STUDY OF STABILITY PHOTOACTIVE NANOCOMPOSITE

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1 STUDY OF STABILITY PHOTOACTIVE NANOCOMPOSITE Jana SEIDLEROVA a, Michaela CIHLAROVA a, Lucia ROZUMOVA a, Klara DROBIKOVA a a Vysoká Škola Báňská - Technická Univerzita Ostrava, 17. listopadu 15/2172, Ostrava Poruba, Czech Republic, Jana.seidlerova@vsb.cz Abstract In connection with the reduction of the amount of greenhouse gases in the atmosphere, in few last years great attention is directed to the possibility of reducing the content of these gases and major pollutants. One of the possibilities is photocatalytic degradation with the use of catalytic effects of metal oxides like TiO 2, ZnO, and others. The increase of the photo active effect of these compounds is achieved in the form of nanoparticles. On the other hand, it is not yet known and defined their effect on living organisms. Consequently it is very effective is anchor them to an inert material and to prepare composites, where they should be tightly bound, without losing its photoactive effect. In this work two samples of nanocomposites of the photoactive kaolinite were studied, the content of TiO 2 was varied (51.6 wt. %, and 58 wt. % respectively). This was done with final finishing (drying at 100 C, respectively calcination at 600 ºC). Both samples were leached according to the norm EN for 24 hours in deionized water and also in the extraction reagents, in which the ph was adjusted with H 2 SO 4, or HCl. In the prepared extracts, the concentration of Ti was monitored and also other elements that can be released from the matrix of nanocomposite. It has been proved that the observed nanocomposites are very stabile and the TiO 2 was not released even with the use of extraction reagents at ph 1. Keywords: titanium dioxide nanocomposite, photoactive nanocomposite, stability kaolinite/tio 2 composite 1. INTRODUCTION After the Second World War, a sharp rise in industrial activity. The negative impact of human activity is increasing the concentration of inorganic and organic greenhouse gases, such as CO 2, CH 4, N 2 O, CFCs in the atmosphere. One possibility of decreasing theirs contents is photocatalytic degradation by metal oxide, for example TiO 2, ZnO and others. The anatase which is one of the three mineral forms of titanium dioxide II, the other two being brookite and rutile 1,2. anatase C 860 brookite 1040 C rutile is often use as photocatalyst of resistant organic compounds (herbicides, pesticides, synthetic pigments in water and air. It is very stable under UV radiation and low cost. The degradation of nitrogen oxides, formaldehyde and toluene was observed in the gaseous phase too. Some particles of anatase powder, however, clustered into larger units and that can negatively affect the catalysis 3. Photodegradation activity of TiO 2 increases if it is prepared as a nanoparticle. Despite the fact that TiO 2 is considered as material with very low toxicity, there are many studies dealing possible hazards of nanoparticles 4. On the other hand is not yet known and defined the effect of nanoparticles on human organisms generally. Therefore it is very effective fixed nanoparticles to an inert material and preparing nanocomposite, in which the nanoparticles should be tightly bind without losing its photoactive properties. This is the way to prevent inlet of nanoparticles to environment and negatively affect it. The matrix may enrich the final composite about other complementary function 5. For environment a suitable inert materials for nanoparticle fixing are clay minerals, especially montmorilonite and kaolinite 5,6. After preparation nanocomposite montmorilonite/tio 2 or kaolinite/tio 2 is necessary not only study the photocalatytic effect, but the risks of using it too. Risk monitoring is important throughout the hole life cycle because the nanoparticle can be released into the environment during manufacture, usage and

