /

Maximum redox capacity was determined by keeping 1 gn/of

hydrazine sulphate sorbed Duolite ES467 in excess of solutions of

112

reducing metal ions in the stoppered conical flask and shaking

thoroughly in a temperature controlled shaker for six hours. The

amount of metal ion initially taken minus the amount of metal ion

fmally found titrimctrically gave the total amount reduced by the

exchanger. The maximum capacity in equivalents was determined by

multiplying the volume of titrant with the concentration of titrant for

every metal ions. The results are given in Table 3.9.

Table 3.9 : Maximum redox capacity for some reducible substances

S.No. Substance Reduced Maximum amount Reduced (meq/gm)

0.30

0.31

0.31

0.306

0.203

0.306

0.30

1.

2.

3.

4.

5.

6.

7.

Fe(III)

Mo (VI)

V(V)

Sb(V)

Ce(IV)

Cr (VI)

As(V)

Rate of Reduction

The rate of reduction was determined by taking a weighed

amount of exchanger in stoppered conical flask and shaking

thoroughly with the solution concerned in a shaker. After appropriate

intervals of time the content of the flask were filtered and the reduced

113

Species formed was determined. The results are shown in Table 3.10

and in Figure 3.1.

Table 3.10 : Rate of Reduction of Vanadium (V) to Vanadium (IV)

Amount of Vanadium (V) taken - 0.500 meq.

Time (min) Amount of V(IV) found (meq)

1 0.135

5 0.230

10 0.295

15 0.300

20 0.310

30 0.310

40 0.310

60 0.310

90 0.310

120 0.310

DISCUSSION

The uptake of hydrazine sulphate by Duolite ES467 is found to

be 0.33 meq/gm. The chemical stability of the sorbed substance has

been studied in different concentration of acids and bases. Dilute

acidic, dilute basic and neutral solutions can be safely used for the

reduction processes.

114

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115

The results presented in Table 3.2 to 3.8 show the successful

reduction of Fe(III) to Fe(II), V(V) to V(IV). Mo(VI) to Mo(V). Sb(V)

to Sb(III), Cr(VI) to Cr(III), Ce(IV) to Ce(III) and As(V) to As(in).

The results indicate that the maximum amounts of Fe(III), V(V),

Mo(VI), Sb(V), Cr(VI), Ce(IV) and As(V) which can be reduced by

one gram of the exchanger are 0.30 meq, 0.31 meq, 0.31 meq, 0.306

meq, 0.306 meq, 0.203 meq and 0.30 meq respectively. For the

reduction of higher amounts of these substances, higher amounts of

the exchanger should be taken. It has been observed that except for

Ce(IV) the maximum redox capacity of one gram of the exchanger

ranges between 0.30 to 0.31 milliequivalents/gm (Table 3.9). This

shows that the total capacity of the column is utilized for every

reduction reaction mentioned above. The number of milliequivalents of

Ce(IV) reduced is only 0.203 which is far less then the number of

milliequivalents of hydrazine sulphate present in the exchanger.

The results of the redox studies show that the reduction of only

those substances are possible whose redox potentials are higher than

that of reducing agent incorporated with in the exchanger i.e.

hydrazine. Attempts to reduce Sn(IV) to Sn(ll) have been failed since

Sn(IV)/Sn(II) couple has a lower redox potential than hydrazine/NHj

couple. Redox potentials of some of the reducible species are given in

Table 3.11 to support the above discussion.

116

Table 3.11 : Standard Redox Potential of some Redox Couples

S.No. Redox Couple E" volts

1. Cr(VI) + 3e-= Cr(III) 1.33

2. Fe(III) + e- = Fe(II) 0.77

3. Ce(IV) + e-= Ce(III) 1.61

4. Sb(V) + 2e- = Sb(III) 0.58

5. V(V) + e-= V(IV) 1.00

6. Mo(VI) + e- = Mo(V) 0.53

7. As(V) + 2e- = As(III) 0.56

8. N2H4 + 2H2O + 2e- = NH^Caq) + 20H- 0.1

The rate of reaction indicates the time required for redox process

to complete under a given set of conditions. The rate of reduction of

V(V) to V(IV) is illustrated in Figure 3.1. It can be seen that only 20

minutes are required for complete conversion of V(V) to V(IV). This

fast rate of reduction is not found with the exchangers having Fe(III)

or Mo(VI) as oxidizing groups. The exchanger can be regenerated by

putting it in the hydrazine sulphate solution again for overnight.

