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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
One-step synthesis of CDTA coated magnetic nanoparticles for selective removal of Cu(II) from aqueous solution
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Haixia Lü a,∗ , Xiaoming Wang a , Jingqi Yang a , Zenghong Xie b a
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College of Materials Science and Engineering, Fuzhou University, Fuzhou 350108, China Institute of Food Safety and Environmental Monitoring, Fuzhou University, Fuzhou 350108, China
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Article history: Received 25 November 2014 Received in revised form 9 March 2015 Accepted 31 March 2015 Available online xxx
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Keywords: Magnetic nanoparticles Cu(II) CDTA
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1. Introduction
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A novel 1,2-cyclohexylenedinitrilotetraacetic acid (CDTA) modified Fe3 O4 magnetic nanoparticles (MNPs) was synthesized by one-step solvothermal method and used as solid phase extraction (SPE) material to preconcentrate trace copper coupled with flame atomic absorption spectrometry (FAAS). The synthesized adsorbents were characterized by field emission scanning electron microscopy and X-ray powder diffraction with a nanoscale. The optimum conditions for the absorption process were investigated on several commonly tested experimental parameters such as pH of the solution, ultrasound time, sample volume, concentration and volume of elution solution. The influences of some anions and cations metals on the recoveries of Cu(II) ions were also investigated, and no considerable interference was observed. The maximum adsorption capacity of Fe3 O4 magnetic nanoparticles and CDTA modified Fe3 O4 magnetic nanoparticles were found to be 27.50 mg/g and 78.24 mg/g for Cu(II). The developed method was applied to the determination of Cu(II) in tap and lake water samples with recoveries ranging from 96.4% to 99.1%. © 2015 Published by Elsevier B.V.
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Copper is one of the essential elements that are required to maintain the normal structure, function, and proliferation of cells. However, excessive amount of copper can cause abnormal metabolism [1]. Due to these reasons, the accurate and precise determinations of copper ion are important for analytical chemists [2,3]. Flame atomic absorption spectrometry (FAAS) has been widely used for the determination of the heavy metals at trace levels owing to its selectivity, low cost and easy instrument usage. Nevertheless, it has some difficulties, such as the presence of lower levels of metals ions in samples than the limit of detection of flame atomic absorption spectrometry, and the presence of interfering effects of the matrix components of the working media [4,5]. In order to overcome these limitations, several preconcentration techniques such as solid phase extraction (SPE) [6], ion exchange [7], cloud point extraction [8], membrane filtration [9], liquid–liquid extraction [10] and coprecipitation [11] have been extensively developed. Among different separation and preconcentration techniques, SPE is advantageous over other sample pretreatment techniques in terms of simpler and faster operation, higher enrichment factors
∗ Corresponding author. Tel.: +86 591 22866131; fax: +86 591 22866131. E-mail address: hx [email protected] (H. Lü).
with better recoveries, quicker phase separation, lower cost and reduced consumption of organic solvents as well [12]. Thus, the development of new sorbent material for SPE is in demand. To date, many novel adsorbents, such as nano-materials [13], ion imprinted material [14], mesoporous materials [15], carbon nanotubes [16] and magnetic nanoparticles [17] have been employed in SPE. However, magnetic solid phase extraction (MSPE) with magnetic nanoparticles (MNPs) as the adsorbents has aroused great interest in analytical community [3,18,19]. In this procedure, there is no need for packing of the column with the sorbent in case of batch mode operation, since the phase separation can be quickly and easily accomplished by applying an external magnetic field. Therefore, the use of magnetic materials in solid phase extraction has received considerable attention [20,21]. Recently, several researchers have used multi-step functionalized Fe3 O4 nanoparticles as MSPE adsorbents to separate and preconcentrate trace copper. Xiang [22], etc. fabricated PEMs on a magnetic silica stepwise as an MSPE sorbent for the extraction of trace Cu(II) with adsorption capacity of 14.7 mg/g. The magnetic nano-adsorbent developed by the binding of mercapto-containing dithizone (H2 Dz) on silica-coated Fe3 O4 nanoparticles could be used for removal of Cu(II) ions from aqueous solution, and the adsorption capacity was 20.5 mg/g [23]. The prepared magnetic beads (PMMA–DVB) were surface modified by aminolysis reaction with ethylene diamine, resulted as amino-functionalized magnetic bead (PMMA–DVB–NH2) [24] exhibited a magnetization value of
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20.3 emu/g, and the high adsorption affinity for aqueous Co2+ , Ni2+ and Cu2+ reached to 50.3, 49.6 and 51.7 mg/g, respectively. However, the preparation of those absorbents with multiple steps is time consuming and also difficult to control the amount of ligands incorporated into the polymer. Zhang and co-authors [25], introduce a one-pot solvothermal route synthesis of hierarchical porous Fe3 O4 to removal Congo red (CR) efficiency in waste water, which is considered as the preferred method for the preparation of absorbents. To the best of our knowledge, the analysis of real water samples has not been well documented with 1,2cyclohexylenedinitrilotetraacetic acid modified Fe3 O4 magnetic nanoparticles (MNPs–CDTA). In this study, MNPs–CDTA was synthesized by a simple one-step solvothermal and used as solid phase extraction material to preconcentrate trace Cu(II) coupled with FAAS for the analysis of Cu(II). The adsorbent was characterized by field emission scanning electron microscopy, Fourier transform infrared, powder X-ray diffraction, magnetic property measurement system. The adsorption properties of the adsorbent toward Cu(II) ions in aqueous solution were investigated systematically for adsorption capacity, effect of water chemistry and regeneration. 2. Experimental 2.1. Chemicals and reagents Ferric chloride hexahydrate (FeCl3 ·6H2 O), ethylene glycol (EG), sodium acetate anhydrous (NaAc), ethanol, copper chloride (Cu(Cl)2 ·2H2 O), acetic acid, hydrochloric acid and nitric acid were purchased from Tianjin Fu Chen Chemical Reagents Factory(Tianjin, China). 1,2-Cyclohexylenedinitrilotetraacetic acid was purchased from Fluka (America). All reagents were of analytical grade and were used without further purification. Double-distilled water was used throughout the study. 2.2. Instrumentation
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Copper concentration was determined by a TAS-986 Beijing Pgeneral Company (Beijing, China) flame atomic absorption spectrometer (FAAS) in an air-acetylene flame, with a copper hollow cathode lamp of wavelength 324.7 nm. All pH measurements were recorded with a digital pHS-10C pH meter Xiaoshan Instrument Factory (Hangzhou, China). Field emission scanning electron microscopy (FSEM) images were recorded on ZEISS SUPRA 55 (Germany). X-ray powder diffraction (XRD) data were collected on Rigaku Ultima III with Cu K␣ radiation ( = 0.1542 nm) at 40 kV and 30 mA (Japan). Fourier transform infrared (FT-IR) spectra of the magnetic nanoparticles were recorded by Nicolet 5700-Fourier transform infrared spectrometer (Thermo Electron Scientific Instruments Corp. America). The magnetization and hysteresis loops were measured at room temperature by a magnetic property measurement system (SQUID-XL, Quantum Design, America).
