Fe(III)-citrate enhanced sunlight-driven photocatalysis of aqueous Carbamazepine

Abstract

We investigated the effect of Fe(III)-citrate complexes on the photodegradation of Carbamazepine (CBZ) upon 365 nm irradiation in aqueous solution. A preliminary study of a {CBZ/Fe(III)-citrate} mixture in the dark and at room temperature showed no evidence of reaction. CBZ degradation efficiency depends on the pH of the medium, an effect attributed mainly to the speciation of Fe(III)-citrate. The influence of [CBZ] or [Fe(III)-citrate] on the kinetics of the reaction was studied. The reaction is biphasic, the first stage ends after ca. fifteen minutes and accounts for the major percentage of degradation. The presence of Fe(III)-citrate complex largely enhances the formation of Fe2+ and HO radicals; they form at the same rate at the beginning of the reaction. Increasing [O2] improved the degradation rate, and the use of i-PrOH as a scavenger confirmed the participation of HO in CBZ photodegradation. CBZ photodegradation was also studied under natural sunlight showing a degradation only slightly lower than under artificial light. HPLC/MS analysis confirmed 11% yield epoxycarbamazepine as the only reaction product observable with this technique after 180 min irradiation. An appropriate mechanism is proposed for CBZ transformation. CBZ phototransformation reached 65% at pH = 6.24, 87% at pH = 4.30 and ca. 100% at pH = 2.86 after 180 min upon 365 nm irradiation and the mineralization efficiency reaches 70% of TOC removal after 6 h of treatment. Our evidences show the epoxide photoproduct is just an intermediate that further reacts towards mineralization. This work highlights the important role of Fe(III)-carboxylate complexes may have on the fate of persistent organic pollutants in aquatic environments when irradiated with UV-A light.