Synthesis, Characterization, and Photocatalytic Activity of Polyaniline

Sep 8, 2014 - Study of the various physicochemical properties indicates granulometric nature, fairly good thermal and chemical stability, uniform elut...
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Synthesis, Characterization, and Photocatalytic Activity of Polyaniline-Sn(IV)iodophosphate Nanocomposite: Its Application in Wastewater Detoxification Md. Dilwar Alam Khan,* Arshia Akhtar, Syed Ashfaq Nabi, and Meraj Alam Khan Analytical Research Laboratory, Department of Chemistry, Aligarh Muslim University, Aligarh, India−202002 S Supporting Information *

ABSTRACT: A new and novel nanocomposite cation exchanger polyaniline-Sn(IV)iodophosphate (PANI-SnIP) has been synthesized using a sol−gel method by the incorporation of precipitates of Sn(IV)iodophosphate into the matrices of polyaniline. The ion exchange capacity of the composite synthesized at pH 1.0 was found to be 1.2 mequiv g−1 for Na+ ion. The characterization of the material using simultaneous thermogravimetry−differential thermal analysis (TGA-DTA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals the composite nature of the material with uniform surface morphology and formation of particles of size ranging from 20−25 nm. Study of the various physicochemical properties indicates granulometric nature, fairly good thermal and chemical stability, uniform elution, and bifunctional behavior of the exchanger. The selectivity of the composite for Hg2+, Pb2+, and Ce4+ in different solvent media along with their reproducible quantitative separation from binary mixture as well as real samples makes it a potential environmental wastewater detoxicant. The limit of detection (LOD) and limit of quantification (LOQ) for Hg2+ were found to be 0.53 and 1.9 μg L−1, respectively. The photocatalytic activity of the nanocomposite has been demonstrated by the photo degradation of Methylene Blue (MB) under solar irradiation.

1. INTRODUCTION With the ever-increasing industrialization and manifold increase in automobile exhaust, the problem of pollution has become a matter of great concern. The toxic heavy metal ions released from industries and automobile exhausts have many adverse effects on both aquatic and terrestrial life. The industrial effluents containing lead, arsenic, mercury, cadmium, organic dyes, etc., are continuously discharged into the water stream and these materials in turn enter the human body through inhalation and ingestion of food and drinking water. These hazardous materials cause severe damages to kidney, brain, liver and reproductive system on prolonged accumulation in the body. Mercury compounds like organic mercurial CH3Hg+ can penetrate through the placental barrier and enter fetal tissues. Its poisoning may lead to several diseases like Hunter−Russell syndrome, Acrodynia, and Minamata.1 The key anthropogenic sources of mercury emission includes burning of fossil fuels, processing of ores, the chlor-alkali industry, batteries, thermometers, pesticides, dental amalgam, etc. Burning of fossil fuels (primarily coal) is the largest single source of emissions from human sources accounting for about 45% of the total anthropogenic emissions.2 The extensive use of lead in the industry (lead wire or pipes, lead-acid batteries, metal recycling, and foundries) is one of the major causes of environmental contamination.3,4 Lead poisoning is very harmful as it interferes with many biological processes of the body and affects the normal enzyme activity. Its exposure may cause impairments in intellectual functioning, kidney damage, infertility, miscarriage, and hypertension.5 Therefore, heavy metal ions separation from the water and food material has been the subject of extensive technological research.6 © 2014 American Chemical Society

Although the inorganic ion-exchangers have been potentially applied for the removal of toxic metal ions like Pb2+, Cd2+, Hg2+, and As+7,8 making ion selective membrane electrode,9 separation of radionuclide, electrodialysis, etc., but they suffer certain limitations like poor mechanical strength and nonreproducibility.10 The uses of organic resins are limited by their poor thermal and chemical stability. Thus, continuous efforts are being made by the researchers to explore the intrinsic properties of inorganic and organic ion exchanger and to prepare a new class of composite ion exchange materials that can be effectively applied in diverse fields. The phosphates of the tetravalent metals are regarded as one of the best types of inorganic ion exchanger due to their thermal stability and resistance to action of strong acids and alkali.11,12 The composite materials bearing phosphate group have been synthesized and were successfully employed owing to their high ion exchange capacity, thermal and chemical stability, reproducibility and preferential ion selectivity.13−15 It has been observed that the insertion of zirconium hydrophosphate, which form both single and aggregated nanoparticles in the polymer matrix, increased the electrical conductivity of the cation-exchange resin from 0.2 to 0.7 Ω−1 m−1 with an increase in total ion exchange capacity from 600 to 1800 mol m−3.16 Recently the organic−inorganic composite ion exchange materials based on conducting polymers like polypyrrole, polyaniline, poly o-anisidine, etc., have revolutionized the separation science due to their unique proton dopability, Received: Revised: Accepted: Published: 15253

