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Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48
Accepted Manuscript Title: Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48 Author: Mansoor Anbia Kazem Kargosha Sanaz Khoshbooei PII: DOI: Reference:
S0263-8762(14)00337-2 http://dx.doi.org/doi:10.1016/j.cherd.2014.07.018 CHERD 1651
To appear in: Received date: Revised date: Accepted date:
6-2-2014 17-7-2014 22-7-2014
Please cite this article as: Anbia, M., Kargosha, K., Khoshbooei, S.,Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48, Chemical Engineering Research and Design (2014), http://dx.doi.org/10.1016/j.cherd.2014.07.018 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.
Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48 Mansoor Anbia∗a, Kazem Kargoshab, Sanaz Khoshbooei c a
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Research Laboratory of Nanoporous Materials, Faculty of Chemistry, Iran University of Science and Technology, Tehran 16846, Iran b
Research Laboratory of Spectroscopy, Chemistry and Chemical Engineering Research Center of Iran, P.O. Box
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14335-186, Tehran, Iran c
Research Laboratory of Advanced Materials, Chemistry and Chemical Engineering Research Center of Iran, P.O.
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Box 14335-186, Tehran, Iran
Corresponding Author: Tel: 0098 21 77240516; Fax: 0098 21 772491204; Email: [email protected]∗
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Abstract A novel magnetic functionalized MCM-48 mesoporous silica with amine (–NH2) and melamine-based dendrimer amines (MDA) were synthesized that can be easily separated from aqueous solutions by applying a magnetic field. The synthesis adsorbent (MDA-magMCM-48) was characterized by low angle XRD, TEM, FT-IR,
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TGA and N2 adsorption-desorption isotherm techniques. Batch adsorption experiments were carried out to study the sorption behavior of MDA-magMCM-48 towards Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions. The adsorption of metal ions was well modeled by pseudo-second-order model and Langmuir sorption isotherm with maximum
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adsorption capacities of 127.24, 125.80, 115.60 and 114.08 mg g-1 Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions, respectively. MDA–magMCM-48 was regenerated and found to be suitable for reuse in successive adsorption-
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desorption cycles three for times without significant loss in adsorption capacity.
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Keywords: Magnetic Mesoporous Adsorbent, Heavy Metal ions Removal, Aqueous Media.
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1. Introduction Removal of heavy metals from aqueous solution is one of the major problem in wastewater treatment because they are mostly toxic even at very low concentration. These pollutants enter in water from industrial applications, including mining, refining and production of textiles, paints and dyes. A wide variety of techniques to remove heavy
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metals from water is available such as ion exchange, reverse osmosis, nanofiltration, precipitation, coagulation/coprecipitation and adsorption (Freeman, 1989; Cheremisinoff, 2002). Adsorption is one of the effective method for heavy metals pollution remedy, due to the fact that adsorption process offers flexibility in design and operation. In
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addition, the regeneration of adsorbent with economic operation may be possible because adsorption is generally reversible (Tang et al., 2008; Paulino et al., 2011). New generation of magnetic sorbents combined magnetic iron
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oxides together with a sorbent material such as activated carbons, clays, zeolites, polymers, biopolymers and silica (Yavuz et al.,2009; Oliveira et al.,2008; Oliveira et al.,2002; Oliveira et al.,2003; Lim and Chen, 2007; Chen et al.,2011) Magnetic mesoporous nano-composite, as a kind of novel functional material, has aroused increasing
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interests for its large surface area, suitable pore size, and uniform pore size distribution. MCM-48 is an important member of the ordered mesoporous molecular sieve family, shows good performance in both catalysis and adsorption processes because of its higher specific surface area (≥1000 cm2 /g) and three-dimensional pore structure
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framework (Hartmann and Bischof, 1999; Igarashi et al., 2007). Beside selecting a functional material to modify the surface is of great importance in developing high performance magnetic adsorbent (Pang et al., 2011). Researchers have used ligands containing multi-amine groups in a chain (Aguado et al., 2009; Vasiliev et al., 2009) or ligands
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involving dendrimer-amines (Jiang et al., 2007) to increase sorption efficiency of heavy metals into the mesoporous structure. Melamine-based dendrimer amines (MDAs) are ideal dendrimer ligands due to intensively binding amine
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sites and also due to their enhanced hydrophilic silica surface compared to analogous adsorbents (Li et al., 2011).
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In this study by introducing Fe3O4 which features super paramagnetism into the prepared mesoporous adsorbent (MCM-48), magnetically separable mesoporous silica (magnetic MCM-48)has been successfully synthesized and modified by melamine. Magnetic separation of this adsorbent makes it a convenient adsorbent for the fast removal of heavy metals from aqueous solutions.
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2. Experimental 2.1. Materials All the reagents used were of analytical grade. Tetraethylorthosilicate (TEOS 98%), cetyltrimethyl ammonium bromide (CTAB, 99%), 3-aminopropyltriethoxysilane (APTES, 98%), N,N-di-isopropylethylamine (DIPEA), 2,4,6-
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trichloro-1,3,5-triazine (cyanuric chloride), ethylenediamine (EDA), Iron(II) Chloride Tetrahydrate (FeCl2·4H2O), Iron(III) Chloride (FeCl3), NH4OH, hydrochloric acid (HCl, 37%), methanol, dichloromethane, tetrahydrofuran, toluene, nitric acid (HNO3, 1%), Pb(NO3 ) 2, Cu(NO3 ) 2.3H2O, Cd(NO3 ) 2.4H2O and K2CrO7 were from E. Merck
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(Darmstadt, Germany).
2.2. Preparation of magnetic Fe3O4 nanoparticles
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The Fe3O4 nanoparticles were prepared by chemical coprecipiation method (Li et al., 2008). Fe3O4 NPs were synthesized by mixing FeCl2·4H2O (2.0 g), FeCl3 (5.2 g) and 0.85 mL hydrochloric acid into 25 mL deionized water degassed with nitrogen before use. The mixture was added to a stirred 250 mL NaOH solution (1.5 M) with nitrogen
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gas passing continuously through the solution during the reaction. The produced magnetic NPs were rinsed with deionized water (5×50 mL) and then resuspended in deionized water (230 mL). The generated NPs concentration
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was estimated to be about 10mg.mL−1.
2.3. Synthesis of magnetic MCM-48 mesoporous silica
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The procedure for preparation of MCM-48 (Kim et al., 2005) was modified by introduction of nanoparticles in reaction mixture. Typically, 6 g cetyltrimethylammonium bromide (CTAB), 35 mL deionized water, 0.549 g NaOH were mixed in flask then this mixture was added to 20 mL of the prepared Fe3O4 spheres slowly under vigorous stirring. After 3 h of stirring, 6.6 mL tetraethylorthosilicate (TEOS) was added drop wise and the stirring was continued until the gel became homogeneous. The whole synthesis was done on a heating mantle at 30-35 ºC. The mixture was filled into a Teflon-lined steel autoclave and statically heated at 135 ºC for 48 h. The resultant was separated by magnetic field and washed several times with deionized water. After vacuum dried at 70 ºC, it was calcined at 540 ºC in air for 6 h. This material is denoted as magMCM-48.
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2.4. Synthesis of amino-modified magMCM-48 To prepare the amino-modified magMCM-48 sample, the procedure was carried out as follows (Anbia and Lashgari, 2009; Tarlani et al., 2006) magMCM-48 (2.0 g) was suspended in (100 mL) toluene and the mixture was stirred for an hour and then to this mixture (3.0 mL) APTES was added and the mixture was refluxed overnight. The
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solid product was separated by applying magnetic field. It was then soxhlet extracted with toluene in order to remove the silylating reagent residue. Finally it was dried at 70 ºC under vacuum. This material was labeled as NH2-
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magMCM-48.
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2.5. Synthesis of MDA–magMCM-48
The MDA–magMCM-48 was synthesized from cyanuric chloride and EDA according to a procedure similar to
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that described previously in literature (Acosta et al., 2004, Liang et al., 2008). Cyanuric chloride (5.5 g; 30 mmol) and DIPEA (7.1 mL: 46 mmol) were dissolved in dried tetrahydrofuran (300 mL) and stirred at 0ºC for 3h under argon atmosphere. NH2–magMCM-48 was added to the mixture and stirred for 24h at 0ºC. The chlorine atom in
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cyanuric chloride was easily replaced by the amine group of the APTES molecule and the DIPEA trap that HCl formed during the substitution reaction. Then the mixture was separated by applying magnetic field and soxhlet extracted with tetrahydrofuran. This solid was transferred back into a clean flask containing a mixture of EDA (4
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mL: 73.84 mmol), dissolved in dried tetrahydrofuran (300 mL) and refluxed for 24 h. The material was separated by magMCM-48.
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2.6. Characterization
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applying magnetic field, then soxhlet extracted with tetrahydrofuran. This resulting substance was denoted MDA–
The X-ray powder diffraction patterns were recorded on a Philips1830 diffractometer using Cu-Kα radiation with a 0.02 step size and 1s step time over the range of 1° <2θ< 10°. Adsorption–desorption isotherms of the synthesized samples were measured at 77K on micrometrics model ASAP2010 sorptometer. Pore size distributions were calculated by the Barrett-Joyner-Halenda (BJH) method, while surface area of the sample was measured by Brunaure–Emmet–Teller (BET) method. The Fourier transform infrared spectra for the unmodified and modified samples were measured on a DIGILABFTS 7000 instrument under attenuated total reflection (ATR) mode using a diamond module. Compositional analyses of magMCM-48 were carried out using an energy dispersive X-ray analysis (EDX) set up attached to an SEM (Philips XL-30). Thermo gravimetric analysis was used to determine the thermal stability of the synthesized materials and was carried out from room temperature to 873 K using a TGA/DTA (Mettler Toledo 851) analyzer at a heating rate of 10 K/min under N2 atmosphere. Metal ions concentration, both in the initial and final solutions, was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).
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2.7. Adsorption studies Batch experiments were performed to measure multi-ions adsorption capacities. For the preparation of aqueous metal solutions, Pb (NO3) 2, Cu (NO3) 2.3H2O, Cd (NO3) 2.4H2O and K2CrO7 were used. A stock solution of 1000 mg
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L−1 of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions was prepared by dissolving the required amounts of Pb(II), Cu(II),Cr(VI) and Cd(II) in 1000 mL double distilled water. Solutions of desired concentration were prepared by diluting the stock solution using double distilled water. All sorption experiments were carried out in batch conditions
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using 25 mL of metal ion solution and 0.025 g of MDA-magMCM-48 as magnetic adsorbent. Shaker was used to mix the suspensions (metal solution–adsorbent) at 250 rpm and 25.0 °C for all tested conditions. Samples were
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pipetted at certain intervals and the adsorbent was separated using a magnet (1.2 T) Fig.1. The sample solutions were spiked with HNO3 to 1% (v/v) and injected to ICP-OES for analysis. The amounts of analyte adsorbed by adsorbents (qe mg g-1) and the removal efficiency (%) of the MDA-magMCM-48 were calculated using Eqs. (1) and
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(2)
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Where qe is the equilibrium adsorption capacity of the adsorbent in mg g-1, C0 is the initial concentration in mg L-1
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and Ce is the concentration at equilibrium of metal ions in mg L-1, V is the volume in L of metal ions solution and W is the weight in g of the adsorbent.
2.8. Kinetic study
The kinetics of the adsorption process was investigated to determine the effect of the initial concentration of metal ions on the qe with respect to time and the time required to achieve equilibrium adsorption. The kinetics study was carried out using 0.025 g of MDA–magMCM-48 in 25 mL of different concentrations (10, 25, 30, 50 ,80 mg L-1) of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions solution at pH 4.0. Two simple kinetic models, namely the pseudo-firstorder and the pseudo-second-order, are the most often used to analyze the rate of sorption. The pseudo-first-order kinetic and the pseudo-second-order kinetic are expressed by Eqs. (3) and (4), respectively (Lagergren, 1898, Ho and. Mckay, 1998). ln (qe-qt) = ln qe - k1t
(3)
t/qt =1/ K2 qe2 + (1/qe)t
(4)
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where qe and qt are the adsorbed metal in mg g-1 on the adsorbent at equilibrium and time t, respectively, k1 is the constant of first-order adsorption in min−1 and k2 is the rate constant of second-order adsorption in mg−1 min−1.
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2.9. Isotherm study The relationship between the amounts of a substance adsorbed per unit mass of adsorbent at constant temperature and its concentration in the equilibrium solution is known as adsorption isotherm. These adsorption data for each Pb
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(II), Cu (II), Cr (VI) and Cd (II) metal ions were fitted into both the Langmuir and Freundlich isotherm equations which corresponds to homogeneous and heterogeneous adsorbent surfaces. The Langmuir model is given by Eq (5)
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(Morey et al., 2000):
were qm (mg g-1) and b (L mg-1) are maximum adsorption capacity of adsorbent and the Langmuir constant related to the adsorption energy coefficient, respectively. The essential features of the Langmuir isotherm can also be
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expressed in terms of dimensionless constant separation factor RL, which is defined as Eq (6):
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The RL value indicates the shape of isotherm (Zolfaghari et al., 2011). RL values between 0 and 1 indicate favorable adsorption, while RL > 1 and RL = 0 indicate unfavorable and irreversible adsorption isotherm (Zheng et al., 2008).
