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Magnetization improvement of Fe-pillared clay with application of polyetheramine
Applied Clay Science 48 (2010) 185–190
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Magnetization improvement of Fe-pillared clay with application of polyetheramine Jiang Yu ⁎, Qiu-Xin Yang Research Group of Environmental Catalysis and Separation Process, Department of Environmental Science and Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China
a r t i c l e
i n f o
Article history: Received 14 July 2009 Received in revised form 3 December 2009 Accepted 9 December 2009 Available online 21 December 2009 Keywords: Iron oxide/clay composites Polyetheramine Superparamagnetism Magnetization
a b s t r a c t Polyetheramine D2000 (O,O′-Bis(2-aminopropyl)polypropyleneglycol) was used as structural regulator to modify Fe-pillared clay mineral, and treated with acetic acid vapor prior to calcination for improving the magnetization of magnetically modified clay mineral. The magnetization of the magnetically modified clay mineral was improved to 26.78 emu g−1 with introduction of polyetheramine D2000 to Fe-pillared clay mineral at 70 °C. The molecular spectroscopy including FT-IR and FT-Raman, thermogravimetric analysis (TG) were used to characterize the magnetically modified clay mineral. XRD, SEM and TEM, UV–Vis Diffuse Reflectance spectroscopy (UVDRS) and magnetization measurement were applied to explore the structural information of the magnetically modified clay mineral. The results suggested that the magnetic species of γFe2O3 nanophase particles were embedded on the surface of the modified clay mineral and the magnetization was improved significantly due to the increase of iron content by addition of polyetheramine D2000. A possible mechanism was suggested that the polyetheramine D2000 rodlike micelles were formed at 70 °C and interacted with polyhydrated iron to form adducts, which were treated in acetic acid vapor before calcination at 400 °C to produce magnetic species embedded on the surface of Fe-pillared clay mineral. The performance of the magnetically modified clay mineral was evaluated by adsorption of methyl orange and intensified separation by external magnetic field. The results indicate that its excellent performance on adsorption and magnetic separation makes a comprehensive application potential in chemical engineering and environmental pollution control. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The technologies to the disposal of organic wastewater become dominant assignments and the demands of effective adsorbents and catalysts to remove the contaminants are increasing. However, how to recycle and reuse clay mineral composites from solution has been a challenge for applicant and researcher. Magnetic materials therewith large specific surface area, superparamagnetism and the ability of catalysis, have prominent applications in biological (Wang et al., 2004), medical (Mornet et al., 2006) and environmental (Hu et al., 2007) fields. Magnetization of the modified clay mineral not only restrains the aggregation of nano-scale magnetic particles, but also promotes the separation efficiency of recycling and reusing clay mineral composites from solution (Skoutelas et al., 1999; Bourlinos et al., 2000; Oliveira et al., 2003; Ma et al., 2005; Szabo et al., 2007). The interlayer of montmorillonite has been considered as a reactive site by intercalation to develop functionally inorgano- or organomodified clay minerals. It can improve the physicochemical properties, such as thermal stability, adsorption capacity, and separation efficiency so on (Canizares et al., 1999; Binitha and Sugunan, 2006;
⁎ Corresponding author. Tel./fax: + 86 10 64438933. E-mail address: [email protected] (J. Yu). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.12.007
Meier et al., 2001; Yan et al., 2007; Zhou et al., 2004, 2006). Bourlinos et al. (2000) reported that Fe-pillared clay mineral could be treated in acetic acid vapor and calcined to prepare magnetically modified clay mineral. In order to improve the magnetization of the magnetically modified clay mineral, the intercalation process had to be repeated three times for increasing the load of Fe content within the interlayer of montmorillonite. Organo–inorgano modified clay minerals (Zhu et al., 2007) by surfactant were reported to exhibit much larger specific surface area, adsorptive capacity and thermal stability than organoclay or inorganoclay minerals. Lin et al. (2001) and Wang and Pinnavaia (2003) reported that polyetheramine D2000 with long chain could expand the interlamellar space of montmorillonite by ca. 9 nm. Wang et al. (2008) tried to use polyetheramine D2000 as structural regulator to optimize the size and morphology of nano-TiO2 particles within the interlayer of clay mineral for improving the photocatalytic performance of the TiO2 modified clay mineral. The surfactant was proved to be effective to adjust the content and structural statue of inorganic pillars in the interlayer of the modified clay mineral. This paper aims to improve the magnetization of Fe-pillared clay mineral by increasing the load of magnetic species with application of polyetheramine D2000 as structural regulator. The effect of the reaction temperature on the formation of magnetic species was investigated. The magnetically modified clay mineral was characterized comprehensively
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by FT-IR/Raman, XRD and SEM/TEM, etc. Its adsorption and separation properties were evaluated by the removal efficiency of methyl orange with assistant of an external magnetic field.
2. Experimental 2.1. Materials The sodium-montmorillonite (Na+-MT) was provided by Fenghong Ltd., Zhejiang Province, with cation exchange capacity (CEC) of 73 meq/100 g. Na+-MT was pretreated with deionized water and ethanol, and then dried at 45 °C and crushed into powder, griddled through 200 mesh. FeCl 3·6H2O, A.R., was used without any pretreatment. The polyetheramine named Jeffamine D-2000 (O,O′-Bis(2aminopropyl)polypropyleneglycol) is shown in Fig. 1. It is a difunctional primary amine with average molecular weight of about 2000, and the primary amine group is located on the second carbon atom at the end of the aliphatic chain. It was obtained as a gift from Huisheng International Trade Ltd. without any pretreatment before use.
