Temperature effects on the vacuum-UV (VUV)-initiated oxidation and mineralization of organic compounds in aqueous solution using a xenon excimer flow-through photoreactor at 172 nm

The 172 nm irradiation of aqueous solutions of organic compounds with a xenon excimer (Xe-2*) flow-through photoreactor leads to the oxidation and mineralization of the organic content of the water. In view of potential technical applications, it is of fundamental interest to investigate temperature effects on the efficacy of these processes. Therefore, water samples containing Rhodamin B (RhB) or methanol as model substrates were vacuum-UV (VUV) irradiated under controlled thermal conditions. The pseudo-first-order bleaching kinetics of RhB solutions and the pseudo-zero-order reaction kinetics of oxidation and mineralization of aqueous methanol solutions were quantitatively established by UV/Vis spectrophotometry, by measurement of the methanol concentration using capillary gas chromatography and the total organic carbon (TOC) content of the solutions, respectively. In the water temperature range from 20 to 50 degrees C no significant effects on the pseudo-first-order rate constant of RhB bleaching (k(RhB)) and the pseudo-zero-order rate constants of methanol oxidation (k(MeOH)) and TOC diminution (k(TOC)) were observed with our particular flow-through photoreactor system using a Xe-2* excilamp.