Synthesis, characterization and analytical applications of a new and novel ‘organic–inorganic’...

Reactive & Functional Polymers 55 (2003) 277–290www.elsevier.com/ locate/ react

S ynthesis, characterization and analytical applications of a newand novel ‘organic–inorganic’ composite material as a cation

exchanger and Cd(II) ion-selective membrane electrode:polyaniline Sn(IV) tungstoarsenate

*Asif Ali Khan , M. Mezbaul AlamAnalytical and Polymer Research Laboratory, Department of Applied Chemistry, Faculty of Engineering and Technology,

Aligarh Muslim University, Aligarh 202 002,India

Received 29 July 2002; received in revised form 18 October 2002; accepted 19 February 2003

Abstract

Composite materials formed by the combination of inorganic ion exchangers of multivalent metal acid salts and organicconducting polymers (polyaniline, polypyrrole, polythiophene, etc.), providing a new class of ‘organic–inorganic’ hybrid ionexchangers with better mechanical and granulometric properties, good ion-exchange capacity, higher stability, reproducibilityand selectivity for heavy metals. Such a type of ion exchanger ‘polyaniline Sn(IV) tungstoarsenate’ was developed bymixing polyaniline into inorganic precipitate of Sn(IV) tungstoarsenate. This material was characterized using atomicabsorption spectrometry, elemental analysis, Fourier transform infrared spectroscopy, simultaneous thermogravimetry–differential thermogravimetry, X-ray and scanning electron microscopy studies. Ion-exchange capacity, pH-titrations, elutionand distribution behavior were also carried out to characterize the material. On the basis of distribution studies, the materialwas found to be highly selective for Cd(II) and its selectivity was tested by achieving some important binary separations likeCd(II)–Zn(II), Cd(II)–Pb(II), Cd(II)–Hg(II), Cd(II)–Cu(II), etc., on its column. Using this composite cation exchanger aselectroactive material, a new heterogeneous precipitate based selective ion-sensitive membrane electrode was developed forthe determination of Cd(II) ions in solutions. The membrane electrode is mechanically stable, with a quick response time,and can be operated within a wide pH range. The selectivity coefficients for different cations determined by mixed solutionmethod were found to be less than unity. The electrode was also found to be satisfactory in electrometric titrations. 2003 Elsevier Science B.V. All rights reserved.

Keywords: Organic–inorganic composite material; Cation exchanger; Polyaniline Sn(IV) tungstoarsenate; Cd(II) ion-selective membraneelectrode

1 . Introduction in diverse fields such as purification of nuclearreactor cooling water at high temperature and

Exploration of inorganic ion exchangers is pressure, development of ion-selective elec-always of interest because of their applications trodes, construction of ion-exchange membranes

and their applications to electrodialysis, extrac-tion of uranium from sea water and separation*Corresponding author. Fax:191-571-270-1260.

E-mail address: [email protected](A.A. Khan). of metal ions, etc. Advancement in inorganic

1381-5148/03/$ – see front matter 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S1381-5148(03)00018-X

mailto:[email protected]

278 A.A. Khan, M.M. Alam / Reactive & Functional Polymers 55 (2003) 277–290

ion exchangers is not only due to their high from smelters and factories processing Cd andthermal stability and resistivity towards radia- also from the incineration or disposal of cad-tion fields but also for their unusual selectivity mium-bearing products. Cadmium enters naturalfor ionic species and versatility in separation. water through industrial discharges mainly fromInorganic ion exchangers of double salts, based electroplating industry and nickel–cadmiumon tetravalent metal acid (TMA) salts often battery industry or the deterioration of galvan-exhibit much better ion-exchange behavior as ized water pipes. Cd is therefore a potentialcompared with single salts[1]. Derivatization of pollutant in the environment. The utility of thisinorganic ion exchangers by organic molecules composite ion exchanger has been explored for

21depends on the nature of the inorganic matrix. the quantitative separation of Cd from someTMA salts can be derivatized by organic moi- binary mixtures on its column.eties bearing inorganic groups such as –OH, Precipitate based ion-selective membrane–COOH, –SO H, –NH , etc., which also act as electrodes are well known as they are success-3 2

ion exchangers, and are known as organo–inor- fully employed for determination of severalganic ion exchangers or as derivatized tetraval- anions and cations[14]. The ion-exchangeent metal acid (DTMA) salts. Many organic– membranes obtained by embedding ion ex-inorganic composite ion exchangers have been changers as electroactive materials in a polymerdeveloped earlier by incorporation of organic binder, i.e., epoxy resin (Araldite) or poly-monomers in the inorganic matrix, by way of styrene or poly(vinyl chloride) (PVC), havepillaring or non-pillaring methods[2–13]. been extensively studied as potentiometric sen-

