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 (Fe III -NTA) complexes. The results indicate that CBZ degradation by Fe III -NTA/H 2 O 2 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 −13 M, was strongly dependent on the concentration of Fe III , the initial pH, and H 2 O 2 :Fe III and NTA:Fe III molar ratios. Optimal conditions of [Fe III ] = 1 × 10 −4 M, [H 2 O 2 :Fe III ] = 155:1 and [NTA:Fe III ] = 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, k app , was 0.0419 (±0.002) min −1 . The value of k app increased with increasing pH from 5.0 to 9.0 due to the strong pH-dependence of Fe III -NTA complexes; Fe III (NTA)(OH) 2 2− was the most likely active iron species to activate H 2 O 2 to produce OH. The temperature dependence of CBZ degradation by Fe III -NTA/H 2 O 2 was characterized by an activation energy of 76.16 kJ mol −1 . A potential mechanism for the formation of OH by Fe III -NTA/H 2 O 2 and possible degradation pathways of CBZ are proposed.