Magnetic modification of Ghassoul

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ScienceDirect Materials Today: Proceedings 5 (2018) S45–S51

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NanoOstrava_2017

Magnetic modification of Ghassoul Jana Seidlerováa, Klára Drobíkováa,b,*, Ondřej Životskýc, Kateřina Mamulová Kutlákováa, Vladimír Tomášeka a

Nanotechnology Centre, VŠB - Technical University of Ostrava, 17. listopadu. 15, Ostrava - Poruba 708 33, Czech Republic b IT4Innovations, VŠB - Technical University of Ostrava, 17. listopadu 15, Ostrava - Poruba 708 33, Czech Republic c Department of physics, VŠB - Technical University of Ostrava, 17. listopadu. 15, Ostrava - Poruba 708 33, Czech Republic

Abstract Ghassoul, a unique mixture of stevensite and sepiolite, comes from the only known deposit in the world, Jbel Ghassoul in Morocco. Ghassoul was found to be very good adsorbent of metal and organic pollutants and it can be also used for the preparation of cordierite ceramics. The presented study is focused on the preparation and study of magnetically modified Ghassoul. The microwave-assisted precipitation of iron oxides from water solution using FeSO4.7H2O as precursor was used for preparation magnetic form of Ghassoul. Both the native material and the prepared magnetic Ghassoul were characterized by chemical and phase analysis (X-ray fluorescence analysis, total content of selected elements after acid decomposition in acid mixture was determined by atomic absorption spectroscopy with flame atomization and atomic emission spectrometry with inductively coupled plasma, content of Fe(II) according to the Czech standard CSN 72 2041 and powder X-ray diffraction methods). The magnetic iron oxides on the Ghassoul surface were observed by transmission electron microscope. Saturation magnetization and coercive field were obtained from hysteresis loops measured using the Vibrating Sample Magnetometer. Verification of adsorption properties was carried out with Cd2+ ions. It was proved that the prepared magnetically modified clay minerals contained iron oxides nanoparticles of -Fe2O3 and Fe3O4 which were very strongly bound on the surface. The magnetic measurements have detected that saturation magnetization was approximately two orders higher and coercive field a little bit lower in comparison with the natural clay sample. The results show that the presence of magnetic iron particles on Ghassoul surface did not affect the adsorption properties negatively but make magnetic separation of adsorbent from aqueous solution possible. © 2018 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of NanoOstrava2017. Keywords: Ghassoul, magnetic modification, clay minerals, nanoparticles, adsorption.

* Corresponding author. Tel.: +420 597 321 551 E-mail address: [email protected] 2214-7853 © 2018 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of NanoOstrava2017.

