Desalination 289 (2012) 1–11

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Desalination

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Development of nano-composite adsorbent for removal of heavy metals fromindustrial effluent and synthetic mixtures; its conducting behavior

Rani Bushra ⁎, Mohammad Shahadat, A.S. Raeisssi, Syed Ashfaq NabiAnalytical Research Laboratory, Department of Chemistry, Aligarh Muslim University, Aligarh-202002, India

⁎ Corresponding author. Tel.: +91 571 2404014.E-mail address: bushra.chem07@gmail.com (R. Bush

0011-9164/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.desal.2011.12.013

a b s t r a c t

a r t i c l e i n f o

Article history:Received 21 October 2011Received in revised form 14 December 2011Accepted 15 December 2011Available online 27 January 2012

Keywords:NanostructureCompositeAdsorptionSelectivitySeparations and ion exchange

A semi-crystalline stable composite cation exchange adsorbent for the treatment of heavy metal ions has beensynthesized at pH 1.0 by sol–gel method which was characterized by FTIR, XRD, SEM, TGA and TEM analysis.Ion exchange capacity, pH titration, elution behavior and distribution studies were also carried out to determinethe primary ion-exchange characteristics of thematerial. Thematerial shows exchange capacity of 1.47 meq g−1

(for Na+ ions). The compositematerial exhibits improved ion-exchange capacity, chemical and thermal stability.It can be used up to 200 °Cwith 88% retention of initial ion-exchange capacity. pH titration data reveal its bifunc-tional behavior. The distribution coefficient values (Kd) of metal ions have been determined in various solventsystems. On the basis of Kd values the material was selective for Ba(II), Hg(II), and Pb(II) ions. The limit of detec-tion (LOD) and the limit of quantification (LOQ) for Pb(II) was found to be 0.97 and 2.93 μg L−1, respectively.A number of important and analytically difficult quantitative separations of metal ions have been achievedusing columns packedwith this exchanger. The composite cation exchanger is applied for the treatment of sew-age water and synthetic mixture successfully and can be used as a conducting material.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

There are so many causes of water pollution. Toxic metal ion is oneof them, which has become a major environmental problem that isgradually affecting our ecosystem adversely, due to this human beingis suffering from many diseases. The toxic heavy metals are releasedfrom anthropogenic sources such as metallurgical, galvanizing, metalfinishing, electroplating,mining, power regeneration, electronic devicesmanufacturing and tannery industries [1]. These metals, when presentin the water more than the permitted limit, become injurious to thehealth. So, it is indispensable to remove the heavy metals from thewater before it is supplied for potable and others useful purposes.

A number of methods have been developed for the removal of theseheavy metals e.g. solvent extraction, adsorption, preconcentration, re-verse osmosis and ion exchanger [2]. Ion exchangers have several ad-vantages over other methods because it is relatively clean, energyefficient and show selectivity for certain ions even in the solution oflow concentration of the target ion. Furthermore, it has better exchangecapacity, high removal efficiency, fast kinetics [3,4] and can also be uti-lized in metal recovery process, which are of economical importance[5]. A number of organic and inorganic ion-exchangers have been devel-oped but there are certain limitations existing with them. The maindrawbacks associatedwith organic ion-exchangers are of poormechan-ical strength and low thermal stability under high radiation conditions

ra).

rights reserved.

while inorganic ion-exchangers are not suitable for column applica-tions. Hence, in order to overcome all the above limitations, compositeion-exchangers have been synthesized by incorporating organic poly-mer with the matrix of inorganic precipitate. The composite materialsshow better exchange capacity, granulometric properties, reproducibil-ity, chemical stability along with thermal stability and also possess bet-ter selectivity for heavy metals compared to pure inorganic and organicmaterials. These composite ion-exchangematerials can also be used as acatalyst [6,7] ion-exchanger [8–10], ion selective electrode [11] and alsofinds a large number of applications in pollution control and watertreatment [12]. The present work describes synthesis, characteriza-tion, analytical applications and conducting behavior of poly-o-toluidineZr(IV)tungstate cation exchanger.

