Fabrication, characterization and theoretical ...

Environmental Nanotechnology, Monitoring & Management 10 (2018) 171–178

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Fabrication, characterization and theoretical investigation of novel Fe3O4@ egg-shell membrane as a green nanosorbent for simultaneous preconcentration of Cu (II) and Tl (I) prior to ETAAS determination ⁎

T

⁎

Matin Naghizadeha,b, , Mohammad Ali Tahera, , Leila Zeidabadi Nejada,b, Firouzeh Hassani Moghaddama,b a b

Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran Young Researchers Society, Shahid Bahonar University of Kerman, Kerman, Iran

A R T I C LE I N FO

A B S T R A C T

Keywords: Magnetite eggshell membrane Electrothermal atomic absorption spectrometry Copper Thallium Adsorption energy

Eggshell membrane modified by Fe3O4 magnetite were prepared and used as an adsorbent for simultaneous extraction and preconcentration of copper and thallium ions via magnetic solid phase extraction (MSPE) method. After adsorption, these ions were desorbed with hydrochloric acid followed with specific determination by electrothermal atomic absorption (ETAAS). The prepared Surface modification of eggshell membrane with doped Fe3O4 magnetite nanoparticles was investigated with field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM) and X-ray diffraction (XRD) spectrometry was used to characterize the adsorbent. The MSPE requirement was optimized. The detection limits of 0.96 and 0.17 ng/L were obtained for copper and thallium, respectively. The linear range was 0.020–0.420 ng/mL for copper and 0.005–0.065 ng/mL for thallium. The relative standard deviations of the method for eight replicate determination of 0.100 and 0.015 ng/mL of Cu (II) and Tl (I) were ± 2.62% and ± 4.51%, sequentially. The technique was employed for the determination of target ions in different environmental samples with high recoveries. For understanding the interaction between Fe3O4 and CaCO3, the adsorption structures and energies of a CaCO3 on the Fe3O4 (111) surface have been computed at the level of density functional theory.

1. Introduction Hen egg is the most popular food in the world. Eggshell membrane principally includes of fibrous proteins such as collagen type I. nevertheless, eggshell membranes have also been explained to contain glycosaminoglycans, such as dermatan sulfate, sulfated glycoproteins, and glucosamine (Guijarro-Aldaco et al., 2011; Jain and Anal, 2016; Mohammad-Rezaei et al., 2014; Razmi et al., 2016). It is worth mentioning that recently pertinent attentions have been assigned to the application of biomaterials as sorbent media for performing sample pretreatment. Biological cells and natural bio mass has been described for the separation and preconcentration of nanoparticle sulfur and arsenic (Chen et al., 2013; Cheng et al., 2011; Liu and Huang, 2011; Meski et al., 2010). As a cheap and green biomass, eggshell membrane (ESM) is readily available. Hence, the determination of mercury, aluminum, copper and thallium in food items plays an important role in the context of environmental protection and environment and human health (Abdolmohammad-Zadeh and Talleb, 2014; Bennett et al., 2016; Fayazi ⁎

et al., 2016; Guijarro-Aldaco et al., 2011; Zou and Huang, 2013). The development of new sorbents which can serve several analytical advantages over the detection of Cu (II) and Tl (I) in aqueous media such as high sensitivity, excellent stability, low cost, and rapid analysis of samples. Magnetic solid-phase extraction (MSPE) has been intensively used for environmental analysis at trace levels. Magnetic sorbents and manipulate in complex multiphase systems with an external magnetic field (Moghaddam et al., 2015; Naghizadeh et al., 2015). Therefore, the main the benefit of MSPE includes low cost, rate, simplicity and reusability. The eggshell membrane (ESM) is natural biomaterials with an intricate lattice network of stable, microporous, water insoluble fibers and a very high surface area. In this study, a facile and totally green method to in situ synthesizes Fe3O4 nanoparticles on ESM. Here, we successfully prepared an adsorbent based on a magnetically doped eggshell membrane. Then, this a green adsorbent was applied in MSPE for preconcentration of Cu (II) and Tl (I) simultaneously prior to electrothermal atomic absorption spectrometric (ETAAS) determination. The interaction of molecules with metal oxide surfaces is important in

