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Functionalized magnetic nanoparticles supported on activated carbon for adsorption of Pb(II) and Cr(VI) ions from saline solutions
Accepted Manuscript Title: Functionalized Magnetic Nanoparticles Supported on Activated Carbon for Adsorption of Pb(II) and Cr(VI) Ions from Saline Solutions Authors: M.H. Fatehi, J. Shayegan, M. Zabihi, I. Goodarznia PII: DOI: Reference:
S2213-3437(17)30098-2 http://dx.doi.org/doi:10.1016/j.jece.2017.03.006 JECE 1512
To appear in: Received date: Revised date: Accepted date:
22-10-2016 27-2-2017 7-3-2017
Please cite this article as: M.H.Fatehi, J.Shayegan, M.Zabihi, I.Goodarznia, Functionalized Magnetic Nanoparticles Supported on Activated Carbon for Adsorption of Pb(II) and Cr(VI) Ions from Saline Solutions, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2017.03.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Functionalized Magnetic Nanoparticles Supported on Activated Carbon for Adsorption of Pb(II) and Cr(VI) Ions from Saline Solutions
M.H. Fatehia, J. Shayegana,*, M. Zabihib and I. Goodarzniaa a Chemical b
& Petroleum Engineering Department, Sharif University of Technology, Tehran, Iran
Chemical Engineering Department, Sahand University of Technology. Tabriz, Iran
* Corresponding author, E-mail address: [email protected]
Abstract: Adsorption ability of prepared magnetic nanoparticles supported on activated carbon (AC-MNPs) was evaluated to synthesize an efficient and a low cost adsorbent for removal of Pb(II) and Cr(VI) ions from single and binary component aqueous solutions in the presence of salinity. Magnetic adsorbent was prepared by co-precipitation over activated carbon derived from almond shell by physical activation method. AC-MNPs was modified by oxygen containing functional groups to enhance the adsorption capacity of adsorbent. XRD, XPS, BET, Boehm, TEM, FT-IR, DLS and XRF were used to characterize the AC@Fe3O4@SiO2-NH2-COOH. Characterization analyses indicated the high dispersion of Fe3O4 crystallites on the activated carbon. TEM, XRD and DLS results revealed that size of Fe3O4 crystallites were below 17 nm. XPS results of the adsorbents before and after Pb(II) and Cr(VI) ions adsorption indicated that these metal ions successfully adsorbed. There were found from operating experiments that Cr(VI) ions have a negligible effect on adsorption of Pb(II) ions in binary solutions. However, removal efficiency of metal ions was reduced which were reached 80% and 53% for Pb(II) and Cr(VI), respectively. Results also illustrated that the effect of salinity on the adsorption of metal ions at pH > 7 was negligible.
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Keywords: Nanoparticles, Magnetic, Activated Carbon, Pb(II), Cr(VI), Adsorption, Salinity.
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Introduction Adsorption is considered one of the most effective techniques among various methods including ion exchange [1], liquid–liquid extraction [2], membrane filtration [3], biosorption [4], electrodialysis [5], and electro-coagulation [6] for the last decades due to its high efficiency and low cost adsorbents uses for removal of heavy toxic metals. The presence of toxic materials such as heavy metals and organic pollutants in wastewater poses serious problems and risks for human. Within heavy metals, mercury (Hg(II)), chromium (Cr(VI)) and lead (Pb(II)) have been considered as the most significant detrimental due to their high toxicity [7]. Adsorbents separation from solution as a final step is the serious drawbacks of adsorption experiments. There are traditional methods for removal of adsorbents from solution such as a filtration and sedimentation. However, much attention has been paid to the easy separation by using magnetic nanoparticles (MNPs) due to special and interesting properties including the responding to an applied magnetic field, high surface area, and appropriate adsorption capacity. The low feasibility of magnetic nanoparticles in engineering practice is the major drawbacks [8]. The most common materials used in the preparation of support for MNPs which generally comprises SiO2 [9-12], carbon [13-14], montmorillonite [15], polymer materials [16], and activated carbon [17-18]. As shown in open literature review, there are few studies carried out on the dispersing functionalized coated Fe3O4 over the activated carbons. Stability, high surface area, low cost and hydrophobicity properties in the activated carbon have come to be regarded as a support of MNPs to utilize in wastewater treatment. Agricultural solid wastes containing: almond shell, walnut shell, apricot stones, and olive stones [19] used as a raw material for preparation of activated carbon by chemical or physical activation methods.
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On the other hand, the activated carbon can be interested due to various functional groups on its surface which may be the choice for metal ions adsorption. However, abundant oxygen functional groups can be added to the dispersed magnetic nanoparticles supported on activated carbons. In the present work, activated carbon derived from almond shell was used as a support of Fe3O4 to remove Pb(II) and Cr(VI) ions from wastewater. Prepared magnetic adsorbent was characterized by TEM, BET, FT-IR, DLS, XRF, XPS and XRD. Batch experiments were carried out to determine the adsorption capacity of magnetic nanoparticles for removal of heavy metal ions under different operating conditions including temperature, pH, initial concentration and contact time. Performance of the novel AC-MNPs was evaluated in the presence of salinity. Finally, the adsorption capacity of prepared adsorbent was experimental investigated for the high salinity sample collected from Asmari oil field at 30 km from Ahvaz, Iran. 1 Experimental Material 2.1 Preparation of functionalized coated magnetic activated carbon (AC@Fe3O4@SiO2-NH2COOH)
Preparation of MNPs supported on activated carbon was carried out by using conventional co-precipitation method as previously reported with many researchers [20-21]. Briefly, 10.812 g of FeCl3.6H2O (40 mmol) and 3.976 g of FeCl2.4H2O (20 mmol) according to analytical computations from Equation 1 were dissolved in 300 ml deionized water using mechanical stirring at 70oC for 2 hours.
(1)
4
Afterward, 5 g of the powdered almond shell activated carbon (100 mesh) derived from physical activation method by water vapor, was added to achieve AC-Fe3O4 weight ratios of 1:1. Then, solution slowly stirred for half hour under an inert argon flow as carrier gas. In order to form the black precipitate of AC-MNPs, 5M aqueous NaOH was added by rate of 0.05 ml/s in to the suspension to obtain pH of 10–11 for one hour. Precipitated (AC@Fe3O4) were collected by magnetic separation after 24-hour aging at room temperature and repeatedly washed with hot distilled water and ethanol dilution, then dried at 50oC overnight. Silica-coated AC-MNPs was prepared by dispersing 2.5 g of AC@Fe3O4 into a 500 ml of ethanol–water mixture (4:1), which was heated to 60oC under an argon flow. Tetraethyl orthosilicate (TEOS) was added dropwise to the solution in the presence of a constant argon flow for 6 hour and pH of mixture was controlled at 9.0 by adding 5M NaOH solution during mixing. New product in this step was magnetically separated and washed with distilled water and ethanol and then dried at 50oC overnight. Preparation of amino-functionalized silica-coated AC-MNPs was carried out by dispersing 2 g of AC@Fe3O4@SiO2 into a heated 200 ml of ethanol–water (1:1) solution at 70oC under an argon flow. 5 ml of 3-aminopropyl triethoxysilane (APTES) was added dropwise to the solution in the presence of a constant argon flow and the mixture pH was adjusted to 11.0 by adding KOH solution. After 5 h mixing, the amino-functionalized silicacoated AC-MNPs was magnetically separated and repeatedly washed with distilled water to remove any undesirable materials and then dried at 50oC overnight. Finally, the AC@Fe3O4@SiO2-NH2 was stirred with 10% succinic anhydride in N,Ndimethylformamide (DMF) solution under argon flow at room temperature for 5 hour. AC@Fe3O4@SiO2-NH2-COOH was magnetically separated and repeatedly washed with
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distilled and then dried at 50oC overnight. All steps of the adsorbent preparation are seen in Fig. 1. All chemical materials and reagents such as FeCl3.6H2O, FeCl2.4H2O, TEOS, APTES, succinic anhydride, DMF, NaOH, and KOH were purchased from Merck Company.