Efforts have been made to improve the sors, i.e., ion sensors, chemical sensors or morechemical, thermal and mechanical stability of commonly ion selective electrodes. Besides theion exchanger and to make them highly selec- electrodes that respond directly to the change intive for certain metal ions. An inorganic ion concentration of particular ion for which it isexchanger based on organic polymeric matrix made, a number of electrodes are used formust be an interesting material, as it should indirect determination of certain ions. An at-possess the mechanical stability due to the tempt has also been made to obtain a newpresence of organic polymeric species and the heterogeneous precipitate based membrane elec-basic characteristics of an inorganic ion ex- trode by using the polyaniline Sn(IV) tung-changer regarding its some selectivity for some stoarsenate composite cation exchanger as elec-specific metal ions. It was therefore considered troactive material for the determination ofto synthesize such hybrid ion exchangers with a Cd(II) ions present in the solutions. This papergood ion-exchange capacity, high stability, re- presents the preparative conditions, ion-ex-producibility and selectivity for heavy metal change properties, physicochemical propertiesions, indicating its useful environmental appli- and analytical applications of this organic–inor-cation. A number of organic–inorganic compo- ganic composite material used as a cationsite samples of polyaniline Sn(IV) tungstoarse- exchanger and Cd(II) ion-selective membranenate have been synthesized in our laboratory. electrode.

Cadmium is considered as highly toxic ele-ment and responsible for several cases ofpoisoning through water, food and smoking. 2 . Experimental21When excessive amounts of Cd are ingested,

21it replaces Zn at key enzymatic sites, causing 2 .1. Reagents and instrumentsmetabolic disorders, kidney damage, renaldysfunction, anemia, hypertension, bone mar- The main reagents used for the synthesis ofrow disorders, cancer and toxicity to aquatic the material were obtained from CDH, Lobabiota. Cadmium is released into the atmosphere Chemie, E-Merck and Qualigens (India). All

A.A. Khan, M.M. Alam / Reactive & Functional Polymers 55 (2003) 277–290 279

other reagents and chemicals were of analytical- adding the solution of 0.1 M stannic chloride toreagent grade. A digital pH-meter (Elico LI-10, an aqueous mixture of 0.1 M sodium arsenateIndia), Fourier transform infrared (FT-IR) spec- and 0.1 M sodium tungstate in different volumetrophotometer (Nicolet 400D, USA), an auto- ratios and at different pH values. The whitematic thermal analyzer (V2.2A DuPont 9900), precipitates were obtained when the pH of thean elemental analyzer (Carlo-Erba 1180), a mixture was adjusted by adding ammonia waterdouble beam atomic absorption spec- with constant stirring.trophotometer (GBC 902, Australia), an electron After this, the gel of polyaniline was added tomicroscope (LEO 435 VP) with attached imag- the inorganic precipitate of Sn(IV) tungstoarse-ing device, a digital flame photometer (Elico CL nate and mixed thoroughly with constant stir-22D, India), a UV–Vis spectrophotometer (Elico ring. The resultant green colored gel was al-EI 301E, India), a temperature controlled shaker lowed to settle overnight at room temperatureand a digital potentiometer (Equiptronics EQ (2562 8C). The supernatant liquid was decanted609, India) with a saturated calomel electrode as and the gel was filtered under suction andreference electrode were used. washed with 1 M HNO to remove excess3

reagent. The excess acid was removed bywashing with DMW and again washed with2 .2. Preparation of the reagent solutionsacetone by soxhlation. The materials were dried

0.1 M Sodium arsenate (Na HAsO? 7H O) in an air oven at 508C for 48 h. The dry2 4 2

and sodium tungstate (Na WO?2H O) were products were crushed into small granules of2 4 2

prepared in demineralized water (DMW) while uniform size suitable for column separations0.1 M stannic chloride (SnCl? 5H O) was when immersed in DMW. They were then4 2

prepared in 4 M HCl. Solutions of 10% (v/v) treated with large excess of 1 M HNO for 24 h3

doubly distilled aniline (C H NH ) and 0.1 M at room temperature with occasional shaking,6 5 2

potassium persulphate (K S O ) were prepared intermittently replacing the supernatant liquid2 2 8

in 1 M HCl. with a fresh acid to ensure the complete conver-1sion to the H -form. The excess acid was

removed after several washing with DMW. The2 .3. Preparation of polyaniline Sn(IV)materials were finally dried at 508C in the oven,tungstoarsenatesieving to obtain particles of a particular size