2. Experimental

2.1. Materials and methods

Zirconium(IV)oxychloride [Loba Cheme Pvt. Ltd.], sodium tung-state (BDH, India) ortho-toluidine (Merck limited). The other re-agents used were of analytical grade. A digital pH meter Elico EL-10(Elico India) was used for pH measurements. Shimadzu GraphicordUV-240 spectrophotometer with 10-mm matched quartz cellsfor spectrophotometric determination, Infrared (IR) spectra wererecorded on a Fourier Transform-IR Spectrometer from Perkin Elmer(1730, USA) using KBr disc method. Thermogravimetric Analysis/Differential Thermal Analysis (TGA/DTA) analysis was carried out byDTG −60 H; C305743 00134, (Schimadzu, Japan) analyzer at a rate of

Fig. 1. The binding of poly-o-toluidine into the matrix of zirconium(IV)tungstate.

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10 °C min−1 in nitrogen atmosphere. An X' Pert PRO analytical diffrac-tometer (PW-3040/60 Netherlands, Holland with CuK∝ radiationλ=1.5418 Å) was used for X-ray diffraction (XRD) measurement.Scanning Electron Microscope (SEM; LEO, 435 VF) instrument wasused for SEM images of the material at different magnifications. Trans-mission Electron Microscopy (TEM) analysis was carried out by JeolH-7500 Microscope. FAAS measurements were made with a ModelGBC-932-Plus flame atomic absorption spectrometer (GBC Scientific,Australia). A temperature controlled shaker (MSW-275, India) wasused for shaking. Muffle furnace (Narang Scientific works-India) wasused for heating samples at different temperatures. A four-in-line-probe electrical conductivity-measuring instrument (Scientific Equip-ment India) was used for measuring the DC electrical conductivity.

2.2. Preparation of reagents

0.1 M solution of zirconium(IV)oxychloride (A) and sodium tung-state (B) were prepared in demineralized water while 20% solutions(v/v) of ortho-toluidine and 0.1 M potassium persulphate were pre-pared in 1.0 M HCl.

2.3. Preparation of poly-o-toluidineZirconium(IV)tungstate

Poly-o-toluidine gel (C) was prepared by mixing 20% solution ofo-toluidine and 0.1 M solution potassium persulphate in equal vol-ume ratio with continuous stirring below 10 °C for 1 h, a green gelof poly-o-toluidine was obtained. The inorganic precipitate of Zr(IV)tungstate was prepared at room temperature (25±2 °C) by adding so-dium tungstate (0.1 M) solution gradually to an aqueous solution of zir-conium(IV)oxychloride (0.1 M) in different volume ratios. The whiteprecipitates were obtained and the pH was adjusted by adding 1.0 M

Table 1Conditions for the synthesis of poly-o-toluidine zirconium(IV)tungstate cation exchanger.

S. no Amol L−1

Bmol L−1

C%v/v

Mixing ratiov/v/v

Temperat

Z-1 0.1 0.1 – 1:1 25±2 °CZ-2 0.1 0.1 – 1:2 25±2 °CZ-3 0.1 0.1 – 2:1 25±2 °CZ-4 0.1 0.1 – 1:1 25±2 °CZ-5 0.1 0.1 20 1:1:1 25±2 °CZ-6 0.1 0.1 20 1:1:1 25±2 °CZ-7 0.1 0.1 20 1:1:1 25±2 °CZ-8 0.1 0.1 20 2:1:1 25±2 °CZ-9 0.1 0.1 20 1:2:1 25±2 °C

A. Zirconium (IV)oxychloride, B. Sodium tungstate, C. Stock solution of 20% poly-o-toluidin

solution of nitric acid or ammonia. The gel of poly-o-toluidine wasthen added to the inorganic precipitate of Zr(IV)tungstate and mixedthoroughly with constant stirring. The resultant green gel so obtainedwas kept for 24 h at 25±2 °C for digestion. The supernatant liquidwas filtered off by suction. The gel was washed with demineralizedwater till the filtrate was neutral. The product was dried in an ovenat 50±2 °C and dried material was broken into small granules on im-mersion in demineralized water which were converted into H+ formby placing in 1 M HNO3 solution for 24 h. The excess acid from the ma-terial was removed through washings many times with demineralizedwater and eventually dried at 50±2 °C, thus, nine samples of the com-posite material were synthesized. On the basis good yield, highestion exchange capacity (for Na+ ions), sample Z-9was selected for detailstudies. The proposed structure of the compositematerial demonstratesFig. 1.

