Synthesis and application of ion-imprinted polymer nanoparticles for the determination of nickel ions

Accepted Manuscript Synthesis and application of ion-imprinted polymer nanoparticles for the determination of nickel ions Shahryar Abbasi, Mahmoud Roushani, Hossein Khani, Reza Sahraei, Ghobad Mansouri PII: DOI: Reference:

S1386-1425(14)01820-4 http://dx.doi.org/10.1016/j.saa.2014.11.107 SAA 13090

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

15 July 2014 22 November 2014 24 November 2014

Please cite this article as: S. Abbasi, M. Roushani, H. Khani, R. Sahraei, G. Mansouri, Synthesis and application of ion-imprinted polymer nanoparticles for the determination of nickel ions, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.11.107

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Synthesis and application of ion-imprinted polymer nanoparticles for the determination of nickel ions Shahryar Abbasi*, a, Mahmoud Roushani *, a, Hossein Khania, Reza Sahraeia, Ghobad Mansourib Department of Chemistry, Ilam University, Ilam, Iran Department of Chemistry, Payame Noor Universtiy, PO Box 19395-3697, Tehran, Iran

* Corresponding authors: Tel/fax: +98 841 2227022 E-mail addresses: [email protected] (S. Abbasi), [email protected] (M. Roushani)

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ABSTRACT Novel Ni (II) ion-imprinted polymers (Ni-IIP) nanoparticles were prepared by using Ni (II) ion-1, 5 - diphenyl carbazide (DPC) complex as the template molecule and methacrylic acid, ethylene glycol dimethacrylate (EGDMA) and

2,2′azobisisobutyronitrile (AIBN) as the

functional monomer, cross-linker and the radical initiator respectively. The synthesized polymer particles were characterized physically and morphologically by using infrared spectroscopy (IR), thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. Some parameters such as pH, weight of the polymer, adsorption time, elution time, eluent type and eluent volume which affects the efficiency of the polymer were studied. The preconcentration factor, relative standard deviation, and limit of detection of the method were found to be 100, 1.9%, and 0.002 µg mL -1, respectively. The prepared ion-imprinted polymer particles have an increased selectivity toward Ni (II) ions over a range of competing metal ions with the same charge and similar ionic radius. The method was applied to the determination of nickel in tomato and some water samples.

Keywords: Ion imprinted polymer, nanoparticles, nickel, preconcentration.

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1. Introduction The toxicity and effect of trace heavy metals on human health and the environment has attracted considerable attention and concern in recent years. Heavy metals are categorized as environmentally toxic materials that can harm the natural environment at low concentrations with an inherent toxicity, a tendency to accumulate in the food chain, and a particularly low decomposition rate [1]. Nickel is one of the essential elements in the organism and can strengthen the secretion of the insulin, lower the blood sugar level, stimulate the hematopoiesis function, promote the regeneration of the red corpuscles, and treat the anemia and cirrhosis. Nickel still has buffer action to lung worry, asthma and heart–lungs function in disfigurement [2]. Nickel enters waters from dissolution of rocks and soils, biological cycles, atmospheric fallout, especially from industrial processes and waste disposal [3]. These facts explain the importance of monitoring nickel concentration in natural waters and food samples from public health and environmental point of view. According to the international regulation on water quality, the approved content of nickel in drinking water is 20.0 µg L−1 [4]. Thus, determination of nickel in drinking water requires much higher sensitivity than what is achievable with flame atomic absorption spectrometry. Therefore; a preliminary separation and preconcentration prior to its determination could be a good choice. Modern instrumental methods including spectrometry, inductively coupled plasma mass spectrometry (ICPMS), inductively coupled plasma – atomic emission spectroscopy (ICP-AES), atomic absorption spectroscopy (AAS), etc [5–7], have been used for determination of traces of metal ions in various media. However, in these determinations, low concentration levels of 3

analytes and high levels of matrices are the main problems [8]. To solve these problems, a separation/preconcentration step prior to analysis is required. Up to now, several method have been designed for separation/preconcentration of nickel from various matrices, including solidphase extraction (SPE) [9, 10], liquid–liquid extraction (LLE) [11], ion-exchange [12], flotation [13], cloud point extraction [14], etc., are among the most widespread used methods. Although relatively good analytical performance can be obtained with the above-mentioned pretreatment techniques, inconveniences such as lengthy separation, high consumption of reagent, multi-stage, and unsatisfactory enrichment factor can be listed as their disadvantages. In recent years ionimprinted polymers (IIPs), as selective sorbents for a particular chemical form of the given element, have received much attention [15-17]. The high selectivity of IIPs can be explained by the polymer memory effect toward the metal ion interaction with a specific ligand, coordination geometry, metal ion coordination number, charge and size [18]. In this study, a novel nano structure Ni (II) ion-imprinted polymer has been synthesised for faster extraction of Ni (II) ions from various matrixes using methacrylic acid (MAA) as a monomer, ethyleneglycoldimethacrylate (EGDMA) as a cross-linking agent, and 1, 5 diphenylcarbazide as a specific ligand for Ni (II). The extraction characteristics of the nonimprinted (NIP) and imprinted with Ni (II) - DPC complex (IIP) polymer nanobeads have been compared. The sorption and desorption characteristics have been investigated using batch procedures. Also the Ni (II) selectivity versus other interfering metal ions has been studied.