2 disposal. Define and norm treatment to study stability nanocomposite materials have not described yet. One of the procedure that is used to evaluate the waste, defined in Czech waste s legislative in regulation 294/ This procedure is based on monitoring potential content of pollutants in aqueous extract. If deionized water replaced with another extraction reagent, it is possible to study the material stability in various surroundings. 2. EXPERIMENTAL 2.1 Materials The stability studies have been done on two photocatalytic kaolinite /TiO 2 nanocomposites with different TiO 2 content and the method of preparation. The sample A was dried at 100 C, sample B calcinated at temperature 600 C for 2 hours. The chemical composition (show table 1) was determined using energy dispersive fluorescence spectrometer SPECTRO XEPOS. Content of Ca, Mg and Na were determined after total decomposition using atomic emission spectrometer with inductively coupled plasma SPECTRO CIROS VISION (Ca and Mg) and atomic absorption spectrometer with flame atomization UNICAM 969 (Na). Method of sample preparation and methods of characterization in detailed describe Mamulová at al. 8. Table 1 Chemical composition of native kaolin and nanocomposite of TiO 2, LOI - lost of ignition Kaolinite [wt. %] Sample A [wt. %] Sample B [wt. %] Al 2 O SiO SO K 2 O Ca Mg Na TiO Fe 2 O LOI As a extract solution was used deionized water (DM) with ph 5.90 and two different extraction reagents which were prepared from deionized water and concentrated HCl (extraction reagent I) or H 2 SO 4 (extraction reagent II) with different ph, see table 2. Table 2 Extraction reagents, DM deionized water Extraction reagent I Extraction reagent II No. ph No. ph I II I II I II I II I II I II Characterization methods Analytical methods: The ph, conductivity, concentration Ti, Al, Si, Ca Mg, Na, K and sulphate were determined for characterization of extract. The ph was measured by inolab SenTix 41 with combined electrode (the specific electrode - glass electrode, reference electrode - calomel electrode) and integrated

3 temperature sensor. Conductivity was measured using inolab Cond 730. The concentrations of mentioned elements in the extracts were determined by atomic emission spectrometer with inductively coupled plasma (AES - ICP) SPECTRO CIROS CVISION (Ti, Al, Si, Ca and Mg) and by atomic absorption spectrometer with flame atomization (AAS - FA) UNICAM 969 (Na and K). Determination of Ti concentration which presents in solution as TiO 2 particles by AES - ICP verified before experiments. The determination of sulphate (only in extract from deionized water) were used ion chromatograph (IC) WATERS, with conductivity detectors Waters 431. Extract preparation: The extracts were prepared according the regulation ČSN EN It is discontinued method of leaching of solid material in extraction solution. The ratio solid and liquid is S:L = 1:10, leaching pass for 24 hours in continuous rotation container. Filtration through the filtrate paper (84 g.m -2 ) was used to separate solid sample. The ph and conductivity were determined immediately after filtration, the concentration of listed metal after stabilization of solution with concentrated HNO RESULTS AND DISCUSSION Dependence of ph of extracts after their interaction with the studied samples on the initial ph of extraction solution and deionized water shows Fig 1. A comparison of the initial ph of extraction solution with the ph of the extract shows that the ph of the extract has set up at a particular value, except the extract with the most aggressive extraction solution (ph 1) I-6 and II-6. The extract from sample A and B can interact with the most aggressive extraction reagent preserve the value of ph 1. ph of the extract of samples after theirs contact with the extraction reagents with ph 3 and deionized water has been reduced significantly. The dependence shows, that extraction solution dissolved ions, which increase acidity of the extract. The high stability of the prepared nanocomposite can be deduced from the values of conductivity, which are illustrates Figure 2. Except solutions obtained by the interaction of sample A, respectively B with extraction reagent I and II at ph 1, the specific conductivity comparable with the value of aqueous extract. The extraction reagent at ph 1 can cause decomposition the whole structure of the material and therefore there are more ions in solution. Fig. 1 ph of extract after leaching sample A and B in deionized water (DM) or extraction reagent I or II with different initial ph Fig. 2 Specific conductivity of prepared extract from sample A or B and deionized water (DM) or extraction reagent I or II with different initial ph In Figure 3 is shown the part of Ti which leached from its total content in samples A and as a dependence on ph of extraction solution. After interacting sample with the deionized water and with the extraction reagents with an initial ph 3, leached less than % Ti. A slight increasing leached amount of Ti can be seen by the extracts I at ph 1, respectively extract II at ph 1 and 2. In spite of that fact the digested part of Ti is less than 0.006% from the total content of Ti in sample A and B. The results show that TiO 2 is fixed in structure very strongly in both samples.