2.4. Ion exchange capacity

To determine ion exchange capacity, one gram of the exchanger(H+ form) was taken into a glass column (0.5 cm, internal diame-ter) plugged with glass wool at the bottom. The length of bed wasapproximately 1.5 cm in height. Alkali and alkaline earth metal ni-trates (0.1 M) were used to elute H+ ions from the cation-exchanger.The flow rate of column is maintained at 1.0 mL min-1. The collect-ed effluent was titrated against standard solution of 0.1 M sodiumhydroxide.

2.5. pH titration

In order to determine the nature of the ionogenic group, pH ti-trations were performed in various alkali and alkaline earth metal

ure pH Appearance of bead Exchange capacity(meq g−1) for Na+

Yield(g)

0.7 White 0.6 1.621.0 White 0.92 2.201.0 White 0.76 1.941.5 White 0.70 1.980.7 Green 0.0 0.01.0 Green 1.24 2.431.5 Green 1.16 2.891.0 Green 1.20 3.101.0 Green 1.47 3.39

e.

Table 2Ion-exchange capacity of various exchanging ions on poly-o-toluidine zirconium(IV)tungstate cation exchanger.

Exchanging ions Ionic radii(A°)

Hydrated ionic radii(A°)

IEC(meq g−1)

Li+ 0.68 3.40 1.35Na+ 0.97 2.76 1.47K+ 1.33 2.32 1.55Mg2+ 0.78 7.00 1.63Ca2+ 1.43 5.90 1.72Sr2+ 1.27 6.30 1.84Ba2+ 1.43 5.90 1.90

IEC, ion exchange capacity.

Fig. 2. Effect of eluent concentration on ion-exchange ca

Fig. 3. Elution behavior of poly-o-to

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chlorides and their corresponding hydroxides using Topp and Pep-per method [13]. In this method 0.5 g of the exchanger (H+ form)is taken in each of several 250 mL conical flasks which werefollowed by the addition of equimolar solution of 0.1 M solutionsof alkali or alkaline earth metal chlorides and their correspondinghydroxides in different volume ratios. The final volume is adjustedto 50 mL to maintain the ionic strength.

2.6. Effect of eluent concentration

To find out the optimum concentration of the eluent for completeelution of H+ ions, a fixed volume (250 mL) of NaNO3 solution of

pacity of poly-o-toluidine zirconium(IV)tungstate.

luidine zirconium(IV)tungstate.

Fig. 4. pH-titration curves of poly-o-toluidine zirconium(IV)tungstate with various alkali metal hydroxides.

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different concentrations were passed through the columns, containing1.0 g of the exchanger (H+ form) with a flow rate of 0.5 mLmin−1.The effluents were titrated against a standard solution of 0.1 M NaOHto find the H+ ions eluted out.

Fig. 5. pH-titration curves of poly-o-toluidine zirconium(IV)

2.7. Elution behavior

A column containing 0.5 g of exchanger (H+ form) was eluted with1.0 M sodium nitrate solution. The effluent was collected in 10.0 mL

tungstate with various alkaline earth metal hydroxides.

Table 3Effect of temperature on the ion-exchange capacity of poly-o-toluidine zirconium(IV)tungstate cation exchanger on heating time for 1 h.

Temperature (°C) Color IEC (meq g−1) for Na+ ions % retention of IEC

50 Green 1.47 100.0100 Green 1.33 90.2200 Green 1.30 88.5300 Black 1.22 83.3400 Black 1.12 76.3500 Muddy color 0.89 60.3

IEC, ion exchange capacity.

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fractions. Each fraction of 10.0 mL was titrated against a standard solu-tion of sodium hydroxide.