2. Experimental 2.1. Materials 4

Methacrylic

acid

(MAA),

ethyleneglycoldimethacrylate

(EGDMA)

and

2,2′-

azobisisobutyronitrile (AIBN) were obtained from Aldrich (Milwaukee, WI, USA). Ethanol was of reagent grade from Merck Chemical Company and was used as received. 1, 5 diphenylcarbazide, reagent grade Ni (NO3)2. 6H2O and nitrate or chloride salts of other cations (all from Merck) were used without any further purification. A stock standard solution of Ni2+ (1000 µ g mL -1) was prepared by dissolving 0.4955 g of Ni (NO3)2. 6H2O in distilled-deionized water containing a few drops of concentrated nitric acid. The solution was made up to the mark in a 100 mL volumetric flask. This stock solution was diluted further, when necessary.

2.2. Apparatus The determination of nickel and other metal ions was performed using a Chem Tech flame atomic absorption spectrometer (CTA, 2000, UK) equipped with a CTA 2000 singleelement hollow cathode lamp, and a deuterium background corrector at respective wavelengths (resonance line) using an air-acetylene flame, while the instrumental parameters were those recommended by the manufacturer. A 780 pH Meter (Metrohm), equipped with a combined Ag/AgCl glass electrode, was used for pH measurement. Scanning electron micrographs were recorded using a Philips XL30 series instrument using a gold film for loading the dried particles on the instrument. Gold films were prepared by a Sputter Coater model SCD005 made by BALTEC (Switzerland). A Varian model 300 Bio equipped with 10 mm quartz cell was used for recording the UV-Vis spectra at 25.0±0.1ºC. The FTIR spectra (4000–400 cm-1) were recorded on a Bruker (Germany) FTIR Vertex 70 spectrometer. Thermogravimetery analysis (TGA) and differential thermal analysis (DTA) were carried out using a Stanton Redcroft, STA–780 series

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with an aluminum crucible, applying heating rate of 10 º C/min in a temperature range of 50–600 ºC, under air atmosphere with the flow rate of 50 mL min -1. The sample mass used was about 3.0 mg. Eppendorf Varied-Pipettes (10–100, 100–1000 µ L) were used to deliver accurate volumes. All glassware and storage bottles were soaked in 10% HNO3 overnight and thoroughly rinsed with deionized water prior to use.

2.3. Preparation of Ni2+-ion imprinted polymeric nanoparticles The nickel ion-imprinted nanobeads were prepared by precipitation polymerization technique [19]. For this purpose, 2.0 mmol of 1, 5 - diphenylcarbazide was added into 25.0 mL of ethanol as porogen solvent, and then treated with 1.0 mmol of Ni (NO3)2.6H2O as imprint metal ion at room temperature with continuous stirring for 30 min. In the polymerization procedure, MAA (4.7 mmol), EGDMA (30.0 mmol) and 0.4 mmol of AIBN were added as functional monomer, crosslinker and free radical initiator, respectively, to the first step solution and stirred at room temperature. The polymerization mixture was purged with N2 gas for 10 min to remove the molecular oxygen, since it traps the radicals and retards the polymerization. Then, the reaction vial was sealed and heated in an oil bath at

60 °C for 24 h under magnetic stirring

at 400 rpm to complete the thermal polymerization. After polymerization, the excess amount of solvent was removed by centrifugation of the resulting suspension solution. The imprint ion, i.e. Ni2+ ion was leached from the above polymer material by stirring with 3 × 50 mL of HNO3 (50%; v/v) for about 18 h [20] and, after centrifugation, the nickel contents of the supernatant solutions were determined by atomic absorption spectrometer. This step was carried out several times until the supernatant solution was free from Ni2+ ions. The nanoparticles were then washed with ethanol and the sorbent repeatedly washed with doubly distilled-deionized water until 6

neutral pH. The resulting nanoparticles were dried under a vacuum oven at 50 °C to obtain IIP particles for possible preconcentrative separation of Ni2+ ion from aqueous solutions. In the same way, the control non-imprinted polymeric (NIP) nanomaterials were similarly prepared using an identical procedure but without the addition of the imprint ion (i.e. Ni2+ ion). Powder nanoparticles of 62-200 nm in diameter were achieved and then applied for future sorption and desorption studies.

