Rational Designs on TiO 2 -based Nanocomposites for Solar Photocatalytic Purification
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Rational Designs on TiO2-based Nanocomposites for Solar Photocatalytic Purification Shanmin Gao1,2 and Tao Xu*1 1 Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, U.S.A. 2 School of Chemistry and Materials Science, Ludong University, Yantai 264025, Shandong, PR China ABSTRACT We report an template-free process to fabricate S-C-codoped and (I2)n-C-codoped meso/nanoporous TiO2 nanocrystallites. Methylene blue solutions are used as a model pollute to evaluate the sorption and photocatalytic activity of the samples under visible light radiation. The high photocatalytic activity in visible light region of our samples is attributed to numerous oxygen vacancies, large specific surface area and the continuous states in the band gap of TiO2 introduced by I2 or S doping. * T.X. Email: [email protected] INTRODUCTION Semiconductor-catalyzed photo-oxidation powered by sunlight is a promising and cleaner scheme for energy- and environment-sustainable degradation of organic and biological pollutants in wastewater[1,2]. Anatase TiO2 has attracted much attention due to its abundance, high photostability, and environmentally benign properties[3]. Several critical problems, however, impede the efficiency of TiO2-based photocatalysts for wastewater treatment. (1) The large band gap of pure TiO2 (~3.2 eV) only slightly overlaps with the solar spectrum in the UV regions, so, it is crucial to enhance the light harvesting efficiency of TiO2 in the visible region[4,5]. (2) The photo-induced electron-hole pairs can either be trapped or recombine at the defect states inside the bulk of TiO2 structure before reaching the external surface[6,7]. (3) The conflicting requirements of particle size. Small particles possess more surface area. However, reduction in particle size introduces more internal crystal defects and particle-particle interfaces that act as charge trap states to diminish the effective transport of photoinduced charges to the external surface sites[8,9]. (4) The constraint in the effective mass transport and the subsequent surface adsorption of the organic species in the photocatalyst matrix[10]. For all these reasons, it is highly desirable to design anatase TiO2-based photocatalysts with visible light-driven photoactivity, strategically designed structures for large attainable surface area, fast charge transport to surface sites and facile mass flow channels for molecular transport, and surface engineering for enhanced adsorption of organic pollutant molecules. EXPERIMENTAL DETAILS
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The preparation, characterization and photocatalytic activity measurements have been described elsewhere[11,12]. The samples after heat treatment were denoted as STC-T for S-C-codoped TiO2 samples and PIT-T for (I2)n-C-codoped TiO2 samples, where the second T refers to temperature used for the heat treatment. For comparison, C-doped TiO2 was also prepared using the same method under calcination temperature of 400°C(denoted as TC-400), except that no sulfur or I2 hydrosol was used. DISCUSSION S-C-codoped TiO2
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