| Electrochemical advanced oxidation process(EAOPs)is a process based on electrochemical generation of strong oxidative reactive species such as hydroxyl radicals(·OH)to destroy and mineralize pollutants in wastewater.Anodic oxidation degrades pollutants mainly through ·OH generated by the oxidation of water on the surface of the anode.However,anodic catalytic materials such as platinum(Pt)and boron-doped diamond(BDD)have problems such as high cost and complicated manufacturing,which limit their large-scale application.Titanium dioxide(TiO2)has been widely studied as an environmentally friendly,durable and inexpensive semiconductor material,such as(TNA)/Ti,which has been reported as an inactive anode.However,during the anodic polarization process,the Ti surface is easily oxidized to form a TiO2 layer,resulting in poor electrical conductivity.Therefore,TiO2 is often combined with carbon materials(graphene,carbon nanotubes,etc.)to improve the conductivity of TiO2 to promote its application.In this study,TiO2/graphite(TiO2/C)composite electrode was used as anode to study the anodic oxidation behavior of TiO2 different from the photocatalytic electron hole theory and its related applications.The main contents of this study are as follows:(1)The electrochemical behavior of graphite electrode modified with TiO2/C composite catalyst as anode was studied,and the anodic oxidation mechanism in different potential ranges was proposed.In the range of 0.2 V～1.2 V,the cyclic voltammetry(CV),chronoamperometry(i-t)and electron paramagnetic resonance spectroscopy(EPR)characterization of the system with hydrogen peroxide(H2O2)addition were carried out,which proved that H2O2 was an intermediate of anodic oxidation.The electrocatalytic reaction mechanism of TiO2 on both the generation of H2O2 and decomposition of H2O2 into ·OH was proposed.In the range of 1.4 V～2.0 V,·OH was quantitatively analyzed at different potentials,combined with the influence of H2O2 on the generation of ·OH and density functional theory(DFT),proposed the reaction pathway of ·OH by direct oxidation of H2O at high potential.It was directly proved by the EPR experiment for the first time that the strength of oxygen vacancies was consistent with the trend of ·OH generation,and it was proposed that oxygen vacancies were important active sites for the generation of ·OH.The structural change of TiO2 during the reaction was observed by in-situ Raman,proving the relationship between the change of Ti-OH structure and the decomposition of H2O2:the adsorbed H2O2 behaves as Ti-OH bond,and the decomposition of H2O2 into ·OH accompanied by the disappearance of Ti-OH bond.The effect of H2O2 commonly found in EAOPs on the anodic electrochemical behavior of TiO2 was also discussed.Under high potential,high concentration of H2O2 would inhibit the generation of ·OH.(2)The electrochemical anodic oxidation process based on this catalytic material was applied to the degradation of methylene blue(MB),the anodic oxidation ability of TiO2/C was evaluated,and the degradation reaction parameters were optimized.The experiments proved that the optimal conditions for MB degradation were:applied voltage of 1.1 V vs.Ag/AgCl,pH=3,MB concentration of 5.5 mg/L,room temperature,and magnetic stirring speed was 500 rpm.The degradation rate was over 74%when the reaction was carried out for 100 min.At this potential,the anodic oxidation degradation contribution is mainly provided by adsorbed ·OH(Ti-OH),which can also effectively degrade MB.(3)For the first time,based on the electrocatalytic mechanism of cathodic oxygen reduction and anodic oxidation of TiO2/C composite catalytic materials,a permeable electrochemical reaction wall(PERB)was constructed for groundwater remediation using TiO2/C composite modified electrodes as cathode and anode,and its performance of pollutant degradation was investigated.Taking tetracycline hydrochloride(TTC)as the target pollutant,the simultaneous degradation of pollutants by cathode and anode was realized.In PERB,anodizing reaction occurs at the anode,while electro-Fenton-like reaction occurs at the cathode,and the cathode and anode simultaneously generate ·OH.which improves the effective utilization of current.The synergistic effect of cathode and anode achieves effective removal of TTC,and anodization plays a more important role in actual operation. |
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