Preparation Of Unsaturated Polyester Ce(IV) Phosphate ...shodhganga.inflibnet.ac.in/bitstream/10603/17950/15/15_chapter 7.pdf · ... PET was used for the synthesis of ... dependent

A. Khan, Ph.D. Thesis AMU, Aligarh

Preparation Of Unsaturated Polyester Ce(IV) Phosphate CompositeCationExchanger From Post Consumer Waste Plastic, Its Ion

Exchange Behavior And Electro Analytical Applications

7.1 In

ackaging presents a major growth area where there has been an increasing demand for

plastics and 52% of the plastics produced in India are utilized for packaging. Among the

commodity plastics, polyethylene (PE) and polyethylene terephthalate (PET) are

predominantly used in packaging. Low-density polyethylene (LDPE) is used in the

manufacture of carry bags and PET is used in packaging beverages like soft drink and

mineral water. PET in particular presents a major growth area in the years to come. Indian

PET consumption has grown at an annual rate of 30% and the current PET consumption is

estimated to be around 45,000 tones per annum [1]. India will probably see a rise in waste

generation from less than 40,000 metric tones per year to over 125,000 metric tones by the

year 2030 [2]. High consumption of plastics inevitably leads to the production of large

amounts of plastic waste especially because a substantial part of produced plastics is used for

packaging. Perrier Vittel, a division of Nestlé S.A., the world's largest food company is the

largest bottled water company in the world. Perrier Vittel serves customers in 140 countries

on five continents with more than 70 bottled water brands. The large amount of disposable

bottles presently produced makes imperative the search for alternative procedures for

recycling or reuse of these materials, since they are non-biodegradable [3].

troduction

P

Therefore, suppression of the environment pollution by the plastics waste is a task of

great and increasing importance. Due to their unique properties, plastics can hardly be

substituted by other materials and, therefore, their collection and recycling is the only way to

avoid environmental pollution. In our laboratory, PET was used for the synthesis of polymer

mortar composite [4]. The recycled PET is used to produce fiber, strapping, sheeting, bottles

and containers, alloys and compounds [5]. Studies have also been conducted using

unsaturated polyester made from recycled PET to produce polymer concrete [6, 7]. The PET

reprocessing is costly.

Chapter-7 160


Ion-exchange technique is the well known analytical technique for the treatment of

water for a very long time. Polymeric-inorganic composite ion-exchangers with better

mechanical and granulometric properties, high ion-exchange capacity, higher chemical,

thermal and mechanical stabilities, highly reproducible and possessing good selectivity for

heavy metals, are useful in environmental applications. Few such excellent ion-exchange

materials have been developed in our laboratory and used in environmental analysis [8-12].

It is well accepted fact that the progress of mankind today is directly or indirectly

dependent on advanced technology materials that perform better and open new dimensions in

research and development. In recent years among the major development in materialism

composite materials, a class of engineering material, offer several outstanding properties as

compared to conventional materials, used in chemical sensors, chromatography, selective

material, and optical applications. As an ion-exchanger composite, it is now used in

analytical, electroanalytical, medical, agriculture, potable water, and environmental science

which belongs to directly or indirectly organic as well as inorganic origin. Both origins

exhibit merits and demerits over one another in practice.

Therefore, opening a land of promising applications in many fields as optics,

electronics, ionics, mechanics, membranes, functional & protective coatings, catalysis,

sensors, biology, medicine, biotechnology, etc, looking to the 21st century, advanced

composite sciences will be one of the fields that will contribute to a high level of scientific

and technological developments. Polymeric– inorganic materials will play a major role in the

development of advanced functional materials, recyclable and respecting the environment.

In present research work, polymeric-inorganic composite material unsaturated

polyester Ce(IV) phosphate is prepared from post consumer waste plastic and characterized

by different techniques. The material is used in making ion-selective electrode.