July 14, 2014 September 2, 2014 September 8, 2014 September 8, 2014 dx.doi.org/10.1021/ie502804s | Ind. Eng. Chem. Res. 2014, 53, 15253−15260

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Scheme 1. Synthesis of Polyaniline-Sn(IV)iodophosphate (PANI-SnIP) Nanocomposite

The 10% aniline (v/v) and ammonium persulfate (0.1 M) were prepared in 1 M HCl solution. 2.2. Apparatus. A digital pH meter Elico EL-10 (Elico, India) was used for the pH measurement. The infrared (IR) spectra were recorded on a Fourier transform infrared (FTIR) spectrometer from PerkinElmer (1730, USA) using the KBr disc method. Simultaneous thermogravimetry−differential thermal analysis (TGA-DTA) were carried out on a DTG-60 H; C305743 00134, (Schimadzu, Japan) analyzer. An X’Pert PRO analytical diffractometer (PW-3040/60, Netherlands) with Cu Kα radiation λ = 1.5418 Å was used for X-ray diffraction (XRD) measurement. A scanning electron microscopy instrument (SEM; LEO, 435 VF) was used for capturing SEM images. Transmission electron microscopy (TEM) analysis was carried out on a Jeol H-7500 Microscope. Flame atomic absorption spectrometry (FAAS) measurements were done with a Model GBC-932-Plus flame atomic absorption spectrometer (GBC Scientific, Australia). 2.3. Synthesis of Polyaniline-Sn(IV)iodophosphate (PANI-SnIP) Nanocomposite. 2.3.1. Synthesis of Polyaniline. The polymerization of aniline was initiated by adding ammonium persulfate (0.1 M) into 10% solution (v/v) of double distilled aniline in 1:1 ratio while maintaining the temperature at 5 ± 2 °C under constant stirring for 1 h.20 The

electrical conductivity, granulometric nature, high thermal and mechanical stability, cost-effective synthesis, and selectivity for heavy metal ions.17−19 Although many aspects of these composite ion exchange materials have been studied but their catalytic activities are needs to be explored. The present paper deals with the synthesis of a novel nanocomposite ion exchange material polyaniline-Sn(IV)iodophosphate (PANI-SnIP) and to investigate its inherent properties in order to explore its potential applications in the monitoring of environmental pollution. The different parameters have been studied and the nanocomposite was found to be highly effective in the selective removal of Hg2+ and Pb2+ from industrial wastewater.

2. EXPERIMENTAL SECTION 2.1. Reagents and Methods. The main reagents used for the synthesis i.e. aniline and ammonium persulfate were procured from E-Merck (India), stannic chloride pentahydrate and orthophosphoric acid from Loba Cheme Pvt. Ltd. (India), and potassium iodate from S. D. Fine Chemicals (India). The rest of the reagents and chemicals used were of analytical grade. The solution of stannic chloride (0.1 M) was prepared in 1 M HCl solution while potassium iodate (0.1 M) and orthophosphoric acid (0.1 M) were prepared in demineralised water. 15254

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was determined by usual column process after cooling at room temperature. Simultaneous TGA-DTA study of the composite was carried out using a thermo gravimetric analyzer by heating the sample from 10 to 800 °C at a constant heating rate (10 °C min−1) in the nitrogen atmosphere. 2.7. Morphological Characterization of the Composite Material. In order to explore the various morphological features of the newly synthesized composite material, FTIR, XRD, SEM, and TEM analyses were carried out and the material was characterized accordingly. 2.8. Distribution (Sorption) Studies. The sorption study was carried out to assess the overall ability of the nanocomposite in removing the ions of interest from a sample under different sets of condition. Distribution coefficients (Kd values) of metal ions on the PANI-SnIP (S-9) were determined by usual batch method in different solvent systems like demineralized water (DMW), formic acid (HCOOH), and dimethyl sulfoxide (DMSO) of varying concentrations. For this various 200 mg portions of the exchanger in the H+ form were taken in Erlenmeyer flasks with 20 mL different metal nitrate solutions in the required medium and kept for 24 h with intermittent shaking at room temperature (25 ± 2 °C) to attain the equilibrium. The metal ions in the solution before and after equilibrium were determined by titrating with standard EDTA solution.23 The distribution coefficients were calculated using the following relation:

polymerization leads to the formation of a green colored gel like polyaniline. 2.3.2. Synthesis of Sn(IV)iodophosphate. The inorganic precipitate of Sn(IV)iodophosphate was prepared by gradually adding a mixture of potassium iodate (0.1M) and orthophosphoric acid (0.1M) into the solution of stannic chloride pentahydrate (0.1M) in the volume ratio of 1:1:2 (SnCl4: KIO3: H3PO4). The mixing was done with constant stirring for 2 h at room temperature (25 ± 2 °C) while maintaining the pH of the mixture at 1.0 by the addition of dilute hydrochloric acid or ammonia. The white colored precipitate so formed was allowed to settle overnight. After decanting off the supernatant liquid, the remaining white precipitate was washed with deminerlaized water to remove excess reagents. 2.3.3. Synthesis of Polyaniline-Sn(IV)iodophosphate. The gel of polyaniline was added to the white inorganic precipitate of Sn(IV)iodophosphate and mixed thoroughly with constant stirring (600 rpm) for about 2 h at room temperature (25 ± 2 °C) using a magnetic stirrer. The resultant green colored gel was kept for 24 h at the same temperature in mother liquid for complete digestion.21 The supernatant liquid was decanted off and the gel was filtered under suction. The excess acid was removed by washing with demineralized water and the material was dried in an oven at 50 °C. In order to convert the synthesized material into H+ form, it was subsequently treated with HNO3 solution (1 M) for 24 h with occasional shaking and intermittently replacing the supernatant solution with fresh acid. The excess acid was removed after several washing with demineralized water and the material was finally dried at 50 °C. The particles of size 80−120 mesh were obtained by sieving and kept in desiccators. Optimization of various synthesis conditions was done to obtain the good yield and ion exchange capacity (Supporting Information, Table S1). The proposed reaction scheme along with the structure of the final product is shown in Scheme 1. 2.4. Ion Exchange Capacity. For the determination of ionexchange capacity, 1.0 g of the exchanger (composite material) in H+ form was taken into a glass column (internal diameter 0.5 cm) plugged with glass wool at the bottom. The exchanger was stripped off H+ ions by allowing sodium nitrate solution (0.1 M) to pass through the column at a flow rate of 0.5 mL min−1. The H+ ion content of the effluent was then determined by titrating the effluent against a standard solution of sodium hydroxide using phenolphthalein indicator. The effects of the size of exchanging ions and eluent concentration on ion exchange capacity and elution behavior were also studied by passing the alkali and alkaline earth metal nitrate solutions through the exchanger. 2.5. Functionality Behavior of Exchanger: pH Titration. For determining the functionality behavior and nature of the ionogenic group of PANI-SnIP, the pH titration studies were carried out using Topp and Pepper method.22 A 0.5 g portion of the exchanger in H+ form was taken in each of the several 50 mL flasks followed by the addition of equimolar mixtures of alkali and alkaline earth metal chlorides and their corresponding hydroxide solutions such as LiCl−LiOH, NaCl− NaOH, KCl−KOH, MgCl2−Mg(OH)2, CaCl2−Ca(OH)2, and SrCl2−Sr(OH)2 systems. The final volume was adjusted to 50 mL to maintain the constant ionic strength. 2.6. Thermal Behavior. To study the effect of thermal treatment on ion exchange capacity, 1.0 g of the material in H+ form was heated at different temperatures in a muffle furnace for 1 h at each temperature and then Na+ ion exchange capacity

Kd =

Kd =

amount of metal ion in the exchanger phase (mequiv g −1) amount of metal ion left in the solution phase (mequiv mL−1)

