Tannic acid oxidation by electroperoxone

Abstract

Highlights:Graphical/Tabular Abstract  Electroperoxone as a combination of ozone and electrooxidation processes has been tested for tannic acid oxidation.  Hydroxyl radical is generated by the reaction of ozone with in-situ produced H2O2.  Molecular ozone and hydroxyl radical have been involved together in tannic acid oxidation.Electoperoxone (E-peroxone) process enabling in-situ H2O2 production can supersede the conventional peroxone process that is required external addition of H2O2 into ozone to produce hydroxyl radicals (OH•). Eperoxone process provides electrochemically H2O2 production using the sparged oxygen during ozone generation by an ozone generator. This environment is achieved by placing an electrooxidation apparatus into an ozonation system. A highly oxidative medium rises in the E-peroxone system including the produced H2O2, dissolved ozone, and OH• radicals produced via both ozone self-decomposition and the reaction of ozone with H2O2. Tannic acid oxidation has been tested in this medium and potentially responsible oxidant species have been evaluated. The effect of ozone concentration and applied current change has also investigated in this study. Figure A. The produced oxidant species in the E-peroxone system and the comparison of oxidation processes through tannic acid degradation against timePurpose: This paper examines the combined use of ozone and electrooxidation (i.e. E-peroxone) to oxidize tannic acid. Theory and Methods:Two carbon-PTFE cathodes and Ti/IrO2-Ta2O5 anode were placed in an 800 ml circular ozone reactor. Ozonation and electrooxidation processes were operated both individually and in combination. The comparison of the oxidation efficiencies of the processes has been indicated as the normalized value of the tannic concentration and the dissolved organic carbon. The oxidation species produced were also observed as well as the removal efficiency. Results:Tannic acid oxidation by E-peroxone provided 10% more removal efficiency than that of ozonation. The oxidation of tannic acid is dominated by molecular ozone in the early stage of the reaction, and then the OH• radicals are abundantly produced in the aqueous medium, causing further oxidation of tannic acid. However, OH• radicals depleted after a while due to a decrease in pH value corresponding to carboxylic acid formation. According to observation on the effect of operating conditions on the removal efficiency, the amount of ozone that releases to the bulk solution should be increased and the applied current should be adjusted so as not to produce excess H2O2 to avoid the possible inhibitory effect of H2O2 on OH• radicals. Conclusion:The E-peroxone process has some advantages, such as in-situ H2O2 production using excess oxygen released from the ozone generator. Hydroxyl radicals can be effectively produced in this way, however, the role of the OH• radicals in oxidation may vary depending on the reactivity of the target substance against ozone and the pH of the aqueous medium. In the case of tannic acid, molecular ozone was do...