2.2. Instrumental characterization FT-IR spectra were recorded on a Nicolet 8700 spectrometer. Samples were ground to powder and pressed in KBr pellets. FT-IR spectra with a spectral resolution of 2 cm−1 were collected over an average of 32 scans. FT-Raman spectra were collected on a Bruker FTS100 apparatus with a Nd:YAG laser source (λexc = 1064 nm). The operating power for the exciting laser radiation was kept to 100 mW for all samples. Samples were analyzed directly as powder. Typically, 200 – 300 scans from 3500– 50 cm−1 with a spectral resolution of 2 cm−1 were averaged to optimize the signal-to-noise ratio. The scanning electron microscopy (SEM) measurement was carried out in a JEOL JSM-6700F cold field emission scanning electron microscope operating at 5.0 kV accelerating voltage. The samples were dispersed in ethanol and dropped on the tinfoil. The transmission electron microscopy (TEM) images were taken on a FEI Tecnai20 electron microscope operating at 120 kV accelerating voltage. The samples were dispersed in ethanol with ultrasonic and dropped on the copper grids. XRD analyses were preformed on a Rigaku (Japan) D/Max 2500 VB2+/PC X-ray powder diffractometer operating with Cu Kα radiation (λ = 1.54056 Å), and a generator voltage of 40 kV and a current of 200 mA in 2θ ranging from 3° to 90°. UV–Vis diffuse reflection spectra (UVDRS) were recorded from 230–850 nm on TU-1901 ultraviolet–visible spectrophotometer (Beijing Purkinje General Instrument Co. Ltd.) with integration sphere by BaSO4 as the normative contrast powder. The powder samples were pressed as pellets with 25 mm diameter in a model for use. TG analyses were carried on a Perkin-Elmer TGS-2 thermogravimetric analyzer at 10 °C/min from 0 °C to 400 °C in N2. Magnetic measurements were obtained at room temperature with a Lake Shore 7410 vibrating sample magnetometer (VSM).
Fig. 1. Chemical structure of polyetheramine D2000 (O,O′-Bis(2-aminopropyl) polypropylene glycol).
Fig. 2. Synthetic pathways of the magnetically modified clay Femag-MT.
2.3. Synthesis of magnetically modified clay mineral 1 g Na+-montmorillonite was dispersed in 50 mL deionized water and stirred for 6 h for the preparation of montmorillonite dispersion. A similar iron-exchanged clay mineral was obtained followed the method by Bourlinos et al. (2000) with addition of 100 mL 0.4 M FeCl3⋅6H2O solution dropwise to the clay dispersion for 4 h (Fe-MT). And then, 100 mL of the mixture of 0.855 mM polyetheramine D2000 and 1.7 mM HCl was added to the dispersion of Fe-MT. After mixed at 70 °C for 9 h, the mixture was kept for one night. The sample was collected by centrifugation and washed with water and ethanol until no Cl− detected by AgNO3. The solid was dried under vacuum, and crushed into powder (Fe/D-MT). Following that, the powder was exposed in glacial acetic acid vapor for 2 h at 80 °C, and then dried at the same temperature for a few minutes in order to remove the surface-adsorbed acetic acid to get brown powder of Fe/D/Ac-MT. Finally, the brown powder was calcined at 400 °C for 1 h in air for the formation of the magnetically modified clay mineral of Femag-MT. The synthetic route to the magnetically modified clay mineral is shown in Fig. 2. The D2000 modified MT (D2000-MT) was prepared by mixing polyetheramine D2000 and the dispersion of montmorillonite for 4 h at room temperature.
Fig. 3. XRD patterns of MT, Fe-MT, Fe/D-MT, Fe/D/AC-MT and Femag-MT.
J. Yu, Q.-X. Yang / Applied Clay Science 48 (2010) 185–190
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Fig. 6. The thermogravimetric curves of Fe/D/Ac-MT (solid line) and D2000-MT (dot line).
Fig. 4. FT-IR spectra of montmorillonite and the modified montmorillonite.
2.4. Adsorption Methyl orange solution was used to evaluate the adsorption and separation properties of the magnetically modified clay mineral. The concentrations of the initial methyl orange solution and the modified clay mineral were 10.4 mg L−1 and 5.0 mg L−1, respectively. The removal efficiency of methyl orange was calculated according to the concentration of methyl orange solution treated by the magnetically modified clay mineral at a specific reaction time. The concentration of methyl orange solution was analyzed on an UV–Vis spectrophotometer at 464 nm.
Fig. 5. Raman spectra of the samples of Fe/D-MT, Fe/D/AC-MT.
Fig. 7. SEM micrographs of Fe/D-MT (a) and Femag-MT (b) prepared at 70 °C.
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Fig. 8. TEM micrograph of Femag-MT prepared at 70 °C.