I−F V × (mL g −1) F M

where I is the initial amount of metal ion present in the solution phase, F is the final amount of metal ion left in the solution phase after treatment with exchanger, V is the volume of the metal solution (mL), and M is the amount of exchanger used (g). 2.9. Separation of Metal Ions. 2.9.1. Quantitative Separation of Metal Ions in Binary Synthetic Mixtures. To explore the separation possibility using PANI-SnIP, a number of binary separations were carried out by column method. 1.0 g of the exchanger in H+ form (80−100 mesh) was packed in a glass column (0.5 cm internal diameter) with a glass wool support at the bottom. The column was rinsed thoroughly with demineralized water and the mixture of two metal ions (0.1 M) solution containing 1 mL each was loaded on the column and allowed to pass gently maintaining a flow rate of 0.5 mL min−1 until the level was just above the surface of the material. The collected effluent was recycled through the column two to three times in order to ensure complete sorption of the metal ions onto the beads. The separation was then achieved by eluting the trapped metal ions with appropriate eluent. The effluents were collected in 10 mL fractions to determine the metal ion contents by titrating against the standard EDTA solution. The Hg2+ and Pb2+ ions were also selectively separated from the synthetic mixtures containing Zn2+, Fe3+, Co3+, La3+, Hg2+, Er3+ and Mg2+, Zn2+, Cd2+, Al3+, Pb2+, and Th4+, respectively. 2.9.2. Determination of Hg2+ and Pb2+ in Paper Mill and Brass Industry Wastewater. For the determination of Hg2+ and Pb2+ in wastewater, industrial effluents were collected from the Hindustan Paper Mill (Assam, India) and Brass industry (Aligarh, India). The homogeneous water samples were taken 15255

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found to be 1.0 M for the complete removal of H+ ions. The elution behavior shows that the exchange is quite fast initially and an eluent volume of 150 mL is sufficient for almost complete elution of H+ ions from 1.0 g of the exchanger (graph omitted). This is a clear manifestation of the suitability of the exchanger for column operations. The pH titration curves (Supporting Information, Figure S1) for LiCl−LiOH, NaCl−NaOH, KCl−KOH and MgCl2− Mg(OH)2, CaCl2−Ca(OH)2, and SrCl2−Sr(OH)2 systems in the presence of PANI-SnIP show two inflection points indicating bifunctional behavior of the cation exchanger. A low pH value (∼2.3) of the solution when no OH− ions were added to the system and a steep edge at ∼1.3 mmol g−1 reveals the strong acidic cation exchange behavior. With the addition of OH− ions, the solution is progressively neutralized and at the same time the ion-exchange is essentially driven to completion. In acidic medium the exchange of metal ions follows the order K+ > Na+ > Li+ and Ca2+ > Mg2+ > Sr2+. The pH of the solution increases rapidly thereafter with further addition of OH− ions up to the second point of inflection. Above pH 10 the exchanger begins to hydrolyze. The chemical stability study of the composite shows that the composite is appreciably stable in different acids (HCl, HNO3, H2SO4) and bases (NaOH, KOH, NH3) up to 2 M strength and few dilute organic solvents like DMF, DMSO (up to 10% v/v). This stability is may be due to the presence of binding polymer that prevents the dissolution of any group or leaching of constituent elements into the solution. Thus, the exchanger may be applied successfully with diverse solvents in column operations. To have a look into the effect of heating on the ion exchange capacity, the composite is subjected to thermal treatment for 1 h at different temperature and the results are summarized in the Supporting Information, Table S3. The results show that there is a detrimental effect of heating on the ion exchange capacity of the exchanger. Although the ion exchange capacity decreases on heating, the exchanger is stable up to 300 °C with the retention of 90.8% of its initial ion exchange capacity and a mere weight loss of 18.3%. The simultaneous TGA-DTA curve (Supporting Information, Figure S2) of the composite material shows a continuous weight loss of about 10.7% up to 190 °C, which is due to the removal of free external water molecules.26 Further weight loss in the region 190 to 545 °C may be attributed to the condensation of phosphate group to pyrophosphate and IO3 group into I2O5, which also accounts for a decrease in ion exchange capacity after 190 °C.27,28 Above 545 °C, the weight loss is due to complete decomposition of organic part and formation of metal oxides of the exchanger. On the basis of chemical composition studies the molar ratio of Sn:I:P:O:C:N:H in the exchanger was estimated to be 1:1:2.9:19.8:15.8:2.4:25.7 which suggests the following tentative formula of the composite cation exchanger

