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Synthesis and characterization of polyacrylamide zirconium (IV) iodate ion-exchanger: Its application for selective removal of lead (II) from wastewater
⁎Corresponding author. Tel.: +91 9412501208. nafisurrahman05@gmail.com (Nafisur Rahman) cht17nr_amu@yahoo.com (Nafisur Rahman)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Polyacrylamide zirconium (IV) iodate was synthesized using the sol–gel technique. The synthesis conditions such as reactant concentrations and temperature were changed to optimize the ion exchange properties of the hybrid organic–inorganic ion exchange material. Zirconium oxychloride (0.1 M) was added to 0.1 M potassium iodate in the presence of 0.4 M acrylamide and heated at 70 °C for 6 h to yield the polyacrylamide zirconium (IV) iodate with maximum capacity. The ion exchange capacity was found to be 3.27 meq/g for Pb(II). The hybrid material has been characterized on the basis of chemical composition FTIR, XRD, TGA-DTA, SEM and EDX studies. Sorption studies showed that the hybrid cation exchanger has a high selectivity to Pb(II) in comparison to other metal ions. Its selectivity was evaluated by performing some important binary separations like Hg(II)–Pb(II), Cu(II)–Pb(II), Ni(II)–Pb(II), Fe(III)–Pb(II) and Cd(II)–Pb(II). In addition, the selective separation of Pb(II) was also achieved from a synthetic mixture containing a large number of metal ions with a recovery of ∼98.5%. The proposed method was successfully applied for the selective removal of Pb(II) from wastewater samples.
Keywords
Organic–inorganic hybrid
Polyacrylamide zirconium (IV) iodate
Cation exchanger
Selective separation
1 Introduction
The contamination of groundwater, which is a principal source of water, is a serious health and environmental problem all over the world. Pollution of ground water due to industrial effluent and municipal waste is a major concern in many cities and clusters in India. Contamination of water by heavy metals through the discharge of industrial waste water is a very serious environmental problem. Among the various heavy metals, lead (II) is a well known toxic metal ion which can be introduced to liquid wastes from the manufacturing processes of storage batteries, smelting and refining of lead, inks, paints and from the processes of mining. The elevated level of lead (>0.05 mg/L) and other heavy metals in the local water stream is a major concern to public. It has been desired that their concentration levels be reduced in industrial and municipal effluents before discharge into the water streams.
Various methods such as chemical precipitation (Brbooti et al., 2011; Chen et al., 2012), solvent extraction (Konczyk et al., 2013), ultra filtration (Wang et al., 2012), reverse osmosis (Dialynas and Diamadopoulos, 2009), adsorption (Sulaymon and Ali, 2012) and ion exchange (Kamel et al., 2011) have been employed for the removal of lead and other toxic metal ions from water. Among the various methods employed for the removal of toxic metal ions, the ion exchange method has drawn the attention of researchers because of its selectivity and high efficiency of sorption from liquid media. Recently, interest has been generated in the preparation of some organic–inorganic hybrid materials because these materials possess attractive mechanical properties, rigid inorganic backbone and flexibility of organic functional groups that provide specific chemical reactivity (Pandey and Mishra, 2011; Abd-El-latif and El-Kady, 2008).
Literature survey revealed that many inorganic ion exchange materials have been used for the separation of metal ions. Sodium titanate and peroxotitanate are effective ion-exchange materials for the removal of a wide variety of materials from aqueous solutions (Hobbs, 2011; Hobbs et al., 2005). In our previous work the preparation of zirconium (IV) iodate was reported (Gupta et al., 2005) which showed an ion exchange capacity of 0.54 meq/g for Na+. Recently, hybrid types of ion-exchange materials have been synthesized by combining the organic polymeric species with inorganic precipitates (El-Naggar et al., 2012; Ahmadi et al., 2012).
In recent years the use of anion exchange resin for the removal and separation of metal ions is of wide interest due to its simplicity, elegance and range of variable experimental conditions (Rahman et al., 2012; Won et al., 2008). However, some drawbacks are associated with such type of resins which include: thermal stability, limited surface area, hydrophobicity of polymer backbones, instability in harsh chemical environment and swelling in solvents (Ju et al., 2000; Tien et al., 2001) On the other hand, inorganic ion exchangers have a higher thermal and radiation stability, rigid structure and swell to a limited extent during use. Researchers have attempted to develop hybrid organic–inorganic composite ion exchangers. These materials have received much attention due to thermally stable inorganic backbone and flexibility of organic functional groups with a high potential for new applications (Pandey and Mishra, 2011; Fan et al., in press).