2.4. Extraction procedure Batch experiments were used for investigation of factors in sorption and desorption steps. Extraction of Ni (II) ions from modeling solutions and real samples is followed by two steps: sorption and desorption. In sorption step, the pH of sample solution was adjusted to 9.0 by addition of 0.1 M sodium hydroxide or hydrochloric acid solutions. Then, 50.0 mg of dried polymer was suspended in aqueous solution containing 1.00 µg mL

-1

concentration of Ni (II)

and stirred for 15.0 min with a magnetic stirrer and then centrifuged (5 min, 6000 rpm) and the supernatant solution removed. The Ni (II) ions preconcentrated onto IIP nanoparticles were eluted using 5.0 mL of HCl (1.0 M), while stirring for 5.0 min. The suspensions were then centrifuged and eluent solutions containing Ni (II) ions were removed from the nanoparticles. The resulting solutions were centrifuged and the nickel contents of the solutions were determined by flame atomic absorption spectrometry (FAAS). Extraction percent of nickel was calculated by the following equation: Extraction (%) = 

   

100

(1)

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Ci and Cf are the concentrations of nickel ion before and after extraction in the solution. The distribution ratio (mL g -1) of Ni2+ ions between the IIP particles and aqueous solution was also determined by the following equation:   

kd=







(2)

Where V is the volume of initial solution and m is the mass of IIP materials. Selectivity coefficients and relative selectivity coefficients (k′) for Ni2+ ions relative to foreign ions in the solution are defined as:  



 



  



(3)



 !"#$ %&#"&'

Where (



and (

(4) 

are the distribution ratios of nickel and foreign ion, respectively. In order

to obtain the reusability of the prepared ion-imprinted polymeric nanobeads, the sorption experiments (adsorption-elution cycle) were repeatedly performed using the same particles.

2.5. Real samples preparation 2.5.1. Determination of nickel in water samples

The water samples such as Ilam city water (water sample was collected from Ilam, Iran, and placed in bottle for 24 h for sedimentation of probable particles), River water (Gangir, Eivan Gharb, Ilam) and mineral water were centrifuged, filtered and subjected to UV digestion for 2 h.

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After adjusting the pH samples to 9.0, they were stored in a cool place and analyzed, following the procedure given in section 2. 4. 2.5.2. Determination of nickel in tomato

Tomatoes were purchased from a supermarket and the juice squeezed out. The juice was filtered using Whatman 42 paper and centrifuged for 10 min at 3000 rpm [21]. Two milliliters of this solution was transferred to a volumetric flask, diluted to 10 mL and analyzed following the procedure given in section 2.4.

3. Results and discussion 3.1. Preliminary complexation studies Evidence for the formation of ternary complex Ni (II)-DPC was followed by the UVVisible absorption spectra. The absorption spectrum of DPC (5.0 × 10-5 M) in ethanol solvent is illustrated in Fig. 1 (a), which showed a very weak maximum at 400 nm. When Ni2+ was added with different concentrations (0.5 × 10-5, 2.0 × 10-5, 3.0 × 10-5, 5.0 × 10-5, 7.5 × 10-5 and 1.0 × 10-4M), an adsorption peak was produced at 545 nm and absorbance increased with the increase in the concentration of nickel (Fig. 1 (b)). These results clearly indicate that the ternary complex Ni (II)-DPC was readily formed in ethanol solvent. Furthermore, the stoichiometry of the complex was determined from the absorbance–mole ratio plot at maximum wavelength of the complex (545 nm). A distinct inflection point at mole ratio about 0.5 (Fig.1 c) strongly supports the formation of a complex of stoichiometry Ni (DPC)2 [22].

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3.2. Characterization of Ni (II) ion imprinted polymer 3.2.1. Colorimetry After synthesis of unleached, leached IIP and NIP, colorimetric studies were carried out to compare the changes in the color of prepared powders (Scheme. 1). An obvious change in the color from red of unleached IIPs to yellow after leaching process, clearly indicate the successful removal of nickel ions from the polymeric matrix. Meanwhile, adsorption process caused an instant color change in the leached IIPs from yellow to the red due to fast extraction of nickel ions into the imprinted polymeric matrix at desired pH.

3.2.2. FTIR spectra The resulting imprinted particles were characterized by FTIR spectroscopy. The FTIR spectra of unleached and leached ion-imprinted polymer (IIP) were recorded using KBr pellet method. Fig. 2 shows the FT-IR spectra of the un-leached and leached IIP nanoparticles. By comparing the IR spectra of the polymers, it was observed that both the polymeric materials have a similar polymer backbone. Moreover, similarities between the IR spectra of these materials suggested that the leaching process does not affect the polymeric network [23]. In the IR spectra, the absorptions due to N-H (3564.9 cm-1), C-N (1157.1 cm-1) and C‗O (1730.2 cm-1) were observed [24]. The N–H bands at 3564.9

cm-1, C-N band at 1157.1 cm-1and C‗O band at

1730.2cm-1 in unleached IIP were shifted to 3442.7, 1149.5 and 1733.6 cm-1 in leached IIP. This amount of reduction in band frequencies indicates that the nickel ions have been coordinated 10

with non-bonding electron pairs of nitrogen in N–H and C‗O groups in DPC, and consequently the presence of Ni2+ ions in unleached IIP structure is demonstrated. Moreover, the presence of C‗O, C-N and N–H bands in the IR spectra of these materials indicated that DPC had been sufficiently immobilized in the polymer matrix.