117

REFERENCES

1. E.E. Ergozhin, R. Bakirova, B.A. Mukhitdinova and S.R.

Rafikov, Otkrytiya Izobert Prom. Obraztsy Tovarnyeznaki.

52(39), 68(1975).

2. E.S. Boichinova, R.G. Safma, V.V. Belova and L.G. Karitonova,

Zh, Prikl Khim., 49, 1385 (1976).

3. V.V. Volkin, S.A. Kolesova, M.V. Zilberman, L.A. Pykhtina,

V.V. Tetenou and A.V. Kalyuzhnvi, Zh. Prikl. Khim., 49, 1728

(1976).

4. J.R Rawat and S.I.M. Kamoonpuri, Annali dichimica (Rome),

79(5-6), 297 (1989).

5. E.E. Ergozhin, R.Kh. Bakirova, M.A. Mukhitdinova, T.Ya.

Smimova and K.I. Ergazieva, Izobreteniya, 7, 242 (1992).

6. E.E. Ergozhin, R.B. Alshabarova, S. Rafikov, B.A.

Mukhitdenova and B.A. Zhubanov, Obraztsy Tovarny Znaki,

51(36), 82 (1974).

7. S.K. Mandal and B.R. Sant, Anal. Lett., 8(8), 585 (1975).

8. V. Nguyen, Tapachi Hoa Hoc, 14(4), 19 (1976).

9. J.R Rawat and M. Iqbal, Ann. Chim. (Rome), 69, 241 (1974).

10. J.R Rawat, M. Iqbal and H.M.A.A. Aziz, J. Ind. Chem. Sac,

LX, 993 (1983).

l i b

11. E.E. Ergozhin, B.A. Mukhitdinova and R.Kh. Bakirova,

Vysokomal Soedin. Sen B., 30(1), 20 (1988).

12. T.S. Bondarenko and E.S. Boichinova, Zh. Prikl Khim., 66(10),

2213 (1993).

13. I.M. Kolthoff and R. Belcher, "Volumetric Analysis", Intersci.

Publisher Inc. N.Y., Vol. Ill, Page 524 (1957).

14. A.I. Vogel, "Quantitative Inorganic Analysis" Ilnd edn.

Longmans, London, Page 277 (1951).

15. Ibid, p. 276.

16. I.M. Kolthoff and R. Belcher, "Volumetric Analysis",

Interscience Publishers Inc. N.Y., Vol. Ill, Page 340 (1957).

17. Ibid, p. 367.

18. Ibid, p. 342

19. Ibid, p. 319.

20. Ibid, p. 239.

21. Ibid, p. 316.

Chapter - IV

ELECTRON EXCHANGE STUDIES ON

STANNIC MOLYBDATE

INTRODUCTION

Electron exchangers are insoluble in the medium of oxidation and

reduction and are readily separated from the substances in solution

with which they have reacted and thus do not cause the interference

which is unavoidable in common redox system. A large number of

these material are reported in previous chapter. Stannic molybdate has

been synthesized in our laboratories and has been used as inorganic

ion exchanger for the separation of metal ions (1,2). Also, Stannic

molybdate papers have been used for the chromatographic and

electrochromatographic separation of metal ions (3,4) and were found

to be selective towards cations. The selectivity of stannic molybdate

was mainly due to the ion exchange behaviour of the material and its

action as ionic sieve. Stannic molybdate papers have been used for the

chromatographic separation and identification of phenols. (5). The

material has been used for the detection of ferrous ions (6) because of

the reducing action of ferrous and oxidizing action of stannic

molybdate where the molybdate reduces to molybdenum blue. This led

us to use stannic molybdate as electron exchanger.

The present work describes the electron exchange studies on

stannic molybdate. The determination of Iron (II), stannous (H),

ascorbic acid, thioglycolic acid, hydrazine and hydroquinone have

been quantitatively achieved by their oxidation.

120

EXPERIMENTAL

Reagents

Stannic chloride (Loba), Ammonium heptamolybdate (Merck)

were used. All other chemicals were of Analytical grade.

Apparatus

An electrically temperature controlled SICO shaker was used for

shaking.

