Photosensitized oxygenation reactions as an alternative towards the degradation of fenamates and related pollutants using visible light

Abstract

Fenamates are a well-known family of non-steroidal anti-inflammatory compounds widely used in medicine. These compounds are found in surface waters and may be the cause of unwanted effects on the ecosystems, in consequence it is desirable to degrade and/or eliminatethem from aqueous media. Sensitized photooxidation is a promising pathway to achieve it since it is a process that uses solar light, diminishing costs, and can be performed in homogeneous or heterogeneous media. In order to optimize this process, we studied the leading variables of the photooxidation process. evaluating the mechanism of sensitized photooxidation of fenamates and related compounds (Fs & RC) as a means to degrade and/or eliminate these substances from aqueous media, and for the further development of photosensitized methods for water remediation by tertiary treatments. Studying the mechanism of the process allowed us to propose a way to control and predict degradation of these compounds in order to improve water quality. Our results indicate that photosensitized transformation of Fs & RC proceeds mainly through a Type II photooxygenation, and photodegradation seem to yield substituted iminebenzoquinones of different regiochemistry instead of other recalcitrant products. The pseudo-first order kinetic constants for degradation of Fs & RC upon irradiation with red led light in air-saturated water/methanol 3:2 solutions in the presence of methylene blue as sensitizer were determined, their values ranged between 4.42×10–4–0.82×10–4s–1.Under these conditions 100 % degradation was reached in a minimum time of 150 (diphenylamine) and 200–300 min (fenamic acid, mefenamic acid and tolfenamic acid).