Synthesis and engineering of titanosilicate ETS-10 for enhanced photocatalytic activity in an optical fiber reactor

Semiconductor photocatalysis has attracted attention recently as an alternative to traditional physical, chemical, or biological technologies for environmental remediation. In 2007, the photocatalyst market has been predicted to reach US ;Using an in-situ isomorphous substitution method, the transition metal ions were successfully incorporated into ETS-10 framework structure. This was confirmed by chemical (EDX), structural (XRD), and optical (UV-vis) analyses. All transition metal-substituted ETS-10 (M-ETS-10) showed lower bandgap energy (3.79-3.89 eV) compared to as-synthesized ETS-10 (i.e., 4.03 eV), in addition to introducing new charge transfer transitions in the visible light range. This is consistent with their improved photocatalytic activities compared to the unmodified ETS-10 in both UV and visible light ranges.;All silver-exchanged (Ag+-ETS-10) samples showed 1-2 orders of magnitude higher photocatalytic activity than unmodified ETS-10, and the activity increased with increasing AgNO3 concentration. The results suggested the photoreduction of Ag+ during photocatalysis as the main factor responsible for the improved activity. Unlike the results obtained using Ag+-ETS-10, an optimum photocatalytic activity was achieved for the Ag nanoparticle-modified ETS-10 (Ag0-ETS-10) prepared from Ag+-ETS-10 using 6 mM aqueous AgNO3 solution. The enhanced activity of Ag0-ETS-10 at low silver loadings suggested the effective electron trapping role of Ag nanoparticles during photocatalytic degradation of MB. Surface plasmon resonance of these Ag nanoparticles might have also contributed to the improved activity, especially in the visible light range.;Light transmission analysis in ETS-10-coated single optical fiber showed thickness-independence of the light attenuation along the fiber, which suggested the uniform optical fiber surface coverage for all ETS-10 thin films. However, the refracted light decayed relatively slower through the thicker films. This may be because ETS-10 crystals in multilayer ETS-10 films were more loosely packed compared to those in the monolayer ETS-10 film.;Kinetic study performed in the optical fiber reactor (OFR) showed that the external mass transfer limitation could be successfully eliminated by increasing flow rate above 3 L min-1. The highest photocatalytic activity was obtained for the ETS-10 films with thickness ∼1.5 microm, prepared by triple dip coating. Although higher conversion of MB, and thus higher reaction rate constant, was always achieved at higher light intensity in the OFR system, the apparent quantum efficiency decreased with increasing light intensity. This was likely due to the dominant electron-hole recombination effect at high light intensity. Both as-synthesized and modified ETS-10 showed ∼5 times higher apparent quantum efficiency in the OFR system compared to that in the slurry reactor. Ag+-ETS-10 and Ag+-Co-ETS-10 prepared using 15 mM aqueous AgNO3 solution showed even higher efficiency than P25 in the OFR system. The improved apparent quantum efficiency suggested OFR as an effective photocatalytic system for the potential photocatalytic applications in water treatment.