7.2 Material and Methods

7.2.1 Reagents

Soft drink waste PET (polyethylene trephthalate) bottles were obtained in the form of

beverage bottles from the City of Aligarh; U.P; India. After the caps and labels were

removed, the bottles were shredded to sizes of approximately 1.5–3.0 cm. The shredded PET

was washed by tap water and dried at room temperature. The adhesives on the bottles were

Chapter-7 161


not purposely removed, most of them still remained. Cerric sulphate and Disodium hydrogen

phosphate, Zinc acetate, Maleic anhydride (MA), Pthalic anhydride (PthA), Diethyleneglycol

(DEG) were obtained from CDH and Qualigens (India Ltd.,). All other reagents and

chemicals were of analytical grade.

7.2.2 Instruments

A FTIR spectrophotometer (Perkin Elmer, U.S.A, model Spectrum-BX); digital pH–meter

(Elico Li-10, India); X-ray diffractometer ― Phillips (Holland), model PW 1148/89; UV/VIS

spectrophotometer ― Elico (India), model EI 301E; a thermal analyzer ― V2.2A DuPont

9900; an elemental analyzer ― Elementary Vario EL III, Carlo-Erba, model 1108; an

electronic balance (digital, Sartorius-21OS, Japan) were used in this study.

7.2.3 Glycolysis experiment

The conversion of polyethylene terephthalate (PET) in presence of glycol and catalysts is

known as alcoholysis or glycolysis. A one-liter three-necked round bottom flask (reactor)

was used for all glycolysis experiments. In order to ensure that the water content in the

reactor was as low as possible, the reactor was heated to 100 0C and held at that temperature

for at least 5 min. The reactor was equipped with a thermometer and a reflux condenser. A

magnetic stirrer was put in the reactor to ensure proper mixing. The ratio of diethylene glycol

to PET used in the glycolysis experiment was 4:1 by weight. Glycolysis temperature,

glycolysis time and amount of the catalyst for the depolymerization of PET flakes were given

in Table 7.1. Glycolysis temperature was set at 85 0C and time was 4 h while the amount of

the catalyst was 0.25% by weight of PET.

7.2.4 Synthesis of unsaturated polyester (UPE)

After glycolysis, the maleic and phthalic anhydrides were added into the reactor for non-

catalyzed melt polyesterification reaction. The reaction was carried out at 190 0C for 8 h, and

0.5% hydroquinone by weight of PET was added to check back polymerization. The slurry

was then allowed to cool at room temperature.

Chapter-7 162


7.2.5 Preparation of Ce(IV) phosphate

The method of preparation of the inorganic precipitate of Ce(IV) phosphate ion-exchanger

was very similar to that of Alberti [13] and Constantino [14] with slight modification [15] by

mixing a solution of 0.1 M Ce(SO4)2.4H2O, prepared in 1 M H2SO4 at the flow rate of 0.5 ml

min-1 to a solution of H3PO4 in different molarities by maintaining pH of the solution one. A

yellowish gel type slurries were obtained that was kept 24 h at room temperature in each

case.

7.2.6 Preparation of unsaturated polyester Ce(IV) phosphate composite cation

exchanger

The composite cation-exchanger was prepared by the sol-gel mixing of unsaturated polyester

obtained by polycondensation of Bis-(hydroxyethylene) trephthalate (BHET) with maleic

and phthalic anhydrides. BHET fraction of glycolyzed product of PET was prepared by

optimal glycolysis conditions i.e. amount of the catalyst taken as 0.25% by weight of PET,

glycolysis temperature 85 0C, glycolysis time 4 h and (1:4) (PET : glycol) ratio. In this

process when the gels of unsaturated polyester samples were added to the white inorganic

precipitate of cerium(IV) phosphate with a constant stirring at room temperature, the

resultant mixture was turned slowly into white colored slurries. The resultant white colored

slurries were kept for 24 hours at room temperature.

Now the unsaturated polyester based composite cation-exchanger gels were filtered

off, washed thoroughly with DMW to remove excess acid and any adhering traces. The

washed gels were dried over P4O10 at 40 0C in an oven. The dried products were immersed in

DMW to obtain small granules. They were converted to the H+ form by keeping it in 1 M

HNO3 solution for 24 hours with occasionally shaking intermittently replacing the

supernatant liquid. The excess acid was removed after several washing with DMW. The

material was finally dried at 40 0C and sieved to obtain particles of particular size range

(~125 μm). Hence a number of unsaturated polyester Ce(IV) phosphate composite cation-

exchanger samples were prepared and on the basis of Na+ ion-exchange capacity (i.e.c.),

sample S-1 (Table 7.1 ) was selected for further studies.