3. Result and discussion 3.1. Synthesis characterization Iron ion has been reported to be hydrolysized in aqueous solution to form polyhydrated iron and transformed to iron acetate in acetic acid vapor. In 1977, Jewur and Kuriacose (1977) pointed out that iron acetate could be pyrolysized to form γ-Fe2O3 magnetic particle with loss of carbon dioxide and acetone. In 2000, Bourlinos et al. (2000) first reported to prepare magnetically modified clay minerals by Fepillared clay mineral treated in acetic acid vapor, but the intercalation procedure should be repeated three times for increasing the content of magnetic species. Wang et al.'s (2008) work indicated that the interlamellar space of TiO2-pillared clay mineral was expanded with addition of polyetheramine D2000 as structural regulator and increased the content of TiO2 within the interlayer of clay mineral. Herein, polyetheramine D2000 was used as a polymeric surfactant to tailor the magnetic species in Fe-pillared clay mineral and expected to improve the saturation magnetization of Fe-pillared clay mineral in this work. Fig. 3 presents the XRD patterns of the samples of MT, Fe-MT, Fe/DMT, Fe/D/AC-MT and Femag-MT. d001 of Fe-MT increased to 1.42 nm from 1.26 nm (d001, MT) due to the intercalation of polyhydrated iron. After addition of polyetheramine D2000, d001 of Fe/D-MT moved to 1.79 nm, but was far from d001 (ca.9 nm) of D2000 modified montmorillonite by Lin et al. (2001). Those suggest that fewer polyetheramine D2000 were intercalated to the interlayer of the modified clay mineral and most polyetheramine D2000 were embedded on the surface of clay. We observe that there was no obvious change in d001 of Fe/D/AC-MT after it was exposed to acetic acid vapor. Therefore, the formation of iron
acetate did not change the size of polyhydrated iron after it interacted with acetic acid. With formation of magnetic species by calcination at 400 °C, Fe/D/AC-MT was transformed to Femag-MT. But, d001 of FemagMT decreased to 1.22 nm similar to d001 (1.26 nm) of the original clay MT, and the corresponding reflection became smaller and broader compared with the original MT. Therefore, the magnetic species did not exist in the interlamellar space of Femag-MT. Fig. 4 shows the FT-IR spectra of MT and the modified clay minerals. There were fewer IR spectral differences between MT and Fe-MT (Fig. 4a), which implied that the modified clay mineral kept its original structural configuration after intercalation. However, Fe/ACMT gave out two distinct vibration peaks at 1726 and 1451 cm−1 assigned to the symmetric and asymmetric stretching vibrations of the –COO− of acetate anion (Bourlinos et al., 2000). Obviously, Fe-MT was transformed to Fe/AC-MT due to the interaction of iron ion within the interlamellar space of montmorillonite in acetic acid vapor. Additionally, the stretching vibrations of the combined water molecules from 3620 to 3630 cm−1 became weaker after polyetheramine D2000 was introduced to the modified clay minerals due to water loss (Fig. 4b). We also observe the symmetric and asymmetric stretching vibrations of C–H bonds in the region of 2857 to 2985 cm−1, and –COO− of acetate anion at 1726 and 1457 cm−1 in the modified clay minerals. So, polyetheramine D2000 was introduced into Fe-MT successfully to form Fe/D-MT and transformed into Fe/D/AC-MT after treated in acetic acid vapor. The Raman spectra in Fig. 5 also proved that polyetheramine D2000 was introduced to the modified clay minerals because all of them showed the deformation vibration of –NH2 at 1578 cm−1 and the vibrations of C–O–C at 936 cm−1 and 1100 cm−1. Fig. 6 is the comparative thermogravimetric results of Fe/D/AC-MT and D2000-MT. D2000-MT was decomposed at ca.230 °C due to the loss of the organic composition. While Fe/D/AC-MT presented two stages of mass loss with 10.2% and 9.8% corresponding to a stage of room temperature to ca. 230 °C and another stage of ca. 230 °C to 400 °C, respectively. The pyrolysis of iron acetate to magnetic species just only occurred at 400 °C. Therefore, the mass loss of Fe/D/AC-MT at the first stage from room temperature to 230 °C could be attributed to the removal of the adsorbed water on the surface of Fe/D/AC-MT. The second mass loss stage could be attributed to the decomposition of polyetheramine D2000. 3.2. Structural characterization Contradistinguishing with the JCPDS database, it revealed the presence of Maghemite-C (card 39-1346) with the reflections at 2θ = 30.18° and 35.60°. The characteristic for the spine-type structure in Fig. 3 indicates that the magnetic species of γ-Fe2O3 were formed in Femag-MT after Fe/D/AC-MT was calcined at 400 °C. These results are in good agreement with the reports by Jewur and Kuriacose (1977) and Pinheiro et al. (1987) that iron acetate could be transformed into crystalline magnetic phases after pyrolysis. Bourlinos et al. (2000) figured out that the magnetic species of γFe2O3 transferred to the surface of clay mineral after iron acetate within the interlamellar space was calcined. The XRD results in Fig. 3 definitely indicated that no magnetic species existed within the
Fig. 9. The schematics of formation and immobilization of hollow rodlike nano-iron oxide particle on the surface of clay ( : polyhydrated iron, , : D2000 micelle, : clay).
: polyetheramine D2000
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Fig. 12. Magnetization versus magnetic field curve of Femag-MT. Fig. 10. SEM micrograph of Fe/D-MT prepared at room temperature.
interlamellar space of Femag-MT. The SEM images in Fig. 7 showed lots of rodlike particles with a size of 200 nm × 50 nm on the surface of Fe/D-MT and Femag-MT. These rodlike particles obviously originated from iron oxides. The TEM image in Fig. 8 not only presented the same microstructures of the rodlike particles as SEM showed but also revealed that the rodlike particles had hollow microstructures (Fig. 8). 3.3. Possible mechanism of rodlike structural formation Polyetheramine D2000 is a kind of polymeric surfactant composed of two hydrophilic amine-end groups and a long hydrophobic PPO (polypropylene oxide) chain. Tohru and Kohei (2006) reported that the aggregation behavior of PPO was quite sensitive to temperature changes. At low temperature, the polymer dissolved in water as a unimer. The unimer solution underwent a phase separation to give a turbid solution with temperature increase. Further increase in temperature produced a transparent micellar solution. Therefore, the rodlike particles could be seen as adducts of polyetheramine D2000 micelles and polyhydrated iron by chemical interaction and then embedded on the surface of clay mineral. Fig. 9 describes the schematic of the rodlike micellar formation and its immobilization on the surface of Femag-MT. Four stages are suggested for the preparation of Femag-MT. I: In the dispersion of polyhydrated iron, clay MT and polyetheramine D2000, polyetheramine D2000 micelle was composed of
Fig. 11. Diffuse reflectance ultraviolet–visible spectrum of MT, Fe/D-MT, Femag-MT.
