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
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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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45
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• o o « n o « n o o o o
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o d d d d d d d d
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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
e O
M
O \.^ 1^
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w
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IS
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n
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50
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•o o v u g iA V -^ U M M o e w
^ M k. S V Ml
< o.
.1 B r= o ^ B » ^ a. E B S"© — 3 C* = - S 3 E W e 3 E -Z
< -fi
•9 4> _
2 •• « O >M^ »• E — 0
U
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1 ^ J "© E S
1
o X o o o o
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0.6 h
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CeXlO"3(mmoles/ml) Fig. 2.2 SoT,jio„ isotherms of Nickel (II) on Duolite
65
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.
bb
Fig. 2.4
10 20 30 40 Ce X 10"^ (mmoles/ml)
Sorption isotherms of Cobalt (II) on Duolite ES467.
67
Fig. 2.5
10 20 30 40
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Sorption isotherms of Iron (III) on Duolite ES467.
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0.5
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X Cd (ID Lo Ni ( ID
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^ 1 - ^
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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
o
o
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§ £
9 E I -
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o CM
c
c C/3 (^ O c o es ."2 '5 O (*. o *^ CB
o d
•(•uj6/bauj) pesipixo { i i )us P lunoiuv 1'
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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