Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13 ... minerals has been a fascinating interest mainly for industrial applications.
Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13
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Preparation and Physicochemical Properties of Metal Complexes Immobilized on Montmorillonite K10 (MMT K10) Nur Fatin Diana Che Husin, Farah Wahida Harun, Juliana Jumal, Siti Salhah Othman Universiti Sains Islam Malaysia, Faculty of Science and Technology, 71800, Nilai, Negeri Sembilan, Malaysia ARTICLE INFO Article history: Received 23 March 2014 Accepted 24 April 2015 Available online 28 April 2015 Keywords: Heterogeneous catalyst Montmorillonite K10 Molybdenum complexes Vanadium complexes.
ABSTRACT Series of heterogeneous catalyst were synthesized by the direct immobilization of various concentrations of MoO2(acac)2 and VO(acac)2 on montmorillonite (MMT) K10 clay. The immobilized catalysts were characterized by x-ray powder diffraction (XRD), atomic absorption spectroscopy (AAS), thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) with KBr pellet method. The basal spacing for Mo-MMT K10 and V-MMT K10 obtained from XRD analysis suggests that the clay structure were retained. AAS analysis revealed that as the concentration of the metal increased, the elemental compositions of Mo and V complexes on MMT-K10 samples were also increased. The bands that appear in the region of 1300-400 cm-1 from FTIR are attributed to the stretching vibration from SiO2 tetrahedra, indicating the structure of the clay. Besides from the thermal analysis, the higher concentration of metal complexes (Mo and V) immobilized on MMT-K10 structure make them being better hydrophobic nature thus lower the loss of physisorbed water molecules weakly bound to the material.
© 2015 IWNEST Publisher All rights reserved. To Cite This Article: Nur Fatin Diana Che Husin, Farah Wahida Harun, Juliana Jumal, Siti Salhah Othman., Preparation and Physicochemical Properties of Metal Complexes Immobilized on Montmorillonite K10 (MMT K10). J. Ind. Eng. Res., 1(5), 8-13, 2015
INTRODUCTION Clays have considerable potential as heterogeneous catalytic materials due to their large surface area and cation exchange capacity [1]. Recently, catalytic reaction for organic synthesis by montmorillonite (MMT) clay minerals has been a fascinating interest mainly for industrial applications. Montmorillonite, the major clay mineral of bentonite is commercially available clay that can be treated to improve its catalytic properties [2]. There were many published reports regarding the catalysis by synthetic or modified clays.One of it was by Kaur and Kishore [3] who reviewed that the changes of the clay minerals by assimilating different metal cations, molecules or complexes, being able to form an effective catalyst in various types of reactions. MMT can be modified by converting the property of MMT from hydrophilic to hydrophobic using organic reagents [4]. Acidtreated montmorillonite has also been used as catalyst for numerous reactions over the last few decades e.g. dimerization of unsaturated fatty acid to dicarboxylic acids [5], the epoxidation of short-chain alkenes [1,17] and the epoxidation of vegetable oils such as soybean oil and castor oils [6]. Immobilization of homogeneous catalyst is another method in preparing the heterogeneous catalyst because using homogeneous catalyst was found to be expensive and contaminate the environment. Early transition metal complexes such as molybdenum and vanadium have been revealed to be the most active catalyst and have good catalytic activity [4]. The purposes of this study are to synthesis and characterize the immobilized metal complex on montmorillonite K10 that could be used in epoxidation reaction for upcoming studies. . Experimental: 2 2.1. Materials: Toluene was acquired from Merck and used as solvent. MoO2(acac)2 and VO(acac)2 complexes were supplied from Sigma Aldrich. Commercial montmorillonite (MMT-K10) clay received from Sigma Aldrich was used as support for immobilization of metal complexes. 2.2. Immobilization on Montmorillonite K-10 Clay: The montmorillonite K10 clay was thermally treated in an oven at 110◦Cfor5h prior to use. The clay (10.0 g) was submersed in a solution of 0.05 M, 0.1 M, 0.15 M and 0.2 M of MoO2 (acac)2 in dry toluene (100 mL). Corresponding Author: Farah Wahida Harun, Universiti Sains Islam Malaysia, Faculty of Science and Technology, 71800, Nilai, Negeri Sembilan, Malaysia.
