Construction Of Three-dimensional Boron-doped Diamond Electrode Material And Its Wastewater Treatment Research

Boron-doped diamond（BDD）electrode has stood out to become a protagonist on the electrochemical stage due to its wide electrochemical window,low background current and high stability.Usually,electrode materials is either as anode for electrochemical oxidation or as cathode for electrochemical reduction.The BDD electrode can be used for both electrochemical oxidation and electrochemical reduction,and possesses the advantage of multi-function.In this study,Boron-doped diamond electrode is to key ties of electrochemical oxidation of vanillin in wastewater,electrochemical reduction of nitrate in wastewater and electrochemical reduction of nitrogen to ammonia,which is aimed at solving water pollution and nitrogen cycle problems.Firstly,we regulated the phase composition and micro-morphology of electrode materials by optimizing the deposition parameters of BDD films.Next,we construct a hierarchical three-dimensional structure composed of titanium mesh（Ti-Mesh）,titanium dioxide nanosheet（Ti O₂-NS）and BDD film（worm-like）.Based on the above strategy,BDD@TiO₂-NS electrode,BND@TiO₂-NS electrode（Boron-doped nano-diamond electrode）and BSND@Si electrode（Boron-silicon co-doped nano-diamond electrode）with different electrochemical properties were obtained.Subsequently,the structure of the samples were characterized by Raman Spectroscopy,Field Emission Scanning Electron Microscopy and X-ray Energy Dispersive Spectroscopy.Besides,the electrochemical redox performance of the samples were tested by Ultraviolet Spectrophotometer and Electrochemical Workstation.The results are as follows:（1）The morphology of the BDD@TiO₂-NS electrode is a sort of polyhedral diamond with less sp2 hybrid component,which gives the BDD@Ti O₂-NS electrode a high oxygen evolution potential of 1.98 V（vs.Ag/Ag Cl）and a wide electrochemical window of 2.48 V（vs.Ag/Ag Cl）,and also increases the electrochemical active surface area by 1.7 times.Compared with BDD@Ti-Mesh electrode,the electrochemical degradation of vanillin by BDD@Ti O₂-NS electrode is faster and the energy consumption is lower.The electrical properties of Ti O₂-NS substrate were further optimized by sulfur doping,so as to further accelerate the degradation efficiency of vanillin under neutral conditions and appropriate current density.（2）During the preparation of BND@TiO₂-NS electrode,the BND film began to grow obviously after two hours of induction period.Then,the deposition time was further extended to four hours,massive vermicular nano-ultrafine diamond with effective boron doping completely covered Ti O₂-NS substrate and exhibited hierarchical three-dimensional structure.The electrochemical active surface area of the BND@Ti O₂-NS electrode significantly increased by about 5.7 times compared to the BND@Ti-Mesh electrode.Simultaneously,nitrate removal rate of the BND@Ti O₂-NS electrode increased from 25.03%to 36.93%,and the nitrogen selectivity enhanced from 65.89%to 78.25%at the optimal working potential,in which the amount of harmful intermediate NO₂^-was less.As the electrode continued to reducing nitrate for five hours,the current density kept stable,and the nitrate removal rate reached 53.87%.After five cycles,the nitrate removal rate and N₂selectivity remained basically stable.（3）For the boron and silicon co-doped nano-diamond（BSND）film,with the appropriate introduction of 5 sccm silicon and boron-doping amount from 18 sccm to30 sccm,the electrode retained the structural characteristics of diamond and electrochemical activity.Notwithstanding the faradaic efficiency of the electrode deteriorated at-0.9 V（vs.RHE）,the ammonia yield of nitrogen reduction was significantly improved,that is,the ammonia yield raised to 2.20μg h^-1cm^-2from 1.04μg h^-1cm^-2.The nitrogen reduction reaction undergo five hours,the electrode could still maintain a considerable amount of ammonia production for a so long time,suggesting excellent stability.