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2.3. Procedures
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2.3.1. Preparation of MNPs–CDTA nanoparticles Magnetic MNPs–CDTA was prepared by a modified solvothermal method as previously reported [26]. Briefly, FeCl3 ·6H2 O (2.025 g) were dissolved in EG (72 mL) under stirring to form a clear solution, then NaAc (5.4 g) and CDTA (0.80 g) were added to the solution under vigorous stirring at 50 ◦ C for 30 min. The obtained yellow mixture was put into a Teflon-lined stainless-steel autoclave (100 mL), thereafter the autoclave was sealed and heated in a furnace at 198 ◦ C for 8 h, and then cooled to room temperature.
After completion of the reaction, the obtained black precipitates were separated and collected with a permanent hand-held magnet and washed repeatedly with absolute ethanol and deionized water, and dried under vacuum at 50 ◦ C for 24 h. Finally, the products (MNPS–CDTA) were collected for further use. Fe3 O4 magnetic nanoparticles (MNPs) were prepared in the same procedure without addition of CDTA. 2.3.2. Extraction procedure The adsorption of Cu(II) by MNPs–CDTA was performed at room temperature. The solution of Cu(II) was prepared by dissolving an appropriate quantity of Cu(Cl)2 ·2H2 O in the double-distilled water to give a final concentration range from 1 to 160 mg/L. And the mixture was adjusted to a certain pH value using 0.2 mol/L HAc and 0.2 mol/L NaAc. 5 mg magnetic MNPs–CDTA was added to 20 mL 2 mg/L copper solution and the mixture was ultrasonicated for 10 min. Then the magnetic adsorbent was removed magnetically from the solution using a permanent hand-held magnet. After extraction, the concentrations of the metal ions in the supernatant were directly determined by flame atomic absorption spectrometer (FAAS). Unless otherwise specified, the absorption experiments were performed in aqueous solution at pH 7 and 25 ◦ C. After eluting the MNPs with 2 mL the solution 0.1 mol/L of HCl for 10 min, the preconcentrated analyte in the eluent was then determined by FAAS.
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3. Results and discussion
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3.1. Sorbent characterization
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3.1.1. Morphology and BET of MNPs and MNPs–CDTA Representative FSEM images are shown in Fig. 1. Fig. 1 reveals that the MNPs and MNPs–CDTA are mainly mono-dispersed and have a rough spherical surface with the average particle size of ca.277.46 nm and ca.151.08 nm, respectively. The presence of CDTA significantly decreased the average particle size of primary nanocrystals of the products. But the MNPs–CDTA have a more essentially mono-dispersed size distribution comparing with MNPs, which demonstrates that coating process does significantly result in the aggregation of the prepared materials in solution [27]. The BET surface area and average pore diameter had been characterized and the values of MNPs and MNPs–CDTA are16.34 m2 /g and 108.87 nm, 26.28 m2 /g and 286.34 nm, respectively. 3.1.2. Surface functional group of MNPs–CDTA The FT-IR spectrums were exhibited in Fig. 2. In Fig. 2a, the strong IR band at 584 cm−1 confirms the Fe O vibration [28], while in Fig. 2b, a strong peak at 3400 cm−1 which can be assigned to axial stretching vibration of O H. The FT-IR spectrum exhibited bands at 1050, 2920 and 1610 cm−1 , which are the vibrational frequencies of C N, C H and C O, respectively, indicating the existence of CDTA. From these changes between a and b shown in IR spectra, it can be reasonably concluded that Fe3 O4 nanoparticles have been successfully modified with CDTA. 3.1.3. Crystal structure of MNPs and MNPs–CDTA The crystalline structures of the MNPs and MNPs–CDTA nanoparticles were identified with XRD and the results are presented in Fig. 3. The XRD patterns show the characteristic peaks for Fe3 O4 at 30.1 (2 2 0), 35.3 (3 1 1), 43.2 (4 0 0), 53.6 (4 2 2), 57.2 (5 1 1) and 62.8 (4 4 0), which are in agreement with the database in JCPDS file (JCPDS no. 19-06290) [29], indicative of a cubic spinel structure of the magnetit. The same characteristic peaks were also observed for MNPs–CDTA, indicating the stability of the crystalline phase of Fe3 O4 nanoparticles during the modification and functionalization. Also according to this result, the average crystallite
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Fig. 1. FSEM images and average particle size distribution.
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size of MNPs and MNPs–CDTA microspheres is 36.9, and 20.9 nm, respectively, as estimated from the (3 1 1) diffraction peak by the Scherrer equation [30,31]. The XRD results also demonstrate high crystallinity of prepared MNP-CDTA. 3.1.4. Magnetic results To examine the magnetic properties, the nanoparticles were studied by a magnetic property measurement system at room temperature. As shown in Fig. 4, all the samples exhibit a typical superparamagnetic behavior without a hysteresis loop due to their nanometer sizes, meaning that the thermal energy can overcome the anisotropy energy barrier of a single particle. Under a large external field (H), the magnetization (M) of the particles aligns with the field direction and reaches its saturation value, and the magnetization saturation values of these samples are 75.35 emu/g (MNPs) and 72.96 emu/g (MNPs–CDTA) at 300 K. These magnetization saturation values are high enough to separate MNPs and MNPs–CDTA from aqueous solution because saturation magnetization of 16.3 emu/g is sufficient for magnetic separation with a conventional permanent magnet [32]. The as-synthesized adsorbent dispersed in water can be easily collected by external magnetic field within several minutes (Fig. 4 lower right), and then can be readily re-dispersed with slightly shake, the results reveal that the particles exhibit well magnetic responsible and re-disperse property, suggesting their potential application of magnetic adsorbent.
3.2. Investigation of the effect of various parameters on the adsorption
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3.2.1. Effect of pH The acidity of the aqueous solution exerts profound influence on the adsorption process because it can affect the solution chemistry of contaminants and the state of functional groups on the surface of adsorbents [33]. The effect of pH soution on Cu(II) adsorption was investigated at pH 3.0–7.5. As shown in Fig. 5, almost no Cu(II) is adsorbed on MNPs and only a small amount of Cu(II) is adsorbed onto MNPs–CDTA at pH 3.0 and pH 4.0. The adsorption amount of Cu(II) increases with increasing pH values from 4.0 to 7.0 for both MNPs and MNPs–CDTA. The smaller adsorption capabilities of MNPs and MNPs–CDTA at lower pH levels, are probably due to the significant competition between Cu(II) and hydrogen ions for the same adsorption sites [34]. Cu(II) in aqueous solution can present in several forms, such as Cu(II), Cu(OH)+ , Cu(OH)2 , Cu(OH)3 − and Cu(OH)4 2− . And Cu(II) is the predominant species at pH < 7.0. The adsorption capability at pH > 7.5 was not studied because the removal of Cu(II) is possibly accomplished by simultaneous precipitation of Cu(OH)2 and adsorption of Cu(OH)+ and Cu(OH)3 − in the solution [35]. So the optimum pH for Cu(II) ion adsorption is found in the pH range of 6.5–7.5 and that the
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results showed that ultrasound time of 10 min for Cu(II) was found to be sufficient to saturation at pH 7.0. The results indicated that sorbent had rapidly adsorption kinetics. Also, the desorption procedure were carried out. The results shows that ultrasound time of 10 min was fit for desorption. In our work, the ultrasound time of 10 min was chosen as the adsorption and desorption equilibrium time.
