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Zhaoxia (Ivy) Ji, Julo Warzywoda, and Al Sacco, Jr. Semiconductor photocatalysis has attracted increasing attention in recent years as an alternative to traditional physical, chemical, or biological technologies for environmental remediation. The photocatalyst market is expected to reach US $10 billion in the near future. Engelhard titanosilicate ETS-10 is a microporous (~4.9 Å x 7.6 Å) zeotype material (Figure 1). The well-defined monatomic -O-Ti-O-Ti-O- chains in ETS-10 with a band gap energy of ~4.03 eV make this semiconductor material a good candidate for photocatalytic applications. Due to the uniform micropore system, this material shows shape selectivity during the photodegradation of organic chemicals with various molecule size [Calza et al., Chem. Commun., 2001, 2130]. The photocatalytic activity of ETS-10 after transition metal ion exchange or isomorphous substitution might be comparable or even higher than that of standard titania P25 [Uma et al., Micropor. Mesopor. Mater., 67, 2004, 181].
Figure 1: Titanosilicate ETS-10 framework structure. In this project, the main effort was focused on designing an effective immobilized ETS-10 photocatalysis system for photodegradation of organic chemicals. For that, a monolith optical fiber photocatalytic reactor system was designed to achieve high light utilization. Nano-sized ETS-10 crystals with high surface area were hydrothermally synthesized using anatase as the Ti source and N-Brand sodium silicate as the Si source (Figure 2a). These crystals were then used to prepare ETS-10 films on optical fibers (Figure 2b) that will be used as the means of light transmission and distribution into ETS-10 photocatalyst. Sol-gel process with a single dip-coating step resulted in nearly complete surface coverage of the optical fibers (Figure 2c). High resolution FE-SEM shows an apparent a(b)-out-of-plane preferred orientation of these ETS-10 crystals (Figure 2d).
Figure 2. FE-SEM images of (a) submicron ETS-10 crystals; (b) an optical fiber substrate; (c) a nearly monolayer of ETS-10 crystals deposited on the optical fiber from a single dip coating; and (d) a(b)-out-of-plane preferred oriented ETS-10 crystals (Ji et. al., Micropore. Mesopor. Mater., 101, 2007, 279.) To improve the photocatalytic efficiency of ETS-10, transition metal ions such as V4+, Cr3+, Mn2+, Fe3+, Co2+ were successfully incorporated into ETS-10. UV-Vis spectroscopic analysis showed absorption in the visible range for the transition metal modified ETS-10 samples (Figure 3). It is expected that these modified ETS-10 crystals will show higher photocatalytic activity than as-synthesized ETS-10. Currently, the photocatalytic investigation of the as-synthesized and modified ETS-10 is being performed in the designed optical fiber reactor system. The obtained photocatalytic efficiency will be quantified and compared with that reported for standard TiO2 photocatalyst.
Figure 3. UV-Vis absorption spectra of the as-synthesized ETS-10 samples and transition metal incorporated ETS-10 samples. |
