Optimization of Ultrasonic Irradiation as an Advanced Oxidation Technology

Abstract

The optimization of ultrasonic irradiation as an advanced oxidation technology can be achieved by adjusting the ultrasonic frequency and saturating gas during sonolysis. The sonolytic production of hydrogen peroxide (H 2 O 2 ) and hydroxyl radical ( • OH) has been investigated at the ultrasonic frequencies of 20, 40, 80, and 500 kHz, respectively, in the presence of four different saturating gases (i.e., Kr, Ar, He, O 2 ) at each frequency. H 2 O 2 was measured with a KI dosimeter, and the formation of • OH was monitored by trapping with terephthalic acid. Both the applied frequency and the physicochemical properties of the saturating gases influence the sonochemical rates of production of • OH and H 2 O 2 . At 20 kHz, the rate contants for the production of H 2 O 2 vary over an order of magnitude as a function of the nature of the dissolved gas (0.0508 and 1.31 µM min -1 ). Similar trends are observed for the production of • OH at the same frequencies and under an identical set of saturating gases. The highest rates of production of H 2 O 2 (pH 7, 2.94 µM min -1 ) and • OH (pH 11, 0.391 µM min -1 ) are observed during sonolysis of Kr-saturated solutions at 500 kHz. Sonolysis of He-saturated solutions at 20 kHz results in the lowest rates of production of H 2 O 2 (0.0508 µM min -1 ) and • OH (0.0310 µM min -1 ). Decreasing differences among the saturating gases at higher frequencies are attributed to changes in bubble dynamics and thermodynamics as the resonant bubble radius decreases from 177 µm at 20 kHz to 7 µm at 500 kHz.

Production of chloride and hypochlorite for analytical purposes by sonochemical degradation of organochlorines

“…After the monochloramine production, 2 mL of RS were added and diluted to 10 mL prior the measurement at 645 nm. In order to evaluate the analytical usefulness of the hypochlorite generated a set of experiments were carried out with reference NH 4 + solutions in the concentration range from 0.25 to 2 mg L -1 .…”

“…In order to attain this goal, 100 mL of a 0.01 mol L -1 NaOH solution containing 500 μL of laboratory effluent sample containing predominantly CCl 4 and different amounts of hexane, acetonitrile and methanol 5,2005 were subjected to ultrasonic irradiation over 120 min for the production of aqueous hypochlorite solution. After the sonication, 400 μL of the resulting aqueous solution were submitted to the Berthelot method, as previously described, employing NH 4 + reference solutions from 0.5 to 5 mg L -1 .…”

“…The solutions and biphasic mixtures of organochlorines were obtained by the addition of liquid residues from chromatographic analysis in water. The liquid residues were derived from a poly(ethylene) quality control laboratory which were constituted mainly by CCl 4 and low quantities of hexane, methanol, acetonitrile and poly(ethylene) fragments. The laboratorial effluent containing residues of the herbicide Thiamethoxam ® (Novartis, 25%, m/m) was obtained from solutions of this herbicide used to develop the chromatographic determination procedure.…”

“…2 The production of free radical can take place even in situations as simple as the ultrasonic irradiation of pure water. 3,4 In this way, the sonochemical generation of reagents can deal with primary species, such as the radicals H and OH, and/ or secondary species, such as H 2 O 2 produced by rearrangement of OH radicals.…”

“…The dependence between the production of chloride obtained from the sonication of effluents containing organochlorines and the irradiation time was evaluated for CCl 4 , CHCl 3 , CH 2 Cl 2 and Thiamethoxam ® . It was observed that under saturation conditions the production of chloride was highest for CHCl 3 .…”