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MNPs–CDTA gets a better quantity than the MNPs. The further experiments were carried out at pH 7.0. 3.2.2. Effect of type, concentration and volume of eluent As the ions are not removed from the sorbent completely with an inappropriate eluent, the eluent solution is an important factor for elution efficiency and recovery. To elute the copper ions from the MNPs–CDTA absorbent, a variety of selected eluent solutions (including 1.0 mol/L HCl, HAc, H2 SO4 and HNO3 ) were investigated. It was found that HCl solution as an effective elution of copper ions from the absorbent obtained better recovery 99.8 ± 1.3%. Therefore, HCl solution was chosen as the eluent for all copper extraction studies. The effect of different concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mol/L) and eluent volume (1.0, 2.0, 3.0 and 4.0 mL) of HCl on the recovery of copper was also examined. It was found that quantitative recovery can be obtained with 2 mL of 0.6 mol/L HCl. 3.2.3. Time of adsorption and desorption The effect of ultrasound time is another important factor in evaluating the affinity of the sorbent to Cu(II). To determine the rate of loading of Cu(II) on the sorbent, the recommended procedure was carried out. The contact time varied from 2 to 30 min and the
3.2.4. Influence of interfering ions The copper ions are usually in matrices containing interfering ions, which decreases the accuracy of copper ion determination. In order to investigate the selectivity of the sorbent, the effect of different cations and anions on the adsorption of Cu(II) on the sorbent were studied using the established procedure. As some anions and cations metals, various concentrations of Na+ , Cl− , NO3 − , SO4 2− , Mg2+ , Ca2+ , Ni2+ , Pb2+ , Co2+ and Cd2+ were added to individual copper-containing solutions. The results showed that 10,000-fold Na+ , 8000-fold Cl− and NO3 − , 6000-fold SO4 2− , 250fold Mg2+ and Ca2+ , 5-fold Ni2+ and 2-fold Pb2+ , Co2+ and Cd2+ ions did not affect the separation process. The results obtained indicate that co-existing ions had no obvious influence on the recovery of the analytes and the method had good tolerance to matrix interference. 3.3. Adsorption capacity The adsorption capacity was tested following the extraction procedure. 5 mg of the sorbent was equilibrated with 20 mL of various initial concentrations of Cu(II) for 10 min. In order to reach the “saturation”, the initial metal ions concentrations were increased till the plateau values (adsorption capacity values) were obtained and the result was shown in Fig. 6. As calculated by the equation described in the previous reference [36], the maximum adsorption capacity of MNPs and MNPs–CDTA has been found to be 27.50 mg/g and 78.24 mg/g for Cu(II), respectively, which likely due to the addition of amino and carboxylate groups of CDTA. Adsorption capacity for copper ion extraction from this absorbent are compared with other previously established MSPE methods [22–24,27,37], and the results show that the presented method has advantages and superior capacities that make it a preferable method for copper ion determination.
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qmax = 77.62 mg/g b = 0.6060 L/mg R2 = 0.9990
KF = 13.0218 n = 2.62 R2 = 0.9342
Lake water
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Tap water
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Unfound 97.2 196.4
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3.4. Adsorption isotherms Langmuir [38] and Freundlich [39] equations are two common isotherm models to describe the behavior of adsorbents and the correlation between adsorption parameters. In this work, two models were used to test the adsorption process of sorbents. The Langmuir model assumes monolayer coverage of adsorbate over a homogeneous adsorbent surface. The binding sites are also assumed to be energetically equivalent and distant from each other, so there are no interactions between molecules adsorbed on adjacent sites. The Langmuir model can be described by qe =
qmax bCe (1 + bCe )
where qe is the amount of adsorbed Cu(II) in the adsorbent(mg/g), Ce is the equilibrium ion concentration in solution (mg/L), b is the Langmuir constant (L/mg), and qmax is the maximum adsorption capacity (mg/g). The Freundlich expression is an exponential equation that describes reversible adsorption and is not restricted to the formation of the monolayer. This empirical equation takes the form qeq =
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where KF and n are the Freundlich constants; Ceq is the equilibrium ion concentration in solution (mg/L). The adsorption kinetic of MNPs–CDTA were investigated at pH 7.0, with 5 mg of MNPs–CDTA and 20 mL varied Cu(II) concentrations (1–160 mg/L) at room temperature. The adsorption data were analyzed by Langmuir and Freundlich isotherms model. As can be seen from Table 1, the Langmuir isotherm presents a reasonable fitting to the experimental data with the correlation coefficients (R2 = 0.9990). And the calculation value of maximum adsorption capacity (qmax ) was found to be 77.62 mg/g, with a low difference of the experiment adsorption capacity (78.24 mg/g). These findings demonstrate that the Cu(II) sorption onto MNPs–CDTA possibly takes place by a homogeneous adsorbent surface over monolayer coverage of adsorbate, which may be ascribed to the hydroxy and carboxyl groups present in MNPs–CDTA. 3.5. The breakthrough volume
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Table 2 Analytical results for the determination of Cu(II) in water samples.
Langmuir adsorption isotherm
An important parameter in SPE is the breakthrough volume, which is the maximum sample volume that should percolate through a given mass of sorbent after which an analyte starts to elute from the sorbent resulting in non-quantitative recoveries. The breakthrough volume was experimentally evaluated by adding 5 mg of MNPs–CDTA in a solution containing 10 g copper ions in different volumes of solution varying from 20 to 200 mL. The results indicated the maximum sample volume can be up to 180 mL and therefore the enrichment factor was obtained as 90.