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Farah Wahida Harun et al, 2015 Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13
This step was performed for 18 h under stirring at room temperature and inert atmosphere (nitrogen-flow). The solid was then separated by filtration and was thoroughly washed with hot toluene to eliminate any unreacted metal complex [6]. Lastly, K10-Mowasdriedat80◦Cfor5h. All the steps were repeated by using vanadium complex; VO(acac)2. Table 1 denotes the immobilized catalyst samples that are used throughout this article. Table 1: Immobilized catalyst samples. Concentration of metal complexes 0.05 M 0.1 M 0.15 M 0.2 M
Immobilized molybdenum complexes on MMT-K10 K10-Mo1 K10-Mo2 K10-Mo3 K10-Mo4
Immobilized vanadium complexes on MMT-K10 K10-V1 K10-V2 K10-V3 K10-V4
2.3. Catalyst Characterization: X-ray diffractograms was obtained with a diffractometer,usingCuKαradiation(40kV,40mA,λ=1.5406 A˚); source for 2θ ranging from 2◦ to 80◦. The catalysts in powder form were deposited on the glass sample holder prior to analysis using Bruker AXS Germany diffractometer model D8 Advance. The molybdenum and vanadium content of the obtained solid; K10-Mo and K10-V were quantitatively discovered by atomic absorption spectroscopy (AAS). The metal content in samples was measured via extraction method where 20 ml of 1.0 M HCl was added to 0.1 g of molybdenum and vanadium immobilized samples. The mixture was then shaked for 1 hour, after which the samples were centrifuged and decanted [7]. This step was repeated several times until the samples were free from subsequent metals, evidenced by a change in colour to light grey which was the initial colour of unmodified MMT-K10. This step was vital to ensure all the concentration of Mo and V ions immobilized in the interlayer of MMT K-10 were collected. Infrared (IR) spectra were obtained using a Varian equipment model 3100. Self-supporting pellets were prepared with KBr and catalysts applying 50 kg/cm2 pressures. These pellets were further used for recording FTIR spectra in the spectral range 3800 and 800 cm-1, using KBr background. The thermal analysis of the immobilized MMT was investigated by using TGA analyzer (BP model RB-3000) with the heating rate of 10 °C / min from 25°C to 800 °C under flowing of nitrogen (100 ml/min) and from 800 °C to 1000 °C under flowing of oxygen gas with similar gas flow rate [6]. RESULTS AND DISCUSSIONS 3.1. XRD data: X-ray diffraction (XRD) is an important technique to obtain the structural information of materials. An XRD pattern is a plot of the intensity of x-rays scattered at different angles by a sample. In this study, the structure of raw MMT-K10 and metal complexes immobilized MMT-K10 at different concentrations were evaluated. Then the data analysis was described by basal spacing and integrated peak intensities. The x-ray diffractogram of K10Mo and K10-V samples are shown in Figure 1 and 2 respectively. Meanwhile Table 2 and 3 show the basal spacing (d-spacing) values for selectead peaks. The d-spacing is the distance between similar faces of adjacent layers, which is measured in angstroms (Å).
Fig. 1: X-ray diffractogram of K10-Mo.
Fig. 2: X-ray diffractogram of K10-V.
From the figures, it is clear that the intensity as well as the sharpness of the XRD peaks confirmed the high crystallinity of the material [8].Apart from that, a ll MMT-K10 samples shown similar diffraction peaks that indicate the structure has been kept even after the introduction of metal-complexes [6]. To support this argument, one can see from Table 2 that the basal spacing of peak d001 (2θ≈8.9°) for immobilizedand unmodified was maintained at ca. 10.0 Å. These similarities suggesting that the clay structure is retained during the complex immobilization. This situation well agrees with the value of 9.9 Å for MMT-K10 and molybdenum complexes immobilized between the clay layers of MMT-K10 found by Farias and the co-workers.[6].