3.2.3. X-ray diffraction (XRD) The XRD patterns of the unleached (a), leached (b) and NIP (c) nanosized ion imprinted polymer are shown in Fig. 3. In un-leached IIP, the corresponding peak to the 2θ values of 10.010, 22.010, 24.410, 26.570, 28.730 and 34.490 disappeared after leaching, leaving vacant sites in the matrix while the rest of the polymer backbone remained unaffected. This behavior confirms complete removal of the nickel from the material during leaching process. In all of the above cases, the XRD of leached IIPs was similar to the corresponding XRD patterns of control polymers.

3.2.4. Scanning electron microscopic (SEM) The morphology of the Ni (II)-IIP was assessed by scanning electron microscopy, and the SEM micrograph is shown in Fig. 4. The SEM pattern showed particles with the size of about 62–200 nm. As a result, Ni (II)-IIP can be used as a nano-size selective solid phase for very fast extraction of ultra trace amounts of nickel.

3.2.5. Results of thermal analysis for the polymer samples

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Thermal behaviors of the prepared NIP and Ni-IIP nanoparticles before and after leaching were studied under identical conditions using TGA and DTA techniques. Fig. 5 represents TGA/DTA curves for the NIP nanoparticles. As seen in Fig. 5 a, an endothermic event was observed in the DTA curve of the NIP sample. This peak is observed due to the starting thermal decomposition of the ligand around 255 °C. This peak is followed by two continuous exothermic peaks which are responsible for the main decomposition of complex. On the other hand, TGA thermogram of this sample showed a main mass loss step for the decomposition of nanoparticles. This step was started at about 300 °C and continued until 480 °C. The TGA curve indicates about 88% total mass loss for the thermal decomposition of this sample in this temperature range. Thermal behavior of the Ni-IIP sample is studied and the results are shown in Fig. 5b. As seen in TGA/DTA curves, thermal stability of this sample is significantly different from NIP nanoparticles. A mild exothermic event was observed on the DTA curve of the sample which is followed by two sharp exothermic peaks. These sharp peaks are along with another small exothermic phenomenon. TGA thermogram of this sample shows a main decomposition step with about 84% loss in the mass of sample. This mass loss step is started at about 240 °C and continued until temperature of 500 °C. Thermal behavior of the polymer sample after leaching was also investigated and the results are presented in Fig. 5c. TGA/DTA curves for this sample are relatively comparable with the NIP nanoparticles. A small exothermic event was observed in the DTA curve of this sample which followed by two continuous exothermic phenomena. TGA thermogram for this sample shows that main decomposition of the compound is started at about 250°C and continuous until

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about 550 °C. On the other hand, the TGA curve indicates about 98% mass loss for thermal decomposition of the sample in this temperature range. These results suggest that the thermal decomposition of the leached polymer (in the absence of metallic nickel ions) is approximately complete and during its decomposition in the temperature range of 250 -550 °C, the whole of hydrocarbon compositions of the nanoparticles changed to the gaseous products. A comparison between thermal behaviors of the leached and un-leached samples shows that nanoparticles in both samples decompose exothermally during a single step; however, the mass loss for both samples is considerably different. This observed difference in mass loss of the samples is due to the presence and absence of the nickel ion, respectively, in the Ni-IIP nanoparticles and leached samples.

3.3. Sorption/desorption experiments 3.3.1. Effect of pH For metal, ionic complexation with ligands is highly dependent on the equilibrium pH of the medium, and the pH value of the solution is an important parameter for adsorbing metal ions. To evaluate the effect of pH on the extraction efficiency, the pH of 50.0 mL of sample solutions containing 1.00 µg mL

-1

of nickel ion was adjusted in the range of 2.0–12.0. The results

obtained for the influence of pH on the Ni (II) extraction efficiency are presented in Fig. 6. The Ni (II) adsorption of Ni (II) -imprinted polymer increased from pH 2.0 to 9.0 but decreased from pH 9.0 to 12.0. Therefore the maximum binding capacity was obtained at pH 9.0. As expected, due to the presence of nitrogen and oxygen donor atoms in DPC and functional monomers (MAA), the complex formation with metal ion is highly dependent on the pH of solution. At low 13

pH, the donor nitrogen and oxygen atoms in the DPC-MAA network may be protonated and therefore, negligible amounts of nickel ions can be adsorbed to the polymeric network. When the pH is increased, the protonation of ligand is suppressed and the condition becomes more favorable for complex formation and sorption of Ni (II) ions to the imprinted sorbent. Also, the adsorption amount of nickel ions on the IIP nanobeads is decreased at

pH > 9.0. So, the

solution at pH 9.0 was chosen as the optimum pH for the next experiments.

3.3.2. Effect of type and concentration of eluent A series of selected eluents, including HCl, H2SO4 and HNO3 were used for elution of Ni (II) ions from imprinted nanoparticles. According to results, it is found that HNO3 (1.0 M) provided the most effective elution of Ni (II) ions from imprinted nanoparticles. After selection of the proper eluent, several 5.0 mL portions of nitric acid solutions with different concentrations (i.e., 0. 1, 0.5, 1.0 and 2.0 M) were used for leaching of nickel ions from the imprinted sites in the polymer network in order to study the optimum eluent concentration. It was found that desorption of adsorbed Ni (II) ions increased with increasing nitric acid concentration. This is most probably due to increased protonation of the nitrogen and oxygen atoms as the donor atoms in the DPC structure of imprinted polymer. Thus, 5.0 mL of 1.0 M nitric acid was selected as optimal eluent solution.