At first, green colored polyaniline gels were range (| 125 mm) and kept in a desiccator.obtained by mixing the acidic solutions of 10% Hence, a number of samples of polyanilineaniline (C H NH ) and 0.1 M potassium per- Sn(IV) tungstoarsenate were prepared by chang-6 5 2

sulfate (K S O ) in different volume ratios with ing the mixing volume ratios of the reagents. On2 2 8

continuous stirring by a magnetic stirrer below the basis of appearance, percentage of yield,110 8C for an hour. Inorganic precipitate ion Na ion-exchange capacity and reproducibility,

exchanger gels of Sn(IV) tungstoarsenate were following sample was chosen for furtherprepared at room temperature (2562 8C) by studies:

1Sample Mixing volume ratio Appearance Naof beads ion-exchange

Sn W As pH of the K S O Aniline after drying capacity2 2 821(0.1 M) (0.1 M) (0.1 M) inorganic (0.1 M) (10%) (mequiv. g )

precipitate

S-1 1 1 1 1.0 1 1 Greenish 1.67granular


2 .4. Ion-exchange capacity followed by equimolar solutions of alkali metalchlorides and their hydroxides in different vol-

A 1-g amount of the dry cation exchanger, ume ratio, the final volume being 50 ml to1sample S-1 in the H -form was placed in a maintain the ionic strength constant. The pH of

glass column having an internal diameter (I.D.) the solution was recorded every 24 h until|1 cm and fitted with glass wool support at the equilibrium was attained which needed| 5bottom. The bed length was approximately 1.5 days, and pH at equilibrium was plotted against

2cm long. 1 M alkali and alkaline earth metal the milliequivalents of OH ions added. The1nitrates as eluents were used to elute the H results are shown inFig. 1.

ions completely from the cation-exchange col-umn, maintaining a very slow flow rate (| 0.5

21 2 .6. Chemical dissolutionml min ). The effluent was titrated against astandard (0.1 M) NaOH solution and the ion-

Portions (250 mg) of the cation exchanger in21exchange capacities in mequiv. g were as 1the H -form were equilibrated with 25 ml each1 1 1 21follows: Li , 1.46; Na , 1.67; K , 1.54; Mg ,of different acids (such as HCl, HNO , H SO ,21 21 21 3 2 41.73; Ca , 1.78; Sr , 1.86 and Ba , 2.03.acetic acid, formic acid, oxalic acid and citricacid); bases (such as NaOH, KOH); organic

2 .5. pH-titration solvents (such asn-butanol, acetone, dimethylsulfide) and also NH and DMW for 24 h with3pH-titrations were performed by the method occasional shaking. The supernatant liquid was

of Topp and Pepper[15]. A total of 500 mg analyzed for ‘tin’ and ‘arsenic’ by atomicportions of the cation exchanger was placed in absorption spectrophotometry (AAS), whileeach of the several 250-ml conical flasks, ‘tungsten’ was analyzed by the Vis spectro-

photometric method[16]. The results are sum-marized inTable 1.

2 .7. Thermal stability

To study the effect of drying temperature onthe ion-exchange capacity, 1-g samples of the

1material in the H -form were heated at varioustemperatures in a muffle furnace for 1 h each

1and the Na ion-exchange capacity was de-termined by column process after cooling them

21at room temperature. The results in mequiv. gare given below: 1.67 (508C); 1.43 (1008C);1.27 (2008C); 0.92 (4008C); 0.78 (5008C);0.59 (6008C).

2 .8. Chemical composition

After dissolving in hot concentrated hydro-chloric acid, the sample S-1 was analyzed for‘tin’ and ‘arsenic’ by AAS and ‘tungsten’ by aFig. 1. pH-titration curves for polyaniline Sn(IV) tungstoarsenate

composite cation exchanger with various alkali metal hydroxides. standard spectrophotometric method. Carbon,


T able 1The solubility of polyaniline Sn(IV) tungstoarsenate in various solvent systems

Solvent Sn W As(20 ml) (mg/20 ml) (mg/20 ml) (mg/20 ml)