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To test the stability and potential reusability of the sorbent, several loading and elution operations cycles were carried out. The operating capacity was calculated from the loading and elution tests. The result showed that the column was relatively stable up
to at least 6 extraction–elution cycles without evident decrease of recoveries. Under the selected conditions, eight portions of standard solutions were enriched and analyzed simultaneously following the general procedure. The relative standard deviations (R.S.D.s) of the method was lower than 5.0%, which indicated that the method had good precision for the analysis of trace Cu(II) in solution samples. And the detection limit of the method was calculated based on three times of the standard deviation of 8 runs of the blank solution. The detection limit of the proposed method as defined by IUPAC [40] was 2.4 ng/mL. 3.7. Application of the method The proposed method was then applied to the determination of Cu(II) in tap water, lake water samples as the following procedure: 5 mg of the sorbent was equilibrated with 50 mL of water samples for 10 min, then was eluting with 2 mL 0.6 mol/L HCl solution. For the analysis of the water samples, the standard addition method was used and the results for the recovery of both metals are presented in Table 2. As shown in Table 2 the recoveries of analytes were in the range of 96.4–99.1%. It demonstrated the suitability of the sorbent for the preconcentration of Cu(II) from water samples prior to FAAS analysis. 4. Conclusion The proposed one-step method for the synthesis of the novel MNPs–CDTA sorbent was simple, fast and inexpensive. The magnetic nano-adsorbent has been prepared for removal of trace Cu(II) from aqueous solution. The absorbents have a monodispersed rough spherical morphology and high crystallinity. The short loading time (10 min) of the present matrix makes the analytical procedure reasonably fast. The adsorption process can be better simulated by Langmuir isotherm equation which provided a better R2 (R2 > 0.9990). The MNPs–CDTA showed a high adsorption capacity and an efficient adsorption toward Cu(II) in aqueous medium. The proposed method can be applicable to the preconcentration and separation of trace Cu(II) ion in a variety of water samples with low method detection limit, high accuracy (recovery ranging from 96.4 to 99.1%) and high precision (R.S.D. ranging from 0.5 to 1.2%). Acknowledgement This work was supported by the National Natural Science Foun- Q3 dation of China (21307013). References [1] Y. Pang, G. Zeng, L. Tang, Y. Zhang, Y. Liu, X. Lei, Z. Li, J. Zhang, G. Xie, Desalination 281 (2011) 278–284. [2] P. Saravanan, V.T.P. Vinod, B. Sreedhar, R.B. Sashidhar, Mater. Sci. Eng., C 32 (2012) 581–586. [3] H. Bagheri, A. Afkhami, M. Saber-Tehrani, H. Khoshsafar, Talanta 97 (2012) 87–95. [4] T.O. Germiniano, M.Z. Corazza, M.G. Segatelli, E.S. Ribeiro, M.J.S. Yabe, E. Galunin, C.R.T. Tarley, React. Funct. Polym. 82 (2014) 72–80.
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[5] M.H. Mashhadizadeh, M. Amoli-Diva, M.R. Shapouri, H. Afruzi, Food Chem. 151 (2014) 300–305. 390 [6] M. Behbahani, F. Najafi, M.M. Amini, O. Sadeghi, A. Bagheri, P.G. Hassanlou, J. 391 Ind. Eng. Chem. 20 (2014) 2248–2255. 392 [7] B. Mandal, U.S. Roy, D. Datta, N. Ghosh, J. Chromatogr. A 1218 (2011) 393 5644–5652. 394 [8] D. Citak, M. Tuzen, Food Chem. Toxicol. 48 (2010) 1399–1404. 395 [9] U. Divrikli, A.A. Kartal, M. Soylak, L. Elci, J. Hazard. Mater. 145 (2007) 459–464. 396 [10] G. Lasarte-Aragones, R. Lucena, S. Cardenas, M. Valcarcel, Anal. Chim. Acta 807 397 (2014) 61–66. 398 [11] C. Duran, D. Ozdes, D. Sahin, V.N. Bulut, A. Gundogdu, M. Soylak, Microchem. J. 399 98 (2011) 317–322. 400 [12] A. Asghari, B. Mohammadi, J. Ind. Eng. Chem. 20 (2014) 824–829. 401 [13] H. Abdolmohammad-Zadeh, A. Jouyban, R. Amini, Talanta 116 (2013) 604–610. 402 [14] H. Lu, H. An, Z. Xie, Int. J. Biol. Macromol. 56 (2013) 89–93. ˜ 403 [15] J. Ganán, S. Morante-Zarcero, D. Pérez-Quintanilla, I. Sierra, Mater. Lett. 132 404 (2014) 19–22. 405 [16] S.K. Wadhwa, M. Tuzen, T. Gul Kazi, M. Soylak, Talanta 116 (2013) 205–209. 406 [17] M. Park, S. Seo, S.J. Lee, J.H. Jung, Analyst 135 (2010) 2802–2805. 407 [18] M. Faraji, Y. Yamini, A. Saleh, M. Rezaee, M. Ghambarian, R. Hassani, Anal. Chim. 408 Acta 659 (2010) 172–177. 409 [19] N. Zhang, H. Peng, B. Hu, Talanta 94 (2012) 278–283. 410 Q4 [20] J.F. Liu, J. Ding, B.F. Yuan, Y.Q. Feng, Analyst (2014). 411 [21] Y. Zou, Y. Chen, Z. Yan, C. Chen, J. Wang, S. Yao, Analyst 138 (2013) 5904–5912. [22] G. Xiang, Y. Ma, X. Jiang, P. Mao, Talanta 130 (2014) 192–197. 388 389
[23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40]
G. Cheng, M. He, H. Peng, B. Hu, Talanta 88 (2012) 507–515. Z. Lin, Y. Zhang, Y. Chen, H. Qian, Chem. Eng. J. 200–202 (2012) 104–112. D. Zhang, D. Xu, Y. Ni, C. Lu, Z. Xu, Mater. Lett. 123 (2014) 116–119. J. Wang, S. Zheng, Y. Shao, J. Liu, Z. Xu, D. Zhu, J. Colloid Interface Sci. 349 (2010) 293–299. Y. Liu, M. Chen, H. Yongmei, Chem. Eng. J. 218 (2013) 46–54. G.H. Du, Z.L. Liu, X. Xia, Q. Chu, S.M. Zhang, J. Sol–Gel Sci. Technol. 39 (2006) 285–291. H.M. Jiang, Z.P. Yan, Y. Zhao, X. Hu, H.Z. Lian, Talanta 94 (2012) 251–256. F. Chen, R. Liu, S. Xiao, M. Lin, Mater. Lett. 130 (2014) 101–103. J. Gao, X. Ran, C. Shi, H. Cheng, T. Cheng, Y. Su, Nanoscale 5 (2013) 7026–7033. Z. Ma, Y. Guan, H. Liu, J. Polym. Sci., A: Polym. Chem. 43 (2005) 3433–3439. D. Zhang, C.L. Zhang, P. Zhou, J. Hazard. Mater. 186 (2011) 971–977. G. Zhao, H. Zhang, Q. Fan, X. Ren, J. Li, Y. Chen, X. Wang, J. Hazard. Mater. 173 (2010) 661–668. G. Sheng, J. Li, D. Shao, J. Hu, C. Chen, Y. Chen, X. Wang, J. Hazard. Mater. 178 (2010) 333–340. J. Wang, X. Ma, G. Fang, M. Pan, X. Ye, S. Wang, J. Hazard. Mater. 186 (2011) 1985–1992. F. Zhang, J. Lan, Z. Zhao, Y. Yang, R. Tan, W. Song, J. Colloid Interface Sci. 387 (2012) 205–212. H. Mittal, V. Parashar, S.B. Mishra, A.K. Mishra, Chem. Eng. J. 255 (2014) 471–482. Y. Gao, Y. Yuan, D. Ma, L. Li, Y. Li, W. Xu, W. Tao, J. Nucl. Mater. 453 (2014) 82–90. F. Xie, X. Lin, X. Wu, Z. Xie, Talanta 74 (2008) 836–843.