2.8. Selectivity (sorption) studies

The distribution coefficient (Kd) of metal ions was determined bybatch method in different solvents of analytical interest. Distribution

Fig. 6. TGA curve of poly-o-toluid

Fig. 7. FTIR spectra of poly-o-toluidine zirc

coefficient is actually used to access the overall ability of the materialto remove the ions of interest. Various portions of (300 mg each) ofpoly-o-toluidineZr(IV)tungstate (H+ form) were taken in Erlenmeyerflasks and titrated with 30 mL of different metal nitrate solution inthe required medium and subsequently shaken for 6 h in temperaturecontrolled shaker at 25±2 °C to attain the equilibrium. The metal ionconcentration before and after the equilibrium was determined by ti-tration against a standard solution of 0.01 M di-sodium salt of EDTA.The distribution coefficients were calculated using the equation:

Kd ¼ milli equivalent of metal ions = gm of ion� exchangermilli equivalent of metal ions = mL of solution

mLg−1

Kd ¼ I−FF

� VM

mLg−1

where I is volume of EDTA used for metal ion solution without treat-ment with exchanger.F is the volume of EDTA consumed by metal ionleft in solution phase after treatment.

The sorption of metal ions involves the ion exchange of the H+

ions in exchanger phase with that of metal ions in solution phase

ine zirconium(IV)tungstate.

onium(IV)tungstate cation exchanger.

Fig. 8. Powder X-ray diffraction pattern of poly-o-toluidine zirconium(IV)tungstate cation exchanger.

Fig. 9. Scanning electron microphographs (SEM) of poly-o-toluidine zirconium(IV)tungstate cation exchanger at different magnifications.

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Fig. 10. TEM image of poly-o-toluidine zirconium(IV)tungstate nano-composite cation exchanger.

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For example:

2R−Hþ þM2þ⇌R2−Mþ 2Hþ

Exchangephase Solutionphase Exchangephase Solutionphase

where R=poly-o-toluidineZr(IV)tungstate.

2.9. Quantitative separations of metal ions in synthetic binary mixtures

Quantitative separations of some selective metal ions were achievedon columns of poly-o-toluidineZr(IV)tungstate. 1 g of exchanger (H+

form) was packed in a glass column (0.5 cm, internal diameter) with aglass wool support at the bottom. The column was washed thoroughlywith demineralized water and the mixture of two metal ions (eachwith initial concentration 0.1 M) was loaded on it and allowed to pass

through the column at a flow rate of 1 mL min−1 till the solution levelwas just above the surface of the composite material. The process wasrepeated twice or thrice to ensure the complete absorption of metalions on the bed. The separation of metal ions is achieved by collectingthe effluent in 10 mL fractions and titrating against the standard solutionof 0.01 M di-sodium salt of EDTA.

2.10. Selective separation of metal ion from a synthetic mixture

Selective separation of Ba2+ and Hg2+ from the synthetic mix-tures containing (Fe3+, Cu2+, Al3+, Sr2+, Ca2+, Zn2+, Ba2+) and(Ca2+, Sr2+, Fe3+, Cu2+, Cd2+, Hg2+) was achieved on poly-o-toluidineZr(IV)tungstate columns. The amount of the Ba2+ and Hg2+

ions in the synthetic mixture was varied keeping amount of theother metal ions constant.

Table 4Distribution coefficients (mL g−1) Kd of metal ions on poly-o-toluidine zirconium(IV)tungstate cation exchanger in different solvent systems.

Metalion

DMSO(0.4 M)

DMSO(0.2 M)

DMSO(0.1 M)

0.4 MHNO3

0.2 MHNO3

0.1 MHNO3

0.4 Maceticacid

0.2 Maceticacid

0.1 Maceticacid

Mg2+

100 180 209 210 258 322 155 290 317

Zn2+ 152 277 316 145 190 220 172 200 259Sr2+ 80 106 126.52 108 119 120 89 105 149Ca2+ 132 148 160.66 70 100 118 127 220 228Ba2+ 1020 1200 1420 1920 2010 2100 2000 2220 2467Pb2+ 187 202 367 357 411 491 1510 1855 2050Cd2+ 140 164 194 120 171 285 672 888 920Cu2+ 110 135 157.74 100 108 138 62 77 110Ni2+ 289 305 400 139 168 299 112 134 168Hg2+ 927 1108 1329 719 880 940 620 750 980Al3+ 108 228 358.82 109 129 140 120 150 199Fe3+ 68 97 105.55 – 5 15 25 52 81Bi3+ 501 520 625 228 320 415 390 500 667Th4+ 232 250 285 181 200 239 250 320 372