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Farah Wahida Harun et al, 2015 Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13
Table 3 lists the peak intensities values for diffraction peaks at 19.9° and 35° of unmodified and immobilized MMT-K10 at different concentration of metal complexes. The diffraction peaks at 19.9° and 35° are also corresponding to montmorillonite [9]. After immobilization, the intensities of diffraction peaksatboth2θangles are slightly decreased [9], probably indicating the presence of molybdenyl ion and vanadyl ion within MMT containing metal complex [10]. Table 2: Theintensityvaluesat2θ=8.9°. Sample MMT-K10 K10-Mo1 K10-Mo2 K10-Mo3 K10-Mo4 K10-V1 K10-V2 K10-V3 K10-V4 Table 3: Theintensityvaluesat2θ=19.9°and35°. Sample 2θ MMT-K10 19.8 K10-Mo1 19.9 K10-Mo2 19.9 K10-Mo3 19.9 K10-Mo4 19.9 K10-V1 19.9 K10-V2 19.8 K10-V3 19.8 K10-V4 19.8
2θ 8.9 8.9 8.9 8.9 8.9 8.9 8.9 8.9 8.9
d001 (Å) 9.95 9.95 9.89 9.89 9.83 9.89 9.89 9.89 9.89
Intensity 363 299 227 235 231 328 343 234 232
Intensity 901 828 523 512 911 1011 1020 465 1094 2θ 35.0 35.1 35.1 35.0 35.0 35.1 35.0 35.0 35.0
Intensity 222 169 169 144 153 205 190 158 150
3.2. FTIR analysis: FTIR spectra were recorded in the region between 800 and 4000 cm-1. Figure 3 and 4 show the IR spectra of K10-Mo and K10-V respectively together with the spectrum of unmodified MMT K10. The IR spectra are well matched with the previous works [6, 11]. Clearly, the broad bands appear at 3750 to 3000 cm-1 and this can be attributed to the O-H stretching due to adsorbed water molecules on the structure of the clay. The band near 3618 cm-1 (shoulder)was due to OH stretching vibrations coordinated to octahedral cations (mainly Al) and the band at 1632 cm−1 was related to OH deformation. K10 spectrum also showed a broad and intense band over the range of 1000–1200 cm-1 associated with Si–O stretching vibrations of the tetrahedral layer; a shoulder at about 915 cm-1 corresponds to Al–OH–Al bending. As the surface charge was concentrated with oxygen that involved in Si-O-Si linkages, the hydrogen from the –OH group which was bonded to the oxygen from Si-O-Si linkage absorbed near 3440 cm-1. Thus overlapping the region of absorption associated water-water linkages and enhances the peak intensity [12].
Fig. 3: FTIR spectra for MMT-K10 and K10-Mo samples. Cardoso [13] reported that the bands that appear in the region of 1300-400 cm-1 are attributed to the stretching vibration of from SiO2 tetrahedra. According to Kurian and Sugunan [14] peak that appears in the region of 1200-1000 cm-1 is due to the asymmetric stretching vibration of apical oxygen of SiO2 tetrahedra. The broad band in this region is due to stretching and binding vibrations of Si-O bonds related to basal oxygen. 3.3. Atomic Absorption Spectroscpoy (AAS): The total amount of molybdenum and vanadium complexes immobilized on montmorillonite K10 clay was analyzed by AAS method. The AAS analysis method gives the possibility to determine the elemental composition
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Farah Wahida Harun et al, 2015 Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13
[15] of immobilized molybdenum and vanadium complexes on MMT-K10 samples with a great sensibility. Generally, the values of K10-Mo presented a higher concentration of immobilized metal complexes on MMTK10 in comparison to the K10-V which had a lower concentration. As can be seen, as the concentration of the metal complexes used increased; the values of the immobilized metal were gradually increased for K10-Mo, whereas slightly decreased for K10-V2 sample in K10-V probably due to the metal leaking during filtration process.