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The Freundlich model can be expressed by the following equation (Ho et al., 2002):
where kf (mg g-1) and n (L mg-1) are the Freundlich constants related to adsorption capacity and intensity, respectively. The nonlinear regression analysis was carried out with SigmaPlot software (SigmaPlot 10.0, SPSS Inc, USA) in order to predict both the kf and the n parameters.
3.Results and discussion 3.1. Characterization of synthesized adsorbent SEM and TEM images of the magMCM-48 are presented in Fig. 1. The magMCM-48 typically exhibits a Spherelike morphology and Fe3O4 nanoparticles are distributed in the mesoporous MCM-48.
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Fig.2.
The low-angle XRD spectra of magMCM-48, NH2–magMCM-48 and MDA-magMCM-48 are recorded in Fig.3. The XRD patterns of magMCM-48 exhibit strong (211) peak and proportional (220) peak intensities. In comparison
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between the XRD patterns before and after modification with melamine-based dendimer amine complexes, the peaks of magMCM-48 remained. This confirms that the overall ordered structure of the mesoporous silica is not seriously perturbed. The intensities of the XRD peaks for NH2–magMCM-48 and MDA-magMCM-48 are
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substantially lower than those measured for magMCM-48, which is probably caused by the pore filling effect of the
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Fig.3.
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magMCM-48 channels (Liang et al., 2008).
The amine groups and melamine-based dendrimers in the silicate frameworks were also identified using FT-IR.
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Fig. 4 shows the FT-IR spectra of the modified sample along with the unmodified mesoporous mag-MCM-48. The typical Si–O–Si bands at 462, 810 and 1075 cm−1 present in all samples are attributed to the condensed silica network (Socrates, 2004) magMCM-48 exhibits an absorption band at about 3400 cm−1, attributed to the –OH
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stretching vibrations of silanol groups. The band at 1695 cm−1 is probably attributed to NH2 bending, especially intensive for the NH2 –magMCM-48 sample, indicating the presence of primary amine. The stretching bands at 2950
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and 3076 cm−1 are attributed to asymmetric and symmetric C–H stretching in the propyl chain. The band at 1642 cm−1 (MDA–magMCM-48 spectrum) is the evidence of an aromatic triazine ring in the MDA–magMCM-48 sample
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and confirms that the melamine-based dendrimer are formed (Yoo et al., 2006). These results confirm that magMCM-48 with aminopropyl and melamine-based dendrimer groups has been successfully modified. Fig.4.
Thermogravimetric analysis (TGA) curves for NH2–magMCM-48 and the MDA–magMCM-48 samples show very slow but continuous weight loss. The weight loss observed below 150 ºC in representative samples is associated with desorption of water. The weight loss between 150 and 840 ºC was used as the baseline amount for the organic moieties of each sample, however, most of the weight loss above 600 ºC is due to the dehydroxylation of the silicate networks. In Fig.5, the aminopropyl loaded on the surface of magMCM-48 was calculated to be about 0.36 mmol g-1 (8.01% weight loss) in the NH2–magMCM-48 sample and amount of the dendrimer ligand was calculated to be about 0.69mmol g-1 (17.49% weight loss) on the surface of the MDA–magMCM-48 sample.
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Fig.5. Fig. 6 shows the adsorption/desorption isotherms of nitrogen at 77K on MDA-magMCM-48. which exhibits a type IV profile according to the BET classification. The pore diameter value about 3.46 nm is observed for MDAmagMCM-48 in the pores size distribution (BJH) analysis of nitrogen desorption isotherm. Fig. 5 shows one strong peak for the pore diameter 3.46 nm. The results for N2 adsorption–desorption containing the pore diameters, the
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BET surface and the total pore volume of the calcined MDA-magMCM-48 sample are recorded in Table 1.
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Table 1.
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Fig. 6.
3.2. Adsorption studies
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3.2.1. Effect of initial concentration
Initial concentration is one of the important factors for determining the adsorption capacity of an adsorbent. The effects of initial concentration (10, 25, 30, 50, 80 mg L-1) on metal ions adsorption were carried out with 0.025 g of
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MDA– magMCM-48 adsorbent dose in 25 mL of multi- ions metal solution at pH 4.0, each containing 50 mg L-1 of
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Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions. Fig.7 shows the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions with its concentration. It is observed that the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions is high at lower concentration and gradually decreases as the concentration of metal ions increase.
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This is due to the fact that after the formation of mono-ionic layer at lower concentration on the adsorbent surface, further formation of the layer is highly hindered at higher concentration due to the interaction between metal ions present on the surface and in the solution. In addition, at low concentration of the of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions, the ratio of the initial number of moles of the metal ions to the available surface area of the adsorbent is large and subsequently, the fraction of the adsorption becomes independent of the initial concentration of the metal ion, But at higher concentration, the sites available for adsorption becomes lesser and hence, the removal efficiency of the metal ions at higher concentration decreases (Kanthimathi et al., 2012; Panda et al., 2011).The optimum concentration of the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions is found to be 50 mgL-1 due to maximum adsorption capacity.
Fig.7.
3.2.2. Effect of the adsorbent dose
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The effect of the dose of MDA-magMCM-48 (0.2,0.5,1, 1.2 and 1.5 g L-1), adsorbent on removal of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions at 50 mg L-1 has been studied. pH of the working solution was adjusted to 4.0 by adding 0.1M NaOH. These results are depicted in (Fig. 8). It is clear that the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions increases as the amount of the adsorbent increases owing to the enhanced total surface area of the adsorbent. The results revealed that the metal removal percentage is dependent on the optimal
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increase of the adsorbent dose, due to a consequential increase in interference between binding sites at the higher dose or an insufficiency of metal ions in solution with respect to available binding sites. The maximum metal ions removal was attained at about 1 g L-1 dose of MDA–magMCM-48 (97.8% for Pb (II), 94.92% for Cu (II), 91.8% for
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Cr (VI) and 88.52% for Cd (II) and was almost the same even at higher doses. Therefore, the MDA-magMCM-48
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Fig.8.
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with 1 g L-1 dose was chosen as the optimum amount of the adsorbent for further experiments.
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3.2.3. Effect of chemical modification
In order to evaluate the efficiency of the prepared adsorbents, the effect of MDA-magMCM-48 ( before and after functionalization) on adsorption of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions at 50 mg L-1 and pH, 4.0 were studied
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The experiments were performed to optimize the adsorbent conditions (1 g L-1 of each adsorbent type) for removal of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions. The Fig. 9 shows the adsorption of each metal ion on magMCM-
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48, NH2-magMCM-48 and MDA-magMCM-48. It is seen that the order of adsorption in terms of the treated and untreated adsorbent is: MDA-magMCM-48>NH2-magMCM48>mag-MCM-48. MDA-magMCM-48 which shows
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much higher metal ions removal efficiency compared to magMCM-48 and NH2-magMCM-48, which may be due to the grafted dendrimer amine groups on the surface of silica and its more active adsorption sites. Due to interaction between the lone pair of electrons on nitrogen (the synthesized adsorbent) and the metal ions M(II) species, the adsorption takes place. The multifunctional amine groups on the surface of the MDA-magMCM-48 are responsible for higher removal efficiency of MDA–magMCM-48 compared to NH2–magMCM-48. Therefore MDA–magMCM48 was chosen as an appropriate adsorbent.
Fig.9
3.2.4. Effect of the solution pH The surface charge and the protonation degree of the adsorbent were significantly influenced by the pH value, (Deng and Ting, 2005).
To investigate the effect of the different solution pH on adsorption, 0.025 g of MDA–
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magMCM-48 in 25 mL of different metal ions solution containing 50 mg L-1 of Pb (II), Cu (II), Cr (VI) and Cd (II) was shaken separately for 90 min. The pH was adjusted to values ranging from 2 to 6 using 1M HCl and 0.1M NaOH solution. The conical flasks were agitated at 250 rpm using shaker to reach equilibrium. After magnetic separation of adsorbent, the concentration of the remaining metal ions in aqueous phase was measured. These results are depicted in Fig.10. The metal uptake increases with the increase of the pH from 2 till it reaches a maximum at 4,
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and decreases at the pH values higher than 4. To explain this observation, the presence of dominant metal ions M(II) species at pH> 6 are M(OH)2 and at pH< 6 M(OH)+, therefore, most ions are not accessible to adsorb at higher pH values and consequently the removal efficiency is decreased. The removal efficiency was 66.65%, 61.11%,84.23%
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and 52.54% for Pb(II), Cu(II),Cr(VI) and Cd(II), respectively at pH 2 and these values increased to 97.8%, 94.92%, 91.8% and 88.52% for Pb(II), Cu(II),Cr(VI) and Cd(II), respectively, with pH increase to 4. This is because at low
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pH values there is an excessive protonation of the lone pair of electrons on nitrogen, resulting in a decrease in the sorption of heavy metal ions (Benhamou et al., 2009; Heidari et al., 2009). Also, at a very low solution pH, the concentration of the hydrogen ions is high, directly competing with the heavy metal ions for active binding sites.
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Therefore, the increase in metal removal as the pH increases can be explained on the basis of a decrease in competition between proton ions (H+) and positively charged metal ions at the adsorbent surface sites. It is well known that Cr (VI) exists mainly in the form of HCrO4- or Cr2O72- at low pH, and as CrO42- at high pH (Natale et al.,
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2007; Hu et al., 2005; Park and Jang, 2002). Therefore sorption of Cr (VI) metal ion due to the charge of surface sites (NH3+ at pH lower than 4) is more in comparison with Pb(II), Cu(II) and Cd(II)metal ions. It is clear that negatively charged HCrO4- and Cr2O72- are easily adsorbed on the positively charged MDA-magMCM-48 at low pH
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values due to the electronic attraction (Hu et al., 2009). The maximum adsorption was observed at pH 4.0 for all
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ions. However, on increasing the pH further, the metal speciation in solution may become an important factor and the increase in heavy metal removal has been attributed to reduced solubility and to precipitation of solid metal
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hydroxide. In the present study, adsorption could not be carried out beyond pH 6.0 due to precipitation of Pb(OH)2, Cu(OH)2, and Cd(OH)2 and the (CrO42-) at higher pH values, therefore, the experiments were performed at the pH value of 6. When pH was increased from 4 to 5, the removal efficiency of Cd(II) decreased from 88.52% to 74.3% and Cr(VI) from 91.8%to 63.6% while that of Pb(II) and Cu(II) remained the same at pH 5(Fig.9). It may be due to the lower Ksp value of Cd (II) compared to Pb (II), Cu (II) and Cr (VI) while increasing the pH resulted quickly in a decrease of its solubility. The electrostatic repulsion between negative Cr (VI) species and the lone pair of electrons on the surface of MDA-magMCM-48 leads to decrease of adsorption of Cr (VI) ions. However, when the pH is increased from 5 to 6, the removal efficiency of all studied ions was decreased because of ion precipitation for Pb (II), Cu (II) and Cd (II) and electrostatic repulsion of Cr (VI) metal ions.
Fig. 10
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3.2.5. Effect of contact time Contact time is another effective factor in batch adsorption process. In order to establish an equilibration time for the maximum uptake, the adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 was studied as a function of contact time. For this purpose 0.025 g of MDA–magMCM-48 in 25 mL of multi-ions solution
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containing 50 mg L-1 of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions was shaken for 10,30,60,90,120 and 180 min. Fig.11 shows the variation of the removal efficiency of the Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions MDAmagMCM-48 with contact time. The adsorption rate was very fast and achieved adsorption equilibrium within 90
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min. The rapid uptake (more than 70% equilibrium adsorption in first 10 min) revealed a high affinity between the heavy metals and the adsorbent, which was directly be attributed to the MDA-grafted magnetic porous adsorbent. In
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addition, the heavy metals removal sequence onto MDA-magMCM-48 was in the order of Pb(II) > Cu(II) > Cr(VI) > Cd(II). Physico-chemical properties of metal ions such as electro-negativity, atomic weight and ionic radius may
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be responsible for the selectivity observed (Heidari et al., 2009).
3.2.6. Kinetic study
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Fig.11
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Adsorption kinetic model not only allows estimation of adsorption rate but also provides insights into rate expression characteristic of possible reaction mechanism. It was pointed out that pseudo second-order adsorption
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model was based on the assumption that the rate-controlling step of chemisorption involved valence forces through sharing or exchange of electrons between adsorbent and adsorbate, was able to better describe the adsorption kinetic (Murugesan et al., 2011; Reddad et al., 2002). As recorded in Table 2, the experimental data are in well agreement with the pseudo-second-order model, which suggests that the adsorption rate of the heavy metals was controlled by chemical processes. The adsorption rate is related to the content of the active adsorption sites on the matrix of the adsorbent and also on the metal ionic radius (Jing et al., 2009). According to Table 2, Pb(II) ions with a greater ionic radius show the higher adsorption rate. The reason for this can be explained by the fact that the Pb(II) ions win over the other ions competition for occupying the active sites on the silica surface due to the higher atomic weight, greater electro-negativity and ionic radius of Pb(II) and smaller Z/R (charge/radius) ratio than those of Cu(II), Cr(VI) and Cd(II) (Heidari et al., 2009; Jing et al., 2009). As seen in Table 2, when the initial ions concentration increases from30 to 80mg L-1, the pseudo-second-order constants diminish. It means that the value of k depends on the C and the adsorption rate decreases when the initial ions concentration increase.