Table 6Selective separations of Ba2+ from a synthetic mixture of, Cu2+, Ca2+, Sr2+, Fe3+, Zn2+,Al3+ and Ba2+ on poly-o-toluidine zirconium(IV)tungstate cation exchanger columns.

S. no. Amount of Ba2+

loaded (mg)Amount of Ba2+

found (mg)% recovery Eluent

usedEluent volume(mL)

1 1.96 1.90 97 0.1 MHNO3

90

2 3.92 3.72 95 0.1 MHNO3

100

3 5.88 5.35 96 0.1 MHNO3

120

Table 7Selective separations of Hg2+ from a synthetic mixture of Ca2+, Sr2+, Fe3+, Cd2+, Cu2+

and Hg2+ on poly-o-toluidine zirconium(IV)tungstate cation exchanger columns.

S. no. Amount of Hg2+

loaded (mg)Amount of Hg2+

found (mg)Recovery%

Eluentused

Eluent volume(mL)

1 3.34 3.13 94 0.1 MHCl

90

2 6.68 6.41 96 0.1 MHCl

90

3 10.02 9.81 98 0.1 MHCl

110

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2.11. Electrical conductivity measurements

The sample of composite material was treated with HCl solution(0.1 M) and washed repeatedly with DMW to remove excess acid,dried at 50 °C in the oven. For the conductivity measurement 300 mgmaterial was finely grounded and pellets were made at a pressure of25 KN. The thickness of pellet was measured by a micrometer. Thus theelectrical conductivity measurements for treated (0.1 M HCl solution)untreated sample of poly-o-toluidineZr(IV)tungstate composite wasperformed by increasing temperatures (between 30 to 200 °C) usingfour-in-line-probe DC electrical conductivity-measuring instrument.

3. Results and discussion

Table 1 describes that for the development of composite ion-exchanger a number of samples of poly-o-toluidineZr(IV)tungstatewere prepared by sol–gel method. The ion-exchange capacity of thesynthesized material depends upon the pH and mixing ratio of the re-agents. It is inferred from Table 1 that with increasing pH (0.7 to 1.5)of the reaction mixture, ion-exchange capacity of composite materialdecreases (because at higher pH, the hydrolysis of composite materi-al occurs). Poly-o-toluidine gel was prepared by oxidative couplingusing K2S2O8 in acidic aqueous medium. The binding of poly-o-toluidine in to the matrix of Zr(IV)tungstate.

In order to investigate the working capacity of the compositeexchanger, ion-exchange capacity for some monovalent and diva-lent cations were determined (Table 2) which follows the sequenceLi+bNa+bK+ and Mg2+bCa2+bSr2+bBa2+, respectively. The ionexchange capacity for alkali and alkaline earth metal ions increaseswith decrease in hydrated ionic radii [14]. Hence, it may be inferred

Table 5Quantitative separation of metal ions from a binary mixture using poly-o-toluidine zirconiu

S. no. Metal ion separation Amount loaded(mg)

Amount found(mg)

1 Zn2+ 6.538 6.44Pb2+ 20.72 19.17

2 Ca2+ 4.008 3.79Hg2+ 20.06 18.55

3 Fe3+ 5.58 5.95Hg2+ 20.06 19.16

4 Zn2+ 6.538 6.31Ba2+ 13.73 12.98

5 Ni2+ 5.86 5.78Ba2+ 13.73 12.84

6 Ca2+ 4.01 3.99Pb2+ 20.72 19.99

that the ions with smaller hydrated radii enter the pores of theexchanger more easily, resulting in higher sorption [15,16]. Theinteresting feature shown by the material is that ion-exchange ca-pacity for alkaline earth metal ions, was found to be greater thanalkali metal ions.

