Plasmachemical decolourisation of Bromothymol Blue by gliding electric discharge at atmospheric pressure

The colour of aqueous solutions of 3,3′-dibromothymolsulfonephtalein (Bromothymol Blue) fades when they are exposed to a gliding electric discharge, due to the nature of impinging plasma species at the liquid surface. For treatment times >10 min, alkaline BTB solutions turned from blue to yellow due to acidic effects and also fading resulting from both decolourisation and degradation. The addition of NaN3 reduced the decolourisation rate from 99.1% without NaN3 to 68.2% and lowered the pH to 6.7. In contrast, H2O2 increased the extent of decolourisation from 60.6% to 94.0% after 5 min treatment. Additionally, an increase in decolourisation rate of the plasma treated solutions' post-discharge was observed for the first time.