| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 101 === The use of periodic illumination with UV–LEDs for enhancing decomposition, photonic efficiency and total organic carbon (TOC) removal of photocatalytic processes in water has been investigated. The effect of illumination period, dark period, solution pH, light intensity, initial concentration of target compound and dissolved oxygen concentration on photodegradation, photonic efficiency and TOC removal has been studied by UV–LED/TiO2 process in a batch photoreactor. The results have shown that there are obvious effects on the decomposition, photonic efficiency and TOC removal at 60 min total irradiation time under continuous and periodic illumination. The decomposition of target compound was increased for experiments conducted with increasing dark period. It is believed that the replenished surface coverage of target compound increased and the photogenerated electron–hole recombination decreased for experiments conducted with increasing dark period. Besides, the photocurrent experiments further confirmed the decreasing photogenerated electron–hole recombination when dark period increased. There are different reaction mechanisms under continuous and periodic illumination by photocatalytic process.
When the dissolved oxygen concentration was 8.5 or 32.0 mg/L, dark period has significant effect on the degradation efficiency. The results are may be depleted O2 re–adsorb onto the TiO2 surface and more O2‧- are possibly presented during dark period with these higher dissolved oxygen concentrations, which could advance the replenished surface coverage of target compound. The photocatalytic decomposition of DMP by UV–LED/TiO2 process under periodic illumination could be well modeled by the the proposed approach. The electric energy saving increased significantly for experiments conducted with increasing dark period.
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