for analysis from their point of discharge by the industry into the natural water sources. The sample solutions were immediately filtered and converted into a clear solution by adding small amount of nitric acid. The pH of the solutions was maintained at an optimal pH value of 4.0 by adding HCl or NH3. An aliquot (100 mL) solution was then passed through the column containing 0.5 g of the composite (80−100 mesh) at a flow rate of 0.5 mL min−1. The sorbed metal ions were then eluted with suitable eluent and analyzed for Hg2+ and Pb2+ using FAAS. 2.10. Photocatalytic Activity. The photocatalytic activity of the nanocomposite was assessed by the photodegradation of Methylene Blue (MB) dye under natural sunlight (Aug. 2013, Aligarh, India). Photocatalytic experiments were carried out in a 500 mL capacity borosilicate photochemical batch reactor. A working solution of MB (20 μg mL−1) in demineralized water was freshly prepared prior to undertake the experiment at its natural pH (6.7). The photochemical degradation was carried out by taking 200 mL of working solution with 0.2 g of nanocomposite in the reactor. Before exposure to sunlight, the solution was magnetically stirred in dark for 20 min to steady the adsorption of MB dye over the surface of nanocomposite catalyst. The suspension was then irradiated under natural sunlight with periodic withdrawal of sample solution at an interval of 1 h for measurement of decolourization and degradation by UV−vis spectrophotometer.

3. RESULTS AND DISCUSSION It is evident from the study, that the mixing ratio of reactants and pH of the inorganic precipitate has pronounced effect on the ion exchange capacity and yield of the synthesized composite ion exchange material. The ion exchange capacity increases with the increase in anionic phosphate group (ionogenic group) up to certain extent. The optimum pH and mixing ratio of inorganic part was found to be 1.0 and 1:1:2 (SnCl4:KIO3:H3PO4), respectively. Among all the composites, the one with ion exchange capacity of 1.20 was selected for further studies as it is having highest ion exchange capacity. The ion exchange capacities of rest of the composite samples were found to be 0.65, 0.42, 0.90, 1.05, and 0.84. The affinity of alkali and alkaline earth metal ions toward the material follows the sequence Li+ < Na+ < K+ and Mg2+ < Ca2+ < Sr2+ < Ba2+, respectively (Supporting Information, Table S2). This is in accordance with the decrease in their hydrated ionic radii. The smaller ion enters the pores easily and thus results in higher degree of sorption.24,25 It is apparent from Figure 1 that the eluent concentration plays a significant role in the release of H+ ions from the exchanger. The optimum concentration was

Sn(IO3)(H 2PO4 )3 (C6H4NH − )2 ·nH 2O

Therefore, it can be assumed that weight loss of ∼10.6% up to 190 °C as evident from TGA curve is due to loss of these nH2O molecules. The value of “n”, the external water molecules, has been calculated using Alberti’s equation29

18n =

X(M + 18n) 100

where X is the percent water content in the exchanger which is equivalent to percent weight loss (∼10.6%) by heating up to 190 °C in this case and (M + 18n) is the molecular weight of

Figure 1. Effect of eluent concentration on ion exchange capacity of PANI-SnIP composite cation exchanger. 15256

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the material. The calculation gives ∼5 for the external water molecules (n) per molecule of the composite cation exchanger. The FTIR spectrum of the PANI-SnIP composite (Figure 2) shows two very weak bands around ∼3500 and ∼3150 cm−1

Figure 2. FTIR spectrum of PANI-SnIP nanocomposite.

which represents the N−H stretching vibration.30 Two sharp bands at ∼1600 and ∼1510 cm−1 correspond to the N−H bending vibration while the bands at 1270−1300 cm−1 of medium intensity account for C−N stretching vibration of the polyaniline.31 A strong sharp band at 1380 cm−1 accounts for the CH2 bending vibration whereas a strong broad band at 900−1210 cm−1 corresponds to H2PO4− and HPO42− groups.32 The appearance of small bands adjoining to ∼800−500 cm−1 may indicate the presence of an IO3− group and metal oxide bond in the nanocomposite.33,34 Although spectrum of polyaniline is amorphous in nature, the X-ray diffraction spectrum of nanocomposite (Figure 3)

Figure 3. XRD spectrum of PANI-SnIP nanocomposite.

