Study On The Modification Of Carbon Cathode Materials And Its Application In Electro-Fenton Process

As a new advanced oxidation technology,electro-Fenton process has been attracting more and more people's attention due to its advantages of rapidity,high efficiency,environmental friendliness and simple operation.In electro-Fenton process,the concentration of hydrogen peroxide is the source of the strong oxidant?hydroxyl radical?in the system,which determines the ability of electro-Fenton process to oxidize and degrade pollutants.In this study,we used the mixture of carbon nanotubes,carbon black,and polytetrafluoroethylene to modify traditional graphite felt materials to improve the yield of in-situ generated hydrogen peroxide by the cathode.In addition,a new type of high-efficiency jet reactor was developed to maximize the performance of hydrogen peroxide generation,and the treatment of contaminants by electro-Fenton process was examined.The main contents of this research are as follows:1)The surface morphology and pore structure of graphite felt was modified by ultrasonic impregnation using carbon nanotube and polytetrafluoroethylene mixture.It was found that the modified graphite felt was more capable of producing hydrogen peroxide,and the accumulation of hydrogen peroxide of it was more than 25 times of the unnmodifed one.In the electrolyte solution of0.05 M Na₂SO₄,the current density was 20 mA·cm^-2,pH=7,without any air or oxygen,after reaction of 60 min,the H₂O₂ yield of the unmodified electrode was9.96 mg·L^-1,while the H₂O₂ concentration of the modified electrode GF?1:7?was 254.55 mg·L^-1.2)In order to improve electrocatalytic reduction of oxygen by modified electrode,keeping the quality of carbon materials?carbon nanotubes and carbon black?unchanged and making carbon nanotubes account for 0%,20%,40%,60%,80%of the total mass of carbon materials.It was found that when the carbon nanotubes were 60%?that is,the mass ratio of the carbon nanotubes and the carbon black was 3:2?,the hydrogen peroxide production of the electrodes was the largest.In the electrolyte solution of 0.05 M Na₂SO₄,the current density was 20 mA·cm^-2,pH=7,and without any exposure of air or oxygen,the H₂O₂concentration of the system was 471.73 mg·L^-1 at 60 min.It was about 47 times higher than the unmodified electrode and was 1.85 times higher than the GF?1:7?electrode modified only with carbon nanotubes.Meanwhile,the hydrogen peroxide yield and energy consumption were 8.15 mg·h^-1·cm^-2 and 7.85kWh·kg^-1,respectively.The modified electrode was analyzed using SEM,contact angle,XPS,LSV and CV.It was found that the modified electrode had plenty of micropores and mesopores on the surface,and the electrochemical response ability and electrocatalytic activity were dramatical.The specific surface area was huge,which provided numerous active sites for the reduction of oxygen at the cathode to produce hydrogen peroxide.The modified graphite felt was used as cathode to treat tetracycline hydrochloride and diclofenac sodium at a concentration of 50 mg·L^-1 by EF and the removal rate was 100%.Moreover,after 10 times of work,the electrode could still remove more than 99%diclofenac sodium,and the electric Fenton system was very stable.Finally,the degradation path of diclofenac was explored by LC-MS.3)In order to give full play to the best electrochemical performance of the electrode,a new type of high efficiency jet reactor was designed.In the reactor,when the electrolyte was 0.05 M Na₂SO₄,pH=7,current density was 24 mA·cm^-2,and water flow rate was 10 L·h^-1,the concentration of hydrogen peroxide in the solution was 1418.57 mg·L^-1 after 120 min reaction,which is 37%higher than that of the ordinary reactor.100%of Orange IV can be removed within 30 min by electro-Fenton process using this reactor.Moreover,acid fuchsin,rhodamine B,alizarin yellow R,tetracycline hydrochloride and diclofenac sodium can be effectively removed,which means that the system has good applicability.The principle of degradation of pollutants by electro-Fenton was analyzed and it was found that hydroxyl radical is the key substance in the system,which is a non-selective oxidant.