Chapter-7 163


7.3 Characterization

7.3.1 FTIR studies

The FTIR spectrum of unsaturated polyester Ce(IV) phosphate (sample S-1); Ce(IV)

phosphate (sample S-4) and unsaturated polyester (sample S-7) in the original form were

recorded in the powder form (compressed KBr pellets) method at room temperature.

7.3.2 X-ray studies

Powder X-ray diffraction (XRD) pattern was obtained in an aluminum sample holder for the

sample S-1 in the original form using a PW 1148/89 based diffractometer with Cu Kα

radiations.

7.3.3 Scanning electron microphotographic (SEM) studies

SEM photographs of the original form of unsaturated polyester (S-7); inorganic precipitate of

Ce(IV) phosphate (S-4 ); and organic-inorganic composite material unsaturated polyester

Ce(IV) phosphate (S-1); were obtained by the scanning electron microscope at various

magnifications.

Table 7.1 Conditions of preparation and ion-exchange capacity of unsaturated polyester Ce(IV) phosphate composite cation-exchanger material. (DEG = Diethylene Glycol; MA = Maleic Anhydride; PthA= Pthalic Anhydride)

S.No. Mixing volume ratios(ml)

Glycolysis of PET Polyesterification after glycolysis

Ion-exchange capacity (meq.g-1)

Ce(SO4)2.4H2O in 1M H2SO4

H3PO4 PET(g) DEG(ml) Heating Time(h)

Heating Temp.(0C)

MA(g) PthA(g)

S-1 100 100 (2M)

1 10 4 85 0.5 0.5 3.62

S-2 50 50 (2M)

2 15 4 85 1 1 2.7

S-3 250 100 (2M)

3 15 4 85 1 1 2.3

S-4 100 100 (2M)

- - - - - - 1.14

S-5 75 75 (2M)

4 20 4 85 1.5 1.5 1.58

S-6 75 125 (1M)

5 25 4 85 2 2 1.69

S-7 - - 1 10 4 85 0.5 0.5 0.17 S-8 125 100

(4M) 6 30 4 85 2.5 2.5 1.06

Chapter-7 164


7.3.4 TGA studies

Simultaneous TGA and DTA studies of the composite cation-exchange material in original

form were carried out by an automatic thermo balance on heating the material from 10 to

1000 0C at a constant rate (10 0C min−1) in the air atmosphere (air flow rate of 400 ml min-1).

7.3.5 Ion-exchange capacity (i.e.c.)

The ion-exchange capacity, which is generally taken as a measure of the hydrogen ion

liberated by neutral salt to flow through the composite cation-exchanger was determined by

standard column process. One gram of the dry cation-exchanger sample in the H+-form was

taken into a glass column having an internal diameter (i.d.) ~1 cm and fitted with glass wool

support at the bottom. The bed length was approximately 1.5 cm long. 1 M alkali and

alkaline earth metal nitrates as eluants were used to elute the H+ ions completely from the

cation-exchange column maintaining a very slow flow rate (~ 0.5 ml min-1). The effluent was

titrated against a standard 0.1 M NaOH using phenolphthalein indicator.

7.3.6 Selectivity (sorption) studies

The distribution coefficient (Kd values) of various metal ions on unsaturated polyester Ce(IV)

phosphate composite were determined by batch method in various solvents systems. Various

100-100 mg of the composite cation-exchanger beads in the H+-form were taken in

Erlenmeyer flasks with 20 ml of different metal nitrate solutions in the required medium and

kept for 24 hour with continuous shaking for 6 hours in a temperature controlled incubator

shaker at 25±2 °C to attain equilibrium. The initial metal ion concentration was so adjusted

that it did not exceed 3% of its total ion-exchange capacity. The metal ions in the solution

before and after equilibrium were determined by titrating against standard 0.005 M solution

of EDTA. The alkali and alkaline earth metal ions [K+, Na+, Ca2+] were determined by flame

photometry and some heavy metal ions such as [Pb2+, Cd2+, Cu2+, Hg2+, Ni2+, Mn2+, Zn2+]

were determined by atomic absorption spectrophotometry (AAS). The distribution quantity

is given by the ratio of amount of metal ion in the exchanger phase and in the solution phase.

