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TRANSFORMATION OF ZEOLITE NaY SYNTHESIZED
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FROM RICE HUSK SILICA TO NaP DURING
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HYDROTHERMAL SYNTHESIS
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Supattra Khabuanchalad, Pongtanawat Khemthong, Sanchai
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Prayoonpokarach and Jatuporn Wittayakun
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School of Chemistry, Institute of Science, Suranaree University of Technology,
Nakhon Ratchasima 30000. Tel.:0-4422-4256; Fax.: 0-4422-4185; Email:
jatuporn@sut.ac.th

Corresponding author
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1
Abstract
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Rice husk silica (RHS) powder with approximately 98% purity was used as
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a silica source for zeolite syntheses. This study investigated the transformation of
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zeolite NaY to zeolite NaP during hydrothermal synthesis at 100°C by fixing the
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ratio of SiO2, Al2O3, and Na2O at 10:1:4.6, the optimum ratio for NaY synthesis.
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The studied parameters included aging time (1, 2 and 3 days) and crystallization
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time (1, 2, 3, 4 and 5 days). The transformation was observed by powder X-ray
8
diffraction (XRD). The aging time did not have much effect on the transformation
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because when the crystallization time was fixed at one day, the synthesis with one
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day aging produced pure phase NaY and that with 2 and 3 days produced only a
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small amount of NaP. In contrast, changes of crystallization time, with fixed aging
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time at one day, caused a significant transformation. The transformation of NaY to
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NaP was observed in the synthesis with crystallization of 2 days and the amount of
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NaP increased with the crystallization time. The NaY phase was not observed after
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the crystallization time of 4 days and NaP with cleaner phase was obtained after
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crystallization of 5 days. Consequently, the synthesis condition with aging time of
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one day and crystallization time of five days was the optimum condition for the
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transformation. Scanning electron micrographs at this optimum condition showed
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narrow size distribution in the range of 7-14 µm.
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Keywords : Zeolite synthesis, NaP, NaY, Rice Husk Silica, Crystallization time,
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Aging time, Hydrothermal.
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Introduction
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Zeolite P class includes a series of synthetic zeolite phases such as cubic
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configuration (also termed B or Pc) or tetragonal configuration (also termed P1). Its
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conformation depends on the extra-framework ion, the state of dehydration and the
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chemical composition (Nery et al., 2003). The zeolite P class has the typical oxide
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formula: M2/nO·Al2O3·1.80-5.00SiO2·5H2O; where M is an n-valent cation,
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normally an alkali metal. Crystallines of zeolite P with a Si/Al ratio from 0.9 to
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1.33 are useful as molecular sieves and detergent builders (Huang et al., 2001).
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Zeolite P can be synthesized from various silica sources and methods, for
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examples, from a natural clay, Kaolinite
and crystallization at 75–85°C
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(Sathupunya et al., 2002); from coal fly ash by agitation at 120°C (Murayama et
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al., 2002) or from sodium aluminate and sodium silicate solution by hydrothermal
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treatment in microwave oven (Zubowa et al., 2007).
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Sang et al. (2006) synthesized small crystals of zeolite NaY by
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hydrothermal method and found that the crystallization at 120°C caused the
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formation of zeolite NaP instead of zeolite NaY. Moreover, in the synthesis of
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zeolite NaY with rice husk silica by our group, zeolite NaP was observed when the
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crystallization at 100°C was longer than 48 hours (Wittayakun et al., 2008). Thus,
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we investigated further to determine the synthesis conditions such as aging and
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crystallization time that facilitated the transformation of NaY to NaP.
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Here we report the transformation of zeolite NaY, synthesized with the
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rice husk silica as reported previously, to NaP under different aging time (1,2 and
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3 days) and crystallization time (1,2,3,4 and 5 days). The product from each
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condition was characterized by X-Ray Diffraction (XRD). The sample with the
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1
highest degree of transformation was characterized further by Fourier Transform
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Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Laser
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Diffraction Particle Size Analyzer (DPSA) and Simultaneous Differential Thermal
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Analysis (TGA-DTA).
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Experimental
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Materials
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Chemicals for the preparation of rice husk silica (RHS) and zeolite
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synthesis were hydrochloric acid (37% HCl, Carlo-Erba), sodium aluminate (~55 –
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56% of NaAlO2, Riedel-de Haën), sodium hydroxide (97% NaOH, Carlo-Erba),
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and rice husk (local rice mill in Lampang, Thailand). The standard zeolites were
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NaY with Si/Al molar ratio 5.7 (JRC with Tosoh Crop) and NaP (Fluka).
