Study On Degradation Of Diclofenac And Ibuprofen By Y And Ultrasonic Irradiation In Aqueous Solution

Diclofenac (DCF) and ibuprofen (IBP) are two typical over-the-counter (OCT) non-steroidal anti-inflammatory drugs (NSAIDs), which are widely used becase of their good anti-inflammatory and analgesic effects. These two drugs and their metabolites have been detected in the surface water around the world, causing adverse impacts on the aquatic organisms and damages to human beings implicitly. This study chose electron beam and 60Co as the radiation sources to study the degradation of diclofenac and ibuprofen through the reactions with the hydroxyl radical (·OH) or the hydrated electron (e’aq) under different gas-saturated conditions as well as the degradation mechanism by ultrasonic irradiation.Electron beam and y irradiation were used to treat DCF and IBP solutions. N2O saturated solution was added to scavenge e-aq, while Isopropyl alcohol was added to scavenge ·OH under the N2 or Ar saturated conditions. LC analysis was used to determine the concentrations of DCF and IBP. The degradation mechanisms DCF and IBP by the two radicals were derived. The first order reaction constants by the electron beam were determined at different concentrations of DCF, and they were fitted to estimate the absolute reaction constants,which were (9.29±0.11)×109 M-1 s-1 for ·OH and(1.53± 0.03)×109 M-1 s-1 for e-aq. In the condition of irradiation of 60Co, the pseudo-first-order constant of reaction of 1 mM DCF with ·OH was 0.38 kGy-1 with irradiation energy and the initial reaction efficiency was 60.6%. The pseudo-first-order constant of reaction of 1 mM DCF with e-aq was 0.23 kGy-1 with irradiation energy and the initial reaction efficiency was 64.4%. The pseudo-first-order constants of reaction of 0.5 mM IBP with ·OH was 1.2 kGy-1 with irradiation energy and the initial reaction efficiency was 83.2%, and the reaction of IBP with e-aq was minimal. LC-MS was used to derive the by-products generated during the reactions of DCF and IBP with ·OH and (or) e-aq, and determine the degradation pathways of the two drugs. The primary degradation by-products of DCF and IBP by ·OH oxidation were hydroxylation substances, and the attack of ·OH manly occurred in the aromatic ring of the molecules. Meanwhile, the process of e-aq reduction was mainly dechlorination. The bioluminescence of the marine bacterium Vibrio fischeri (T3) was used to assess the change of the toxicity of DCF after irradiation. Reactions with both ·OH and e-aq could effectively reduce the toxicity of DCF. However, e-aq was more effective because of its high dechlorination efficiency.Terephthalic acid (TPA) was used as the hydroxyl radical scavenger to derive the yield of 2h-TPA in the pure water and 0.5 mM hydrogen peroxide solution by the ultrasonic irradiation of 80 W and 585 kHz under the air, oxygen, argon, and nitrogen saturated conditions. The concentrations of hydroxyl radical in these two solutions were calculated. The theoretical degradation equations of DCF and IBP under different gas saturated conditions were derived based on the second order constants of DCF or IBP and the concentrations of hydroxyl radical. In addition, the yield of hydrogen peroxide and its reaction equations were also derived under different saturated gas conditions. Furthermore, DCF and IBP solutions were treated with ultrasonic irradiation under air, oxygen, argon and nitrogen saturated conditions at the temperature of 4℃ and the pH of 7. Study results indicated that the degradation rates of DCF and IBP were different under the four gas saturated conditions by ultrasonic irradiation, with the degradation of DCF fastest under the argon condition and IBP fastest under the air condition. In the paper, theoretical model and equations were established to determine the processes of the degradation of DCF and IBP by ultrasonic irradiation. Scavengers were added to capture the hydroxyl radicals in the zone of bulk solution and bubble formed during ultrasonic irradiation. For example, the addition of TPA was to scavenge hydroxyl radicals in the zone of bulk solution, and the addition of IPA was to scavenge hydroxyl radicals in the zone of bubble. The pseudo first order reaction constants of DCF and IBP were calculated with the addition of the two hydroxyl radical scavengers, as well as the constants without any scavengers. The proportions of degradation in the three zones by ultrasonic irradiation were calculated using the established hypothetical model and equations.The degradation mechanisms of DCF and IBP were different under different saturated gas conditions. Oxidation of DCF in the pesupercritical interface was the main reaction under aerobic conditions, while oxidation by hydroxyl radicals was the main reaction under the inert gas conditions. The main degradation processes of IBP were different from DCF. Oxidation of IBP by hydroxyl radicals in the bubble zone was the main reaction under air, argon, and nitrogen saturated conditions, while the oxidation in the pesupercritical interface was the most important under oxygen saturated condition. The proportion of the three zones and the effects of H2O2 were analyzed under different saturated gas conditions by ultrasonic irradiation with the addition of 0.5 and 5 mM H2O2.In the case of DCF, low concentration of H2O2 (0.5 mM) facilitated the oxidation of hydroxyl radicals, while high concentration of H2O2 (5 mM) mainly affected the oxidation in the pesupercritical interface under aerobic conditions. Under inert gases conditions, there was no significant difference in the oxidation constants in the pesupercritical interface between low and high H2O2 concentrations, and oxidation by hydroxyl radical were the main reaction. H2O2 had a different impact on the degradation of IBP. The addition of H2O2 faciliated the oxidation by hydroxyl radical under the four gas saturated conditions, hence accelerated the degradation process. In addition, the efficiency and mechanism of dechlorination during the degradation of DCF by ultrasonic irradiation were analyzed. The efficiencies of dechlorination were 88%,100%,87% and 83% under the air, oxygen, argon, and nitrogen saturated conditions, respectively. The main reason of the difference was the different degradation process under the different gas saturated conditions.