2.2 Adsorbent Characterizations
Boehm test was used for specified of the surface functional groups of the magnetic activated carbon nanoparticles. Surface area of the samples was determined from nitrogen (N2) adsorption and desorption isotherms at 77 K using an ASAP-1100 micromesetics equipment. Before measurements, the samples were outgassed at 120oC and ambient pressure. The specific surface area was measured using the Brunauer-Emmett-Teller (BET) and t-plot, and the average pores sizes were also measured by Barrett-Joyner-Halenda (BJH) theories [22]. The pore volume was obtained from the amount of N2 adsorbed at a relative pressure of 0.99. The X-ray diffraction (XRD) patterns for the prepared samples were performed using model D-64295 equipment from STOE Company. XRD analysis was carried out at 30 kV, 20 mA, copper Kα radiation and scanning rate of 3o/min. The size distribution profile of MNPs was determined by Dynamic Light Scattering (DLS) by Nano AS (red badge) ZEN 3600 from UK. The products for transmission electron microscopy (TEM) micrographs were obtained by CM30-Philips instrument equipped with a Schottky field emission gun operated at 150 keV to determine the morphology and element distribution of nanoparticles. Fourier transformed infrared spectroscopy (FT-IR, Nicolet IS10) was carried out to analyze the molecular structure of the product at a resolution of 4 cm−1. To analyze the chemical elements of the prepared adsorbent, X-ray fluorescence was carried out by Spectro-Xepos device from Germany. XPS analysis was performed on AXIS Ultra DLD (Kratos Analytical, UK).
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2.3 Batch Adsorption Studies
Pb(II) and Cr(VI) adsorption on the AC@Fe3O4@SiO2-NH2-COOH nanoparticles was studied in aqueous solution using batch experiments within the pH range of 2 to 9 and the adsorption temperature were adjusted to desired values by shaking incubator (Fine Tech, SKIR-601L, Korea) as follow. Stock solutions of metal ions were prepared by dissolving the necessary amount of their salt (Potassium dichromate and Lead(II) nitrate) in deionized water and diluted to obtain the desired concentrations prior to adsorption experiments. Each adsorption experiments were conducted with 0.05 g adsorbent and 50 ml of metal solution with a desired concentration in two conical flasks, simultaneously. The flasks containing adsorbent and adsorbate were agitated for predetermined time intervals a mechanical shaker with maximum rate of shaking incubator. To evaluate the effect of salinity on removal of metal ions by prepared nanoparticles, several studies were carried out under various NaCl concentrations in metal ions solutions which cover the salinities of seawater. At the end of agitation, the magnetic particles were gathered magnetically by the aid of the cubic permanent hand-held magnet (0.5 T magnetic strength). The amount of metal ions in the final 25 ml volume were determined by atomic absorption spectrophotometer (Varian, spectra-110-220/880 Australia Pty. Ltd.) equipped with a Zeeman atomizer. The obtained results for two similar solutions were averaged and then reported. Removal efficiency of metal ions was calculated by equation as follow: RE
(C o C e )
100
(2)
Co
Where RE is removal efficiency, C0 and Ce (mg/L) are initial and equilibrium concentration, respectively. The amount of metal ions adsorption is measured with the equation as follow: q
( C o C e )V
(3)
W
7
Where q (mg/g) is adsorbed amount, C0 and Ce (mg/L) are initial and equilibrium concentration, respectively, V is the volume of solution (L), and W is adsorbent weight (g). 2 Results and Discussion 3.1 Function of magnetic nanoparticle adsorbent 3.1.1 Functional Groups
The amounts of acidic and basic groups of prepared magnetic adsorbent (AC@Fe3O4@SiO2-NH2-COOH) including phenolic, lactonic, carboxylic, and basic groups were determined by the Boehm test, presented in Table 1. The significant amounts of acidic groups (1.735 mequiv./g) that are indicative of oxygen-containing functional groups on the surface of the samples make them an appropriate adsorbent for high adsorption of heavy metal ions from aqueous solutions [23]. 3.1.2 Crystal Pattern
Figure 2 exhibits the crystal structures pattern of the AC@Fe3O4 and AC@Fe3O4@SiO2NH2-COOH samples while magnetic nanoparticles supported on almond activated carbon. Diffraction patterns reveal six characteristic peak for Fe3O4 at 2Ɵ = (30.72, 35.58, 43.82, 54.31, 57.21 and 62.83) corresponding to (220), (311), (400), (422), (511), and (440) Bragg reflections, respectively. These diffraction peaks are in good agreement with ICDD (The International Center for Diffraction of Data) (00-011-0614) by X’Pert HighScore software version 1.0d produced by PANalytical BV Almelo, the Netherlands. There are two different phases distinguished from the XRD profiles; the amorphous phase represents the activated carbon [24] and the peaks are observed due to Fe3O4 crystallites. Meanwhile, the results disclose that functional groups and amorphous silica phase on AC@Fe3O4 have no effect on forming the Fe3O4 crystals. The crystallite sizes were calculated by Scherrer equation given by equation (4):
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(4)
Where D is the mean crystallite diameter (nm), K is the dimensionless shape factor (spheres = 0.89), λ is the X-ray wavelength (X-ray tube: Cu, λ= 0.154 nm), β is the line broadening at half the maximum intensity and θ is the Bragg angle. The results indicate that the size of Fe3O4 crystallites formed on the activated carbon were less than 17 nm. Therefore, nano size of Fe3O4 crystallites were generated over activated carbon. 3.1.3 Micrographs and Particle Size
The TEM micrographs and particle size distribution of the prepared magnetic nanoparticles (AC@Fe3O4@SiO2-NH2-COOH and AC@Fe3O4) supported on almond activated carbon are seen in Fig. 3. It was found from these images that dark black and light black dots represented Fe3O4 and SiO2 crystallites, which was confirmed by XRD analysis [25-27]. The average Fe3O4 crystallites sizes were measured by Clemex software to be between 5 to 50 nm over almond activated carbon. The results also established this truth that AC-MNPs with high dispersion were formed over almond activated carbon which also confirmed Scherrer equation results and highlighted role of activated carbon as support. Comparison between samples was notable that the functionalization did not significantly effect in the particle agglomeration. The
architectural
porosity
of
almond-activated
carbon,
AC@Fe3O4
and
AC@Fe3O4@SiO2-NH2-COOH were analyzed by N2 adsorption-desorption test, which indicates type–IV isotherm that is typical for mesoporous adsorbent shown in Fig. 4 according to the IUPAC classification. Important features of type IV isotherms is the presence of micropores associated with mesopores. The surface area for the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH is calculated 860, 490 and 432 m2/g by BET theory, respectively [28]. It is shown the surface area decreased by forming Fe3O4 on the 9
activated carbon which is confirming the XRD Results. However, the activated carbon as hydrophobic adsorbent has supplied porous media for forming magnetic nanoparticles. The surface area and total pore volume of the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH obtained by BET, BJH and t-plot analyses are summarized in Table 2. The BET surface area decreased with adding Fe3O4 and SiO2 as the pores of the activated carbon were significantly blocked by the precipitating Fe3O4 and SiO2 thus reducing the surface area for adsorption of nitrogen over the activated carbon. 3.1.4 Core-Shell Structure
FT-IR
spectra
of
AC@Fe3O4,
AC@Fe3O4@SiO2,
AC@Fe3O4@SiO2-NH2
and
