Magnesium Oxide (MgO) is an attractive material for a wide range of application .... McKenna, D. Koller, A. Sternig, N. Siedl, N. Govind, and P. V. Sushko, ACS.
RESEARCH ARTICLE Copyright © 2012 American Scientific Publishers All rights reserved Printed in the United States of America
Advanced Science Letters
Vol. 5, 1–3, 2012
Synthesis of MgO Nanopowder via Non Aqueous Sol–Gel Method Taimur Athar1 , Abdul Hakeem1 , and Waqar Ahmed2 ∗ 2
1 Indian Institute of Chemical Technology, Tarnaka, Hyderabad (A.P.), 500-007, India Institute of Nanotechnology and Bioengineering, University of Central Lancashire, United Kingdom
Magnesium Oxide (MgO) is an attractive material for a wide range of application such as catalysis, treatment waste and an additive to paints, refractory materials and superconductive materials. It yield significant advantage when it is manufactured and used on a nanoscale dimensions. In this study cubic MgO nanoparticles were prepared by using non-aqueous sol–gel process with good morphology and with limited surface area properties and monodispersity. The nanoparticle was characterized by various analytical techniques such as TEM, SEM, XRD, TGA/DTA, FT-IR and Raman spectroscopy. The average particle size with 43 nm and surface area of 2.81 m2 /g was obtained. The non-aqueous process offers the better understanding for controlling the reaction mechanism at a molecular level with high cyrstallinity and well defined uniform morphologies.
Keywords: Sol–Gel, Monodispersity, Surface Area, Uniform Morphologies.
1. INTRODUCTION From ancient times MgO plays a very prominent role based on surface properties. It is used in catalysis, toxic waste remediation, or as an additive in refractory materials, paints and superconductor materials based on its versatile basic properties.1–3 It is used in many organic reactions,4 as a supporting catalyst due to their adsorbent tendency with an enhanced surface area and with their intrinsically high surface reactivity.5–7 Many synthetic approach has been applied for the synthesis of ultra-pure MgO such as Vapor phase oxidation,8 Hydrothermal,9 High temperature solid state synthesis,10 alkoxide based preparation,11 Micro wave irradiation12 and sol–gel synthesis.13 Among all these techniques non aqueous sol–gel technique is preferred because it is easy to control particle properties via soft chemical approach. Simple and cost effective, eco-friendly to synthesize MgO nanoparticles synthesis was carried out with monodispersity and with limited uniform particle size, shape and porosity having high surface chemical reactivities.
2. CHARACTERIZATION OF SAMPLE Solvents were distilled under nitrogen prior to use. Starting materials were purchased from Aldrich and used as such. Analysis was carried out at room temperature under anhydrous conditions. FT-IR spectra were recorded on a Bruker spectrometer (VERTEX 80v) in the 4000–400 cm−1 range. The samples were analyzed as such, by collecting and averaging 64 scans with ∗
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Adv. Sci. Lett. Vol. 5, No. xx, 2012
4 cm−1 resolution. Raman spectroscopy were recorded by using Lab RAM HR800 using 632 nm Laser as the excitation source. X-ray studies was obtained on a Rigaku diffractometer (DMAX2500) using CuK radiation ( = 0154 nm), scanning was performed from 10 to 80 in 2. Thermal analysis was carried out in flow of dried air (100 cm3 /min) on a thermo balance (TA Instrument, SDT-2960). The programmed heating rates were 10 C/min and the sample was heated from room temperature to 1000 C. X-ray diffraction and electron microscopic studies helps to better understand the structural changes that take place in thermal treatment. Transmission electron microscopic images were taken by using a JEOL electron microscope (JEM-2100) equipped with a slow-scan CCD camera operating at 200 kV. TEM specimens were obtained from the homogenous colloidal solution. The solutions were dropped on a copper grid coated with an amorphous carbon film and subsequently dried in vacuum. The Brunauer–Emmett–Teller (BET) was analyzed by using an automatic physico-sorption analyzer (Micromeritics ASAP 2020).14–15 All samples were degassed at 80 C prior to nitrogen adsorption measurements.16
3. EXPERIMENTAL METHODS Synthesis of MgO nanoparticles was carried out via non aqueous sol–gel process: Alkali solution of toluene (A.R Aldrich) was prepared by dissolving 2 gm of KOH (35.71 mmol) pellets in 20 ml of toluene with vigorous stirring for 12 hrs. Then followed by addition of 3 gm (14.75 mmol) of MgCl2 · 6H2 O (A.R Aldrich) into this
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doi:10.1166/asl.2012.2190
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RESEARCH ARTICLE
Fig. 1.