Table 2.
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3.2.7. Isotherm study
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The nonlineared Langmuir and Freundlich adsorption isotherms of the Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions obtained with the adsorbent dose of 1 g L-1 and the temperature of 25 ◦C are shown in Fig12. The b, qm, n, Kf values and the nonlinear regression correlation coefficients (R2) for Langmuir and Freundlich isotherms are listed in
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Table 3.The correlation coefficients indicate that adsorption is fitted better by the Langmuir (R2 = 0.992–0.998) than the Freundlich model (R2 = 0.985–0.988), as shown in Fig. 11. Therefore, the adsorption process can be described
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by the formation of monolayer coverage of the adsorbate on the adsorbent surface. The maximum adsorption capacity (qm) was determined as 127.24, 125.80, 115.60 and 114.08 mg g-1 for Pb (II), Cu (II), Cr (VI) and Cd (II), respectively. For clarifying the favorableness for adsorption of each metal ion, we also calculated the separation
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factor (RL), as summarized in Table 4, i.e. 0 < RL <1, revealing that the adsorption of the selected metal ions was
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favorable.
Table 3.
Fig.12
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te
d
Table 4.
3.2.8. Desorption
Desorption ability of the MDA–magMCM-48 was evaluated by HCl acid with different concentrations (0.1, 0.2, 0.3 and 0.4 M) treatment and depicted in Fig.13 (A). The 0.3M HCl was more suitable concentration. The adsorbent was reused in three successive adsorption–desorption cycles. Fig. 12 (B) shows the removal efficiency Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions over three successive adsorption–desorption cycles. It was observed that nearly over 93% removal efficiency was reached in the first cycle for Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions. Even though the efficiency decreases with the increasing of cycle, over 87% efficiency was obtained in the third absorption–desorption cycle, demonstrating that the prepared adsorbent is cost-effective, and its regeneration by 0.3 M HCl acid is quite effective.
Fig.13
13
Page 13 of 39
3.2.9. Comparison with other adsorbents The value of qm is maximum adsorption capacity of adsorbent, and is useful in scale-up considerations. Table 5 shows a comparison of the adsorbent capacity of various adsorbents for Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions.
ip t
Table 5
cr
4. Conclusion
MDA-grafted magnetic porous adsorbent combining magnetic separation technique and porous properties has
us
been developed for removal of heavy metals from aqueous system. The results show that MDA–magMCM-48 has a significant adsorption capacity for Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions, compared to NH2-magMCM-48 and untreated mag-MCM-48. The adsorption of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions is well modeled by pseudo-
an
second-order model and Langmuir sorption isotherm, and the adsorbent has presented a preferential binding capacity of Pb(II) > Cu(II) > Cr(VI)>Cd(II). This adsorbent can be used repeatedly by effective regeneration using 0.3 M HCl acid. Thus it could be concluded that the MDA-magMCM-48 with convenient separation capability great
Ac ce p
te
d
M
potential as an adsorbent for removal metal ions from aqueous solution.
14
Page 14 of 39
Reference Acosta, E.J., Carr C.S., Simanek ,E.E., Shantz, D.F., 2004. Engineering nanospaces: iterative synthesis of melaminebased dendrimers on amine-functionalized SBA-15 leading to complex hybrids with controllable chemistry and porosity. Adv. Mater., 16, 985–989.
ip t
Aguado, J., Arsuaga, J.M., Arencibia, A., Lindo, M., Gascón ,V., 2009. Aqueous heavy metals removal by adsorption on amine-functionalized mesoporous silica. J. Hazard Mater. ,163, 213–221.
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Anbia, M., Lashgari, M., 2009. Synthesis of amino-modified ordered mesoporous silica as a new nano sorbent for the removal of chlorophenols from aqueous media. J. Chem. Eng., 150, 555–560.
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Benhamou,A., Baudu, M., Derriche, Z.,Basly, J.P., 2009. Aqueous heavy metals removal on aminefunctionalized Si-MCM-41 and Si-MCM-48. J. Hazard Mater., 171, 1001–1008. Chen,X.,Lam,K.F.,Yeung,K.L.,2011.Selective removal of chromium using magnetic MCM-41 nanosorbents, . J. Chem. Eng., 172, 728-734.
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Cheremisinoff, N.P., 2002. in: Butterworth, Heineman (Eds.), Handbook of Water and Wastewater Treatment Technologies.
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Deng, S.B., Ting, Y.P., 2005.Characterization of PEI-modified biomass and bio sorption of Cu(II) Pb(II) and Ni(II). Water Res.,39, 2167–2177. Freeman, H.F., 1989. Standard Handbook of Hazardous Waste Treatment and Disposal, McGraw–Hill, New York.
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Hartmann, M., Bischof, C., 1999. Mechanical stability of mesoporous molecular sieve MCM-48 studied by adsorption of benzene, n-heptane, and cyclohexane. J. Phys. Chem. B., 103 (30), 6230- 6235.
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Heidari, A., Younesi, H., Mehraban, Z., 2009. Removal of Ni(II), Cd(II), and Pb(II) from a ternary aqueous solution by amino functionalized mesoporous and nano mesoporous silica. J. Chem. Eng., 153, 70–79.
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Ho, Y., Porter, J., McKay, G., 2002. Equilibrium isotherm studies for the sorption of divalent metal ions onto peat: copper, nickel and lead single component systems. Water. Air. Soil Pollut., 141, 1–33. Ho, Y.S., Mckay, G., 1998. Kinetic model for lead (II) sorption on peat. Adsorpt. Sci.Technol., 16, 243–255. Hu, J, Chen, GH, Lo, I.M.C., 2005. Removal and recovery of Cr (VI) from wastewater by maghemite nanoparticles.Water Res., 39, 4528-36. Hu, J., Wang, S.W., Shao1, D.D., Dong, Y.H., Li, J.X., Wang, X.K., 2009. Adsorption and Reduction of Chromium(VI) from Aqueous Solution by Multi walled Carbon Nanotubes. The Open Environmental Pollution & Toxicology Journal ,1, 66-73.
Igarashi, N., Hashimoto, K., Tatsumi, T., 2007. Catalytical studies on trimethylsilylated Ti-MCM-41 and Ti-MCM 48 materials. Micropor. Mesopor. Mater., 104 , 269-280. Jiang, Y., Gao, Q., Yu, H., Chen, Y., Deng, F., 2007. Intensively competitive adsorption for heavy metal ions by PAMAM–SBA-15 and EDTA–PAMAM–SBA-15 inorganic-organic hybrid materials. Micropor. Mesopor. Mater., 103, 316–324.
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Jing, X., Liu, F., Yang, X., Ling, P., Li, L., Long, C., Li, A., 2009. Adsorption performances and mechanisms of the newly synthesized N,N-di (carboxymethyl) dithiocarba-mate chelating resin toward divalent heavy metal ions from aqueous media. J. Hazard Mater., 167, 589–596.
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Kanthimathi, G., Kotteeswaran, P., Thilai Arasu, P., Govindaraj, P., Kottaisamy, M., 2012. A Comparative Study of the Adsorption Efficiency of the Newly Synthetic Nano Iron Oxide and Commercial Activated Charcoal Towards the Removal of the Nickel(II) Ions. J. Chem. Eng., 9(4), 2384-2393.
cr
Kim, T.W., Kleitz, F., Paul, B., Ryoo, R., 2005. MCM-48-like Large Mesoporous Silicas with tailored Pore structure: facile synthesis domain in a ternary triblock copolymer-butanol-water system. J. A. C. S., 127, 76017610.
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Lagergren, S., 1898. About the theory of the so-called adsorption of soluble substances. Kungliga Svenska Vetenskapsakademius, Hadndlingar , 24, 1–39. Li, G., Zhao, Z., Liu, J., Jiang ,G., 2011. Effective heavy metal removal from aqueous systems by thiol functionalized magnetic mesoporous silica. J. Hazard Mater., 192, 277– 283.
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Li, J., Zhao, X., Shi, Y., Cai, Y., Mou, S., Jiang, G., 2008. Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols environmental water samples coupled with liquid chromatography/spectrophotometry detection. J. Chromat. A., 1180, 24–31. Liang, Z., Fadhel, B., Schneider, C.J., Chaffee, A.L., 2008. Stepwise growth of melamine based dendrimers into mesopores and their CO2 adsorption properties. Micropor. Mesopor. Mater., 111, 536–543.
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Lim, S.F., Chen, J.P.,2007. Synthesis of an innovative calcium–alginate magneticsorbent for removal of multiple contaminants, Appl. Surf. Sci., 253, 5772–5775.
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Morey, M.S., O’Brien, S., Schwarz, S., Stucky, G.D., 2000. Hydrothermal and post synthesis surface modification of cubic, MCM-48, and ultra large pore SBA-15 mesoporous silica with titanium. Chem. Mater., 12, 898–911. Murugesan, A., Ravikumar, L., SathyaSelvaBala, V., SenthilKumar, P., Vidhyadevi, T., 2011. Removal of Pb(II), Cu(II) and Cd(II) ions from aqueous solution using poly azomethine amides: equilibrium and kinetic approach. Desalination, 271,199–208. Natale,D. F., Lancia ,A., Molino, A., Musmarra, D., 2007.Removal of chromium ions form aqueous solutions by adsorption on activated carbon and characterization. J. Hazard Mater., 145, 381-90. Oliveira, L.C.A., Petkowicz, D.I., Smaniotto, A., Pergher, S.B.C.,2008. Magnetic zeolites: a new adsorbent for removal of metallic contaminants from water. Water Res.,38 ,3699–3704. Oliveira, L.C.A., Rios, R.V.R.A., Fabris, J.D.V., Garg, K., Sapag, R.M., Lago, R.M., 2002. Activated carbon iron oxide magnetic composites for the adsorption of contaminants in water, Carbon, 40, 2177–2183. Oliveira, L.C.A., Rios, R.V.R.A., Fabris, J.D.V., Garg, K., Sapag, R.M., Lago, R.M., 2003. Clay–iron oxide magnetic composites for the adsorption of contaminants in water, Appl. Clay Sci., 22,169–177. Panda, L, Das, B, Rao, D. S , Mishra, B. K, 2011. Application of dolochar in the removal of cadmium and hexavalent chromium ions from aqueous solutions. J. Hazard Mater., 192, 822-831.
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Pang, Y., Zeng, G., Tang, L., Zhang, Y., Liu, Y., Lei, X., Li, Z., Zhang, J., Xie, G., 2011. PEI-grafted magnetic porous powder for highly effective adsorption of heavy metal ions. Desalination, 281, 278–284. Park, S.J, Jang, Y.S, 2002. Pore structure and surface properties of chemically modified activated carbons for adsorption mechanism and rate of Cr (VI). J. Colloid Interf. Sci., 249, 458-63.
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Paulino, A.T., Belfiore, L.A., Kubota, L.T., Muniz, E.C., Almeida, V.C., Tambourgi, E.B., 2011. Effect of magnetite on the adsorption behavior of Pb(II), Cd(II), and Cu(II) in chitosan-based hydrogels. Desalination, 275, 187–196.
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Reddad, Z., Gerente, C., Andres, Y., Cloirec, P.L., 2002. Adsorption of several metal ions onto a low-cost bio sorbent: kinetic and equilibrium studies. Environ. Sci. Technol., 36, 2067–2073.
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Socrates, G., 2004. Infrared and Raman characteristic group frequencies: tables and charts, 3rd eds., John Wiley & Sons, Ltd,.
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Tang ,L., Zeng, G.M., Shen, G.L., Li, Y.P., Zhang ,Y., Huang, D.L., 2008. Rapid detection of picloram in agricultural field samples using a disposable immune membrane based electrochemical sensor. Environ. Sci. Technol., 42, 1207–1212. Tarlani, A., Abedini ,M., Nemati, A., Khabaz, M., Amini, M. M., 2006. Immobilization of keggin and preyssler tungsten heteropolyacidson various functionalized silica. J. Colloid Interface Sci., 303, 32–38.
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Vasiliev, A.N., Golovko, L.V., Trachevsky, V.V., Hall, G.S., Khinast, J.G., 2009. Adsorption of heavy metal cations by organic ligands grafted on porous materials. Micropor. Mesopor. Mater. ,118, 251–257.
