Removal of Paracetamol in the Presence of Iron(III) Complexes of Glutamic and Lactic Acid in Aqueous Solution Under NUV Irradiation

Abstract

[Abstract] Low concentrations of drugs and their metabolites occurring on the aquatic environment are of significant concern due to their potential effects. This work reports on the removal from aqueous solution, of paracetamol or acetaminophen (APAP) as a model pharmaceutical pollutant, promoted by the photo-Fenton system generated by the photolysis of two organic iron(III) complexes, FeIII-Glutamate & FeIII-Lactate, under 365 nm irradiation (2 < pH < 4). UVA photolysis of these complexes is relatively fast: ca.73% of the FeIII-Glu complex decomposed after 1 h of irradiation (t½=6.4 min, pH = 3.40), 91% in the case of FeIII-Lact complex (t½=6.4 min, pH = 3.0). FeIII + Lact system showed a maximum pseudo-first order rate constant at pH ca. 3, while for FeIII + Glu system it increases with pH. NUV irradiation of FeIII-carboxylic acid complexes promotes APAP photodegradation, that is faster with lactate. The maximum pseudo-first order rate constant was observed at pH = 3 for FeIII + Lact + APAP, while it slightly increased with pH for FeIII + Glu + APAP. The rate constant decreases for both systems as APAP concentration increases, likely due to the formation of FeIII-APAP complexes. At t > 180 min, a second, slower, process is observed. Addition of 1% of t-BuOH and anaerobic conditions inhibit APAP photodegradation, which indicates APAP photodegradation in the presence of FeIII-Glu and FeIII-Lact complexes is limited by formation of H2O2, the source of HO. Seven transformation photoproducts were identified by HPLC-MS, mainly hydroxylated derivatives. Reaction pathways are identified, highlighting the role of the photoformed FeIII-carboxylate long-lived radicals, dissolved O2 and HO in the abatement of pollution due to emerging organic contaminants such as APAP.