Corresponding authors at: Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Boulevard, P.O. Box 76169-133, Kerman, Iran. E-mail addresses: [email protected] (M. Naghizadeh), [email protected] (M.A. Taher).

https://doi.org/10.1016/j.enmm.2018.06.001 Received 1 February 2017; Received in revised form 11 April 2018; Accepted 4 June 2018 2215-1532/ © 2018 Elsevier B.V. All rights reserved.


M. Naghizadeh et al.

2. Material and methods

Table 1 Instrumental parameters for determination of copper and thallium by ETAAS.

2.1. Reagents and materials

Instrumental parameters Parameter

Cu

Tl

Wavelength (nm) Spectral bandwidth (nm) Lamp current (mA) Signal measurement Sample volume (μL)

327.4 0.5 4 Peak Height 20

276.8 0.5 10 Peak Height 20

Fresh hen eggs were bought from the town supermarket. The eggs albumen and yolk were removed and the broken eggs were immersed in 1% acetic acid solution for 1 h in order to obtain the ESM easily. Stock solutions of copper and thallium were prepared by dissolving of Cu (NO3)2.3H2O and thallium (I) stock solution (1000 mg/L) were purchased Merck (Merck, www.merckgroup.com) into deionized water. The concentration of Cu (II) and Tl (I) was determined by electrothermal atomic absorption spectrometry using a model Spectra AA 220 apparatus (Varian, www.varianinc.com). The optimum operating parameters for ETAAS are given in Table 1. The samples were weighed using an electronic balance Mettler AE-160 (Greifensee, www.mt.com). The pH calibration was taken out with a Metrohm 827 pH-meter (Herisau, www.metrohm.com) supplied with a consolidated glass–calomel electrode. Magnetic stirrer hot plate (2000 rpm) and oven model 100 (Memmert, www.memmert.com) were employ to homogenize. To disband the nanoparticles in solutions, a Sonorex digitec model DT 225H with 35 KHz ultrasonicator (Bandelin, (www.bandelin.com) was used. Fourier transform infrared (FT-IR) spectra were taken using a Tensor 27 spectrometer (Bruker, www.bruker.com). Field emissionscanning electron microscopy (FE-SEM) images were obtained on a model Sigma (Zeiss, www.zeiss.com). The powder X-ray diffraction (XRD) patterns were examined on a model X'PertPro diffractometer (Panalytical, www.panalytical.com) using Cu Kα radiation in the 2ɵ

many areas including catalysis and environmental science. Magnetite (Fe3O4) is one of the most important transitions metal oxides found with very industrial applications, for example in corrosion control, heterogeneous catalysis and magnetic storage of information (Mohammadi et al., 2014; Saljooqi et al., 2014). Investigating electronic structures and stabilities properties of the Fe3O4 (111), (110) and (001) surfaces showed that surface stability of (111) > (001) > (110) on the basis of the computed surface energies (Maghsoudi and Jalali, 2017; Noh et al., 2015; Pursell et al., 2012). Fe3O4 crystallizes into a cubic reversed spinel structure wherever the oxygen anions form a close-packed face centered cubic sublattice with Fe2+ and Fe3+ in the interstitial sites, and there are two cation sites; the tetrahedral coordinated Fe3+ and the equally octahedral coordinated Fe2+ and Fe3+ (Yu et al., 2012a). Accordingly, in this article, we study the interaction between CaCO3 and Fe3O4 (111) surface.

