The photocatalytic degradation of sodium diclofenac in different water matrices using g-C3N4 nanosheets: A study of the intermediate by-products and mechanism

Abstract

The photocatalytic degradation of sodium diclofenac (a nonsteroidal anti-inflammatory drug) in both ultrapure water and tap water with nanosheets of graphitic carbon nitride (g-C3N4) as catalyst and utilising two different sources of visible light (low-power (4 × 10 W) white light LEDs and natural sunlight) was carried out and compared. The highest depletion rate was observed for the system with tap water and natural sunlight. All photodegradations followed pseudo-first-order kinetics. A degradation pathway for sodium diclofenac has been proposed and four photodegraded products formed along with the diclofenac depletion have been detected by liquid chromatography coupled with high-resolution mass spectrometry using a QToF instrument. The accurate mass obtained for the detected ions together with the MS/MS data allowed us to propose chemical structures for the by-products. Moreover, a study to identify the main active species involved in the degradation mechanism was undertaken by introducing scavengers to quench the photodegradations: a N2 atmosphere for superoxide radicals (·O2−), triethanolamine for photoexcited holes (h+) and tert-butanol for hydroxyl radicals (·OH).