internal “hydrophobic core” by aliphatic PPO chain and external “hydrophilic layer” by –NH+ 4 formed at 70 °C; II: The end group of –NH+ 4 on the external “hydrophilic layer” interacted with polyhydrated iron by chemical interaction to form an adduct; III: The adduct of polyetheramine D2000 micelle and polyhydrated iron by chemical interaction was embedded on the surface of the modified clay mineral; IV: After polyhydrated iron was transformed to iron acetate in acetic acid vapor, acetate iron was pyrolyzed to form the magnetic species of γ-Fe2O3 at 400 °C, meanwhile, the internal core of “hydrophilic layer” was decomposed and then formed a hollow rodlike microstructure as the TEM image which was shown in Fig. 8. At room temperature, there was not any rodlike particle observed on the surface of the modified clay mineral as Fig. 10 shows. So, it is necessary to conduct the preparation of the magnetically modified clay mineral at a higher temperature in order to form polyetheramine D2000 micelles, which could improve the content of iron oxide on the surface of the modified clay mineral. Fig. 11 presents the comparison of the diffuse reflectance ultraviolet– visible spectra among MT, Fe/D-MT and Femag-MT. It can be seen that the modified clay minerals were sensitive to the irradiation of the UV– Vis light. Especially, Femag-MT presented a furthermore stronger absorbance to the UV–Vis light in comparison with Fe/D-MT, which implied that the magnetic clay mineral could be applied as a photocatalyst besides easily separable absorbents.
Fig. 13. Removal efficiency of methyl orange solution as a function of adsorption time.
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mineral. The adduct acted as the precursors of magnetic species of γFe2O3 nanophase particles to improve the saturation magnetization up to 26.78 emu g−1 after treated in acetic acid vapor and calcined at 400 °C. The magnetically modified clay mineral can be used as absorbent and photocatalyst to remove organic pollutants effectively in aqueous solution. It can take the advantage of its superparamagnetization to recycle and reuse the magnetic clay mineral easily by external magnetic field. These important properties are expected to possess comprehensive prospects in chemical applications and environmental engineering.
Acknowledgements This work is supported by National Natural Science Foundation of China (No. 50672101). The authors would express thanks to Sun Lei, the Center for Biological Electron Microscopy, for taking TEM images, and to the National Institute of Metrology PR China for VSM measurement.
References
Fig. 14. The picture of magnetic separation of methyl orange by external magnet.
3.4. Performance characterization This work aims to improve the saturation magnetization of the magnetically modified clay mineral with application of polyetheramine D2000. By Bourlinos et al.'s (2000) work, the intercalation process should be conducted three times for increasing the content of polyhydrated iron. But they only got the magnetically modified clay mineral with saturation magnetization up to 4.1 emu g−1. Szabo et al. (2007) also reported a magnetic clay mineral prepared by pH adjustment and repeated intercalation with saturation magnetization up to 8.56 emu g−1. The magnetization curve of Femag-MT in Fig. 12 gave a saturation magnetization at 26.78 emu g−1 much higher than what Bourlinos et al. (2000) and Szabo et al. (2007) reported. Femag-MT was observed that there was no hysteresis and the curve was completely reversible. Furthermore, the coercivity and remanence magnetization were very low and could be ignored. This so-called superparamagnetic property can intensify the separation and recovery performance of magnetically modified clay mineral composites as absorbents or catalysts from aqueous solution. The adsorption of methyl orange by Femag-MT is shown in Fig. 13. As time went on, methyl orange solution turned to light-colored gradually. The concentration of methyl orange decreased from 10.4 mg L−1 to 1.613 mg L−1 after 40 min. 84% methyl orange was removed. Fig. 14 clearly indicates that Femag-MT could be separated and recovered easily with a magnet from aqueous solution without being centrifuged. 4. Conclusions The magnetically modified clay mineral was synthesized with an addition of polyetheramine D2000 as a structural regulator to tailor Fepillared clay mineral in acetic acid vapor. Polyetheramine D2000 rodlike micelle was formed with nano-size of about 200 × 50 nm in aqueous solution at 70 °C, and interacted with polyhydrated iron to produce an adduct embedded on the surface of the magnetically modified clay
Binitha, N.N., Sugunan, S., 2006. Preparation, characterization and catalytic activity of titania pillared montmorillonite clays. Micropor. Mesopor. Mater. 93, 82–89. Bourlinos, A.B., Karakassides, M.A., Simopoulos, A., Petridis, D., 2000. Synthesis and characterization of magnetically modified clay composites. Chem. Mater. 12, 2640–2645. Canizares, P., Valverde, J.L., Kou, M.R.S., Molina, C.B., 1999. Synthesis and characterization of PILCs with single and mixed oxide pillars prepared from two different bentonites. A comparative study. Micropor. Mesopor. Mater. 29, 267–281. Hu, J., Lo, I.M.C., Chen, G.H., 2007. Performance and mechanism of chromate (VI) adsorption by δ-FeOOH-coated maghemite (γ-Fe2O3) nanoparticles. Sep. Purif. Technol. 58, 76–82. Jewur, S.S., Kuriacose, J.C., 1977. Studied on the thermal decomposition of ferric acetate. Thermochim. Acta. 19, 195–200. Lin, J.J., Cheng, I.J., Wang, R., Lee, R.J., 2001. Tailoring basal spacings of montmorillonite by poly(oxyalkylene)diamine intercalation. Macromolecules 34, 8832–8834. Ma, X.C., Xu, F., Chen, L.Y., Zhang, Z.D., Du, Y., Xie, Y., 2005. Magnetic fluids for synthesis of the stable adduct γ-Fe2O3/CTAB/Clay. J. Cryst. Growth. 280, 118–125. Meier, L.P., Nueesch, R., Madsen, F.T., 2001. Organic pillared clays. J. Colloid Interface Sci. 238, 24–32. Mornet, S., Vasseur, S., Grasset, F., Veverka, P., Goglio, G., Demourgues, A., Portier, J., Pollert, E., Duguet, E., 2006. Magnetic nanoparticle design for medical applications. Prog. Solid State Chem. 34, 237–247. Oliveira, L.C.A., Rios, R.V.R.A., Fabris, J.D., Sapag, K., Garg, V.K., Lago, R.M., 2003. Clay– iron oxide magnetic composites for the adsorption of contaminants in water. Appl. Clay Sci. 22, 169–177. Pinheiro, E.A., Filho, P.P.A., Galembeck, F., 1987. Magnetite crystal formation from iron (III) hydroxide acetate. An ESR study. Langmuir 3, 445–448. Skoutelas, A.P., Karakassides, M.A., Petridis, D., 1999. Magnetically modified Al2O3 pillared clays. Chem. Mater. 