Fig. 1. Optimized structured of Fe3O4 surface. 172



(0.3 mol/L) was a supplement as eluent and ultrasonicated for 3 min. subsequently, the magnet was used again to collect the MESM, and the eluent was transferred to a test tube for consequent ETAAS analysis. 2.4. Computational models All quantum chemical calculations are carried out apply the common theoretical and computational method based on all-electrons density functional theory (DFT) with the hybrid, non-local transfer and exchange function of Beck-Lee, Parr and Yang (B3LYP) and the 631G(d) basis set, as perform in GAUSSSIAN09 (Dos Santos et al., 2016; Frisch et al., 2009). Fe3O4 (111) was chosen for this investigation because Fe3O4 (111) is one predominant natural grow to face its catalyst activity is higher than of other surfaces which are displayed in Fig. 1. In addition, Fetet and Feoct terminated surfaces have been considered as the most stable terminations, which were used as the model to investigate the interaction between the CaCO3 and Fe3O4(111) surface. As shown in Fig. 2, the bottom three layers arranged for the Fetet and Feoct terminated surface. The adsorption energy Ead is defined as: Ead = (EFe3O4 + ECaCO3) ⎯ Esystem, where E Fe3O4, ECaCO3, and Esystem are the energies of the surface, CaCO3 molecule and the adsorption system, respectively. As shown in Fig. 2, there are two adsorption sites for CaCO3: the Feoct atom and the Fetet atom. On the Feoct and Fetet atoms, the CaCO3 molecule is anchored on the surface, forming two strong bonds; the O atom of the CaCO3 forms covalent bonds with the Feoct and Fetet atoms with a distance of 1.98 and 2.21 Ȧ. The calculated adsorption energy of −1.12 eV at the Fe site indicates strong binding. The calculated adsorption energy at the Fetet site is −0.71 eV, much lower than the value at the Feoct site. Nano-scale magnetite particles are approximately one billion times smaller (by volume) than micro-scale magnetite particulates and exhibit many different properties. Producing octahedral sites in the magnetite structure contain ferrous and ferric species. The electrons coordinated with these iron species are thermally delocalized and migrate within the magnetite structure causing high conductivity exchange constants. Magnetic strength will be decreased with increasing the amount of membrane because CaCO3 don’t have magnetic properties. The optimum ratio of membrane and unit cell of Fe3O4 is 2:1. From the theoretical point of view we can to achieve the best result if Fe2O3 is twice the amount of CaCO3.

Fig. 2. Optimized structure of a CaCO3 molecule adsorbed at the Fetet and Feoct sites.

range 10–80°. Magnetic measurements were carried out using a vibrating sample magnetometer (VSM) model MDKFD (www.lakeshore. com). 2.2. Preparation of Fe3O4 magnetite doped eggshell membrane Firstly, the broken fresh eggshell was incubated in diluted 1% acetic acid at 22 °C for 1 h. Afterward, the ESM was easily separated and cut into small pieces (1 cm2) and was cleaned with a copious amount of twice distilled water. This is used as the substrate and membrane. Then, the preparation of Fe3O4 magnetic doped eggshell membrane was based on dissolving FeCl3·6H2O (11.68 g) and FeCl2·4H2O (4.30 g) in 200 mL deionized water. This solution was stirred with a magnetic stirrer (2000 rpm) at 50 °C for 1 h. Nitrogen gas was continually bubbled through this solution to expel oxygen. Then, the EM was immersed in solution following that, 10 mL of 25% NH3 was rapidly added to the solution. After that, the color of the bulk suspension changed from orange to black quickly by adsorption was on it. Iron oxides will be adsorption on the eggshell membrane. The magnetite eggshell membrane (MESM) was collected by a magnet after washing numerous times by deionized water and then with ethanol because ethanol is a polar solvent with a low boiling point and to wash impurities. Finally, they were dried in an oven at 50 °C for 12 h.