In other words, the distribution coefficient is the measure of a fractional uptake of metal ions

competing for H+ ions from a solution by an ion-exchange material and hence

Chapter-7 165


mathematically can be calculated using the formula given as:

)1-g (mlsolutionofml/ ions metal of moles m

exchanger-ion of gm / ions metal of moles mdK = . ..….7.1

i.e. Kd = [ (I−F) / F] × [ V / M ] (ml g-1) ……7.2

Table 7.2 Kd-values of some metal ions on unsaturated polyester Ce(IV) phosphate

composite cation-exchanger column in different solvent systems.

Metal ion

Solvents

Fe2+ Ba2+ Cd2+ Ni2+ Hg2+ Ca2+ Sr2+ Cr3+ Cu2+ Pb2+ Zn2+ Tl+

DMW 102 69 8 25 33 20 8 6 88 177 25 120.1M HNO3

50 3 42 67 521 79 47 88 212 550 36 50

0.01M HNO3

100 55 12 45 65 53 65 33 231 340 370 130

0.001M HNO3

115 64 60 400 40 820 55 52 4 214 120 50

0.1M HClO4

25 100 68 32 50 22 11 98 9 320 200 25

0.01M HClO4

30 20 18 91 00 43 43 38 73 300 250 66

0.001M HClO4

78 53 17 500 9 69 44 85 12 700 810 13

0.1M HCl 469 90 15 56 83 22 70 12 0 50 92 1500.01M HCl 90 120 23 89 58 81 45 58 650 978 120 300.001M HCl

23 40 42 96 27 45 61 87 99 875 130 50

10% DMSO

3 125 18 20 501 100 91 88 70 888 290 150

10% Formic acid

225 20 0 5 70 25 76 125 96 180 0 50

Buffer 10 22 308 190 66 240 99 8 36 248 550 200 201M CaCl2 140 33 66 120 59 450 47 55 67 255 120 201M BaOH 6 89 21 120 89 77 780 73 38 660 140 20

where I is the initial amount of metal ion in the aqueous phase, F is the final amount of metal

ion in the aqueous phase, V is the volume of the solution (ml) and M is the amount of cation-

exchanger (g).

Chapter-7 166


Chapter-7 167

7.3.7 Separation factor

For the preferential uptake of metal ion, in the separation of a mixture of two metal ions,

separation factor is determined. It can be defined and calculated as:

( )( )BKAKfactorSeparation

d

dAB =)(α .…..7.3

where Kd (A) and Kd (B) are the distribution coefficient for the two competing species A and

B in the ion-exchange system. The separation factor is the preference of the ion-exchangers

for one of the two counter ion species (Table 7.3).

7.3.8 Chemical composition

After dissolving sample S-1 in concentrated hydrochloric acid, phosphorus was analyzed by

Vis-spectrophotometric method while Ce was analysed by atomic absorption

spectrophotometer. Carbon, hydrogen, oxygen and nitrogen contents of the material were

determined by elemental analysis.

Table 7.3 Separation factor of different metal ions on unsaturated polyester Ce(IV) phosphate composite cation-exchanger materials.

Separation factor

DMW 1 × 10-3

HClO4

1 × 10-3 M HCl

1.14 100 38.04

22.13 41.18 20.83 7.08 1.40 9.12 2.57 13.21 21.88 22.13 15.91 14.35 7.08 1.40 9.11 2.01 58.33 8.84

7.4 Preparation of unsaturated polyester Ce(IV) phosphate cation-exchange membrane

Ion-exchange membrane of unsaturated polyester Ce(IV) phosphate was prepared as the

method reported by Khan et al. [15] in earlier studies. To find out the optimum membrane

composition, different amount of the composite material was grounded to a fine powder and

mixed thoroughly with a fixed amount (200 mg) of PVC dissolved in 10 ml Tetrahydrofuran.