11, 2754–2759. Szabo, T., Bakandritsos, A., Tzitzios, V., Papp, S., Korosi, L., Galbacs, G., Musabekov, K., Bolatova, D., Petridis, D., Dekany, I., 2007. Magnetic iron oxide/clay composites: effect of the layer silicate support on the microstructure and phase formation of magnetic nanoparticles. Nanotechnology 18, 1–9. Tohru, I., Kohei, Y., 2006. Aggregation behavior of polypropylene oxide with electric charges at both ends in aqueous solution. J. Colloid Interface Sci. 300 (2), 774–781. Wang, Z., Pinnavaia, T.J., 2003. Intercalation of poly(propyleneoxide) amines (Jeffamines) in synthetic layered silicas derived from ilerite, magadiite, and kenyaite. J. Mater. Chem. 13, 2127–2131. Wang, D., He, J., Rosenzweig, N., Rosenzweig, Z., 2004. Superparamagnetic Fe2O3 beadsCdSe/ZnS quantum dots core–shell nanocomposite particles for cell separation. Nano Letters. 4, 409–413. Wang, C.J., Yu, J., Xing, J.M., Liu, H.Z., 2008. Structure and properties of polymer modified TiO2 pillared Montmorillonite. Front. Chem. China 3 (3), 309–313. Yan, L.G., Wang, J., Yu, H.Q., Wei, Q., Du, B., Shan, X.Q., 2007. Adsorption of benzoic acid by CTAB exchanged montmorillonite. Appl. Clay Sci. 37, 226–230. Zhou, C.H., Li, X.N., Ge, Z.H., Li, Q.W., Tong, D.S., 2004. Synthesis and acid catalysis of nanoporous silica/alumina–clay composites. Cataly. Today 93–5, 607–613. Zhou, C.H., Tong, D.S., Bao, M.H., Du, Z.X., Ge, Z.H., Li, X.N., 2006. Generation and characterization of catalytic nanocomposite materials of highly isolated iron nanoparticles dispersed in clays. Top. Catal. 39 (3–4), 213–219. Zhu, L.Z., Tian, S.L., Zhu, J.X., Shi, Y., 2007. Silylated pillared clay (SPILC): a novel bentonite-based inorgano–organo composite sorbent synthesized by integration of pillaring and silylation. J. Colloid Interface Sci. 315, 191–199.
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Magnetization improvement of Fe-pillared clay with application of polyetheramine Jiang Yu ⁎, Qiu-Xin Yang Research Group of Environmental Catalysis and Separation Process, Department of Environmental Science and Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China
a r t i c l e
i n f o
Article history: Received 14 July 2009 Received in revised form 3 December 2009 Accepted 9 December 2009 Available online 21 December 2009 Keywords: Iron oxide/clay composites Polyetheramine Superparamagnetism Magnetization
a b s t r a c t Polyetheramine D2000 (O,O′-Bis(2-aminopropyl)polypropyleneglycol) was used as structural regulator to modify Fe-pillared clay mineral, and treated with acetic acid vapor prior to calcination for improving the magnetization of magnetically modified clay mineral. The magnetization of the magnetically modified clay mineral was improved to 26.78 emu g−1 with introduction of polyetheramine D2000 to Fe-pillared clay mineral at 70 °C. The molecular spectroscopy including FT-IR and FT-Raman, thermogravimetric analysis (TG) were used to characterize the magnetically modified clay mineral. XRD, SEM and TEM, UV–Vis Diffuse Reflectance spectroscopy (UVDRS) and magnetization measurement were applied to explore the structural information of the magnetically modified clay mineral. The results suggested that the magnetic species of γFe2O3 nanophase particles were embedded on the surface of the modified clay mineral and the magnetization was improved significantly due to the increase of iron content by addition of polyetheramine D2000. A possible mechanism was suggested that the polyetheramine D2000 rodlike micelles were formed at 70 °C and interacted with polyhydrated iron to form adducts, which were treated in acetic acid vapor before calcination at 400 °C to produce magnetic species embedded on the surface of Fe-pillared clay mineral. The performance of the magnetically modified clay mineral was evaluated by adsorption of methyl orange and intensified separation by external magnetic field. The results indicate that its excellent performance on adsorption and magnetic separation makes a comprehensive application potential in chemical engineering and environmental pollution control. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The technologies to the disposal of organic wastewater become dominant assignments and the demands of effective adsorbents and catalysts to remove the contaminants are increasing. However, how to recycle and reuse clay mineral composites from solution has been a challenge for applicant and researcher. Magnetic materials therewith large specific surface area, superparamagnetism and the ability of catalysis, have prominent applications in biological (Wang et al., 2004), medical (Mornet et al., 2006) and environmental (Hu et al., 2007) fields. Magnetization of the modified clay mineral not only restrains the aggregation of nano-scale magnetic particles, but also promotes the separation efficiency of recycling and reusing clay mineral composites from solution (Skoutelas et al., 1999; Bourlinos et al., 2000; Oliveira et al., 2003; Ma et al., 2005; Szabo et al., 2007). The interlayer of montmorillonite has been considered as a reactive site by intercalation to develop functionally inorgano- or organomodified clay minerals. It can improve the physicochemical properties, such as thermal stability, adsorption capacity, and separation efficiency so on (Canizares et al., 1999; Binitha and Sugunan, 2006;
⁎ Corresponding author. Tel./fax: + 86 10 64438933. E-mail address: [email protected] (J. Yu). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.12.007
Meier et al., 2001; Yan et al., 2007; Zhou et al., 2004, 2006). Bourlinos et al. (2000) reported that Fe-pillared clay mineral could be treated in acetic acid vapor and calcined to prepare magnetically modified clay mineral. In order to improve the magnetization of the magnetically modified clay mineral, the intercalation process had to be repeated three times for increasing the load of Fe content within the interlayer of montmorillonite. Organo–inorgano modified clay minerals (Zhu et al., 2007) by surfactant were reported to exhibit much larger specific surface area, adsorptive capacity and thermal stability than organoclay or inorganoclay minerals. Lin et al. (2001) and Wang and Pinnavaia (2003) reported that polyetheramine D2000 with long chain could expand the interlamellar space of montmorillonite by ca. 9 nm. Wang et al. (2008) tried to use polyetheramine D2000 as structural regulator to optimize the size and morphology of nano-TiO2 particles within the interlayer of clay mineral for improving the photocatalytic performance of the TiO2 modified clay mineral. The surfactant was proved to be effective to adjust the content and structural statue of inorganic pillars in the interlayer of the modified clay mineral. This paper aims to improve the magnetization of Fe-pillared clay mineral by increasing the load of magnetic species with application of polyetheramine D2000 as structural regulator. The effect of the reaction temperature on the formation of magnetic species was investigated. The magnetically modified clay mineral was characterized comprehensively
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by FT-IR/Raman, XRD and SEM/TEM, etc. Its adsorption and separation properties were evaluated by the removal efficiency of methyl orange with assistant of an external magnetic field.