AC@Fe3O4@SiO2-NH2-COOH were demonstrated in Fig. 5. All graphs represent significant absorption bands at around 581 and 637 cm-1 which corresponds to Fe–O vibration related to Fe3O4. Another bands at around 1631 and 3423 cm-1 are associated with the vibrations of absorbed water molecules. Furthermore, a broad band at around 1071 cm-1 and a band at 805 cm-1 in Fig.5. b, which can be assigned as vibration modes of Si–O–Si, indicate that the Fe3O4 core is successfully coated by silica shell. Additionally, the characteristic peaks at 2849 and 2919 cm-1 ascribed to the C–H stretching vibration of the propyl group in the pendant APTES can be clearly observed in the FT-IR spectrum of AC@Fe3O4@SiO2–NH2, which compared with AC@Fe3O4@SiO2 spectrum, confirms that APTES molecules have been bonded successfully to the surface of the silica-coated MNPs. The frequency of N–H asymmetric and symmetric stretching vibrations of the amine group fall in the 3300–3400 cm-1 range and are obscured by the water band. Finally, the bands in 1555, 1653 and 1721 cm-1 represents amide and carboxyl functional groups. The Size of prepared magnetic nanoparticles (AC@Fe3O4@SiO2-NH2-COOH) were measured by hydrodynamic light scattering (DLS) analysis is shown in Fig. 6. The mean hydrodynamic diameters of magnetic nanoparticles were determined to be 7.57 nm which is
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in good agreement with XRD and TEM results. Results also illustrate the narrow distributions of magnetic nanoparticles. XRF analysis was performed for AC@Fe3O4@SiO2-NH2-COOH, and the chemical elements of samples were reported in Table 3. It is obvious from results that supported magnetic adsorbent has the same amount of carbon and Fe which can confirm the preparation method to reach AC-Fe3O4 weight ratios of 1:1. X-ray photoelectron spectroscopic (XPS) analysis of the AC@Fe3O4@SiO2-NH2-COOH before and after adsorption of Pb(II) and Cr(VI) was carried out for understanding of the adsorption mechanism, and the XPS spectra is shown in Fig. 7. The binding energy at 103.4 eV, 154.2 eV, 288.3 eV, 400.5 eV, 531.6 eV, 710.8 eV and 724.5 eV (Fig. 7(a)) correspond to Si 2p, Si 2s, C 1s, N 1s, O 1s, Fe 2p3/2, and Fe 2p1/2, respectively, indicating the presence of amine and carboxyl functional groups on the surface of silica Fe3O4 nanoparticle. Which is also consistent with the result based on FT-IR. It is necessary to note that the peak at 138.1 eV and 578.3 eV (Fig. 7(b)) can be assigned to Pb 4f7/2, and Cr 2p3/2, respectively, suggesting the successful adsorption of Pb(II) and Cr(VI) on the AC@Fe3O4@SiO2-NH2-COOH. The little increase of binding energy related to N 1s and O 1s after adsorption of metal ions (Fig.7(b)) which might have explained by charge transfer between amine and oxygen containing group with of Pb(II) and Cr(VI) by coordination.
3.2 Single Adsorption System 3.2.1 Effect of pH
Removal efficiency of Pb(II) and Cr(VI) from solutions with various salinity (1000, 10000, 20000 and 30000 ppm NaCl) on AC@Fe3O4@SiO2-NH2-COOH as a function of pH is shown in Fig. 7. It is clear that adsorption of Pb(II) and Cr(VI) increases sharply with increasing pH from 2-7. Henceforth, Pb(II) adsorption increases mildly with increasing pH from 7-12 while maximum adsorption was found in pH 12. Surface charge and functional 11
groups of AC@Fe3O4@SiO2-NH2-COOH can be the most important reasons to reach such as results. It is shown in Fig. 7 that effect of pH on removal of heavy metal ions in range of (712) is insignificant. Therefore, AC@Fe3O4@SiO2-NH2-COOH can be efficient adsorbent to remove Pb(II) and Cr(VI) from aqueous solutions in immense range of pH. Furthermore, role of salinity solution was studied on metal ion adsorption with pH effect, simultaneously. Antonym effect of salinity on adsorption of heavy metal ions (Pb(II) and Cr(VI)) is obvious at pH<7 while no significant difference has been shown at pH>7 due to the formation of metal hydroxide precipitates at high pH value. As seen in Fig. 7, it is obvious that adsorption of Pb(II) and Cr(VI) ions reduces as increasing NaCl concentration in acidic solution. 3.2.2 Effect of Temperature
Sorption of Cr(VI) and Pb(II) was realized in various temperatures in range of 25-45 oC under constant operating conditions including salinity concentration of 20000 ppm, initial concentration of 50 ppm and pH value of 7. As shown in Fig. 8, adsorption of Pb(II) and Cr(VI) ions enhances with increasing temperature from 25 to 45oC which reveals the endothermic the nature of adsorption process. The solution concentration of metal ions reduces with time and reached equilibrium within 80-100 min. Indeed, in selected range of temperature, diffusion resistance has significant role in the overall transport of the metal ions in the other words, diffusion is the bottleneck of process. Therefore, diffusion coefficient increases with increasing temperature, consequently, the removal efficiency increases. Similar results were obtained in previous work [19]. 3.2.3 Effect of Initial Concentration and Contact Time
As shown in Fig. 9, experimental results indicate linearly enhancement of adsorption amount of Pb(II) and Cr(VI) ions over prepared magnetic nanoparticles with increasing initial concentration of metal ions as many reports have been published similar results. Zabihi et al. [19], investigated mercury adsorption with activated carbon derived from walnut shells, the results revealed that mercury adsorption capacity increased linearly as increasing initial 12
concentration of Hg(II) ions in mother solutions. Also, Ahmadpour et al. [29] found that the removal efficiency of metal ions increased from 80-90% while initial concentration of metal ions increased from 5 to 500 ppm. Furthermore, few reports have been published elsewhere to study the effect of salinity on adsorption capacity of magnetic adsorbents. For example, Liu et al. [30] discovered that the uptake of Cu(II) increased with increasing initial concentration from 1 to 6 ppm. It can be found insignificant impact of NaCl salinity on the removal of copper ions by magnetic nanoparticles due to the stronger complex of copper ions and oxygen functional groups of surface than metal and chloride ions. Effect of initial concentration was evaluated in wide range of initial concentration 10-100 ppm and other variables were kept constant. The results are shown for removal of Pb(II) and Cr(VI) ions by AC@Fe3O4@SiO2NH2-COOH at salinity of 20000 ppm, temperature of 25oC and pH of 7 where the minimum effect of salinity was measured. Similar trend is obtained in the present study, lead and chrome ions adsorption on AC@Fe3O4@SiO2-NH2-COOH increases with increasing initial concentration. Uptake of Pb(II) and Cr(VI) ions is sharp initially, and then gradually raise to overtake equilibrium in 80 min. It can be justified that in initial time of adsorption, the vacant active sites and metal ions concentration gradient was relatively high. In addition, occupying the active sites over magnetic nanoparticles reduces with time.
3.3 Binary Adsorption System
To study competitive effects of Pb(II) and Cr(VI) ions on each other in binary solutions, removal efficiency of AC@Fe3O4@SiO2-NH2-COOH was determined for single and binary component solutions as seen in Fig. 10. All experiments were carried out in presence of 20000 ppm of NaCl at pH value of 7 and the adsorption temperature of 25 oC. It can be found that removal efficiency of Pb(II) and Cr(VI) ions in single component solutions were obtained 84.3% and 70%, respectively. Calculated removal efficiency were reduced in binary component solution which were achieved 80% and 53% for Pb(II) and Cr(VI), respectively. 13
However, measured removal efficiency of Pb(II) was illustrated mildly reduction in comparison with Cr(VI) removal efficiency in binary metal solution. Reducing in adsorption capacity might be explained by available active sites, affinity strength, competition for occupation the same active sites, and chemistry properties of metal ions [16] such as ionic bonding. According to the open literature review, high tendency of Pb(II) ions to adsorb on magnetic nanoparticles with carboxylic and oxygen functional groups [16]. Adsorption capacity of prepared supported magnetic nanoparticles is higher for Pb than Cr ions due to ion size. Cr ions with small size have the higher tendency to generate the heavily hydrated and larger ions than lead ions. Similar reason was also reported in previous studies [31]. In the present study, performance of prepared AC-MNPs was investigated with high saline solution from Asmari oil field. Concentration of total heavy metal ions (Zn, Cr, Mn, Cu and Pb) was measured about 52 ppm and acheived removal efficiency was obtained 76%.
