Microstructure effect of nanocrystalline titanium dioxide prepared by microemulsion technique on photocatalytic decompos
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Enrico Traversa Department of Chemical Science and Technology, University of Rome “Tor Vergata,” Rome, Italy (Received 24 January 2006; accepted 23 June 2006)
Titanium dioxide (TiO2) was synthesized in the water-in-oil (w/o) microemulsion system of n-heptane/water/sodium bis (2-ethylhexyl) sulfosuccinate (AOT) surfactant. This study reports the effect of microstructure of the synthesized TiO2 nanoparticles on the photocatalysis degradation of phenol in an aqueous solution, as compared to commercial TiO2 (P25) and TiO2 synthesized by bulk precipitation. The results indicated that the rate of phenol decomposition catalyzed by the synthesized TiO2 from microemulsion techniques is faster than those of TiO2 synthesized by bulk precipitation and commercial P25. This is due to the small crystal size of TiO2 prepared by the microemulsion technique. The exposed titanium sites on the surface controlled by the morphology of synthesized TiO2 are critical for photocatalytic activity.
I. INTRODUCTION
The excellent chemical and electronic properties of ceramics, semiconductors, and metallic catalysts have attracted a great deal of attention in the development of new technologies for the future (e.g., the high activity of metallic catalysts).1–3 Nano-sized particles possess better physical and chemical properties when compared to bulk materials, in particular for applications using changes in surface properties, due to their larger surface/bulk ratio.3 Thus, particle size is a crucial parameter for controlling the electronic and chemical properties of materials. Producing a so-called “nanoparticle,” whose diameter is in the range of 1–30 nm, has become a major interdisciplinary area of research over the past 10 years. Among metal oxides, TiO2 is extremely interesting because it is inexpensive and has been utilized in many industrial applications due to its various unique properties.4–8 TiO2 has excellent photocatalytic activity, which can be used to eliminate toxic molecules such as volatile organic compounds (VOCs) in wastewater treatment.6–8 A conventional method that has been applied to prepare this metal oxide is the precipitation technique.9–11 Although the precipitation technique is easy, the morphology and size of the metal oxide are difficult to control, resulting in unreliable properties in real applications. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0373 J. Mater. Res., Vol. 21, No. 12, Dec 2006
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There are many methods that can be used to control the size of nanoparticles.9,11,20,22–27 Microemulsion is one of the most interesting techniques that can be successfully used as a microreactor to control the size of various organic14,32 and inorganic materials10–13,15–17,32 because of their thermodynamic stability in the microenvironment. The microemulsion of a non-ionic surfactant has been heavily researched for synthesized nanocrystalline TiO2 because a high volume of water up taking in the oil phase yields large
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