The photocatalytic degradation of naproxen with g-C3N4 and visible light: Identification of primary by-products and mechanism in tap water and ultrapure water

Differences in the photocatalytic degradation rates of naproxen (a nonsteroidal anti-inflammatory drug) in ultrapure water and tap water were assessed using g-C3N4 nanosheets as photocatalyst and irradiating with natural sunlight and low-power (4 × 10 W) white light LEDs. The graphitic carbon nitride (g-C3N4) photocatalyst was synthesised and characterised. All the photodegradations followed pseudo-first-order kinetics. Liquid chromatography with tandem mass spectrometry (UPLC-QToF-MS) was used to identify the intermediates generated in the degradation of naproxen by accurate mass and MS/MS data. Among the by-products detected, 2-(naphthalene-2-yl)propanal, a compound with structural warning for genotoxic carcinogenicity, has been reported for the first time. This persistent by-product was completely depleted with g-C3N4 and natural sunlight in 50–70 min. According to the kinetics of by-products and spectrometry data a plausible transformation pathway has been proposed. Furthermore, the main active species involved in the photodegradation with g-C3N4 were study to fully understand the process. To accomplish this goal, different scavengers were introduced in the degradation of naproxen to quench possible superoxide radicals (·O2−), photoexcited holes (h+) and hydroxyl radicals (·OH).