Fig. 4: FTIR spectra for MMT-K10 and K10-V samples. Table 4: Positions of the unmodified and immobilized MMT K10 absorption bands. Peak Assignment OH stretching vibrations OH stretching vibrations coordinated to octahedral cations Stretching H-O-H vibrations (physisorbed interlayer water) OH deformation Si-O stretching vibrations Al-OH-Al bending
Wavenumbers (cm-1) 3750 to 3000 3618 3400 1632 1000-1200 915
Fig. 5: Graph of AAS at different concentration of metal complexes (Mo and V). 3.4. Thermal analysis: Figure 6 illustrates the thermogram from TGA analysis of MMT K10. All immobilized samples also show similar pattern of weight loss and thus the data are tabulated as in Table 5. Generally, the descending TGA plot indicates the percent mass as a function of sample temperature, indicating a weight loss occurred. Valuable information was provided by TGA measurements which include thermal stabilities and moisture content.
Fig. 6: TGA curve for MMT-K10.
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Farah Wahida Harun et al, 2015 Journal of Industrial Engineering Research, 1(5) Special 2015, Pages: 8-13
Table 5: Onset temperature, inflection point, weight loss and total mass loss of MMT-K10 and immobilized MMT-K10. SAMPLE Onset Temperature Inflection point Wt % loss Wt % loss Total mass loss ( °C ) ( °C ) (< 150%) (350°C -550°C) (up to 1000°C) MMT-K10 73 83 7.0 % 1.5 % 11.7 % K10-Mo1 73 87 7.1 % 2.2 % 15.1 % K10-Mo2 73 84 4.8 % 2.2 % 14.9 % K10-Mo3 73 237 3.4 % 2.4 % 15.8 % K10-Mo4 73 251 4.4 % 2.7 % 17.7 % K10-V1 73 87 7.0 % 2.4 % 14.4 % K10-V2 73 72 6.1 % 2.5 % 14.0 % K10-V3 73 254 3.8 % 4.4 % 25.1 % K10-V4 73 237 4.8 % 4.3 % 29.6 %
TGA results show that the MMT-K10 undergoes thermal degradation beginning at 73 °C (onset temperature), the greatest rate of change on the curve which is also known as inflection point at 83 °C and the total mass loss of 11.7%. The residue remaining was 88.31% at ca. 900 oC. TGA curves of K10-Mo3, K10-Mo4, K10-V3 and K10-V4 exhibit high inflection points which were denoted by a sharp mass loss curve beginning approximately at 250 °C. This suggests the presence of higher metal substances immobilized on the catalysts. While Farias [6] suggested the presence of guest substances adsorbed even though having been washed with organic solvents. The weight loss was expressed within two temperature ranges. The first weight loss below 150 °C was due to loss of physisorbed water in the voids of mesoporous structure. Whereas the second weight loss between 350 550 °C was depicted to the water loss from the condensation of adjacent silanol (Si-O-H) groups to form siloxane (Si-O-Si) bond [16]. As shown from the table above, MMT-K10 exhibited a wt % H2O loss of ca. 7 % below 150 °C and 1.5 % for the second weight loss between 350 and 550 °C. Similar trend was observed to the other samples (immobilized Mo and V on MMT-K10), which exhibit higher weight loss in temperature range below 150 °C than 350 to 550 °C, except for K10-V3 sample. All the immobilized MMT-K10 samples exhibit a lower wt % H2O loss in the voids of mesoporous structure compared to MMT-K10 (except for K10-Mo1 and K10-V1 where they have similar wt % H2O loss), probably due to low concentration of metal complexes. This situation indicates that K10-Mo and K10-V at various metal complexes concentrations have a better hydrophobic nature [16] than pure MMT-K10. In addition, among all those samples in temperature
