Kinetics And Mechanism Of Ebselen Oxidation By Potassium Ferrate

Ebselen（EBS）has been extensively used as anti-inflammatory analgesic.Because it has good antioxidant properties,ebselen was used in new diseases treatment recently,like neuroprotective and anticancer.Several studies have also reported oxidation of ebselen with peroxide and photolysis,but these reactions have slow reaction rate.The widespread application and persistence of EBS may lead to contaminants of water environment.Potassium ferrate has a strong oxidizing capacity and is environmentally friendly,which is good for many persistent pollutants.At the same time,ferrate was reduced to Fe（Ⅲ）which has flocculation properties.For these reasons,potassium ferrate will have great application prospect.The present work investigated the oxidation of EBS by ferrate including degradation kinetics,identification of oxidation products,theoretical analysis and possible reaction pathways,toxicity assessment,removal of EBS from actual water matrices and effect of water matrix.The EBS degradation performance with two other oxidants（hypochlorite and permanganate）was also compared.These will propose new ideas and technology support.At first,the removal effect and oxidation kinetics for the reaction of ferrate with EBS were determined.Experiments show that ferrate can effectively degrade EBS.This result indicates that with the dosage of potassium ferrate increasing,the reaction rate of EBS with ferrate increased.The rate constant of oxidation of EBS by ferrate decreased with the increase of pH.Compared to borate buffer,reaction of ferrate with EBS was inhibited in phosphate buffer.With the increase of temperature,reaction went faster and rate constant rose.This result shows that ferrate was superior to sodium hypochlorite and potassium permanganate.The rate of EBS with potassium permanganate in acid solution was better than neutral and basic solution.The effect of EBS degration with sodium hypochlorite was better with pH rising.Theoretical calculations indicate the reaction site was likely located on the Se atom.Through LC-MS/MS analysis,EBS degration produced three kinds of oxidation products（OP-1～3）.Ferrate degrades EBS with cleavage of Se-C bond,hydrolysis and addition of oxygen atom.Toxicity of a EBS solution was decreased after ferrate oxidation.Inhibition rate of luminescent bacteria decreased from 99%in the initial to 10%at the reaction end.EBS was transformed to low toxic intermediate products.The reaction rate of EBS in pure water was obviously higher than the one in natural water.The effect of EBS degration have little decrease in Songhua river water and secondary effluent.,but have great decrease in groundwater.As it can be seen,coexisting anions(like Ca²⁺、Mg²⁺)and cation(like Cl^-、SiO₃^2-HCO₃^-)had almost no effect on the final removal of EBS.And the inhibition was enhanced with the increase of the concentrations of HA.When HA concentrations increased from 1 mgC/L to 5 mgC/L,the rate constant for the reaction of ferrate with EBS decreased from 2.9×10² M^-1s^-1 to0.94×10²M^-1s^-1.