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1. Introduction The negative impact of persistent pollutants on human health is described in a number of publications [1], therefore it is desirable to remove the pollution on a maximal scale. Both in practice and in laboratory scale, a wide range of methods and procedures are used for removing pollutants from the environment. These methods are usually divided according to the principle, the environment (gaseous, liquid, solid), or the nature of the pollutant. One of the most commonly used methods for gaseous and liquid environments is adsorption. This method is based on the mutual interaction of the adsorbent and the pollutant by contacting the gaseous or liquid product containing a pollutant adbent. A very frequent adsorbent is activated carbon [2-4], layered materials – phyllosilicates [5-9], slags [10,11], ash [12-14], and finally, biomaterials that are waste products (sawdust, orange peel, rice husks, etc.) [15-17]. New adsorbents are constantly being proposed to improve the adsorption efficiency, reduce the cost of cleaning technology and improve the functionality of the material. In the case of liquid environment, it is necessary to separate the cleansed liquid which is performed by filtration. This separation can be realized using magnetic field by application of a prepared adsorbent with magnetic properties. Commonly non-magnetic adsorbents (e.g. biosorbents, clay minerals) have already been modified by magnetic nanoor microparticles in order to prepare magnetically responsive composites allowing a significant simplification of the separation process whilst, in certain cases, improving their adsorption properties. Many of these adsorbents have been prepared in laboratory conditions and tested. Bentonite was modified by ferro-fluids, e.g. by Mockovcikova et al. [5] who focused on adsorption and removal of low concentrations of Cd, Ni and Zn ions. Other authors describe the adsorption of heavy metal ions on magnetically modified zeolites [5,6], bentonites [7,8] and montmorillonite [9]. New composites have also been prepared by combining two or more adsorbents, for example a magnetic nanosorbent from orange peel waste by co-precipitation of Fe3O4 nanoparticles with nanoparticles of hydroxyapatite [18] or zeolite [19,20]. These adsorbents have been successfully used to remove Cd2+ and Zn2+ ions from aqueous solutions. Some magnetic composites have also been modified by organic matter. Effective removal of heavy metal ions (Cd2+, Zn2+, Pb2+ and Cu2+) from an aqueous solution by polymerized magnetically modified nanoparticles was described by Ge et al. [20]. These authors have prepared new magnetically modified nanoparticles using 3-aminopropyltriethoxysilane and copolymers of acrylic acid and crotonic acid. This adsorbent could effectively remove metal ions with a maximum adsorption capacity at pH 5.5, and it could be used repeatedly. Various types of magnetic adsorbents, including many types of magnetically sensitive biocomposites, have been prepared and used to remove organic pollutants. Particular attention is paid to the removal of persistent compounds, especially organic dyes and polycyclic compounds. Several studies show the significant potential of these magnetic adsorbents for the above-mentioned group of compounds in detail [10,21]. Magnetic materials applicable in environmental technologies can be prepared by two basic procedures, namely: 1) direct synthesis of ferromagnetic, ferromagnetic [22] or 2) superparamagnetic nano- and micro particles. Typical materials are represented by magnetite, maghemite, various ferrite types, metallic iron, cobalt or nickel. For magnetic modification of the originally non-magnetic (diamagnetic) materials with suitable adsorption properties, it is possible to use, for example, various biological materials (e.g. polysaccharides, lignocellulosic material, food and agricultural waste, microbial or algal biomass, etc.), activated carbon, biochar, clay materials, etc. The simplest procedure is the precipitation of iron oxides from Fe(II) and Fe(III) ions in an alkaline medium. Alternative techniques are based on the use of magnetic fluids, microwave synthesis, or mechanochemical approaches [23]. 2. Materials and methods Ghassoul particles ≤ 40 m (G) was used for magnetic modification and adsorption experiment. Composite of Ghassoul /Fe3O4 (MG) was prepared by precipitation procedure using FeSO4.7H2O and microwave-assisted heating for 10 min at power 700, 2450 Mhz 24. After cooling, the MG was separated by filtration (pore size 0.23 μm) and dried at laboratory temperature. Chemical compositions of the G and the prepared magnetic modification MG were determined using an X-ray energy dispersive fluorescence spectrometer (XRFS), SPECTRO XLAB, Spectro. For this measurement, samples

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were fused with dilithium tetraborate and rapidly cooled to prepare the glass disc. The amount of carbonates in the studied materials was determined according to the ČSN 72 0121 standard [25]. Na, K, Mg, Li and Ca were determined, after acid digestion, by Atomic emission spectrometry with inductively coupled plasma (AES-ICP), SPECTRO CIROS VISION, Spectro. The amount of FeO in the studied G and MG was determined according to the ČSN 72 2041, Part 11 [26]. To determine the phases and structure of prepared samples (G and MG), X-ray powder diffraction analysis (XRPD), BRUKER AXS was used. X-ray powder diffraction patterns were recorded under Co Ka irradiation (k = 1.789 Å) using the Bruker D8 Advance diffractometer equipped with a fast position sensitive detector VÅNTEC 1. Reflection mode was used for all measurements. Phase composition was evaluated using database PDF 2 Release 2004 (International Centre for Diffraction Data). Powder samples (G and MG) were characterized by the transmission electron microscope JEOL 1200 EX at Institute of Electrical Engineering, Slovak Academy of Sciences in Bratislava (Slovak Republic). Powder samples (G and MG) were stirred in distilled water, than an appropriate amount of a specimen was put on a carbon grid. Accelerating voltage 120 kV and backscattered electron detector were used. Saturation magnetization and coercive field were obtained from hysteresis loops measured using the Vibrating Sample Magnetometer (VSM Microsense EV9) with maximal applied magnetic field of 20 kOe (saturation magnetization). Primary adsorption properties of the prepared composite (MG) were verified by batch adsorption techniques to study the effect of presence iron oxides on adsorption Cd2+ ions from water solution and verify interaction between iron oxides and G in MG. The 0.01 g of MG (and also G for comparision) was stirred in 100 ml solution with various concentrations of Cd2+ ions for one hour. Than the G/MG was separated using filtration through filter PRAGOPOR (pore size 0.23 μm) and the concentration of Cd2+ ions in filtrate was determined by flame atomization atomic FA-AAS (UNICAM 969, CHROMSPEC). To determine total concentration of Fe in filtrate, the part of filtrate was decomposed using concentrate HNO3 (65 %, Suprapur) at 95 oC. After filtrate decomposition, the total concentration of Fe was determined by FA-AAS. 3. Results and discussion The chemical composition of the native G and composite MG determined in the dried sample revealed the high amount of Si and Mg (Table 1). Table 1. The chemical composition of the native G and the composite MG. Parameter