Zirconium (IV) iodate, belonging to the group of tetravalent metal acid salts, is a cation exchanger with a poor mechanical strength. Therefore, a suitable copolymer such as acrylamide was added to the inorganic precipitate to make it stable and can be used for chromatographic separation of metal ions. The present paper deals with the synthesis, characterization and ion exchange behaviour of polyacrylamide zirconium (IV) iodate.
2 Experimental
2.1 Reagents and instruments
The main reagents used for the synthesis of the material were zirconium (IV) oxychloride octahydrate (Otto Chemie Pvt. Ltd., Mumbai, India), acrylamide (Otto Chemie Pvt. Ltd., Mumbai, India), and potassium iodate (Merck, India). All other chemicals and reagents used were of Analytical grade.
A digital pH meter (Cyberscan pH 2100), UV–Visible spectrophotometer (UV/Vis mini.1240 Shimadzu, Japan), FTIR spectrophotometer (Interspec 2020, Spectrolab, UK), an elemental analyser (Carlo-Erba 1180), an automatic thermal analyser (DTG, 60 H Shimadzu), X-ray diffractometer (X′ PROPANanalytical, Netherland), scanning electron microscope (JEOL JSM-6100, Japan) and a water bath incubator shaker were used.
2.2 Preparation of polyacrylamide zirconium (IV) iodate
Various samples of hybrid organic–inorganic cation exchanger polyacrylamide zirconium (IV) iodate were prepared by adding one volume of 0.1 M aqueous solution of zirconium oxychloride to two volumes of a (1:1) mixture of (0.1 M) potassium iodate and acrylamide drop wise with constant stirring using a magnetic stirrer at a temperature of 70 ± 2 °C. The pH was maintained at 1 by adding 1 M HNO3. The gelatinous precipitate so formed was stirred at 70 °C for 6 h and kept in mother liquor for another 24 h. The gelatinous precipitate was filtered and washed with distilled water several times to remove excess acid. The product was dried in an oven at 50 °C. The dried material was broken into small granules and treated with 1 M HNO3 solution for 24 h with occasional shaking to convert the ion-exchanger in H+ form. The excess acid from the material was removed after several washings with distilled water and finally dried at 50 °C.
2.3 Ion-exchange capacity
The ion exchange capacity (IEC) of the material was determined by the column method. 500 mg of the dry exchanger in H+ form was packed into a glass tube of internal diameter of 0.8 cm with glass wool at its bottom. The column was washed with distilled water to remove any excess acid which remained sticking on the granules. To determine IEC of alkali, alkaline earth, metal ions and lead ion, 1.0 M solution of the respective metal nitrate was passed through the column at a flow rate of 1 mL min−1 till the effluent showed the absence of H+ ions. The effluents were collected and titrated against a standard solution of NaOH to determine the total H+ ions released which is equivalent to the cation retained by the material (Lutfullah and Rahman, 2012). To study the reproducibility of the exchanger, the exhausted ion-exchanger was regenerated by keeping it in 1 M HNO3 solution for 24 h. It was then washed with distilled water till it became neutral. The exchange capacity was determined and repeated three times.
2.4 Chemical composition
To determine the chemical composition of polyacrylamide zirconium (IV) iodate (sample PZ-5) 200 mg of the sample was dissolved in a minimum volume of concentrated H2SO4 and diluted to 100 ml with distilled water. Zirconium and iodate were determined spectrophotometrically using Alizarin red S (Snell and Snell, 1959) and pyrogallol (Snell and Snell, 1949) as colouring reagents, respectively. Percentage of carbon, hydrogen and nitrogen was analysed with the help of CHN analyser.
2.5 Chemical stability
To study the chemical stability of polyacrylamide zirconium (IV) iodate, 0.2 g of the sample was equilibrated with 20 ml of different concentrations of H2SO4, HNO3, HCl, acetic acid and bases .The amount of zirconium (IV) and iodate released was determined by the method described earlier.