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Wang, J., Ma, X., Fang, G., Pan, M., Ye, X., Wang, S., 2011. Preparation of iminodiacetic acid functionalized multiwalled carbon nanotubes and its application as sorbent for separation and preconcentration of heavy metal ions. J. Hazard. Mater., 186, 1985–1992
Ac ce p
Yavuz, C.T., Prakash, A., Mayo, J.T., Colvin, V.L., 2009. Magnetic separations: from steel plants to biotechnology. Chem. Eng. Sci., 64, 2510–2521. Yoo, S., Lunn, J.D., Gonzalez, S., Ristich, J.A., Simanek, E.E., Shantz, D.F., 2006. Engineering nanospaces: OMS/dendrimer hybrids possessing controllable chemistry and porosity. Chem. Mater., 18, 2935–2942. Zhang, L., Yu. C., Zhao, W., Hua, Z., Chen, H., Li, L., Shi, J., 2007. SBA-15 functionalized with Trimethoxysilylpropyle Dithyenetriamine. J. Non-Cryst. Solids, 353, 4055 Zheng, H., Han, L., Maa, H., Zheng, Y., Zhang, H., Liu, D., Liang, S., 2008. Adsorption characteristics of ammonium ion by zeolite 13X. J. Hazard Mater., 158, 577–584. Zolfaghari, G., Esmaili-Sari, A., Anbia, M., Younesi, H., Amirmahmoodi, S., Ghafari-Nazari, A., 2011. Taguchi optimization approach for Pb (II) and Hg(II) removal from aqueous solutions using modified mesoporous carbon, J. Hazard Mater., 192, 1046–1055. Table List: Table 1. Textural properties of MDA-magMCM-48. Table 2. Kinetic adsorption parameters obtained using pseudo-first-order and pseudo-second-order models.
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Table 3. Langmuir and Freundlich parameters for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) onto MDA– magMCM-48. Table 4. RL values for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) based on the Langmuir equation.
cr
ip t
Table 5. Comparison of adsorption capacity Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions onto some adsorbents.
us
Figure List:
Fig.1. Schematic illustration of magnetic separation of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
an
magMCM48.
Fig.2. Images of (a) Scanning Electron Microscopy (SEM) and (b) Transmission Electron Microscopy (TEM) of magMCM-48.
M
Fig.3. XRD patterns of magMCM-48, NH2-magMCM-48, MDA-magMCM-48. Fig.4. FT-IR spectra of magMCM-48, NH2-magMCM-48, MDA-magMCM-48. Fig.5. Thermogravimetric curves of NH2– magMCM-48 and MDA– magMCM-48.
d
Fig.6. N2 adsorption and desorption isotherms at 77 K of MDA-magMCM-48. The inset shows the BJH pore size
te
distribution of MDA-magMCM-48 calculated from the desorption branch of the isotherm. Fig.7. Effect of initial concentration on adsorption of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
magMCM48.(Contact time = 90 min, agitation speed = 250 rpm, adsorbent dosage = 1 g L−1, pH = 4.0). Fig.8. Effect of adsorbent dose on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal percentage by MDAmagMCM48 ( initial concentration of metal ion 50mg L-1, initial pH value 4.0, agitation time 90 min, agitation speed 250 rpm and at 25 ◦C).
Fig. 9.Effect of chemical modification of mag-MCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (adsorbent dosage = 1 g L−1,initial concentration of metal ion 50mgL-1, initial pH value 4.0, contact time 90 min, agitation speed 250 rpm and at 25 ◦C). Fig. 10. Effect of pH on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ion 50mgL-1, adsorbent dosage = 1 g L−1, contact time 90 min, agitation speed 250 rpm and at 25 ◦C). Fig.11. Effect of contact time of MDA-magMCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ions 50mg L-1, adsorbent dosage = 1 g L−1, initial pH value 4.0,agitation speed 250 rpm and at 25 ◦C). Fig.12. Adsorption isotherm of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 at the adsorbent dose of 1g L-1, pH 4.0 and ambient temperature.
18
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Fig.13. Effect of HCl concentration on desorption of Pb(II), Cu(II),Cr(VI) and Cd(II) (A), Regeneration of MDAmagMCM-48 for adsoption of Pb(II), Cu(II),Cr(VI) and Cd(II) at the adsorbent dose of 1g L-1, pH 4.0, initial
Ac ce p
te
d
M
an
us
cr
ip t
concentration 50 mg L-1 and ambient temperature(B).
19
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Table 1: Textural properties of MDA-magMCM-48. d spacing (nm)
A BET (m 2 g -1 )
) cm 3 g -1 Vp (
MDA-magMCM-48
3.46
511
0.44
Ac ce p
te
d
M
an
us
cr
ip t
Adsorbent
20
Page 20 of 39
ip t cr
Metal
Experimental
ions
conc.(mg/L)
qe(mg/g)
Cr(VI)
Cd(II)
29.39
0.030
50
48.90
0.028
77.10
0.030
30
28.60
0.024
50
47.46
80
73.77
30
27.70
50
45.90
k2(g.mg-1 min-1)
9.87
0.983
8.81×10-3
29.41
0.997
13.89
0.989
6.51×10-3
48.54
0.998
0.988
3.58×10
-3
76.92
0.998
0.960
8.55×10-3
28.01
0.995
-3
47.62
0.998
24.54
d
80
Calculated
R2
qe(mg/g)
te
Cu(II)
30
9.79
R2
qe(mg/g)
0.031
15.45
0.997
5.71×10
0.034
24.68
0.998
3.59×10-3
74.63
0.999
0.028
9.62
0.982
8.82×10-3
27.47
0.997
0.995
5.74×10
-3
45.87
0.998
-3
69.93
0.999
Ac ce p
Pb(II)
Calculated
k1(min-1)
M
Metal
Pseudo-second-order
an
Pseudo-first-order
us
Table 2: Kinetic adsorption parameters obtained using pseudo-first-order and pseudo-second-order models.
0.029
15.17
80
69.77
0.032
21.50
0.994
4.21×10
30
26.89
0.022
11.58
0.995
8.13×10-3
27.73
0.999
0.998
6.95×10
-3
43.10
0.999
5.48×10
-3
64.51
0.999
50 80
44.26 66.55
0.025 0.022
13.57 17.50
0.998
21
Page 21 of 39
ip t cr
us
Table 3: Langmuir and Freundlich parameters for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) onto MDA– magMCM-48.
b (L/mg)
R2
Pb(II)
127.24
0.534
Cu(II)
125.80
0.229
Cr(VI)
115.60
0.150
Cd(II)
114.08
n
R2
0.992
41.64
1.68
0.998
0.997
24.22
1.61
0.987
0.995
17.65
1.66
0.985
0.105
0.996
13.79
1.63
0.988
Ac ce p
te
Kf
d
q m (mg/g)
M
Metal ions
Freundlich
an
Langmuir
22
Page 22 of 39
ip t cr us
Table 4: RL values for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) based on the Langmuir equation.
Cu(II)
10
0.16
0.30
25
0.07
0.15
30
0.06
0.60
50
0.04
0.08
80
0.02
0.05
d
M
Pb(II)
Cr(VI)
Cd(II)
0.40
0.48
0.21
0.27
0.18
0.24
0.12
0.16
0.08
0.11
Ac ce p
te
Initial conc.(mg/L)
an
RL Value
23
Page 23 of 39
ip t cr us
Table 5: Comparison of adsorption capacity Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions onto some adsorbents.
113
SBA-15 functionalized with Trimethoxysilylpropyle Dithyenetriamine
11
Cu(II) 9.4
Cd(II) _
Cr(II) _
1.1
1.0
1.1
_
L.Zhang et.al,2007
57.7
_
18.2
_
A.Heidari et.al, 2009
8.98
6.64
6.61
8.96
J.Wang et.al, 2011
127.24
125.80
114.08
115.6
This study
Pb(II) _
50
References J.Aguado et.al,2008
Ac ce p
mag-MCM-48 modified with melamine
1µg
te
Multi-walled carbon nanotubes functionalized with iminodiacetic acid
d
50
MCM-41 modified with 3aminopropyltriethoxysilane
an
SBA-15 functionalized with N-[3(Trimethoxysilyl)propyl]ethylenediamine
qm (mg/g)
M
C0 ( mg/L)
Adsorbent
24
Page 24 of 39
ip t cr us
an
Fig.1. Schematic illustration of magnetic separation of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
te
d
M
magMCM48.
25
Page 25 of 39
ip t cr us an M d te Ac ce p
Fig.2. Images of (a) Scanning Electron Microscopy (SEM) and (b) Transmission Electron Microscopy (TEM) of magMCM-48.
26
Page 26 of 39
<211> magMCM-48 NH2-magMCM-48
cr
Intensity.a,u
ip t
MDA-magMCM-48
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
an
1.0
us
<220>
2Teta,Degree
Fig.3. XRD patterns of magMCM-48, NH2-magMCM-48, MDA-magMCM-48.
M
Ac ce p
te
d
27
Page 27 of 39
ip t cr us an
M
Fig.4. FT-IR spectra of magMCM-48, NH2-magMCM-48, MDA-magMCM-48.
Ac ce p
te
d
28
Page 28 of 39
105 MDA-magMCM-48 NH2-magMCM-48
95
ip t
Weight loss %
100
90
cr
85
75 0
100
200
300
400
500 0
Temprature C
us
80
600
700
800
M
an
Fig.5. Thermogravimetric curves of NH2– magMCM-48 and MDA– magMCM-48.
Ac ce p
te
d
29
Page 29 of 39
ip t cr us an M d te Ac ce p
Fig. 6. N2 adsorption and desorption isotherms at 77 K of MDA-magMCM-48. The inset shows the BJH pore size distribution of MDA-magMCM-48 calculated from the desorption branch of the isotherm.
30
Page 30 of 39
ip t
100
cr
98
us
94 92
an
90 88 86
Pb Cu Cr Cd
84 82 0
20
M
Removal efficiency%
96
40
60
80
100
d
C0(mg/L)
te
Fig.7. Effect of initial concentration on adsorption of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
magMCM48.(Contact time = 90 min, agitation speed = 250 rpm, adsorbent dosage = 1 g L−1, pH = 4.0).
31
Page 31 of 39
110 100
ip t
80
cr
70 60
Pb Cu Cr Cd
50
us
Removal efficiency%
90
40
an
30 20 0.0
0.2
0.4
0.6
0.8
1.0
1.4
1.6
M
Dose of adsorbent(g)
1.2
Fig.8. Effect of adsorbent dose on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal percentage by MDA-
Ac ce p
te
speed 250 rpm and at 25 ◦C).
d
magMCM48 ( initial concentration of metal ion 50mg L-1, initial pH value 4.0, agitation time 90 min, agitation
32
Page 32 of 39
ip t cr us an
Fig. 9.Effect of chemical modification of mag-MCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (adsorbent dosage = 1 g L−1,initial concentration of metal ion 50mgL-1, initial pH value 4.0, contact time 90 min, ◦
Ac ce p
te
d
M
agitation speed 250 rpm and at 25 C).
33
Page 33 of 39
ip t cr us
an
Fig. 10. Effect of pH on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ion ◦
50mgL-1, adsorbent dosage = 1 g L−1, contact time 90 min, agitation speed 250 rpm and at 25 C).
M
Ac ce p
te
d
34
Page 34 of 39
100 95
ip t
85 80 Pb Cu Cr Cd
75
cr
Removal Efficiency %
90
65 60 20
40
60
80
100
120
140
160
an
0
us
70
Contact Time (min)
180
200
Fig.11. Effect of contact time of MDA-magMCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (
M
initial concentration of metal ions 50mg L-1, adsorbent dosage = 1 g L−1, initial pH value 4.0,agitation speed 250 ◦
rpm and at 25 C).
Ac ce p
te
d
35
Page 35 of 39
ip t cr us an M d te
Ac ce p
Fig.12. Adsorption isotherms of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 at the adsorbent dose of 1g L-1, pH 4.0 and ambient temperature.
36
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us
cr
ip t
B
an
A
Ac ce p
te
d
M
Fig.13. Effect of HCl concentration on desorption of Pb(II), Cu(II),Cr(VI) and Cd(II) (A), Regeneration of MDAmagMCM-48 for adsoption of Pb(II), Cu(II),Cr(VI) and Cd(II) at the adsorbent dose of 1g L-1, pH 4.0, initial concentration 50 mg L-1 and ambient temperature(B).
37
Page 37 of 39
Ac ce p
te
d
M
an
us
cr
ip t
Graphical Abstract
38
Page 38 of 39
Highlights Modified magnetic mesoporous adsorbent was successfully synthesized. The obtained adsorbent was used to removal of Pb (II), Cu (II), Cr (VI) and Cd (II).
ip t
The adsorbent was presented a preferential binding capacity of Pb (II) > Cu (II) > Cr (VI) >Cd (II).
Ac ce p
te
d
M
an
us
cr
The adsorbent was found to be suitable for reuse in successive adsorption‐desorption cycles.
