Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers

Abstract

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.

Degradation of 2,4-dinitrophenol by combining sonolysis and different additives

“…Considering that there was no reaction between CCl 4 and • OH radicals [17], an increase in • OH radicals concentration and an enhancing effect in DNP degradation were achieved in the presence of CCl 4 . Zheng et al [16] drew a similar conclusion when they studied the effect of CCl 4 on the ultrasonic degradation of phenol.…”

“…CCl 4 was found to remarkably facilitate the sonolysis of phenol [16]. However, the increasing degradation efficiencies of CCl 4 for various pollutants usually presented a distinct difference.…”

Sonochemical Degradation of Phenol in the Presence of Inorganic Catalytic Materials

“…Zheng et al [92] investigated the effect of CCl 4 , perfluorohexane (volatile) and iodate (non-volatile) hydrogen atom scavenger for improving the phenol degradation. They reported the enhancing effect with the volatile H atom scavenger.…”

Sonochemical Treatment of Water Polluted by Chlorinated Organocompounds. A Review

“…(ii) Low ultrasonic frequencies are expected to induce destructive effects only for hydrophobic solutes, which easily diffuse into their long-lived cavity bubbles to undergo pyrolytic destruction inside the collapsing bubble, or hydroxylation and thermal decomposition at the interface, where pressure gradients and temperatures are still high enough to induce thermal effects [ 74 ]. For low frequencies, radical scavenging and recombination reactions can inhibit the mass injection of the radicals into the solution [75]. (iii) Finally, medium frequency gives rise to short-lived cavitational bubbles, which develop much higher pressures and temperatures and larger energies are released into the surrounding liquid during their more rapid and violent collapse [76].…”