Figure 4. SEM images of (a) Sn(IV)iodophosphate, (b) polyaniline, (c) PANI-SnIP nanocomposite at a magnification of 1000×.

shows the presence of some low intensity peaks at 2θ values 37, 43, and 77 which indicates that some crystallinity has appeared in the polymer matrix upon composite formation. SEM of polyaniline, Sn(IV)iodophosphate, and polyaniline-Sn(IV)iodophosphate (Figure 4) at the same magnification depicts the morphological changes which occurred after binding of inorganic precipitate with the organic polymer matrix. The binding pattern and uniform surface morphology as reflected from the SEM image of the composite indicates absence of impure phases.35 The TEM (Figure 5) exhibits the formation of chainlike structure with interstitial spaces which facilitates the sorption of metal ions. It further confirms the particles size of

range 20−25 nm indicating the formation of nanocomposite material. The potential of the nanocomposite material in separation of metal ions has been explored by carrying out the distribution studies of metal ions in demineralised water (DMW), formic acid (HCOOH), and dimethyl sulfoxide (DMSO) solvent system of different concentrations (Supporting Information, Table S4). In most of the cases a lower Kd value is observed in the presence of formic acid than that of the corresponding value in dimethyl sulfoxide. This may be due to the slower release of H+ ions in formic acid medium causing decreased sorption as compared to dimethyl sulfoxide, thus less sorption 15257

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significant changes in the concentration of MB was observed after 8 h of irradiation under sunlight indicating that MB cannot be degraded easily by sunlight photolysis. In the presence of PANI-TIP nanocomposite catalyst, the absorption intensity has noticeably decreased with the increase in time of irradiation thus indicating a decrease in the relative concentration ([C]t/ [C]0) of MB solution (Figures 6 and 7). It is estimated that in

Figure 5. TEM image of PANI-SnIP nanocomposite.

of metal ions as expected. However, there are exceptions in the case of Hg2+ and some rare earth metal ions. The data also reveals the selectivity of the composite material for Hg2+, Pb2+, and Ce4+. The separation capability of the nanocomposite has been demonstrated by achieving some important binary separations of metal ions of analytical utility (Table 1). The

Figure 6. Absorption spectral pattern of MB during photocatalytic degradation process in the presence of PANI-SnIP nanocomposite photocatalyst under solar irradiation.

Table 1. Quantitative Binary Separations of Some Metal Ions Achieved Using PANI-SnIP binary system

amount loaded (mg)

amount found (mg)

% recovery

eluent useda

eluent volume (mL)

Zn (II) Hg (II) Cu (II) Hg (II) Fe (III) Hg (II) Zn (II) Pb (II) Cd (II) Pb (II) Fe (III) Ce (IV) La (III) Ce (IV) Th (IV) Ce (IV)

6.53 20.05 6.35 20.05 5.58 20.05 6.53 20.72 11.24 20.72 5.58 14.01 13.89 14.01 23.20 14.01

6.40 19.47 6.29 19.66 5.36 19.45 6.43 20.13 11.03 19.99 5.42 13.46 13.61 13.46 22.33 13.31

98.02 97.14 99.00 98.07 96.21 97.05 98.44 97.20 98.11 96.52 97.16 96.11 98.00 96.07 96.25 95.00

A B A B A B A+B A A+B A A+B C A C A C

60 70 70 80 70 80 60 70 60 70 80 70 70 80 60 80

a

Figure 7. Change in relative concentration of MB solution as a function of irradiation time in the (a) absence and (b) presence of photocatalyst (PANI-SnIP). Irradiation time is 8 h.

the presence of the catalyst about 71% of MB was degraded within 8 h of irradiation. The photocatalytic activity in the nanocomposite might be initiated by the production of e− by conducting PANI upon absorption of visible light which facilitates the electron−hole pair formation with charge separation.36

A = 0.1 M HCOOH; B = 0.1 M DMSO; C = 0.01 M DMSO.