3.3.3. Effect of IIP weights

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The percentage of preconcentration of nickel ions with different weights of IIP was also investigated. 50.0 mL of aqueous solution containing 1.0 µg mL -1 nickel ions at pH 9.0 was used and other conditions were the same as above. The results indicate no difference between 50.0 and 70.0 mg of IIP nanoparticles in enrichment of nickel ions and specific binding of nickel ions onto active sites in the IIP. Consequently, 50.0 mg of IIP particles were used for further studies.

3.3.4. Effect of adsorption and desorption times The effect of sorption and desorption times on the binding quantity of Ni (II) ion was investigated in a batch system. In a typical uptake kinetics test, 50.0 mg of the sorbent was added to 50.0 mL of a 1.0 µg mL -1 solution of Ni (II) at pH 9.0. The resulting suspension was stirred for different periods of time (i.e., from 5 to 30 min) under magnetic stirring. After centrifugation, the supernatant solution was removed and the Ni (II) ions were determined by atomic absorption spectrometer. The results indicated that quantitative sorption of Ni (II) can be achieved over a period of 15.0 min. Therefore, the optimum adsorption time of 15.0 min was selected and used in all subsequent studies. In ion-imprinted polymer technique, after the sorption of analyte on IIP, a time interval is necessary to break the bonding between ligand and metal ions. In order to investigate the optimum desorption time, various times were examined in the range of 3.0-15.0 min, while other parameters were kept in optimum condition. According to the results, extraction recovery was increased up to 7.0 min and it remained constant at in longer times. Therefore, 7.0 min is the best quantitative time for the elution of metal ions from the imprinted polymer.

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3.3.5. Effect of sample volume In the analysis of real samples, the sample volume is one of the important parameters influencing the preconcentration factor. Therefore, the effect of sample volume on quantitative adsorption of Ni (II) ion was investigated. For this purpose, 50.0 mg of IIP was suspended in different sample volumes (25.0, 50.0, 100.0, 200.0, 300.0, 400.0, 500.0, 600.0, 700.0, and 800.0 mL), and the total amount of loaded Ni (II) was kept constant in 1.00 µg. All solutions were extracted under the optimum condition by the proposed method. The results demonstrated that the dilution effect was not significant for sample volumes of nickel ions up to 500.0 mL. However, at higher sample volumes, the recovery decreased significantly. Thus, a high preconcentration factor of 100 was obtained in which the quantitative extraction of nickel by the prepared IIP is possible.

3.3.6. The adsorption capacity The adsorption capacity (maximum amount of nickel ion adsorbed for 1.00 g of IIP particles) is an important factor to evaluate the IIPs [25]. To measure the adsorption capacity (Q), imprinted or non-imprinted polymers (50.0 mg) were equilibrated with Ni2+ solutions (50.0 mL) within the concentration range of 1.00–100.00 µg mL-1 at pH 9.0. The adsorption value increased with the increase of concentration of Ni2+ (1.00–50.00 µg mL-1), and a saturation value was achieved in the concentration range of 50.00–100.00 µg mL -1. The adsorption capacity of the imprinted and non-imprinted polymers was calculated to be 40.25 and 15.63 mg g

-1

,

respectively. The resulting plot of Q vs. initial concentration of nickel ion is shown in Fig. 7. The capacity of imprinted particles is larger than that of non-imprinted ones. This difference indicates that the imprinting plays an important role in the adsorbent behavior. During the preparation of

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the imprinted adsorbent, the presence of Ni2+ encouraged an orderly ligand arrangement. After removal of Ni2+, the imprinted cavities and specific binding sites of functional groups in a predetermined orientation are formed; however, no such specificity is found in non-imprinted polymers [26]. Thereby the memory effect owned by imprinted materials to the template metal ion allows them to possess a shorter response time and higher adsorption capacity to metal ions than NIP.

3.3.7. Regeneration and reusability In order to examine the reusability of the prepared IIP nanoparticles, the sorption experiments were repeatedly performed by using the same particles. For this purpose, IIP particles were subjected to several loading and elution operations, under the same experimental conditions (i.e., amount of IIP, 50.0 mg; initial amount of nickel metal ion, 1.0 µg mL-1; pH, 9.0; treatment period, 15.0 min). After each use, 5.0 mL of 1.0 M HNO3 in methanol was used for elution of the adsorbed Ni2+ ions and regeneration of the IIP. Imprinted nanoparticles enabled the selective extraction of nickel ions from aqueous solutions and after 8 times of adsorption/ desorption cycle, the recovery of adsorption capacity of Ni2+ on IIPs nanoparticles was decreased only 4.9%. The results showed (Fig. 8) that IIPs nanoparticles could be repeatedly used without any significant loss in the initial binding affinity.

