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

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/H2O2 can be described by pseudo first-order kinetics and mainly attributed to hydroxyl radical (OH) attack. Ten intermediates were identified 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 H2O2:Fe(III) and NTA:Fe(III) molar ratios. Optimal conditions of [Fe(III)]=1 × 10(-4)M, [H2O2: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, 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 Fe(III)-NTA complexes; Fe(III)(NTA)(OH)2(2-) was the most likely active iron species to activate H2O2 to produce OH. The temperature dependence of CBZ degradation by Fe(III)-NTA/H2O2 was characterized by an activation energy of 76.16 kJ mol(-1). A potential mechanism for the formation of OH by Fe(III)-NTA/H2O2 and possible degradation pathways of CBZ are proposed.