Hyunku Joo

Preparation and characterization of a nano-sized Mo/Ti mixed photocatalyst

Abstract Nano-sized molybdenum-doped TiO 2 (Mo/Ti) mixed oxide photocatalysts were prepared with the Mo 5+ content varying from 0 up to 2.5 mol%, to shift the absorption onset into the visible region and to enhance the efficiency of photocatalytic activity by retarding the (e − –h + ) recombination. Prepared Mo/Ti mixed oxides were characterized by ultraviolet and visible spectroscopy (UV/VIS), transmission electron microscopy–electron diffraction pattern (TEM–EDP), X-ray diffraction (XRD), energy dispersive X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS). Photonic efficiency was also investigated with the degradation rate of dichloroacetate (DCA) and light intensity measured by actinometry. TEM–EDP and XRD patterns showed that particles were in the form of anatase with the diameter of ca. 4 nm. The appreciable red-shift in the UV/VIS absorption spectra was monitored at each preparation stage — aging and dialyzing. The red-shift varied with addition of Mo, in the case of 2.5% Mo/Ti the UV/VIS absorption started at around 0.22 eV less than in nano-sized pure TiO 2 (about 3.42 eV). EDAX verified that the amount of Mo in the prepared mixed oxides was as required, and XPS analysis revealed that Mo(V) existed in the TiO 2 lattice. The measured photonic efficiency increased to 0.28 with DCA at 0.5 mol% Mo, and then decreased as the Mo content increased above 0.5 mol% Mo. This could be explained in terms of the changing prevailing phenomena — electron trapping and recombination — as the amount of dopant increased in terms of the distance between the trapped sites of the charge carriers.

The use of plastic optical fibers in photocatalysis of trichloroethylene

Abstract In this study, plastic optical fibers (POFs) were considered as light-transmitting media and substrates for the potential use in photocatalytic environmental purification system and the performance of POFs was also compared with that of quartz optical fibers (QOFs). After the characteristic of POFs in terms of light transmittance was determined in the beginning, detailed investigation was further conducted through the photocatalytic degradation of trichloroethylene. It is concluded that the use of POFs is preferred to QOFs since the advantages such as ease of handling, lower cost, relatively reasonable light attenuation at the wavelength of near 400xa0nm can be obtained.

Photodegradation of methyl tertiary butyl ether (MTBE) vapor with immobilized titanium dioxide

Abstract A study on the photocatalytic degradation of methyl tertiary butyl ether (MTBE) vapor was performed with respect to reaction parameters, kinetics, and mechanism. A conventional TiO 2 -coated plate system was used for this initial work on vaporized MTBE. On irradiating with UVBLB (∼5xa0mW/cm 2 ), 0.6xa0mg/cm 2 of TiO 2 (P25) photocatalyst showed the highest reaction rate (0.85xa0μmol/min) for 25.76xa0μmole of MTBE (1000xa0ppmv). The numerical values obtained depended predictably with respect to light intensity, initial concentration, and quantity of P25. The photocatalytic degradation of MTBE followed Lanmuir-Hinshelwood kinetics with a linearity of 0.989. As far as the mechanism of degradation is concerned, attack by generated hydroxyl radicals on the methoxy group in the MTBE structure dominated and proceeded through tert-butyl formate (TBF) as an intermediate, instead of methyl group to proceed through producing 2-methoxy-2-methyl propionaldehyde (MMP). TBF finally degrades to CO 2 through acetone, which was shown easily converted to CO 2 . This study shows that the use of sunlight seems to be possible given adequate tools for concentrating the light.

The enhancement of redox reactions with mixed oxide catalysts by the sol–gel process

Abstract The enhancement of the photocatalytic activity of TiO 2 was investigated as a function of added amount of other oxides to promote desired oxidation or reduction reactions. Mixed oxides of Nb 2 O 5 or Li 2 O with TiO 2 were prepared by the sol–gel process. The target material of dichloroacetic acid (DCA) was chosen for oxidation reactions and K 2 Cr 2 O 7 for reduction. While the Nb 2 O 5 /TiO 2 had a deleterious effect on the decomposition rate of DCA, the excess electrons due to the doping of Nb 2 O 5 into TiO 2 promoted the reduction process for Cr 6+ . Li 2 O (1xa0wt%) with TiO 2 was found the most efficient photocatalyst for DCA oxidation, resulting in photocatalytic activity of 50%.

The Photodecomposition of Acetaldehyde in Gas Phase Using Immobilized TiO2 on Porous α-Al2O3 Tube

Abstracts A study on the photocatalytic degradation of acetaldehyde using immobilized TiO2 on porous α- Al2O3 tube was performed. Among various TiO2-immobilization methods such as a sol-gel and a suspension coating, suspension coating method (method B) showed the highest photodecomposition rate of acetaldehyde, and the most effective coating thickness of TiO2 layer in method B was about 10 μm. Apparently, all reactions followed 1st order kinetics and the temperature did not affect the photodecomposition of acetaldehyde in the range of 25 ~ 70 °C. As far as oxidants were concerned, O2 revealed a positive effect on the photooxidation, but H2O behaved in a opposite way. Platinum loading on immobilized TiO2 on Al2O3 tube by using photoreduction enhanced the photocatalytic reaction rate of acetaldehyde.