Construction Of Direct Z-scheme CdS/polyimide Heterojunction And Their Photocatalytic Performance Under Visible Light

With the acceleration of industrialization,globle energy shortage and environmental problems are becoming more and more serious.Semiconductor photocatalysis is promising to solve both problems by converting solar energy into chemical energy.In recent years,as a new kind of organic conjugated polymer semiconductor photocatalyst,polyimide has become a hot research of our group due to its low cost and various preparation methods.Polyimide has a band gap matching the visible spectrum and two-dimensional lamellar structures.However,polyimide has a few of deficiencies,such as limited visible light absorption,low carrier migration and separation efficiency,which limit the photocatalytic activity.So,it is necessary to construct an efficient and stable photocatalytic system.CdS is one of the most popular inorganic semiconductors photocatalysts.However,the application of CdS is limited by the photo-corrosion phenomenon.In this paper,we construct CdS/polyimide heterojunction photocatalysts which has good visible light absorption.The close contact interface between CdS and PI can accelerate the transfer and separation of photogenerated carriers.The most important is that the composite material system possesses stable and efficient hydrogen production activity and high performance for photodegradation of organic pollutants under visible light.A novel direct Z-scheme CdS/polyimide heterojunction was fabricated by in situ growth of CdS nanoparticles on polyimide（PI）ultrathin nanosheets through solvothermal method.The CdS/PI heterojunction has a wider absorption range in the visible region,which is benifical for improving the separation of photogenerated electrons and holes.The highest H₂-production activity achieved on 15%CdS/PI sample reaches to 613μmol h^-1g^-1 under visible-light irradiation,which is nearly 5and 60 times higher than that of neat CdS and 1%Pt/PI,respectively.Most importantly,the excellent photostability is also achieved over 15%CdS/PI.The direct Z-scheme charge transfer mechanism is not only improves the separation and transfer of photogenerated carriers,but also can inhibit the photo-corrosion of CdS.A new type of conjugated polymer semiconductor（PTCDI）was first synthesized through solvothermal method.Then,the novel direct Z-scheme CdS/polyimide heterojunction was fabricated by in situ growth of CdS nanoparticles on PTCDI ultrathin nanosheets.The degradation efficiency of 25%CdS/PTCDI can reach to 86%within 50 min,which was 11 and 2.3 times higher than that of pure CdS and PTCDI.The 25%CdS/PTCDI heterojunctions have presented a slight red-shifted of adsorption edge toward visible region.Meanwhile,the EIS,I-t curves and PL spectrums also prove the higher charge separation efficiency of CdS/PTCDI heterojunctions.The photocatalytic performance during cyclic runs also indicated that the 25%CdS/PTCDI heterojunction has good stability and efficient depression for the photo-corrosion of CdS.Superoxide radical was confirmed to be the main reactive oxygen species in the system.The excellent photocatalytic activity of CdS/PTCDI is closely related to the direct Z-scheme charge transfer mechanism.The direct Z-scheme charge transfer mechanism plays a critical role in photocatalysis progress.It not only can improve the photodegradation efficiency,but also can inhibit the photo-corrosion of CdS.