4 M HNO 2.13 0.25 1.273

4 M HCl 5.99 1.03 3.524 M H SO 2.03 0.65 1.312 4

0.1 M NaOH 16.31 13.30 22.070.1 M KOH 24.59 35.86 36.411 M NH 13.84 1.15 6.873

1 M NH NO 0.13 0.53 1.804 3

1 M CH COOH 0.69 1.28 1.213

1 M CH COONa 0.51 1.13 2.203

1 M Citric acid 7.02 1.10 0.941 M Oxalic acid 13.96 4.40 8.311 M Formic Acid 0.21 0.86 3.64Dimethyl sulfide (DMS) 0.23 0.08 1.48n-Butanol 0.48 0.19 2.17Acetone 0.07 0.63 0.51DMW 0.05 0.15 0.45

hydrogen and nitrogen contents of the material mmol of metal ions/g of ion exchanger]]]]]]]]]]]]were determined by elemental analysis. The K 5d mmol of metal ions/ml of solution

percent composition of the material was: Sn,21(ml g )7.60; W, 11.85; As, 37.14; C, 9.00; H, 1.79; N,

211.41. i.e., K 5(I2F ) /F3V /M (ml g ), whereI isd

the initial amount of metal ion in the aqueous2 .9. Selectivity studies phase,F is the final amount of metal ion in the

aqueous phase,V is the volume of the solutionThe distribution coefficients (K -values) ofd (ml) and M is the amount of cation exchanger

metal ions on the sample material (S-1) were (g).determined by the batch method in varioussolvent systems. Various 200-mg portions of the 2 .10. Quantitative separation of metal ions

1exchanger in the H -form were taken in Erlen-meyer flasks with 20 ml different metal nitrate Quantitative separations of some importantsolutions in the required medium and kept for metal ions of analytical utility were achieved on24 h with intermittent shaking or continuous ‘polyaniline Sn(IV) tungstoarsenate’ (sample S-shaking for 6 h in a shaker at 2562 8C to attain 1) column. A 2-g amount of the cation ex-

1equilibrium. The initial metal ion concentration changer in the H -form was packed in an openwas so adjusted that it did not exceed 3% of its glass column (35 cm height and|0.6 cm I.D.).total ion-exchange capacity. The metal ions in After washing the column thoroughly withthe solutions before and after equilibrium were DMW, the mixture of two metal ions of 0.01 Mdetermined by EDTA titration[17]. The alkali each, was loaded on it, and was allowed to pass

1 1 21and alkaline earth metal ions (K , Na , Ca ) gently (maintaining a flow rate of 2–3 drops/were determined by flame photometry and some min) until the level was above the surface of the

21 21 21heavy metal ions, such as Pb , Cd , Cu , material. The process was repeated two or three31 21 21 21 21Cr , Hg , Ni , Mn and Zn were de- times to ensure complete adsorption of the

termined by AAS. Distribution coefficients were mixture on bead. The separation was achievedcalculated using the formula given as: by passing a suitable solvent at a flow rate of 1


21ml min through the column as eluent. The reproducible behavior and chemical and thermalmetal ions in the effluent were determined stability.quantitatively by AAS and EDTA titration. Polyaniline gel was prepared by oxidative

coupling using K S O in acidic aqueous2 2 8

medium as given in the following reaction:2 .11. Fabrication of ion selective electrode

The cation exchanger (100 mg) was groundto a fine powder, and was mixed thoroughlywith Araldite (Ciba-Geigy) (100 mg) on What-man’s filter paper No. 42, and a master mem-brane of 0.35 mm thickness was prepared. Apiece of membrane was cut out and fixed at oneend of a pyrex glass tube (0.8 cm O.D.30.6 cmI.D.) with Araldite. The tube was filled with 0.1

The effect of temperature on the reactionM cadmium nitrate. A saturated calomel elec-seems to be very pronounced. Aniline undertrode was inserted in the tube for electricalwent oxidative coupling only at below 108Ccontact and another saturated calomel electrodevery efficiently, leading to a good quantity ofwas used as external reference electrode. Thepolyaniline with fairly good yield. The forma-whole arrangement can be shown as:tion of inorganic precipitate Sn(IV) tungstoarse-

Internal reference Internal electrolyte nate was significantly affected by the pH of theU U21electrode (SCE) (0.1 M Cd ) mixture, and the most favorable pH of themixture was |1.0. The preparation of theExternal referenceMembrane Sample solutionU U inorganic precipitate at pH lower or higher thanelectrode (SCE)1.0 lead to decrease in yield and ion-exchangecapacity of the material. The mixing volumeIn advance of measurements of the electroderatio of the mixture is also critical. The bindingpotential (at 2562 8C) for a series of standard

27 21 of polyaniline into the matrix of Sn(IV) tung-solutions of Cd(NO ) (10 M–10 M), the3 2stoarsenate can be shown as:membrane of the electrode was conditioned by

soaking in 0.1 M Cd(NO ) solution for 7 days3 2

and for 1 h at least before use. In order to studythe characteristics of the electrode, the follow-ing parameters were evaluated: lower detectionlimit, slope response curve, response time andworking pH range.