39
Page 39 of 39
S0263-8762(14)00337-2 http://dx.doi.org/doi:10.1016/j.cherd.2014.07.018 CHERD 1651
To appear in: Received date: Revised date: Accepted date:
6-2-2014 17-7-2014 22-7-2014
Please cite this article as: Anbia, M., Kargosha, K., Khoshbooei, S.,Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48, Chemical Engineering Research and Design (2014), http://dx.doi.org/10.1016/j.cherd.2014.07.018 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.
Heavy metal ions removal from aqueous media by modified magnetic mesoporous silica MCM-48 Mansoor Anbia∗a, Kazem Kargoshab, Sanaz Khoshbooei c a
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Research Laboratory of Nanoporous Materials, Faculty of Chemistry, Iran University of Science and Technology, Tehran 16846, Iran b
Research Laboratory of Spectroscopy, Chemistry and Chemical Engineering Research Center of Iran, P.O. Box
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14335-186, Tehran, Iran c
Research Laboratory of Advanced Materials, Chemistry and Chemical Engineering Research Center of Iran, P.O.
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Box 14335-186, Tehran, Iran
Corresponding Author: Tel: 0098 21 77240516; Fax: 0098 21 772491204; Email: [email protected]∗
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Abstract A novel magnetic functionalized MCM-48 mesoporous silica with amine (–NH2) and melamine-based dendrimer amines (MDA) were synthesized that can be easily separated from aqueous solutions by applying a magnetic field. The synthesis adsorbent (MDA-magMCM-48) was characterized by low angle XRD, TEM, FT-IR,
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TGA and N2 adsorption-desorption isotherm techniques. Batch adsorption experiments were carried out to study the sorption behavior of MDA-magMCM-48 towards Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions. The adsorption of metal ions was well modeled by pseudo-second-order model and Langmuir sorption isotherm with maximum
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adsorption capacities of 127.24, 125.80, 115.60 and 114.08 mg g-1 Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions, respectively. MDA–magMCM-48 was regenerated and found to be suitable for reuse in successive adsorption-
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desorption cycles three for times without significant loss in adsorption capacity.
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Keywords: Magnetic Mesoporous Adsorbent, Heavy Metal ions Removal, Aqueous Media.
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1. Introduction Removal of heavy metals from aqueous solution is one of the major problem in wastewater treatment because they are mostly toxic even at very low concentration. These pollutants enter in water from industrial applications, including mining, refining and production of textiles, paints and dyes. A wide variety of techniques to remove heavy
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metals from water is available such as ion exchange, reverse osmosis, nanofiltration, precipitation, coagulation/coprecipitation and adsorption (Freeman, 1989; Cheremisinoff, 2002). Adsorption is one of the effective method for heavy metals pollution remedy, due to the fact that adsorption process offers flexibility in design and operation. In
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addition, the regeneration of adsorbent with economic operation may be possible because adsorption is generally reversible (Tang et al., 2008; Paulino et al., 2011). New generation of magnetic sorbents combined magnetic iron
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oxides together with a sorbent material such as activated carbons, clays, zeolites, polymers, biopolymers and silica (Yavuz et al.,2009; Oliveira et al.,2008; Oliveira et al.,2002; Oliveira et al.,2003; Lim and Chen, 2007; Chen et al.,2011) Magnetic mesoporous nano-composite, as a kind of novel functional material, has aroused increasing
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interests for its large surface area, suitable pore size, and uniform pore size distribution. MCM-48 is an important member of the ordered mesoporous molecular sieve family, shows good performance in both catalysis and adsorption processes because of its higher specific surface area (≥1000 cm2 /g) and three-dimensional pore structure
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framework (Hartmann and Bischof, 1999; Igarashi et al., 2007). Beside selecting a functional material to modify the surface is of great importance in developing high performance magnetic adsorbent (Pang et al., 2011). Researchers have used ligands containing multi-amine groups in a chain (Aguado et al., 2009; Vasiliev et al., 2009) or ligands
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involving dendrimer-amines (Jiang et al., 2007) to increase sorption efficiency of heavy metals into the mesoporous structure. Melamine-based dendrimer amines (MDAs) are ideal dendrimer ligands due to intensively binding amine
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sites and also due to their enhanced hydrophilic silica surface compared to analogous adsorbents (Li et al., 2011).
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In this study by introducing Fe3O4 which features super paramagnetism into the prepared mesoporous adsorbent (MCM-48), magnetically separable mesoporous silica (magnetic MCM-48)has been successfully synthesized and modified by melamine. Magnetic separation of this adsorbent makes it a convenient adsorbent for the fast removal of heavy metals from aqueous solutions.
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2. Experimental 2.1. Materials All the reagents used were of analytical grade. Tetraethylorthosilicate (TEOS 98%), cetyltrimethyl ammonium bromide (CTAB, 99%), 3-aminopropyltriethoxysilane (APTES, 98%), N,N-di-isopropylethylamine (DIPEA), 2,4,6-
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trichloro-1,3,5-triazine (cyanuric chloride), ethylenediamine (EDA), Iron(II) Chloride Tetrahydrate (FeCl2·4H2O), Iron(III) Chloride (FeCl3), NH4OH, hydrochloric acid (HCl, 37%), methanol, dichloromethane, tetrahydrofuran, toluene, nitric acid (HNO3, 1%), Pb(NO3 ) 2, Cu(NO3 ) 2.3H2O, Cd(NO3 ) 2.4H2O and K2CrO7 were from E. Merck
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(Darmstadt, Germany).
2.2. Preparation of magnetic Fe3O4 nanoparticles
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The Fe3O4 nanoparticles were prepared by chemical coprecipiation method (Li et al., 2008). Fe3O4 NPs were synthesized by mixing FeCl2·4H2O (2.0 g), FeCl3 (5.2 g) and 0.85 mL hydrochloric acid into 25 mL deionized water degassed with nitrogen before use. The mixture was added to a stirred 250 mL NaOH solution (1.5 M) with nitrogen
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gas passing continuously through the solution during the reaction. The produced magnetic NPs were rinsed with deionized water (5×50 mL) and then resuspended in deionized water (230 mL). The generated NPs concentration
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was estimated to be about 10mg.mL−1.
2.3. Synthesis of magnetic MCM-48 mesoporous silica
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The procedure for preparation of MCM-48 (Kim et al., 2005) was modified by introduction of nanoparticles in reaction mixture. Typically, 6 g cetyltrimethylammonium bromide (CTAB), 35 mL deionized water, 0.549 g NaOH were mixed in flask then this mixture was added to 20 mL of the prepared Fe3O4 spheres slowly under vigorous stirring. After 3 h of stirring, 6.6 mL tetraethylorthosilicate (TEOS) was added drop wise and the stirring was continued until the gel became homogeneous. The whole synthesis was done on a heating mantle at 30-35 ºC. The mixture was filled into a Teflon-lined steel autoclave and statically heated at 135 ºC for 48 h. The resultant was separated by magnetic field and washed several times with deionized water. After vacuum dried at 70 ºC, it was calcined at 540 ºC in air for 6 h. This material is denoted as magMCM-48.
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2.4. Synthesis of amino-modified magMCM-48 To prepare the amino-modified magMCM-48 sample, the procedure was carried out as follows (Anbia and Lashgari, 2009; Tarlani et al., 2006) magMCM-48 (2.0 g) was suspended in (100 mL) toluene and the mixture was stirred for an hour and then to this mixture (3.0 mL) APTES was added and the mixture was refluxed overnight. The
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solid product was separated by applying magnetic field. It was then soxhlet extracted with toluene in order to remove the silylating reagent residue. Finally it was dried at 70 ºC under vacuum. This material was labeled as NH2-
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magMCM-48.
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2.5. Synthesis of MDA–magMCM-48
The MDA–magMCM-48 was synthesized from cyanuric chloride and EDA according to a procedure similar to
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that described previously in literature (Acosta et al., 2004, Liang et al., 2008). Cyanuric chloride (5.5 g; 30 mmol) and DIPEA (7.1 mL: 46 mmol) were dissolved in dried tetrahydrofuran (300 mL) and stirred at 0ºC for 3h under argon atmosphere. NH2–magMCM-48 was added to the mixture and stirred for 24h at 0ºC. The chlorine atom in
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cyanuric chloride was easily replaced by the amine group of the APTES molecule and the DIPEA trap that HCl formed during the substitution reaction. Then the mixture was separated by applying magnetic field and soxhlet extracted with tetrahydrofuran. This solid was transferred back into a clean flask containing a mixture of EDA (4
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mL: 73.84 mmol), dissolved in dried tetrahydrofuran (300 mL) and refluxed for 24 h. The material was separated by magMCM-48.
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2.6. Characterization
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applying magnetic field, then soxhlet extracted with tetrahydrofuran. This resulting substance was denoted MDA–
The X-ray powder diffraction patterns were recorded on a Philips1830 diffractometer using Cu-Kα radiation with a 0.02 step size and 1s step time over the range of 1° <2θ< 10°. Adsorption–desorption isotherms of the synthesized samples were measured at 77K on micrometrics model ASAP2010 sorptometer. Pore size distributions were calculated by the Barrett-Joyner-Halenda (BJH) method, while surface area of the sample was measured by Brunaure–Emmet–Teller (BET) method. The Fourier transform infrared spectra for the unmodified and modified samples were measured on a DIGILABFTS 7000 instrument under attenuated total reflection (ATR) mode using a diamond module. Compositional analyses of magMCM-48 were carried out using an energy dispersive X-ray analysis (EDX) set up attached to an SEM (Philips XL-30). Thermo gravimetric analysis was used to determine the thermal stability of the synthesized materials and was carried out from room temperature to 873 K using a TGA/DTA (Mettler Toledo 851) analyzer at a heating rate of 10 K/min under N2 atmosphere. Metal ions concentration, both in the initial and final solutions, was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).
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2.7. Adsorption studies Batch experiments were performed to measure multi-ions adsorption capacities. For the preparation of aqueous metal solutions, Pb (NO3) 2, Cu (NO3) 2.3H2O, Cd (NO3) 2.4H2O and K2CrO7 were used. A stock solution of 1000 mg
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L−1 of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions was prepared by dissolving the required amounts of Pb(II), Cu(II),Cr(VI) and Cd(II) in 1000 mL double distilled water. Solutions of desired concentration were prepared by diluting the stock solution using double distilled water. All sorption experiments were carried out in batch conditions
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using 25 mL of metal ion solution and 0.025 g of MDA-magMCM-48 as magnetic adsorbent. Shaker was used to mix the suspensions (metal solution–adsorbent) at 250 rpm and 25.0 °C for all tested conditions. Samples were
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pipetted at certain intervals and the adsorbent was separated using a magnet (1.2 T) Fig.1. The sample solutions were spiked with HNO3 to 1% (v/v) and injected to ICP-OES for analysis. The amounts of analyte adsorbed by adsorbents (qe mg g-1) and the removal efficiency (%) of the MDA-magMCM-48 were calculated using Eqs. (1) and
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(2)
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Where qe is the equilibrium adsorption capacity of the adsorbent in mg g-1, C0 is the initial concentration in mg L-1
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and Ce is the concentration at equilibrium of metal ions in mg L-1, V is the volume in L of metal ions solution and W is the weight in g of the adsorbent.
2.8. Kinetic study
The kinetics of the adsorption process was investigated to determine the effect of the initial concentration of metal ions on the qe with respect to time and the time required to achieve equilibrium adsorption. The kinetics study was carried out using 0.025 g of MDA–magMCM-48 in 25 mL of different concentrations (10, 25, 30, 50 ,80 mg L-1) of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions solution at pH 4.0. Two simple kinetic models, namely the pseudo-firstorder and the pseudo-second-order, are the most often used to analyze the rate of sorption. The pseudo-first-order kinetic and the pseudo-second-order kinetic are expressed by Eqs. (3) and (4), respectively (Lagergren, 1898, Ho and. Mckay, 1998). ln (qe-qt) = ln qe - k1t
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t/qt =1/ K2 qe2 + (1/qe)t
(4)
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where qe and qt are the adsorbed metal in mg g-1 on the adsorbent at equilibrium and time t, respectively, k1 is the constant of first-order adsorption in min−1 and k2 is the rate constant of second-order adsorption in mg−1 min−1.
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2.9. Isotherm study The relationship between the amounts of a substance adsorbed per unit mass of adsorbent at constant temperature and its concentration in the equilibrium solution is known as adsorption isotherm. These adsorption data for each Pb
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(II), Cu (II), Cr (VI) and Cd (II) metal ions were fitted into both the Langmuir and Freundlich isotherm equations which corresponds to homogeneous and heterogeneous adsorbent surfaces. The Langmuir model is given by Eq (5)
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(Morey et al., 2000):
were qm (mg g-1) and b (L mg-1) are maximum adsorption capacity of adsorbent and the Langmuir constant related to the adsorption energy coefficient, respectively. The essential features of the Langmuir isotherm can also be
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expressed in terms of dimensionless constant separation factor RL, which is defined as Eq (6):
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The RL value indicates the shape of isotherm (Zolfaghari et al., 2011). RL values between 0 and 1 indicate favorable adsorption, while RL > 1 and RL = 0 indicate unfavorable and irreversible adsorption isotherm (Zheng et al., 2008).
