Removal of paracetamol in the presence of iron(III) complexes of glutamic and lactic acid in aqueous solution under NUV irradiation

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, Fe-III-Glutamate & Fe-III-Lactate, under 365 nm irradiation (2 < pH < 4). UVA photolysis of these complexes is relatively fast: ca.73% of the Fe-III-Glu complex decomposed after 1 h of irradiation (t(1/2)=6.4 min, pH = 3.40), 91% in the case of Fe-III-Lact complex (t(1/2)=6.4 min, pH = 3.0). Fe-III + Lact system showed a maximum pseudo-first order rate constant at pH ca. 3, while for Fe-III + Glu system it increases with pH. NUV irradiation of Fe-III-carboxylic acid complexes promotes APAP photodegradation, that is faster with lactate. The maximum pseudo-first order rate constant was observed at pH = 3 for Fe-III + Lact + APAP, while it slightly increased with pH for Fe-III + Glu + APAP. The rate constant decreases for both systems as APAP concentration increases, likely due to the formation of Fe-III-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 Fe-III-Glu and Fe-III-Lact complexes is limited by formation of H2O2, the source of HO center dot. Seven transformation photoproducts were identified by HPLC-MS, mainly hydroxylated derivatives. Reaction pathways are identified, highlighting the role of the photoformed Fe-III-carboxylate long-lived radicals, dissolved O-2 and HO center dot in the abatement of pollution due to emerging organic contaminants such as APAP.

Automated summary

This study used Fe-III-Glutamate and Fe-III-Lactate complexes as photo-Fenton systems to accelerate the removal of APAP, a model pharmaceutical pollutant, from aqueous solution. The UVA photolysis rates of these organic iron(III) complexes varied under different pH conditions, and the rates of APAP photodegradation were also influenced by pH and APAP concentration.