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RHS was prepared by acid-leaching method reported previously
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(Khemthong et al., 2007). Briefly, rice husk was washed and dried at 100°C
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overnight; refluxed with 3 N HCl for 6 hours; filtered and washed again with water
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until the filtrate was neutral and dried at 100°C overnight before the pyrolysis in a
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furnace (Carbolite, CWF1200) at 550°C for 6 hours to remove the hydrocarbon
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and volatile organic compounds. The obtained RHS contain amorphous silica with
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approximately 98%wt purity. This RHS was dissolved in 3.5M NaOH solution to
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produce Na2SiO3 for further zeolite synthesis.
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Transformation of zeolite NaY to NaP
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The transformation was investigated with the synthesis gel of zeolite NaY
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prepared similarly to that of a previous work by Khemthong et al. (2008) by
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mixing a seed gel and feedstock gel. The seed gel was prepared by dissolving
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1
NaOH and NaAlO2 in DI water followed by the addition of Na2SiO3 solution and
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kept at room temperature for 1 day. The feedstock gel was prepared with similar
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method to that of the seed gel except that it was used immediately without aging.
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In the synthesis, both gels were mixed to form overall gel, aged (kept undisturbed)
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at room temperature, and crystallized at 100oC. After the crystallization step, the
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resulting white powder was separated by filtration, washed and dried at 100oC.
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The transformation of zeolite NaY to NaP was investigated by changing
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aging time or crystallization time. In the first set, the overall gel were aged at
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various time (1, 2, and 3 days) and crystallized for 1 day. These conditions were
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chosen because the aging time of 1 day and the crystallization of 1 day was the
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optimum condition for the synthesis of NaY. Another set of the experiment, the
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effect of crystallization time was investigated by fixing the aging time at one day
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and vary the crystallization time to 1, 2, 3, 4 and 5 days.
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The product from each condition was characterized by XRD with nickel
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filter Cu Kα radiation scanning from 4 to 50°. The XRD pattern was compared
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with that of standard NaY and NaP. A product with the highest degree of
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transformation was characterized further by Fourier Transform Infrared
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Spectroscopy (FTIR) (Spectrum GX, Perkin-Elmer) using KBr as a medium. IR
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spectra were scanned in the range of 4,000 cm-1 to 400 cm-1 with a resolution of 4
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cm-1. Crystallite size and morphology were studied by Scanning Electron
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Microscopy (SEM) with a JEOL JSM-6400 with applied potential 10 - 20 kV.
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Particle size distribution of zeolites was determined by Laser Diffraction Particle
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Size Analyzer (DPSA ) (Malvern Instruments, Mastersizer 2000) with the sample
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dispersed in distilled water and analyzed by He-Ne laser. The standard volume
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1
percentiles at 10, 50, and 90, or denoted as d(0.1), d(0.5), and d(0.9), respectively,
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were recorded from the analysis and used to calculate the width of the distribution.
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The width was calculated from the equation below:
d (0.9)  d(0.1)
d (0.5)
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Thermal stabilities were investigated by TGA on a Simultaneous
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Differential Thermal Analysis (SDT 2690) by heating from 0oC to 1000°C with a
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heating rate of 10°C/min in nitrogen flow (100 ml/min).
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Results and Discussion
Effect of aging time on transformation of NaY to NaP
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The XRD patterns of the sample prepared at aging time of 1,2 and 3 days
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were compared with that of NaY and NaP standards in Fig.1. The spectrum of one-
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day aging sample was similar to that of standard zeolite Y without any other peaks
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indicating that pure phase of NaY was obtained. With increased aging time, the
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peaks at 12.5, 21.6 and 28.1 degree with low intensity emerged in the products
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from two- and three-day aging time. The positions of those extra peaks were the
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characteristic peaks of NaP, indicating that longer aging time than 1 day cause the
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transformation of NaY to NaP. The transformation was not significant at these
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conditions. It was found in the next section that the transformation occurred faster
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at higher temperature. Thus, this transformation is endothermic.