3 . Results and discussion

However, sample S-1 of polyaniline Sn(IV)In this work, various samples of new andtungstoarsenate exhibited high granulometricnovel polyaniline based ‘organic–inorganic’and mechanical properties, showing a goodcomposite ion-exchange materials were de-reproducible behavior as is evident from the factveloped by incorporating polyaniline into inor-that these materials obtained from various bat-ganic matrices of Sn(IV) tungstoarsenate.ches did not show any appreciable deviation inAmong them, sample S-1 possessed high per-their ion-exchange capacities. It was also foundcentage of yield, better ion-exchange capacity,


1 1that the values of the H -adsorption and H - for 1 h, the ion-exchange capacity of the driedliberation capacities are in close agreement. The material decreased as the temperature increased.ion-exchange capacity of the composite cation However, the material was found to possess

1exchanger for alkali metal ions (except Na ) higher thermal stability as it maintained aboutand alkaline earth metal ions increased accord- 55% of the initial ion-exchange capacity bying to the decrease in their hydrated ionic radii. heating up to 4008C. From a comparative study

1The column elution experiments indicated a of heating effect on Na ion-exchange capacitydependence of the concentration of the eluent of polyaniline Sn(IV) tungstoarsenate withon the rate of elution, which is a usual behavior those of other ion exchangers, as shown inFig.for such materials. The minimum molar con- 2, it is apparent that this composite cationcentration of NaNO as eluent was 1 M for the exchanger is more thermally stable than others.3

1maximum release of H ions from 1 g of the Scanning electron microscopy (SEM) photo-cation exchanger. The elution was appreciably graphs of Sn(IV) tungstoarsenate and polyani-fast as only 140 ml of the effluent was sufficient line Sn(IV) tungstoarsenate obtained at different

1for almost complete elution of the H ions from magnifications (Fig. 3), indicating the bindingits column within 5 h. This material possessed a of inorganic ion-exchange material by organic

1better Na ion-exchange capacity (1.67 mequiv. polymer, i.e., polyaniline. It has been revealed21g ) as compared to simple Sn(IV) tungstoarse- that Sn(IV) tungstoarsenate shows a plate like

21nate (1.12 mequiv. g ) and some other similar morphology. After the binding of polyanilinematerials, i.e., double salts of tetravalent metals, with Sn(IV) tungstoarsenate, the morphologyprepared earlier (Table 2). has been changed. The detail analysis of these

The pH-titration curves obtained under SEM photographs informs that its particle sizeequilibrium conditions for LiOH/LiCl, NaOH/ may be about 3.0mm. The X-ray powderNaCl and KOH/KCl systems indicated bifunc- diffraction pattern of this cation exchanger intional behavior of the material as shown inFig. original form (sample S-1) clearly exhibited the1. It appears to be a strong cation exchanger as presence of two sharp peaks withd-values 3.31

˚ ˚indicated by a low pH (|2.5) of the solution A and 1.66 A at angles (2u ) 26.915 and2when no OH ions were added to the system. 55.2108, respectively, that suggesting a1 1The rate of H –Na exchange was faster than semicrystalline nature of the material.

1 1 1 1those of H –K and H –Li exchanges. The The thermogravimetry (TGA) analysis curvetheoretical ion-exchange capacity for these ions (Fig. 4) of the material showed a continuous

21was found to be|3.2 mequiv. g . weight loss of mass (about 6.0%) up to 1988C,The solubility experiments showed that the which may be due to the removal of the external

material has reasonably good chemical stability. water molecules[20]. An inflection point ob-As the results indicated that the material was served at 99.018C may be due to the formationresistant to 4 M HNO and 4 M H SO with of As O by removal of water molecules from3 2 4 2 5

higher solubility in NH and in alkaline media initial composition As O?nH O. Slow weight3 2 5 2

and slightly higher solubility in HCl, citric acid loss observed between 2008C and 2718C mayand oxalic acid. The chemical dissolution in be due to a slow decomposition of the material.DMW, acetone, DMS,n-butanol, formic acid, Further weight loss between 2758C and 6728CCH COOH, CH COONa, NH NO was almost may be due to complete decomposition of the3 3 4 3

negligible. This chemical stability may be due organic part of the material. At 6758C onwardsto the presence of binding polymer, which can a smooth horizontal section which representsprevent the dissolution of heteropolyacid salt or the complete formation of the oxide form of theleaching of any constituent elements into the material. These transformations have also beensolution. On heating at different temperatures supported by differential thermal analysis

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T able 2Comparison of the preparation and properties of polyaniline Sn(IV) tungstoarsenate with those of other cation exchangers