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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
One-step synthesis of CDTA coated magnetic nanoparticles for selective removal of Cu(II) from aqueous solution
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Haixia Lü a,∗ , Xiaoming Wang a , Jingqi Yang a , Zenghong Xie b a
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College of Materials Science and Engineering, Fuzhou University, Fuzhou 350108, China Institute of Food Safety and Environmental Monitoring, Fuzhou University, Fuzhou 350108, China
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Article history: Received 25 November 2014 Received in revised form 9 March 2015 Accepted 31 March 2015 Available online xxx
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Keywords: Magnetic nanoparticles Cu(II) CDTA
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1. Introduction
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A novel 1,2-cyclohexylenedinitrilotetraacetic acid (CDTA) modified Fe3 O4 magnetic nanoparticles (MNPs) was synthesized by one-step solvothermal method and used as solid phase extraction (SPE) material to preconcentrate trace copper coupled with flame atomic absorption spectrometry (FAAS). The synthesized adsorbents were characterized by field emission scanning electron microscopy and X-ray powder diffraction with a nanoscale. The optimum conditions for the absorption process were investigated on several commonly tested experimental parameters such as pH of the solution, ultrasound time, sample volume, concentration and volume of elution solution. The influences of some anions and cations metals on the recoveries of Cu(II) ions were also investigated, and no considerable interference was observed. The maximum adsorption capacity of Fe3 O4 magnetic nanoparticles and CDTA modified Fe3 O4 magnetic nanoparticles were found to be 27.50 mg/g and 78.24 mg/g for Cu(II). The developed method was applied to the determination of Cu(II) in tap and lake water samples with recoveries ranging from 96.4% to 99.1%. © 2015 Published by Elsevier B.V.
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Copper is one of the essential elements that are required to maintain the normal structure, function, and proliferation of cells. However, excessive amount of copper can cause abnormal metabolism [1]. Due to these reasons, the accurate and precise determinations of copper ion are important for analytical chemists [2,3]. Flame atomic absorption spectrometry (FAAS) has been widely used for the determination of the heavy metals at trace levels owing to its selectivity, low cost and easy instrument usage. Nevertheless, it has some difficulties, such as the presence of lower levels of metals ions in samples than the limit of detection of flame atomic absorption spectrometry, and the presence of interfering effects of the matrix components of the working media [4,5]. In order to overcome these limitations, several preconcentration techniques such as solid phase extraction (SPE) [6], ion exchange [7], cloud point extraction [8], membrane filtration [9], liquid–liquid extraction [10] and coprecipitation [11] have been extensively developed. Among different separation and preconcentration techniques, SPE is advantageous over other sample pretreatment techniques in terms of simpler and faster operation, higher enrichment factors
∗ Corresponding author. Tel.: +86 591 22866131; fax: +86 591 22866131. E-mail address: hx [email protected] (H. Lü).
with better recoveries, quicker phase separation, lower cost and reduced consumption of organic solvents as well [12]. Thus, the development of new sorbent material for SPE is in demand. To date, many novel adsorbents, such as nano-materials [13], ion imprinted material [14], mesoporous materials [15], carbon nanotubes [16] and magnetic nanoparticles [17] have been employed in SPE. However, magnetic solid phase extraction (MSPE) with magnetic nanoparticles (MNPs) as the adsorbents has aroused great interest in analytical community [3,18,19]. In this procedure, there is no need for packing of the column with the sorbent in case of batch mode operation, since the phase separation can be quickly and easily accomplished by applying an external magnetic field. Therefore, the use of magnetic materials in solid phase extraction has received considerable attention [20,21]. Recently, several researchers have used multi-step functionalized Fe3 O4 nanoparticles as MSPE adsorbents to separate and preconcentrate trace copper. Xiang [22], etc. fabricated PEMs on a magnetic silica stepwise as an MSPE sorbent for the extraction of trace Cu(II) with adsorption capacity of 14.7 mg/g. The magnetic nano-adsorbent developed by the binding of mercapto-containing dithizone (H2 Dz) on silica-coated Fe3 O4 nanoparticles could be used for removal of Cu(II) ions from aqueous solution, and the adsorption capacity was 20.5 mg/g [23]. The prepared magnetic beads (PMMA–DVB) were surface modified by aminolysis reaction with ethylene diamine, resulted as amino-functionalized magnetic bead (PMMA–DVB–NH2) [24] exhibited a magnetization value of
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20.3 emu/g, and the high adsorption affinity for aqueous Co2+ , Ni2+ and Cu2+ reached to 50.3, 49.6 and 51.7 mg/g, respectively. However, the preparation of those absorbents with multiple steps is time consuming and also difficult to control the amount of ligands incorporated into the polymer. Zhang and co-authors [25], introduce a one-pot solvothermal route synthesis of hierarchical porous Fe3 O4 to removal Congo red (CR) efficiency in waste water, which is considered as the preferred method for the preparation of absorbents. To the best of our knowledge, the analysis of real water samples has not been well documented with 1,2cyclohexylenedinitrilotetraacetic acid modified Fe3 O4 magnetic nanoparticles (MNPs–CDTA). In this study, MNPs–CDTA was synthesized by a simple one-step solvothermal and used as solid phase extraction material to preconcentrate trace Cu(II) coupled with FAAS for the analysis of Cu(II). The adsorbent was characterized by field emission scanning electron microscopy, Fourier transform infrared, powder X-ray diffraction, magnetic property measurement system. The adsorption properties of the adsorbent toward Cu(II) ions in aqueous solution were investigated systematically for adsorption capacity, effect of water chemistry and regeneration. 2. Experimental 2.1. Chemicals and reagents Ferric chloride hexahydrate (FeCl3 ·6H2 O), ethylene glycol (EG), sodium acetate anhydrous (NaAc), ethanol, copper chloride (Cu(Cl)2 ·2H2 O), acetic acid, hydrochloric acid and nitric acid were purchased from Tianjin Fu Chen Chemical Reagents Factory(Tianjin, China). 1,2-Cyclohexylenedinitrilotetraacetic acid was purchased from Fluka (America). All reagents were of analytical grade and were used without further purification. Double-distilled water was used throughout the study. 2.2. Instrumentation
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Copper concentration was determined by a TAS-986 Beijing Pgeneral Company (Beijing, China) flame atomic absorption spectrometer (FAAS) in an air-acetylene flame, with a copper hollow cathode lamp of wavelength 324.7 nm. All pH measurements were recorded with a digital pHS-10C pH meter Xiaoshan Instrument Factory (Hangzhou, China). Field emission scanning electron microscopy (FSEM) images were recorded on ZEISS SUPRA 55 (Germany). X-ray powder diffraction (XRD) data were collected on Rigaku Ultima III with Cu K␣ radiation ( = 0.1542 nm) at 40 kV and 30 mA (Japan). Fourier transform infrared (FT-IR) spectra of the magnetic nanoparticles were recorded by Nicolet 5700-Fourier transform infrared spectrometer (Thermo Electron Scientific Instruments Corp. America). The magnetization and hysteresis loops were measured at room temperature by a magnetic property measurement system (SQUID-XL, Quantum Design, America).
