Synthesis of ANA and GIS Zeolites with Sol-Gel and Microwave, Papers of Health sciences

Download Synthesis of ANA and GIS Zeolites with Sol-Gel and Microwave and more Papers Health sciences in PDF only on Docsity! ANA and GIS zeolite synthesis directly from alumatrane and silatrane by sol-gel process and microwave technique Mathavee Sathupunyaa, Erdogan Gularib, Sujitra Wongkasemjita,* aThe Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand bThe Department of Chemical Engineering, College of Engineering, University of Michigan, Michigan, USA Received 1 August 2001; received in revised form 13 February 2002; accepted 24 February 2002 Abstract Alumatrane and silatrane were successfully used as precursors to produce aluminosilicate via the sol-gel process. Due to their ability in retarding hydrolysis process, forming meso-porous material was easier. Both NaCl and NaOH can be used as hydrolysis agents, however, NaOH had highly influenced crystalline formation. The higher NaOH concentration, the better crystalline for- mation was observed. Gel transformation was an endothermic reaction. The maximum transformation occurred at 106
C, as determined by differential scanning calorimetry (DSC). By using NaOH/H2O as a hydrolysis agent and treating amorphous metal oxide gel by microwave technique, the crystalline aluminosilicate was formed and narrow particle size distribution was obtained. By fixing the ratio of SiO2, Al2O3, Na2O and H2O at 1:0.25:3:410, GIS was synthesized at hydrothermal treatment of 3 h at 110
C, while analcium (ANA) was produced at 130
C for 8 h. GIS obtained had 4.55 mm in size while ANA’s size was 9.96 mm. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alumatrane; Silatrane; Microwave technique; Sol-gel process; Zeolite 1. Introduction Zeolites or crystalline aluminosilicates are widely used in separation and refinery industries as catalysts, adsor- bents and ion exchangers due to their meso and micro- porous structures.1 Most of zeolites used come from either nature or synthesis. Synthetic zeolites are obtained via the sol-gel process to firstly produce amorphous gel from an interaction between aluminate and silicate or silica sol. To obtain any crystalline phase, further hydrothermal treatment is needed. This treatment can be conducted by either conventional or microwave heating. Microwave heating is a fast and energy efficient tech- nique, which prevents other side reactions owing to their exact nature in interaction.2 Energy transfer from microwave to material occurs either through resonance or relaxation, resulting in rapid heating, causing simul- taneous, abundant nucleation and fast dissolution of gel.25 These advantages enhance the crystallization rate in a very short time, leading to small particle size with narrow particle size distribution and high purity.5 Generally, the starting materials used for zeolites synthesis are metal salts (metal aluminate and metal sili- cate or silica sol) or metal alkoxides. In some cases, such as high silica zeolites or hexagonal structure type, the association of organic templates is necessary. Organic parts incorporate with inorganic parts via the so-called self-assembling process to form inorganic–organic micelle. The process organizes metal ions to form particle nuclei, flocculating after a more or less lengthy growing state.69 Organic templates generally and successfully used are crownethers or tertiary ammonium salts. How- ever, surfactants at around the critical (cmc) point are also employed in some works. This technique leads to gels and meso-structure materials but does not go for- ward to meso-porous solid due to the obstruction of the remaining organic portions. Moreover, micelle forma- tion also increases flocculating stability, reducing film drainage and coalescence.10,11 Metal alkoxides are sometimes used to increase the self-assembling ability since their organic parts can incorporate in micelle and their hydrolytic inertness increases as increasing both the size of the organic parts (steric effect) and the number of alcohol groups in the ligand (chelate or cage effect). Analcium (ANA) and Na-P1 (GIS) are of importance and interest, especially, ANA, which has ability in 0955-2219/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PI I : S0955-2219(02 )00042-0 Journal of the European Ceramic Society 22 (2002) 2305–2314 www.elsevier.com/locate/jeurceramsoc * Corresponding author. Tel.: +62-662-218-4133; fax: +62-662- 215-4459. E-mail address: dsjitra@chula.ac.th (S. Wongkasemjit). matrix storage for radioactive materials.12 ANA is pro- duced at 130–160
C using Teflon-lined autoclave (con- ventional heating) and aluminum sulfate/sodium metasilicate as precursors, at 165–185
C using Cetyl trimethylammonium bromine (CTAB) as a template at pH 10–12.5 or at 1300
C if started from nanostructured KAlSiO4 precursor. 1316 GIS can be synthesized from natural clay, such as Kaolinite, Aidoudi, by crystal- lization at 75–85
