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

Abstract

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 NaN 3 reduced the decolourisation rate from 99.1% without NaN 3 to 68.2% and lowered the pH to 6.7. In contrast, H 2O 2 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.