Photocatalytic degradation of ibuprofen in water using TiO2/UV and g-C3N4/visible light: Study of intermediate degradation products by liquid chromatography coupled to high-resolution mass spectrometry

• Published in: Chemosphere (Oxford) 2019-01, Vol.215, p.605-618
• Main Authors: Jiménez-Salcedo, Marta, Monge, Miguel, Tena, María Teresa
• Format: Article
• Language: English
• Subjects: Advanced oxidation process; Carbon nitride 2D nanosheets; Ibuprofen; Photocatalytic degradation; Titanium oxide nanoparticles; Water treatment
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2018.10.053

The photocatalytic degradation of ibuprofen with TiO2 nanoparticles (NPs) and UV light and with graphitic carbon nitride (g-C3N4) 2D nanosheets and visible light are proposed and compared as advanced oxidation treatments for the removal of ibuprofen in water. By-products formed with both photocatalytic systems have been tentatively identified based on the results of ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry, using a quadrupole-time of flight mass spectrometer in positive and negative ionization modes, which allowed to obtain the elementary composition of their precursors and fragment ions. The removal of ibuprofen and the by-product formation were studied at three pH values. Ibuprofen depletion followed pseudo fist-order kinetics with rate constants of 0.04, 1.0 and 0.0006 min−1 at pH 2.50, 5.05 and 12.04 for TiO2/UV and 0.03, 0.007 and 0.0005 min−1 at pH 2.51, 5.05 and 11.33 for g-C3N4/vis, respectively. Around eighteen by-products have been detected with slight differences between the two photocatalytic systems studied. The evolution of the main common by-products (tentatively identified as 1-(4-ethylphenyl)-2-methylpropan-1-one, 1-(4-isobutylphenyl)ethan-1-ol, 1-(4-ethylphenyl)-2-methylpropan-1-ol and 1(-4-acetylphenyl)-2-methylpropan-1-one) were monitored and the results were consistent with reaction pathways based on hydroxyl radical attacks following/followed by decarboxylation. Moreover, some by-products have been reported for the first time in the photocatalytic oxidation of ibuprofen. [Display omitted] •TiO2 and g-C3N4 were compared as photocatalysts for Ibuprofen degradation.•Eighteen intermediate by-products were detected by UPLC-QTOFMS.•Accurate mass and elementary composition allowed tentative identification.•Six of them are reported for the first time in photocatalytic studies.•Two of them were classified as more toxic than ibuprofen.