3. Results and discussion 3.1. FT-IR spectroscopy The FT-IR spectrum of The FT-IR spectroscopy was measured and characterized the MESMs in Fig. 3. Fe3O4 nanoparticles show the absorption peak at 576 cm−1 which corresponding to the FeeO vibration in Fig. 3A. Peak at 3411 cm−1 which corresponding to eOH and eNH2 stretching vibrations. 3051, 2923 and 2886 cm−1 which were attributed to the CeH asymmetric stretching vibration in ]CeH and ]CH2. 1652 cm−1 related to C]O stretching mode assigned as amide I vibration. 1443, 1103 and 630 cm−1 related to C]C, CO and CeS stretching vibrations respectively. There was a most significant peak at 1413 cm−1 which were attributed to the carbonate in the basic ingredient of eggshells. And the other two strong peaks at about 874 cm−1 and 711 cm−1 were assigned to the out-plane deformation modes and in-plane deformation of calcium carbonate, respectively.

2.3. Magnetic solid-phase extraction procedure MSPE was carried out as follows. A portion of 2 mL sample solutions containing Cu (II) and Tl (I) was transferred into a 100 mL glass flask and the pH was adjusted to 7.0 using HCl and NaOH solutions. Then, 0.025 g of the synthesized MESM was added and the mixture was ultrasonicated for 3 min. In this step, the analytes were adsorbed on the adsorbent. Cu (II) and Tl (I) ions are trapped and training within the membrane, causing the Vander Waals bonding. Then, a piece of a magnet was placed outside the flask to collect adsorbent and the supernatant was decanted directly. In desorption step, 2.0 mL HCl

3.2. FE-SEM images The surface morphological images of the synthesized MESM nanoparticles was characterized by FE-SEM images and shown in different magnification (Fig. 4) and also for determining the particle shape and size distribution of Fe3O4 nanoparticles on solid substrates. The formation of Fe3O4NPs on the surface of ESM was evident via FE-SEM. The FE-SEM images showed that these Fe3O4 nanoparticles had entrapped 173



Fig. 3. FT-IR spectra of (A) Fe3O4 nanoparticles and (B) MESM.

3.5. Optimization of method

in the membrane eggshell successfully. In FE-SEM images, however, due to the presence of an even coating of Fe3O4NPs, cross-linking protein fibers of inner membrane eggshell were sufficiently covered, providing a uniform and stable platform for separation Cu (II) and Tl (I) ions.

Several experimental changeable influences the extraction recovery of copper and thallium ions were examined, containing, (a) sample pH (b) the eluting solvent (c) the adsorbent amount (d) ultrasonic time and (e) sample volume. In all experiments, a one-at-a-time strategy was used. We found the following experimental conditions to give best results: (a) A sample pH value of copper and thallium ions by the as-prepared modified MESMs is significantly dependent on the pH value of the aqueous solution. The influence of pH on the extraction recovery of a target, ions was tested in the range 2–10 when the other parameters were kept constant. The results in Fig. 7 reveal that the absorbance was nearly constant in the pH range of 5.0–8.0 accordingly, a pH = 7 was selected for subsequent optimization studies and real sample analysis. At low pH the chelating protonation, allowing the analyte ions and H+ absorbent modified to not be absorbed in it. When the pH was further enhanced from 8.0 to 10, the recovery percentages reduce quietly. Because the precipitation reactions may occur for Cu (II) and Ti (I) ions. Therefore, pH 7.0 was selected in the following experiments Fig. 7. (b) The effect of type and volume of eluent on the recovery of Cu (II) and Tl (I) were investigated. As can be seen from Fig. 8, the sorption of these ions on the adsorbent at an acidic solution is low. It means that desorption can be done in this media. Hence, several acidic solutions

3.3. XRD patterns A typical XRD pattern of the MESM nanoparticles is shown in Fig. 5. The diffraction peaks (2ϴ = 29.5°, 36.2°, 40.1°, 44.2°, 48.7°, 57.7°, 62.1°) related to (220), (311), (113), (400), (116) (511) (440), can be indexed to face-centered cubic structure of the MESM with space group Fd3m. The highest peak was chosen (29.5°) for the size calculation. According to the Debye–Scherrer equation crystal size of the nanoparticles from 26 to 27 nm. 3.4. Magnetic measurements Fig. 6 shows that the saturation magnetization value was 67.4 emu/ g. It also shows that iron oxide nanoparticles trapped well inside the membrane and creates a strong magnetic effect that this feature can be used for separation and preconcentration Cu (II) and Tl (I) ions made as soon as possible. 174



Fig. 4. FE-SEM (A1 &A2) and (B1 &B2) images of the MESM.

