Electrochemical Oxidation Of Phenol Wastewater With Boron-Doped Diamond Anodes

Boron-doped diamond（Boron-doped diamond,hereinafter referred to as BDD）electrode has attracted more and more attention due to its excellent electrochemical properties.It has a wide potential window,excellent conductivity,high stability,corrosion resistance and so on.These characteristics meet the electrode requirements of electrochemical water treatment technology,and BDD electrode has been widely studied in the field of electrochemical organic wastewater oxidation treatment.Firstly,BDD electrode based on Si was prepared by microwave plasma chemical vapor deposition.Scanning electron microscope（SEM）,X-ray diffraction（XRD）and Raman spectrometer（Raman）were used to characterize the morphology and structure of boron-doped diamond electrode.The cyclic voltammetry（CV）technique was employed to study the performance of the electrode.The results show that the prepared diamond films with a thickness of about 3μm have good quality,wide potential window（3.65V）and high oxygen evolution potential（2.45V）in neutral solutions.Secondly,the degradation of phenol wastewater by BDD electrode anodic oxidation was studied.The electrochemical behavior of phenol on BDD electrode surface had been studied by cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）and chronoamperomertry;We use a BDD electrode as the anode and a Pt electrode as cathode to degrade phenol,and the effects of pH,anodic current density,initial concentration of phenol and electrolyte concentration on the degradation efficiency of phenol on BDD anodes were evaluated.The results show that there are two processes of direct and indirect oxidation of phenol on the surface of BDD electrode,And in the process of indirect oxidation·OH could oxidize and degrade phenol.The degradation rate of phenol is significantly affected by its initial concentration,current density,electrolyte concentration;the coexistence of Cl^-and SO₄^2-is advantageous to the oxidative degradation of phenol.When pH,anodic current density and reaction time were 5,24 mA/cm² and 180 min,as well as concentrations of NaClO₄ and phenol as 0.5 mol/L and 300 mg/L,the removal rate and TOC removal are up to 85%and 77%;furthermore,this degradation process can be described by the first order kinetic equation.Thirdly,the intermediate products in the process of phenol degradation have been detected by using UV spectrophotometer and gas chromatography and mass spectrometry.The results showed that UV scanning absorption spectra showes that new substances appeared in UV region in the process of phenol degradation,and the intermediate of phenol degradation was found to be benzoquinone,hydroquinone,maleic acid and adipic acid by Gas Chromatography-Mass Spectrometer（GC-MS）analysis..Finally,the formation of·OH in the electrochemical oxidation process on BDD electrode was investigated.Using coumarin as trapping agent,the formation rate of·OH in BDD electrode system was determined by fluorescence spectrometry.The experimental results show that when the electrolysis condition is 2 mA/cm²,the optimum initial concentration of trapping agent cou is 3 mmol/L,the reaction time is less than 30 min,and the formation rate of·OH is 6.07μmol/（L·min）.