PbFeα

PbCuα

PbCdα

PbNiα

PbBaα

PbNiα

PbSrα


Chapter-7 168

The resultant slurries were poured to cast in glass tube having 10 cm in length 5 mm in

diameter. These glass tubes were left for slow evaporation for several hours. In this way,

three sheets of different thicknesses were obtained as given in Table 7.4. A fixed area of the

membranes was cutted using sharp edge blade.

Table 7.4 Characterization of ion-exchange membrane

7.4.1 Characterization of membrane

The important factors to check the performance of the membrane, three parameters were

determined as reported earlier [16-19].

7.4.2 Water content (% total wet weight)

First the membranes were soaked in water to elute diffusible salt, blotted quickly with

Whatmann filter paper to remove surface moisture and immediately weighted. These were

further dried to a constant weight in a vacuum over P2O5 for 24 h. The water content (total

wet weight) was calculated as:

4.7.........100W% w ×−

= dWweightwetTotalWw

where Wd = weight of the dry membrane and Ww = weight of the saoked/wet membrane.

7.4.3 Porosity

Porosity (ε) was determined as the volume of water incorporated in the cavities per unit

membrane volume from the water content data:

Unsaturated polyester Ce(IV)Phosphate composite

Thickness of the membrane (mm)

Water content as %

weight of wet

membrane

Porosity Swelling

M-1 0.29 6.4516 6.8965×10-4 - M-2 0.36 7.6912 7.6920×10-4 - M-3 0.42 8.6956 9.5238×10-4 -


5.7......LA

W

w

w

ρε dW−

=

where Ww = weight of the soaked/wet membrane, Wd = weight of the dry membrane, A =

area of the membrane, L = thickness of the membrane and ρw = density of water.

7.4.4 Thickness and swelling

The thickness of the membrane was measured by taking the average thickness of the

membrane by using screw gauze. Swelling is measured as the difference between the average

thicknesses of the membrane equilibrated with 1 M NaCl for 24 h and the dry membrane.

7.4.5 Fabrication of ion-selective membrane electrode

The membrane sheet of 0.29 mm thickness obtained by the above procedure was cut in the

shape of disc and mounted at the lower end of a Pyrex glass tube (o.d. 0.8 cm, i.d. 0.6) with

araldite. Finally the assembly was allowed to dry in air for 24 h. The glass tube was filled

with 0.1 M lead nitrate solution. A saturated calomel electrode was inserted in the tube for

electrical contact and another saturated calomel electrode was used as external reference

electrode. The whole arrangement can be shown as:

Internal

reference

electrode (SCE)

Internal

electrolyte

0.1 M Pb2+

Membrane Sample

solution

External

reference

electrode (SCE)

Following parameters were evaluated to study the characteristics of the electrode such as

lower detection limit, electrode response curve, response time and working pH range.

7.4.6 Electrode response or membrane potential

To determine the electrode response, a series of standard solutions of varying concentrations

ranging from 10-1 – 1-10 were prepared. External electrode and ion-selective membrane

electrode were plugged in digital potentiometer and the potentials were recorded.

Chapter-7 169


For the determination of electrode potentials the membrane of the electrode was

conditioned by soaking in 0.1M Pb(NO3)2 solution for 5-7 days and for 1 h before use. When

electrode was not in use, electrode must be kept in 0.1 M Pb(NO3)2 solution. Potential

measurement was plotted against selected concentration of the respective ion in aqueous

solution.

7.4.7 Effect of pH

pH solution ranging from 1-13 were prepared at constant ion concentration i.e (1 × 10-3 M).

The value of electrode potential at each pH was recorded and plot of electrode potential

versus pH was plotted.

7.4.8 The response time

The method of determining response time in the present work is being outlined as follows:

The electrode is first dipped in a 1 × 10-3 M solution of Pb(NO3)2 and 10 fold higher

concentration. The potential of the solution was read at zero second; just after dipping of the

electrode in the second solution and subsequently recorded at the intervals of 5 s. The

potentials were then plotted vs. the time.