Synthesis

Stannic molybdate gel was prepared by mixing aqueous solutions

of 0.02M stannic chloride and 0.05 M ammonium heptamolybdate in

the (molar) ratio of 1:2. It was digested at room temperature, washed

with water, filtered and dried at room temperature. To convert it to the

hydrogen form it was immersed in 1-2M nitric acid for 24 hrs. it was

then washed several times with distilled water, filtered and dried in air.

RESULTS

Redox Studies

Oxidation of some oxidisable ions and organic compounds

possessing lower redox potentials (7) than Mo(VI)/Mo (V) couple

have been carried out by batch process. Oxidation of Fe (II), Sn(II),

ascorbic acid, thioglycolic acid, hydrazine and hydroquinone to their

respective higher oxidation states were performed by taking weighed

121

amount of exchanger (1 gm) in stoppered conical flasks and shaking

thoroughly with their solutions in a temperature controlled shaker for

six hours. Sn (II) and thioglycolic acid were determined iodometrically

(8,9), Sn (IV) was determined by method reported in literature (10),

hydrazine was determined by standard KBrO, solutions (11), ascorbic

acid was determined by standard solution of chloramine T (12), and

Iron (II) and hydroquinone were determined by titrating with a

standard solution of Ceric sulphate (13,14) before and after oxidation.

The amount taken initially minus the amount found finally gave the

total amount oxidised by the exchanger. The results obtained are

presented in Table 4.1 to 4.6.

Rate of Oxidation

The rate of oxidation was determined by taking a weighed

amount of exchanger in stoppered conical flasks and shaking

thoroughly with the solution concerned in shaker. After appropriate

intervals of time, the contents of the flasks were filtered and oxidised

species formed were determined. The results are presented in Table

4.7 and plotted in Figure 4.1.

DISCUSSION

The electron exchangers may be considered as solid oxidizing

and reducing agents. They contain the species forming a redox couple

and after having oxidised (or reduced) a substrate the electron

122

Table 4.1. Oxidation of Tin (II) to Tin (IV)

S.No. Amount of exchanger Sn (II) taken Sn (IV) found (gm) (meq) (meq)

1.

2.

3.

4.

5.

1.0

1.0

1.0

1.0

1.0

0.29

0.40

0.48

0.61

0.72

0.25

0.38

0.455

0.600

0.685

Table 4.2. Oxidation of Iron (II) to Iron (III)

S.No. Amount of exchanger Fe (II) taken Fe (IV) found (gm) (meq) (meq)

1.

2.

3.

4.

5.

1.0

1.0

1.0

1.0

1.0

0.10

0.15

0.20

0.25

0.35

0.10

0.125

0.15

0.24

0.295

123

Table 4.3. Oxidation of Hydrazine to Ammonia

S.No. Amount of exchanger Hydrazine taken Ammonia found (gm) (meq) (meq)

1.

2.

3.

4.

5.

1.0

1.0

1.0

1.0

1.0

0.225

0.31

0.405

0.585

0.675

0.200

0.305

0.380

0.530

0.645

Table 4.4. Oxidation of Thioglycolic Acid to Dithioglycolic Acid

S.No. Amount of exchanger CH,SHCOOH (SCHjCOOH)^ (gm) taken (meq) found (meq)

1.

2.

3.

4.

5.

1.0

1.0

1.0

1.0

1.0

0.10

0.15

0.25

0.30

0.375

0.10

0.12

0.18

0.205

0.290

124

Table 4.5. Oxidation of Hydroquinone to Quinone

S.No. Amount of exciianger Hydroquinone Quinone found (gm) talcen (meq) (meq)

I.

2.

3.

4.

5.

l.O

1.0

1.0

1.0

1.0

0.30

0.42

0.54

0.62

0.72

0.060

0.086

0.075

0.070

0.085

Table 4.6. Oxidation of Ascorbic Acid to Deascorbic Acid

S.No.

1.

2.

3.

4.

5.

