PREPARATION AND CHARACTERIZATION OF THE COMPOSITES BASED ON THE ZINC OXIDE CAPTURED ON THE SURFACE OF KAOLINITE

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1 PREPARATION AND CHARACTERIZATION OF THE COMPOSITES BASED ON THE ZINC OXIDE CAPTURED ON THE SURFACE OF KAOLINITE Barbora JANÍKOVÁ, Lucie NEUWIRTHOVÁ, Lenka MATĚJOVÁ, Vlastimil MATĚJKA VŠB Technical University of Ostrava, 7. listopadu, , Ostrava Poruba, Abstract Nanostructured zinc oxide is intensively studied semiconductor showing photocatalytical activity. There are several precursors which can be used for the preparation of nanostructured zinc oxide like zinc acetate, zinc sulphate and many others. Zinc chloride is another compound which can serve as a zinc source for zinc oxide preparation. Nowadays the environmental aspects connected to applications of nanoparticles are widely discussed. As a possible solution how to avoid possible negative impacts of nanoparticles is their fixation on the surface of suitable substrate. In this work we focused on the preparation of kaolinite/zno composite with the amount and 2 wt.% of ZnO. The chemical composition of prepared samples was investigated by using X-ray fluorescence method, the phase composition was studied by using X-ray diffraction method and photocatalytic activity of prepared composites was determined by means of UV induced discoloration of aqueous suspension prepared by the mixing of the composite with aqueous solution of acid orange 7. The obtained results indicate the kaolinite/zno composites as the efficient photocatalysts. Keywords Kaolinite, zinc oxide, nanocomposites, photocatalysis. INTRODUCTION The photocatalysis is a well-known technique used for cleaning of water and air [, 2]. Although a number of the photocatalysts have been already studied, nanosized titanium dioxide (TiO2) in its anatase modification is still the most studied one [3]. The photocatalytic properties of TiO2 are connected to the nanodimesion of the particles which on the other hand evokes a big question about their eco-friendly character []. Thus, several efforts have been already done on the fixing of nanoparticles on the surface of bigger particles of suitable carriers, e.g. phyllosilicates [], silicon oxide [6] and zeolites [7] what leads to formation of new compositelike materials. The particles of the matrix can serve either as rigid carriers, or can bring complementary functionality to the newly formed composite [8]. Zinc oxide (ZnO) is next photocatalytic material with the band gap energy 3.37 ev [9], which is slightly higher in comparison to TiO2 in anatase form, of which the band gap is often reported to be 3.20 ev [3]. There are numbers of the reports regarding to different procedures for ZnO preparation which vary mainly in the ZnO precursor as well as in the process of the synthesis. Moezzi et al. [0] summarized the main synthesis procedures used for industrial production of ZnO as well as for its laboratory preparation. Regarding to the price, the ZnO is suggested as cheaper in comparison to TiO2, on the other hand is often reported as less stable with enhanced tendency to photocorrosion, while potentially soluble and harmful zinc containing species can also originate. Similarly to TiO2, the efforts for capturing of ZnO on the surface of suitable carriers have been already reported. Fatimah et al. [] studied the utilization of montmorillonite as a substrate for growing of ZnO and proved enhanced photodegradation activity of resulting composite against methylene blue, while Li et al. [2] used oxidized graphite for growing of ZnO and also observed enhanced photodegradation activity of the prepared composites using the discoloration of methylene blue. The aim of this contribution is preparation of the kaolinite/zno composite with and 2 wt.% of ZnO, using the method based on the decomposition of previously synthesized precursor kaolinite/na2zn3(co3) (H2O)3.