Fig. 5. XRD pattern of MESM nanoparticles. Fig. 6. VSM curve of MESM.

were used as eluent and the results showed that HCl with the concentration of 0.3 mol/L was the best ones. Also, the eluent should elute analytes quantitatively in a small volume. Thus, the volume range of 0.5–5 mL was tested and finally, 2 mL of 0.3 mol/L HCl was chosen for the elution Fig. 9. (c) In the MSPE technique, the amount of magnetic membrane is one of the principal factors affecting on the extraction of the analytes. Hence, this parameter was studied in the range 0.010–0.100 g. the results show the recovery percentage improve with an increase in the adsorbent content which could be due to the availability of more sorption place and great surface area. Up to a certain value (0.025 g), no further the increase in percent happens as an improvement in an adsorbent content. Hence, 0.025 g was used in the all subsequent experiments Fig. 10. (d) In this method, to obtain adsorption and desorption times, ultrasonic was used. For both adsorption and

desorption, ultrasonic times in the range 1–5 min were optimized. The experimental results indicated that 3 min was sufficient for achieving quantitative recovery of copper and thallium ions for both adsorption and desorption. (e) The sample volume is an essential parameter to obtain a high enrichment factor. Experimental analysis showed that, when sample volumes were 1000 mL and 900 mL, quantitative recovery was obtained and theoretical enrichment factors were 500 and 450 for both target ions Fig. 11.

3.6. Adsorption capacity The adsorption capacity is an important factor in calculating the 175



Fig. 7. Effect of pH on the extraction efficiency of Cu (II) and Tl (I), Experimental Conditions were the following: 0.025 g sorbent, Eluent: HCl 0.3 mL 2.0 mol/L, the concentration of Cu (II) was 0.100 ng/mL and Tl (I) was 0.015 ng/mL; (N = 3).

Fig. 10. Effect of magnetite eggshell membrane amount on the extraction efficiency of Cu (II) and Tl (I), Experimental conditions were same as Fig. 7 except of pH was 7.0.

Fig. 11. Effect of sample volume on the extraction efficiency of Cu (II) and Tl (I), Experimental conditions were same as Fig. 7 except of pH was 7.0.

Fig. 8. Effect of type and concentration of eluent on the extraction efficiency of Cu (II) and Tl (I), Experimental conditions were same as Fig. 7 except of pH was 7.0.

Table 2 Temperatures program for determination of copper and thallium by ETAAS. Step

Furnace temp. (°C)

Time (s)

Argon flow rate (mL/min)

Drying Drying Drying Ashing Ashing Atomization Atomization Tube cleaning

85 95 120 a 800, b250 800, 250 2100, 2200 2300, 2200 2500, 2200

5.0 40 10 a 6.0, b5.0 2.0, 1.0 1.1, 1.0 2.0, 2.0 2.0, 2.0

300 300 300 300 300 0.0 0.0 300

a b

Fig. 9. Effect of eluent volume on the extraction efficiency of Cu (II) and Tl (I), Experimental conditions were same as Fig. 7 except of pH was 7.0.

Copper. Thallium.

preconcentration of purpose analytes externally any serious matrix interference in various real samples (Table 2).