1Ion-exchange materials Reagents Mixing ratio pH of the Na -exchange

inorganic capacity21precipitates (mequiv. g )

Polyaniline Sn(IV) tungstoarsenate 0.1 M Tin(IV)chloride10.1 M sodium tungstate10.1 M sodium 1:1:1:1:1 1.0 1.67

(sample S-1) arsenate110% aniline10.1 M K S O2 2 8

Sn(IV) tungstoarsenate 0.25 M Tin(IV)chloride10.25 M sodium tungstate10.25 M sodium arsenate 2:1:1 1.0 1.06

[18]

Sn(IV) tungstoarsenate 0.1 M Tin(IV)chloride10.1 M sodium tungstate10.1 M sodium arsenate 1:1:1 1.0 1.55

(as prepared)

Polyaniline Sn(IV) arsenophosphate 0.1 M Tin(IV)chloride10.1 M sodium arsenate10.1 M H PO 1 1:1:1:1:1 1.0 1.583 4

[13] 10% aniline10.1 M (NH ) S O4 2 2 8

Polyaniline Zr(IV) tungstophosphate 0.1 M Zirconium oxychloride10.1 M sodium tungstate10.1 M ammonium 2:1:2:1:2 1.0–2.0 1.46

[19] sodium hydrogen phosphate1aniline10.4 M (NH ) S O4 2 2 8

Polyaniline Sn(IV) tungstate (as prepared) 0.1 M Tin(IV)chloride10.1 M sodium tungstate110% aniline10.1 M K S O 1:1:1:1 1.0 0.752 2 8

Polyaniline Sn(IV) arsenate 0.1 M Tin(IV)chloride10.1 M sodium arsenate110%aniline10.1 M K S O 1:1:1:1 1.0 0.872 2 8

(as prepared)

Polyaniline 10% Aniline10.1 M K S O 1:1 – 0.172 2 8

(as prepared)


Fig. 2. Comparison of heating effect upon ion-exchange capacity.

(DTA). The DTA curve indicates two exother- 1:1:1.75:11.71:27.74:1.57, which can suggestmic peaks with maxima at 84.46 and 480.208C the following tentative formula of the material:that confirm the removal of external water

2[(SnO )(WO )(As O ) ( –NH ) ]?2 3 2 5 4 2molecules and structural transformations, re-nH Ospectively. 2

The FT-IR spectrum of the exchanger in theand its structure can be written as:1H -form indicated the presence of external

water molecules in addition to the –OH groupsand metal oxides present internally in the ma-terial. In the spectrum two weak broad bands

21around 3500 cm are found, which can beattributed to O–H stretching frequency. A

21medium band around 1600 cm can be attribu-ted to H–O–H bending band, being also repre-sentative of the strongly bonded –OH groups inthe matrix [21]. The O–H stretching bandsmerge together and are shifted to lower fre-quency in the spectrum of the exchanger. This isdue to the possibility of H-bonding. The sharp

21peak around 1300 cm may represent the32presence of [AsO ] group in the material. The4

21additional band at about 1400 cm can be Assuming that only the external water mole-ascribed to stretching vibration of C–N[22]. cules are lost, at 1988C the |7.0% weight lossThis indicates that the material contains a of mass represented by the TGA curve must beconsiderable amount of aniline. It was also due to the loss ofnH O from the above2observed that there is no difference in the FT-IR structure. The value of ‘n’, the external water1 1spectra between the H -form, Na -form and molecules, can be calculated using Alberti’soriginal form of the sample S-1 dried at 508C. equation[23]:

The molar ratio of Sn, W, As, C, H and N in18n 5X(M 118n) /100the material was estimated to be

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Fig. 3. Scanning electron microphotographs of chemically prepared Sn(IV) tungstoarsenate at the magnifications of 1003 and 50003 (a, a9) and polyaniline Sn(IV)tungstoarsenate at the magnifications of 1003 and 25003 (b, b9).


al. The calculation gives|5 for the externalwater molecules (n) per molecule of the cationexchanger (sample S-1).