2. Experimental 2.1. Materials The sodium-montmorillonite (Na+-MT) was provided by Fenghong Ltd., Zhejiang Province, with cation exchange capacity (CEC) of 73 meq/100 g. Na+-MT was pretreated with deionized water and ethanol, and then dried at 45 °C and crushed into powder, griddled through 200 mesh. FeCl 3·6H2O, A.R., was used without any pretreatment. The polyetheramine named Jeffamine D-2000 (O,O′-Bis(2aminopropyl)polypropyleneglycol) is shown in Fig. 1. It is a difunctional primary amine with average molecular weight of about 2000, and the primary amine group is located on the second carbon atom at the end of the aliphatic chain. It was obtained as a gift from Huisheng International Trade Ltd. without any pretreatment before use.
2.2. Instrumental characterization FT-IR spectra were recorded on a Nicolet 8700 spectrometer. Samples were ground to powder and pressed in KBr pellets. FT-IR spectra with a spectral resolution of 2 cm−1 were collected over an average of 32 scans. FT-Raman spectra were collected on a Bruker FTS100 apparatus with a Nd:YAG laser source (λexc = 1064 nm). The operating power for the exciting laser radiation was kept to 100 mW for all samples. Samples were analyzed directly as powder. Typically, 200 – 300 scans from 3500– 50 cm−1 with a spectral resolution of 2 cm−1 were averaged to optimize the signal-to-noise ratio. The scanning electron microscopy (SEM) measurement was carried out in a JEOL JSM-6700F cold field emission scanning electron microscope operating at 5.0 kV accelerating voltage. The samples were dispersed in ethanol and dropped on the tinfoil. The transmission electron microscopy (TEM) images were taken on a FEI Tecnai20 electron microscope operating at 120 kV accelerating voltage. The samples were dispersed in ethanol with ultrasonic and dropped on the copper grids. XRD analyses were preformed on a Rigaku (Japan) D/Max 2500 VB2+/PC X-ray powder diffractometer operating with Cu Kα radiation (λ = 1.54056 Å), and a generator voltage of 40 kV and a current of 200 mA in 2θ ranging from 3° to 90°. UV–Vis diffuse reflection spectra (UVDRS) were recorded from 230–850 nm on TU-1901 ultraviolet–visible spectrophotometer (Beijing Purkinje General Instrument Co. Ltd.) with integration sphere by BaSO4 as the normative contrast powder. The powder samples were pressed as pellets with 25 mm diameter in a model for use. TG analyses were carried on a Perkin-Elmer TGS-2 thermogravimetric analyzer at 10 °C/min from 0 °C to 400 °C in N2. Magnetic measurements were obtained at room temperature with a Lake Shore 7410 vibrating sample magnetometer (VSM).
Fig. 1. Chemical structure of polyetheramine D2000 (O,O′-Bis(2-aminopropyl) polypropylene glycol).
Fig. 2. Synthetic pathways of the magnetically modified clay Femag-MT.
2.3. Synthesis of magnetically modified clay mineral 1 g Na+-montmorillonite was dispersed in 50 mL deionized water and stirred for 6 h for the preparation of montmorillonite dispersion. A similar iron-exchanged clay mineral was obtained followed the method by Bourlinos et al. (2000) with addition of 100 mL 0.4 M FeCl3⋅6H2O solution dropwise to the clay dispersion for 4 h (Fe-MT). And then, 100 mL of the mixture of 0.855 mM polyetheramine D2000 and 1.7 mM HCl was added to the dispersion of Fe-MT. After mixed at 70 °C for 9 h, the mixture was kept for one night. The sample was collected by centrifugation and washed with water and ethanol until no Cl− detected by AgNO3. The solid was dried under vacuum, and crushed into powder (Fe/D-MT). Following that, the powder was exposed in glacial acetic acid vapor for 2 h at 80 °C, and then dried at the same temperature for a few minutes in order to remove the surface-adsorbed acetic acid to get brown powder of Fe/D/Ac-MT. Finally, the brown powder was calcined at 400 °C for 1 h in air for the formation of the magnetically modified clay mineral of Femag-MT. The synthetic route to the magnetically modified clay mineral is shown in Fig. 2. The D2000 modified MT (D2000-MT) was prepared by mixing polyetheramine D2000 and the dispersion of montmorillonite for 4 h at room temperature.
Fig. 3. XRD patterns of MT, Fe-MT, Fe/D-MT, Fe/D/AC-MT and Femag-MT.
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Fig. 6. The thermogravimetric curves of Fe/D/Ac-MT (solid line) and D2000-MT (dot line).
Fig. 4. FT-IR spectra of montmorillonite and the modified montmorillonite.