Amount of exchanger (gm)

1.0

1.0

1.0

1.0

1.0

C,H,Oj taken (meq)

0.16

0.272

0.356

0.436

0.568

C.H^O^ found (meq)

0.132

0.272

0.350

0.420

0.558

125

Table 4.7. Rate of Oxidation of Sn(II) to Sn(IV)

Amount of Stannous ion taken-1.0 meq

Time (Min) Amount of Sn(II) oxidised (meq)

1 0.200

5 0.320

10 0.460

20 0.530

30 0.590

40 0.615

60 0.660

90 0.685

120 0.685

150 0.685

126

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127

exchanger can be regenerated by a suitable oxidizing or reducing

agent. The most important advantage of electron exchangers over

dissolved oxidizing and reducing agents is their insolubility and hence

an electron exchanger can be easily separated from the solution

containing a substrate being oxidised or reduced. The solution is free

from the contamination of any redox agents or its product, only

transfer of electrons takes place between the exchanger and the

solution. The only possible change in the solution, except for the

redox reaction of the substrate, is a change in pH. Another advantage

is that they can be readily regenerated after use by a suitable oxidizing

or reducing agent.

In the present electron exchanger the Mo(VI)/Mo(V) couple is

responsible for oxidation process.

The results presented in Tables 4.1 to 4.6 show that when one

gram of the exchanger is taken the method works for low amounts of

ions, for higher amounts, larger amount of exchanger must be taken,

the maximum redox capacity by column process is 0.700 meq/gm.

When solutions containing higher amount of stannous ions are passed

through one gram of the exchanger only 0.700 meq is oxidised and

rest comes out unoxidised. The electron exchange phenomenon

depends on the oxidation potentials of the various redox couples and

only those reductants are oxidised by the exchanger for which the

oxidation potential is less than that of the Mo(VI)/Mo(V) redox

12b

system. Standard oxidation potentials of some of the redox couples are

given in Table 4.8. This is further confirmed by Ce(III) and V(IV)

which could not be oxidised because the redox potential of the Ce(ni)/

Ce(IV) and V(IV)/V(V) couples are much higher than that of the

Mo(VI)/Mo(V) couple.

Table 4.8. Standard potentials of some redox couples

Redox couples E* volts

Sn2W2e- = Sn^" 0.14

C,H,0, = C,H,0, + 2H* + 2e- 0.18

HSCH^COOH = HOOC CH .SS.CH^ COOH 0.23

Nj.H, + 2H20+2e- = NH, (aq) + 20H- 0.1

SHjMoO, (aq) + 2H*+2e- = (MoO ) MoO, + 4H2O 0.6

The results of Figure 4.1 show that the process of oxidation of

stannous ion takes nearly one and a half hour to reach the equilibrium

in the batch process indicating the time required for oxidation process

to complete under a given set of conditions.

Since it i the molybdate group, with its Mo(VI)/Mo(V) redox

couple which is responsible for oxidation processes it is suggested that

molybdate is bonded at a place which is available for electron

exchange. When bonded, the molybdate does not change its place but

takes part in the electron exchange process.

Stannic molybdate, when exhausted for oxidation purposes may

be reoxidised (regenerated by HNO3).

129

REFERENCES

1. M. Qureshi and J.P. Rawat, J. Inorg. Nucl. Chem., 30, 305

(1968).

2. M. Qureshi, K. Husain and J.P. Gupta, J. Chem. Soc. A., 1, 29

(1971).

3. M. Qureshi and J.P. Rawat, Sepan ScL, 7(3), 297 (1972).

4. J.P. Rawat and R Singh, Ann. Chim., 64(11), 873 (1974).

5. J.P. Rawat, S.Q. Mujtaba and P.S. Thind, Fresenius Z. Anal.

Chem., 279(5), 368 (1975)

6. M. Qureshi and J.P. Rawat, Chemist-Analyst. 56, 89 (1967).

7. F. Helfferich, "Ion exhcange", MacGraw-Hill, New York, p.

563, (1968).

8. I.M.Kolthoff and R. Belcher, "Volumetric analysis",

Interscience, New York, Vol. 3, p. 319 (1957).

9. Ref. 8, p. 388.

10. Ref. 8, p. 323.

11. Ref. 8, p. 524.

12. Ref. 8, p. 642, 639.

13. Ref. 8, p. 147, 127, 131.

14. Ref. 8, p. 164.

Chapter - V

THIN LAYER CHROMATOGRAPHIC BEHAVIOUR OF

ORGANO PHOSPHATE PESTICIDES ON

HYDRATED STANNIC OXIDE LAYERS

INTRODUCTION

TLC of pesticides has attracted the attention of scientists for

several years. Even recently, TLC is widely applied as a qualitative and

quantitative method for analysis of pesticides(l). Indiscriminate

application of various types of pesticides has led to the increase in

environmental pollution and has displayed various types of acute

toxicity(2). Hence, the availability of safe drinking water and food

products have become a matter of special concem(3).

