Eiko Obuchi

Photocatalytic treatment of water containing dinitrophenol and city water over TiO2/SiO2

Abstract The photocatalytic degradation of dinitrophenol (DNP) was studied in an aqueous solution over porous TiO2/SiO2 in a laboratory scale fixed bed circulation type reactor. DNP is consecutively decomposed to NO3− and NH4+ via NO2− and about 90% of aromatic compounds decomposed completely to CO2 in 100 min. Reaction rate equations were found to obey a first order rate law. A pilot scale fixed bed flow reactor packed with the commercially available titania/silica was set outdoors under solar light for treating city water. Concentration of total organic carbon (TOC) and double bonded organic compounds were found to decompose on the photocatalyst under sunbeam. The experiment was done during 3 months and the catalyst was fouled because of the adhesion of red iron agglomerates. We examined a method to remove the adhesion metal by dipping the fouled catalyst into hydrochloric acid, nitric acid and citric acid, and deionized water for 1 week. Activity recovered for the catalyst washed by acid, but activity does not recover as for the catalyst washed in deionized water.

Effect of transition metal doping under reducing calcination atmosphere on photocatalytic property of TiO2 immobilized on SiO2 beads

TiO2 immobilized on SiO2 (TiO2/SiO2) have been prepared by sol-gel method and various ions of transition metals (Cr3+, Co2+ Ni2+, CU2+, and Zn2+) were doped on the photocatalyst using wet impregnation method under reducing calcination atmosphere. The photocatalytic activity of metal doped TiO2/SiO2 towards phenol degradation under black light irradiation were investigated and compared with undoped TiO2/SiO2. The results showed that the photoresponse of Cu2+ and Zn2+ doped TiO2/SiO2 were larger than undoped TiO2/SiO2, indicating that the photogenerated carriers were separated more efficiently in Cu2+ and Zn2+ doped TiO2/SiO2. The reactivity was in the order of Cu2+ > Zn2+ > Ni2+ > Cr3+ > Co2+. The different photoreactivity was ascribed to combine effect of the different ionic radii and photocorrison tendency of the dopants. The sample was also characterized by surface analytical methods such as X-ray diffraction, scanning electron micrograph/electron dispersive X-ray analyzer and UV-Vis absorption spectrum.

Photocatalytic Decomposition of Formaldehyde Using Titania Coated Lime Tile

Abstract A traditional and popular Japanese house decorating lime tile, commercially available “Limix”, was used to photodecompose the formaldehyde after coating the tile with a titania sol, which solves the problem of sick-building syndrome. A total of five kinds of lime tile samples with titania sol coating and without coating were examined by using a flow-type photoreactor based on the JIS standard to test their photocatalytic activities. The photocatalytic mechanism in the coated lime tile was also analyzed by Electron Paramagnetic Resonance Spectroscopy (EPR). The results show that a high removal efficiency of formaldehyde was achieved when using the lime tile combined with commercially available zeolite compared to the lime tile immobilized titania photocatalyst. The EPR spectrum indicates that oxygen centered radicals and surface trapped holes are present in the titania sol, but it is much different from the spectrum observed in the pure anatase and Degussa P25 titania. It means that there are different characteristics among these systems on the photocatalysis mechanism.