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    Magnesium Oxide Nanoparticles as Destructive Sorbent for Toxic Agents

    S. Bakardjieva,* J. ubrt*, V. tengl, F. Oplutil**, M. Olanska**

    * Institute of Inorganic Chemistry ASCR, 25068 e, Czech Republic**Military Technical Institute of Protection, Brno, Veslaska 230, 62800 Brno, Czech Republic

    Magnesium oxide is an interesting basic oxide that has many applications. For example, magnesiumoxide with ultrafine, nanoscale particles and high specific surface area has shown great promise asdestructive adsorbent for toxic chemical agents [1]. Magnesium oxide is obtained mainly by thermaldecomposition of magnesium hydroxide or carbonate [2] and recently by the sol-gel process [3]. In the

    present paper sonochemical synthesis followed by supercritical drying was used to prepare MgOnanoparticles from Mg(OCH3)2 and Mg(OC2H5)2.We report the characterization of the morphology(SEM), particle size (XRD and HRTEM), the specific surface area (BET) and DTA behaviour of MgO.The detoxification activities of the MgO samples were evaluated using mustard.

    Mg(OCH3)2 was dissolved in toluene, whereas Mg(OC2H5)2 was dissolved in methanol. Obtainedmixtures were irradiated with ultrasound by employing a direct immersion titanium horn. Ultrasoundirradiation was terminated when clear gel solution was obtained. The supercritical drying of hydroxidegels was performed in autoclave [4].

    On the basis of DTA results the hydrated MgO precursors obtained from autoclave were heated attemperature range 360-1200C. DTA curve shows that water started to evolve at ~100C and achievesmaximum at 139C. Carbon dioxide and H2O from decomposition of residual OCH3 and OC2H5groups was detected in the gas phase at ~300C and peaked at 396C. The limit of the calcinations

    temperature was 1200C. At this temperature the final solid produced were found to consistnanoparticles of MgO (periclase). The specific surface area and particle size are shown in Tab.1. Thespecific surface area decreases and particle size increases with increasing temperature of the annealingof precursors. X-ray diffraction patterns of the precursor Mg15/1 and the samples prepared by therethermal treatment are similar and exhibit characteristic peaks for MgO (periclase ICDD PDF 450496)[5]. With increasing annealing temperature the intensity of the peaks has been evolved. Nodiffraction lines of Mg(OH)2 were detected. SEM micrographs of the selected sample in shown in Fig.1.Precursor particles (Mg15/1) have uniform morphology as periclase particles (Mg15/360, Mg15/400,Mg15/500 and Mg15/800). HRTEM image of MgO crystallites (see Fig.2) obtained at 1200C (sampleMg15/1200) shows one type of domains corresponding to Fm-3m MgO. The face-centered cubic unitcell has been used to index the ED pattern inserted in Fig 2. The particle size from HRTEM is similar to

    that of the calculated size from X-ray diffraction. The Sherrer equation was applied to estimate acrystalline size (see Tab.1.) The precursors and samples of magnesium oxides were taken forexperimental evaluation of their reactivity with mustard. The largest percentage of the conversionmustard into non-toxic products after the elapse of the reaction was 77%.

    Reference:

    [1] J. V. Stark and K. J. Klabunde, Chem. Mater. 8 (1996) 1913[2] M. A. Aramendia et al.,J. Mater. Chem. 6 (1996) 1943[3] S. S. Choi and S. T. Hwang,J. Mater. Res. 15 (2000) 842

    476 Microsc Microanal 10(Suppl 2), 2004

    DOI: 10.1017/S1431927604881479 Copyright 2004 Microscopy Society of America

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    [4] V. Stengl et al.,Mater. Lett. 57 (2003) 3998[5] JCPDS PDF 2, Resease 50, ICDD, Newtown Square, 2000

    TABLE 1. Specific surface areas and crystallite sizes of nanoscale MgO samples

    Sample T [C] SBET[m2g

    -1] Phase

    identified by

    XRD

    L44,2[nm]

    Mg15/360 360 537 Periclase 1,7Mg15/400 400 377 Periclase 2,9Mg15/500 500 288 Periclase 4,2Mg15/800 800 123 Periclase 8,6

    Mg15/1000 1000 78 Periclase 14,2Mg15/1200 1200 51 Periclase 23,5

    FIG.1. SEM micrograph of the MgO sample Mg15/500

    FIG.2. HRTEM image and ED of a crystallite MgO sample Mg15/1200

    477Microsc Microanal 10(Suppl 2), 2004