MESMs. It is the highest analytes quantity taken up by 1.0 g of synthesized nanoadsorbent. For determining this factor, 50 mg of the nanoadsorbent were subjected to several loadings with 25 mL sample solutions containing Cu (II) and Tl (I) with pH = 7.0 and then, followed by the determination of employed analytes using ETAAS. The rate of adsorption capacity increased with the increase of initial concentrations of purpose ions and later it gives a grade. The static adsorption capacity (15.12 mg/g for copper ions and 13.46 mg/g for thallium ions) was obtained.

3.8. Analytical performance Analytical performance such as linear range (LR), limits of detection (LODs) and repeatability was studied under the optimized working conditions. The obtained linearity was 0.020–0.420 ng/mL for Cu (II) and 0.005–0.065 ng/mL for Tl (I). The LODs (defined as 3Sdblank/m, where Sd is the standard deviation of the blank readings for ten replicate analysis and m is the slope of the calibration curve) was 0.96 ng/ L and 0.17 ng/L for copper and thallium, respectively. further, the resultant repeatability function as a relation standard deviations (RSD, N = 8) was calculated as 2.6% and 4.5% for 0.100 ng/mL and 0.015 ng/mL concentration of Cu (II) and Tl (I), respectively.

3.7. Effect of coexisting ions interference Under the optimized state, the interference of numerous cations and anions on the recovery of copper and thallium ions was investigated. Results obtained showed that MESMs is a good applicant to 176



Table 3 Effect of potentially interfering ions. Foreign ion

Foreign ion/Cu ratio

Foreign ion/Tl ratio

Recovery (%)a

Na+ Cl− K+ NO3− NH4+ CH3COO− Ca2+ Zn2+ Al3+ Co2+ Mo6+ Cr3+ Fe3+ Fe2+ EDTA

2000 2000 2000 2000 1750 1750 1500 1500 1400 1400 1300 1300 1300 1200 500

2000 2000 2000 1700 1500 1500 1500 1400 1300 1300 1200 1200 1200 1200 750

101.1 ± 2.8 97.4 ± 1.1 99.2 ± 4.5 102.4 ± 2.1 96.4 ± 3.6 97.1 ± 5.2 103.4 ± 3.6 97.5 ± 2.8 99.7 ± 3.3 100.6 ± 1.8 95.2 ± 4.5 103.5 ± 2.1 99.2 ± 1.3 96.7 ± 4.5 97.2 ± 3.2

Table 5 Comparison of proposed method with other reported preconcentration techniques. Method

Analyte

PFa or EFb

R.S.D. (%)

LRc (ng/mL)

LOD (ng/L)

Ref.

ASVd ASV FAAS GFAASe ETAAS FAAS ETAAS ETAAS ETAAS

Cu Cu Cu Tl Tl Tl Tl Tl Cu

– – 143 100 50 77 20 100 500

3.99–4.86 – 4.6 6.4 5.1 5.6 5.9 5.0 2.62

0.01–90 1.27–6.35 – 600–2500 3000–22,000 20,000–200,000 – 50–1800 0.020–0.420

7 298 190 4 700 2500 9 6.3 0.96

21 22 23 24 25 26 27 11 This work

Tl

450

4.51

0.005–0.065

0.17

a b

Under optimum conditions. a Mean ± standard deviation (N = 3).

c d e

Table 4 Determination of copper and thallium ions in real samples. Spiked (ng/mL)

Founda (ng/mL) Recovery (%)

Cu

Tl

Cu

Tl

Cu

Tl

– 0.010 0.030 0.0 0.010 0.030 0.0 0.010 0.030

– 0.015 0.025 0.0 0.015 0.025 0.0 0.015 0.025

0.0180 0.0284 0.0478 0.0190 0.0293 0.0497 2.5648 2.5751 2.5952

0.0150 0.0303 0.0402 0.0243 0.0394 0.0480 1.5892 1.6039 1.6137

– 104.0 99.3 – 103.0 102.3 – 103.0 101.3

– 102.0 100.8 – 100.7 98.4 – 98.0 98.0

Human hair (pg/g)

