Modified Preparation Of Ti/Sb-SnO₂ Electrode And Its Degradation Performance Of Microplastics

In recent years,the production of synthetic plastics derived from fossil fuels has been increasing,and the imperfect management of waste plastics has caused serious plastic pollution.Microplastics have been identified as emerging water pollutants,and microplastic pollution has shown a continuous and increasingly serious trend.Microplastics in water have the characteristics of small size,long residence time,high stability,large crushing potential,and enrichment of other pollutants.Microplastics can directly enter the body through the intake of water by organisms,accumulate in organisms,and also enter the human body through the food chain.Additives such as plasticizers and flame retardants used in the preparation of plastics can cause toxic effects in organisms.The surface of microplastics may also enrich a variety of highly toxic persistent organic pollutants（POPs）.Polystyrene（PS）is the most common plastic polymer in our lives.It is used to make disposable plates,cups and lunch boxes.It is also one of the most common types of microplastics in the water environment.Therefore,this paper selects PS with a common size of 150μm in natural water as the target pollutant.Advanced oxidation technology has a good removal effect on refractory pollutants in water.Electrocatalytic oxidation is a kind of advanced oxidation,which has attracted the attention of researchers because of its low operating cost,mild reaction conditions and green environmental protection.Electrocatalytic oxidation technology is to generate hydroxyl or superoxide and other activated substances on the anode surface to oxidize and degrade the target pollutants in water under the condition of external electric field.Therefore,the anode material is the core of electrocatalytic oxidation.The biggest challenge in the development of electrocatalytic oxidation technology is mainly the problem of electrodes.The first is to reduce the cost of electrodes,the second is to enhance the catalytic activity of electrodes,and the last is to prolong the service life of electrodes.In this paper,Ti/Sb-SnO₂ electrode was modified by doping rare earth elements and adding intermediate layer,and the degradation performance of PS in water was studied.The main of this study（1）The main purpose of doping rare earth modification is to enhance the electrocatalytic activity of the electrode.Four rare earth elements La,Sm,Nd and Ce were selected to prepare rare earth doped Ti/Sb-SnO₂ electrodes.The four modified electrodes were analyzed and tested.It was found that the La-doped Ti/La-Sb-SnO₂electrode had the highest oxygen evolution potential（2.23 V）,the highest oxidation peak current（2.4 m A/cm²）and the lowest total resistance compared with Sm,Nd and Ce.The degradation rate of PS and the formation rate of·OH on Ti/La-Sb-SnO₂electrode were also the highest among the four electrodes.The preparation process of Ti/La-Sb-SnO₂ electrode was optimized.The results show that the Ti/La-Sb-SnO₂electrode with the best performance can be obtained under the conditions of active coating prepared by sol-gel method,active layer number of 10,heat treatment temperature of 450°C ratio of Sn:La is 100:3.The SEM,EDS and XRD results of the optimal electrode show that the cracks in the active layer of the electrode become shallow,the particles on the surface become smaller,and the crystal structure of SnO₂is optimized.The optimal electrode has the best reaction conditions for the degradation of PS.The electrolysis time is 3 h,the current size is 1.4 A,the electrode spacing is 1.5cm,the electrolyte is 0.22 mol/L sodium sulfate,and the initial solution pH=7.Under this condition,the degradation rate of PS by Ti/La-Sb-SnO₂electrode is 28.3%,which is 1.77 times that of Ti/Sb-SnO₂ electrode.（2）The modification of adding intermediate layer is carried out on the basis of the optimal Ti/La-Sb-SnO₂ electrode explored in the above experiments,in order to prolong the service life of the electrode.Ti/La-Sb-SnO₂ electrode with three different interlayers was prepared by adding Mn,Co or Ru interlayers between Ti substrate and La-Sb-SnO₂ active coating.The three electrodes were analyzed and tested.The addition of the three intermediate layers decreased the catalytic activity of the electrode and the degradation performance of the microplastics to varying degrees.The addition of the Co intermediate layer had the least effect on the catalytic activity and PS degradation performance of the Ti/La-Sb-SnO₂ electrode.The electrode life of Ti/Co/La-Sb-SnO₂is the longest,which is close to 5 times that of the electrode without intermediate layer.The preparation process of Ti/Co/La-Sb-SnO₂ electrode was optimized.It was concluded that the Ti/Co/La-Sb-SnO₂ electrode with the best performance could be prepared by sol-gel method,heat treatment temperature of 400°C and Sn:Co molar ratio of 5:1.The SEM,EDS and XRD results of the optimal electrode show that the cracks in the Co intermediate layer are denser,and the Co element in the intermediate layer partially penetrates into the surface of the active layer.The optimal electrode has the best reaction conditions for PS degradation.The current is 1.6 A,the electrode spacing is 1.5 cm,the electrolyte is 0.18 mol/L sodium sulfate,and the initial solution pH is 7.Under this condition,the degradation rate of PS by Ti/Co/La-Sb-SnO₂ electrode is 28.0%.It can be found that the degradation rate after the optimization of the process conditions is very small compared with the Ti/La-Sb-SnO₂ electrode without the intermediate layer.