In order to explore the potentiality of thematerial in the separation of metal ions, dis-tribution studies for 24 metal ions were per-formed in seven solvent systems. It is apparentfrom the data given inTable 3 that the K -d

values can vary with the composition and natureof the contacting solvents. On the basis ofdistribution studies, the most promising propertyof the material was found to be the high

Fig. 4. Simultaneous TGA–DTA curve of polyaniline Sn(IV) selectivity towards Cd(II), which is a majortungstoarsenate (as prepared). polluting metal in the environment. The sepa-

ration capability of the material has been dem-onstrated by achieving some important binary

21 21 21 21where,X is the percent weight loss (|6.0%) in separations such as Cd –Zn , Cd –Pb ,21 21 21 21 21 31 21the exchanger by heating up to 1988C, and Cd –Hg , Cd –Mg , Cd –Cr , Cd –21 21 21(M118n) is the molecular weight of the materi- Cu and Mg –Ba .Table 4summarizes the

T able 3K -values of some metal ions on polyaniline Sn(IV) tungstoarsenate in different solvent systemsd

23 22 21Metal DMW 1310 M 1310 M 1310 M 0.1 M CH COOH1 0.1 M CH COOH1 0.1 M HNO 13 3 3

ion HNO , HNO , HNO , 0.1 M CH COONa 0.1 M CH COONa 0.1 M NH NO3 3 3 3 3 4 3

pH 3 pH 2 pH 1 (1:2) (2:1) (1:1)

1Na 36 33 100 21 9 12 201K 446 525 485 295 148 192 35

21Mg 33 35 35 10 84 105 521Ca 117 123 38 32 238 217 114

21Sr 198 140 39 38 767 600 1421Ba 440 333 180 50 2500 2600 2521Cu 180 180 170 56 240 600 821Ni 400 233 180 25 300 700 3321Pb 203 600 100 64 900 500 21021Cd 2920 4228 1400 450 544 810 2721Mn 233 267 141 71 650 700 50

21Zn 263 350 281 275 400 2067 12021Hg 133 367 350 300 833 1500 24321Co 300 275 44 30 550 600 83

21Bi 1000 2200 1100 1000 138 600 66731Cr 767 475 191 40 38 200 3631Al 86 71 40 44 250 440 14031Fe 100 83 43 22 300 400 6931La 225 170 155 63 550 767 1341Th 340 360 300 266 130 210 9241Ce 122 114 75 40 133 300 71Ag 67 92 114 74 44 86 1821UO 75 85 107 130 160 245 562

1Tl 155 100 117 86 100 130 30


T able 4Some binary separations of metal ions achieved on the polyaniline Sn(IV) tungstoarsenate column

Separations Amount loaded Amount found % Error Eluent Volume ofachieved (mg) (mg) used eluent (ml)

Cd(II) 1686.0 1663.5 21.4 A 40Zn(II) 980.85 993.9 11.3 B 50

Cd(II) 1967.0 1967.0 0.0 A 50Pb(II) 2591.3 2621.1 21.2 C 50

Cd(II) 1742.2 1719.7 21.3 A 40Hg(II) 1905.7 1935.8 11.6 B 50

Cd(II) 1124.0 1107.1 21.5 A 40Mg(II) 364.7 370.7 11.7 B 60

Cd(II) 1686.0 1674.7 20.7 A 40Cr(III) 780.0 790.2 11.3 D 60

Cd(II) 1124.0 1135.2 11.0 A 40Cu(II) 635.5 627.9 21.2 C 50

Mg(II) 243.1 243.1 0.0 B 40Ba(II) 1373.0 1359.3 21.0 C 50

A50.1 M HNO ; B5DMW; C50.1 M HNO 10.1 M NH NO (1:1); D50.1 M CH COOH10.1 M CH COONa (1:2).3 3 4 3 3 3

salient features of these separations. It was also The heterogeneous precipitate Cd(II) ion-selective membrane electrode obtained fromobserved that Cd(II) retained strongly on thepolyaniline Sn(IV) tungstoarsenate exchangercation exchanger column. The weakly retainedmaterial gives linear response (Fig. 5) in themetal ions appear out of the column faster than

21 24Cd(II) and Cd(II) was eluted after by HNO given range of 1310 –1310 M with a3

solution. slope of 27 mV per decade change in Cd(II) ionconcentration and the slope value is nearly closeto Nernstian value, 29.6 mV/concentration de-

24 cade for divalent cations. Below 1310 M, anon linear response was observed but the cali-bration curve could be utilized for the determi-

24nation of Cd(II) down to 1310 M. A con-stant potential was obtained after 25 s and itwas also observed that the electrode potentialremained unchanged within the pH range 3.0–8.0.