2 The amount of ZnO in prepared composites was determined by using X-ray fluorescence spectroscopy. The synthesis procedure was monitored by using X-ray diffraction method and the photodegradation activity of calcined composites was evaluated using UV induced discoloration of acid orange MATERIALS AND METHODS 2. Materials Kaolinite KKAF (LB Minerals s.r.o.) was used without any additional treatment, ZnCl2 p.a. and Na2CO3 were purchased from Lachema and the model azo-dye acid orange 7 (AO7) was obtained from Synthesia a.s.. For all of the experiments distilled water was used. 2.2 Synthesis of kaolinite/zno composites The whole process of the kaolinite/zno composite preparation was based on two main steps. In the first step, the kaolinite/na2zn3(co3) (H2O)3 composite was prepared using the reaction of aq. solution of ZnCl2 with aq. solution of Na2CO3 in the presence of kaolinite. The resulting precursor is then dried at 00 C. During the second step, the resulting kaolinite/na2zn3(co3) (H2O)3 precursor is transformed into the kaolinite/zno composite by its h long calcination at 600 C. The samples were assigned as ZinkaXT, where X denotes the amount of ZnO in prepared composites (0 wt.%, 2 2 wt.%), while T denotes the temperature of heat treatment ( drying at 00 C, 6 calcination at 600 C). 2.3 Characterization methods X-ray fluorescence The chemical composition of the prepared samples was determined by using the energy dispersive fluorescence spectrometer (XRFS) SPECTRO XEPOS (SPECTRO Analytical Instruments GmbH) equipped with the 0 W Pd X-ray tube. The samples analyzed were prepared in the form of pressed tablets (wax was used as binder) for this measurement. SEM - EDX The morphology of composite particles was observed by SEM Philips XL 30 microscope (PHILIPS). The samples were coated with an Au/Pd film and the SEM images were obtained by using a secondary electron detector. The elemental composition of samples was determined by using the energy dispersive X-ray analysis (EDS). X-ray diffraction The XRPD patterns were recorded under CoKα irradiation ( =.789 Å), using the Bruker D8 Advance diffractometer (Bruker AXS) equipped with a fast position sensitive detector VÅNTEC. Measurements were carried out in the reflection mode, powder samples were pressed in a rotational holder. The phase composition was evaluated using the database PDF 2 Release 200 (International Centre for Diffraction Data). Photodegradation test The photodegradation activity of the prepared composites was evaluated in a liquid phase, using discoloration of AO7. In order to achieve the adsorption equilibrium in the first part of the experiment, the suspension containing 0.0 g of the photocatalyst, 0 ml of distilled water and.2 ml of the AO7 aqueous solution (c0 = 0-3 mol dm -3 ) was stirred in the dark for 2 h. After 2 h of the adsorption period the suspension was exposed to UV irradiation (fluorescent BLB tube, OSRAM) for and 3 h. The extent of AO7 photodegradation was evaluated by the change in the intensity of absorption maximum of AO7 (at 80 nm), using the fiber optic spectrometer USB000 (OceanOptics).

3 , Brno, Czech Republic, EU 3. RESULTS AND DISCUSSION The chemical composition of the original kaolinite KKAF and prepared ZinkaX composites obtained by using XRFS method is shown in Table. Table Chemical composition (wt.%) of original kaolinite KKAF and Zinka0 and Zinka2 composites. Oxides (wt.%) Na2O MgO Al2O3 SiO2 K2O TiO2 Fe2O3 ZnO LOI KKAF Zinka0 < Zinka LOI loss on ignition The chemical composition of the Zinka0 and Zinka2 composites revealed that the kaolinite was successfully enriched by zinc in both composites. Original KKAF does not contain any zinc and prepared composites consist of presumed amount of Zn, while other elements are proportionally decreased (see Table ). In the case of KKAF the LOI value represents the amount of interlayer water in original kaolinite, in the case of Zinka composites the enhanced LOI values are attributed to the decomposition of thermally nonstable Na2Zn3(CO3) (H2O)3, which heating is followed by releasing of CO2 and H2O. The phase composition of prepared composites was studied using X-ray diffraction method and the XRD patterns of the Zinka2 and Zinka26 composites are shown in Fig Theta - Scale Fig. XRD patterns of the kaolinite/zno composite with wt.% of ZnO after drying at 00 C (Zinka2) (pattern assigned as 00) and calcined at 600 C (Zinka26) (pattern assigned as 600). - kaolinite, 2 - quartz, 3 - mica, - Na2Zn3(CO3) (H2O)3, - zinc oxide. Freshly synthesized composite dried at 00 C consisted of kaolinite as a main phase of raw kaoline, quartz and mica as kaoline admixtures and Na2Zn3(CO3) (H2O)3 as a product of ZnCl2 reaction with Na2CO3. After the calcination of the dried composites at 600 C the kaolinite dehydroxylation occured. While this process was clearly evidenced by disappearing of the kaolinite diffraction lines, the next clearly evident change was connected to formation of ZnO which originated during the thermal decomposition of Na2Zn3(CO3) (H2O)3. The kaoline admixtures, quartz and mica, remained unchanged. The morphology of the particles of raw kaolinite and the Zinka26 composite was studied by using SEM technique and obtained micrographs are shown in Fig. 2 and Fig. 3 respectively.

