TiO2 Photocatalytic Degradation of Diclofenac: Intermediates and Total Reaction Mechanism Article uri icon

abstract

  • Abstract: Diclofenac (DCF) photocatalytic degradation with TiO2-P25 illuminated with UV-A light in aqueous media was investigated. The photodegradation rate was assessed by HPLC and UV–vis spectroscopy, while the mineralization rate was obtained by total organic carbon measurements. The formation and degradation of intermediate compounds were investigated by UV–vis, IR and 1H NMR spectroscopy and GC/MS analysis. UV–vis absorbance and HPLC results indicated that DCF is completely transformed into some aromatic compounds after several hours of irradiation. TOC analysis indicated that some intermediate compounds are degraded slowly since 90%25 mineralization was achieved after several hours of irradiation. FT-IR studies demonstrated a rapid conversion of diclofenac into a lactam, which was converted into several aromatic compounds. GC/MS and HPLC analysis indicated that the initial photoproducts are two lactams and several aromatic anilines and phenols. 1H NMR studies indicated DCF degrades by a rather simple mechanism generating a recalcitrant intermediate acid, namely 2-hydrophenyl acetic acid which is oxidized in several steps by hydroxyl radicals. 1H NMR studies also indicated that an oxidation route via a quinone is actually a very minor pathway. Based on this and previous investigations, a total photocatalytic degradation mechanism for DCF is presented, first involving hydroxyl radical reactions to generate anilines and phenols, which were all converted into polyhydroxylated compounds and eventually into low molecular saturated and unsaturated amines and carboxylic acids. Basic studies about diclofenac photocatalytic degradation are required for future applications of this process in the removal of DCF and other structurally related pharmaceutical compounds from any water body. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, Springer Science Business Media, LLC, part of Springer Nature.
  • Abstract: Diclofenac (DCF) photocatalytic degradation with TiO2-P25 illuminated with UV-A light in aqueous media was investigated. The photodegradation rate was assessed by HPLC and UV–vis spectroscopy, while the mineralization rate was obtained by total organic carbon measurements. The formation and degradation of intermediate compounds were investigated by UV–vis, IR and 1H NMR spectroscopy and GC/MS analysis. UV–vis absorbance and HPLC results indicated that DCF is completely transformed into some aromatic compounds after several hours of irradiation. TOC analysis indicated that some intermediate compounds are degraded slowly since 90%25 mineralization was achieved after several hours of irradiation. FT-IR studies demonstrated a rapid conversion of diclofenac into a lactam, which was converted into several aromatic compounds. GC/MS and HPLC analysis indicated that the initial photoproducts are two lactams and several aromatic anilines and phenols. 1H NMR studies indicated DCF degrades by a rather simple mechanism generating a recalcitrant intermediate acid, namely 2-hydrophenyl acetic acid which is oxidized in several steps by hydroxyl radicals. 1H NMR studies also indicated that an oxidation route via a quinone is actually a very minor pathway. Based on this and previous investigations, a total photocatalytic degradation mechanism for DCF is presented, first involving hydroxyl radical reactions to generate anilines and phenols, which were all converted into polyhydroxylated compounds and eventually into low molecular saturated and unsaturated amines and carboxylic acids. Basic studies about diclofenac photocatalytic degradation are required for future applications of this process in the removal of DCF and other structurally related pharmaceutical compounds from any water body. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, Springer Science%2bBusiness Media, LLC, part of Springer Nature.

publication date

  • 2020-01-01