Preparation And Photoelectrocatalytic Performance Of Geopolymer Photoanode Materials

With the advancement of technology and development of industry,the problem of organic wastewater in our country has intensified,which is a serious threat to human health and ecological environment.Photoelectrocatalysis oxidation is one of the common methods for the purification of dye wastewater.Its high degradation efficiency and lack of secondary pollution have gained widespread attention from researchers,and the development of economically efficient and easily produced photoanode materials is the key of this technology.Geopolymer is a kind of green cementing material with the advantages of chemical corrosion resistance,low energy consumption,low emission in the production process and wide source of raw materials,and has the potential as a photoanode material.A series of geopolymer photoanodes were prepared by coating method using stainless steel sheet as the conductive substrate,metakaolin and silica fume as silica-alumina raw materials and sodium hydroxide solution as alkali-activator,and the electrodes were characterized in terms of microscopic morphology,composition structure,optical properties and electrochemical properties;the photoelectrocatalytic degradation performance of the electrodes on dye wastewater was investigated;their degradation kinetics and degradation mechanism were analysed,laying the foundation for further research and application of geopolymer electrodes for photoelectrocatalytic treatment of dye wastewater.The results of the work are as follow:To improve the electrical conductivity of geopolymers,carbon fiber geopolymer electrodes（CFGE）were prepared by doping carbon fibers into geopolymers.The effect of carbon fiber content on the photoelectrocatalytic activity of CFGE and the related mechanism were investigated.It was shown that the introduction of carbon fiber could significantly improve the conductivity of the composite electrode;the electrical conductivity was improved by 17.75 times,when the carbon content was increased from0wt%to 6wt%;the interfacial charge transfer resistance of the 6CFGE sample was reduced from 66.219 kΩto 0.1467 kΩcompared to 0CFGE;and the carbon fibers could effectively inhibit the compounding of photogenerated electrons and holes in the composite electrode.In addition,the photoelectrocatalytic performance of the electrodes was evaluated by degrading rhodamine B dye in a photoelectrocatalysis/persulfate system.6CFGE electrode showed the highest degradation efficiency,with a degradation rate of over 98%at 6 min.There was a synergistic effect between photocatalysis and electrocatalysis with a synergy factor of 1.713,and the sulfate radicals and hydroxyl radicals in solution made the main contribution to the degradation reaction.To further increase the photoelectrocatalytic activity of carbon fiber geopolymer electrodes,a series of Fe₂O₃/carbon fiber geopolymer electrodes（Fe₂O₃/CFGE）were prepared by introducing Fe₂O₃（narrow band gap semiconductor）as the active component.It was shown that Fe₂O₃ was successfully loaded into the carbon fiber geopolymer matrix without damaging the structure of geopolymer.The doping of 10wt%Fe₂O₃ effectively improved the optical responsiveness of composite and broadened its wavelength threshold from 391 nm to 503 nm.The 10Fe₂O₃/CFGE sample had the higher oxygen evolution potential and the lower interfacial charge transfer resistance,which exhibited the higher photoelectrocatalytic degradation activity compared with the sample without Fe₂O₃.The degradation rate of basic violet 5BN dye at a concentration of 5 mg/L was95.1%at a voltage of 0.8 V and a p H of 7.3,with hydroxyl radicals playing a major role in the degradation of the dye.