3 Conclusion This study presents the preparation of novel magnetic nanoparticles supported on almond activated carbon with oxygen containing-functional groups loading which is an efficient absorbent to remove Pb(II) and Cr(II) ions in single and binary solutions. Negligible effect of salinity is obtained from results while pH value is upper than 7. Fe3O4 nanoparticles were formed on the activated carbon with high dispersion which was confirmed by TEM, XRD and DLS analysis. High removal efficiency for Pb(II) and Cr(VI) ions were achieved 84.3% and 70% in single solution, respectively. Antonym effect of metal ions on each other, was investigated by binary solutions which shows the significant effect of Pb(II) ions on adsorption of Cr(II) over prepared AC-MNPs. In contrary, there is negligible effect of Cr(II) on removing Pb(II) from binary solutions while the maximum removal efficiency was reached 80% and 53% for Pb(II) and Cr(VI), respectively. However, AC-MNPs can be used for
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removal of metal ions, simultaneously. High efficiency and simple separation of prepared functionalized AC-MNPs can be favorable to utilize in saline wastewater treatment.
4 Acknowledgement The authors are greatly acknowledging the assistance of Azmoon Sanat Sabz environmental specialized laboratory, Tehran, Iran.
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[24] M. Ousmane, L.F. Liotta, G.D. Carlo, G. Pantaleod, A.M. Veneziad, G. Deganello, L. Retailleau, A. Boreave, A.G. Fendler, Supported Au catalysts for low-temperature abatement of propene and toluene, as model VOCs: Support effect, Applied Catalysis B: Environmental 101 (2011) 629–637. [25] J. Wang, G. Zhao, Y. Li, H. Zhu, X. Peng, X. Gao, One-step fabrication of functionalized magnetic adsorbents with large surface area and their adsorption for dye and heavy metal ions, Dalton Trans. 43 (2014) 11637-11645. [26] L.M. Rossi, N.J.S. Costa, F.P. Silva, R. Wojcieszak, Magnetic nanomaterials in catalysis: advanced catalysts for magnetic separation and beyond, Green Chem. 16 (2014) 29062933. [27] S. Venkateswarlu, M. Yoon, Surfactant-free green synthesis of Fe3O4 nanoparticles capped with 3,4 dihydroxyphenethylcarbamodithioate: stable recyclable magnetic nanoparticles for the rapid and efficient removal of Hg(II) ions from water, Dalton Trans. 44 (2015) 18427-18437. [28] M. Zabihi, F. Khorasheh, J. Shayegan, Supported copper and cobalt oxides on activated carbon for simultaneous oxidation of toluene and cyclohexane in air, RSC Advances 5 (2015) 5107-5122. [29] A. Ahmadpour, M. Zabihi, M. Tahmasbi, T. RohaniBastami, Effect of adsorbents and chemical treatments on the removal of strontium from aqueous solutions, Journal of Hazardous Materials 182 (2010) 552-556. [30] Y. Liu, M. Chen, Y. Hao, Study on the adsorption of Cu(II) by EDTA functionalized Fe3O4 magnetic nano-particles, Chemical Engineering Journal 218 (2013) 46–54 [31] M. R. Lasheen, N. S. Ammar, H. S. Ibrahim, Adsorption/desorption of Cd(II), Cu(II) and Pb(II) using chemically modified orange peel: Equilibrium and kinetic studies, Solid State Sciences 14 (2012) 202-210.
19
Figure Captions: Fig. 1. Schematic Diagram of preparing magnetic adsorbent Fig. 2. XRD micrographs of two magnetic nanoparticles (a) AC@Fe3O4 and (b) AC@Fe3O4@SiO2-NH2-COOH. Fig. 3. TEM results of prepared magnetic nanoparticle AC@Fe3O4 and AC@Fe3O4@SiO2NH2-COOH. Fig. 4. N2 adsorption isotherm at 77 k for prepared the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH. Fig. 5. FT-IR spectra of (a) AC@Fe3O4, (b) AC@Fe3O4@SiO2, (c) AC@Fe3O4@SiO2-NH2 and (d) AC@Fe3O4@SiO2-NH2-COOH. Fig. 6. DLS results for AC@Fe3O4@SiO2-NH2-COOH. Fig. 7. XPS spectra of AC@Fe3O4@SiO2-NH2-COOH (a) before and (b) after simultaneously adsorption of Pb(II) and Cr(IV). Fig. 8. Effect of pH on the adsorption of (a) Pb(II) and (b) Cr(VI) on AC@Fe3O4@SiO2-NH2COOH, (contact time=120 min, initial concentration = 50ppm). Fig. 9. Effect of temperature of (a) Pb(II) and (b) Cr(VI) solutions versus contact time on AC@Fe3O4@SiO2-NH2-COOH. (Salinity= 20000 ppm, pH=7). Fig. 10. Effect of initial concentration of (a) Pb(II) and (b) Cr(VI) solutions versus contact time on AC@Fe3O4@SiO2-NH2-COOH. (Salinity= 20000 ppm, pH=7 and temperature =25oC). Fig. 11. Removal of Pb(II) and Cr(VI) on AC@Fe3O4@SiO2-NH2-COOH from binary solutions (salinity= 20000 ppm, pH=7 and temperature =25oC).
20
21
22
23
24
25
26
27
Table 1. The Boehm test results for AC@Fe3O4@SiO2-NH2-COOH (mequiv./g).
Lactonic
Carboxylic
Phenolic
groups
groups
Groups
Groups
groups= Total oxygen groups
0.01
0.330
0.980
0.425
1.735
Raw Material
AC@Fe3O4@SiO2-NH2-COOH
Total acidic
Basic
28
Table 2. BET, t-plot and BJH results for prepared the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH. BET
BJH
t-plot
Ref.
Surface area (m2/g)
Total pore volume (cm3/g)
Volume pore (cm3/g)
Surface area (m2/g)
Almond AC
860.70
0.4697
0.1831
913
25
AC@Fe3O4
490
0.3745
0.2193
500
This work
AC@Fe3O4@SiO2NH2-COOH
432
0.3564
0.2155
431.44
Sample
29
This work
Table 3. XRF results for AC@Fe3O4@SiO2-NH2-COOH.
