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DEGRADATION OF NITROBEZENE BY THE Fe+3/H2O2/UV-Vis PROCESS: EFFECTS OF REACTIONS CONDITIONS ON THE 1,3-DINITROBENZENE FORMATION
LUCIANO CARLOS; ADRIAN BADINI; CARLOS LUZI; FERNANDO S. GARCÍA EINSCHLAG; ALBERTO L. CAPPARELLI
Cubatao, San Pablo, Brasil
Simposio; IX Latin-American Meeting on Photochemistry and Photobiology; 2008
The Fenton reaction combines Fe+2/Fe+3 and H2O2 to produce highly reactive hydroxyl radicals, which may readily oxidize hazardous pollutants found in wastewater 1. Fenton reaction rates are strongly increased by irradiation with UV/visible light, considerably enhancing the overall degradation of organic compounds 2. In a previous study on the nitrobenzene (NB) degradation by Fentons reagent we found 1,3-dinitrobenze (DNB) as a primary reaction product 3. The DNB is highly toxic and due to its low reactivity towards hydroxyl radicals it may require longer reaction times for its complete removal. In this work, the oxidation of nitrobenzene by photo-Fenton treatment (Fe+3/H2O2/UV-Vis) has been studied, focusing special attention on the DNB formation. The experiments were carried out in an annular photochemical reactor at 25ºC and the pH was adjusted to approximately 3.0. A medium-pressure Hg lamp was used as the source of UV-Vis radiation. The reactions products were identified by CG-MS. The concentration profiles of nitrobenzene and its by-products were followed by HPLC. The results showed that NB is completely removed by foto-Fenton process in less than 60 minutes. Within the experimental domain, NB degradation follows pseudo-first-order kinetics, the efficiency of the process being strongly dependent on NB, Fe+3 and H2O2 concentrations. The formation of 2-nitrophenol, 3-nitrophenol, 4-nitrofenol, phenol and DNB as primary reactions product was confirmed by CG-MS analysis. Among the aromatic products, DNB required the longest reaction times for its complete depletion. Initial concentrations of Fe+3 and H2O2 have a strong influence on DNB yields. An increase in [Fe+3]0 enhances the DNB production whereas an increase in [H2O2]0 reduces DNB levels during the treatment.