2.6 Characterization of ion-exchanger
FTIR spectrum of polyacrylamide zirconium (IV) iodate dried at 50 °C was recorded using the KBr pellet method. Powder X-ray diffraction pattern was recorded using a PW-3050/60 diffractometer with Cu Kα radiation (α = 1.54 Å). Simultaneous TGA and DTA studies of polyacrylamide zirconium (IV) iodate in H+-form were carried out by DTG .60 H Shimadzu Thermal analyser on heating the material from 20 to 800 °C at a rate of 20 °C per minute in a nitrogen atmosphere. The microphotographs of polyacrylamide zirconium (IV) iodate and lead (II) sorbed polyacrylamide zirconium (IV) iodates were obtained by scanning electron microscope at various magnifications.
2.7 Sorption studies
To explore the analytical application of polyacrylamide zirconium (IV) iodate , the distribution coefficient (Kd) of metal ions such as Mg2+, Ca2+, Sr2+, Ba2+, Zn2+, Cd2+, Hg2+, Fe3+, Mn2+, Cu2+, Pb2+, Ni2+, Al3+, Cr3+and Th4+ was determined in de-ionized water and different concentrations of nitric acid. Various 0.2 g portions of the exchanger in H+ form were taken in Erlenmeyer flasks with 20 ml of 0.001 M different metal ion solutions in the required medium and kept for 24 h at room temperature with occasional shaking to attain equilibrium. The metal ion in the solution before and after sorption was determined by EDTA titration. The distribution coefficient was evaluated using the expression:
2.7.1 Quantitative separation
Quantitative binary separations of some metal ions were achieved using a polyacrylamide zirconium (IV) iodate column. Two grams of the ion exchange material in H+ form was packed into a glass column (height = 30 cm, i.d. = 0.8 cm) with a glass wool support at the end. The column was washed thoroughly with deionized water. 2.0 ml of binary mixture of the metal ion to be separated was passed onto the column. The solution was allowed to flow through the column and the metal ions adsorbed on the exchanger were eluted with an appropriate solvent. The flow rate of the eluent was maintained at 0.5 ml min−1 throughout the elution process.
2.7.2 Selective separation
For the selective separation different sets of the synthetic mixtures were taken in which the amount of the Pb2+ was varied keeping the amount of other metal ions constant. The synthetic mixture contains Mg2+ (0.1215 mg), Ca2+ (0.2004 mg) , Sr2+ (0.4381 mg), Ba2+ (0.6860 mg), Zn2+ (0.3265 mg), Cd2+ 0.5620 mg), Hg2+ (1.002 mg), Fe3+ (0.2792 mg), Mn2+ (0.2746 mg), Cu2+ (0.3177 mg) , Ni2+ (0.2934 mg), Al3+ (0.1349 mg), Cr3+ (0.2599 mg), Th4+ (1.1602 mg) , and varying amount of Pb2+ (Set I: 2.349 mg; Set II: 1.892 mg and Set III: 1.1745 mg). Different sets of synthetic mixtures were loaded onto the polyacrylamide zirconium (IV) iodate columns. All the metal ions studied except Pb2+ were eluted first with demineralized water, 0.01 M HNO3 for Hg2+and then the Pb2+ was eluted with 0.30 M HNO3. The amount of Pb2+ was determined titrimetrically using 0.002 M EDTA solution.
2.7.3 Determination of Pb(II) in waste water samples
The waste water samples were collected in polyethylene bottles from different cities of India. Samples near the surface were taken by the grab sampling method (Canadian Council of ministers of the Environment, 2011).
First the waste water samples were filtered through a Whatman No. 40 filter paper. Each filtered sample (100 ml) was passed through the column packed with polyacrylamide zirconium (IV) iodate, then the column was washed with 0.01 M HNO3 to remove all other metal ions. Finally Pb2+ was eluted with 0.3 M HNO3 and determined titrimetrically with 0.002 M EDTA. The lead (II) content in the water samples was also determined by a reference method Ahmad and Mosaddeque-Al (2001).
