Photo-Degradation of Methamidophos (An Insecticide) in Water Using Dye-Modified Nano-Crystalline TiO2Supported onto Activated Carbon Surfaces

Abstract

Anatase TiO2 surfaces have been treated with 2, 4, 6-triphenylpyrylium hydrogen sulfate (TPPHS) or tripyridylporhpyrinatomanganese(II) (MnP) dyes to yield the modified TiO2/ dye surfaces. The modified TiO2/dye surface was then supported onto activated carbon (AC) surfaces to yield a new class of catalytic system AC/TiO2/dye. The catalytic activities of naked TiO2, dye solution, TiO2/dye, and AC/TiO2/dye systems were examined in photo-degradation of Methamidophos (insecticide) in water, using both UV and visible light. All examined systems showed catalytic activity when used either in the UV or the visible regions, but the AC/TiO2/ dye showed the highest activity. The dye role, in enhancing activity of modified surfaces in UV degradation of the examined contaminants, is understandable by a charge-transfer catalytic effect. AC role can be explained by its ability to adsorb contaminant molecules and bringing them closer to catalytic sites. There was no significant temperature effect on catalyst efficiency in Methamidophos photo-degradation. Oxygen is essential for semiconductor photocatalytic degradation of Methamidophos, but higher oxygen concentrations lead to a downturn of the reaction rate.