Application of on-line FTIR methodology to study the mechanisms of heterogeneous advanced oxidation processes

Abstract

On-line FTIR-methodology was used to study the routes of 1,4-dioxane degradation in heterogeneous photocatalysis with titanium dioxide (TiO2) and heterogeneous photo-Fenton with zero valent iron (Fe0). To determine the multiple decomposition mechanisms of this environmental pollutant, heterogeneous Fe0-catalyst was compared with a homogenous iron catalyst and different photocatalytic systems with UV radiation and solar light were studied. In addition, the influence of H2O2 addition profile was assessed to optimize of the reagent dose and reaction time. Complete removal of 1,4-dioxane and 85% mineralization of TOC were achieved by UV photo-Fenton with Fe0, while solar light could work as cost-effective alternative, achieving 65% removal of 1,4-dioxane. Although constant addition of H2O2 was crucial for the rapid oxidation of organic matter, significant degradation was reached by only half of the stoichiometric amount of H2O2. Meanwhile, apparently similar treatment efficiencies were observed in both UV-assisted and solar photocatalysis (almost 60% of 1,4-dioxane removal). The degradation routes for 1,4-dioxane in both advanced oxidation processes were established and presented based on extensive chromatography analysis, whereas FTIR monitoring served as a powerful tool for on-line reaction monitoring. Ethylene glycol diformate was detected as the major primary intermediate in TiO2-photocatalysis, whereas ethylene glycol was found as the main initial by-product in Fe0-based photo-Fenton. An alternative route of 1,4-dioxane degradation through methoxyacetic and acetic acids was observed, being more pronounced in photo-Fenton processes and accentuated further in the presence of Fe0.