XRD spectum of MgO.
solution and then refluxed for 3 hrs. The compound was separated out by filtration, and then washed thoroughly with distilled water (till filtrate becomes neutral). The compound was oven dried for 6 hrs at 100 C followed by calcination at 550 C (with an increase in temperature of 2 C/min for 4 hrs) was carried out in atmospheric condition. White fine powder was obtained with 85% yield.
4. RESULTS AND DISCUSSION In non aqueous sol–gel process the formation of metal oxide nanoparticles take place by providing oxygen from alkali hydroxide or by any organic constituents present in precursor. C6 H6
MgCl2 · 6H2 O + 2KOH −−−−→ MgO + 2KCL + 7H2 O Hexane
The characterization was successively carried out with the help of FT-IR by observing significant frequencies at 400–4000 cm−1 that confirm the formation of MgO nanoparticles with size effect.17 A symmetric frequency observed at 522 cm−1 and asymmetric frequency observed at 875 cm−1 corresponds to cubic Mg–O bond. The other peak that was observed was due to the presence of Mg–OH bond. The presence of OH peak occurs due to absorption of water at 3000–38000 cm−1 during sample preparation. With an increase of the calcinations temperature the absorption peaks are intensified thereby supporting the formation of pure phase. 4.1. XRD Analysis Wide-angle XRD analysis as shown below gives the information that initially the particles are formed in amorphous phase. During synthesis and then subsequently heat treatment at 550 C for
Fig. 2.
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Adv. Sci. Lett. 5, 1–3, 2012
SEM image of MgO.
Fig. 3.
TEM image with SAED of MgO.
4 hours (at the rate of 2 C/min) in an inert atmosphere changes the amorphous state into crystalline phase retaining particle properties under controlled. The mean particle size was found to be 43.3 nm as calculated by using Debye-Scherrer equation. D = K/ cos The peaks were assigned at (2 = 285) and (2 = 405) corresponds to the synthesis of a pure cubic homogeneous particle size and phase which corresponds to the JCPDS file [45-0946] which is consistent with the results as reported in the literature. The presence of intense peaks shows that the powders are crystalline form with pure phase after high temperature treatment. 4.1.1. EDX The presence of desired chemical composition ratio was found to 1:1 as supported by the TEM and SAED techniques in the calcined sample. 4.2. SEM and TEM Scanning electron micrograph images shows that the presence of irregular particle with micro pores has a great tendency for agglomeration due to their surface energy leading to the formation of large surface area. The existence of big particle takes place due to Ostwald ripening process with a limited porosity and crystalinity. TEM images show a spherical particle with an average size of about 40 nm agrees well with results provided by XRD. The d-spacing values of sample matches well with the standard JCPDS FILE (30-0794) with clear crystalinity as supported by SAED.
Fig. 4.
Thermal analysis of MgO.
RESEARCH ARTICLE
Adv. Sci. Lett. 5, 1–3, 2012
5. CONCLUSION
Intensity
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The present study shows that crystalline MgO nanopowders can be synthesized from non aqueous sol gel process leads to the formation of solid takes place with yield of 85% after calcination. Non aqueous sol gel process is a cost effective with an easy availability of raw materials which favors the scaling up of industrial production with controlled morphology and size.
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Wavenumber(cm–1) Fig. 5.
Raman spectrum of MgO.
4.3. Thermal Analysis Thermal analysis of MgO nanoparticles was carried out to find the crystallinity temperature. The first weight loss occurs at 129.1 C due to vaporization of absorbed water. The second weight loss occurs at 225.8 C it is due to removal of organic moieties thereafter no significant weight loss was observed at higher temperatures supporting the formation of highly crystalline cubic MgO at 749.8 C. Finally the formation of crystalline particle takes place at 860 C as supported by DSC Thermogram due to nucleation 950.8 C. 4.4. Raman Analysis The peaks below 1500 cm−1 is associated to D-band also known as breathing mode. The peaks at 1500 cm−1 and 3000 cm−1 represent as a G-band. The ratio of the intensities of D and G band (i.e., ID /IG related to the indirect measurement of the crystallite size and its defects. This data is consistent as reported Ref. [18]. The Raman spectrum obtained from the MgO shows a strong peak at various region indicating the cubic structure as designated to the tangential modes of MgO in the amorphous phase.
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Received: 3 March 2011. Accepted: 25 September 2011.
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