maximum of AB25 absorption at 602 nm.
In the present study, plasma is generated in the closed reactor chamber, where argon gas is pumped through at flow rate of 300 sccm. Before the start of each experiment, the system has been purified with argon flow of 1 sLm for
10 minutes, in order to remove residual air from the chamber. The use of argon provides a controllable atmosphere where side reactions with formation of HNO3, various oxides NxOy and HNO2 are strongly suppressed. This makes interpretation of results simpler and also excludes any effect of HNO3 as a strong acid on the stability of TiO2. It has to be noted that air dissolved in water has not been removed prior to the experiments. Correspondingly, some traces of N2 and O2 coming from the dissolved in water air can be observed, but their effect on AB25 destruction is very low and can be neglected. Indeed, it was observed that liquid conductivity is increased during the treatment but this effect is very low compared to the same discharge working in ambient air. For example, we observed an increase of the conductivity from 50 μS cm-1 to
125 μS cm-1 after 120 minutes of treatment. With glow discharge working in the ambient air at the same current, the final conductivity is much higher (about 4.2 mS cm-1). In our opinion, the observed small increase of the conductivity is because of dissolved N2 in water but it is still low and does not affect the discharge properties.