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1
Effect of crystallization time on the transformation of NaY to NaP
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The effect of crystallization time on the transformation of NaY to NaP was
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investigated with the aging time of 1-day because it showed no effect on the
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transformation. The XRD patterns of products with crystallization time from one
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to five days are displayed in Fig.2 along with that of standard zeolites. Only the
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sample with 1-day crystallization time showed pure phase of NaY with the first 4
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peaks at 6.5, 10.1, 15.6 and 23.7 degree. Characteristic peaks of NaP started to
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emerge in the sample with 2-day crystallization and the intensities of those peaks
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increased with longer crystallization time. The main peak of NaY was not
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observed after crystallization for 4 days and NaP became a major component.
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Because there was another phase along with NaP, this condition was not suitable
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for the synthesis of zeolite P.
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The first peak of NaP (2 = 12.5) from this study splitted into 2 peaks but
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the position was similar to that of the standard NaP. It was possible that there
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were two types of NaP in this sample and this was confirmed by SEM in the next
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section. From literatures, the position of this peak of NaP with different
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morphology was slightly different (within 0.5 degree) (Sathupunya et al. 2002),
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Zubowa et al. 2007).
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Characterization of product with 5- day crystallization.
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The product obtained after 5-day crystallization contained NaP as major
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component. It was further characterized by FTIR, SEM, DPSA, and TGA-DTA.
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The FTIR spectrum in transmittance mode in Fig. 3 shows peaks at 3487, 1638,
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1002, 773, 690, 571 and 465 cm-1. These peaks were similar to those of zeolite P
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reported by Flanigen et al. (1971). The peaks at 571-460 cm-1 and 1002 cm-1 were
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assigned to T-O (T = Si, Al) bending and Si-O, Al-O tetrahedral vibration,
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respectively. The appearance of the peaks at 690, 1638 and 3487 cm -1 was
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attributed to the double ring external linkage, vibration of water molecule and OH
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stretching, respectively (Albert et al., 1998).
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SEM micrograph in Fig. 4 illustrates the morphology of product from the
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crystallization of 5 days. There were two types of particles: spherical and
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multifaceted. The spherical shape was similar to that of NaP reported by
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Sathupunya et al. (2002) and the multifaceted shape was similar to that of NaP
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reported by Zubowa et al. (2007). The mixed morphology might be the reason that
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the XRD peak at 12.5 degree (Fig. 2) splitted into two peaks.
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Particle size distribution of the product with 5-day crystallization obtained
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from DPSA is showed in Fig. 5. The major population had particle size in the
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range of 4-25 µm with a small population with the size in the range of 0.7-3 µm.
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Note that the particle size from DPSA were the size and distribution of bulk
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particles which might composed of several small particles aggregated together,
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and thus were different from the results from SEM which displayed images of
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isolate crystals.
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Thermal stability of the product with 5-day crystallization obtained from
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TGA-DTA experiment is showed in Fig. 6. The weight loss during heating was
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approximately 17% up to 400°C, accompanied by three endothermic peaks at
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about 60, 100 and 150°C which attributed to the loss of water (Zubowa et al.,
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2007). Further weak endothermic peaks were observed at about 200, 300 and
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600°C. These three peaks were resulted from a three step endothermic water loss
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1
and at 900°C at which the zeolite P was irreversibly converted into nepheline, a
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dense NaAlSiO4 phase (Albert et al., 1998).
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Conclusions
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Two parameters that affected the transformation of zeolite NaY to zeolite
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NaP were aging time and crystallization time. When the crystallization time was
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fixed at 1 day, the aging time of 1 day was suitable to produce pure phase of
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zeolite NaY whereas 2 and 3 days aging time produced a small amount of NaP.
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The crystallization time showed more significant effect on the transformation. The
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phase of NaY was not observed after crystallization for 4 days and crystallization
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time of 5 days, NaP was a major product.
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With 5-day crystallization time, NaP was a major product with trace
amount of NaY.
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Acknowledgements
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Research Funding for this research was from Suranaree University of
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Technology Research Fund, SUT Scholarship for Outstanding Students and
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Scholarship from Commission on Higher Education, Ministry of Education for S.
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Khabuanchalad.
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1
References
2
Albert, B.R., Cheetham, A.K., Stuart, J.A., and Adams, C.J. (1998). Investigation
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on P zeolites:Synthesis, characterization and structure of highly crystalline
4
low-silica NaP. Microporous and Mesoporous Materials., 21:133-142.