Chemical Element wt.%
AC@Fe3O4@SiO2-NH2-COOH
C
Fe
Si
O
Other Element
25.14
22.18
14.12
28.32
10.24
30
S2213-3437(17)30098-2 http://dx.doi.org/doi:10.1016/j.jece.2017.03.006 JECE 1512
To appear in: Received date: Revised date: Accepted date:
22-10-2016 27-2-2017 7-3-2017
Please cite this article as: M.H.Fatehi, J.Shayegan, M.Zabihi, I.Goodarznia, Functionalized Magnetic Nanoparticles Supported on Activated Carbon for Adsorption of Pb(II) and Cr(VI) Ions from Saline Solutions, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2017.03.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Functionalized Magnetic Nanoparticles Supported on Activated Carbon for Adsorption of Pb(II) and Cr(VI) Ions from Saline Solutions
M.H. Fatehia, J. Shayegana,*, M. Zabihib and I. Goodarzniaa a Chemical b
& Petroleum Engineering Department, Sharif University of Technology, Tehran, Iran
Chemical Engineering Department, Sahand University of Technology. Tabriz, Iran
* Corresponding author, E-mail address: [email protected]
Abstract: Adsorption ability of prepared magnetic nanoparticles supported on activated carbon (AC-MNPs) was evaluated to synthesize an efficient and a low cost adsorbent for removal of Pb(II) and Cr(VI) ions from single and binary component aqueous solutions in the presence of salinity. Magnetic adsorbent was prepared by co-precipitation over activated carbon derived from almond shell by physical activation method. AC-MNPs was modified by oxygen containing functional groups to enhance the adsorption capacity of adsorbent. XRD, XPS, BET, Boehm, TEM, FT-IR, DLS and XRF were used to characterize the AC@Fe3O4@SiO2-NH2-COOH. Characterization analyses indicated the high dispersion of Fe3O4 crystallites on the activated carbon. TEM, XRD and DLS results revealed that size of Fe3O4 crystallites were below 17 nm. XPS results of the adsorbents before and after Pb(II) and Cr(VI) ions adsorption indicated that these metal ions successfully adsorbed. There were found from operating experiments that Cr(VI) ions have a negligible effect on adsorption of Pb(II) ions in binary solutions. However, removal efficiency of metal ions was reduced which were reached 80% and 53% for Pb(II) and Cr(VI), respectively. Results also illustrated that the effect of salinity on the adsorption of metal ions at pH > 7 was negligible.
1
Keywords: Nanoparticles, Magnetic, Activated Carbon, Pb(II), Cr(VI), Adsorption, Salinity.
2
Introduction Adsorption is considered one of the most effective techniques among various methods including ion exchange [1], liquid–liquid extraction [2], membrane filtration [3], biosorption [4], electrodialysis [5], and electro-coagulation [6] for the last decades due to its high efficiency and low cost adsorbents uses for removal of heavy toxic metals. The presence of toxic materials such as heavy metals and organic pollutants in wastewater poses serious problems and risks for human. Within heavy metals, mercury (Hg(II)), chromium (Cr(VI)) and lead (Pb(II)) have been considered as the most significant detrimental due to their high toxicity [7]. Adsorbents separation from solution as a final step is the serious drawbacks of adsorption experiments. There are traditional methods for removal of adsorbents from solution such as a filtration and sedimentation. However, much attention has been paid to the easy separation by using magnetic nanoparticles (MNPs) due to special and interesting properties including the responding to an applied magnetic field, high surface area, and appropriate adsorption capacity. The low feasibility of magnetic nanoparticles in engineering practice is the major drawbacks [8]. The most common materials used in the preparation of support for MNPs which generally comprises SiO2 [9-12], carbon [13-14], montmorillonite [15], polymer materials [16], and activated carbon [17-18]. As shown in open literature review, there are few studies carried out on the dispersing functionalized coated Fe3O4 over the activated carbons. Stability, high surface area, low cost and hydrophobicity properties in the activated carbon have come to be regarded as a support of MNPs to utilize in wastewater treatment. Agricultural solid wastes containing: almond shell, walnut shell, apricot stones, and olive stones [19] used as a raw material for preparation of activated carbon by chemical or physical activation methods.
3
On the other hand, the activated carbon can be interested due to various functional groups on its surface which may be the choice for metal ions adsorption. However, abundant oxygen functional groups can be added to the dispersed magnetic nanoparticles supported on activated carbons. In the present work, activated carbon derived from almond shell was used as a support of Fe3O4 to remove Pb(II) and Cr(VI) ions from wastewater. Prepared magnetic adsorbent was characterized by TEM, BET, FT-IR, DLS, XRF, XPS and XRD. Batch experiments were carried out to determine the adsorption capacity of magnetic nanoparticles for removal of heavy metal ions under different operating conditions including temperature, pH, initial concentration and contact time. Performance of the novel AC-MNPs was evaluated in the presence of salinity. Finally, the adsorption capacity of prepared adsorbent was experimental investigated for the high salinity sample collected from Asmari oil field at 30 km from Ahvaz, Iran. 1 Experimental Material 2.1 Preparation of functionalized coated magnetic activated carbon (AC@Fe3O4@SiO2-NH2COOH)
Preparation of MNPs supported on activated carbon was carried out by using conventional co-precipitation method as previously reported with many researchers [20-21]. Briefly, 10.812 g of FeCl3.6H2O (40 mmol) and 3.976 g of FeCl2.4H2O (20 mmol) according to analytical computations from Equation 1 were dissolved in 300 ml deionized water using mechanical stirring at 70oC for 2 hours.
(1)
4
Afterward, 5 g of the powdered almond shell activated carbon (100 mesh) derived from physical activation method by water vapor, was added to achieve AC-Fe3O4 weight ratios of 1:1. Then, solution slowly stirred for half hour under an inert argon flow as carrier gas. In order to form the black precipitate of AC-MNPs, 5M aqueous NaOH was added by rate of 0.05 ml/s in to the suspension to obtain pH of 10–11 for one hour. Precipitated (AC@Fe3O4) were collected by magnetic separation after 24-hour aging at room temperature and repeatedly washed with hot distilled water and ethanol dilution, then dried at 50oC overnight. Silica-coated AC-MNPs was prepared by dispersing 2.5 g of AC@Fe3O4 into a 500 ml of ethanol–water mixture (4:1), which was heated to 60oC under an argon flow. Tetraethyl orthosilicate (TEOS) was added dropwise to the solution in the presence of a constant argon flow for 6 hour and pH of mixture was controlled at 9.0 by adding 5M NaOH solution during mixing. New product in this step was magnetically separated and washed with distilled water and ethanol and then dried at 50oC overnight. Preparation of amino-functionalized silica-coated AC-MNPs was carried out by dispersing 2 g of AC@Fe3O4@SiO2 into a heated 200 ml of ethanol–water (1:1) solution at 70oC under an argon flow. 5 ml of 3-aminopropyl triethoxysilane (APTES) was added dropwise to the solution in the presence of a constant argon flow and the mixture pH was adjusted to 11.0 by adding KOH solution. After 5 h mixing, the amino-functionalized silicacoated AC-MNPs was magnetically separated and repeatedly washed with distilled water to remove any undesirable materials and then dried at 50oC overnight. Finally, the AC@Fe3O4@SiO2-NH2 was stirred with 10% succinic anhydride in N,Ndimethylformamide (DMF) solution under argon flow at room temperature for 5 hour. AC@Fe3O4@SiO2-NH2-COOH was magnetically separated and repeatedly washed with
5
distilled and then dried at 50oC overnight. All steps of the adsorbent preparation are seen in Fig. 1. All chemical materials and reagents such as FeCl3.6H2O, FeCl2.4H2O, TEOS, APTES, succinic anhydride, DMF, NaOH, and KOH were purchased from Merck Company.
2.2 Adsorbent Characterizations
Boehm test was used for specified of the surface functional groups of the magnetic activated carbon nanoparticles. Surface area of the samples was determined from nitrogen (N2) adsorption and desorption isotherms at 77 K using an ASAP-1100 micromesetics equipment. Before measurements, the samples were outgassed at 120oC and ambient pressure. The specific surface area was measured using the Brunauer-Emmett-Teller (BET) and t-plot, and the average pores sizes were also measured by Barrett-Joyner-Halenda (BJH) theories [22]. The pore volume was obtained from the amount of N2 adsorbed at a relative pressure of 0.99. The X-ray diffraction (XRD) patterns for the prepared samples were performed using model D-64295 equipment from STOE Company. XRD analysis was carried out at 30 kV, 20 mA, copper Kα radiation and scanning rate of 3o/min. The size distribution profile of MNPs was determined by Dynamic Light Scattering (DLS) by Nano AS (red badge) ZEN 3600 from UK. The products for transmission electron microscopy (TEM) micrographs were obtained by CM30-Philips instrument equipped with a Schottky field emission gun operated at 150 keV to determine the morphology and element distribution of nanoparticles. Fourier transformed infrared spectroscopy (FT-IR, Nicolet IS10) was carried out to analyze the molecular structure of the product at a resolution of 4 cm−1. To analyze the chemical elements of the prepared adsorbent, X-ray fluorescence was carried out by Spectro-Xepos device from Germany. XPS analysis was performed on AXIS Ultra DLD (Kratos Analytical, UK).