3.3.8. Selectivity study The imprinted polymers are also characterized by a uniform distribution of chelating sites [27]. In IIPs, the cavities created after removal of the template are complementary to the imprint ion in size and coordination geometries. Furthermore, the unique shape of the nickel ion may be

17

expected to lead to much greater selectivity for the nickel ion by ion imprinting. In comparison with other metal ions, in the case of non-ion imprinted sorbent, the random distribution of ligand functionalities in the polymeric network results in no specificity in rebinding affinities. Cu2+, Fe3+, Pb2+, Al3+, Cd2+, Zn2+, Mg2+ and Co2+ are chosen as the competitor ions as they have the same charge and similar size Both the imprinted and nonimprinted polymers were used to obtain 2 sets of experimental data. Polymer material (50.0 mg) was added to 50.0 mL aqueous solutions containing 1.00 µg mL-1 Ni2+/M

n+

. The pH was then adjusted accordingly to pH 9.0. After the

adsorption-equilibrium, the mixtures were filtered and the concentration of each ion in the remaining solution was measured by atomic absorption spectroscopy. The measured values gave the concentrations of the unextracted ions, from which extraction efficiency was evaluated. Table. 1 summarizes the distribution ratios (Kd), selectivity coefficients (k) and relative selectively coefficients (k) calculated using Eqs. (2, 3 and 4) respectively. From the data in Table. 1, the following can be observed: (1) the selectivity coefficients of NIP for Ni (II) with respect to foreign ions are very low; (2) the selectivity coefficients of Ni (II)-IIP for Ni (II) with respect to foreign ions are very high; (3) the relative selectivity coefficients indicate adsorption affinity and selectivity of imprinting material for the template with respect to non-imprinting material. The above results imply that the imprinted cavities and specific binding sites in a predetermined orientation were formed in the Ni (II)-IIP, and the size of foreign ions does not match well with the cavity imprinted by Ni (II), resulting in high recognition ability and high selectivity of Ni (II)-IIP for Ni (II) ions.

3.3.9. Analytical figures of merit

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The analytical performance data for the batch preconcentration procedure are given in Table. 2. Under the optimized conditions described above, the calibration curve for Ni2+ was linear over the concentration range of 0.009 to 1.80 µg mL-1 with the correlation coefficient (R2) of 0.9976. According to the IUPAC definition, the detection limit (3s of the blank signal intensity divided by slope of the calibration curve) of this method was 0.002 µg mL-1 with the preconcentration step. The relative standard deviation (RSD) was 1.9% for 1.00 µg mL-1 nickel level (n = 6), indicating favorable precision of the proposed method.

3.3.10. Real sample analysis The applicability of the ion imprinted polymer for preconcentration of trace levels of Ni (II) was tested using Ilam city water, River water (Gangir, Eivan Gharb, Ilam), mineral water, and tomato samples. The mentioned samples were prepared according to the Section 2.5. For the preconcentration procedure, pH of real samples was adjusted to 9.0 spiked with nickel ions and used in the extraction procedure. The concentration of sorbed Ni (II) ions was determined based on standard addition method and recovery tests (Table. 3). It was found that the quantitative extraction of nickel ions was performed successfully by the Ni (II)-IIP even in the presence of various diverse ions.

4. Conclusion The ion-imprinted polymer procedure is a useful technique for the preparation of sorbent for preconcentration of metal ions, such as nickel from aqueous solutions. In conclusion, the

19

results presented here demonstrate the efficiency of the precipitation polymerization procedure based on DPC as a novel sorbent for selective determination of nickel ions. Rapid kinetics of adsorption and desorption of nickel ion on the resulting imprinted sorbent provides a fast preconcentration procedure for nickel ion in aqueous solutions. The new sorbent revealed an excellent selectivity toward nickel ion over a range of strong competing metal ions. The prepared Ni-IIP nanoparticles were shown to be promising for extraction coupled with atomic absorption spectrometer for the determination of nickel ions in aqueous samples.

5. Acknowledgements The authors are grateful to the Ilam University Research Council for financing the project.

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References [1] L. Sun, D. Hao, W. Shen, Zh.Qian, C. Zhu, Pyridine-functionalized mesoporous silica as an adsorbent material for the determination of nickel and lead in vegetables grown in close proximity by electrothermal atomic adsorption spectroscopy, Microchim. Acta 177 (2012) 357364. [2] L. Na Li, N. Bing Li, H. Qun Luo, A new chemiluminescence method for the determination of nickel ion, Spectrochim. Acta A 64 (2006) 391–396. [3] S. Dadfarnia, A. M. Haji Shabani, M. Shirani Bidabadi, A. A. Jafari, A novel ionic liquid/micro-volume back extraction procedure combined with flame atomic absorption spectrometry for determination of trace nickel in samples of nutritional interest, J. Hazard. Matter 173 (2010) 534–538. [4] Guide lines for Drinking Water Quality. Health Criteria and Other Supporting Information, vol. 2, 2nd ed., World Health Organization, Geneva, 1998. [5] I. Narin, M. Soylak, The use of 1-(2-pyridylazo)-2-naphthol (PAN) impregnated ambersorb 563 resin on the solid phase extraction of traces heavy metal ions and their determination by atomic absorption spectrometry, Talanta 60 (2003) 215–221. [6] S. Dadfarnia, C.W. McLeod, On-line trace enrichment and determination of uranium in waters by flow injection inductively coupled plasma mass spectrometry, Appl. Spectrosc 48 (1994) 1331–1336. [7] S. Dadfarnia, A.M. Haji Shabani, F. Tamaddon, M. Rezaei, Immobilized salen (N,N-bis (salicylidene)ethylenediamine)

