title: Kinetic assessment of the potassium ferrate(VI) oxidation of antibacterial drug sulfamethoxazole.
abstract: Sulfamethoxazole (SMX), a worldwide-applied antibacterial drug, was recently found in surface waters and in secondary wastewater effluents, which may result in ecotoxical effects in the environment. Herein, removal of SMX by environmentally-friendly oxidant, potassium ferrate(VI) (K(2)FeO(4)), is sought by studying the kinetics of the reaction between Fe(VI) and SMX as a function of pH (6.93-9.50) and temperature (15-45 degrees C). The rate law for the oxidation of SMX by Fe(VI) is first-order with respect to each reactant. The observed second-order rate constant decreased non-linearly from 1.33+/-0.08 x 10(3) M(-1)s(-1) to 1.33+/-0.10 x 10(0) M(-1)s(-1) with an increase of pH from 7.00 to 9.50. This is related to protonation of Fe(VI) (HFeO(4)(-) <==> H(+) + FeO(4)(2-); pK(a,HFeO(4)) = 7.23) and sulfamethoxazole (SH <==> H(+) + S(-); pK(a,SH)=5.7). The estimated rate constants were k(11)(HFeO(4)(-) + SH) = 3.0 x 10(4) M(-1)s(-1), k(12)(HFeO(4)(-) + S(-)) = 1.7 x 10(2) M(-1)s(-1), and k(13) (FeO(4)(2-) + SH) = 1.2 x 10(0) M(-1)s(-1). The energy of activation at pH 7.0 was found to be 1.86+/-0.04 kJ mol(-1). If excess potassium ferrate(VI) concentration (10 microM) is used than the SMX in water, the half-life of the reaction using a rate constant obtained in our study would be approximately 2 min at pH 7. The reaction rates are pH dependent; thus, so are the half-lives of the reactions. The results suggest that K(2)FeO(4) has the potential to serve as an oxidative treatment chemical for removing SMX in water.
authors.affiliation: Department of Chemistry, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA. vsharma@fit.edu
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Santosh K
authors.initials: SK
authors.lastname: Mishra
authors.forename: Ajay K
authors.initials: AK
authors.lastname: Ray
mesh_terms: D000900:Anti-Bacterial Agents / Q000032:analysis*; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D017680:Potassium Compounds / Q000737:chemistry*; D013420:Sulfamethoxazole / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000592:standards
chemical_list: D000900:Anti-Bacterial Agents; D058085:Iron Compounds; D017680:Potassium Compounds; D014874:Water Pollutants, Chemical; C044384:potassium ferrate; D013420:Sulfamethoxazole