Sharma Virender K, Mishra Santosh K, Ray Ajay K
Department of Chemistry, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA.
Chemosphere. 2006 Jan;62(1):128-34. doi: 10.1016/j.chemosphere.2005.03.095. Epub 2005 Jun 13.
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.
磺胺甲恶唑（SMX）是一种全球广泛应用的抗菌药物，最近在地表水和二级废水排放物中被发现，这可能会对环境产生生态毒性影响。在此，通过研究高铁酸钾（VI）（K₂FeO₄）这种环境友好型氧化剂与SMX之间的反应动力学，考察其在pH值（6.93 - 9.50）和温度（15 - 45℃）变化时对SMX的去除效果。Fe（VI）氧化SMX的速率定律对每种反应物均为一级反应。随着pH值从7.00增加到9.50，观察到的二级反应速率常数从1.33±0.08×10³ M⁻¹s⁻¹非线性下降至1.33±0.10×10⁰ M⁻¹s⁻¹。这与Fe（VI）（HFeO₄⁻⇌H⁺ + FeO₄²⁻；pKₐ,HFeO₄ = 7.23）和磺胺甲恶唑（SH⇌H⁺ + S⁻；pKₐ,SH = 5.7）的质子化有关。估算的反应速率常数为k₁₁（HFeO₄⁻ + SH） = 3.0×10⁴ M⁻¹s⁻¹，k₁₂（HFeO₄⁻ + S⁻） = 1.7×10² M⁻¹s⁻¹，以及k₁₃（FeO₄²⁻ + SH） = 1.2×10⁰ M⁻¹s⁻¹。在pH值为7.0时，活化能为1.86±0.04 kJ mol⁻¹。如果使用的高铁酸钾（VI）浓度（10 μM）超过水中的SMX浓度，根据我们研究获得的反应速率常数，在pH值为7时反应的半衰期约为2分钟。反应速率取决于pH值；因此，反应的半衰期也取决于pH值。结果表明，K₂FeO₄有潜力作为一种氧化处理化学品用于去除水中的SMX。