as

a

complexing

agent

for

on-line

sorbent

extraction/precocentration and flow injection-flame atomic absorption spectrometry, Anal. Chim. Acta 539 (2005) 69–75. [8] Y.A. Zolotov, N.M. Kuzmin, Preconcentration of Trace Elements, Elsevier, Amsterdam, 1990.

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[9] V.A. Lemos, L.S.G. Teixeira, M. de A. Bezerra, A.C.S. Costa, J.T. Castro, L.A.M. Cardoso, D.S. de Jesus, E.S. Santos, P.X. Baliza, L.N. Santos, New materials for solid-phase extraction of trace elements, Appl. Spectrosc. Rev 43 (2008) 303–334. [10] A.R. Turker, New corbents for solid-phase extraction for metal enrichment, Clean-Soil, Air,Water 35 (2007) 548–557. [11] H. Eskandari, H. Ghaziaskar, A.A. Ensafi, A sensitive and simple extractive spectrophotometric method for determination of microgram amount of cobalt by using Lbenzilmonoxime, Anal. Sci 17 (2001) 327–331. [12] M. Tuzen, E. Melek, M. Soylak, Celtek clay as sorbent for separation preconcentration of metal ions from environmental samples, J. Hazard. Mater 136 (2006) 597–603. [13] H. Karami, M. Ghaedi, A. Shokrollahi, H.R. Rajabi, M. Soylak, B. Karami, Development of a selective and sensitive flotation method for determination of trace amount of cobalt, nickel, copper and iron in environmental samples, J. Hazard. Mater 151 (2008) 26–32. [14] J.L. Manzoori, G. Karim-Nezhad, Development of a cloud point extraction and preconcentration method for Cd and Ni prior to flame atomic absorption analysis, Anal. Chim. Acta 521 (2004) 173–177. [15] M. B. Gholivand, M. Shamsipur, S. Dehdashtian, H. R. Rajabi, Development of a selective and sensitive voltammetric sensor for propylparaben based on a nanosized molecularly imprinted polymer–carbon paste electrode, Mater. Sci. Eng 36 (2014) 102–107. [16] V. Vatanpoura, S. S. Madaeni, S. Zinadinia, H. R. Rajabi, Development of ion imprinted technique for designing nickel ion selective membrane, J. Membr. Sci 373 (2011) 36–42. [17] M. Shamsipur, H. R. Rajabi, M. H. Beyzavi, H. Sharghi, Bulk polymer nanoparticles containing a tetrakis (3-hydroxyphenyl)porphyrin for fast and highly selective separation of mercury ions, Microchim. Acta 180 (2013) 791–799. [18] I. Dakova, I. Karadjova, V. Georgieva, G. Georgiev, Ion-imprinted polymethacrylic microbeads as new sorbent for preconcentration and speciation of mercury, Talanta 78 (2009) 523- 529. 22

[19] M. Shamsipur, A. Besharati-Seidani, Synthesis of a novel nanostructured ion-imprinted polymer for very fast and highly selective recognition of copper (II) ions in aqueous media, React. Funct. Polym. 71 (2011) 131-139. [20] M. Shamsipur, H.R. Rajabi, Flame photometric determination of cesium ion after its preconcentration with nanoparticles imprinted with the cesium-dibenzo-24-crown-8 complex, Microchim. Acta 180 (2013) 243-252. [21] S. Abbasi, H. Khani, R. Tabaraki, Determination of ultra trace levels of copper in food samples by a highly sensitive adsorptive stripping voltammetric method, Food. Chem 123 (2010) 507-512. [22] S. Balt, E. Van Dalen, The reaction of diphenylcarbazide and diphenylcarbazone with cathions, Anal. Chim. Acta 29 (1963) 466-471. [23] S. Daniel, P. Prabhakara Rao, T. Prasada Rao, Investigation of different polymerization methods on the analytical performance of palladium (II) ion imprinted polymer materials, Anal. Chim. Acta 536 (2005) 197-206. [24] A. Dehno Khalaji, S. Mehrani, V. Eigner, M. Dusek, Synthesis, experimental and theoretical studies on its crystal structure and FT-IR spectrum of new thiosemicarbazone compound E-2-(4isopropylbenzylidene)thiosemicarbazone, J. Molecu. Struc 1047 (2013) 87–94. [25] H.R. Rajabi, M. Shamsipur, S.M. Pourmortazavi, Preparation of a novel potassium ion imprinted polymeric nanoparticles based on dicyclohexyl 18C6 for selective determination of K+ ion in different water samples, Mater. Sci. Eng. C 33 (2013) 3374-3381. [26] Q. He, X.J. Chang, H. Zheng, N. Jiang, Z. Hu, X.Y. Wang, Determination of chromium(III) and total chromium in natural waters using a surface ion-imprinted silica gel as selective adsorbent, Inter. J. Environ. Anal. Chem. 88 (2008) 373-384. [27] L.S. Molochnikov, E.G. Kovalyova, A.A. Zagorodni, M. Muhammed, Y.M. Sultanov, A.A. Efendiev, Coordination of Cu (II) and Ni (II) in polymers imprinted so as to optimize amine chelate formation Polymer 44 (2003) 4805-4815.

