| Graphitic carbon nitride（g-C3N4）has been regarded as a new star material in the field of photocatalysis,due to its advantages of high physical and chemical stability,visible light activity,easy to prepare and modify,and its special optical properties,which can oxidize the water to O2 or reduce the water to H2.For photocatalytic materials,the key to improve their photo-catalytic activity is to design the material from molecular level.In this thesis,we designed the g-C3N4 by modification of copolymerization and semiconductor combination method.As a result,we have synthesized a series of modified g-C3N4,which are solar light extented,defective,and Co3O4/g-C3N4 materials.The photocatalytic activities of modified g-C3N4 were evaluated by hydeogen evolution under visible light.Moreover,we also investigated the relationship between microstructure and photocalytic hydrogen production.The researches are summarized as follow:（1）A series of solar light extented CN-THDTx photocatalysts were prepared through thermal polymerization.We studied the morphology,structure and optical properties of CN-THDTx.Results showed that doped THDT could optimize the structure and morphology,enhance light absorption of g-C3N4.In addition,the negative shift of conduction band improved the reduction ability of water splitting.Specifically,the CN-THDT0.15 demonstrated the best performance,and the photocatalytic activity of hydrogen production increased 2 times under visible illumination.（2）One-step copolymerization strategy to introduce defects in g-C3N4.The idea utilized the copolymerization method but selecting monomers with one capped reactive sites.The presence of defects is confirmed by XPS,EPR,and PL measurements.Consequently,the size or type of the capping groups plays a vital role in determination of the final morphology,band gap,separation efficiency of photo-excited carriers and photocatalysis activity ultimately.Among the three studied monomers,the DPT modification exhibits the best performance.Further increasing the ending size or reducing the amounts of reactive sites will destroy the carbon nitride structure.The resulted CN-DPT exhibits higher photoactivity in hydrogen production than pristine g-C3N4 under visible light.Considering the method neither complicate the procedure nor increase the cost,the present novel and versatile defect introducing strategy can be extended to prepare various defective g-C3N4,holding a great potential in practical applications.（3）One step to synthesize Co3O4/g-C3N4 composites for noble metal free photocatalytic hydeogen evolution.The purpose of this part is to design a photocatalyst which can drive the photocatalytic hydrogen evolution without noble metal as a co-catalyst.The results demonstrated Co3O4/g-C3N4 had the ability of water splitting to hydrogen under visible illumination in the absence of Pt.The amount of Co3O4 plays a vital role in determination of the separation efficiency of photo-excited carriers and photocatalysis activity.Among this modified g-C3N4,Co3O4/g-C3N4 exhibited much higher photoactivity of hydrogen production than pristine g-C3N4 under visible light.Moreover,introducing DPT monomer in Co3O4/g-C3N4 could further increase the photocatalytic activities. |
