Study Preparation Of Polyimide-based Composites For The Photocatalytic Degradation Dye Properties

The increasingly serious water pollution has become a global problem.One of the methods to solve the water pollution problem is the application of photocatalytic technology,which can effectively use solar energy to degrade pollutants,and has the advantages of fast and efficient reaction process and no secondary pollution.The focus of photocatalysis technology is the research on photocatalysts with high efficiency and stability.Polyimide?PI?is a polymer semiconductor material with visible light response.Its unique chemical stability and easily regulated structure make it have a good application prospect in the field of photocatalysis.Based on these facts,in this paper,several polyimide-based composite materials were synthesized and used for photocatalytic degradation of dyes under UV-visible light irradiation to evaluate their photocatalytic activities.Also,the stability of these photocatalysts and the mechanism of the photocatalysis were studied.The main research contents are as follows.?1?The PI/WO₃/ZnO?PWZ?composite photocatalysts were prepared by one-pot calcination after ZnO was prepared by precipitation method.The phase structure,composition and morphology of the as-prepared photocatalytic materials were characterized by XRD,FT-IR,SEM,EDS and etc.The effects of ZnO contents,heating rate,and reaction temperature in the prepareration of PWZ composites on the photocatalytic degradation activity were investigated using rhodamine B?RhB?solution as a water pollution model.The best photocatalytic activity was found on the PWZ?0.2g,3°C/min,325°C?composite prepared under the optimal conditions,in which the ZnO content was 0.2 g,the heating rate was 3°C/min,and the reaction temperature was325°C.When 50 m L of concentration of 20 mg/L RhB solution was degraded by the PWZ?0.2 g,3°C/min,325°C?composite under UV-visible light irradiation for 50minutes,the degradation rate of 99.6%was obtained.After 5 cycles,the degradation rate of RhB can still attain to 96.8%,suggesting the good stability of the PWZ?0.2 g,3°C/min,325°C?composite.In addition,it was found that the PWZ?0.2 g,3°C/min,325°C?composite exhibited good activity for photocatalytic degradation of Congo red?CR?dye.The photoelectrochemical tests indicated that more efficient separation of photogenerated electrons and holes can be achieved for the PWZ?0.2g,3°C/min,325°C?composite photocatalyst,and thus higher photocatalytic activity was obtained.The capture experiments of active species indicated that the main active species was?O₂^-in the photocatalytic degradation of RhB catalyzed by the PWZ?0.2g,3°C/min,325°C?composite.?2?PI and Bi₂WO₆ were synthesized by calcination and solvothermal process,respectively.Then the PI/Bi₂WO₆ composite photocatalysts were prepared by ultrasound-assisted deposition method.The phase structure,composition and morphology of the as-prepared photocatalytic materials were tested by XRD,FT-IR,SEM,EDS and etc.The photocatalytic degradation activity of Bi₂WO₆ synthesized in water?DW?,ethanol?EA?and ethylene glycol?EG?solvents and their corresponding PI/Bi₂WO₆ composite photocatalysts were investigated using RhB dye solution as a water pollution model.The optimized photocatalysts with best performance were 1:2PI/Bi₂WO₆?DW?,1:1 PI/Bi₂WO₆?EA?,and 1:1 PI/Bi₂WO₆?EG?composites.When 50mL of concentration of 20 mg/L RhB solution was degraded by the 1:1 PI/Bi₂WO₆?EG?composite under UV-visible light irradiation for 24 minutes,the degradation rate of99.2%was obtained.The cyclic experiments showed that the photocatalytic stability of PI/Bi₂WO₆ composite photocatalysts were higher than that of their corresponding monomer Bi₂WO₆.After four cycles,the degradation rate of RhB catalyzed by the 1:1PI/Bi₂WO₆?EG?composite could still reach to 95.6%.The photoelectrochemical tests showed that the separation efficiency of photogenerated electron and hole in the PI/Bi₂WO₆ composite photocatalyst was significantly improved,and so the catalytic activity was enhanced.The capture experiments of active species suggested that the main active species was?O₂^-in the photocatalytic degradation of RhB catalyzed by the1:1 PI/Bi₂WO₆?EG?composite.?3?PI,PI/MoO₃ and g-C₃N₄ were prepared by calcination method,and PI/MoO₃/g-C₃N₄ composite photocatalyst was prepared by deposition method.Using XRD,FT-IR,SEM,EDS and other characterization techniques to test the phase structure,composition and morphology of photocatalytic materials.Using the RhB dye solution as a water pollution model,the photocatalytic degradation activity of the prepared PI/MoO₃ composite photocatalyst was investigated,and the best performance PI/MoO₃-C?C means that the content of ammonium molybdate is 0.1 g?was optimized.On this basis,the degradation activity of PI/MoO₃/g-C₃N₄ composite photocatalyst with different ratio was investigated,and the best 1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst was optimized.Under UV-visible light,when irradiated for 10 min,the RhB degradation rate of 1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst reached 98.4%for a 50 mL volume of RhB solution with a concentration of 20 mg/L,indicating that1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst had high photocatalytic activity.Cycle experiments showed that the 1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst had higher photocatalytic stability than PI/MoO₃-C.Photoelectrochemical tests showed that the photoelectron and hole separation efficiency of 1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst was significantly improved,so that the catalytic activity was enhanced.The capture experiment of active species showed that during the degradation of RhB by1:1 PI/MoO₃/g-C₃N₄ composite photocatalyst,O₂^-was the main active species,and h⁺was the secondary active species.