6
2.3 Batch Adsorption Studies
Pb(II) and Cr(VI) adsorption on the AC@Fe3O4@SiO2-NH2-COOH nanoparticles was studied in aqueous solution using batch experiments within the pH range of 2 to 9 and the adsorption temperature were adjusted to desired values by shaking incubator (Fine Tech, SKIR-601L, Korea) as follow. Stock solutions of metal ions were prepared by dissolving the necessary amount of their salt (Potassium dichromate and Lead(II) nitrate) in deionized water and diluted to obtain the desired concentrations prior to adsorption experiments. Each adsorption experiments were conducted with 0.05 g adsorbent and 50 ml of metal solution with a desired concentration in two conical flasks, simultaneously. The flasks containing adsorbent and adsorbate were agitated for predetermined time intervals a mechanical shaker with maximum rate of shaking incubator. To evaluate the effect of salinity on removal of metal ions by prepared nanoparticles, several studies were carried out under various NaCl concentrations in metal ions solutions which cover the salinities of seawater. At the end of agitation, the magnetic particles were gathered magnetically by the aid of the cubic permanent hand-held magnet (0.5 T magnetic strength). The amount of metal ions in the final 25 ml volume were determined by atomic absorption spectrophotometer (Varian, spectra-110-220/880 Australia Pty. Ltd.) equipped with a Zeeman atomizer. The obtained results for two similar solutions were averaged and then reported. Removal efficiency of metal ions was calculated by equation as follow: RE
(C o C e )
100
(2)
Co
Where RE is removal efficiency, C0 and Ce (mg/L) are initial and equilibrium concentration, respectively. The amount of metal ions adsorption is measured with the equation as follow: q
( C o C e )V
(3)
W
7
Where q (mg/g) is adsorbed amount, C0 and Ce (mg/L) are initial and equilibrium concentration, respectively, V is the volume of solution (L), and W is adsorbent weight (g). 2 Results and Discussion 3.1 Function of magnetic nanoparticle adsorbent 3.1.1 Functional Groups
The amounts of acidic and basic groups of prepared magnetic adsorbent (AC@Fe3O4@SiO2-NH2-COOH) including phenolic, lactonic, carboxylic, and basic groups were determined by the Boehm test, presented in Table 1. The significant amounts of acidic groups (1.735 mequiv./g) that are indicative of oxygen-containing functional groups on the surface of the samples make them an appropriate adsorbent for high adsorption of heavy metal ions from aqueous solutions [23]. 3.1.2 Crystal Pattern
Figure 2 exhibits the crystal structures pattern of the AC@Fe3O4 and AC@Fe3O4@SiO2NH2-COOH samples while magnetic nanoparticles supported on almond activated carbon. Diffraction patterns reveal six characteristic peak for Fe3O4 at 2Ɵ = (30.72, 35.58, 43.82, 54.31, 57.21 and 62.83) corresponding to (220), (311), (400), (422), (511), and (440) Bragg reflections, respectively. These diffraction peaks are in good agreement with ICDD (The International Center for Diffraction of Data) (00-011-0614) by X’Pert HighScore software version 1.0d produced by PANalytical BV Almelo, the Netherlands. There are two different phases distinguished from the XRD profiles; the amorphous phase represents the activated carbon [24] and the peaks are observed due to Fe3O4 crystallites. Meanwhile, the results disclose that functional groups and amorphous silica phase on AC@Fe3O4 have no effect on forming the Fe3O4 crystals. The crystallite sizes were calculated by Scherrer equation given by equation (4):
8
(4)
Where D is the mean crystallite diameter (nm), K is the dimensionless shape factor (spheres = 0.89), λ is the X-ray wavelength (X-ray tube: Cu, λ= 0.154 nm), β is the line broadening at half the maximum intensity and θ is the Bragg angle. The results indicate that the size of Fe3O4 crystallites formed on the activated carbon were less than 17 nm. Therefore, nano size of Fe3O4 crystallites were generated over activated carbon. 3.1.3 Micrographs and Particle Size
The TEM micrographs and particle size distribution of the prepared magnetic nanoparticles (AC@Fe3O4@SiO2-NH2-COOH and AC@Fe3O4) supported on almond activated carbon are seen in Fig. 3. It was found from these images that dark black and light black dots represented Fe3O4 and SiO2 crystallites, which was confirmed by XRD analysis [25-27]. The average Fe3O4 crystallites sizes were measured by Clemex software to be between 5 to 50 nm over almond activated carbon. The results also established this truth that AC-MNPs with high dispersion were formed over almond activated carbon which also confirmed Scherrer equation results and highlighted role of activated carbon as support. Comparison between samples was notable that the functionalization did not significantly effect in the particle agglomeration. The
architectural
porosity
of
almond-activated
carbon,
AC@Fe3O4
and
AC@Fe3O4@SiO2-NH2-COOH were analyzed by N2 adsorption-desorption test, which indicates type–IV isotherm that is typical for mesoporous adsorbent shown in Fig. 4 according to the IUPAC classification. Important features of type IV isotherms is the presence of micropores associated with mesopores. The surface area for the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH is calculated 860, 490 and 432 m2/g by BET theory, respectively [28]. It is shown the surface area decreased by forming Fe3O4 on the 9
activated carbon which is confirming the XRD Results. However, the activated carbon as hydrophobic adsorbent has supplied porous media for forming magnetic nanoparticles. The surface area and total pore volume of the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH obtained by BET, BJH and t-plot analyses are summarized in Table 2. The BET surface area decreased with adding Fe3O4 and SiO2 as the pores of the activated carbon were significantly blocked by the precipitating Fe3O4 and SiO2 thus reducing the surface area for adsorption of nitrogen over the activated carbon. 3.1.4 Core-Shell Structure
FT-IR
spectra
of
AC@Fe3O4,
AC@Fe3O4@SiO2,
AC@Fe3O4@SiO2-NH2
and
AC@Fe3O4@SiO2-NH2-COOH were demonstrated in Fig. 5. All graphs represent significant absorption bands at around 581 and 637 cm-1 which corresponds to Fe–O vibration related to Fe3O4. Another bands at around 1631 and 3423 cm-1 are associated with the vibrations of absorbed water molecules. Furthermore, a broad band at around 1071 cm-1 and a band at 805 cm-1 in Fig.5. b, which can be assigned as vibration modes of Si–O–Si, indicate that the Fe3O4 core is successfully coated by silica shell. Additionally, the characteristic peaks at 2849 and 2919 cm-1 ascribed to the C–H stretching vibration of the propyl group in the pendant APTES can be clearly observed in the FT-IR spectrum of AC@Fe3O4@SiO2–NH2, which compared with AC@Fe3O4@SiO2 spectrum, confirms that APTES molecules have been bonded successfully to the surface of the silica-coated MNPs. The frequency of N–H asymmetric and symmetric stretching vibrations of the amine group fall in the 3300–3400 cm-1 range and are obscured by the water band. Finally, the bands in 1555, 1653 and 1721 cm-1 represents amide and carboxyl functional groups. The Size of prepared magnetic nanoparticles (AC@Fe3O4@SiO2-NH2-COOH) were measured by hydrodynamic light scattering (DLS) analysis is shown in Fig. 6. The mean hydrodynamic diameters of magnetic nanoparticles were determined to be 7.57 nm which is
10
in good agreement with XRD and TEM results. Results also illustrate the narrow distributions of magnetic nanoparticles. XRF analysis was performed for AC@Fe3O4@SiO2-NH2-COOH, and the chemical elements of samples were reported in Table 3. It is obvious from results that supported magnetic adsorbent has the same amount of carbon and Fe which can confirm the preparation method to reach AC-Fe3O4 weight ratios of 1:1. X-ray photoelectron spectroscopic (XPS) analysis of the AC@Fe3O4@SiO2-NH2-COOH before and after adsorption of Pb(II) and Cr(VI) was carried out for understanding of the adsorption mechanism, and the XPS spectra is shown in Fig. 7. The binding energy at 103.4 eV, 154.2 eV, 288.3 eV, 400.5 eV, 531.6 eV, 710.8 eV and 724.5 eV (Fig. 7(a)) correspond to Si 2p, Si 2s, C 1s, N 1s, O 1s, Fe 2p3/2, and Fe 2p1/2, respectively, indicating the presence of amine and carboxyl functional groups on the surface of silica Fe3O4 nanoparticle. Which is also consistent with the result based on FT-IR. It is necessary to note that the peak at 138.1 eV and 578.3 eV (Fig. 7(b)) can be assigned to Pb 4f7/2, and Cr 2p3/2, respectively, suggesting the successful adsorption of Pb(II) and Cr(VI) on the AC@Fe3O4@SiO2-NH2-COOH. The little increase of binding energy related to N 1s and O 1s after adsorption of metal ions (Fig.7(b)) which might have explained by charge transfer between amine and oxygen containing group with of Pb(II) and Cr(VI) by coordination.