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2.3. Procedures
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2.3.1. Preparation of MNPs–CDTA nanoparticles Magnetic MNPs–CDTA was prepared by a modified solvothermal method as previously reported [26]. Briefly, FeCl3 ·6H2 O (2.025 g) were dissolved in EG (72 mL) under stirring to form a clear solution, then NaAc (5.4 g) and CDTA (0.80 g) were added to the solution under vigorous stirring at 50 ◦ C for 30 min. The obtained yellow mixture was put into a Teflon-lined stainless-steel autoclave (100 mL), thereafter the autoclave was sealed and heated in a furnace at 198 ◦ C for 8 h, and then cooled to room temperature.
After completion of the reaction, the obtained black precipitates were separated and collected with a permanent hand-held magnet and washed repeatedly with absolute ethanol and deionized water, and dried under vacuum at 50 ◦ C for 24 h. Finally, the products (MNPS–CDTA) were collected for further use. Fe3 O4 magnetic nanoparticles (MNPs) were prepared in the same procedure without addition of CDTA. 2.3.2. Extraction procedure The adsorption of Cu(II) by MNPs–CDTA was performed at room temperature. The solution of Cu(II) was prepared by dissolving an appropriate quantity of Cu(Cl)2 ·2H2 O in the double-distilled water to give a final concentration range from 1 to 160 mg/L. And the mixture was adjusted to a certain pH value using 0.2 mol/L HAc and 0.2 mol/L NaAc. 5 mg magnetic MNPs–CDTA was added to 20 mL 2 mg/L copper solution and the mixture was ultrasonicated for 10 min. Then the magnetic adsorbent was removed magnetically from the solution using a permanent hand-held magnet. After extraction, the concentrations of the metal ions in the supernatant were directly determined by flame atomic absorption spectrometer (FAAS). Unless otherwise specified, the absorption experiments were performed in aqueous solution at pH 7 and 25 ◦ C. After eluting the MNPs with 2 mL the solution 0.1 mol/L of HCl for 10 min, the preconcentrated analyte in the eluent was then determined by FAAS.
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3. Results and discussion
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3.1.1. Morphology and BET of MNPs and MNPs–CDTA Representative FSEM images are shown in Fig. 1. Fig. 1 reveals that the MNPs and MNPs–CDTA are mainly mono-dispersed and have a rough spherical surface with the average particle size of ca.277.46 nm and ca.151.08 nm, respectively. The presence of CDTA significantly decreased the average particle size of primary nanocrystals of the products. But the MNPs–CDTA have a more essentially mono-dispersed size distribution comparing with MNPs, which demonstrates that coating process does significantly result in the aggregation of the prepared materials in solution [27]. The BET surface area and average pore diameter had been characterized and the values of MNPs and MNPs–CDTA are16.34 m2 /g and 108.87 nm, 26.28 m2 /g and 286.34 nm, respectively. 3.1.2. Surface functional group of MNPs–CDTA The FT-IR spectrums were exhibited in Fig. 2. In Fig. 2a, the strong IR band at 584 cm−1 confirms the Fe O vibration [28], while in Fig. 2b, a strong peak at 3400 cm−1 which can be assigned to axial stretching vibration of O H. The FT-IR spectrum exhibited bands at 1050, 2920 and 1610 cm−1 , which are the vibrational frequencies of C N, C H and C O, respectively, indicating the existence of CDTA. From these changes between a and b shown in IR spectra, it can be reasonably concluded that Fe3 O4 nanoparticles have been successfully modified with CDTA. 3.1.3. Crystal structure of MNPs and MNPs–CDTA The crystalline structures of the MNPs and MNPs–CDTA nanoparticles were identified with XRD and the results are presented in Fig. 3. The XRD patterns show the characteristic peaks for Fe3 O4 at 30.1 (2 2 0), 35.3 (3 1 1), 43.2 (4 0 0), 53.6 (4 2 2), 57.2 (5 1 1) and 62.8 (4 4 0), which are in agreement with the database in JCPDS file (JCPDS no. 19-06290) [29], indicative of a cubic spinel structure of the magnetit. The same characteristic peaks were also observed for MNPs–CDTA, indicating the stability of the crystalline phase of Fe3 O4 nanoparticles during the modification and functionalization. Also according to this result, the average crystallite
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size of MNPs and MNPs–CDTA microspheres is 36.9, and 20.9 nm, respectively, as estimated from the (3 1 1) diffraction peak by the Scherrer equation [30,31]. The XRD results also demonstrate high crystallinity of prepared MNP-CDTA. 3.1.4. Magnetic results To examine the magnetic properties, the nanoparticles were studied by a magnetic property measurement system at room temperature. As shown in Fig. 4, all the samples exhibit a typical superparamagnetic behavior without a hysteresis loop due to their nanometer sizes, meaning that the thermal energy can overcome the anisotropy energy barrier of a single particle. Under a large external field (H), the magnetization (M) of the particles aligns with the field direction and reaches its saturation value, and the magnetization saturation values of these samples are 75.35 emu/g (MNPs) and 72.96 emu/g (MNPs–CDTA) at 300 K. These magnetization saturation values are high enough to separate MNPs and MNPs–CDTA from aqueous solution because saturation magnetization of 16.3 emu/g is sufficient for magnetic separation with a conventional permanent magnet [32]. The as-synthesized adsorbent dispersed in water can be easily collected by external magnetic field within several minutes (Fig. 4 lower right), and then can be readily re-dispersed with slightly shake, the results reveal that the particles exhibit well magnetic responsible and re-disperse property, suggesting their potential application of magnetic adsorbent.
3.2. Investigation of the effect of various parameters on the adsorption
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3.2.1. Effect of pH The acidity of the aqueous solution exerts profound influence on the adsorption process because it can affect the solution chemistry of contaminants and the state of functional groups on the surface of adsorbents [33]. The effect of pH soution on Cu(II) adsorption was investigated at pH 3.0–7.5. As shown in Fig. 5, almost no Cu(II) is adsorbed on MNPs and only a small amount of Cu(II) is adsorbed onto MNPs–CDTA at pH 3.0 and pH 4.0. The adsorption amount of Cu(II) increases with increasing pH values from 4.0 to 7.0 for both MNPs and MNPs–CDTA. The smaller adsorption capabilities of MNPs and MNPs–CDTA at lower pH levels, are probably due to the significant competition between Cu(II) and hydrogen ions for the same adsorption sites [34]. Cu(II) in aqueous solution can present in several forms, such as Cu(II), Cu(OH)+ , Cu(OH)2 , Cu(OH)3 − and Cu(OH)4 2− . And Cu(II) is the predominant species at pH < 7.0. The adsorption capability at pH > 7.5 was not studied because the removal of Cu(II) is possibly accomplished by simultaneous precipitation of Cu(OH)2 and adsorption of Cu(OH)+ and Cu(OH)3 − in the solution [35]. So the optimum pH for Cu(II) ion adsorption is found in the pH range of 6.5–7.5 and that the
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results showed that ultrasound time of 10 min for Cu(II) was found to be sufficient to saturation at pH 7.0. The results indicated that sorbent had rapidly adsorption kinetics. Also, the desorption procedure were carried out. The results shows that ultrasound time of 10 min was fit for desorption. In our work, the ultrasound time of 10 min was chosen as the adsorption and desorption equilibrium time.
