Enhancement of TiO 2 Photocatalytic Activity by N- Doping Using the Gas Phase Impregnation Method
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Enhancement of TiO2 Photocatalytic Activity by N- Doping Using the Gas Phase Impregnation Method Chennan Li1, Sesha S. Srinivasan2, Nikolai Kislov3, Mark Schmidt1, Elias K. Stefanakos1, D. Yogi Goswami1 1 Clean Energy Research Center, College of Engineering, University of South Florida, Tampa, FL, USA 2 Department of Physics, CEAPS, Tuskegee University, Tuskegee, AL, USA 3 NanoCVD Inc, University of South Florida Campus, Tampa, FL, USA ABSTRACT This paper investigated an inexpensive way to improve the overall photocatalytic activity of TiO2 by N- doping using anhydrous ammonia as the nitrogen source. Doping amount could be further optimized by controlling the reaction time. Experiments showed that photocatalytic effect has one threshold concentration. Lower or higher reaction will decrease the photocatalytic efficiency. Experiments showed that the suitable reaction temperature should be lower than 650oC. INTRODUCTION The demand for water has increased tremendously in terms of quantity and quality with the rapid industrialization over the past two decades [1]. Many methods including some advanced oxidation processes (AOP) have been studied for many years to provide safe water for human use. However, the development of such processes did not meet the previous expectation due to different reasons [2]. In recent years, interest has been focused on the use of semiconductor materials as photocatalysts such as TiO2 for the removal of organic and inorganic species from aqueous or gas phase. This method has been suggested in environmental protection due to its ability to oxidize the organic and inorganic contaminants [3]. Besides, the catalyst itself is unchanged during the process and no consumable chemicals are required, which results in considerable savings and a simpler operation of the equipment involved [4]. However, there are still some technological problems that need to be solved. In particular, the development of visible-light responsive photocatalysts suited to mass production has been considered to be indispensable. Researchers have done a lot of work to improve the TiO2 activities in visible light [5–10] including N-doping because TiO2 can almost only be activated by UV light. However, there is also debate whether or not N-doping improves photocatalytic activity. Generally speaking, there are three schools of thought regarding the effect of nitrogen doping: 1. Positive Effect on Photocatalytic Activity [11, 12] 2. No Effect on Photocatalytic Activity [13 - 16] 3. Negative Effect on Photocatalytic Activity [17, 18, 19] What must be noted is that photocatalytic effect is application specific, and that mistakes may be made in casting overreaching conclusions. It is also apparent that the methods used to synthesize and test the catalyst have a significant effect on the results as similar studies offer conflicting conclusions as even the authors themselves note. Therefore in this study, we developed our own system and focus on systematically optimize the doping parameters.
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