2.4. Adsorption Methyl orange solution was used to evaluate the adsorption and separation properties of the magnetically modified clay mineral. The concentrations of the initial methyl orange solution and the modified clay mineral were 10.4 mg L−1 and 5.0 mg L−1, respectively. The removal efficiency of methyl orange was calculated according to the concentration of methyl orange solution treated by the magnetically modified clay mineral at a specific reaction time. The concentration of methyl orange solution was analyzed on an UV–Vis spectrophotometer at 464 nm.
Fig. 5. Raman spectra of the samples of Fe/D-MT, Fe/D/AC-MT.
Fig. 7. SEM micrographs of Fe/D-MT (a) and Femag-MT (b) prepared at 70 °C.
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Fig. 8. TEM micrograph of Femag-MT prepared at 70 °C.
3. Result and discussion 3.1. Synthesis characterization Iron ion has been reported to be hydrolysized in aqueous solution to form polyhydrated iron and transformed to iron acetate in acetic acid vapor. In 1977, Jewur and Kuriacose (1977) pointed out that iron acetate could be pyrolysized to form γ-Fe2O3 magnetic particle with loss of carbon dioxide and acetone. In 2000, Bourlinos et al. (2000) first reported to prepare magnetically modified clay minerals by Fepillared clay mineral treated in acetic acid vapor, but the intercalation procedure should be repeated three times for increasing the content of magnetic species. Wang et al.'s (2008) work indicated that the interlamellar space of TiO2-pillared clay mineral was expanded with addition of polyetheramine D2000 as structural regulator and increased the content of TiO2 within the interlayer of clay mineral. Herein, polyetheramine D2000 was used as a polymeric surfactant to tailor the magnetic species in Fe-pillared clay mineral and expected to improve the saturation magnetization of Fe-pillared clay mineral in this work. Fig. 3 presents the XRD patterns of the samples of MT, Fe-MT, Fe/DMT, Fe/D/AC-MT and Femag-MT. d001 of Fe-MT increased to 1.42 nm from 1.26 nm (d001, MT) due to the intercalation of polyhydrated iron. After addition of polyetheramine D2000, d001 of Fe/D-MT moved to 1.79 nm, but was far from d001 (ca.9 nm) of D2000 modified montmorillonite by Lin et al. (2001). Those suggest that fewer polyetheramine D2000 were intercalated to the interlayer of the modified clay mineral and most polyetheramine D2000 were embedded on the surface of clay. We observe that there was no obvious change in d001 of Fe/D/AC-MT after it was exposed to acetic acid vapor. Therefore, the formation of iron
acetate did not change the size of polyhydrated iron after it interacted with acetic acid. With formation of magnetic species by calcination at 400 °C, Fe/D/AC-MT was transformed to Femag-MT. But, d001 of FemagMT decreased to 1.22 nm similar to d001 (1.26 nm) of the original clay MT, and the corresponding reflection became smaller and broader compared with the original MT. Therefore, the magnetic species did not exist in the interlamellar space of Femag-MT. Fig. 4 shows the FT-IR spectra of MT and the modified clay minerals. There were fewer IR spectral differences between MT and Fe-MT (Fig. 4a), which implied that the modified clay mineral kept its original structural configuration after intercalation. However, Fe/ACMT gave out two distinct vibration peaks at 1726 and 1451 cm−1 assigned to the symmetric and asymmetric stretching vibrations of the –COO− of acetate anion (Bourlinos et al., 2000). Obviously, Fe-MT was transformed to Fe/AC-MT due to the interaction of iron ion within the interlamellar space of montmorillonite in acetic acid vapor. Additionally, the stretching vibrations of the combined water molecules from 3620 to 3630 cm−1 became weaker after polyetheramine D2000 was introduced to the modified clay minerals due to water loss (Fig. 4b). We also observe the symmetric and asymmetric stretching vibrations of C–H bonds in the region of 2857 to 2985 cm−1, and –COO− of acetate anion at 1726 and 1457 cm−1 in the modified clay minerals. So, polyetheramine D2000 was introduced into Fe-MT successfully to form Fe/D-MT and transformed into Fe/D/AC-MT after treated in acetic acid vapor. The Raman spectra in Fig. 5 also proved that polyetheramine D2000 was introduced to the modified clay minerals because all of them showed the deformation vibration of –NH2 at 1578 cm−1 and the vibrations of C–O–C at 936 cm−1 and 1100 cm−1. Fig. 6 is the comparative thermogravimetric results of Fe/D/AC-MT and D2000-MT. D2000-MT was decomposed at ca.230 °C due to the loss of the organic composition. While Fe/D/AC-MT presented two stages of mass loss with 10.2% and 9.8% corresponding to a stage of room temperature to ca. 230 °C and another stage of ca. 230 °C to 400 °C, respectively. The pyrolysis of iron acetate to magnetic species just only occurred at 400 °C. Therefore, the mass loss of Fe/D/AC-MT at the first stage from room temperature to 230 °C could be attributed to the removal of the adsorbed water on the surface of Fe/D/AC-MT. The second mass loss stage could be attributed to the decomposition of polyetheramine D2000. 3.2. Structural characterization Contradistinguishing with the JCPDS database, it revealed the presence of Maghemite-C (card 39-1346) with the reflections at 2θ = 30.18° and 35.60°. The characteristic for the spine-type structure in Fig. 3 indicates that the magnetic species of γ-Fe2O3 were formed in Femag-MT after Fe/D/AC-MT was calcined at 400 °C. These results are in good agreement with the reports by Jewur and Kuriacose (1977) and Pinheiro et al. (1987) that iron acetate could be transformed into crystalline magnetic phases after pyrolysis. Bourlinos et al. (2000) figured out that the magnetic species of γFe2O3 transferred to the surface of clay mineral after iron acetate within the interlamellar space was calcined. The XRD results in Fig. 3 definitely indicated that no magnetic species existed within the
Fig. 9. The schematics of formation and immobilization of hollow rodlike nano-iron oxide particle on the surface of clay ( : polyhydrated iron, , : D2000 micelle, : clay).