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The Freundlich model can be expressed by the following equation (Ho et al., 2002):
where kf (mg g-1) and n (L mg-1) are the Freundlich constants related to adsorption capacity and intensity, respectively. The nonlinear regression analysis was carried out with SigmaPlot software (SigmaPlot 10.0, SPSS Inc, USA) in order to predict both the kf and the n parameters.
3.Results and discussion 3.1. Characterization of synthesized adsorbent SEM and TEM images of the magMCM-48 are presented in Fig. 1. The magMCM-48 typically exhibits a Spherelike morphology and Fe3O4 nanoparticles are distributed in the mesoporous MCM-48.
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Fig.2.
The low-angle XRD spectra of magMCM-48, NH2–magMCM-48 and MDA-magMCM-48 are recorded in Fig.3. The XRD patterns of magMCM-48 exhibit strong (211) peak and proportional (220) peak intensities. In comparison
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between the XRD patterns before and after modification with melamine-based dendimer amine complexes, the peaks of magMCM-48 remained. This confirms that the overall ordered structure of the mesoporous silica is not seriously perturbed. The intensities of the XRD peaks for NH2–magMCM-48 and MDA-magMCM-48 are
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substantially lower than those measured for magMCM-48, which is probably caused by the pore filling effect of the
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Fig.3.
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magMCM-48 channels (Liang et al., 2008).
The amine groups and melamine-based dendrimers in the silicate frameworks were also identified using FT-IR.
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Fig. 4 shows the FT-IR spectra of the modified sample along with the unmodified mesoporous mag-MCM-48. The typical Si–O–Si bands at 462, 810 and 1075 cm−1 present in all samples are attributed to the condensed silica network (Socrates, 2004) magMCM-48 exhibits an absorption band at about 3400 cm−1, attributed to the –OH
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stretching vibrations of silanol groups. The band at 1695 cm−1 is probably attributed to NH2 bending, especially intensive for the NH2 –magMCM-48 sample, indicating the presence of primary amine. The stretching bands at 2950
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and 3076 cm−1 are attributed to asymmetric and symmetric C–H stretching in the propyl chain. The band at 1642 cm−1 (MDA–magMCM-48 spectrum) is the evidence of an aromatic triazine ring in the MDA–magMCM-48 sample
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and confirms that the melamine-based dendrimer are formed (Yoo et al., 2006). These results confirm that magMCM-48 with aminopropyl and melamine-based dendrimer groups has been successfully modified. Fig.4.
Thermogravimetric analysis (TGA) curves for NH2–magMCM-48 and the MDA–magMCM-48 samples show very slow but continuous weight loss. The weight loss observed below 150 ºC in representative samples is associated with desorption of water. The weight loss between 150 and 840 ºC was used as the baseline amount for the organic moieties of each sample, however, most of the weight loss above 600 ºC is due to the dehydroxylation of the silicate networks. In Fig.5, the aminopropyl loaded on the surface of magMCM-48 was calculated to be about 0.36 mmol g-1 (8.01% weight loss) in the NH2–magMCM-48 sample and amount of the dendrimer ligand was calculated to be about 0.69mmol g-1 (17.49% weight loss) on the surface of the MDA–magMCM-48 sample.
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Fig.5. Fig. 6 shows the adsorption/desorption isotherms of nitrogen at 77K on MDA-magMCM-48. which exhibits a type IV profile according to the BET classification. The pore diameter value about 3.46 nm is observed for MDAmagMCM-48 in the pores size distribution (BJH) analysis of nitrogen desorption isotherm. Fig. 5 shows one strong peak for the pore diameter 3.46 nm. The results for N2 adsorption–desorption containing the pore diameters, the
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BET surface and the total pore volume of the calcined MDA-magMCM-48 sample are recorded in Table 1.
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Table 1.
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Fig. 6.
3.2. Adsorption studies
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3.2.1. Effect of initial concentration
Initial concentration is one of the important factors for determining the adsorption capacity of an adsorbent. The effects of initial concentration (10, 25, 30, 50, 80 mg L-1) on metal ions adsorption were carried out with 0.025 g of
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MDA– magMCM-48 adsorbent dose in 25 mL of multi- ions metal solution at pH 4.0, each containing 50 mg L-1 of
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Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions. Fig.7 shows the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions with its concentration. It is observed that the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions is high at lower concentration and gradually decreases as the concentration of metal ions increase.
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This is due to the fact that after the formation of mono-ionic layer at lower concentration on the adsorbent surface, further formation of the layer is highly hindered at higher concentration due to the interaction between metal ions present on the surface and in the solution. In addition, at low concentration of the of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions, the ratio of the initial number of moles of the metal ions to the available surface area of the adsorbent is large and subsequently, the fraction of the adsorption becomes independent of the initial concentration of the metal ion, But at higher concentration, the sites available for adsorption becomes lesser and hence, the removal efficiency of the metal ions at higher concentration decreases (Kanthimathi et al., 2012; Panda et al., 2011).The optimum concentration of the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions is found to be 50 mgL-1 due to maximum adsorption capacity.
Fig.7.
3.2.2. Effect of the adsorbent dose
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The effect of the dose of MDA-magMCM-48 (0.2,0.5,1, 1.2 and 1.5 g L-1), adsorbent on removal of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions at 50 mg L-1 has been studied. pH of the working solution was adjusted to 4.0 by adding 0.1M NaOH. These results are depicted in (Fig. 8). It is clear that the removal efficiency of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions increases as the amount of the adsorbent increases owing to the enhanced total surface area of the adsorbent. The results revealed that the metal removal percentage is dependent on the optimal
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increase of the adsorbent dose, due to a consequential increase in interference between binding sites at the higher dose or an insufficiency of metal ions in solution with respect to available binding sites. The maximum metal ions removal was attained at about 1 g L-1 dose of MDA–magMCM-48 (97.8% for Pb (II), 94.92% for Cu (II), 91.8% for
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Cr (VI) and 88.52% for Cd (II) and was almost the same even at higher doses. Therefore, the MDA-magMCM-48
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Fig.8.
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with 1 g L-1 dose was chosen as the optimum amount of the adsorbent for further experiments.
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3.2.3. Effect of chemical modification
In order to evaluate the efficiency of the prepared adsorbents, the effect of MDA-magMCM-48 ( before and after functionalization) on adsorption of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions at 50 mg L-1 and pH, 4.0 were studied
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The experiments were performed to optimize the adsorbent conditions (1 g L-1 of each adsorbent type) for removal of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions. The Fig. 9 shows the adsorption of each metal ion on magMCM-
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48, NH2-magMCM-48 and MDA-magMCM-48. It is seen that the order of adsorption in terms of the treated and untreated adsorbent is: MDA-magMCM-48>NH2-magMCM48>mag-MCM-48. MDA-magMCM-48 which shows
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much higher metal ions removal efficiency compared to magMCM-48 and NH2-magMCM-48, which may be due to the grafted dendrimer amine groups on the surface of silica and its more active adsorption sites. Due to interaction between the lone pair of electrons on nitrogen (the synthesized adsorbent) and the metal ions M(II) species, the adsorption takes place. The multifunctional amine groups on the surface of the MDA-magMCM-48 are responsible for higher removal efficiency of MDA–magMCM-48 compared to NH2–magMCM-48. Therefore MDA–magMCM48 was chosen as an appropriate adsorbent.
Fig.9
3.2.4. Effect of the solution pH The surface charge and the protonation degree of the adsorbent were significantly influenced by the pH value, (Deng and Ting, 2005).
To investigate the effect of the different solution pH on adsorption, 0.025 g of MDA–
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magMCM-48 in 25 mL of different metal ions solution containing 50 mg L-1 of Pb (II), Cu (II), Cr (VI) and Cd (II) was shaken separately for 90 min. The pH was adjusted to values ranging from 2 to 6 using 1M HCl and 0.1M NaOH solution. The conical flasks were agitated at 250 rpm using shaker to reach equilibrium. After magnetic separation of adsorbent, the concentration of the remaining metal ions in aqueous phase was measured. These results are depicted in Fig.10. The metal uptake increases with the increase of the pH from 2 till it reaches a maximum at 4,
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and decreases at the pH values higher than 4. To explain this observation, the presence of dominant metal ions M(II) species at pH> 6 are M(OH)2 and at pH< 6 M(OH)+, therefore, most ions are not accessible to adsorb at higher pH values and consequently the removal efficiency is decreased. The removal efficiency was 66.65%, 61.11%,84.23%
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and 52.54% for Pb(II), Cu(II),Cr(VI) and Cd(II), respectively at pH 2 and these values increased to 97.8%, 94.92%, 91.8% and 88.52% for Pb(II), Cu(II),Cr(VI) and Cd(II), respectively, with pH increase to 4. This is because at low
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pH values there is an excessive protonation of the lone pair of electrons on nitrogen, resulting in a decrease in the sorption of heavy metal ions (Benhamou et al., 2009; Heidari et al., 2009). Also, at a very low solution pH, the concentration of the hydrogen ions is high, directly competing with the heavy metal ions for active binding sites.
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Therefore, the increase in metal removal as the pH increases can be explained on the basis of a decrease in competition between proton ions (H+) and positively charged metal ions at the adsorbent surface sites. It is well known that Cr (VI) exists mainly in the form of HCrO4- or Cr2O72- at low pH, and as CrO42- at high pH (Natale et al.,
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2007; Hu et al., 2005; Park and Jang, 2002). Therefore sorption of Cr (VI) metal ion due to the charge of surface sites (NH3+ at pH lower than 4) is more in comparison with Pb(II), Cu(II) and Cd(II)metal ions. It is clear that negatively charged HCrO4- and Cr2O72- are easily adsorbed on the positively charged MDA-magMCM-48 at low pH
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values due to the electronic attraction (Hu et al., 2009). The maximum adsorption was observed at pH 4.0 for all
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ions. However, on increasing the pH further, the metal speciation in solution may become an important factor and the increase in heavy metal removal has been attributed to reduced solubility and to precipitation of solid metal
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hydroxide. In the present study, adsorption could not be carried out beyond pH 6.0 due to precipitation of Pb(OH)2, Cu(OH)2, and Cd(OH)2 and the (CrO42-) at higher pH values, therefore, the experiments were performed at the pH value of 6. When pH was increased from 4 to 5, the removal efficiency of Cd(II) decreased from 88.52% to 74.3% and Cr(VI) from 91.8%to 63.6% while that of Pb(II) and Cu(II) remained the same at pH 5(Fig.9). It may be due to the lower Ksp value of Cd (II) compared to Pb (II), Cu (II) and Cr (VI) while increasing the pH resulted quickly in a decrease of its solubility. The electrostatic repulsion between negative Cr (VI) species and the lone pair of electrons on the surface of MDA-magMCM-48 leads to decrease of adsorption of Cr (VI) ions. However, when the pH is increased from 5 to 6, the removal efficiency of all studied ions was decreased because of ion precipitation for Pb (II), Cu (II) and Cd (II) and electrostatic repulsion of Cr (VI) metal ions.
Fig. 10
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3.2.5. Effect of contact time Contact time is another effective factor in batch adsorption process. In order to establish an equilibration time for the maximum uptake, the adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 was studied as a function of contact time. For this purpose 0.025 g of MDA–magMCM-48 in 25 mL of multi-ions solution
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containing 50 mg L-1 of Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions was shaken for 10,30,60,90,120 and 180 min. Fig.11 shows the variation of the removal efficiency of the Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions MDAmagMCM-48 with contact time. The adsorption rate was very fast and achieved adsorption equilibrium within 90
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min. The rapid uptake (more than 70% equilibrium adsorption in first 10 min) revealed a high affinity between the heavy metals and the adsorbent, which was directly be attributed to the MDA-grafted magnetic porous adsorbent. In
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addition, the heavy metals removal sequence onto MDA-magMCM-48 was in the order of Pb(II) > Cu(II) > Cr(VI) > Cd(II). Physico-chemical properties of metal ions such as electro-negativity, atomic weight and ionic radius may
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be responsible for the selectivity observed (Heidari et al., 2009).
3.2.6. Kinetic study
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Fig.11
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Adsorption kinetic model not only allows estimation of adsorption rate but also provides insights into rate expression characteristic of possible reaction mechanism. It was pointed out that pseudo second-order adsorption
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model was based on the assumption that the rate-controlling step of chemisorption involved valence forces through sharing or exchange of electrons between adsorbent and adsorbate, was able to better describe the adsorption kinetic (Murugesan et al., 2011; Reddad et al., 2002). As recorded in Table 2, the experimental data are in well agreement with the pseudo-second-order model, which suggests that the adsorption rate of the heavy metals was controlled by chemical processes. The adsorption rate is related to the content of the active adsorption sites on the matrix of the adsorbent and also on the metal ionic radius (Jing et al., 2009). According to Table 2, Pb(II) ions with a greater ionic radius show the higher adsorption rate. The reason for this can be explained by the fact that the Pb(II) ions win over the other ions competition for occupying the active sites on the silica surface due to the higher atomic weight, greater electro-negativity and ionic radius of Pb(II) and smaller Z/R (charge/radius) ratio than those of Cu(II), Cr(VI) and Cd(II) (Heidari et al., 2009; Jing et al., 2009). As seen in Table 2, when the initial ions concentration increases from30 to 80mg L-1, the pseudo-second-order constants diminish. It means that the value of k depends on the C and the adsorption rate decreases when the initial ions concentration increase.
