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Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors

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Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors inorganics Article Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors Mohd Nazri Mohd Sokri 1,2, Yusuke Daiko 1,3, Zineb Mouline 1, Sawao Honda 1,3 and Yuji Iwamoto 1,3,* 1 Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan; [email protected] (M.N.M.S.); [email protected] (Y.D.); [email protected] (Z.M.); [email protected] (S.H.) 2 Department of Energy Engineering and Advanced Membrane Technology Research Centre, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia (UTM), Johor Bahru 81310, Malaysia 3 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan * Correspondence: [email protected]; Tel./Fax: +81-52-735-5276 Academic Editors: Samuel Bernard, André Ayral and Philippe Miele Received: 8 January 2016; Accepted: 1 March 2016; Published: 9 March 2016 Abstract: Polysilazanes functionalized with alkoxy groups were designed and synthesized as single source precursors for fabrication of micro and mesoporous amorphous silica-based materials. The pyrolytic behaviors during the polymer to ceramic conversion were studied by the simultaneous thermogravimetry-mass spectrometry (TG-MS) analysis. The porosity of the resulting ceramics was characterized by the N2 adsorption/desorption isotherm measurements. The Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic analyses as well as elemental composition analysis were performed on the polymer-derived amorphous silica-based materials, and the role of the alkoxy group as a sacrificial template for the micro and mesopore formations was discussed from a viewpoint to establish novel micro and mesoporous structure controlling technologies through the polymer-derived ceramics (PDCs) route. Keywords: perhydropolysilazane; alkyl alcohol; single source precursor; polymer-derived ceramics; micro and mesoporous silica 1. Introduction The organometallic precursor route has received increased attention as an attractive ceramic processing method since it has inherent advantages over conventional powder processing methods such as purity control, compositional homogeneity in the final ceramic product and lower processing temperatures in the ceramics fabrication [1–3]. Moreover, this route provides alternatives towards the synthesis of advanced silicon-based non-oxide ceramics such as silicon nitride (Si3N4)-based ceramics, particularly starting from silicon-based polymers such as polysilazanes [4–6]. Recently, micro and mesoporous structure formations have been often discussed for the polymer-derived amorphous silicon nitride [7,8], silicon carbide [9–14], silicon carbonitride (Si–C–N) [15], silicon oxycarbide (Si–O–C) [16–18] and quaternary Si–M–C–N (M = B [19,20], Ni [21]). During the crosslinking and subsequent high-temperature pyrolysis under an inert atmosphere of polymer precursors, by-product gases such as CH4, NH3 and H2 were detected [5,22], and the microporosity in the polymer-derived non-oxide amorphous ceramics could be assigned to the release of the small gaseous species formed in-situ [8,22]. Iwamoto et al. [23] reported an approach in synthesizing micro and mesoporous amorphous silica using organo-substituted polysilazane precursors, in which the organic moieties acted as a “sacrificial Inorganics 2016, 4, 5; doi:10.3390/inorganics4010005 www.mdpi.com/journal/inorganics Inorganics 2016, 4, 5 2 of 14 Inorganics 2016, 4, 5 2 of 14 template” during polymer to ceramic conversion by heat treatment in air, thus allowing the micro and mesoporous“sacrificial template” structure during formation. polymer to ceramic conversion by heat treatment in air, thus allowing the microIn our and recent mesoporous studies, commercially structure formation. available perhydropolysilazanes (PHPS) was used as a starting polymer.In our The recent PHPS studies, contains commerc many reactiveially available Si–H and perhydropolysilazanes N–H groups which can(PHPS) react was with used chemical as a modifiersstarting polymer. to yield The novel PHPS ternary contains or quaternary many reactive Si-based Si–H non-oxide and N–H ceramics groups which [24–27 ].can In react addition, with comparedchemical modifiers with polysiloxanes to yield novel often usedternary as aor precursor quaternary for silica,Si-based PHPS non-oxide can be easily ceramics oxidized [24–27]. at low In temperaturesaddition, compared to yield purewith silicapolysiloxanes in high ceramic often yieldused dueas a to precursor the weight for gain silica, as shown PHPS in can the followingbe easily equationoxidized [at28 –low30]. temperatures to yield pure silica in high ceramic yield due to the weight gain as