3 Results and discussion
In the present study an attempt has been made to explore the synthesis of polyacrylamide zirconium (IV) iodate and its application for the removal of lead (II) from synthetic solution and waste water samples. Various samples of hybrid cation exchanger were prepared by sol–gel mixing of inorganic precipitate of zirconium (IV) iodate and different molar concentrations of acrylamide (0.01–0.1 M) and lead ion exchange capacity was determined by column process (Table 1). The lead ion exchange capacity was found to depend on the concentration of acrylamide. The maximum capacity was obtained with 0.4 M acrylamide. Therefore polyacrylamide zirconium(IV) iodate was synthesized using 0.4 M acrylamide for further studies(sample PZ-5). This material appears to be a promising hybrid material with good ion exchange capacity, mechanical and chemical stability in comparison to inorganic ion exchanger, zirconium (IV) iodate. The improvement in these characteristics may be due to the binding of polyacrylamide with inorganic moiety i.e., zirconium (IV) iodate. In addition, this hybrid material shows a reproducible behaviour because the material obtained from different batches under the identical conditions possesses almost the same percentage yield and ion exchange capacity.
| Sample | Volume ratio (v/v) | Zr(IV) | Acrylamide | IEC for Pb(II) (meq/g dry exchanger) | |
|---|---|---|---|---|---|
| PZ-1 | 1:1:1 | 0.1 M | 0.1 M | 0.01 M | 0.28 |
| PZ-2 | 1:1:1 | 0.1 M | 0.1 M | 0.05 M | 1.65 |
| PZ-3 | 1:1:1 | 0.1 M | 0.1 M | 0.1 M | 2.15 |
| PZ-4 | 1:1:1 | 0.1 M | 0.1 M | 0.2 M | 2.80 |
| PZ-5 | 1:1:1 | 0.1 M | 0.1 M | 0.4 M | 3.27 |
| PZ-6 | 1:1:1 | 0.1 M | 0.1 M | 0.6 M | 2.87 |
| PZ-7 | 1:1:1 | 0.1 M | 0.1 M | 0.8 M | 2.82 |
| PZ-8 | 1:1:1 | 0.1 M | 0.1 M | 1.0 M | 2.15 |
The ion exchange capacity of the hybrid cation exchanger for alkali and alkaline earth metal ions and lead ion was determined by column process and results are reported in Table 2. The ion exchange capacity increases with a decrease in hydrated ionic radii. Similar observations were also reported for the exchange of alkali and alkaline earth metal ions on zirconium (IV) arsenate vanadate (Qureshi et al., 1995). Moreover, the hybrid material shows a high affinity for Pb(II).
| Metal ions | Ionic radii (A°) | Hydrated radii (A°) | Ion exchange capacity (meq/g) |
|---|---|---|---|
| Na+ | 0.97 | 7.90 | 0.69 |
| K+ | 1.33 | 5.30 | 0.81 |
| Mg2+ | 0.78 | 10.80 | 0.93 |
| Ca2+ | 1.06 | 9.60 | 1.02 |
| Sr2+ | 1.27 | 9.40 | 1.23 |
| Pb2+ | – | – | 3.23 |
Chemical stability of ion exchange materials is an important parameter that is required for their suitability for analytical applications. In view of this the chemical stability of polyacrylamide zirconium (IV) iodate has been evaluated in different concentrations of HCl, HNO3, H2SO4, CH3COOH and NaOH. It was found that the material is fairly stable in 1 M HCl, 1 M HNO3, 1 M H2SO4, 1 M CH3COOH and 0.10 M NaOH.
The FTIR spectrum (Fig. 1) of polyacrylamide zirconium (IV) iodate revealed the presence of external water molecule, metal–oxygen and metal −OH stretching bands. The spectrum shows a broad band in the region 3500–3100 cm−1 which may be due to external water molecules. In the spectrum the band appearing at 3198 cm−1 was indicative of N–H stretching vibration from the amino group of acrylamide. Further the presence of a strong peak at 1654 cm−1 was attributed to the –CH–NH group. The peaks at the 1383 cm−1 indicate the presence of a considerable amount of acrylamide in the material. (Socrates, 1980). In addition, H–O–H bending vibration was also lying in this region. A peak at ∼624 cm−1can be ascribed to the bending motion of the O⚌C–N group (Socrates, 1980). The presence of a peak at ∼735 cm−1 indicates the presence of the iodate group (Socrates, 1980) .TGA and DTA patterns of the polyacrylamide zirconium (IV) iodate are shown in Fig. 2 .The weight loss of mass (9.7%) up to 155 °C is due to the release of external water molecules. A weight loss of ∼9.8% observed from 155 to 260 °C may be due to the condensation of the IO3 group into I2O5 (Nabi et al., 1996).The sharp change in the curve above 260 °C indicates the complete decomposition of organic matter and volatilization of the iodate group in the material. Above 400 °C, the formation of metal oxide takes place. The DTA curve shows two distinct peaks at 110 and 260 °C indicating the corresponding weight loss. X-ray pattern (Fig. 3) of polyacrylamide zirconium (IV) iodate showed very small intensity peaks which suggested the amorphous nature of the material.