G (wt. %)

Al2O3

MG (wt. %)

1.70  0.56

1.38  0.47

CaO

0.84  0.04

0.39  0.06

Fe2O3

0.75  0.05

8.5  0.6

K2O

0.68  0.05

0.23  0.03

LiO2

0.31  0.02

0.31  0.02

MgO

22.3  0.9

19.6  2.6

Na2O

0.85  0.06

< 0.05

SiO2

53.0  4.1

47.9  4.1

SO3

0.63  0.04

0.11  0.03

CO3

0.59  0.05

0.58  0.05

Sr

0.64  0.03

0.45  0.02

LOI

7.17  0.14

no determined

In the both materials, the native G and the composite MG, stevensite (Mg3Si4O10(OH)2), sepiolite (Mg4Si6O15(OH)2), quartz (SiO2), and celestine (SrSO4) were found to be dominant phases. Also, a small amounts of

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clinoenstatite (Mg2Si2O6), gypsum (CaSO4), and dolomite (CaMg(CO3)2) were observed (Fig. 1). Chemical composition of the detected phases agrees well with the results of XRFS analysis (see Table 1) and confirms the nature of G as silicate material, rich in magnesium.

Fig. 1. XRPD patterns of native G (a) and composite MG (b) with detected phase composition: 1-stevensite, 2-sepiolite, 3-quartz, 4-clinoenstatite, 6-dolomite, 7-celestine.

The chemical composition of the composite MG proved that the total content of Fe (expressed as Fe2O3) increased in comparison with the native G. Content of FeO in GM was also increased from 0.12 wt. % to 1.5 wt. %. The presence of iron oxides in prepared composite was confirmed diffraction pattern in Fig. 2. The principal problem of identification of prepared iron oxide particles in composite by powder diffraction is that the magnetite FexOy is marked in diffraction pattern. The FeO in diffraction pattent does not identifided and it can be assumed that determined FeO in MG relate with content of Fe3O4. The imagin in Fig. 2 proved, that the iron oxides were prepared in nanoscale. While Fig. 2a shows the surface of native G, the Fig. 2b, c show the nanoparticles of iron oxides spread out on MG surface, which create conglomeration.

Fig. 2. TEM images of (a) native Ghassoul (G); (b, c) composite of Ghassoul /FexOy (MG).

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Magnetic parameters of native clay sample (G) and its magnetic modification (MG) with approximate accuracy  1% are presented in Table 2. The Henkel plot have been also determined using a relation between the initial (virgin) curve, Mvir(H), and magnetizations at increasing (MUP) and decreasing (MDOWN) positive magnetic fields:

M H   M VIR H   M UP H   M DOWN H  / 2

(1)

Results confirm weak ferromagnetic behaviour of clay sample. At magnetic fields above 1700 coercive field (Oe) the dominating diamagnetic response coming from the plastic cylindrical sample holder was observed. After subtraction of the holder contribution the magnetization of clay at 20 kOe (saturation magnetization) was estimated to be only about 0.02 emu.g-1. Measured Henkel plot indicates weak negative dipolar interactions among particles with minimum originating at magnetic field of about 280 Oe. However, magnetic modification of clay markedly changed studied magnetic dependences. We have detected that saturation magnetization was approximately two orders higher and coercive field a little bit lower in comparison to the native clay sample. Also Henkel plot shows much stronger (two orders higher) negative dipole interactions with the minimum observed between 120 and 300 Oe. Table 2. Magnetic parameters of native clay sample (G) and its magnetic modification (MG). Sample

Saturation magnetization (emu.g-1)

Coercive field (Oe)

Minimum of Henkel plot (emu.g-1)

Magnetic field of Henkel plot minimum (Oe)