shown in the following equation [28–30]. rSiH[SiH2 ´2–NH]NHsnn `+ nnOO22 →Ñ nnSiOSiO22 +` nNHnNH3 ↑3 Ò (1)(1) InIn ourour previousprevious studies,studies, alkoxyalkoxy groupsgroups werewere introducedintroduced toto PHPS,PHPS, andand thethe resultingresulting chemicallychemically modifiedmodified PHPSPHPS waswas convertedconverted toto microporousmicroporous amorphousamorphous silicasilica byby oxidativeoxidative crosslinkingcrosslinking atat 270270 ˝°CC followedfollowed by heat heat treatment treatment at at 600 600 °C˝ Cin inair air (route (route R1 R1in Figure in Figure 1) [31].1)[ 31Mi].croporous Microporous amorphous amorphous silica silicawas also was synthesized also synthesized through through the two the step two conversi step conversionon route, route,(i) room (i) roomtemperature temperature oxidation oxidation of the ofchemically the chemically modified modified PHPS PHPSto afford to affordan air-stable an air-stable alkoxy alkoxy group-functionalized group-functionalized amorphous amorphous silica- silica-basedbased inorganic-organic inorganic-organic hybrid; hybrid; and (ii) andsubsequent (ii) subsequent heat treatment heat treatment at 600 °C in at air 600 (route˝C in R2 air in Figure (route R21) [32]. in Figure In continuation1)[ 32]. In of continuation our ongoing of studies, our ongoing we herein studies, report we the herein effect report of the the heat effect treatment of the heatatmosphere treatment on atmosphereporous structure on porous development structure developmentof the polymer-derived of the polymer-derived amorphous amorphoussilica-based silica-basedmaterials. The materials. polymer/ceramics The polymer/ceramics thermal conversi thermalon conversion under an underargon anflow argon was flow performed was performed on the onpolymer the polymer precursors precursors and the polymer- and the polymer-derivedderived hybrid silica hybrid (route silica R3 and (route R4 in R3 Figure and R4 1). inThe Figure thermal1). Theconversion thermal conversionbehaviors behaviorswere in- weresitu inanalyzed-situ analyzed by the by thesimultaneous simultaneous thermogravimetry-mass spectrometryspectrometry (TG-MS)(TG-MS) analysis.analysis. TheThe relationshipsrelationships betweenbetween thethe heatheat treatmenttreatment atmosphere,atmosphere, gaseousgaseous speciesspecies formedformed inin--situsitu duringduring thethe thermalthermal conversionconversion andand thethe micro and mesoporosity inin the resulting amorphousamorphous silica-based silica-based materials materials are are discussed discussed and and compared compared with with our ourprevious previous results results [32] in [32 order] in orderto achieve to achieve a better a better understanding understanding of the ofthe micro micro and and mesoporous mesoporous structure structure development development in thethe polymer-derivedpolymer-derived amorphous-silicaamorphous-silica basedbased materials.materials. Micro and mesoporous amorphous silica-based materials R1, R4 R2, R3 NH H Si NH NH N N SiH OR R H2Si 2 3 n R-OH H H Oxidation O N SiH SiH SiH O O O R Si SiH O Si Si -n H2 N NH Si O H Si N N N at r.t. 2 O O O O O HN HSi SiH SiH SiH Si Si 2 2 Name R Si O O NH O O HN P0 None SiH2 R P5 n-C5H11 Perhydropolysilazane (PHPS) P10 n-C H Alkoxy group-functionalized 10 21 amorphous silica R1 R2 1h R31h R4 1h 1000 800 1h 1h 1h 1h 600 400 (a) Temperature / ºC / Temperature 200 In air (b) In air (b) Under Ar flow Under Ar flow 0 Time/ min. (a): Cross-linking in air at 270 ºC for 1h. (b): Oxidation at room temperature. Figure 1. Synthesis of micro- and mesoporous amorphous silica-based materials through polymer derivedFigure 1. ceramics Synthesis (PDCs) of micro- routes and investigated mesoporous in this amorphous study. silica-based materials through polymer derived ceramics (PDCs) routes investigated in this study. Inorganics 2016, 4, 5 3 of 14 Inorganics 2016, 4, 5 3 of 14 2.2. Results Results and and Discussion Discussion 2.1.2.1. Polymer Polymer Precursors Precursors and and Alkoxy Alkoxy Group-Functionalized Group-Functionalized Amorphous Silica Silica TheThe chemical chemical structures structures of of the the polymer polymer precursorsprecursors and those those of of the the alkoxy alkoxy group-functionalized group-functionalized inorganic-organicinorganic-organic hybrid hybrid silica silica were were assessedassessed based on on their their FT-IR FT-IR spectra. spectra. As As shown shown in inFigure Figure 2a,2 a, thethe as-received as-received PHPS PHPS exhibited exhibited absorption absorption bandsbands at 3400 ( (ννN–H),N–H), 2150 2150 (ν (νSi–H),Si–H), 1180 1180 (δ (N–H)δN–H) and and 840–1020840–1020 cm cm´1−1( δ(δSi–N–Si)Si–N–Si) [[4,31–33].4,31–33]. The PHPSs modified modified wi withth
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