: polyetheramine D2000
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Fig. 12. Magnetization versus magnetic field curve of Femag-MT. Fig. 10. SEM micrograph of Fe/D-MT prepared at room temperature.
interlamellar space of Femag-MT. The SEM images in Fig. 7 showed lots of rodlike particles with a size of 200 nm × 50 nm on the surface of Fe/D-MT and Femag-MT. These rodlike particles obviously originated from iron oxides. The TEM image in Fig. 8 not only presented the same microstructures of the rodlike particles as SEM showed but also revealed that the rodlike particles had hollow microstructures (Fig. 8). 3.3. Possible mechanism of rodlike structural formation Polyetheramine D2000 is a kind of polymeric surfactant composed of two hydrophilic amine-end groups and a long hydrophobic PPO (polypropylene oxide) chain. Tohru and Kohei (2006) reported that the aggregation behavior of PPO was quite sensitive to temperature changes. At low temperature, the polymer dissolved in water as a unimer. The unimer solution underwent a phase separation to give a turbid solution with temperature increase. Further increase in temperature produced a transparent micellar solution. Therefore, the rodlike particles could be seen as adducts of polyetheramine D2000 micelles and polyhydrated iron by chemical interaction and then embedded on the surface of clay mineral. Fig. 9 describes the schematic of the rodlike micellar formation and its immobilization on the surface of Femag-MT. Four stages are suggested for the preparation of Femag-MT. I: In the dispersion of polyhydrated iron, clay MT and polyetheramine D2000, polyetheramine D2000 micelle was composed of
Fig. 11. Diffuse reflectance ultraviolet–visible spectrum of MT, Fe/D-MT, Femag-MT.
internal “hydrophobic core” by aliphatic PPO chain and external “hydrophilic layer” by –NH+ 4 formed at 70 °C; II: The end group of –NH+ 4 on the external “hydrophilic layer” interacted with polyhydrated iron by chemical interaction to form an adduct; III: The adduct of polyetheramine D2000 micelle and polyhydrated iron by chemical interaction was embedded on the surface of the modified clay mineral; IV: After polyhydrated iron was transformed to iron acetate in acetic acid vapor, acetate iron was pyrolyzed to form the magnetic species of γ-Fe2O3 at 400 °C, meanwhile, the internal core of “hydrophilic layer” was decomposed and then formed a hollow rodlike microstructure as the TEM image which was shown in Fig. 8. At room temperature, there was not any rodlike particle observed on the surface of the modified clay mineral as Fig. 10 shows. So, it is necessary to conduct the preparation of the magnetically modified clay mineral at a higher temperature in order to form polyetheramine D2000 micelles, which could improve the content of iron oxide on the surface of the modified clay mineral. Fig. 11 presents the comparison of the diffuse reflectance ultraviolet– visible spectra among MT, Fe/D-MT and Femag-MT. It can be seen that the modified clay minerals were sensitive to the irradiation of the UV– Vis light. Especially, Femag-MT presented a furthermore stronger absorbance to the UV–Vis light in comparison with Fe/D-MT, which implied that the magnetic clay mineral could be applied as a photocatalyst besides easily separable absorbents.
Fig. 13. Removal efficiency of methyl orange solution as a function of adsorption time.
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mineral. The adduct acted as the precursors of magnetic species of γFe2O3 nanophase particles to improve the saturation magnetization up to 26.78 emu g−1 after treated in acetic acid vapor and calcined at 400 °C. The magnetically modified clay mineral can be used as absorbent and photocatalyst to remove organic pollutants effectively in aqueous solution. It can take the advantage of its superparamagnetization to recycle and reuse the magnetic clay mineral easily by external magnetic field. These important properties are expected to possess comprehensive prospects in chemical applications and environmental engineering.
Acknowledgements This work is supported by National Natural Science Foundation of China (No. 50672101). The authors would express thanks to Sun Lei, the Center for Biological Electron Microscopy, for taking TEM images, and to the National Institute of Metrology PR China for VSM measurement.
References
Fig. 14. The picture of magnetic separation of methyl orange by external magnet.
3.4. Performance characterization This work aims to improve the saturation magnetization of the magnetically modified clay mineral with application of polyetheramine D2000. By Bourlinos et al.'s (2000) work, the intercalation process should be conducted three times for increasing the content of polyhydrated iron. But they only got the magnetically modified clay mineral with saturation magnetization up to 4.1 emu g−1. Szabo et al. (2007) also reported a magnetic clay mineral prepared by pH adjustment and repeated intercalation with saturation magnetization up to 8.56 emu g−1. The magnetization curve of Femag-MT in Fig. 12 gave a saturation magnetization at 26.78 emu g−1 much higher than what Bourlinos et al. (2000) and Szabo et al. (2007) reported. Femag-MT was observed that there was no hysteresis and the curve was completely reversible. Furthermore, the coercivity and remanence magnetization were very low and could be ignored. This so-called superparamagnetic property can intensify the separation and recovery performance of magnetically modified clay mineral composites as absorbents or catalysts from aqueous solution. The adsorption of methyl orange by Femag-MT is shown in Fig. 13. As time went on, methyl orange solution turned to light-colored gradually. The concentration of methyl orange decreased from 10.4 mg L−1 to 1.613 mg L−1 after 40 min. 84% methyl orange was removed. Fig. 14 clearly indicates that Femag-MT could be separated and recovered easily with a magnet from aqueous solution without being centrifuged. 4. Conclusions The magnetically modified clay mineral was synthesized with an addition of polyetheramine D2000 as a structural regulator to tailor Fepillared clay mineral in acetic acid vapor. Polyetheramine D2000 rodlike micelle was formed with nano-size of about 200 × 50 nm in aqueous solution at 70 °C, and interacted with polyhydrated iron to produce an adduct embedded on the surface of the magnetically modified clay
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