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Flanigen, E.M., Khatami, H., and Szymanski, H.A. (1971). Molecular sieve
zeolites. Advances in Chemistry Series., 101:201-228.
Huang, S., Jing, S., Wang, J., Wang, Z., and Jin, Y. (2001). White silica obtained
from rice husk in fluidized propellant bed. Powder Technology., 117:232-238.
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Khemthong, P., Prayoonpokarach, S., Wittayakun, J. (2007). Synthesis and
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Characterization of Zeolite LSX from Rice Husk Silica, Suranaree Journal of
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Science and Technology, 12(4), in press.
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Murayama, N., Yamamoto, H., and Shibata, J. (2002). Mechanism of zeolite
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synthesis from fly ash by alkali hydrothermal reaction. International Journal of
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Mineral Processing., 64:1-17.
15
Nery, J.G., Mascarenhas, Y.P., and Cheetham, A.K. (2003). A study of highly
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crystalline, low-silica, fully hydrated zeolite P ion exchanged with (Mn2+,
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Cd2+, Pb2+, Sr2+, Ba2+) cations. Microporous and Mesoporous Materials.,
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57:229-248.
19
Sathupunya, M., Gularib, E., and Wongkasemjit, S. (2002). ANA and GIS zeolite
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synthesis directly from alumatrane and silatrane by sol-gel process and
21
microwave technique. Journal of the European Ceramic Society., 22:2305–
22
2314.
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1
Wittayakun, J., Khemthong, P., Prayoonpokarach, S., (2008). Synthesis and
2
Characterization of Zeolite NaY from Rice Husk Silica, Korean Journal of
3
Chemical Engineering, 25(4), in press.
4
Zubowa, H.L., Kosslick, H., Muller, D., Richter, M., Wilde, L., and Fricke, R.
5
(2007). Characterization of phase-pure zeolite NaP from MCM-22-type gel
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compositions under microwave radiation. Microporous and Mesoporous
7
Materials., “Article in press”.
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1
List of Figures
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Figure 1 Normalized XRD patterns of zeolite synthesized with different aging time
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compared to the patterns of standard zeolite Y and zeolite P
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Figure 2 Normalized XRD patterns of zeolite synthesized with different
5
crystallization time compared to the patterns of standard zeolite Y and
6
zeolite P
7
8
9
10
11
12
13
14
Figure 3 FTIR spectrum of product obtained from 1-day aging and 5-day
crystallization time
Figure 4 SEM image of products obtained from 1-day aging and 5-day
crystallization time
Figure 5 Particle size distribution of product obtained from 1-day aging and 5-day
crystallization time
Figure 6 TGA-DTA thermogram of product obtained from 1-day aging and 5-day
crystallization time
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16
12
1
2
3
5
6
7
Intensity (Arbitrary Unit)
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standard zeolite P
3 days
2 days
1 day
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standard zeolite Y
9
0
5
10
15
20
25
30
35
40
10
2 Theta
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Figure 1 Normalized XRD patterns of zeolite synthesized with different aging
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time compared to the patterns of standard zeolite Y and zeolite P
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15
16
13
1
2
4
5
6
Intensity (Arbitrary Unit)
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standard zeolite P
5 days
4 days
3 days
2 days
1 day
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standard zeolite Y
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9
0
5
10
15
20
25
30
35
40
2 Thata
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Figure 2 Normalized XRD patterns of zeolite synthesized with
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different crystallization time compared to the patterns of standard zeolite Y
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and zeolite P
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15
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1
2
3
5
6
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Transmittance (%)
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1,638
773
690
571
3,487
465
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1,002
9
10
11
12
4,000
3,600
3,200
2,800
2,400
2,000
1,600
1,200
800
400
Wave number (cm-1)
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Figure 3 FTIR spectrum of product obtained from 1-day aging and 5-day
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crystallization time
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17
15
1
2
3
4
Figure 4 SEM image of products obtained from 1-day aging and 5-day
5
crystallization time
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7
16
1
Volume (%)
30
100
90
80
70
20
60
50
40
10
30
20
10
0
0.01
2
0
0.1
1.0
10.0
100.0
1000.0
Particle Diameter (µm.)
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Figure 5 Particle size distribution of product obtained from 1-day aging and
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5-day crystallization time
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7
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1
2
Figure 6 TGA-DTA thermogram of product obtained from 1-day aging and
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5-day crystallization time
4
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