Photocatalytic Degradation Of Refractory Organic Pollutants By Excimer Lamps

Two systems including excimer lamp photolysis/photocatalytic degradation were used to degrade refractoryorganic pollutants. The performance of photocatalytic reactor was quantitatively evaluated in terms of establishing kinetic model and calculating photonic efficiency. The effect of initial concentration,oxidized ionsor agent on the removal were investigated, and the reaction mechanism of organic pollutants degradation was studied. The feasibility of using the system to degrade practical dyeing and pesticide wastewater was explored. The main resultswere as follows:(1) Kr Br*excilamp with main irradiation wavelength of 207 nm was utilized for photolytic degradation of phenol in aqueous solution. Removal efficiency of phenol and TOCin both photolytic and photocatalytic process were conducted and global photonic efficiency were calculated. The experimental results showed that removal efficiency of phenol and TOC were enhanced via prolonging reaction time, adding considerable catalysts as well as lowing initial concentration. Global photonic efficiencywascalculated and its influence factors were further discussed. Higher photonic efficiencies were obtained by adding catalysts or increasing initial concentration of phenol, while there was no obvious linear correlation between global photonic efficiency and irradiation power. The global photonic efficiency was 5.56% when irradiation power, phenol initial concentration and catalyst dosage were 0.76 W, 1.10 mmol/L and 0.8 g/L, respectively. Moreover, the temporal variation trend of intermediates formed was systematically investigated by high performance liquid chromatography. The concentration of intermediates decreased inthe order: hydroquinone>catechol>benzoquinone>resorcinol. By establishing pseudo first-order kinetic models of phenol and intermediates, we confirmed that the photocatalytic degradation pathway of phenol follows: phenol→aromatic hydrocarbonintermediates→final products.(2) The removal efficiency of dimethyl phthalate(DMP) under four kinds of excimer lamps decreased following the order: KrBr*> KrCl*>XeBr*>Hg. When KrBr* was used to degrade DMP, five active species including O3, O2-?, ?OH, HO2? and H2O2 were formed and its contribution fraction were ?OH of 56.6%, O3 of 12.8%, O2-?/HO2?/H2O2 of 9.5% and UV direct photolysis of 21.1%, implying ?OH radical play the key role in DMP degradation. By studying the influence of different lamps and oxidized matters on DMP degradation under direct photolysis and photocatalytic systems, we confirmed that the photolysis of pollutants was restricted by two factors: direct photolysis depends on the pollutant itself absorbing light and degrading subsequently, while indirect photolysis depends on the added oxidizing agent absorbing UV light and generating active groups.(3) The feasibility of excilampfor wastewater deep treatment was explored by means of investigating TOC removal efficiency of actual wastewater(printing and dyeingpesticide) under Kr Br* excilamp.