POTThe selectivity coefficients,K of variousCd.M

interfering cations for the Cd(II) ion-selectivepolyaniline Sn(IV) tungstoarsenate electrodewere determined by the mixed solution method[24] and the following numerical values wereFig. 5. Calibration curve for polyaniline Sn(IV) tungstoarsenate

membrane electrode in aqueous solutions of Cd(NO ) . obtained:3 2


POT n1Electrode Selectivity coefficients (K ) for interfering cations (M )Cd.M

1 1 21 21 21 21 21 21 21 21 31 31Na K Mg Ca Sr Cu Mn Zn Pb Hg Al Fe

Polyaniline Sn(IV) 0.02 0.03 0.02 0.06 0.08 0.09 0.03 0.04 0.18 0.07 0.04 0.05tungstoarsenate

Thus the selectivity coefficient indicates the Applied Chemistry, Z.H. College of Engineer-n1extent to which a foreign ion (M ) interferes ing and Technology, Aligarh for providing

with the response of the electrode towards its research facilities, and Central Drug Research21primary ion (Cd ). The results reveal that the Institute (Lucknow) and Regional Sophisticated

electrode is selective for Cd(II) in presence of Instrumentation Center (Nagpur) for technicalinterfering cations. assistance.

The analytical utility of this membrane elec-trode has been established by employing it as anindicator electrode in the titration of 0.01 M R eferencesCd(NO ) solution against 0.01 M EDTA solu-3 2

tion. It was observed that a sharp rise in the [1] A . Clearfield (Ed.), Inorganic Ion Exchange Materials, CRCPress, Boca Raton, FL, 1982.titration curve occurs at the equivalence point

[2] C .Y. Yang, A. Clearfield, React. Polym. 5 (1987) 13.(Fig. 6). It has been used in the determination of[3] M .B. Dines, P.D. Giacomo, K.P. Callahan, P.C. Griffith, R.H.21Cd ions in some synthetic samples containing Lane, R.E. Cooksey, Chemically Modified Surfaces in

Catalysis and Electrocatalysis, ACS Symposium Series 192,a number of different metal ions as well asACS, Washington, DC, 1982.samples obtained from electroplating units and

[4] A . Clearfield, in: Proceedings of the International Conferencethe error has been found as64–9%. on Ion Exchange, ICIE ‘91, Tokyo, New Developments in

Ion Exchange, 1991, p. 121.[5] U . Costantino, R. Vivani, in: Proceedings of the International

Conference on Ion Exchange, ICIE ‘91, Tokyo, New De-A cknowledgements velopments in Ion Exchange, 1991, p. 205.

[6] S . Tandon, B. Pandit, U. Chudasma, Transition Met. Chem.21 (1996) 7.The authors are thankful to the Department of

[7] B . Zhang, D.M. Poojary, A. Clearfield, G. Peng, Chem.Mater. 8 (1996) 1333.

[8] G . Alberti, U. Costantino, R. Millini, R.Vivani, J. Solid StateChem. 113 (1994) 289.

[9] G . Alberti, M. Casciola, C. Dionigi, R. Vivani, in: Proceed-ings of the International Conference on Ion Exchange, ICIE‘95, Takamatsu, 1995.

[10] K .G. Varshney, N. Tayal, A.A. Khan, R. Niwas, Coll. Surf.181 (2001) 123.

[11] J .P. Rawat, M. Igbal, Ann. Chim. (1981) 431.[12] D .K. Singh, A. Darbari, Bull. Chem. Soc. Jpn. 61 (1988)

1369.[13] R . Niwas, A.A. Khan, K.G. Varshney, Coll. Surf. 150 (1999)

7.[14] E . Pungor, K. Toth, in: H. Freiser (Ed.), Ion Selective

Electrodes in Analytical Chemistry, Vol. 1, Plenum Press,New York, 1978, p. 143, Chapter 2.

[15] N .E. Topp, K.W. Pepper, J. Chem. Soc. (1949) 3299.[16] N .H. Furman, in: 6th Edition, Standard Methods of Chemical

Analysis, Vol. 1, Van Nastrand, Princeton, NJ, 1963, p. 631.[17] C .N. Reiliy, R.W. Schmidt, F.S. Sadek, J. Chem. Educ. 36

Fig. 6. Precipitation titration of Cd(II) against EDTA solution. (1959) 555.


[18] M . Qureshi, R. Kumar, V. Sharma, T. Khan, J. Chromatogr. [22] R eference 21, p. 250.118 (1976) 175. [23] G . Alberti, E. Torracca, A. Conte, J. Inorg. Nucl. Chem. 28

[19] S . Ikram, Ph.D. Thesis, D.C.E., Delhi, 2000. (1966) 607.[20] C . Duval, in: Inorganic Thermogravimetric Analysis, [24] G .J. Moody, J.R.D. Thomas, Selective Ion Sensitive Elec-

Elsevier, Amsterdam, 1963, p. 315. trode, Marrow, Watford, 1971.[21] C .N.R. Rao, in: Chemical Applications of Infrared Spec-

troscopy, Academic Press, New York, 1963, p. 355.

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