0.0 0.020 0.040

0.0 0.030 0.050

1.435 1.454 1.474

0.863 0.894 0.914

– 95.0 97.5

– 103.3 102.0

Rice (pg/g)

0.0 0.020 0.040

0.0 0.030 0.050

4.112 4.133 4.151

0.243 0.272 0.292

– 105.0 97.5

– 96.6 98.0

Tea leaves (pg/g)

0.0 0.020 0.040

0.0 0.030 0.050

2.275 2.294 2.316

0.054 0.083 0.105

– 95.0 102.5

– 96.6 102.0

Samples

Tap waterb

Well waterc

Rain water

a b c

Preconcentration Factor. Enrichment Factor. Linear Range. Anodic Stripping Voltammetry. Graphite Furnace Atomic Absorption Spectrometry.

reported somewhere else (Asadpour et al., 2012; Chamsaz et al., 2009; Dadfarnia et al., 2007; Durukan et al., 2011; Fayazi et al., 2016; Martiniano et al., 2013; Parakudyil et al., 2011; Zhao et al., 2014) (Table 5). 4. Conclusion Magnetite eggshell membrane with good saturation magnetization has been successfully prepared and used as a novel and effective adsorbent for simultaneous extraction and preconcentration of copper and thallium ions from aqueous solutions prior to the determination by ETAAS. The synthesized adsorbent was characterized by FT-IR spectra, FE-SEM images and VSM analysis. It is a very fast extraction method, because of high surface area of the adsorbent and fast magnetic separation. Ease of operation, minimal sample preparation, lower solvent and reagent consumption, high selectivity and sensitivity are other advantages. Furthermore, to some extent, the developed methodologies here widen the application areas of eggshell wastes and reduce environmental pressures and contamination. Furthermore, the combination of MSPE with the as-prepared nanoadsorbent with ETAAS offers significant analytical performance. We obtain so energetically the most helpful site for CaCO3 adsorption is on the Feoct atom. The formation of the O-Feoct and O-Fetet bonds gives rise to strong adsorption strength.

Mean (N = 3). Kerman drinking water, Kerman, Iran. Shahid Bahonar University of Kerman, Kerman, Iran.

Conflict of interest 3.9. Analysis of the real samples The authors declare that they have no conflict of interest. This technique was applied to determine ultra-trace amounts of Cu (II) and Tl (I) in a variety of samples. The samples happen further analyzed after spiking with another concentrations of copper and thallium ions with high recoveries. Tap water, well water, rain water, human hair, rice and tea leaves samples were analyzed. The analytical results are presented in Table 3. The outcomes found were in good compromise with the certified value. Evidently, the obtained results show that the procedure is suitable for the copper and thallium ions analysis in environmental samples. Thus, these results corroborate that the method is independent of matrix interferences.

Acknowledgements The authors gratefully acknowledge the financial supports from the Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran and Young Researchers Society, Shahid Bahonar University of Kerman, Kerman, Iran. References Abdolmohammad-Zadeh, H., Talleb, Z., 2014. Magnetite-doped eggshell membrane as a magnetic sorbent for extraction of aluminum (III) ions prior to their fluorometric determination. Microchim. Acta 181, 1797–1805. Asadpour, S., Chamsaz, M., Entezari, M.H., Haron, M.J., Ghows, N., 2012. On-line preconcentration of ultra-trace thallium (I) in water samples with titanium dioxide nanoparticles and determination by graphite furnace atomic absorption spectrometry. Arab. J. Chem. Bennett, J., Lee, A.F., Wilson, K., 2016. Catalytic applications of waste derived materials. J. Mater. Chem. A.

3.10. Comparison with other methods A collation of the process with other preconcentration method is determined in Table 4. As seen from the data in this table, the method using MESMs has high enrichment factor and relatively low LOD, wider linear range and lowers RSD that it comparable or better than those 177



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