Effect Of Substrate Materials On The Formation Of Conversion Of Bromine By-Products During Electrochemical Disinfection Of Boron-Doped Diamond Film Electrodes

Boron-doped diamond thin film electrode（BDD）has become one of the preferred electrodes for electrochemical disinfection technology due to its wide electrochemicalpotentialwindow,lowbackgroundcurrent,good electrochemical stability and corrosion resistance.However,with the strong ability of producing electrogenerated hydroxyl radical（·OH）,the production of bromine by-products has become an unavoidable problem in BDD electric disinfection technology.Under the premise of mastering the law of formation of bromine by-products in the process of electric disinfection,the influence of different substrate materials on the formation of bromine by-products in the process of electric disinfection with BDD as electrode was investigated,which can be the technical reference of optimizing anode materials for the design of BDD electric disinfection process.It has certain practical significance for promoting the large-scale application of BDD electric disinfection technology.In this study,three kind of BDD electrodes with different substrate materials（Ta/BDD、Nb/BDD、Si/BDD electrodes）,which are the most common commercially available ones,were selected as anodes to construct an electrochemical system.The material characterization（X-ray diffraction,scanning electron microscopy,Raman spectroscopy）;electrochemical behavioral characterization（cyclicvoltammetry,chronoamperometry,chronoelectric method,linear sweep voltammetry）,electrogenerated active species capture experiments（·OH,·O₂^-,etc.）and the effects of operating conditions such as initial bromide,current density,pH value,temperature and rotation speed on the formation of bromine by-products were investigated.The conversion process of bromide（Br^-）under the BDD anode system with different substrates in the same preparation process was investigated,and the following conclusions were obtained:（1）XRD and Raman spectroscopy analysis showed that the eutectic phenomenon of the substrate material and carbon was observed in the three BDD electrodes with different substrates materials.The Si-C component was dominant in the Si/BDD surface film,while Ta/BDD and Nb/BDD electrodeare coexist the surface elements（Ta,Nb）and the eutectic components（Ta-C,Nb-C）in the surface.The difference in composition also led to significant differences in surface crystal sizes of Ta/BDD,Nb/BDD,and Si/BDD electrodes are 9.61nm,7.46 nm,and 2.90 nm respectively.The infiltration of the substrate element and the eutectic component in the diamond film may affect the conductivity of the electrode material,thereby causing a difference in electrochemical performance of the BDD electrodes of different substrates;（2）The electrochemical behavioral characterization of Br^-on the surface of Ta/BDD,Nb/BDD and Si/BDD electrodes showed that the differences of the composition of the films lead to the differences electrochemical properties of the three BDD electrodes.After cyclic voltammetric scanning analysis,the three electrode potential windows were 2.52V,2.39V and 2.42V,respectively.So the Ta/BDD electrode has the highest oxidation capacity.Both of the chronoamperometry and the chronoelectricity analysis shown that under high concentration of Br^-conditions,the number of electrons and surface balance of Ta/BDD and Nb/BDDelectrodes are higher than that of Si/BDDelectrode.The difference of film composition makes Br^-more oxidized on the surface of Ta/BDD and Nb/BDDelectrodes.The difference in film composition makes Ta/BDD and Nb/BDD electrodes havemoreactivesitefor Br^-.（3）Using salicylic acid and sodium 2,6-dichlorophenolate to capture the yield·OH and·O₂^-in the electrolysis of the three electrodes,it was found that the main active species of the three electrodes were all·OH.The order of total active material is Ta/BDD>Nb/BDD>Si/BDDelectrode;and the ratio of·OH/·O₂^-in Ta/BDD electrode electroactive materials is 1.13×10³,which is larger than the other two electrodes.The high oxidize ability of the Ta/BDD electrode is achieved by generating more·OH.（4）The effects of initial bromine concentration,current density,pH,temperature and other operating conditions on the bromide conversion rate of different electrodes were investigated.It was found that the initial Br^-concentration and current density have a great influence on the bromine conversion rate of the three electrodes.The reaction rates of the three electrodes were neutral>weak alkaline>strong alkaline>acidic.Temperature and speed have little effect on the experiment,indicating that the experiment can avoid the influence of Br^-conversion rate as long as certain conditions are controlled.The effect of different coexisting ions on the experiment of bromine conversionindicates that Cl^-and CO₃^2-can promote the conversion rate of bromide,and SO₄^2-shows the inhibitory effect.（5）In the actual disinfection experiment,the disinfection effects of the three electrodes were similar,except that the formation of bromine by-products was different in the disinfection.All the three electrodes can satisfy the complete disinfection effect under the experimental conditions.