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MNPs–CDTA gets a better quantity than the MNPs. The further experiments were carried out at pH 7.0. 3.2.2. Effect of type, concentration and volume of eluent As the ions are not removed from the sorbent completely with an inappropriate eluent, the eluent solution is an important factor for elution efficiency and recovery. To elute the copper ions from the MNPs–CDTA absorbent, a variety of selected eluent solutions (including 1.0 mol/L HCl, HAc, H2 SO4 and HNO3 ) were investigated. It was found that HCl solution as an effective elution of copper ions from the absorbent obtained better recovery 99.8 ± 1.3%. Therefore, HCl solution was chosen as the eluent for all copper extraction studies. The effect of different concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mol/L) and eluent volume (1.0, 2.0, 3.0 and 4.0 mL) of HCl on the recovery of copper was also examined. It was found that quantitative recovery can be obtained with 2 mL of 0.6 mol/L HCl. 3.2.3. Time of adsorption and desorption The effect of ultrasound time is another important factor in evaluating the affinity of the sorbent to Cu(II). To determine the rate of loading of Cu(II) on the sorbent, the recommended procedure was carried out. The contact time varied from 2 to 30 min and the
3.2.4. Influence of interfering ions The copper ions are usually in matrices containing interfering ions, which decreases the accuracy of copper ion determination. In order to investigate the selectivity of the sorbent, the effect of different cations and anions on the adsorption of Cu(II) on the sorbent were studied using the established procedure. As some anions and cations metals, various concentrations of Na+ , Cl− , NO3 − , SO4 2− , Mg2+ , Ca2+ , Ni2+ , Pb2+ , Co2+ and Cd2+ were added to individual copper-containing solutions. The results showed that 10,000-fold Na+ , 8000-fold Cl− and NO3 − , 6000-fold SO4 2− , 250fold Mg2+ and Ca2+ , 5-fold Ni2+ and 2-fold Pb2+ , Co2+ and Cd2+ ions did not affect the separation process. The results obtained indicate that co-existing ions had no obvious influence on the recovery of the analytes and the method had good tolerance to matrix interference. 3.3. Adsorption capacity The adsorption capacity was tested following the extraction procedure. 5 mg of the sorbent was equilibrated with 20 mL of various initial concentrations of Cu(II) for 10 min. In order to reach the “saturation”, the initial metal ions concentrations were increased till the plateau values (adsorption capacity values) were obtained and the result was shown in Fig. 6. As calculated by the equation described in the previous reference [36], the maximum adsorption capacity of MNPs and MNPs–CDTA has been found to be 27.50 mg/g and 78.24 mg/g for Cu(II), respectively, which likely due to the addition of amino and carboxylate groups of CDTA. Adsorption capacity for copper ion extraction from this absorbent are compared with other previously established MSPE methods [22–24,27,37], and the results show that the presented method has advantages and superior capacities that make it a preferable method for copper ion determination.
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Results (g/L)
Recovery (%)
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qmax = 77.62 mg/g b = 0.6060 L/mg R2 = 0.9990
KF = 13.0218 n = 2.62 R2 = 0.9342
Lake water
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8.8 105.2 207.0
– 96.4 99.1
0.6 0.8 1.2
Tap water
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Unfound 97.2 196.4
– 97.2 98.2
– 0.6 0.5
3.4. Adsorption isotherms Langmuir [38] and Freundlich [39] equations are two common isotherm models to describe the behavior of adsorbents and the correlation between adsorption parameters. In this work, two models were used to test the adsorption process of sorbents. The Langmuir model assumes monolayer coverage of adsorbate over a homogeneous adsorbent surface. The binding sites are also assumed to be energetically equivalent and distant from each other, so there are no interactions between molecules adsorbed on adjacent sites. The Langmuir model can be described by qe =
qmax bCe (1 + bCe )
where qe is the amount of adsorbed Cu(II) in the adsorbent(mg/g), Ce is the equilibrium ion concentration in solution (mg/L), b is the Langmuir constant (L/mg), and qmax is the maximum adsorption capacity (mg/g). The Freundlich expression is an exponential equation that describes reversible adsorption and is not restricted to the formation of the monolayer. This empirical equation takes the form qeq =
1/n KF Ceq
where KF and n are the Freundlich constants; Ceq is the equilibrium ion concentration in solution (mg/L). The adsorption kinetic of MNPs–CDTA were investigated at pH 7.0, with 5 mg of MNPs–CDTA and 20 mL varied Cu(II) concentrations (1–160 mg/L) at room temperature. The adsorption data were analyzed by Langmuir and Freundlich isotherms model. As can be seen from Table 1, the Langmuir isotherm presents a reasonable fitting to the experimental data with the correlation coefficients (R2 = 0.9990). And the calculation value of maximum adsorption capacity (qmax ) was found to be 77.62 mg/g, with a low difference of the experiment adsorption capacity (78.24 mg/g). These findings demonstrate that the Cu(II) sorption onto MNPs–CDTA possibly takes place by a homogeneous adsorbent surface over monolayer coverage of adsorbate, which may be ascribed to the hydroxy and carboxyl groups present in MNPs–CDTA. 3.5. The breakthrough volume
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Table 2 Analytical results for the determination of Cu(II) in water samples.
Langmuir adsorption isotherm
An important parameter in SPE is the breakthrough volume, which is the maximum sample volume that should percolate through a given mass of sorbent after which an analyte starts to elute from the sorbent resulting in non-quantitative recoveries. The breakthrough volume was experimentally evaluated by adding 5 mg of MNPs–CDTA in a solution containing 10 g copper ions in different volumes of solution varying from 20 to 200 mL. The results indicated the maximum sample volume can be up to 180 mL and therefore the enrichment factor was obtained as 90.