The scanning electron micrographs of polyacrylamide zirconium (IV) iodate; and lead adsorbed material and its EDX spectrum are shown in Figs. 4–6. The micrographs of the hybrid material with and without lead loaded showed irregular and fibrous surface (Figs. 4 and 5). The EDX spectrum (Fig. 6) clearly indicates the presence of C, O, Zr, I and Pb.
On the basis of chemical analysis (Table 3) and elemental analysis (Table 4) of polyacrylamide zirconium (IV) iodate, the molar ratio of Zr, Iodate and acrylamide was estimated to be 1:1:4. The formula for the material can be suggested as:
| Element/ions/compounds | Weight(g) | Number of moles | Mole ratio |
|---|---|---|---|
| Zirconium | 0.0363 | 2.94 × 10−4 | 1 |
| Iodate | 0.0489 | 2.94 × 10−4 | 1 |
| Acrylamide | 0.0837 | 1.178 × 10−3 | 4 |
| Elements | Percentage |
|---|---|
| Carbon | 21.23 |
| Hydrogen | 4.129 |
| Oxygen | 29.499 |
| Nitrogen | 8.25 |
| Others | 36.829 |
In order to explore the potential ability of the polyacrylamide zirconium (IV) iodate in the separation of metal ions, the distribution coefficient values for some metal ions were evaluated in distilled water and different concentrations of nitric acid. The results are summarized in (Table 5). The results of the present investigation show that the hybrid organic–inorganic material has a promising capability for the sorption of lead (II) from acid solution .The Kd values of Pb(II) are much higher than the Kd values of other metal ions thus proving it to be a highly selective sorbent material for Pb(II). The separation capability of the synthesized material has been demonstrated by carrying out some important binary separations such as Hg(II)–Pb(II), Cu(II)–Pb(II), Ni(II)–Pb(II), Fe(III)–Pb(II) and Cd(II)–Pb(II). The salient features of these separations are summarized in Table 6. It can be seen from the table 6 that separations are quite sharp, quantitative and reproducible. In addition, the selective separation of Pb(II) from a synthetic mixture has been carried out on the polyacrylamide zirconium (IV) iodate column (Table 7.). The results indicated the high efficiency of the column and the percentage recovery is almost constant (98.51–98.76%) on increasing the loading of the sample. The results given in (Table 8.) indicate the suitability of the polyacrylamide zirconium (IV) iodate for the separation of Pb(II) from waste water collected from different sites. The results obtained by the proposed method are comparable to those obtained by the reference method Ahmad and Mosaddeque-Al (2001). This suggested that the material is highly suitable for enrichment and determination of Pb(II) in water samples.