C. The reaction time varies depending on clay types, which can be 1–60 days.17,18 GIS can also be synthesized either from fly ash waste from power plants by fusion followed by crystallization at 90
C for 7 days.19 or from nuclear waste solution by crystal- lization at 45–90
C.20 However, GIS obtained from the mentioned methods are mostly used as molecular sieve owing to its low purity. Hence in this work, both synthesized silatranes and alumatranes were chosen as precursors for zeolite synthesis due to their ability in constructing inorganic– organic micelle. Other organic templates and surfac- tants have thus no need in the system. Moreover, these atranes are thermodynamically stable in an aqueous- base system since they can form complexes with metal ion to increase the possibility of expanding its coordi- nated sphere. This phenomenon will moderate the alk- oxides reactivity towards the nucleophilic attack of water, as a result, it retards the precipitation to occur.11,21,22 These properties remarkably induce the ability in forming meso-porous framework materials. 2. Experimental 2.1. Materials Fumed silica (SiO2, surface area 473.5 m 2/g, average particle size of 0.007 mm) and aluminum hydroxide hydrate [Al(OH)3, surface area 50.77 m 2/g], were pur- chased from Sigma Chemical Co. and used as received. Triethanolamine [TEA, N(CH2CH2OH)3], and triiso- propanolamine [TIS, N(CH2CHCH3OH)3] were supplied by Carlo Erba Reagenti and Fluka Chemical AG, respectively. Both were used as received. Ethylene glycol (EG, HOCH2CH2OH) was obtained from J.T. Baker Inc. and distilled using fractional distillation prior to use. Sodium hydroxide (NaOH) and sodium chloride (NaCl) were purchased from EKA Chemicals and AJAX Che- micals, respectively. Both were used as received. Aceto- nitrile (CH3CN) was obtained from Lab-Scan Co., Ltd. and distilled using standard purification method. 2.2. Instrumentals Fourier Transform Infrared (FTIR) spectroscopic analysis was conducted using Bruker instrument (EQUINOX55) with a resolution of 4 cm1. The solid samples were prepared by mixing 1% of sample with dried KBr, while the liquid samples were analyzed using Zn–Se window cell. Mass spectra were obtained using a VG Autospec model 7070E from Fison Instrument with VG data system, using the positive fast atomic bom- bardment (FAB+–MS) mode and glycerol as a matrix. CsI was used as a reference, while a cesium gun was used as an initiator. The mass range used was from m/ e=20–3000. Thermal properties were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) mode. TGA was performed with sample size of 10–20 mg using Perkin Elmer instrument: TGA7 analyzer while DSC was conducted with sample size of 5–10 mg on Netzsch instrument: DSC200 Cell at a heating rate of 10
C/min under nitrogen atmosphere. For liquid and gel samples, high- pressure gold cell was used with the sample size of 10–20 mg. Crystallinity of products were characterized using Rigaku X-ray diffractometer at scanning speed of 5
/s, CuKa as a source and CuKb as a filter. The working ranges were 5–90 and 5–50
/2
. SEM micrographs were performed using a Jeol 5200–2AE scanning elec- tron microscope. Electron probe microanalysis (EPMA) was used to analyze sample in micro-scale for both qualitative and quantitative analysis of element, using X-ray mode detector (SEM/Energy Dispersive Spectro- scopy (EDS)). Particle size was determined using Mas- tersize X Ver. 2.15, Malvern instruments. Water was used as a mobile phase. Hydrothermal treatment by microwave heating technique was conducted using MSP1000, CME Corporation (Spec. 1000 W and 2450 MHz). Samples were heated in Teflon-lined digestion vessel using inorganic digestion mode with time-to- temperature program. 2.3. Precursors synthesis 2.3.1. Silatrane synthesis (Si-TEA) Wongkasemjit’s synthetic method23 was used by mix- ing silicon dioxide, 0.10 mol, and triethanolamine, 0.125 mol, in a simple distillation set using 100 ml ethylene gly- col, as solvent. The reaction was done at the boiling point of ethylene glycol under nitrogen atmosphere to remove water as a by-product and ethylene glycol from the sys- tem. The reaction was set for 10 h and the rest of ethylene glycol was removed under vacuum (102 torr) at 110
C. The brownish white solid was washed with dried acetoni- trile for three times. The white powder product was characterized using FTIR, TGA, DSC and FAB+MS. FTIR: 3000–3700 cm1 (w, intermolecular hydrogen bonding) 2860–2986 cm1 (s, nC–H), 1244–1275 cm1 (m, nC–N), 1170–1117 (bs, nSi–O), 1093 (s, nSi–O–C), 1073 (s, nC–O), 1049 (s, nSi–O), 1021 (s, nC–O), 785 and 729 (s, dSi–O–C) and 579 cm1 (w, Si<–N). TGA: one mass loss transition at 390
C and 18.47% ceramic yield corresponding to Si[(OCH2CH2)3N]2H2. DSC: 349
