Abstract
•Safranin O degradation by CCl4/ultrasound process was experimentally and numerically assessed.•The contribution of reactive chlorine species (RCS) and •OH was revealed for the first time.•A pyrolysis reaction model within reactive bubbles is used to quantify the role of RCS and •OH.•RCS and •OH production increased proportionally with the increase of CCl4 concentration.•Saturating gasses, temperature, [CCl4]0 affect both RCS and •OH yielding as well SO degradation.
The present study combines, for the first time, experimental degradation findings and numerical simulation results of CCl4 sonochemistry for (i) understanding the right mechanism by which CCl4 improves Safranin O (SO) sono-bleaching (1.7 MHz, 15 W) and (ii) stating the impact of operational conditions on reactive species distribution toward the degradation process. The hydrophilicity/hydrophobicity of SO are the main keys controlling its elimination as function of the solution pH in the absence of CCl4. In the presence of CCl4, a drastic enhancement in the SO degradation rate was observed. The quantity of reactive chlorine species (RCS) and reactive oxygen species (ROS) produced through CCl4 and H2O sono-pyrolysis within hot bubbles are the key parameters responsible for SO rapid degradation. Theoretical results indicated the increase of RCS and •OH production proportionally with the rise of CCl4 concentration from 0 to 5 mM, conversely to the bubble temperature and CCl4 conversion yield which were reduced. In addition, it was observed that the degradation of SO is more promoted at the liquid temperature of 25 °C, because of the synergy between RCS and •OH radicals at this liquid temperature. However, the competition between RCS and •OH radicals at 45 °C negatively affects the degradation rate.
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