4. APPLICATIONS The potential applications of the nanocomposite cation exchange material are illustrated below. 4.1. Selective Separation of Hg2+ and Pb2+ from Synthetic Mixtures of Metal Ions. High Kd values of Hg2+ and Pb2+ in all solvent systems enables their selective separations from synthetic mixtures of Zn2+, Fe3+, Co3+, La3+, Hg2+, Er3+ and Mg2+, Zn2+, Cd2+, Al3+, Pb2+, and Th4+, respectively, using PANI-SnIP columns (Supporting Information, Table S5 and S6). The quantitative recovery (∼96%) of these metal ions from synthetic mixture is a key indicator of the efficacy of the nanocomposite in removing the heavy metal ions. 4.2. Determination and Quantitative Separation of Hg2+ and Pb2+from Industrial Effluents (Paper Mill and

sequential elution of ions through the column depends upon the metal−ligand stability. The weakly retained metal ions were eluted first followed by the strongly retained ones. The chromatograms (Supporting Information, Figure S3) illustrate the order of elution of different metal ions and eluents used for binary separations. The separations were found to be quite sharp, and recovery is quantitative as well as reproducible. The limit of detection (LOD) and limit of quantification (LOQ) for 10 replicate measurements were found to be 0.53 and 1.9 μg L−1, respectively, for Hg2+. The photocatalytic activity of the nanocomposite has been investigated by performing the photodegradation of Methylene Blue (MB) dye under natural sunlight. It was found that no 15258

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B r a s s I n d u s tr y ) U si n g a P o l y a n i l i n e - S n ( I V ) iodophosphate Column. The practical utility of the synthesized nanocomposite has been established by selective separation of hazardous Hg2+ and Pb2+ from the industrial wastewater (Hindustan Paper Mill, Assam, India, and Brass industry wastewater, Aligarh, India). Both the metal ions were first selectively retained by the nanocomposite and then eluted for the determination using FAAS. The amounts of Hg2+ and Pb2+ in the sample water by recommended method were found to be 5.3 and 8.4 μg L−1, respectively, in paper mill effluent and 6.9 and 9.5 μg L−1 in brass industry wastewater (Table 2).

is available free of charge via the Internet at http://pubs.acs. org/.

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Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are thankful to the Chairman, Department of Chemistry, Aligarh Muslim University, Aligarh (India), for providing necessary research facilities and University Grants Commission, India, for providing UGC-BSR faculty fellowship to S.A.N.

Table 2. Determination of Hg2+ and Pb2+ in Industrial Effluents Using a PANI-SnIP Columna samples paper mill effluent brass industry wastewater

method directd SAe directd SAe

amount of Hg2+ foundb (μg L−1) (% RSD)c 5.3 6.2 6.9 7.5

(3.5) (2.8) (3.1) (2.6)

amount of Pb2+ foundb (μg L−1) (% RSD)c 8.4 9.1 9.5 10.0

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(2.9) (2.5) (3.2) (2.8)

REFERENCES

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Experimental conditions: 100 mL solution, flow rate 0.5 mL min−1, 0.5 g composite. bAverage of three replicate measurements. cPercent relative standard deviation. dRecommended procedure applied without spiking. eRecommended procedure with spiking (standard addition method). a

These heavy metal ions were successfully removed from the effluents using PANI-SnIP column with negligible interference from other metal ions. The close agreement between the results obtained by applying direct method without spiking and standard addition method shows the reliability of the present method in heavy metal ion analysis of wastewater samples without any significant interference.

5. CONCLUSION The newly synthesized polyaniline-Sn(IV)iodophosphate (PANI-SnIP) nanocomposite possesses the characteristic features of a promising cation exchange material with better thermal and chemical stability. The selectivity for Hg2+ and Pb2+ along with their effective quantitative separation from industrial effluents makes it potential environmental wastewaters detoxicant. Also the separation efficiency of the nanocomposite is significant for Hg2+ and Pb2+ ions separation with their quantitative recovery. The photocatalytic activity of the nanocomposite in the degradation of dye makes it suitable for the elimination of reactive dyes from water resources.

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AUTHOR INFORMATION

ASSOCIATED CONTENT

S Supporting Information *

Materials to encourage a better understanding of the nature of the polyaniline-Sn(IV)iodophosphate nanocomposite ion exchange material and the various ion exchange phenomenon. These include optimization of synthesis conditions (Table S1), ion exchange capacity for alkali and alkaline earth metal ions (Table S2), effect of heating on ion exchange capacity (Table S3), distribution coefficient values of metal ions (Table S4), selective separation of Hg2+ and Pb2+ from synthetic mixtures (Table S5 and S6), pH titration curves for PANI-SnIP nanocomposite (Figure S1), simultaneous TGA-DTA curve of PANI-SnIP nanocomposite (Figure S2), and chromatograms of binary separations of metal ions using PANI-SnIP nanocomposite cation exchanger column (Figure S3). This material 15259

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Industrial & Engineering Chemistry Research

Article

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