Siliceous Materials for Immobilization of Photoheterotrophic Bacteria
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Siliceous Materials for Immobilization of Photoheterotrophic Bacteria Mikolaj Stodolny, Michal Thiel, Marcin Wlodarczak, Marek Laniecki Department of Kinetics and Catalysis, Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland ABSTRACT Preparation of transparent silica as potential carrier for photocatalysts and photosynthetic bacteria is presented. SiO2 was obtained by sol-gel techniques using tetraethyl orthosilicate as precursor. Glycol and glycerol were used as solvents. The increase of porosity of the studied materials was reached by application of soluble and commercial potato starch as a filler. Calcinations at 825 K for 6 hours removed all organic compounds. The rate of gelation was enhanced applying hydrochloric acid. Different materials were obtained in a series of syntheses with different concentrations of individual components. Transparency of the obtained materials varied between 50 and 97% (in range of λ 350 - 800 nm). Surface area varied between 300 and 400 m2/g and pore diameter was 5 – 18 nm. Samples were studied with SEM, nitrogen sorption at 77 K and UV-Vis spectroscopy. The obtained transparent materials with occluded TiO2 or CaTiO3 were tested in photocatalytic splitting of water. INTRODUCTION The contamination of environment as well as the increase of fossil fuels prices are the driving forces for search of new, environmentally friendly and cheap sources of energy. It is well documented that use of solar energy can be one of the possible options. Unfortunately, the direct use of solar energy has many limitations - it can be used directly only during the day time, the light intensity varies at different geographical latitude and with different seasons. Therefore the efficient method of solar energy accumulation is required. In nature, the biochemical methods of solar energy accumulation are based on photosynthesis [1,2] or photofermentation [3]. Here, the biomass formation occurs during photosynthesis, whereas photosynthetic bacteria can generate such energy carrier as hydrogen in presence of water, organic matter and light. It is well known that hydrogen can be considered as the one the efficient energy systems in the near future. However, present methods of hydrogen production are based on fossil fuels and in consequence are still dependant on oil and gas deliveries, as well as their constantly increasing prices. In 1972 Fujishima and Honda [4] proposed an alternative route of hydrogen generation – photocatalytic splitting of water. Although from energetic point of view this reaction is “up-hill” reaction, it is still a very promising solution for future generations. At the moment only titania and certain perovskites are considered to be the effective photocatalysts in this reaction. The application of these more or less modified semiconducting materials has the basic limitation – these photocatalysts are active only in the ultraviolet (3% of total solar irradiation). Therefore, since the discovery of photocatalytic splitting of water much effort is directed towards search of
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