Comparative study of imazalil degradation in three systems: UV/TiO2, UV/K2S2O8 and UV/TiO2/K2S2O8

The degradation of imazalil was achieved in three different advanced oxidation processes, namely UV/TiO2, UV/K2S2O8 and UV/TiO2/K2S2O8. The most relevant findings showed that for the UV/TiO2 system, the best efficiency was obtained at alkaline pH for which the rate of degradation is governed by imazalil adsorption onto TiO2, while for the UV/TiO2/K2S2O8 system, the best efficiency was obtained at acidic pH for which the rate of degradation is governed by persulfate adsorption onto TiO2 surface. In this last case, sulfate adsorption can reduce e(-)/h(+) recombination while sulfate radicals are generated. Concerning the UV/K2S2O8 system, it was shown that pH does not play an important role in the degradation and persulfate concentration is the main factor governing the rate of degradation. Experiments with tert-butanol were achieved at different pH and the results showed that at pH = 6.5 and with a ratio [K2S2O8]/[imazalil] = 100, hydroxyl radicals were responsible for 67.6% of the degradation in the UV/TiO2 system, 3.1% in the UV/K2S2O8 system, meaning that the degradation should be mainly attributed to sulfate radicals and 33.2% in the UV/TiO2/K2S2O8 system meaning that both OH center dot and SO4 center dot- were involved in the degradation. Coming to the comparison of photoproducts by using LC/MS/MS (pH=6.5), the conclusion is that hydroxylated products were more produced in the UV/TiO2 system while a mechanism involving a charge transfer would be responsible of the degradation with persulfate systems. TOC analysis shows that total mineralization was reached faster in systems containing persulfate. (C) 2013 Elsevier B.V. All rights reserved.