Available online at www.sciencedirect.com APCBEE Procedia 3 (2012) 93 – 98 ICCCP 2012: 5-6 May 2012, Kuala Lumpur, Malaysia Effects of Cationic Surfactant in Sol-gel Synthesis of Nano Sized Magnesium Oxide Mohd Sufri Mastulia,*, Noor Sabrina Ansaria, Mohd Azizi Nawawia, Annie Maria Mahata a Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor, 40450, Malaysia Abstract In this study, sol-gel method was used to synthesize nano sized of magnesium oxide (MgO). Magnesium acetate tetrahydrate and tartaric acid have been dissolved in ethanol and formed a precursor before calcined at 600 °C for 6 h to produce MgO nanoparticles. A cationic surfactant (cetyltrimethylammonium bromide, CTAB) had used in the sol-gel reaction to reduce agglomeration of the nanoparticles. Two samples (MgO and MgO-CTAB) were characterized using simultaneous thermogravimetric analyzer (STA), X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM) and nitrogen adsorption-desorption measurement. Formation of the samples via a sol-gel route is discussed and confirmed using the STA results. The precursor formed was identified as magnesium tartrate and decomposed to MgO and MgO-CTAB after the calcinations, and gave a single phase of samples as shown by the XRD patterns. The used of CTAB in this sol-gel method gives the MgO nanoparticles with less agglomeration. This was proved by the FESEM micrographs, the MgO-CTAB has spherical shape and the agglomeration seems to be less than the MgO. It suggests that the cationic surfactant controls the morphology of the samples. © 2012 2012 Published Publishedby byElsevier ElsevierB.V. B.V. Selection and/or peer review under responsibility of Asia-Pacific © Selection and/or peer review under responsibility of Asia-Pacifi c Chemical, Chemical, & Biological & Environmental Engineering Society Biological Environmental Engineering Society Keywords: MgO, Sol-gel, Nanoparticles, Cationic surfactant 1. Introduction Magnesium oxide (MgO) is an important oxide material that used in many applications such as catalysis, * Corresponding author. Tel.: +60-355436594; fax: +60-355444562. E-mail address:
[email protected]. 2212-6708 © 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2012.06.052 / APCBEE Procedia 3 (2012) 93 – 98 catalyst supports. As an alternative. Prior to the measurements. Mg(CH3COO)2. small crystallite size and large surface area are challenging aspects to be studied. which hinder its wide applications [27. 99. The resulting MgO has large particle size and small surface area which are disadvantages for use in some applications. The organic salts such as magnesium methoxide and magnesium ethoxide are rare used in sol-gel reaction for formation of MgO nanoparticles and these discussed in a few reports [15-20].4H2O was initially dissolved in 0. Experimental Details All reagents used in the present work were analytical grade and directly used without further treatment. The X-ray diffraction (XRD. C19H42BrN (Calbiochem. CTAB-free of MgO had been prepared using the same method. The precursors were heated from room temperature to 800 ºC at a rate of 10 ºC min-1. The prospect of easier to control the parameters of sol-gel method has motivated us to synthesize nano sized MgO using sol-gel route assisted with CTAB as a surfactant to reduce the agglomeration of their particles. A sol-gel method is one of the promising approaches due to its simplicity. PANalytical X’pert Pro MPD) with CuKĮ radiation was used to identify the phase of the samples (with and without CTAB). high yield of final product and low reaction temperature. SETARAM SETSYS Evolution 1750). 29-31]. 27. Results and Discussion . Afterwards. the dried sol-gel product (precursor) was grinded into powder before calcined at 600 ºC for 6 h to give MgO-CTAB. The controlled synthesis for MgO with specific morphology.4H2O (Merck. tartaric acid. 99. toxic wastes remediation. C2H5OH (J. The gel was left to stand overnight followed by oven drying at 100 ºC for 24 h. Therefore. A numbers of polymeric surfactant have been used in sol-gel method [10. 7].001 M of CTAB under constant stirring until the solution became transparent. Understanding the growth mechanism is also an important area for study.5% purity). C4H6O6 (Merck. For comparison. pH of the solution was adjusted to pH 5 using 1 M of C4H6O6 and stirred vigorously until a thick gel was formed.9% purity) were used in synthesis of the samples (MgO and MgOCTAB). inorganic magnesium salts are reacted with different complexing agents and give various precursors before decomposed to MgO [21-26].5% purity). The commercial MgO particles have been prepared via thermal decomposition of magnesium salts or magnesium hydroxide [6. The nitrogen adsorption-desorption isotherm for the MgO and MgO-CTAB was obtained from automated gas sorption instrument (Quantachrome AS1Win). 2. 