3.2 Single Adsorption System 3.2.1 Effect of pH
Removal efficiency of Pb(II) and Cr(VI) from solutions with various salinity (1000, 10000, 20000 and 30000 ppm NaCl) on AC@Fe3O4@SiO2-NH2-COOH as a function of pH is shown in Fig. 7. It is clear that adsorption of Pb(II) and Cr(VI) increases sharply with increasing pH from 2-7. Henceforth, Pb(II) adsorption increases mildly with increasing pH from 7-12 while maximum adsorption was found in pH 12. Surface charge and functional 11
groups of AC@Fe3O4@SiO2-NH2-COOH can be the most important reasons to reach such as results. It is shown in Fig. 7 that effect of pH on removal of heavy metal ions in range of (712) is insignificant. Therefore, AC@Fe3O4@SiO2-NH2-COOH can be efficient adsorbent to remove Pb(II) and Cr(VI) from aqueous solutions in immense range of pH. Furthermore, role of salinity solution was studied on metal ion adsorption with pH effect, simultaneously. Antonym effect of salinity on adsorption of heavy metal ions (Pb(II) and Cr(VI)) is obvious at pH<7 while no significant difference has been shown at pH>7 due to the formation of metal hydroxide precipitates at high pH value. As seen in Fig. 7, it is obvious that adsorption of Pb(II) and Cr(VI) ions reduces as increasing NaCl concentration in acidic solution. 3.2.2 Effect of Temperature
Sorption of Cr(VI) and Pb(II) was realized in various temperatures in range of 25-45 oC under constant operating conditions including salinity concentration of 20000 ppm, initial concentration of 50 ppm and pH value of 7. As shown in Fig. 8, adsorption of Pb(II) and Cr(VI) ions enhances with increasing temperature from 25 to 45oC which reveals the endothermic the nature of adsorption process. The solution concentration of metal ions reduces with time and reached equilibrium within 80-100 min. Indeed, in selected range of temperature, diffusion resistance has significant role in the overall transport of the metal ions in the other words, diffusion is the bottleneck of process. Therefore, diffusion coefficient increases with increasing temperature, consequently, the removal efficiency increases. Similar results were obtained in previous work [19]. 3.2.3 Effect of Initial Concentration and Contact Time
As shown in Fig. 9, experimental results indicate linearly enhancement of adsorption amount of Pb(II) and Cr(VI) ions over prepared magnetic nanoparticles with increasing initial concentration of metal ions as many reports have been published similar results. Zabihi et al. [19], investigated mercury adsorption with activated carbon derived from walnut shells, the results revealed that mercury adsorption capacity increased linearly as increasing initial 12
concentration of Hg(II) ions in mother solutions. Also, Ahmadpour et al. [29] found that the removal efficiency of metal ions increased from 80-90% while initial concentration of metal ions increased from 5 to 500 ppm. Furthermore, few reports have been published elsewhere to study the effect of salinity on adsorption capacity of magnetic adsorbents. For example, Liu et al. [30] discovered that the uptake of Cu(II) increased with increasing initial concentration from 1 to 6 ppm. It can be found insignificant impact of NaCl salinity on the removal of copper ions by magnetic nanoparticles due to the stronger complex of copper ions and oxygen functional groups of surface than metal and chloride ions. Effect of initial concentration was evaluated in wide range of initial concentration 10-100 ppm and other variables were kept constant. The results are shown for removal of Pb(II) and Cr(VI) ions by AC@Fe3O4@SiO2NH2-COOH at salinity of 20000 ppm, temperature of 25oC and pH of 7 where the minimum effect of salinity was measured. Similar trend is obtained in the present study, lead and chrome ions adsorption on AC@Fe3O4@SiO2-NH2-COOH increases with increasing initial concentration. Uptake of Pb(II) and Cr(VI) ions is sharp initially, and then gradually raise to overtake equilibrium in 80 min. It can be justified that in initial time of adsorption, the vacant active sites and metal ions concentration gradient was relatively high. In addition, occupying the active sites over magnetic nanoparticles reduces with time.
3.3 Binary Adsorption System
To study competitive effects of Pb(II) and Cr(VI) ions on each other in binary solutions, removal efficiency of AC@Fe3O4@SiO2-NH2-COOH was determined for single and binary component solutions as seen in Fig. 10. All experiments were carried out in presence of 20000 ppm of NaCl at pH value of 7 and the adsorption temperature of 25 oC. It can be found that removal efficiency of Pb(II) and Cr(VI) ions in single component solutions were obtained 84.3% and 70%, respectively. Calculated removal efficiency were reduced in binary component solution which were achieved 80% and 53% for Pb(II) and Cr(VI), respectively. 13
However, measured removal efficiency of Pb(II) was illustrated mildly reduction in comparison with Cr(VI) removal efficiency in binary metal solution. Reducing in adsorption capacity might be explained by available active sites, affinity strength, competition for occupation the same active sites, and chemistry properties of metal ions [16] such as ionic bonding. According to the open literature review, high tendency of Pb(II) ions to adsorb on magnetic nanoparticles with carboxylic and oxygen functional groups [16]. Adsorption capacity of prepared supported magnetic nanoparticles is higher for Pb than Cr ions due to ion size. Cr ions with small size have the higher tendency to generate the heavily hydrated and larger ions than lead ions. Similar reason was also reported in previous studies [31]. In the present study, performance of prepared AC-MNPs was investigated with high saline solution from Asmari oil field. Concentration of total heavy metal ions (Zn, Cr, Mn, Cu and Pb) was measured about 52 ppm and acheived removal efficiency was obtained 76%.
3 Conclusion This study presents the preparation of novel magnetic nanoparticles supported on almond activated carbon with oxygen containing-functional groups loading which is an efficient absorbent to remove Pb(II) and Cr(II) ions in single and binary solutions. Negligible effect of salinity is obtained from results while pH value is upper than 7. Fe3O4 nanoparticles were formed on the activated carbon with high dispersion which was confirmed by TEM, XRD and DLS analysis. High removal efficiency for Pb(II) and Cr(VI) ions were achieved 84.3% and 70% in single solution, respectively. Antonym effect of metal ions on each other, was investigated by binary solutions which shows the significant effect of Pb(II) ions on adsorption of Cr(II) over prepared AC-MNPs. In contrary, there is negligible effect of Cr(II) on removing Pb(II) from binary solutions while the maximum removal efficiency was reached 80% and 53% for Pb(II) and Cr(VI), respectively. However, AC-MNPs can be used for
14
removal of metal ions, simultaneously. High efficiency and simple separation of prepared functionalized AC-MNPs can be favorable to utilize in saline wastewater treatment.
