Development Of Homogeneous/heterogeneous Electro-fenton Oxidation System Based On Super-hydrophobic Carbon Cathode

Water pollution caused by human industrial and agricultural production is an important reason for destroying the global ecological environment and restricting China’s economic development.However,in the case of mass production and use of synthetic organic matters,the traditional sewage treatment technology has poor or even ineffective removal for refractory organic matters in wastewater.In recent twenty years,the treatment of refractory organic wastewater has been a hot spot in the environmental field,and the degradation of organic pollutants by advanced oxidation technology has attracted much attention of researchers all over the world.Among various advanced oxidation technologies,cathodic electro-Fenton oxidation was studied intensively in recent years.In this oxidation system,hydrogen peroxide（H₂O₂）can be generated by the electro-reduction of O₂ at the cathode,and then reacts with Fe²⁺to generate·OH with strong oxidizing power to degrade organic matters.Due to several advantages including mild reaction condition,free of adding H₂O₂,high degradation efficiency and low sludge yield,electro-Fenton oxidation has become a research hotspot and exhibited a good industrial application prospect.In this study,lotus leaf-like superhydrophobic carbon cathode was prepared,and its H₂O₂ production performance and the ability of homogeneous electro-Fenton system to degrade organic pollutants were investigated.On this basis,FeWO₄ catalyst was prepared,and FeWO₄powder catalyst was immobilized as heterogeneous electro-Fenton catalyst,and thus a new heterogeneous electro-Fenton system was constructed to degrade organic pollutants in water.The specific research contents and results are as follows:（1）Porous carbon cathode with lotus leaf-like superhydrophobic surface was prepared by using high-purity graphite powder as electrocatalyst,polytetrafluoroethylene（PTFE）as binder and boric acid（H₃BO₃）as pore-forming agent,in which the surface morphology of the electrode was shapeded by impression molding.The results indicated that the high roughness surface of carbon cathode could made it possess superhydrophobic（water contact angle is greater than 150°）property and strong gas affinity,which could greatly improve the adsorption capacity and mass transfer efficiency of O₂ on the cathode surface,and thus the cathode can quickly produced H₂O₂ through electro-reduction reaction.In the air-saturated Na₂SO₄ solution（p H=2.8）,the H₂O₂ could be accumulated to 527.5 mg L^–1by the reaction of 60 min and the apparent current efficiency（CE）is 35.1%under the optimized reaction conditions.（2）Utilizing the prepared superhydrophobic carbon cathode,a homogeneous electro-Fenton oxidation system was constructed to degrade rhodamine B（Rh B）,methylene blue（MBT）,p-nitrophenol（p-NP）and tetracycline（TC）,and all these organics could be degraded effectively.The results of the printing wastewater treatment indicated that the removal rate of chemical oxygen demand（COD）and total organic carbon（TOC）was 76.8%and 73.5%,respectively.Moreover,the biodegradability of the wastewater was significantly improved.In addition,it was found that the anodic oxidation of chloride ion（Cl^–）is easy to produce active chlorine causing the consumption of H₂O₂,which is not beneficial to the degradation of organic pollutants by electro-Fenton oxidation.（3）FeWO₄ nano-catalyst was successfully prepared by hydrothermal synthesis method,and FeWO₄ nano-particles were immobilized with PTFE as binder and boric acid as pore-forming agent to obtain the heterogeneous Fenton catalyst.Thus,a heterogeneous electro-Fenton oxidation system was developed to degrade organic pollutants in water under neutral conditions.The results indicated that the immobilized FeWO₄ catalyst could catalyze the decomposition of H₂O₂ to produce·OH,·O₂^–and ¹O₂ with strong oxidation,which is the theoretical foundation for the developing of heterogeneous electro-Fenton oxidation system.（4）Under the optimized experimental conditions,40 mg L^–1 tetracycline solution was degraded by the developed heterogeneous electro-Fenton oxidation system,and 100%tetracycline removal could be achieved after 60 min reaction.The results of crude oil tank cleaning wastewater treatment for 8h indicated that the removal rates of chemical oxygen demand（COD）and total organic carbon（TOC）reached 85.0%and 75.2%,respectively,while ammonia nitrogen（NH4⁺-N）and volatile phenol were completely removed.The removal mechanisms of organic pollutants in this oxidation system include adsorption of Fenton catalyst,anodic oxidation and electro-Fenton oxidation,whereas electro-Fenton oxidation plays a dominant role.（5）The immobilized FeWO₄ catalyst has fine activity,low iron ion leaching amount and high mechanical strength,and hence the heterogeneous electro-Fenton oxidation system can not only effectively degrade organic pollutants,but also avoid the problems of iron sludge generation and powder catalyst separation.