Upto this date, the most commonly used stationary phase in TLC

plates has been silica gel. In the recent past much research has been

directed towards the modification of stationary phase in order to achieve

selective interaction with the analyte. Organophosphate pesticides had

been examined on TLC plates coated with alumina, charcoal, and silica

gel(4). Now-a-days, the use of inorganic ion exchangers as coating

material on TLC plates has found a place to achieve important

separations. Thin-layer chromatographic behaviour of carbamate

pesticides and related compounds have been studied on zirconium

phosphate layers(5). Stannic oxide has been widely used as an inorganic

ion exchangers in separation science. An exhaustive study has been

made on its structural determination and behaviour towards some

organic and inorganic species(6-9).

Therefore, we decided to investigate the use of hydrated stannic

131

oxide, an inorganic ion exchanger, as the stationary phase for thin layer

chromatography of organophosphate pesticides

EXPERIMENTAL

Apparatus

A Toshniwal apparatus with an applicator, glass plates (12 x 4

cm), glass jars (15 x 5 cm), a temperature controlled electric oven

(Technico) and an electrical hot plate with magnetic stirrer (Remi 2LH)

were used.

Reagents and Chemicals

Silica gel G (Merck), Stannic chloride (Loba chemie). 20%

chloropyriphos (EC) (Lupin Agrochemicals Ltd.), 25% Methyl demeton

(EC) (Northern Minerals Ltd.), 36% monocrotophos (SL) (Montari

Industries Ltd.), 50% Malathion (EC) (Singhal Pesticides), 85%

Dimecron (Hindustan CIBA-GEIGY Ltd.), 25% Quinolphos (EC)

(Indofil Chemicals Company), 30% Dimethoate (EC) (Rallis India

Limited). All other reagents were of analytical grade.

Preparation of Solutions

Solutions (0.1% w/v) of Chloropyriphos, Methyldemeton,

Monocrotophos, Malathion, Dimecron, Quinolphos and Dimethoate

were prepared in acetone. The test solutions were applied with a fine

capillary to the plates. Iodine chamber, Cupric acetate in dil HCl

132

followed by spray with KI, and 0.5% solution of palladium chloride in

O.IN HCl were used for the detection of pesticides.

Preparation of TLC Plates

Stannic oxide gel was prepared according to the method reported

in literature(lO). A slurry was prepared in distilled water. Calcium

sulphate was added as binder which was found to be suitable to prevent

the coating forming cracks as it dried due to the shrinking of stannic

oxide gel. Furthermore, the binder interaction with the sample molecule

was to be as low as possible in order to avoid undesired interference on

the plates. Thus, a ratio of binder to stannic oxide of 1:2 (w/w) was

chosen. The slurries were applied to the glass plates (12 x 4 cm) using

an applicator. The layer thickness was set to be 0.5 mm. The plates

were first allowed to dry at room temperature and then in an oven at

110°C for one hour. The plates could be stored for several weeks with

unchanged chromatographic properties. The dried plates were developed

to a distance of 10 cm in a suitable mobile phase.

RESULTS

The results of Rp values of organophosphorus pesticides

(chloropyriphos, methyl demeton, monocrotophos, malathion, dimecron,

quinolphos and dimethoate) on hydrated stannic oxide gel and silica gel

in different solvent systems and in their different mixing ratios are

133

reported in Table 5.1 and 5.2 respectively. The separations of

oiganophosphorus pesticides achieved on stannic oxide gel in different

solvent systems are reported in Table 5.3.

DISCUSSION

The relative merits of using hydrated stannic oxide gel and silica

gel plates for the identification of organophosphorus pesticides

summarized in Table 5.1 and 5.2, show that the pattern of Rp values on

hydrated stannic oxide gel is entirely different to that on silica gel and

it was also observed that retention of pesticides on hydrated stannic

oxide gel is greater then on silica gel plates which may be attributed to

the presence of more active sites with hydroxyl groups on the hydrated

stannic oxide surface and/or acid/base pair sites which involve

coodinatively unsaturated surface metal and oxygen ions resulting in

multiple types of physical interaction other than adsorption, ion

exchange partitions and any combination of the two taking place on

silica gel plates.