4 Fig. 2 SEM micrograph of the particles of original KKAF. Fig. 3 SEM micrograph of the particles of the Zinka26 composite. SEM images of both original KKAF (Fig. 2) and the Zinka26 composite (Fig. 3) obtained using the same magnification showed the agglomeration tendency of the particles of the Zinka26 composite. The surface morphology of the particles of both samples revealed the surface of the Zinka26 particles rougher and thus it implies that the ZnO particles grow at the surface of kaolinite particles. The results of UV induced photodegradation activity of the composites with and 2 wt.% of ZnO after h and 3 h long UV irradiation are summarized in Fig.. Fig. Photodegradation activity of the Zinka06 and Zinka26 composites after h and 3 h long irradiation. Due to the big difference in AO7 sorption in the dark the photodegradation activity in Fig. is expressed by means of the amount of degraded AO7 in moles. It is evident that the composite with 2 wt.% of ZnO calcined at 600 C shows significantly higher photodegradation activity in comparison to the composite with wt.% of ZnO. While for the Zinka06 composite the photodegradation activity did not change with a time of irradiation, in the case of the Zinka26 composite the prolonged UV irradiation resulted in approx. 3 times higher photodegradation of AO7.

5 . CONCLUSIONS Composites based on the ZnO particles fixed on the surface of kaolinite were successfully prepared using the thermal decomposition of the kaolinite/na2zn3(co3) (H2O)3 precursor formerly prepared by the reaction of ZnCl2 and Na2CO3. Formation of the kaolinite/zno composite did not influence the kaolinite to metakaolinite transformation as revealed by X-ray diffraction method. The composite with wt.% of ZnO did not show significant photodegradation activity, while the composite with 2 wt.% of ZnO calcined at 600 C shows high photodegradation activity and thus represents promising material for photocatalysis. In next research the stability of the composites against the photocorrosion should be carefully studied mainly with respect to possible negative impact of soluble Zn species on living environment. ACKNOWLEDGEMENT The study was supported by Ministry of Education, Youth and Sports of the Czech Republic within the project LH 28. This paper has been also elaborated in the framework of the Nanotechnology the basis for international cooperation project, reg. No. CZ..07/2.3.00/ supported by Operational Programme 'Education for competitiveness' and financed by the Structural Funds and from the state budget of the Czech Republic. REFERENCES [] MALATO, S., FERNÁNDEZ-IBÁÑEZ, P., MALDONADO, M.I., BLANCO, J., GERNJAK, W. Decontamination and disinfection of water by solar photocatalysis: Recent overview and trends. Catalysis Today, 2009, vol. 7, iss., p. -9. [2] PAZ, Y. Application of TiO2 photocatalysis for air treatment: Patents overview. Applied Catalysis B, 200, vol. 99, p [3] CARP, O., HUISMAN, C. L., KELLER, A. Photoinduced reactivity of titanium dioxide. Progress in Solid State Chemistry, 200, vol. 32, p [] HEINLAAN, M., IVASK, A., BLINOVA, I., DUBOURGUIER, H.-C., KAHRU, A. Toxicity of nanosized and bulk ZnO, CuO and TiO2 to bacteria Vibrio fischeri and crustaceans Daphnia magna and Thamnocephalus platyurus. Chemosphere, 2008, vol. 7, p [] MAMULOVÁ KUTLÁKOVÁ, K., TOKARSKÝ, J., KOVÁŘ, P., VOJTĚŠKOVÁ, S., KOVÁŘOVÁ, A., SMETANA, B., KUKUTSCHOVÁ, J., ČAPKOVÁ, P., MATĚJKA, V. Preparation and characterization of photoactive composite kaolinite/tio2. Journal of Hazardous Materials, 20, vol. 88, p [6] TOKARSKÝ, J., MATĚJKA, V., NEUWIRTHOVÁ, L., VONTOROVÁ, J., MAMULOVÁ KUTLÁKOVÁ, K., KUKUTSCHOVÁ, J., ČAPKOVÁ, P. A low-cost photoactive composite quartz sand/tio2. Chemical Engineering Journal, 203, vol. 222, p [7] KHATAMIAN, M., DIVBAND, B., JODAEI, A. Degradation of -nitrophenol (-NP) using ZnO nanoparticles supported on zeolites and modeling of experimental results by artificial neural networks. Materials Chemistry and Physics, 202, vol. 3, p [8] MATĚJKA, V., MATĚJKOVÁ, P., KOVÁŘ, P., VLČEK, J., PŘIKRYL, J., ČERVENKA, P., LACNÝ, Z., KUKUTSCHOVÁ, J. Metakaolinite/TiO2 composite: Photoactive admixture for building materials based on Portland cement binder. Construction and Building Materials, 202, vol. 3, p [9] COLEMAN, V. A., JAGADISH C. (eds.) Basic properties and application of ZnO, zinc oxide bulk, thin films and nanostructures. Elsevier Ltd [0] MOEZZI, A., McDONAGH, A.M., CORTIE, M.B. Zinc oxide particles: Synthesis, properties and applications. Chemical Engineering Journal, 202, vol. 8-86, p [] FATIMAH, I., WANG, S., WULANDARI, D. ZnO/montmorillonite for photocatalytic and photochemical degradation of methylene blue. Applied Clay Science, 20, vol. 3, p

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