G

0.02

84.52

-0.0010

280

MG

3.22

61.26

-0.1381

120-300

Adsorption properties were verified using Cd2+ ions model solution. The amount of adsorbed Cd2+ ions on G and MG samples at the equilibrium at experimental condition – qe (mg.g-1) – was calculated as follows:

qe 

c0  ce  V m

(2)

where c0 and ce (mg.L-1) are initial and equilibrium concentration Cd2+ ions in model solution, V (L) is the volume of model solution containing Cd2+ ions and m (g) is the mass of adsorbent. The obtained equilibrium data show Fig. 3. The results indicate that the presence of magnetic iron particles on G surface did not affect the adsorption properties negatively. The adsorbed amount of Cd2+ ions on G and MG is similar and is increased with the increase of Cd2+ ions concentration in model solution. The determined concentration of Fe in filtrate after adsorption on G and MG experiment do not exceed more than 10 % and 15 % of the total amount of Fe in the respective samples. Comparison of these results shows that the Fe from native G dissolved in aqueous solution primarily. The results proved that the iron oxide particles are not released to the model solution of adsorbate and, during adsorption; do not lose the magnetic properties.

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qe (mg.g-1)

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180 160 140 120 100 80 60 40 20 0

MG G

0

50

100 ce (mg.L-1)

150

200

Fig. 3. Adsorbent amount of Cd2+ on G and MG.

4. Conclusions Magnetically modified Ghassoul was prepared using microwave-assisted precipitation of iron oxides from water solution using FeSO4.7H2O as a precursor. Chemical and phase composition, magnetic and adsorption properties were compared with those of the native Ghassoul. It was proved that the prepared magnetically modified clay minerals contained iron oxides nanoparticles of -Fe2O3 and Fe3O4 which were very strongly bound on the surface. TEM images further proved that the magnetite particles were present on surface in the form of nanoparticles. The magnetic measurements have detected that saturation magnetization was approximately two orders higher and coercive field a little bit lower in comparison with the natural clay sample. Verification of adsorption properties was carried out with Cd2+ ions and proved that the presence of magnetic iron particles on Ghassoul surface did not affect the adsorption properties negatively. Nanotechnology centre in Ostrava is the first Czech scientific institute where the modification of Ghassoul by magnetic nanoparticles was performed and the resulting product studied. The results show that the prepared magnetically modified Ghassoul is a potentially suitable adsorbent for the pollutants removal from aqueous solutions. Acknowledgements Authors thank to the Ministry of Education of Czech Republic (SP2017/70) for the financial support. The authors would like to express heartfelt thanks to prof. Vávra from Slovak Academy of Sciences in Bratislava for TEM analysis and dr. Motyka for language corrections. References [1] J.Wang, C. Chen, Biotechnol. Adv. 27 (2009) 195-226. [2] K. Kadirvelu, K. Thamaraiselvi, C. Namasivayam, Bioresource Technol. 76 (2001) 63-65. [3] R.C. Bansal, M. GOYAL, Activated Carbon Adsorption, first ed., CRC Press, Boca Raton, 2005. [4] L. Mouni, D. Merabet, A. Bouzaza, L. Belkhiri, Desalination. 276 (2011) 148-153. [5] A. Mockovčiaková, Z. Orolínová, J. Škvarla, J. Hazard. Mater. 180 (2010) 274-281. [6] A.B. Bourlinos, R. Zboril, D. Petridis, Micropor. Mesopor. Mat. 58 (2003) 155-162. [7] M. Matik, M. Václavíková, S. Hredzák, M. Lovás, S. Jakabský, Acta Montan. Slovaca. 9 (2004) 418-422. [8] L.C.A Oliveira, R.V.R.A. Rios, J.D. Fabris, K. Sapag, V.K. Garg, R.M. Lago, Appl. Clay Sci. 22 (2003) 169-177. [9] J. Vereš, Z. Orolínová, Acta Montan. Slovaca. 14 (2009) 152-153. [10] V.K. Gupta, Ind. Eng. Chem. Res. 37 (1998) 192-202. [11] S.V. Dimitrova, D.R. Mehandgiev, Water Res. 32 (1998) 3289-3292. [12] N. Calace, E. Nardi, B.M. Petronio, M. Pietroletti, Environ. Pollut. 118 (2002) 315-319. [13] S.M. Lee, A.P. Davis, Water Res. 35 (2001) 534-540. [14] F. Rozada, M. Otero, A. Morán, A.I. García, Bioresource Technol. 99 (2008) 6332-6338.

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