7.5 Results and Discussion

Unsaturated polyester Ce(IV)phosphate was synthesized by catalytic sol-gel method. The

depolymerization of PET accomplished by esterification reaction using zinc acetate as an

esterification catalyst produced bis-2-hydroxy ethylene terephthalate (BHET) monomers and

oligomers. The BHET fractions of glycolyzed product of PET as prepared by optimal

glycolysis conditions (Table 7.1) were used for the preparation of unsaturated polyester resin

by polycondensation with maleic/phthalic anhydrides by the following reaction mechanism:

Chapter-7 170


C

O

O CH2 CH2 O C

O

CH CH C

O

Ce(IV)(PO4)(HPO4)0.5(H2O)0.5

Ce(IV)(PO4)(HPO4)0.5(H2O)0.5

n

C

O

O CH2 CH2 O C

O

CH C

O

Ce(IV)(PO4)(HPO4)0.5(H2O)0.5n +

Unsaturated polyester (UPA) Cerium phosphate

Unsaturated polyester Ce(IV) phosphate(UPACe(IV)P)

CH

Benzoylperoxide

Various samples of organic-inorganic composite unsaturated polyester Ce(IV)

phosphate cation-exchange material have been developed by the incorporation of unsaturated

polyester into the inorganic matrices of Ce(IV) phosphate. Due to high percentage of yield,

better ion-exchange capacity, reproducible behavior, chemical and thermal stability, sample

S-1 (Table 7.1) was chosen for detail studies. The exchanger possessed a better Na+ ion–

exchange capacity (3.62 meg g-1) as compared to inorganic precipitate of amorphous Ce(IV)

phosphate (1.14 meg g-1).

In Figure 7.1 FTIR spectrum of the composite shows the twisting and wagging

vibration frequencies of the methylene group in the region of 1300– 1200 cm-1 [20]. The

vibration frequency at 1700 cm-1 shows aromatic ring. A small peak in the region of 1600

cm-1 may be due to the presence of carbonyl group of the composite. A peak at ~3000 cm-

1shows the presence of –CH stretching vibration frequency of benzene ring in the plane while

600 cm-1 show –CH out of the plane deformation vibration frequency of benzene ring.

Chapter-7 171


Figure 7.1 FTIR spectra of as prepared unsaturated polyester Ce(IV) phosphate (a),

unsaturated polyester (b) and Ce(IV) phosphate composite cation-exchanger (c).

It is clear from the thermogravimetric analysis (TGA) curve (Figure 7.2) of the

material that upto 85 0C only 5 % weight loss was observed, which may be due to the

removal of external H2O molecules present at the surface of the composite [21]. Further

weight loss of mass approximately 6.5% between 100 to 200 0C may be due to the slight

conversion of inorganic phosphate into pyrophosphate.

DTA

DTG

TGA

Figure 7. 2 Simultaneous TGA-DTA curves of unsaturated polyester Ce(IV) phosphate (as

prepared).

Chapter-7 172


Slow weight loss of mass about 7.5% in between 200-700 ˚C may be due to the slight

decomposition of organic part of the material. A broad peak at ~90 and 550 0C in DTA curve

shows the reaction is exothermic during the change of phase of material.

The X-ray diffraction pattern of this material (S-1 as prepared) recorded in powdered

sample exhibited some small peaks in the spectrum which suggest semi-crystalline nature of

the composite material (Figure 7.3).

Figure 7.3 Power X-ray diffraction pattern of unsaturated polyester Ce(IV) phosphate composite.

The scanning electron microphotograph (SEM) of unsaturated polyester Ce(IV)

phosphate, unsaturated polyester and Ce(IV) phosphate are represented in Figure 7.4. Small

and big flakes are seen in the unsaturated polyester Ce(IV) phosphate composite cation-

exchange material. Thus morphology of the material has been changed with the formation of

organic-inorganic composite material unsaturated polyester Ce(IV) phosphate after adhesion

of organic polymer, UPE (unsaturated polyester) with inorganic precipitate Ce(IV)

phosphate.

