Preparation Of Corn Straw Derivatives Photocatalytic Materials And Hydrogen Production Performance By Different Light Sources

Fossil energy not only brings great convenience to people’s lives,but also causes increasingly severe environmental pollution during its development and use.The development and utilization of green and sustainable energy urgently need to be addressed.Hydrogen can be used as a clean energy source,but the raw material for production is still mainly supplied by fossil energy.Photocatalytic decomposition of water for hydrogen production is a new green hydrogen production method using solar energy for energy conversion.It has been extensively studied in the field of environmental and energy development.Traditional photocatalysts have the disadvantages of poor light trapping ability and low efficiency of photoinduced electron and hole separation.Therefore,it is urgent to develop efficient and stable photocatalysts to improve the performance of photocatalytic hydrogen production.The combination of corn straw derivative carbon materials with traditional photocatalysts not only solves the problem of agricultural straw resource utilization,but also provides a new idea for the construction of green and sustainable photocatalytic hydrogen production system.It is an effective way to further improve the efficiency of photocatalytic water decomposition to produce hydrogen.In this paper,maize straw derivatives were coupled with traditional photocatalysts.A novel and efficient carbon-based composite photocatalytic material was prepared.The morphology,composition,structural properties and electrochemical properties of the composites were analyzed by various characterization methods.The photocatalytic activity and photostability of different carbon-based composites were investigated.Hydrogen production performance of photocatalytic water decomposition under different light source intensities.The mechanism of photocatalytic hydrogen production of carbon-based composites was proposed to improve the efficiency of photocatalytic hydrogen production.The main contents of this paper are as follows:（1）Preparation of TiO₂/Pt/corn straw derivative biochar composite photocatalytic material,using corn straw suspension as sacrificial agent,and analysis of its photocatalytic performance for water splitting and hydrogen production.When the mass concentration of biochar doping is70%,TiO₂/Pt/corn straw derivative biochar exhibits the best photocatalytic hydrogen production performance.At the optimal doping ratio of biochar,as the mass fraction of corn straw sacrificial agent increases,the hydrogen production of the photocatalytic system shows a trend of first increasing and then decreasing.When the mass fraction of sacrificial agent added to the photocatalytic system is 30%,the hydrogen production performance is optimal,and the hydrogen production rate reaches 262.5μmol·h^-1·g^-1is 21.6 times that of pure TiO₂/Pt.In addition,TiO₂/Pt/biochar photocatalytic material shows no significant change in hydrogen production after 5 repeated experiments.Under different light sources and UV irradiation,the photocatalytic system exhibits the best hydrogen production performance.（2）High surface activity and high-efficiency 2D g-C₃N₄/WO₃/biochar/Cu²⁺-doped carbon spheres were prepared for use as composite photocatalysts.Compared with pure g-C₃N₄,WO₃,and g-C₃N₄/WO₃heterostructures,the prepared composite material had higher photocatalytic performance and photostability.The photoelectric properties and mechanism of the photocatalysts were analyzed.The 2D g-C₃N₄/WO₃/biochar/Cu²⁺-doped carbon spheres photocatalyst with 40 wt%Cu²⁺-doped carbon spheres showed excellent photocatalytic performance for hydrogen generation,reaching 1900μmol·h^-1·g^-1（about 6.33 times better than that of pure g-C₃N₄）.This phenomenon was mainly due to a Z-scheme heterojunction in the biochar between the g-C₃N₄and WO₃.The synergy between the g-C₃N₄/WO₃and Cu²⁺-doped carbon spheres（acting as cocatalysts）increased the electron transfer rate and increased the photocatalytic performance of the composite.Under different light sources,the photocatalytic hydrogen production performance of composite materials was ultraviolet light>visible light>sunlight>weak light.（3）A g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst was successfully prepared.The hydrogen production efficiency was 107.75 times（under visible light）and 70.54times（under sunlight）greater than that of pure g-C₃N₄,respectively.The hydrogen production rate using ultraviolet light as a light source was only 1.01 times that of visible light source.The absorption intensity of visible light in composite materials had increased.Under different light sources,the hydrogen production rate was ultraviolet light>visible light>sunlight>weak light.The experimental and characterization results show that g-C₃N₄and WO₃formed a Z-scheme heterojunction on the surface of the g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst.Carbon microspheres modified on g-C₃N₄nanosheets and WO₃had good conductivity and promoted the transfer of photogenerated electrons in g-C₃N₄nanosheets.The addition of carbon microspheres increased the specific surface area of the composite photocatalyst.The g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst showed strong adaptability to the fluctuating light intensity.（4）A composite photocatalyst based on g-C₃N₄/CdS/corn straw carbon microspheres was prepared.The morphology and structure of CdS/g-C₃N₄/corn straw carbon microspheres were characterized,which confirmed that the corn straw carbon microspheres were successfully loaded into the heterojunction of g-C₃N₄and CdS nanosheets.Through the study of photoelectric characteristics and density functional theory simulation,it was found that the energy band of g-C₃N₄/CdS/corn straw carbon microspheres was reduced by 2.04 e V compared with that of pure g-C₃N₄and CdS,and the photogenerated carrier transfer rate was accelerated.The Z-scheme heterostructure between g-C₃N₄and CdS and the graphitized hydrothermal carbon spheres increased the surface active sites of the composite,leading to the generation of synergistic photocatalytic reaction.The photocatalytic experiment showed that g-C₃N₄/CdS/corn straw hydrothermal carbon spheres composite exhibited synergistic photocatalytic performance.When the mass fraction of carbon microspheres was 50%,the synergistic reaction efficiency was the highest,and the H₂yield was 2600μmol·h^-1·g^-1.Under different light sources,the hydrogen production rate of composite materials was visible light>ultraviolet light>sunlight>weak light.（5）TiO₂/WO₃corn straw graphene-like photocatalyst composite suitable was prepared.Based on the photoelectric characteristics and density functional theory simulation results,the energy band of TiO₂/WO₃corn straw graphene-like composite material is reduced to 2.32 e V compared with pure TiO₂and WO₃.The transfer rate of photogenerated carriers is accelerated,and the heterostructure between TiO₂and WO₃interacts with graphene to promote the transfer of photogenerated electrons.Moreover,some photogenerated electrons reside on the graphene surface.Under different light sources,the hydrogen production rate of composite materials was visible light>ultraviolet light>weak light.Consequently,under low light irradiation,the efficiency of photogenerated electron transfer was increased and the hydrogen production performance was improved.The photocatalytic experiment showed that the hydrogen production rate of TiO₂/WO₃corn straw graphene-like composite under low light irradiation 254 nm is only10%lower than that under visible light irradiation.