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STUDIA UNIVERSITATIS BABEŞ-BOLYAI, CHEMIA, LIV, 3, 2009 PHOTO-CATALYSTS BASED ON GOLD - TITANIA COMPOSITES ANCA PETER a , MONICA BAIA b , FELICIA TODERAS b , MIHAELA LAZAR c , LUCIAN BARBU TUDORAN d , VIRGINIA DANCIU e ABSTRACT. Porous TiO2 aerogels with different Au colloidal particles concentrations were synthesized and their functionality to decontaminate the water was evaluated using model pollutants. It was showed that the decrease of noble metal concentration determines a decrease of the composites pore size and specific surface area and of the photo-degradation apparent rate constant. The morphological (porosity, surface area, TEM and TGA) particularities of the synthesized porous composites were also briefly discussed from the perspective of the photo-catalytic results. Since the photodecomposition rate depends on the [OH]surface adsorbed on the surface, additional measurements have been performed. Keywords: Au -TiO2 composite, porosity, TEM microscopy, photo-catalysis, salicylic acid INTRODUCTION TiO2 photo-catalysis has been improved by numerous investigations in recent years, particularly owing to its application for the complete mineralization of almost all organic contaminants to carbon dioxide, water and inorganic constituents [1, 2]. The advantages of using TiO2 are its nontoxic nature and stability, but it is also significant that the low rate of electron transfer to oxygen and the high recombination rate of electron-hole pairs limit the rate of organic compounds photo-oxidation on the catalyst surface [3]. Many investigations have reported that the addition transition metals to TiO2 are two ways to enhance the photo-catalytic reaction rate [3-9]. The noble metals as gold [4, 5], platinum [6, 7] and silver [9] were usually a North University, Faculty of Science, Department of Chemistry-Biology, 430083, Baia Mare, Romania, peteranca@yahoo.com b Babes-Bolyai University, Faculty of Physics, 400084, Cluj-Napoca, Romania c National Institute for Research and Development of Isotopic and Molecular Technologies, Donath 71 – 103, RO-400293, Cluj-Napoca, Romania d Faculty of Biology and Geology, Electron Microscopy Center, Babes-Bolyai University, 5-7 Clinicilor Str., 400006, Cluj-Napoca, Romania e Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, 400028, Cluj-Napoca, Romania
162 A. PETER, M. BAIA, F. TODERAS, M. LAZAR, L. B. TUDORAN, V. DANCIU used to produce the highest Schottky barriers among the metals, in order to facilitate the electron capture. Moreover, the research studies [10, 11] have demonstrated that the gold particles interact with TiO2 surface oxygen vacancies (note that on an oxygen vacancy site, two neighbouring Ti atoms are reduced from Ti 4+ to Ti 3+ ), thus reducing the surface defects. Due to their very low density, high surface area, translucency or transparency to the visible light and to their microstructure, the TiO2 aerogels are the preferred materials as supports for noble metals. On the other hand, the photo-catalytic activity of Au-TiO2 composites has been described as strongly influenced by morphological and structural parameters, such as their structure, surface area, porosity, gold particle size and surface hydroxyl group density [12, 13]. In this paper, we study the photo-catalytic behaviour of a series of Au - TiO2 composites in the aqueous salicylic acid (SA) oxidation. The goal of this study was to investigate the influence of the Au loading on the photocatalytic activity of the Au –TiO2 composites. RESULTS AND DISSCUTION Morphology and Structure of the Composites The morpho-structural characteristics of the Au – TiO2 composites are presented in Table 1. In columns 2 and 3 of the Table 1 are indicated the gold colloid volumes used to the TiO2 gels impregnation and gold content, respectively. One observes an increase of the Au content as the colloid volume increases from 20 to 75 ml. By using a volume higher than 75 ml Au colloid, the Au content slowly decreases, probably due to the saturation of the TiO2 surface with Au particles (Figure 1). The pore size distribution of the obtained composites is presented in Figure 2 A (a-e). The Au -TiO2 composites have a porous structure containing pores ranging from 8 to 55 Å, while TiO2 aerogel contains pores ranging from 20 to 80 Å. So, the Au presence in the composites reduces the composite’s porosity. This behaviour was attributed to the insertion of a small amount of gold nano-particles into the pores. This insertion occurs without damaging the pore structure. Similar changes have been reported in the surface structure of porous titania with the insertion / deposition of ruthenium and platinum nanoparticles by the sono-chemical method [14, 15]. The decrease of porosity by Au deposition can be observed also by analyzing the pore volume values from Table 1. It is interesting to notice that the porosity decreases with the decrease of Au content (Figure 2B). The B1Au and B2Au composites with similar Au content (0.395 % and 0.397%, respectively) have the major pore size ranging from 35 to 40 Å while B4Au composite with 0.131% Au, which contains predominantly 15 A pores. At low Au concentrations, pores with 20 Å diameters are dominant, whereas composites with high Au content (samples B1Au and B2Au) contain pores with diameters higher than 20 Å.
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R /(mol m -2 s -1 ) 0.06 0.05 0.04
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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6 PROFESSOR IOAN BÂLDEA AT HIS 70
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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MATHEMATICAL MODELING FOR THE CRYST
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STUDY OF THE CHROMATOGRAPHIC RETENT
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LOWER RIM SILYL SUBSTITUTED CALIX[8
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THE INTERACTION OF SILVER NANOPARTI
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OPTIMISATION OF COPPER REMOVAL FROM
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Page 123 and 124: 128 ANDRADA MĂICĂNEANU, HOREA BED
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Page 141 and 142: 146 Interfering ion, J - I - DBS -
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Page 149 and 150: 154 Intens. x105 1.5 1.0 0.5 0.0 x1
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