The results of Table 5.1 and 5.2 indicate that in the solvent

systems like cyclohexane, petroleum, n-hexane, toluene, the Rp-values

show almost zero movement (except a few ones which move slightly)

and this effect may be (attributed) regarded to a low polarity of these

solvent systems. On adding the solvents of increasing polarity e.g.

ethylacetate, acetone etc. the compounds show better movement with

134

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137

Table 5. 2 : R Values of Organophosphate Pesticides on Silica Gel G Plates

Mobile Phase

s,

s.

S3

s.

S5

%

s,

Ss

s.

S,o

s„

s,.

s„

SM

S,5

S.6

s„

s.

s„

s.

2 -o

0.59

1.00

0.10

0.94

0.09

0.00

0.79

0.97

0.85

0.39

0.97

0.59

0.28

0.92

0.00

1.00

0.87

1.00

0.36

0.29

0 .B-

U 0.

1.00

1.00

1.00

0.83

0.95

0.67

0.53

1.00

0.93

0.99

0.99

1.00

0.33

1.00

0.17

0.98

0.88

0.76

0.67

1.00

c 0 v> u V B

0.14

1.00

0.73

0.95

0.58

0.95

0.69

0.98

0.77

0.87

1.00""'

1.00

0.54

0.90

0.21

0.76

1.00

1.00

0.90

0.93

«>

1 1 0.54

1.00

0.95

* 0.89

0.35

0.30

0.95

0.80

0.89

0.00

0.95

0.10

0.27

0.89

0.04

1.00

0.96

1.00

0.81

0.76

c 0

OS

0.83

1.00

0.32

0.99

0.48

0.93

0.92

1.00

0.91

0.09

1.00

0.98

0.56

0.93

0.91

0.89

0.97

0.91

0.89

0.80

it 0.56

1.00

0.25

0.63

0.39

0.66

0.59

0.79

0.45

0.52

0.37

0.42

0.00

1.00

0.10

0.32

0.29

0.51

0.55

0.31

c/l

0 _o. 0 c

'5 0 1.00

1.00

1.00

0.98*^

0.95

1.00

0.93

0.98

0.92

0.89

0.99

0.96

0.85

0.79

0.39

1.00

0.89

0.89

0.91

1.00

Contd.

138

MobHe Phase

S '

Sa:

S.3

S:.

S:5

K

s , S:,

s„

S30

S3,

S,:

S33

S34

S35

S3*

S3,

S3S

S39

s

^1

0.45

0.35

1.00

0.21

0.59

0.42

0.46"^

0.30

0.88

0.90

0.90

0.20

0.66

0.54

0.90

1.00

0?"

0.89

0.34

0.34(T)

St 0 .S-U 0.

0.98

0.91

0.87

0.88

0.86

0.96

0.98

0.87

0.69

1.00

0.88

0.93

1.00

0.82

0.89

0.96

0.87

0.58

1.00

1.00

c s B Q

0.85

0.45

0.83

0.77

0.50

1.00

0.91

0.33

0.62

0.71

0.92

0.89

0.39

0.55

0.83

0.80

1.00

0.85

0.87

0.96

1

1 0.65

0.29

0.92

0.68

0.92

0.79

0.75

0.90

0.90

0.97

0.45

0.96

0.85

0.60

0.62

0.92

0.98

1.00

0.87

0.20

e 0

73

2 1.00

0.87

0.93

0.55

0.87

0.68

0.96

0.78

0.49

0.96

0.58

0.85

0.93

0.98

0.70

0.81

0.90

0.79

0.65

0.90

2 b

0.49

0.50

0.25

0.07

0.09

0.12

0.26

0.31

0.50

0.35

0.17

0.15

0.35

0.28

0.08

0.10

0.09

0.35

0.13

0.09

09 0

JZ 0. "o c

'5 0 0.99

0.98

0.90

1.00

0.%

0.99

1.00

0.86

0.89

0.97

1.00

0.90

0.98

0.99

1.00

0.92

0.90

0.89

0.93

0.95

139

Table 5.3 : Separations Achieved Using DifTercnt Solvent Systems on Hydrated Stannic Oxide Gel as Coating Material on TLC Plates :

Compounds

1.

