Kinetic Research And Influencing Factors On Electrochemical Reduction Of Ferrihydrite Mediated By Anthraquinone

The sodium anthraquinone-2-sulfonate（AQS）containing hydroquinone functional group structure was taken as the model dissolved organic matter,the current study mainly discussed the electrochemical reduction of ferrihydrite mediated by AQS.Then,the kinetic characteristics of serial reactions occurring in the“electrode-AQS-ferrihydrite”reaction system were further investigated.Based on this,the kinetic function model was established and the time course of the intermediate product concentration and reaction rate constant were obtained.AQS is known as the electron mediator,which accepted electrons from working electrode and existed in the form of reductive structures(AQS_red).Firstly,AQS_red donated electrons to ferrihydrite and converted itself into AQS_oxi.Then AQS_oxi obtained electrons from the working electrode to generate AQS_red.Thus,two-step serial reactions occurring in the“electrode-AQS-ferrihydrite”can be continuous.Based on this theory,the kinetic and thermodynamic effect of temperature on the interaction process was further studied,which provided theoretical reference for the study of influence factors and characteristics of the electrochemical reduction of ferrihydrite mediated by anthraquinone.The main achievements as below:1、The influencing factors and characteristics of the electron transfer process on the surface of working electrode were investigated.The experimental results showed that when the material of the working electrode was carbon felt,the sensitivity of the electrochemical reduction reaction of AQS on the surface of the working electrode was significantly improved compared with the glassy carbon electrode.And the existence of ultrasonic wave overcame the electrode passivation phenomenon of the carbon felt electrode easily due to the long-term use.When the applied voltage was-0.7V（vs.Ag/AgCl）,it ensures the electrochemical reduction of AQS,that is,the process of AQS_oxi receives electrons from the working electrode to generate AQS_red could be fully carried out.2、On the optimal experimental conditions,the experimental system of"electrode-AQS-ferrihydrite"was established.The experiment results showed that redox mediator,AQS,can facilitate the degree of electrochemical reduction process of ferrihydrite.When AQS was absence,the degree of ferrihydrite electrochemical reduction process was slight.In contrast experiments without addition of AQS,the electrochemical reduction process of ferrihydrite mediated by AQS was significantly intensified.When the amount of AQS increased from 0.005 mmol/L to 0.035 mmol/L,the reduction ratio of the absolute amount of ferrihydrite raised from 10.4%to 35.0%.The time course of the intermediate product(AQS_oxi)concentration(C_AQSoxi)showed a typical characteristic of function model curve y=k₁/（k₂-k₁）·(e^-k₁·t+c-e^-k₂·t+c) derived from consecutive reaction,and the Adj.R² could be high enough to 0.9990.When the concentration ratio of ferrihydrite to AQS does not exceed 133.33,there is little difference in the rate of two-stage serial reaction in the system.Therefore,the participation of AQS and its concentration,and the absolute amount of ferrihydrite both have a certain influence on the fitting parameters of the kinetic function model of the reaction process.3、Exploring the effect of temperature on the interaction of the"electrode-AQS-ferrihydrite"interaction process,in the experimental setting temperature in the range of25～55℃,the reaction rate constant of AQS electrochemical reduction process was gradually increased from 0.0031s^-1 to 0.0069s^-1.It showed that the higher the temperature,the stronger the electron transfer capability of AQS.At the same time,the fitting results of the reaction kinetic function model of the"electrode-AQS-ferrihydrite"interaction showed that the electrochemical reduction process of AQS and the AQS-mediated electrochemical reduction process of ferrihydrite were both endothermic and entropy-increasing reactions.At the same time,increasing temperature can gradually weaken the effect of adding ferrihydrite on the speed of AQS electrochemical reduction.