Carbon, hydrogen, oxygen, phosphorus and cerium contents of the material were

determined by elemental analysis the percent composition of C, H, O, P and Ce was: 14.58%,

1.30%, 46.36%, 11.58%, and 26.16%. The tentative molecular formula of the composite is:

C12H10O5.Ce(IV)(PO4)(HPO4)0.5(H2O)0.5

Chapter-7 173


(a)

(b) (c)

Figure 7. 4 SEM photographs of unsaturated polyester Ce(IV) phosphate (a), unsaturated

polyester (b) and Ce(IV) phosphate (c) at different magnifications.

The composite cation-exchange material possessed a better Na+ ion–exchange

capacity (3.62 meq g-1) as compared to inorganic precipitate of fibrous type Ce(IV)

phosphate (1.14 meq g-1). In order to explore the potential of composite material in the

separation of metal ions Kd values of 12 metal ions were performed in 15 solvent systems

(Table 7.2). The Kd- values vary with the nature of the contacting solvents. It was also

observed from the (Kd) values that Pb2+ was highly adsorbed and Zn2+, Fe2+ and Ba2+ are

significantly adsorbed while the remaining are partially adsorbed on the surface of ion-

exchange material.

The separation factor is the proportion of the concentration ratios of the counter ions

in the ion-exchanger and the solution. If the ion A is preferred, the factor is larger then unity,

and if B is preferred, the factor is smaller then unity. The numerical value of the separation

factor is not affected by the choice of the concentration units. The numerical values of

separation factor (dimensionless) for some metal ions are given in Table 7.3. The values of

Chapter-7 174


separation factor of Pb2+ are greater then unity, which indicates that the proportion of Pb2+ in

the ion exchange material is higher in comparison to the other metal ions.

7.6 Ion selective membrane electrode

A number of samples of the unsaturated polyester Ce(IV) phosphate composite membrane

with good mechanical stability, surface uniformity, materials distribution, and thickness were

prepared. The results of thickness, swelling, porosity and water content capacity of

unsaturated polyester Ce(IV) phosphate composite cation-exchanger membrane are

summarized in Table 7.4. The membrane sample M-1 (thickness 0.29 mm) was selected for

further studies. Thus, low order of water content, swelling and porosity with less thickness of

this membrane suggests that interstices are negligible and diffusion across the membrane

would occur mainly through the exchanger sites.

The heterogeneous precipitate Pb(ІІ) ion-selective membrane electrode obtained from

unsaturated polyester Ce(IV) phosphate cation-exchanger material gives linear response in

the range 1 ×10-1 M and 1 × 10-6 M. Suitable concentration were chosen for sloping portion

of the linear curve.

Figure 7. 5 Calibration curve of unsaturated polyester Ce(IV) phosphate membrane electrode in aqueous solutions of Pb(NO3)2.

Chapter-7 175


Chapter-7 176

The limit of detection determined from the intersection of the two extrapolated segments of

the calibration graph [22] found to be 1 ×10-6 M, and thus the working concentration range

was found to be 1 ×10-1 M to 1 ×10-6 M (Figure 7.5) for Pb2+ ions with a Nerstian slope of

28.97 mV per decade change in Pb2+ion concentration. The slope value is in the range of

Nerstian value, 29±3.00 mV per concentration decade for divalent cation [23].

pH effect on the potential response of the electrode were measured for a fixed (1 × 10-

2 M) concentration of Pb2+ ions in different pH values. It was observed that electrode

potential remains unchanged with in the pH range 4.0-8.0. It is known as working pH range

for this electrode (Figure 7.6).

565

570

575

580

585

590

595

600

605

610

615

0 2 4 6 8 10 12 1pH

Elec

trod

e Po

tent

ial (

mV)

4

Figure 7.6 Effect of pH on the potential response of the unsaturated polyester Ce(IV) phosphate membrane electrode at 1×10-2 M Pb2+ concentration.

Another important factor is the promptness of the response of the ion-selective electrode.

The average response time is defined as the time required for the electrode to reach a stable

potential. It is found that the response time of the membrane sensor is ~14 s (Figure 7.7).


590

600

610

620

630

640

650

660

0 5 10 15 20 25 30Time (Sec)

Elec

trod

e Po

tent

ial (

mV)

Figure 7.7 Response time of Pb2+ ion-selective unsaturated polyester Ce(IV) phosphate

based membrane electrode.

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