| Metal | DMW | 0.001 M HNO3 | 0.01 M HNO3 | 0.1 M HNO3 |
|---|---|---|---|---|
| Mg2+ | 23.00 | 21.56 | 15.49 | 4.52 |
| Ca2+ | 36.43 | 30.65 | 24.08 | 20.77 |
| Sr2+ | 33.73 | 30.05 | 25.12 | 8.68 |
| Ba2+ | 46.77 | 43.93 | 39.39 | 6.58 |
| Cd2+ | 15.78 | 12.33 | 6.55 | 4.60 |
| Mn2+ | 22.15 | 20.11 | 14.94 | 2.09 |
| Zn2+ | 6.57 | 4.51 | 3.77 | 2.63 |
| Cu2+ | 17.94 | 15.72 | 15.00 | 4.70 |
| Fe3+ | 18.03 | 14.28 | 2.98 | 1.75 |
| Pb2+ | 406.66 | 271.42 | 175.86 | 170.02 |
| Al3+ | 68.00 | 61.06 | 6.666 | 6.54 |
| Hg2+ | 52.45 | 48.81 | 26.66 | 24.87 |
| Ni2+ | 20.68 | 16.27 | 12.66 | 8.79 |
| Th4+ | 34.54 | 16.77 | 8.55 | 6.90 |
| Cr3+ | 6.77 | 5.09 | 4.60 | 3.77 |
| S.N. | Metal ions separated | Amount loaded (mg) | Amount found (mg) | % Recovery | Eluent used |
|---|---|---|---|---|---|
| 1 | Hg2+ | 0.5054 | 0.4934 | 97.63 | 0.01 M HNO3 |
| Pb2+ | 0.6588 | 0.6540 | 99.38 | 0.30 M HNO3 | |
| 2 | Cu2+ | 0.240 | 0.247 | 103.0 | DMW |
| Pb2+ | 0.6588 | 0.6630 | 100.6 | 0.30 M HNO3 | |
| 3. | Ni2+ | 0.165 | 0.161 | 98.17 | DMW |
| Pb2+ | 0.6588 | 0.6540 | 99.38 | 0.30 M HNO3 | |
| 4. | Fe3+ | 0.1670 | 0.1619 | 97.0 | DMW |
| Pb2+ | 0.6588 | 0.650 | 98.75 | 0.30 M HNO3 | |
| 5. | Cd2+ | 0.357 | 0.357 | 100.7 | DMW |
| Pb2+ | 0.6588 | 0.6500 | 98.75 | 0.30 M HNO3 |
∗DMW = Demineralized water.
| S.N. | Amount of Pb(II) loaded (mg) | Amount of Pb(II) recovered (mg) | % Recovery | Eluent used |
|---|---|---|---|---|
| 1. | 2.349 | 2.320 | 98.76 | 0.3 M HNO3 |
| 2. | 1.892 | 1.866 | 98.62 | 0.3 M HNO3 |
| 3. | 1.1745 | 1.157 | 98.51 | 0.3 M HNO3 |
Set1: Pb2+ (2.349 mg), Mg2+ (0.1215 mg), Ca2+ (0.2004 mg), Sr2+ (0.4381 mg), Ba2+ (0.6860 mg), Zn2+ (0.3265 mg), Cd2+ (0.5620 mg), Hg2+ (1.002 mg), Fe3+ (0.2792 mg), Mn2+ (0.2746 mg), Cu2+ (0.3177 mg) , Ni2+ (0.2934 mg), Al3+ (0.1349 mg), Cr3+ (0.2599 mg), Th4+ (1.1602 mg) ,
Set2: Pb2+ (1.892 mg) and keeping the same amounts of all the metal ions mentioned in set 1.
Set 3: Pb2+ (1.1745 mg) and keeping the same amounts of all the metal ions mentioned in set 1.
| Sample | Amount of Pb(II) found (μgml−1) | |
|---|---|---|
| Proposed method | Reference method | |
| Wastewater (near Gomti river LUCKNOW) | 22.73 | 23.17 |
| Wastewater (Near Gomti river JAUNPUR) | 7.24 | 7.52 |
| Waste water(Near Ganga river KANPUR) | 14.93 | 15.15 |
| Wastewater (near Ghagra river TANDA, Ambedkar nagar) | 14.25 | 14.54 |
4 Conclusion
The results of this investigation showed that polyacrylamide zirconium (IV) iodate seems to be a promising cation exchanger. The material was found to be fairly stable in 1 M HCl, 1 M HNO3 1 M H2SO4 and 0.10 M NaOH. The analytical importance of the hybrid material was deduced from Kd values for various metal ions in distilled water and different concentrations of HNOn The material showed a high affinity for Pb(II) in comparison to other metal ions studied. On the basis of this behaviour, the separation of Pb(II) from synthetic water samples and wastewater samples collected from different cities of India has been achieved, confirming the analytical utility of this material.
Acknowledgements
The authors are thankful to the chairman, Department of Chemistry, Aligarh Muslim University, Aligarh for providing research facilities. One of the authors (Uzma Haseen) is also thankful to UGC for granting Non-Net fellowship to carry out this work. This work was partially supported by DRS-I programme of UGC.
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