Study On Modification And Photocatalytic Performance Of Polyimide Aerogel

Photocatalysis,an eco-friendly technology,which uses the excellent redox ability of semiconductor photocatalysts driven by solar energy to solve problems in energy shortage and ecological pollution.Previous studies have shown that highly active photocatalysts absorbing solar energy can effectively degrade organic pollutants.The systhesis of photocatalysts with mild production conditions,low cost and good visible light response ability is an important link in the development of photocatalytic technology.Polyimide aerogel（PIA）is a traditional polymer,which has been widely used in coating and aerospace application.In recent years,PIA has received some attention in the field of photocatalysis due to its rich pore structure,large specific surface area,tunable energy band structure and favorable physicochemical stability.However,any single-component semiconductor photocatalysts have many shortcomings,such as low utilization of visible light,severe charge complexation and low photogenerated electron-hole transfer ability,which seriously limit the practical application of photocatalysts.Therefore,this thesis focuses on PIA photocatalysts as the main research object.Through element doping and heterojunction construction,improving the hydrophobic properties and the degradation activity of the photocatalyst to enhance the photocatalytic application potential in wastewater treatment.The specific contents of research are as follows.（1）Cl-doped PIA photocatalysts were prepared by chemical amide reaction and supercritical alcohol drying method.It is found that the introduction of electronegative chlorine will play an electron-gaining role in the donor-acceptor structure of PIA.Due to its suitable atomic radius,chlorine will not destroy the brake amide ring and form charge transfer channel to enhance the light absorption and charge transfer ability.Although the introduction of bromine or iodine will improve the photocatalytic performance,the atomic radius is larger causes poor stability of catalyst.In this work,we explored the effects of different doping amounts on the photocatalytic performance of PIA by optimizing the doping amount of chlorine.The results demonstrated that modified photocatalyst achieved 80%removal of rhodamine B in 180 min,and the degradation rate was 2.3 times higher than that of PIA monomer.（2）The broad spectral response PIA/Bi₂Mo O₆-OVs p-n type heterojunction aerogel photocatalysts were prepared by a one-step supercritical drying method.The introduction of oxygen vacancies can activate oxygen molecules and form defects.Besides,SEM images show flocculated PIA wrapped around the surface of flower-like Bi₂Mo O₆-OVs microspheres,taking full advantage of the large specific surface area of polyimide aerogels and the better photocatalytic properties of Bi₂Mo O₆.Furthermore,the formation of Mo-N chemical bond between the coordination of N atoms and Mo atoms of Bi₂Mo O₆-OVs is confirmed by structure analysis,which improves the stability.The experimental results showed that PIA/Bi₂Mo O₆-OVs have better visible light responsiveness and less resistance to charge transfer by constructing p-n type heterojunction.PIA/Bi₂Mo O₆-OVs achieved 80%photodegradation of rhodamine B in 100 min,and degradation rates are 4and 12 times higher than those of PIA and Bi₂Mo O₆ monomers,respectively.（3）In order to address the disadvantages of PIA strong hydrophobicity and agglomeration in water,the Z type xPIA/Bi₄O₅I₂ heterojunction photocatalyst was prepared by in-situ growing Bi₄O₅I₂ nanosheets on PIA by one-step solvothermal method.The catalyst with the better performance（specific surface area of 42.381 m²/g）can be obtained by adjusting the amount of PIA added.The hydrophobicity of catalysts can be improved by the solvothermal method with using ethylene glycol as solvent.The removal rate of tetracycline hydrochloride（TC）reached 91.3%under dark reaction and simulated sunlight irradiation,which broadened the light absorption range of the materials and improved the utilization efficiency of visible light.This work provides theoretical and data support for the construction of organic inorganic material heterojunction aerogel photocatalysts in the field of wastewater degradation.