Preparation Of Three Dimensional Graphite Carbon Nitride For Efficient Photocatalytic Hydrogen Production

Graphitic carbon nitride（g-C₃N₄）,as a new metal-free polymer,possess many promising properties,such as unique electric,optical,structural and physiochemical properties,which make g-C₃N₄-based material has been widely used in different fields,such as water splitting,environmental remediation,CO₂ reduction and disinfection.However,serious aggregation,insufficient visible light absorption efficiencies and high recombination rate of photoinduced carriers severely restrict the potential of g-C₃N₄ in many applications.The present work utilizes impregnated-chemical reduction strategy and hydrothermal pretreatment route to construct novel three-dimensional graphitic carbon nitride photocatalysts.The effects of three-dimensional structure on the crystal structure,hydrogen production rate and photoelectric properties of the photocatalysts are studied（1）The impregnated-chemical reduction strategy is used to prepare the 3D C/g-C₃N₄ composits with large specific surface area and rich pore structure.The effects of three-dimensional carbon content on the morphology,structure and hydrogen production of the catalyst are studied.The optimal 3D C/g-C₃N₄ shows the largest H₂ evolution rate of 1610μmol h^-1g^-1,which is nearly seven times that of bulk g-C₃N₄.The improved performance arises from the synergistic effect of decreased thickness of nanosheets,more active site exposing,enhanced visible-light utilization as well as effective interfacial contact.（2）Hydrothermal pretreatment route is used to fabricate the 3D UMx,The effects of urea content and hydrothermal pretreatment process on the morphology,structure and hydrogen production performance of the catalyst were studied.The results show that the hydrothermal pretreatment of urea can effectively improve the hydrogen production performance of the photocatalyst.A 10-fold increased hydrogen production rate of 2300μmol h^-1g^-1was achieved when urea was introduced at a molar ratio urea:melamine=2:1.In the process of hydrothermal pretreatment,urea will decompose and produce a lot of ammonia and carbon dioxide,which play the role of porogen and nitrogen source,increasing the specific surface area,a narrowed band gap,as well as more efficient electron transfer and separation.