It was observed from Fig. 2 that for complete elution of H+ ions(from 1.0 g of exchanger), the optimum concentration of the eluentwas found to be 1.0 M. It was also observed (Fig. 3) that the rate ofexchange (H+ ions) is quite fast in the beginning and only 120 mLof NaNO3 solution (1.0 M) is sufficient for complete elution of H+

ions from the column containing 1.0 g exchanger. From this experi-ment it is found that the efficiency of the column is quite satisfactory.The pH titration curves for alkali and alkaline earth metals show twoinflection points which indicate bifunctional strong cation exchangebehavior (Figs. 4 and 5). Initially alkali and alkaline earth metal chlo-rides are added in the absence of base. There is a sharp decrease in pHdue to the release of hydrogen ions. The effect of heating on the com-posite material at different temperatures for 1 h (Table 3) indicatesthat the ion-exchange capacity and physical appearance of the ex-changer changed as temperature increased. The material appears tobe thermally stable up to 200 °C as it retains significant ion-exchangecapacity. From this observation it was inferred that the compositecation-exchanger possessed improved thermal stability and ion-exchange capacity.

m(IV)tungstate cation exchanger columns at room temperature.

% recovery Volume of eluent used(mL)

Eluent used

98 50 0.1 M acetic acid92 70 0.2 M HCl94 60 0.1 M HCl92 90 0.4 M acetic acid

100 70 2 M HCl95 70 4 M HCl96 60 4 M HNO394 90 2 M HCl98 60 0.1 M HNO393 80 2 M HCl99 70 0.1 M acetic acid96 80 0.4 M HCl

Fig. 11. Chromatograms of binary separations of metal ions on poly-o-toluidine Zr(IV)tungstate columns. a=0.1M Acetic acid, b=0.2M HCl, c=0.1M HCl, d=0.4M Acetic acid,e=2M HCl, f=0.4MHCl, g=4MHNO3, h=0.1M HNO3, i=0.4M HCl.

Table 8Determination of Pb2+ industrial waste, Ganga water and tap water on poly-o-toluidine zirconium(IV)tungstate cation exchanger columns. Experimental conditions:100 mL solution, sorption flow rate 2.0 mL min−1, 0.25 g exchanger.

Samples Method Amount of Pb2+ founda

(μg mL−1) (% RSD)b

Elecroplating waste Directc 74.0 (3.2)(Aligarh) SAd 74.9 (2.9)Ganga water Direct 36.4 (3.8)(Narora) SA 37.2 (4.8)Tap water Direct –

(A.M.U. Campus, Aligarh) SA 5.3 (4.8)

‘–’ indicates not detected.a Average of three replicate determinations.b Relative standard deviation.c Recommended procedure applied without spiking.d Recommended procedure after spiking (standard addition method).

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The TGA curve (Fig. 6) of the composite material shows a contin-uous weight loss of mass up to 125 °C which is due to removal ofexternal water molecules [17]. The weight loss from 125 °C to225 °C is due to the loss of interstitial water molecules by the con-densation of \OH groups. Further weight loss between 225 °C and480 °C may be due to complete decomposition of organic part ofthe exchanger. The weight loss onward 480 °C may be due to thecomplete formation of oxides of metal. FTIR spectrum of poly-o-toluidine Zr(IV)tungstate (Fig. 7) indicates a broad band between3000 and 3366 cm−1 is the characteristic of free \NH\ stretchingvibrations suggesting the presence of secondary amino group [18]and \OH group [19]. A sharp peak at ~1600 cm−1 corresponds tothe deformation vibration of free water molecules, while the sharppeak at 1382 cm−1 is due to the deformation vibration of hydroxylgroups. The bands from 1322 to 1112 cm−1 are attributed to the inplane bending of the \CH bands [18]. A broad band in the region of

Fig. 12. Temperature dependence of the electrical conductivity of treated and untreated samples of poly-o-toluidineZr(IV)tungstate nano-composite cation exchanger.

