Investigation of 207 nm UV radiation for degradation of organic dye in water

The photo-degradation of organic dye C.I. Acid Red 213 (AR-213) was achieved by 207 nm UV radiation emitted from a planar KrBr* excimer lamp without addition of oxidants at varying initial pH values. Precipitates were found to be generated when the irradiated solution of initial acid pH was adjusted to alkaline pH and they would disappear again when the solution was readjusted to acidic conditions. The efficiency of COD removal was greatly increased after the filtration of precipitates. Both the decolourisation rate and the COD removal rate reached the maximum in the initial pH 2.8 solution. The same phenomenon was also observed for other kinds of dyes. Direct photolysis was the only pathway in degrading dye molecules for both O2-saturated and N2-saturated solutions. The by-products formed for initial acidic solution were were identified by electro-spray ionisation (ESI) in positive mode and the influence of initial pH on the reaction mechanism of the dye under 207 nm radiation was analysed.