Environmental remediation by an integrated microwave/ UV-illumination method. 1. Microwave-assisted degradation of rhodamine-B dye in aqueous TiO2 dispersions.
The photocatalytic decomposition of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using an integrated microwave/UV-illumination (PD/MW) method. This procedure proved to be superior in the degradation of the dye than the TiO2 photocatalytic degradative method alone. With few exceptions, the integrated PD/MW method also proved superior for other chemical systems. The greater efficacy of the PD/MW technique appears to be the result of the following two considerations: (i) there is enhanced formation of reactive oxygen species (.OH radicals), as attested to by DMPO spin-trap ESR methods and their attack on the dye; and although speculative at this time, (ii) the activity of bulk water or the TiO2 particle surface is somehow affected by microwave radiation. The greater efficacy of the PD/MW degradation method was also observed at low concentrations of molecular oxygen and at low radiant excitance of the light source. A brief mechanistic description is given on the basis of results obtained on the two model compounds, (i) benzoic acid and (ii) pyronin-B dye.
Horikoshi
Satoshi
S
Frontier Research Center for the Global Environment Protection, Meisei University, Hino, Tokyo, Japan.
Hidaka
Hisao
H
Serpone
Nick
N
D004396:Coloring Agents / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D008872:Microwaves; D010100:Oxygen / Q000737:chemistry; D012235:Rhodamines / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014876:Water Pollution / Q000517:prevention & control*
D004396:Coloring Agents; D005456:Fluorescent Dyes; D012235:Rhodamines; C009495:titanium dioxide; D017665:Hydroxyl Radical; D014025:Titanium; C029773:rhodamine B; D010100:Oxygen