4 Fig. 3 The part of Ti from total content in nanocomposites A and B which have been extracted in deionized water (DM) or extraction reagent I and II with different initial ph. According the concentration Al, Si, Mg, K and Ca in extracts is evident that the sample B changed the composition after interaction with extraction reagents more than sample A. The most soluble metal is K and Mg from sample B. It is mean that the method of nanocomposite preparation - drying only or calcinated effect strong of bonding in structure. The figures of characteristic particles and their aggregations, which were acquired using the electron microscopy, are presented on Fig 4 (samples A and B before interaction with deionized water) and 5 (samples A and B after interaction with deionized water). Both kaolinite/tio 2 composite consist of tiny particles is sharper shapes, mostly smaller particles occupy a cylindrical shape, close together (Fig 4). After interaction with deionized water the shape and size of composite particles were not changed dramatically as illustrated Fig 5. To change the shape and size of particles the most aggressive reagent must be used. On the other hand the sample A changed more than sample B. a) b) Fig. 4 Shape of the particle of kaolinite/ TiO 2 nanocomposite A (a) and B (b), magnification 1000 x.

5 a) b) Fig. 5 Shape of the particle of kaolinite/ TiO 2 nanocomposite A (a) and B (b) after leaching of deionized water, magnification 1000 x. 4. CONCLUSION In the present paper the effect of different extraction reagents and deionized water on kaolinite/tio 2 photoactive nanocomposite with different TiO 2 content were studied. To prepare extraction reagents with define ph the concentrated HCl or H 2 SO 4 were used. The extract was prepared according with waste s legislative of Czech Republic using defined 24 hours method of treated. The extract solution content dissolved ions, which increase acidity of the extract. According the Ti concentration in extract is evident that the TiO2 fixed on kaolinite very strongly. TiO2 was not released even with the composite was leached in extraction reagents at ph 1. It is means that the kaolinite/tio2 photoactive nanocomposite is safety for environment. The extract solution content dissolved ions, which increase acidity of the extract. According the Ti concentration in extract is evident that the TiO 2 fixed on kaolinite very strongly. TiO 2 was not released even with the composite was leached in extraction reagents at ph 1. It is means that the kaolinite/tio 2 photoactive nanocomposite is safety for environment. ACKNOWLEDGEMENTS Authors thanks to in the financial support from the projects by the Ministry of Education of the Czech Republic (MSM ). LITERATURE [1] KAMENÍČEK, J. Anorganická chemie. Olomouc: Universita Palackého, přírodovědecká fakulta, pp. ISBN (in Czech) [2] KHATAEE, A. R., KASIRI, M. B. Photocatalytic degradation of organic dyes in the presence of nanostructured titanium dioxide: Influence of the chemical structure of dyes. Journal of Molecular Catalysis A: Chemical, 2010, vol. 328, p [3] YANG, X., KE, X., YANG, D., LIU, J., GUO, CH., FROST, R., SU, H., ZHU, H. Effect of ethanol washing of titania clay mineral composites on photocatalysis for phenol decomposition. Applied Clay Science, 2010, vol. 49, p [4] LI, S. Q., ZHU, R., R., ZHU, H., XUE, M., SUN, X., Y., YAO, S., D., WANG, S., L. Nanotoxicity of TiO 2 nanoparticles to erythrocyte in vitro. Food Chemical Tocixology, 2008, vol 46, p [5] KOČÍ, K., MATĚJKA, V., KOVÁŘ, P., LACNÝ, Z., OBALOVÁ, L. Comparison of the pure TiO2 and kaolinite/tio2 composite as catalyst for CO2 photocatalytic reduction. Catalysis Today, 2011, vol. 161, p [6] VAN DER SLOOT, H. A., MEEUSSEN, J.C.L., VAN ZOMEREN, A., KOSSON, D.S. Developments in the characterisation of waste materials for environmental impact assessment purposes. Journal of Geochemical exploration, 2006, vol. 88, p [7] Regulation of Czech republic No. 294/2005. (in Czech) [8] KUTLÁKOVÁ, K. M., TOKARSKÝ, J., KOVÁŘ, P., VOJTĚŠKOVÁ, S., KOVÁŘOVÁ, A., SMETANA, B., KUKUTSCHOVÁ, J., ČAPKOVÁ, P., MATĚJKA, V. Preparation and characterization of photoactive composite kaolinite/tio 2. Journal of Hazardous Materials, 2010, vol. 188, p [9] Norm number ČSN EN , Praue (in Czech)