C 2306 M. Sathupunya et al. / Journal of the European Ceramic Society 22 (2002) 2305–2314 Fig. 4. Effect of NaOH concentration of microwave heated aluminsilicate synthesized from 1SiO2:0.0115Al2O3:xNa2O:410H2O(Si:Al=87:1,x= 13) at 150
C/15 h. Fig. 5. Effect of Si:Al ratio (2:1–87:1) on microwave heated aluminosilicate synthesized from 1SiO2:x Al2O3:3Na2O:410H2O (x=0.011490.25) at 150
C/15 h. Table 1 Results of crystal analysis Name Analcime Na-Pl Type ANA GIS Crystal system Cubic for ANA–C Octagonal for ANA–O Tetragonal Space group (SG) Ia-3d I-4 3d a (Å) 13.74 9.997 b (Å) 13.74 9.997 c (Å) 13.74 9.997 Unit cell volume (Å3) 2593.94 999.04
(Cu-Ka) (Å) 1.54056 1.54056 Filter Cu-Kß Cu-Kß Data collection range (2
, deg.) 5–50 5–50 Data collection instrument Rigoku X-ray diffractometer Rigoku X-rays diffractometer Matched PDF# 41–1478 for ANA–C 19–1180 for ANA–O 39–219 M. Sathupunya et al. / Journal of the European Ceramic Society 22 (2002) 2305–2314 2309 3.3. Transformation to aluminosilicate After the gel was formed, the gel transformation to aluminosilicate by hydrothermal treatment was first studied using DSC high-pressure cell (Fig. 3) to investi- gate where the maximum transformation should be. It was found that the transformation was certainly endo- thermic reaction, in agreement with Yang work27 due to the dissolution of amorphous metal-oxide network and crystallization of aluminosilicate.28,29 The transition started at 103
C and the maximum transformation occurred at 106
C. The overall energy consumption was 35.93 J/g. After the second run, there was no peak shown up, indicating that the gel had already trans- formed into a crystalline aluminosilicate. Transformation of the gel into crystalline products depended on many factors, and sodium hydroxide con- centration was one of them. The higher the sodium hydroxide concentration used, the higher crystallinity was obtained. This is due to the negative charges con- tained in the framework structure. These charges need to be stabilized by sodium cations.30 As we found from the XRD shown in Fig. 4, once the sodium hydroxide concentration was high enough, increasing sodium hydroxide concentration would not have further effect. Although the loading of Si:Al ratio was changed from 2:1 to 87:1, the same product was obtained, as illu- strated in Fig. 5. Comparing with the literature data result, this product was exactly ANA zeolites consisting of distorted T6-ring chains, which have distorted 4-rings in between, as can be seen in Fig. 6. The crystal data are listed in Table 1. Another factor affecting the final product structure was microwave-heating temperatures. As shown in Fig. 7, lowering the heating temperature resulted in dif- ferent phase formation. Below 110
C, only amorphous Fig. 6. SEM micrographs of (a) analcime zeolite (ANA) and (b) the unit cell structure. Fig. 7. Effect of microwave heating temperature on aluminosilicate synthesized from 1SiO2:0.091Al2O3:3Na2O:410H2O at x
C/15 h (x=90–150
C). 2310 M. Sathupunya et al. / Journal of the European Ceramic Society 22 (2002) 2305–2314 was observed. At 110
C, GIS structure type was observed. Secondary building unit (SBU) was formed from T16 units, two 8-rings connected as a crankshaft chain. Periodic building unit (PBU) was formed when two crankshaft chains and T4-rings were connected in such a way that the cylinder with a T8-ring pore was formed. Each PBU was connected through T4-rings, see Fig. 8. By comparing these two structures, it might be said that higher energy given made the framework be distorted and arranged itself in a more perfect tetra- hedral form. 3.4. Effect of crystallization conditions Crystallization conditions of both products, ANA and GIS, were studied at two different temperatures, 110 and 130
C and at the Si:Al:Na ratio of 2:1:6 as a function of microwave heating time. At 130
C, both phases were obtained at different times (Fig. 9). GIS was completely built first at 80 min. After 240 min, ANA was observed and the pure phase was formed after 480 min (or 8 h) of thermal treatment. The atomic ratio of Si:Al:Na was also varied with time. At the Si:Al ratio loading at 2:1, the amorphous product obtained was at 1.86:1 which was closer to the loading ratio. After GIS was formed, the ratio dropped to 1.71:1 which was closely matched with XRD PDF#39–0219 having Na6Al6Si10O32.12H2OSi:Al:Na=1.67:1:1. It is not a perfect matching due to the presence of very small fraction of ANA formed after 100 min (Figs. 10 and 11). Although amount of ANA was higher as the time went longer, the Si:Al ratio was still the same until it reached 300 min. The Si:Al ratio was increased to 2:1 at 480 min that was the same as XRD PDF#19–1180 Fig. 8. SEM micrographs of (a) Na-Pl zeolite (GIS) and (b) the unite cell structure. Fig. 9. Effect of microwave heating time on alumino silicate synthesized from 1SiO2:0.25Al2O3:3Na2O:410H2O at 130
C/x h (x=19 h). M. Sathupunya et al. / Journal of the European Ceramic Society 22 (2002) 2305–2314 2311