Fenton chemistry promoted by sub-microsecond pulsed corona plasmas for organic micropollutant degradation in water

Differences in the liquid chemistry due to different ground electrode materials (titanium, stainless steel) were compared for corona discharges in water. The plasma was generated by applying positive high voltage pulses that are characterized by short rise times of about 20 ns, a peak voltage of 80 kV and pulse lengths of about 150-160 ns (FWHM). Phenol was admixed to the water for quantification of the bulk reaction chemistry, such as phenol decomposition and H2O2-formation. Optical emission spectroscopy was conducted to relate chemistry to plasma processes. Possible electrode corrosion was determined by atomic absorption spectroscopy (AAS). The post-discharge chemistry strongly depends on ground electrode material. With stainless steel electrodes, decomposition efficiency of phenol increased by about three quarters (74.9 %) when compared with titanium electrodes. This result can be explained by dissolved metal ions corroded from the ground electrode, which catalytically decomposed the H2O2 that had been formed into hydroxyl radicals again. Ground electrodes were corroded due to electrochemical processes. Corrosion rates and overall reaction chemistries cannot readily be described similar to conventional DC electrochemical processes at low voltages. The repetitive application of sub-microsecond high voltage pulses has to be taken into account explicitly. Altogether, electrode materials, ground electrode corrosion and associated catalytic processes are more important for plasma processes in aqueous solutions than was recognized so far. Therefore, the effects need to be taken into account in the analysis of laboratory results as well as the development of respective novel water treatment technologies. (C) 2017 Elsevier Ltd. All rights reserved.