Archive of SID Int. J. Ind. Chem., Vol. 2, No. 3, 2011, pp. 140-143
International Journal of Industrial Chemistry www.ijichem.org Islamic Azad University Quchan Branch
ISSN (online): 2228-5547 ISSN (print): 2228-5970
Synthesis and Characterization of Nano Particle Crystals of NaX Zeolite Mahdi Fathizadeh a, Abdolreza Aroujaliana,b,* a
Department of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic) Tehran, Iran. Food Process Engineering and Biotechnology Research Center, Amirkabir University of Technology (Tehran Polytechnic) Tehran, Iran. *Email:
[email protected]
b
Received: 16 November 2010; Accepted: 22 February 2011 Abstract
In this work, the nano particles of Na-X zeolite were synthesized via hydrothermal method by controlling heat and mixing rate in crystallization during. The particle sizes of NaX zeolite crystals were controlled from 40 nm to 150 nm. Also, the physical properties of NaX-nano were characterized by X-ray diffraction, Field-Emission Scanning Electron Microscope (FESEM), and X-ray Fluorescence (XRF). Results show that the nano X zeolite with average crystal size is 105 nm, Si/Al ratio 1.25 and with Na+1 active site. Keyword: Characterization; Faujasite; Nanocrystal; Size Controlling; Zeolite NaX.
1. Introduction Zeolite X is a highly versatile molecular sieve from the faujasite family of zeolites whose 7.4 Å, three-dimensional pore structure and solid acidity make it useful as a catalyst, adsorbent, membrane, and others [1–3]. This type of zeolite is used for heavy metal adsorption [4], aromatics from aromatic/alkane mixtures [5] and para xylene [6] separation, as well as natural gas desulfurization [7]. The powerful catalytic properties of X zeolite due to its use in the reaction between MeOH and PhNH2 [8], hydrocarbons cracking [9], chlorination of toluene [10] and the ammonia synthesis [11].
Nowadays, the synthesis of zeolites with small particle size has been more interested attention by many researchers [12-14]. The nanozeolite particles can be produced by microcrystal grinding method which does not have a good result. Another way is direct synthesis using hydrothermal method. In most syntheses, organic templates, structure directing agent, seeding crystals and many other additives were often added to induce the formation of zeolite NaX with small crystals [1-3]. In this paper, nano zeolite NaX was synthesized via hydrothermal methods with
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Archive of SID M. Fathizadeh et al / Int. J. Ind. Chem., Vol. 2, No. 3, 2011, pp. 140-143
agitation and temperature controlling. We did not use the addition of organic templates, directing-agent, seeding crystals and other additives in this synthesis.
2. Experimental methods 2. 1. Zeolite synthesis The chemical reagents such as fumed silica (7 nm, Sigma Alderich), NaOH (Merck, Darmstadt, Germany) and NaAlO2 (Sigma Alderich) were used for zeolite synthesis. The nanometer-sized faujasite-X zeolite was synthesized by hydrothermal crystallization in a temperature-controlled shaker. Aluminosilicate gel was prepared by mixing freshly prepared aluminate and silicate solutions together in the molar ratio 5.5 Na2O:1.0 Al2O3:4.0 SiO2:190 H2O. Typically, an aluminosilicate gel containing 5.34 g of NaOH, 2.42 g of NaAlO2, 3.43 g of SiO2, and 50.0 g of H2O was adopted. First, a 250 mL plastic bottle containing freshly prepared sodium aluminate solution and SM-30 and fumed silica, the silicate sources were directly mixed with freshly prepared aluminate solution at room temperature and then immediately moved to a shaker at the desired temperature for hydrothermal crystallization. Hydrothermal crystallization was conducted at 60 °C for 4 days in a shaker with a rotation rate of 250 rpm. The powdered products were recovered with centrifugation, washed with DI water until pH < 8, and then dried at room temperature for 24 h for further characterization. 2. 2. Nanozeolite characterization The X-ray powder diffraction (XRD) patterns were recorded at 25 °C on a Philips instrument (X’pert diffractometer using CuKα radiation) with a scanning speed of 0.03° (2Ө) min -1. The crystallinity of sample was
determined from the peak areas of 6° [111], 16° [331], and 27° [642] and the average crystal dimension was calculated using Scherrer’s equation [5, 6]. Also, the particle size distribution was measured by the Mastersizer 2000 (Malvern instrument). The FESEM (Hitachi, model S-4160) was used to particle size distribution of nanozeolite crystals, and the Si/Al ratio, elemental compositions of nanoparticles was determined by XRF (Philips instrument).
3. Results and discussion The XRD pattern matches very well with the simulated XRD powder pattern for FAU zeolite [5-9] indicating that the synthesized crystal is pure FAU zeolite and shows that nanozeolite NaX sample has more than 95% crystalline (Fig. 1). The nanozeolite NaX is very hydrophilic with entrance pores of approximately 7.4 Å. The average crystal dimension of 105±9 nm was calculated by Scherrer’s equation from the diffraction peaks at 2Ө values of 6° [111], 16° [331], and 27° [642]. The average particle size (Å) was calculated by eq. 1. k Scherrer’s equation : r (1) cos Where k is the shape factor, λ is the x-ray wavelength, typically 1.54 Å, β is the line broadening at half the maximum intensity (FWHM) in radians, and θ is the Bragg angle. The particle size distributions of nanozeolite crystal from dynamic light scattering (DLS) are showed in Fig. 3, results indicated a narrow distribution of particle size, with an average crystal size of 112 nm. The result of DLS is more important than XRD methods. Because the DLS calculates the particle distribution but the Scherrer’s equation measures an average particle size. The FESEM image was recorded for the assynthesized nanozeolite sample is shown in 141 www.SID.ir
Archive of SID M. Fathizadeh et al / Int. J. Ind. Chem., Vol. 2, No. 3, 2011, pp. 140-143
Fig. 2 which clearly indicates that the particle size of nano-NaX is ultrafine and within a range of 40-150 nm which is consistent with the results calculated from the XRD pattern and dynamic light scattering (Fig. 3). Also, the Si/Al ratio of the naozeolite NaX was calculated 1.25 through XRF analysis. The unit cell mass of NaY zeolite was calculated using the composition provided by XRF test: Na106[(Al106Si86O384].
4. Conclusions Temperature controlling and agitation promoted the synthesis of nano zeolite NaX with small crystals (with average particle size 105 nm) from a precursor mixture without any additives. The XRD showed the assynthesized NaX had good crystallinity structure and was pure. Also, FESEM and DLS results confirmed nano size of these crystals.
Table 1. XRF results of nano-NaX Na
Al
Si
O
Si/Al
106
85.594267
85.93759
383.3602
~1.25
Fig. 1. XRD pattern of as-synthesized sample crystallized
Fig. 2. The FESEM image of nanozeolite NaX
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Fig. 3. Distribution of particle size of nanozeolite NaX
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