Preparation And Photoelectrocatalytic Properties Of Carbon Aerogel-Based Photocatalytic Electrode

Nowadays,environmental ecological and energy problems are becoming more and more obvious,and the large amount of organic wastewater discharge is a constant threat to human health and ecological environment.Photoelectrocatalytic oxidation technology is a new type of water treatment technology that is efficient,green and has photoelectrocatalytic properties at the same time.By adding appropriate voltage to the photocatalytic process,the problems of high photogenerated electron-hole complexation rate and slow carrier transport rate in photocatalysis can be effectively solved to enhance the photoelectric synergistic effect and realize the efficient degradation of organic pollutants.The core of photoelectrocatalytic oxidation is the development of new photoelectrodes,which mainly includes the selection and modification of electrode substrates and photocatalysts.Carbon aerogel（CA）is a new carbon material with unique three-dimensional network structure,which has the advantages of high specific surface area,strong adsorption,strong electrical conductivity,high porosity and controllable mass density,etc.It can be applied as an excellent electrode substrate in photoelectrocatalytic process.Based on this,this study selects CA as a photoelectrocatalytic electrode substrate,loads suitable photocatalysts on it to prepare composite photoelectrodes,constructs internal electric field and heterojunction,improves the catalytic activity of photoelectrodes,and applies them to photoelectrocatalytic oxidation of organic wastewater.In this thesis,the BiOI/CA and TiO₂/BiOI/CA photoelectrodes were constructed by using CA as the photocatalytic electrode substrate and loading the visible-light responsive photocatalyst BiOI and TiO₂/BiOI composite photocatalyst with p-n type heterojunction on it to address the problems of weak conductivity,few reaction sites and high photo-generated electron-hole complexation rate of photoelectrodes.A series of characterization tests were conducted to investigate the morphological characteristics,the visible light responsiveness,the complexation of photogenerated electrons and holes,and the enhancement mechanism of the photoelectric synergy effect of the photoelectrodes.Meanwhile,the electrode photoelectrocatalytic performance was evaluated and the photoelectrocatalytic oxidation mechanism was investigated by simulating the photoelectrocatalytic degradation of phenol under the conditions of sunlight irradiation supplemented with an applied bias.The following research conclusions were obtained from the study.（1）In this study,BiOI/CA photoelectrodes with visible light response were obtained by hydrothermal method by successfully loading flower cluster-like BiOI nanospheres on CA,and the composite photoelectrodes were uniform in shape and obvious in structure.It was found that the BiOI/CA composite electrode prepared at a hydrothermal temperature of 140℃has the best phase structure,visible light absorption ability,carrier separation and phenol degradation effect,and can degrade 83.2%of phenol in 2h,which is three times of BiOI/FTO,and has good stability.Active substance capture experiments confirm that·OH and cavities are the main substances of action.This study shows that the complexation of BiOI with CA is beneficial to improve the photocatalytic activity of BiOI.This is mainly because the strong adsorption,large specific surface area and high electrical conductivity of CA enable the BiOI/CA electrode to accumulate more active sites on the surface,more pronounced visible light responsiveness,faster carrier transport rate and lower electron-hole complexation rate.As a result,the BiOI/CA electrode exhibits enhanced photoelectrocatalytic coordination effect and photoelectrocatalytic degradation of organic pollutants.（2）To further reduce the compound rate of photogenerated electron-hole pairs in the photoelectrode and improve the photocatalytic ability,a TiO₂/BiOI/CA electrode with p-n heterojunction was constructed in this paper.Characterization analysis by UV-Vis DRS,photocurrent and impedance tests obtained that when the Ti/Bi molar ratio was 0.4,the TiO₂/BiOI/CA photoelectrode exhibited the best visible light absorption,the lowest photogenerated electron-hole pair complexation rate and the strongest photocatalytic degradation,which could degrade 90.4%of phenol under 120 min of light.Moreover,the stability of the electrode remains at a high level.This is mainly because the energy levels of TiO₂ and BiOI match each other and the p-n heterojunction formed adjusts the energy band structure of the composite material,widens the electron transfer path,forms an internal electric field between the phase interfaces,has a higher electron transfer rate,and reduces the photogenerated electron-hole complex rate.Since·OH andO₂^-are the main active substances in the degradation of phenol,the TiO₂/BiOI/CA photoelectrode will have higher degradation efficiency than the BiOI/CA electrode.This study provides a unique idea for the treatment of organic pollutant wastewater and electrode design related to photoelectrocatalysis.