Table 2.
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3.2.7. Isotherm study
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The nonlineared Langmuir and Freundlich adsorption isotherms of the Pb (II), Cu (II), Cr (VI) and Cd (II) metal ions obtained with the adsorbent dose of 1 g L-1 and the temperature of 25 ◦C are shown in Fig12. The b, qm, n, Kf values and the nonlinear regression correlation coefficients (R2) for Langmuir and Freundlich isotherms are listed in
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Table 3.The correlation coefficients indicate that adsorption is fitted better by the Langmuir (R2 = 0.992–0.998) than the Freundlich model (R2 = 0.985–0.988), as shown in Fig. 11. Therefore, the adsorption process can be described
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by the formation of monolayer coverage of the adsorbate on the adsorbent surface. The maximum adsorption capacity (qm) was determined as 127.24, 125.80, 115.60 and 114.08 mg g-1 for Pb (II), Cu (II), Cr (VI) and Cd (II), respectively. For clarifying the favorableness for adsorption of each metal ion, we also calculated the separation
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factor (RL), as summarized in Table 4, i.e. 0 < RL <1, revealing that the adsorption of the selected metal ions was
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favorable.
Table 3.
Fig.12
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Table 4.
3.2.8. Desorption
Desorption ability of the MDA–magMCM-48 was evaluated by HCl acid with different concentrations (0.1, 0.2, 0.3 and 0.4 M) treatment and depicted in Fig.13 (A). The 0.3M HCl was more suitable concentration. The adsorbent was reused in three successive adsorption–desorption cycles. Fig. 12 (B) shows the removal efficiency Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions over three successive adsorption–desorption cycles. It was observed that nearly over 93% removal efficiency was reached in the first cycle for Pb(II), Cu(II), Cr(VI) and Cd(II) metal ions. Even though the efficiency decreases with the increasing of cycle, over 87% efficiency was obtained in the third absorption–desorption cycle, demonstrating that the prepared adsorbent is cost-effective, and its regeneration by 0.3 M HCl acid is quite effective.
Fig.13
13
Page 13 of 39
3.2.9. Comparison with other adsorbents The value of qm is maximum adsorption capacity of adsorbent, and is useful in scale-up considerations. Table 5 shows a comparison of the adsorbent capacity of various adsorbents for Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions.
ip t
Table 5
cr
4. Conclusion
MDA-grafted magnetic porous adsorbent combining magnetic separation technique and porous properties has
us
been developed for removal of heavy metals from aqueous system. The results show that MDA–magMCM-48 has a significant adsorption capacity for Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions, compared to NH2-magMCM-48 and untreated mag-MCM-48. The adsorption of Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions is well modeled by pseudo-
an
second-order model and Langmuir sorption isotherm, and the adsorbent has presented a preferential binding capacity of Pb(II) > Cu(II) > Cr(VI)>Cd(II). This adsorbent can be used repeatedly by effective regeneration using 0.3 M HCl acid. Thus it could be concluded that the MDA-magMCM-48 with convenient separation capability great
Ac ce p
te
d
M
potential as an adsorbent for removal metal ions from aqueous solution.
14
Page 14 of 39
Reference Acosta, E.J., Carr C.S., Simanek ,E.E., Shantz, D.F., 2004. Engineering nanospaces: iterative synthesis of melaminebased dendrimers on amine-functionalized SBA-15 leading to complex hybrids with controllable chemistry and porosity. Adv. Mater., 16, 985–989.
ip t
Aguado, J., Arsuaga, J.M., Arencibia, A., Lindo, M., Gascón ,V., 2009. Aqueous heavy metals removal by adsorption on amine-functionalized mesoporous silica. J. Hazard Mater. ,163, 213–221.
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Anbia, M., Lashgari, M., 2009. Synthesis of amino-modified ordered mesoporous silica as a new nano sorbent for the removal of chlorophenols from aqueous media. J. Chem. Eng., 150, 555–560.
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Benhamou,A., Baudu, M., Derriche, Z.,Basly, J.P., 2009. Aqueous heavy metals removal on aminefunctionalized Si-MCM-41 and Si-MCM-48. J. Hazard Mater., 171, 1001–1008. Chen,X.,Lam,K.F.,Yeung,K.L.,2011.Selective removal of chromium using magnetic MCM-41 nanosorbents, . J. Chem. Eng., 172, 728-734.
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Cheremisinoff, N.P., 2002. in: Butterworth, Heineman (Eds.), Handbook of Water and Wastewater Treatment Technologies.
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Deng, S.B., Ting, Y.P., 2005.Characterization of PEI-modified biomass and bio sorption of Cu(II) Pb(II) and Ni(II). Water Res.,39, 2167–2177. Freeman, H.F., 1989. Standard Handbook of Hazardous Waste Treatment and Disposal, McGraw–Hill, New York.
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Hartmann, M., Bischof, C., 1999. Mechanical stability of mesoporous molecular sieve MCM-48 studied by adsorption of benzene, n-heptane, and cyclohexane. J. Phys. Chem. B., 103 (30), 6230- 6235.
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Heidari, A., Younesi, H., Mehraban, Z., 2009. Removal of Ni(II), Cd(II), and Pb(II) from a ternary aqueous solution by amino functionalized mesoporous and nano mesoporous silica. J. Chem. Eng., 153, 70–79.
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Ho, Y., Porter, J., McKay, G., 2002. Equilibrium isotherm studies for the sorption of divalent metal ions onto peat: copper, nickel and lead single component systems. Water. Air. Soil Pollut., 141, 1–33. Ho, Y.S., Mckay, G., 1998. Kinetic model for lead (II) sorption on peat. Adsorpt. Sci.Technol., 16, 243–255. Hu, J, Chen, GH, Lo, I.M.C., 2005. Removal and recovery of Cr (VI) from wastewater by maghemite nanoparticles.Water Res., 39, 4528-36. Hu, J., Wang, S.W., Shao1, D.D., Dong, Y.H., Li, J.X., Wang, X.K., 2009. Adsorption and Reduction of Chromium(VI) from Aqueous Solution by Multi walled Carbon Nanotubes. The Open Environmental Pollution & Toxicology Journal ,1, 66-73.
Igarashi, N., Hashimoto, K., Tatsumi, T., 2007. Catalytical studies on trimethylsilylated Ti-MCM-41 and Ti-MCM 48 materials. Micropor. Mesopor. Mater., 104 , 269-280. Jiang, Y., Gao, Q., Yu, H., Chen, Y., Deng, F., 2007. Intensively competitive adsorption for heavy metal ions by PAMAM–SBA-15 and EDTA–PAMAM–SBA-15 inorganic-organic hybrid materials. Micropor. Mesopor. Mater., 103, 316–324.
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Jing, X., Liu, F., Yang, X., Ling, P., Li, L., Long, C., Li, A., 2009. Adsorption performances and mechanisms of the newly synthesized N,N-di (carboxymethyl) dithiocarba-mate chelating resin toward divalent heavy metal ions from aqueous media. J. Hazard Mater., 167, 589–596.
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Kanthimathi, G., Kotteeswaran, P., Thilai Arasu, P., Govindaraj, P., Kottaisamy, M., 2012. A Comparative Study of the Adsorption Efficiency of the Newly Synthetic Nano Iron Oxide and Commercial Activated Charcoal Towards the Removal of the Nickel(II) Ions. J. Chem. Eng., 9(4), 2384-2393.
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Kim, T.W., Kleitz, F., Paul, B., Ryoo, R., 2005. MCM-48-like Large Mesoporous Silicas with tailored Pore structure: facile synthesis domain in a ternary triblock copolymer-butanol-water system. J. A. C. S., 127, 76017610.
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Lagergren, S., 1898. About the theory of the so-called adsorption of soluble substances. Kungliga Svenska Vetenskapsakademius, Hadndlingar , 24, 1–39. Li, G., Zhao, Z., Liu, J., Jiang ,G., 2011. Effective heavy metal removal from aqueous systems by thiol functionalized magnetic mesoporous silica. J. Hazard Mater., 192, 277– 283.
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Li, J., Zhao, X., Shi, Y., Cai, Y., Mou, S., Jiang, G., 2008. Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols environmental water samples coupled with liquid chromatography/spectrophotometry detection. J. Chromat. A., 1180, 24–31. Liang, Z., Fadhel, B., Schneider, C.J., Chaffee, A.L., 2008. Stepwise growth of melamine based dendrimers into mesopores and their CO2 adsorption properties. Micropor. Mesopor. Mater., 111, 536–543.
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Lim, S.F., Chen, J.P.,2007. Synthesis of an innovative calcium–alginate magneticsorbent for removal of multiple contaminants, Appl. Surf. Sci., 253, 5772–5775.
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Morey, M.S., O’Brien, S., Schwarz, S., Stucky, G.D., 2000. Hydrothermal and post synthesis surface modification of cubic, MCM-48, and ultra large pore SBA-15 mesoporous silica with titanium. Chem. Mater., 12, 898–911. Murugesan, A., Ravikumar, L., SathyaSelvaBala, V., SenthilKumar, P., Vidhyadevi, T., 2011. Removal of Pb(II), Cu(II) and Cd(II) ions from aqueous solution using poly azomethine amides: equilibrium and kinetic approach. Desalination, 271,199–208. Natale,D. F., Lancia ,A., Molino, A., Musmarra, D., 2007.Removal of chromium ions form aqueous solutions by adsorption on activated carbon and characterization. J. Hazard Mater., 145, 381-90. Oliveira, L.C.A., Petkowicz, D.I., Smaniotto, A., Pergher, S.B.C.,2008. Magnetic zeolites: a new adsorbent for removal of metallic contaminants from water. Water Res.,38 ,3699–3704. Oliveira, L.C.A., Rios, R.V.R.A., Fabris, J.D.V., Garg, K., Sapag, R.M., Lago, R.M., 2002. Activated carbon iron oxide magnetic composites for the adsorption of contaminants in water, Carbon, 40, 2177–2183. Oliveira, L.C.A., Rios, R.V.R.A., Fabris, J.D.V., Garg, K., Sapag, R.M., Lago, R.M., 2003. Clay–iron oxide magnetic composites for the adsorption of contaminants in water, Appl. Clay Sci., 22,169–177. Panda, L, Das, B, Rao, D. S , Mishra, B. K, 2011. Application of dolochar in the removal of cadmium and hexavalent chromium ions from aqueous solutions. J. Hazard Mater., 192, 822-831.
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Pang, Y., Zeng, G., Tang, L., Zhang, Y., Liu, Y., Lei, X., Li, Z., Zhang, J., Xie, G., 2011. PEI-grafted magnetic porous powder for highly effective adsorption of heavy metal ions. Desalination, 281, 278–284. Park, S.J, Jang, Y.S, 2002. Pore structure and surface properties of chemically modified activated carbons for adsorption mechanism and rate of Cr (VI). J. Colloid Interf. Sci., 249, 458-63.
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Paulino, A.T., Belfiore, L.A., Kubota, L.T., Muniz, E.C., Almeida, V.C., Tambourgi, E.B., 2011. Effect of magnetite on the adsorption behavior of Pb(II), Cd(II), and Cu(II) in chitosan-based hydrogels. Desalination, 275, 187–196.
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Reddad, Z., Gerente, C., Andres, Y., Cloirec, P.L., 2002. Adsorption of several metal ions onto a low-cost bio sorbent: kinetic and equilibrium studies. Environ. Sci. Technol., 36, 2067–2073.
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Socrates, G., 2004. Infrared and Raman characteristic group frequencies: tables and charts, 3rd eds., John Wiley & Sons, Ltd,.
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Tang ,L., Zeng, G.M., Shen, G.L., Li, Y.P., Zhang ,Y., Huang, D.L., 2008. Rapid detection of picloram in agricultural field samples using a disposable immune membrane based electrochemical sensor. Environ. Sci. Technol., 42, 1207–1212. Tarlani, A., Abedini ,M., Nemati, A., Khabaz, M., Amini, M. M., 2006. Immobilization of keggin and preyssler tungsten heteropolyacidson various functionalized silica. J. Colloid Interface Sci., 303, 32–38.
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Vasiliev, A.N., Golovko, L.V., Trachevsky, V.V., Hall, G.S., Khinast, J.G., 2009. Adsorption of heavy metal cations by organic ligands grafted on porous materials. Micropor. Mesopor. Mater. ,118, 251–257.
