Kinetics and mechanism of carbamazepine degradation by a modified Fenton-like reaction with ferric-nitrilotriacetate complexes

Abstract

This study investigated the kinetics and mechanism of carbamazepine (CBZ) degradation over an initial pH range of 5.0–9.0 by a modified Fenton-like reaction using ferric-nitrilotriacetate (FeIII-NTA) complexes. The results indicate that CBZ degradation by FeIII-NTA/H2O2 can be described by pseudo first-order kinetics and mainly attributed to hydroxyl radical (OH) attack. Ten intermediates were indentified during the degradation process, including hydroxy-CBZs, 10,11-epoxy-CBZ, quinonid CBZ derivatives, dihydroxy-CBZs, and hydroxy-CBZ-10,11-diols. The steady-state concentration of OH, ranging from 3.8×10−16 to 2.1×10−13M, was strongly dependent on the concentration of FeIII, the initial pH, and H2O2:FeIII and NTA:FeIII molar ratios. Optimal conditions of [FeIII]=1×10−4M, [H2O2:FeIII]=155:1 and [NTA:FeIII]=3:1 were obtained for the degradation of CBZ at neutral pH (7.0) and ambient temperature (25°C); the corresponding degradation rate constant of CBZ, kapp, was 0.0419 (±0.002) min−1. The value of kapp increased with increasing pH from 5.0 to 9.0 due to the strong pH-dependence of FeIII-NTA complexes; FeIII(NTA)(OH)22− was the most likely active iron species to activate H2O2 to produce OH. The temperature dependence of CBZ degradation by FeIII-NTA/H2O2 was characterized by an activation energy of 76.16kJmol−1. A potential mechanism for the formation of OH by FeIII-NTA/H2O2 and possible degradation pathways of CBZ are proposed.