3. cost-effective. Kollin Chemical. many synthesis methods have been developed to prepare nano sized of MgO with large surface area with controlled morphology as reported in [8-14]. the sol-gel method used is usually caused agglomeration of MgO particles. the samples were degassed in a vacuum at 25 ºC for 9 h. Specific surface area of the samples were calculated using Brunauer-Emmett-Teller (BET) method.94 Mohd Sufri Mastuli et al. So far. and ethanol. However. The decomposition behavior and thermal stability of the precursors were examined using simultaneous thermogravimetric analyzer (STA. 28]. cetyltrimethylammonium bromide or CTAB. A more spherical MgO with less agglomeration was obtained by using cationic surfactant of cetyltrimethylammonium bromide (CTAB) in emulsion-phase method [32]. It is highly required to develop a surfactant-mediated synthesis method to overcome this limitation. The synthetic strategies by which size and shape of the nanostructures are tailored represent key issues in the nanomaterials research. >98% purity). Magnesium acetate tetrahydrate. The morphologies of these samples were observed using field emission scanning electron microscope (FESEM. JEOL JSM-7600F). refractory materials and adsorbents [1-5]. Mg(CH3COO)2. 99. no studies on the use of CTAB in sol-gel method have been reported. Then. 1 shows decomposition behavior and thermal stability of precursors for both samples. STA curve of precursor for (a) MgO. It indicates decomposition of the precursor to magnesium carbonate before calcined to form MgO. For the precursor of MgO. All the predicted weight losses agree with the STA results. a weight loss of 34. MgO and MgOCTAB.95 Mohd Sufri Mastuli et al. 1. These ions form complexes and have been polymerized to form a thick gel and identified as magnesium tartrate (MgC4H4O6). there are two major stages of weight loss as shown in Fig. It indicates a relatively similar to the decomposition behavior and thermal stability of the MgO except one of additional weight loss about 100 ºC for the decomposition of cationic surfactant (CTAB). magnesium acetate tetrahydrate and tartaric acid were hydrolyzed in ethanol to form magnesium (Mg2+) and tartrate (C4H4O62-) ions. A broad exothermic peak is observed which starts at about 500 ºC corresponds to the phase transformation from the amorphous to the crystalline states of the MgO. In temperature range of 100 – 425 ºC.08% represents removal of acetic acid. The small weight loss at below 100 ºC is attributed to the loss of ethanol that still remained in the precursor. This is known as a precursor and calcined to produce MgO. 1(b). a sharp endothermic peak at about 400 ºC with a weight loss of 40. Weight loss of 41. The chemical reactions involved for formation of the MgO are shown in equations below. This weight loss is closed to theoretical value as stated in equation (1).4H2O + C4H6O6 MgC4H4O6 + 2CH3COOH + 4H2O (1) MgC4H4O6 + 5/2 O2 MgCO3 Weight loss of 33. It is worthy to mention that no weight loss occurred above 600 ºC and reveal the MgO-CTAB should be formed. This decomposition should undergo a weight loss of 33. calcinations of the precursor above this temperature should give a single phase of MgO. The STA result of precursor for MgO-CTAB is shown in Fig. (b) MgO-CTAB .41% Calcination MgO + CO2 MgCO3 + 3CO2 + 2H2O (2) (3) Fig. 1(a). respectively. These are further confirmed using STA results.41% as proposed in equation (2). The side products of the sol-gel reaction were acetic acid (CH3COOH) and water (H2O) which were evaporated in oven during drying process.17% takes place immediately after 425 ºC until 580 ºC with a broad endothermic peak at about 450 ºC. Next. Fig.06% Mg(CH3COO)2. / APCBEE Procedia 3 (2012) 93 – 98 In a sol-gel method. Therefore. the micelles were removed and give a spherical shape of MgO as proposed below. / APCBEE Procedia 3 (2012) 93 – 98 The X-ray diffraction (XRD) patterns for MgO and MgO-CTAB are illustrated in Fig. respectively.2448º) implying a larger crystallite size.294 and 61. All the diffraction patterns can be indexed as a face-centered cubic phase of periclase MgO (ICDD No. Fig. 2. the particles are agglomerated into bundles of flaky-spherical morphology. 2(a) showed broadening of peaks for MgO.8 nm and this decreased to 27. Upon calcinations.2676º for the MgO-CTAB. It is also observed that MgO-CTAB having smaller crystallite size and this compliment its XRD pattern. The crystallite sizes are also estimated from the BET results. The XRD peaks are assigned to (111). 2. No diffraction peaks for impurities are present. (311) and (222) reflections. (220). The broadening of the MgO has smaller FWHM (0.: 01-078-0430) with space group of Fm-3m. 3. The XRD peaks as shown in Fig. but it turns to heavy spherical shape with less agglomeration due to presence of the CTAB. (b) MgO-CTAB This is confirmed by FESEM micrograph for the prepared samples as shown in Fig.96 Mohd Sufri Mastuli et al.111 m2 g-1. . From the BET results. (200). which means that the surfactant reduced the crystallite size. This FWHM is increased to 0. This observation agrees with the value of full width at half maximum (FWHM) of the peak (200) used to demonstrate the peak broadening. specific surface area of the MgO and MgO-CTAB are 60. This occurred because the precursor particles were entrapped inside the CTAB micelles during the sol-gel reaction.4 nm with CTAB added. which indicated the high purity of the samples. The MgO crystallites are about 27. As can be seen. 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