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List of tables Table. 1: Distribution ratio (Kd), selectivity coefficient (k) and relative selectively coefficient (k′) values of IIP and NIP material for different cations. Table. 2: Analytical figures of merit of the preconcentration procedure. Table.3: Determination of Ni2+ in real samples.

Figure captions Scheme. 1: photographical images of prepared ion imprinted polymeric nanoparticles. Fig. 1: UV-Vis spectra of 5.0 × 10-5 M 1, 5 - diphenyl carbazide (a) and b addition of different concentrations of Ni (II) (0.5 × 10-5, 2.0 × 10-5, 3.0 × 10-5, 5.0 × 10-5, 7.5 × 10-5 and 1.0 × 10-4M) (b). Fig. 2: FTIR spectra of unleached (a) and leached (b) nickel-IIP. Fig. 3: XRD patterns of unleached (a) and leached (b) Ni-IIP and NIP (c). Fig. 4: SEM photographs of Ni-IIP nanoparticles. Fig. 5: TGA/DTA curves for thermal decomposition of IIP samples (a) NIP, (b) Ni-IIP before (c) and Ni-IIP after leaching. Sample mass 3.0 mg; heating rate 10 °C min-1; Nitrogen atmosphere. Fig. 6: Effect of sample pH on the extraction of nickel ion. Fig. 7: Effect of initial concentration of nickel ion on the adsorption capacity of ion imprinted and non-imprinted polymeric nanobeads. Fig. 8: Effect of 14 adsorption–desorption cycles on the efficiency of Ni-IIP nanoparticles.

24

IIP (unleached)

NIP

Scheme. 1

1

IIP (leached)

c ↑b

↓

a

↓

Fig. 1

2

a

b

Fig. 2

3

a

b

c

Fig. 3

4

Fig. 4

5

(a)

(b)

(c) Fig. 5

6

Fig. 6

7

Fig. 7

8

Fig. 8

9

Table. 1: Distribution ratio (Kd), selectivity coefficient (k) and relative selectively coefficient (k′) values of IIP and NIP material for different cations.

Cation

Kd (IIP) (mL Kd (NIP) (mL g -1) g -1)

k (IIP)

k (NIP)

k´

Ni2+

99000.0

25600.3

----

----

----

Fe3+

1985.1

12588.4

49.9

2.0

25.0

Pb2+

3696.7

20005.3

26.8

1.3

20.6

Al3+

895.6

8522.4

110.5

3.0

36.8

Cd2+

5269.3

25458.8

18.8

1.0

18.8

Zn2+

3098.6

14879.0

31.9

1.7

18.8

Cu2+

18555.4

27456.2

5.3

0.9

5.9

Mg2+

4446.7

23588.4

22.3

1.1

20.3

Co2+

7004.5

30666.2

14.1

0.8

17.6

1

Table. 2: Analytical figures of merit of the preconcentration procedure. Parameters

Optimum value

Precision (RSD)

1.9 %

Detection limit (µg / mL)

0.002 µg mL -1

Linear range (µg / mL)

0.009 – 1.800 µg mL -1

Preconcentration factor

100

pH

9.0

Amount of IIP

50.0 mg

Adsorption Time

15.0 min

Desorption Time

7.0 min

2

Table.3: Determination of Ni2+ in real samples. Sample Mineral water

Ilam city water

River water

Tomato

Amount added (µg mL -1) 0.000 0.050 1.500 0.000 0.050 1.500 0.000 0.050 1.500 0.000 0.070 0.500

Amount found (µg mL -1) 0.015±0.0006 0.066±0.0009 1.509±0.0018 0.012±0.0015 0.065±0.0012 1.524±0.0010 0.019±0.0010 0.068±0.0013 1.522±0.0019 0.054±0.0098 0.129±0.0155 0.546±0.0365

3

RSD (%)

Recovery (%)

3.59 3.66 2.88 3.36 2.50 2.30 3.77 3.33 3.12 4.11 3.89 2.96

102.0 99.6 106.0 100.0 98.8 100.2 107.1 98.4

IIP (unleached)

NIP

IIP (leached)

Highlights  Novel Ni (II) ion-imprinted polymers (Ni-IIP) nanoparticles were prepared.  The proposed method is simple, selective and sensitive.  The method is suitable to the determination of nickel in food and water samples.