Comprehensive experimental and numerical investigations of the effect of frequency and acoustic intensity on the sonolytic degradation of naphthol blue black in water

Abstract

In the present work, comprehensive experimental and numerical investigations of the effects of frequency and acoustic intensity on the sonochemical degradation of naphthol blue black (NBB) in water have been carried out. The experiments have been examined at three frequencies (585, 860 and 1140 kHz) and over a wide range of acoustic intensities. The observed experimental results have been discussed using a more realistic approach that combines the single bubble sonochemistry and the number of active bubbles. The single bubble yield has been predicted using a model that combines the bubble dynamics with chemical kinetics consisting of series of chemical reactions (73 reversible reactions) occurring inside an air bubble during the strong collapse. The experimental results showed that the sonochemical degradation rate of NBB increased substantially with increasing acoustic intensity and decreased with increasing ultrasound frequency. The numerical simulations revealed that NBB degraded mainly through the reaction with hydroxyl radical (OH), which is the dominant oxidant detected in the bubble during collapse. The production rate of OH radical inside a single bubble followed the same trend as that of NBB degradation rate. It increased with increasing acoustic intensity and decreased with increasing frequency. The enhancing effect of acoustic intensity toward the degradation of NBB was attributed to the rise of both the individual chemical bubble yield and the number of active bubbles with increasing acoustic intensity. The reducing effect of frequency was attributed to the sharp decrease in the chemical bubble yield with increasing frequency, which would not compensated by the rise of the number of active bubbles with the increase in ultrasound frequency.

Ultrasonic Destruction of Acid Orange 7: Effect of Humic Acid, Surfactants and Complex Matrices

“…The sonochemical removal of 20 mg/L AO7 was conducted at different input powers of 40, 60, 80, 100 and 120 W and the results are presented in Figure 7. It is clear that the removal efficiency increased significantly with an increase of the applied power from 40 to 120 W. These finding are in line with those of Villaroel et al (2014), Quesada-Pe˜nate et al (2009) andFerkous et al (2015b) that suggested higher degradation rates of various pollutants at higher supplied powers.…”

“…Since higher production of radicals could be achieved under higher power (Ferkous et al, 2015b;Merouani et al, 2010b), more AO7 was degraded during the same sonication time. After 90 min, more than 71% of the dye remained in the solution at 40 W. However, the remained fraction decreased considerably to 40, 13, 8 and 0% with the power increase from 40 to 60, 80, 100 and 120 W, respectively.…”

Persulfate-enhanced sonochemical degradation of naphthol blue black in water: Evidence of sulfate radical formation

“…2. As seen from this figure, sonication alone degraded efficiently NBB, which is mainly due to the • OH radical attack at the bubble/solution interface, as demonstrated early [48,49]. It should also be mentioned that previous efforts have demonstrated that the degradation rate of NBB cannot be associated with a first-order law [48].…”

Toward understanding the mechanism of pure CO2‐quenching sonochemical processes

“…We note here that there are other nitrogen‐containing radicals, i.e. NO 2 • , NO 3 • , as well as reactive atoms such as N that are formed in the case of air bubble . However, their estimated amounts were very low as compared with that of • OH, which is mainly due to the fact that such radicals reacts quickly to form nitrous and nitric acids (HNO 2 and HNO 3 ) as final products of air sonolysis inside the bubble .…”