2.

3.

4.

5.

6.

7.

8.

9.

Monocrotophos (0.00)

Methyl demeton (0.00). Monocrotophos (0.00)

Chlorop>Tiphos (0.00), Methyldemeton (0.00)

Dimethoate (0.00) Malathion (U.OO)

Methyl demeton (0.20), Mono crotophos (0.15)

Monocrot(^hos (0.12), Methyldemeton (0.06)

Monocrotophos (0.00), Methyldemeton (0.14) Malathion (0.22)

Monocrotophos (0.03), Dimethoate (0.20)

Monocrotophos (0.01), Methyl demeton (0.21)

Separated from*

Methyl demetcm (0.98), Chloropyriphos (1.00), Dimecron (0.99) Dimethoate (1.00), Malathion (0.93) C iinolphos (0.95)

Chloropyriphos (0.80), Quinolphos (0.90), Dimecron (0.28)

(^nolphos (0.79). Malathion (0.33), Dimecron (0.18)

Chloropyriphos (1.00). (^nolphos (1.00), Dimecron (0.45)

Dimecron (0.89), Dimethoate (0.75), Chlorophriphos (1.00) Malathion (0.90), (^nolphos (0.96)

Chloropyriphos (0.95), Dimecron (0.86), Dimethoate (1.00), Malathion (0.50), C iino]phos(1.00)

Chloropyriphos (0.%), Dimecron (0.79), Dimethoate (0.98), (^nolphos (0.88)

Chloropyriphos (0.89), Malathion (0.70). (^nolphos (0.90)

Dimecron (0.83), Dimethoate (0.71), Chloropyriphos (0.98) Malathion (0.56), (^nolphos(l.OO)

Solvent System

s,

s,

s..,

S,o

S:7

S20

s...

S^

5 6

Contd.

140

Compounds

10. Monocrotophos (0.01), Methyl demeton (0.25)

11. Monocrotophos (0.06)

12. Monocrotophos (0.00)

Separated from*

Chloropyriphos (0.92), Dimecron (0.83), Dimethoate. (0.87), Malathion (1.00) Quinolphos (0.98)

Methyl demeton (0.%) Chlorof^riphos (0.92), Dimecron (0.76), Dimethoate (0.88), Malathion (0.80). Quinolphos (0.89)

Methyl demeton (0.4S), Chlonniyriphos (0.80), Dimecron (0.51), Dimethoate (0.87), Malathion (0.81). Quinolphos (0.97)

Solvent System

S39

S3.

S25

* Rp values are given in parentheses

141

more compact spots. On increasing the polarity of less polar solvent by

adding solvents of high polarity, we see a substantial increase in Rp

The same effect has been found in other solvent systems. The spot on

hydrated stannic oxide plates was compact in most of the solvent

systems except in few cases where a spot with tail of upto 8 mm was

observed, such streaking occured particularly where more polar solvent

system was used.

The effect of polarity of pesticides was also studied. All the

pesticides are strongly retained on hydrous stannic oxide layers when a

non-polar solvent is used. More polar compounds move to a maximum

with the solvents of high polarity i.e., with very weak retention effect.

Such observations demonstrate the fact that the movement of solute on

hydrous stannic oxide gel is not totally governed by the solvent polarity

but also by the polarity of the solute itself. Further the difference in Rp

values indicate that hydrous stannic oxide provides a certain

selectivity for organophosphorus pesticides.

Considering these factors a number of separations were carried

out and the clean separations achieved are sununarized in Table 5.3. On

reviewing the Rp-values we find that monocrotophos is completely

retained (Rp=0.00) in almost all the different types of solvent systems

and, therefore, it is possible to separate it from other pesticides.

142

The hydroxyl groups present on hydrated stannic oxide surface

may undergo condensation with elimination of water resulting in the

dehydroxylation of oxide surface. The dissociative

OH OH O

I ^ I —» / \ Sn Sn Sn sn

/ | \ / | \ / | \ / | \

H,0

The results are in agreement with the results of Marrow(ll), who

observed the chemisorption behaviour of dehydroxylated oxide surface

with many organic as well inorganic molecules. For example, N-H bond

rupture has been observed for CH NH^ and (CH3)2NH.

^"I"^'

/T^ )f\ ^ '"''"' -^A ' /T\

143

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