2007_6_Nr6_EEMJ

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Orha et al. /Environmental Engineering and Management Journal 6 (<strong>2007</strong>), 6, 541-544 The preparation of Ag-doped zeolite requires two stages, i.e., in the first stage the natural zeolite was chemically treated with 2M HCl and 2M NaNO 3 to obtain the sodium form. The second stage consists of the obtaining of the Ag - doped zeolite by the mixing of the sodium form of the zeolite with 0.1 N AgNO 3 solution for 3 hours (Hagiwara et al., 1990). As a previous stage for the preparation of Agdoped zeolites the ion exchange total capacity of the zeolite for silver was determined. 1.000 g of zeolite with the dimension of pores between 0.8-1.2 mm was shaken with 25 mL of 0.1 N AgNO 3 during 3, 5, 7, 12 and 14 days (Cerjan-Stefanovic et al., 2004). Once equilibrium was established water solution was separated by filtration from the zeolite phase and the Ag amount into zeolite was determined by using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) after sample mineralization. The ICP-AES analysis was made with an ICP-AES SpectroFlame spectrometer. The thermal treatment of Ag – modified zeolite was realized in reducer environment at 500°C, when Ag - doped zeolite (Z-Ag) was formed and the thermal treatment of natural zeolite was not performed. To determine the presence of silver within zeolite lattice, the samples was analyzed by Laser Induced Breakdown Spectroscopy (LIBS). The material ablation and the excitation were performed with Q-switched Nd:YAG laser with an energy of 12- 15 mJ, using an Ag standard. The morphology and the composition of the unmodified/modified zeolite were characterized by using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Infrared Spectroscopy (IR). XRD spectra were recorded at room temperature on a BRUKER D8 ADVANCE X-ray diffractometer using Cu Kα radiation (λ = 1.54184 Å, Ni filter) in a θ: 2θ configuration. The peaks of the XRD patterns were identified using the PCPDFWIN Database of JCPDS, version 2.02 (1999). The SEM images were made in a Jeol JSM-6300LV scanning electron microscope. The AFM images were made in a NanoSurf EasyScan 2.0 atomic force microscope. The IR spectra were recorded in KBr pellet for solid compounds on a Jasco FT/IR-430 instrument. 3. Result and disscusion The results of the ion exchange total capacity of zeolite for silver that was determined by equilibrium of zeolite samples with 0.1 N AgNO 3 are shown in Table 1 . The form type of zeolite, e.g., natural and sodium form did not influence the ion exchange total capacity for silver ion. The Ag amount retained into zeolite as Ag-doped zeolite was 0.0065 mg/g zeolite almost twenty times smaller than the total exchange capacity of zeolite for silver, versus 0.008 mg/g zeolite (with the dimension of pores between 315-500 µm). Table 1. The ion exchange total capacity of the zeolite samples with 0.1 N AgNO 3 solution Zeolite type Contact time mg Ag/g zeolite [days] Z-N 3 0.115 Z-N 5 0.108 Z-N 7 0.102 Z-N 12 0.101 Z-N 14 0.101 Z-Na 3 0.115 Z-Na 5 0.107 Z-Na 7 0.102 Z-Na 12 0.101 Z-Na 14 0.099 Fig. 1 shows the laser spectrum of Ag-doped zeolite versus silver standard one to identify qualitatively the presence of silver into zeolite. Relative Intensity 328.16; 330.5 * - Ag 6500 6000 Ag standard 6000 Z-Ag 5500 5500 5000 5000 4500 4500 4000 4000 * 3500 3500 3000 3000 2500 2500 2000 2000 1500 1500 1000 1000 500 * 500 0 0 320 322 324 326 328 330 332 334 336 Wavelength(nm) Fig.1. The laser spectrum of Ag-doped zeolite (Z-Ag) The comparative XRD spectra of natural and Ag-doped zeolite (Z-Ag) are shown in Fig. 2. Intensity 1400 1200 1000 800 600 400 200 0 * 21.5; 30.5 AgAlO2 Z-Ag * 0 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 2 theta * natural zeolite Fig. 2. X-ray diffraction patterns of the natural zeolite and of the Ag-doped zeolite The intensities of reflection observed at about 10°, 23°, and 30° corresponding to the clinoptilolite amount decreased due to the thermal treatment of Ag 1200 1000 800 600 400 200 542
- doped zeolite (Rivera-Garza et al., 2000). No major differences in the diffraction patterns were observed due to de presence of the low amount of silver into zeolite. However, traces of AgAlO 2 (21.5°; 30.5°) were identified. Figs 3a and 3b illustrates the SEM images of natural and thermally treated Ag-doped zeolite. Obtaining and characterization of Romanian zeolite supporting silver ions a) Fig. 3a. SEM image of the natural zeolite b) Fig. 4. AFM image of the Ag – doped zeolite: a) without thermal treatment; b) treated thermally at 500°C Fig. 3b. SEM image of Z-Ag Significant changes of the morphology of Agdoped zeolite in relation to the natural zeolite were shown in Figs. 3a and 3b, some small particles agglomerated on the zeolitic material were observed (Fig. 3b). AFM was used to provide complementary information from both the internal and external structure of natural and Ag – doped zeolite and to image Ag particles located within the structure of zeolite. The natural zeolite consisted of particles with diameters ranged between 102.7 and 307.9 nm (Orha et al., <strong>2007</strong>) and AFM image of thermal untreated/treated Ag - doped zeolite showed the existence of smaller particles ranged between 106.9 and 160.9 nm (Figs. 4a and 4b). With the existence of smaller particles (nanocrystals) the specific surface area increased, which means that the precipitation of silver oxide on the zeolite surface was avoided. The IR spectra of the thermally treated Agdoped zeolite sample (Z-Ag) and untreated (Agmodified Z) were compared with the IR spectrum of natural zeolite (Z), and are presented in Fig. 5. Fig. 5. IR spectra of natural zeolite (Z), silver doped zeolite (Z-Ag) and silver modified zeolite (Ag modified-Z) The influence of thermal treatment on Ag - doped zeolite was clearly observed especial for the vibration bands in the range between 3000 and 4000 cm -1 . Taking into account the literature data (Rivera- Garza et al., 2000; Rodriguez-Fuentes et al., 1998) the assignation of vibration bands shown in Table 2 can be proposed for the Romanian zeolite from Mirsid. 543
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