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To test the stability and potential reusability of the sorbent, several loading and elution operations cycles were carried out. The operating capacity was calculated from the loading and elution tests. The result showed that the column was relatively stable up
to at least 6 extraction–elution cycles without evident decrease of recoveries. Under the selected conditions, eight portions of standard solutions were enriched and analyzed simultaneously following the general procedure. The relative standard deviations (R.S.D.s) of the method was lower than 5.0%, which indicated that the method had good precision for the analysis of trace Cu(II) in solution samples. And the detection limit of the method was calculated based on three times of the standard deviation of 8 runs of the blank solution. The detection limit of the proposed method as defined by IUPAC [40] was 2.4 ng/mL. 3.7. Application of the method The proposed method was then applied to the determination of Cu(II) in tap water, lake water samples as the following procedure: 5 mg of the sorbent was equilibrated with 50 mL of water samples for 10 min, then was eluting with 2 mL 0.6 mol/L HCl solution. For the analysis of the water samples, the standard addition method was used and the results for the recovery of both metals are presented in Table 2. As shown in Table 2 the recoveries of analytes were in the range of 96.4–99.1%. It demonstrated the suitability of the sorbent for the preconcentration of Cu(II) from water samples prior to FAAS analysis. 4. Conclusion The proposed one-step method for the synthesis of the novel MNPs–CDTA sorbent was simple, fast and inexpensive. The magnetic nano-adsorbent has been prepared for removal of trace Cu(II) from aqueous solution. The absorbents have a monodispersed rough spherical morphology and high crystallinity. The short loading time (10 min) of the present matrix makes the analytical procedure reasonably fast. The adsorption process can be better simulated by Langmuir isotherm equation which provided a better R2 (R2 > 0.9990). The MNPs–CDTA showed a high adsorption capacity and an efficient adsorption toward Cu(II) in aqueous medium. The proposed method can be applicable to the preconcentration and separation of trace Cu(II) ion in a variety of water samples with low method detection limit, high accuracy (recovery ranging from 96.4 to 99.1%) and high precision (R.S.D. ranging from 0.5 to 1.2%). Acknowledgement This work was supported by the National Natural Science Foun- Q3 dation of China (21307013). References [1] Y. Pang, G. Zeng, L. Tang, Y. Zhang, Y. Liu, X. Lei, Z. Li, J. Zhang, G. Xie, Desalination 281 (2011) 278–284. [2] P. Saravanan, V.T.P. Vinod, B. Sreedhar, R.B. Sashidhar, Mater. Sci. Eng., C 32 (2012) 581–586. [3] H. Bagheri, A. Afkhami, M. Saber-Tehrani, H. Khoshsafar, Talanta 97 (2012) 87–95. [4] T.O. Germiniano, M.Z. Corazza, M.G. Segatelli, E.S. Ribeiro, M.J.S. Yabe, E. Galunin, C.R.T. Tarley, React. Funct. Polym. 82 (2014) 72–80.
Please cite this article in press as: H. Lü, et al., Int. J. Biol. Macromol. (2015), http://dx.doi.org/10.1016/j.ijbiomac.2015.03.065
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376
377 378
379
380 381 382 383 384 385 386 387
G Model BIOMAC 4999 1–6 6
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[5] M.H. Mashhadizadeh, M. Amoli-Diva, M.R. Shapouri, H. Afruzi, Food Chem. 151 (2014) 300–305. 390 [6] M. Behbahani, F. Najafi, M.M. Amini, O. Sadeghi, A. Bagheri, P.G. Hassanlou, J. 391 Ind. Eng. Chem. 20 (2014) 2248–2255. 392 [7] B. Mandal, U.S. Roy, D. Datta, N. Ghosh, J. Chromatogr. A 1218 (2011) 393 5644–5652. 394 [8] D. Citak, M. Tuzen, Food Chem. Toxicol. 48 (2010) 1399–1404. 395 [9] U. Divrikli, A.A. Kartal, M. Soylak, L. Elci, J. Hazard. Mater. 145 (2007) 459–464. 396 [10] G. Lasarte-Aragones, R. Lucena, S. Cardenas, M. Valcarcel, Anal. Chim. Acta 807 397 (2014) 61–66. 398 [11] C. Duran, D. Ozdes, D. Sahin, V.N. Bulut, A. Gundogdu, M. Soylak, Microchem. J. 399 98 (2011) 317–322. 400 [12] A. Asghari, B. Mohammadi, J. Ind. Eng. Chem. 20 (2014) 824–829. 401 [13] H. Abdolmohammad-Zadeh, A. Jouyban, R. Amini, Talanta 116 (2013) 604–610. 402 [14] H. Lu, H. An, Z. Xie, Int. J. Biol. Macromol. 56 (2013) 89–93. ˜ 403 [15] J. Ganán, S. Morante-Zarcero, D. Pérez-Quintanilla, I. Sierra, Mater. Lett. 132 404 (2014) 19–22. 405 [16] S.K. Wadhwa, M. Tuzen, T. Gul Kazi, M. Soylak, Talanta 116 (2013) 205–209. 406 [17] M. Park, S. Seo, S.J. Lee, J.H. Jung, Analyst 135 (2010) 2802–2805. 407 [18] M. Faraji, Y. Yamini, A. Saleh, M. Rezaee, M. Ghambarian, R. Hassani, Anal. Chim. 408 Acta 659 (2010) 172–177. 409 [19] N. Zhang, H. Peng, B. Hu, Talanta 94 (2012) 278–283. 410 Q4 [20] J.F. Liu, J. Ding, B.F. Yuan, Y.Q. Feng, Analyst (2014). 411 [21] Y. Zou, Y. Chen, Z. Yan, C. Chen, J. Wang, S. Yao, Analyst 138 (2013) 5904–5912. [22] G. Xiang, Y. Ma, X. Jiang, P. Mao, Talanta 130 (2014) 192–197. 388 389
[23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40]
G. Cheng, M. He, H. Peng, B. Hu, Talanta 88 (2012) 507–515. Z. Lin, Y. Zhang, Y. Chen, H. Qian, Chem. Eng. J. 200–202 (2012) 104–112. D. Zhang, D. Xu, Y. Ni, C. Lu, Z. Xu, Mater. Lett. 123 (2014) 116–119. J. Wang, S. Zheng, Y. Shao, J. Liu, Z. Xu, D. Zhu, J. Colloid Interface Sci. 349 (2010) 293–299. Y. Liu, M. Chen, H. Yongmei, Chem. Eng. J. 218 (2013) 46–54. G.H. Du, Z.L. Liu, X. Xia, Q. Chu, S.M. Zhang, J. Sol–Gel Sci. Technol. 39 (2006) 285–291. H.M. Jiang, Z.P. Yan, Y. Zhao, X. Hu, H.Z. Lian, Talanta 94 (2012) 251–256. F. Chen, R. Liu, S. Xiao, M. Lin, Mater. Lett. 130 (2014) 101–103. J. Gao, X. Ran, C. Shi, H. Cheng, T. Cheng, Y. Su, Nanoscale 5 (2013) 7026–7033. Z. Ma, Y. Guan, H. Liu, J. Polym. Sci., A: Polym. Chem. 43 (2005) 3433–3439. D. Zhang, C.L. Zhang, P. Zhou, J. Hazard. Mater. 186 (2011) 971–977. G. Zhao, H. Zhang, Q. Fan, X. Ren, J. Li, Y. Chen, X. Wang, J. Hazard. Mater. 173 (2010) 661–668. G. Sheng, J. Li, D. Shao, J. Hu, C. Chen, Y. Chen, X. Wang, J. Hazard. Mater. 178 (2010) 333–340. J. Wang, X. Ma, G. Fang, M. Pan, X. Ye, S. Wang, J. Hazard. Mater. 186 (2011) 1985–1992. F. Zhang, J. Lan, Z. Zhao, Y. Yang, R. Tan, W. Song, J. Colloid Interface Sci. 387 (2012) 205–212. H. Mittal, V. Parashar, S.B. Mishra, A.K. Mishra, Chem. Eng. J. 255 (2014) 471–482. Y. Gao, Y. Yuan, D. Ma, L. Li, Y. Li, W. Xu, W. Tao, J. Nucl. Mater. 453 (2014) 82–90. F. Xie, X. Lin, X. Wu, Z. Xie, Talanta 74 (2008) 836–843.
Please cite this article in press as: H. Lü, et al., Int. J. Biol. Macromol. (2015), http://dx.doi.org/10.1016/j.ijbiomac.2015.03.065
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