4 Acknowledgement The authors are greatly acknowledging the assistance of Azmoon Sanat Sabz environmental specialized laboratory, Tehran, Iran.
15
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[16] A. Zayed M. Badruddoza, Z.B. Zakir Shawon, W.J. Daniel Tay, K. Hidajat, M.S. Uddin, Fe3O4/cyclodextrin polymer nanocomposites for selective heavy metals removal from industrial wastewater, Carbohydrate Polymers 91 (2013) 322– 332. [17] S. Nethaji. A. Sivasamy, A.B. Mandal, Preparation and characterization of corn cob activated carbon coated with nano-sized magnetite particles for the removal of Cr(VI), Bioresource Technology 134 (2013) 94–100. [18] J.J Xu, N.Y. Gao, D.Y. Zhao, D.Q. Yin, H. Zhang, Y.Q. Gao, W. Shi, Comparative study of nano-iron hydroxide impregnated granular activated carbon (Fe–GAC) for bromate or perchlorate removal, Separation and Purification Technology 147 (2015) 9–16. [19] M. Zabihi, A. Ahmadpour, A. HaghighiAsl, Removal of mercury from water by carbonaceous sorbents derived from walnut Shell, Journal of Hazardous Materials 167 (2009) 230–236. [20] D. Mohan, A. Sarswat, V.K. Singh, M. Alexandre-Franco, C.U. Pittman Jr, Development of magnetic activated carbon from almond shells for trinitrophenol removal from water, Chemical Engineering Journal 172 (2011) 1111-1125. [21] Y. Zhu, X. Ren, Y. Liu, Y. Wei, L. Qing, X. Liao, Covalent immobilization of porcine pancreatic lipase on carboxyl-activated magnetic nanoparticles: Characterization and application for enzymatic inhibition assays, Materials Science and Engineering C 38 (2014) 278–285. [22] M. Zabihi, A. HaghighiAsl, A. Ahmadpour, Studies on adsorption of mercury from aqueous solution on activated carbons prepared from walnut shell, Journal of Hazardous Materials 174 (2010) 251–256. [23] H. Hasar, Adsorption of nickel(II) from aqueous solution onto activated carbon prepared from almond husk, Journal of Hazardous Materials 97 (2003) 49-57.
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[24] M. Ousmane, L.F. Liotta, G.D. Carlo, G. Pantaleod, A.M. Veneziad, G. Deganello, L. Retailleau, A. Boreave, A.G. Fendler, Supported Au catalysts for low-temperature abatement of propene and toluene, as model VOCs: Support effect, Applied Catalysis B: Environmental 101 (2011) 629–637. [25] J. Wang, G. Zhao, Y. Li, H. Zhu, X. Peng, X. Gao, One-step fabrication of functionalized magnetic adsorbents with large surface area and their adsorption for dye and heavy metal ions, Dalton Trans. 43 (2014) 11637-11645. [26] L.M. Rossi, N.J.S. Costa, F.P. Silva, R. Wojcieszak, Magnetic nanomaterials in catalysis: advanced catalysts for magnetic separation and beyond, Green Chem. 16 (2014) 29062933. [27] S. Venkateswarlu, M. Yoon, Surfactant-free green synthesis of Fe3O4 nanoparticles capped with 3,4 dihydroxyphenethylcarbamodithioate: stable recyclable magnetic nanoparticles for the rapid and efficient removal of Hg(II) ions from water, Dalton Trans. 44 (2015) 18427-18437. [28] M. Zabihi, F. Khorasheh, J. Shayegan, Supported copper and cobalt oxides on activated carbon for simultaneous oxidation of toluene and cyclohexane in air, RSC Advances 5 (2015) 5107-5122. [29] A. Ahmadpour, M. Zabihi, M. Tahmasbi, T. RohaniBastami, Effect of adsorbents and chemical treatments on the removal of strontium from aqueous solutions, Journal of Hazardous Materials 182 (2010) 552-556. [30] Y. Liu, M. Chen, Y. Hao, Study on the adsorption of Cu(II) by EDTA functionalized Fe3O4 magnetic nano-particles, Chemical Engineering Journal 218 (2013) 46–54 [31] M. R. Lasheen, N. S. Ammar, H. S. Ibrahim, Adsorption/desorption of Cd(II), Cu(II) and Pb(II) using chemically modified orange peel: Equilibrium and kinetic studies, Solid State Sciences 14 (2012) 202-210.
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Figure Captions: Fig. 1. Schematic Diagram of preparing magnetic adsorbent Fig. 2. XRD micrographs of two magnetic nanoparticles (a) AC@Fe3O4 and (b) AC@Fe3O4@SiO2-NH2-COOH. Fig. 3. TEM results of prepared magnetic nanoparticle AC@Fe3O4 and AC@Fe3O4@SiO2NH2-COOH. Fig. 4. N2 adsorption isotherm at 77 k for prepared the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH. Fig. 5. FT-IR spectra of (a) AC@Fe3O4, (b) AC@Fe3O4@SiO2, (c) AC@Fe3O4@SiO2-NH2 and (d) AC@Fe3O4@SiO2-NH2-COOH. Fig. 6. DLS results for AC@Fe3O4@SiO2-NH2-COOH. Fig. 7. XPS spectra of AC@Fe3O4@SiO2-NH2-COOH (a) before and (b) after simultaneously adsorption of Pb(II) and Cr(IV). Fig. 8. Effect of pH on the adsorption of (a) Pb(II) and (b) Cr(VI) on AC@Fe3O4@SiO2-NH2COOH, (contact time=120 min, initial concentration = 50ppm). Fig. 9. Effect of temperature of (a) Pb(II) and (b) Cr(VI) solutions versus contact time on AC@Fe3O4@SiO2-NH2-COOH. (Salinity= 20000 ppm, pH=7). Fig. 10. Effect of initial concentration of (a) Pb(II) and (b) Cr(VI) solutions versus contact time on AC@Fe3O4@SiO2-NH2-COOH. (Salinity= 20000 ppm, pH=7 and temperature =25oC). Fig. 11. Removal of Pb(II) and Cr(VI) on AC@Fe3O4@SiO2-NH2-COOH from binary solutions (salinity= 20000 ppm, pH=7 and temperature =25oC).
20
21
22
23
24
25
26
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Table 1. The Boehm test results for AC@Fe3O4@SiO2-NH2-COOH (mequiv./g).
Lactonic
Carboxylic
Phenolic
groups
groups
Groups
Groups
groups= Total oxygen groups
0.01
0.330
0.980
0.425
1.735
Raw Material
AC@Fe3O4@SiO2-NH2-COOH
Total acidic
Basic
28
Table 2. BET, t-plot and BJH results for prepared the almond-activated carbon, AC@Fe3O4 and AC@Fe3O4@SiO2-NH2-COOH. BET
BJH
t-plot
Ref.
Surface area (m2/g)
Total pore volume (cm3/g)
Volume pore (cm3/g)
Surface area (m2/g)
Almond AC
860.70
0.4697
0.1831
913
25
AC@Fe3O4
490
0.3745
0.2193
500
This work
AC@Fe3O4@SiO2NH2-COOH
432
0.3564
0.2155
431.44
Sample
29
This work
Table 3. XRF results for AC@Fe3O4@SiO2-NH2-COOH.
Chemical Element wt.%
AC@Fe3O4@SiO2-NH2-COOH
C
Fe
Si
O
Other Element
25.14
22.18
14.12
28.32
10.24
30