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Wang, J., Ma, X., Fang, G., Pan, M., Ye, X., Wang, S., 2011. Preparation of iminodiacetic acid functionalized multiwalled carbon nanotubes and its application as sorbent for separation and preconcentration of heavy metal ions. J. Hazard. Mater., 186, 1985–1992
Ac ce p
Yavuz, C.T., Prakash, A., Mayo, J.T., Colvin, V.L., 2009. Magnetic separations: from steel plants to biotechnology. Chem. Eng. Sci., 64, 2510–2521. Yoo, S., Lunn, J.D., Gonzalez, S., Ristich, J.A., Simanek, E.E., Shantz, D.F., 2006. Engineering nanospaces: OMS/dendrimer hybrids possessing controllable chemistry and porosity. Chem. Mater., 18, 2935–2942. Zhang, L., Yu. C., Zhao, W., Hua, Z., Chen, H., Li, L., Shi, J., 2007. SBA-15 functionalized with Trimethoxysilylpropyle Dithyenetriamine. J. Non-Cryst. Solids, 353, 4055 Zheng, H., Han, L., Maa, H., Zheng, Y., Zhang, H., Liu, D., Liang, S., 2008. Adsorption characteristics of ammonium ion by zeolite 13X. J. Hazard Mater., 158, 577–584. Zolfaghari, G., Esmaili-Sari, A., Anbia, M., Younesi, H., Amirmahmoodi, S., Ghafari-Nazari, A., 2011. Taguchi optimization approach for Pb (II) and Hg(II) removal from aqueous solutions using modified mesoporous carbon, J. Hazard Mater., 192, 1046–1055. Table List: Table 1. Textural properties of MDA-magMCM-48. Table 2. Kinetic adsorption parameters obtained using pseudo-first-order and pseudo-second-order models.
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Table 3. Langmuir and Freundlich parameters for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) onto MDA– magMCM-48. Table 4. RL values for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) based on the Langmuir equation.
cr
ip t
Table 5. Comparison of adsorption capacity Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions onto some adsorbents.
us
Figure List:
Fig.1. Schematic illustration of magnetic separation of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
an
magMCM48.
Fig.2. Images of (a) Scanning Electron Microscopy (SEM) and (b) Transmission Electron Microscopy (TEM) of magMCM-48.
M
Fig.3. XRD patterns of magMCM-48, NH2-magMCM-48, MDA-magMCM-48. Fig.4. FT-IR spectra of magMCM-48, NH2-magMCM-48, MDA-magMCM-48. Fig.5. Thermogravimetric curves of NH2– magMCM-48 and MDA– magMCM-48.
d
Fig.6. N2 adsorption and desorption isotherms at 77 K of MDA-magMCM-48. The inset shows the BJH pore size
te
distribution of MDA-magMCM-48 calculated from the desorption branch of the isotherm. Fig.7. Effect of initial concentration on adsorption of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
magMCM48.(Contact time = 90 min, agitation speed = 250 rpm, adsorbent dosage = 1 g L−1, pH = 4.0). Fig.8. Effect of adsorbent dose on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal percentage by MDAmagMCM48 ( initial concentration of metal ion 50mg L-1, initial pH value 4.0, agitation time 90 min, agitation speed 250 rpm and at 25 ◦C).
Fig. 9.Effect of chemical modification of mag-MCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (adsorbent dosage = 1 g L−1,initial concentration of metal ion 50mgL-1, initial pH value 4.0, contact time 90 min, agitation speed 250 rpm and at 25 ◦C). Fig. 10. Effect of pH on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ion 50mgL-1, adsorbent dosage = 1 g L−1, contact time 90 min, agitation speed 250 rpm and at 25 ◦C). Fig.11. Effect of contact time of MDA-magMCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ions 50mg L-1, adsorbent dosage = 1 g L−1, initial pH value 4.0,agitation speed 250 rpm and at 25 ◦C). Fig.12. Adsorption isotherm of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 at the adsorbent dose of 1g L-1, pH 4.0 and ambient temperature.
18
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Fig.13. Effect of HCl concentration on desorption of Pb(II), Cu(II),Cr(VI) and Cd(II) (A), Regeneration of MDAmagMCM-48 for adsoption of Pb(II), Cu(II),Cr(VI) and Cd(II) at the adsorbent dose of 1g L-1, pH 4.0, initial
Ac ce p
te
d
M
an
us
cr
ip t
concentration 50 mg L-1 and ambient temperature(B).
19
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Table 1: Textural properties of MDA-magMCM-48. d spacing (nm)
A BET (m 2 g -1 )
) cm 3 g -1 Vp (
MDA-magMCM-48
3.46
511
0.44
Ac ce p
te
d
M
an
us
cr
ip t
Adsorbent
20
Page 20 of 39
ip t cr
Metal
Experimental
ions
conc.(mg/L)
qe(mg/g)
Cr(VI)
Cd(II)
29.39
0.030
50
48.90
0.028
77.10
0.030
30
28.60
0.024
50
47.46
80
73.77
30
27.70
50
45.90
k2(g.mg-1 min-1)
9.87
0.983
8.81×10-3
29.41
0.997
13.89
0.989
6.51×10-3
48.54
0.998
0.988
3.58×10
-3
76.92
0.998
0.960
8.55×10-3
28.01
0.995
-3
47.62
0.998
24.54
d
80
Calculated
R2
qe(mg/g)
te
Cu(II)
30
9.79
R2
qe(mg/g)
0.031
15.45
0.997
5.71×10
0.034
24.68
0.998
3.59×10-3
74.63
0.999
0.028
9.62
0.982
8.82×10-3
27.47
0.997
0.995
5.74×10
-3
45.87
0.998
-3
69.93
0.999
Ac ce p
Pb(II)
Calculated
k1(min-1)
M
Metal
Pseudo-second-order
an
Pseudo-first-order
us
Table 2: Kinetic adsorption parameters obtained using pseudo-first-order and pseudo-second-order models.
0.029
15.17
80
69.77
0.032
21.50
0.994
4.21×10
30
26.89
0.022
11.58
0.995
8.13×10-3
27.73
0.999
0.998
6.95×10
-3
43.10
0.999
5.48×10
-3
64.51
0.999
50 80
44.26 66.55
0.025 0.022
13.57 17.50
0.998
21
Page 21 of 39
ip t cr
us
Table 3: Langmuir and Freundlich parameters for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) onto MDA– magMCM-48.
b (L/mg)
R2
Pb(II)
127.24
0.534
Cu(II)
125.80
0.229
Cr(VI)
115.60
0.150
Cd(II)
114.08
n
R2
0.992
41.64
1.68
0.998
0.997
24.22
1.61
0.987
0.995
17.65
1.66
0.985
0.105
0.996
13.79
1.63
0.988
Ac ce p
te
Kf
d
q m (mg/g)
M
Metal ions
Freundlich
an
Langmuir
22
Page 22 of 39
ip t cr us
Table 4: RL values for adsorption of Pb (II), Cu (II), Cr (VI) and Cd (II) based on the Langmuir equation.
Cu(II)
10
0.16
0.30
25
0.07
0.15
30
0.06
0.60
50
0.04
0.08
80
0.02
0.05
d
M
Pb(II)
Cr(VI)
Cd(II)
0.40
0.48
0.21
0.27
0.18
0.24
0.12
0.16
0.08
0.11
Ac ce p
te
Initial conc.(mg/L)
an
RL Value
23
Page 23 of 39
ip t cr us
Table 5: Comparison of adsorption capacity Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions onto some adsorbents.
113
SBA-15 functionalized with Trimethoxysilylpropyle Dithyenetriamine
11
Cu(II) 9.4
Cd(II) _
Cr(II) _
1.1
1.0
1.1
_
L.Zhang et.al,2007
57.7
_
18.2
_
A.Heidari et.al, 2009
8.98
6.64
6.61
8.96
J.Wang et.al, 2011
127.24
125.80
114.08
115.6
This study
Pb(II) _
50
References J.Aguado et.al,2008
Ac ce p
mag-MCM-48 modified with melamine
1µg
te
Multi-walled carbon nanotubes functionalized with iminodiacetic acid
d
50
MCM-41 modified with 3aminopropyltriethoxysilane
an
SBA-15 functionalized with N-[3(Trimethoxysilyl)propyl]ethylenediamine
qm (mg/g)
M
C0 ( mg/L)
Adsorbent
24
Page 24 of 39
ip t cr us
an
Fig.1. Schematic illustration of magnetic separation of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
te
d
M
magMCM48.
25
Page 25 of 39
ip t cr us an M d te Ac ce p
Fig.2. Images of (a) Scanning Electron Microscopy (SEM) and (b) Transmission Electron Microscopy (TEM) of magMCM-48.
26
Page 26 of 39
<211> magMCM-48 NH2-magMCM-48
cr
Intensity.a,u
ip t
MDA-magMCM-48
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
an
1.0
us
<220>
2Teta,Degree
Fig.3. XRD patterns of magMCM-48, NH2-magMCM-48, MDA-magMCM-48.
M
Ac ce p
te
d
27
Page 27 of 39
ip t cr us an
M
Fig.4. FT-IR spectra of magMCM-48, NH2-magMCM-48, MDA-magMCM-48.
Ac ce p
te
d
28
Page 28 of 39
105 MDA-magMCM-48 NH2-magMCM-48
95
ip t
Weight loss %
100
90
cr
85
75 0
100
200
300
400
500 0
Temprature C
us
80
600
700
800
M
an
Fig.5. Thermogravimetric curves of NH2– magMCM-48 and MDA– magMCM-48.
Ac ce p
te
d
29
Page 29 of 39
ip t cr us an M d te Ac ce p
Fig. 6. N2 adsorption and desorption isotherms at 77 K of MDA-magMCM-48. The inset shows the BJH pore size distribution of MDA-magMCM-48 calculated from the desorption branch of the isotherm.
30
Page 30 of 39
ip t
100
cr
98
us
94 92
an
90 88 86
Pb Cu Cr Cd
84 82 0
20
M
Removal efficiency%
96
40
60
80
100
d
C0(mg/L)
te
Fig.7. Effect of initial concentration on adsorption of Pb(II),Cu(II),Cr(VI) and Cd(II) metal ions onto MDA-
Ac ce p
magMCM48.(Contact time = 90 min, agitation speed = 250 rpm, adsorbent dosage = 1 g L−1, pH = 4.0).
31
Page 31 of 39
110 100
ip t
80
cr
70 60
Pb Cu Cr Cd
50
us
Removal efficiency%
90
40
an
30 20 0.0
0.2
0.4
0.6
0.8
1.0
1.4
1.6
M
Dose of adsorbent(g)
1.2
Fig.8. Effect of adsorbent dose on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal percentage by MDA-
Ac ce p
te
speed 250 rpm and at 25 ◦C).
d
magMCM48 ( initial concentration of metal ion 50mg L-1, initial pH value 4.0, agitation time 90 min, agitation
32
Page 32 of 39
ip t cr us an
Fig. 9.Effect of chemical modification of mag-MCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (adsorbent dosage = 1 g L−1,initial concentration of metal ion 50mgL-1, initial pH value 4.0, contact time 90 min, ◦
Ac ce p
te
d
M
agitation speed 250 rpm and at 25 C).
33
Page 33 of 39
ip t cr us
an
Fig. 10. Effect of pH on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal ( initial concentration of metal ion ◦
50mgL-1, adsorbent dosage = 1 g L−1, contact time 90 min, agitation speed 250 rpm and at 25 C).
M
Ac ce p
te
d
34
Page 34 of 39
100 95
ip t
85 80 Pb Cu Cr Cd
75
cr
Removal Efficiency %
90
65 60 20
40
60
80
100
120
140
160
an
0
us
70
Contact Time (min)
180
200
Fig.11. Effect of contact time of MDA-magMCM-48 on the Pb(II), Cu(II),Cr(VI) and Cd(II) metal ions removal (
M
initial concentration of metal ions 50mg L-1, adsorbent dosage = 1 g L−1, initial pH value 4.0,agitation speed 250 ◦
rpm and at 25 C).
Ac ce p
te
d
35
Page 35 of 39
ip t cr us an M d te
Ac ce p
Fig.12. Adsorption isotherms of Pb (II), Cu (II), Cr (VI) and Cd (II) on MDA-magMCM-48 at the adsorbent dose of 1g L-1, pH 4.0 and ambient temperature.
36
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us
cr
ip t
B
an
A
Ac ce p
te
d
M
Fig.13. Effect of HCl concentration on desorption of Pb(II), Cu(II),Cr(VI) and Cd(II) (A), Regeneration of MDAmagMCM-48 for adsoption of Pb(II), Cu(II),Cr(VI) and Cd(II) at the adsorbent dose of 1g L-1, pH 4.0, initial concentration 50 mg L-1 and ambient temperature(B).
37
Page 37 of 39
Ac ce p
te
d
M
an
us
cr
ip t
Graphical Abstract
38
Page 38 of 39
Highlights Modified magnetic mesoporous adsorbent was successfully synthesized. The obtained adsorbent was used to removal of Pb (II), Cu (II), Cr (VI) and Cd (II).
ip t
The adsorbent was presented a preferential binding capacity of Pb (II) > Cu (II) > Cr (VI) >Cd (II).
Ac ce p
te
d
M
an
us
cr
The adsorbent was found to be suitable for reuse in successive adsorption‐desorption cycles.
39
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