10 R. Bushra et al. / Desalination 289 (2012) 1–11

830–756 cm−1 and at 570 cm−1 can be assigned to the presence ofWO42- and metal-oxide groups respectively [20–22].

In the X-ray diffraction pattern of composite material (Fig. 8)there is no sharp or medium intensity peak which indicates amor-phous nature. The SEM images obtained at two different magnifica-tions also suggest the amorphous nature of the material (Fig. 9).TEM studies reveal that poly-o-toluidineZr(IV)tungstate compositecation exchange material (Fig. 10) shows particles size in range of50–100 nm. Thus, the particle size was found to be in nano-range.

In order to explore the potentiality of the composite cation exchangematerial in separation of metal ions. Distribution coefficient values (Kd)for different metal ions were performed in different solvent systems(Table 4). It has been observed from Table 4 that on decreasing the con-centration of different solvents, the uptake ofmetal ionswas sharply in-creased. The data obtained in Table 4 indicate that metal ions such asBa(II), Hg(II) and Pb(II) ions showed high uptake (high values of distri-bution coefficient). On the basis of higher Kd values the material wasfound to be selective for Ba(II), Hg(II), and Pb(II) ions. Some analyticallyimportant separations (e.g. Zn2+–Pb2+, Ca2+–Hg2+, Fe3+–Hg2+,Zn2+–Ba2+, Ni2+–Ba2+ and Ca2+–Pb2+) of metal ions were per-formed on the columns of poly-o-toluidineZr(IV)tungstate compositeexchanger (Table 5).

Tables 6 and 7 show the results of selective separation of Ba2+ andHg2+ from the synthetic mixtures of other metals. The salient fea-tures of these separations are reflected in the chromatograms shownin Fig. 11, and their results in Table 5. It is clear that the separationsare quite sharp and recovery is quantitative and reproducible. ThePb(II) metal ion was also determined using flame atomic absorptionspectrophotometer. The amount of Pb(II) ions in electroplatingwaste sample and Ganga water was found to be 74.0 μg mL−1 and36.4 μg mL−1. The practical utility of the composite material was dem-onstrated by separating Ba(II) and Hg(II) from synthetic mixtures(Tables 6 and 7) while Pb(II) from industrial wastewater and tapwater (Table 8).

3.1. Analytical figure of detection limit

The validity of the results was tested by standard addition method,by spiking a known amount (10 μg) of individual metal ions to the

water samples. The results pertaining to the analysis of trace amountof metal ion of interest confirms the satisfactory recovery of the ana-lytes. The close agreement of the results found by direct (applying therecommended procedure without spiking) with that found by S.A.(standard addition after spiking) method (Table 8) indicates the reli-ability of the present method for metal analyses in water samples ofvarious matrices without significant interference. The detection limitevaluated as three times the standard deviation (s) of the blank signalalong with the mean blank signals (absorbance) for 15 replicate mea-surements were found to be 0.90 (0.0009) μg L−1 for Pb(II) ion. Theelectrical conductivity (σ) measurements of the composite cation-ex-changer treated with HCl and untreatedwere determinedwith increas-ing temperatures (from 30 °C to 140 °C) and observed that onincreasing the temperature the conductivity of composite materialwas increased (Fig. 12). It was also observed that the conductivity oftreated sample is found to be high than untreated sample which maydue to the charge-transfer reaction between the chains of poly-o-tolui-dineZr(IV)tungstate composite and doping agent, HCl.

4. Conclusion

Novel synthesized amorphous nano-composite cation exchangershows selective behavior toward heavy metal ions and can withstandfairly high temperature. Thermally stable, it retains significant ion-exchange capacity up to 200 °C. It can be used for the quantitativeseparation of metal ions from binary mixture of analytical impor-tance. Determination of Pb(II) metal ions from tapwater and electro-plating wastewater samples by FAAS does not require any priordigestion. The material can be explored further for the removal andrecovery of important metal ions from industrial effluents. Poly-o-toluidineZr(IV)tungstate composite cation exchanger thus, exhibitsthe characteristics of a promising ion-exchanger as well as conduct-ing material.

Acknowledgment

The authors are thankful to the UGC for providing financialsupport.

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