title: Effect of iron ion on doxycycline photocatalytic and Fenton-based autocatatalytic decomposition.
abstract: Doxycycline plays a key role in Fe(III)-to-Fe(II) redox cycling and therefore in controlling the overall reaction rate of the Fenton-based process (H2O2/Fe(III)). This highlights the autocatalytic profile of doxycycline degradation. Ferric iron reduction in the presence of doxycycline relied on doxycycline-to-Fe(III) complex formation with an ensuing reductive release of Fe(II). The lower ratio of OH-to-contaminant in an initial H2O2/Fe(III) oxidation step than in that of classical Fenton (H2O2/Fe(II)) decreased the doxycycline degradation rate. The quantum yield of doxycycline in direct UV-C photolysis was 3.1 × 10(-3) M E(-1). In spite of doxycycline-Fe(III) complexes could produce the adverse effect on the doxycycline degradation in the UV/Fe(III) system some acceleration of the rate was observed upon irradiation of the Fe(III)-hydroxy complex. Acidic reaction media (pH 3.0) and the molar ratio of DC/Fe(III) = 2/1 favored the complex formation. Doxycycline close degradation rates and complete mineralization achieved for 120 min (Table 1) with both UV/H2O2 and UV/H2O2/Fe(III) indicated the unsubstantial role of the reduction of Fe(III) to Fe(II) in UV/H2O2/Fe(III) system efficacy. Thus, factors such as doxycycline's ability to form complexes with ferric iron and the ability of complexes to participate in a reductive pathway should be considered at a technological level in process optimization, with chemistry based on iron ion catalysis to enhance the doxycycline oxidative pathway.
authors.affiliation: Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.
authors.forename: Juri
authors.initials: J
authors.lastname: Bolobajev
authors.affiliation: Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.
authors.forename: Marina
authors.initials: M
authors.lastname: Trapido
authors.affiliation: Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia. Electronic address: Anna.Goi@ttu.ee.
authors.forename: Anna
authors.initials: A
authors.lastname: Goi
mesh_terms: D002384:Catalysis; D004318:Doxycycline / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D010782:Photolysis; D012722:Sewage / Q000737:chemistry*
chemical_list: D012722:Sewage; D006861:Hydrogen Peroxide; D007501:Iron; D004318:Doxycycline
keywords: Autocatalytic decomposition; Doxycycline; Ferric iron reduction; Ferric iron–doxycycline complex; Hydroxyl radical