Factors that have an effect on degradation of diclofenac in aqueous solution by gamma ray irradiation

Abstract

Gamma ray irradiation is considered as an effective way to degrade diclofenac. However, due to the extensive coexisting substances in natural waters, the use of gamma ray irradiation for degradation is often influenced by multiple factors. The various factors that affect degradation efficiency, such as initial diclofenac concentration, initial pH, and the concentration of the additives including H(2)O(2) (·OH radical promoter), CH(3)OH (·OH radical scavenger), thiourea (·OH, H·, and e (aq) (-) scavenger), humic acid, and NO(3)(-) (coexisting substances in natural waters), are investigated. Furthermore, possible intermediate products are identified and corresponding transformation pathways are proposed. Degradation experiments were performed in a 50-mL airtight Pyrex bottle loaded with 25 mL of diclofenac solutions at various initial concentrations of 20.5, 30.4, and 50.1 mg L(-1). The radiation doses were controlled at 0, 0.3, 0.5, 0.7, and 1.0 kGy. Study results indicate that: (1) The degradation efficiency of diclofenac decreases with the increase of its initial concentration. (2) The degradation efficiency is higher under acidic conditions than in neutral and alkaline media. (3) The results obtained when H(2)O(2), CH(3)OH, and thiourea were added show that the degradation of diclofenac takes place via two pathways: oxidation by ·OH radicals and reduction by e (aq) (-) and H·. (4) The extensive coexisting substances in natural waters, such as humic acid and NO(3)(-), do not affect the degradation efficiency. Based on the identified intermediates, it is proposed that transformation pathways are initiated mainly by H·, e (aq) (-) , and ·OH. Gamma ray irradiation effectively degrades diclofenac.