Defect-tuning Of Graphitic Carbon Nitride And Study Of Its Photocatalytic Performances

Energy crisis and environmental pollution seriously threat the survival and development of human beings,thus developing a clean and sustainable energy resource is highly urgent.Nowadays,solar power has received great attentions since it is an inexhaustible and green clean energy resource.Amongst all the technologies applied to utilize solar energy,the photocatalysis technology can convert solar energy to chemical energy,such as photocatalytic water splitting for H₂ production and photocatalytic organic synthesis,and has been considered as one of the most ideal technologies for solar energy utilization.However,as the core of photocatalysis,traditional photocatalysts,such as TiO₂ and CdS,are not suitable for indutrial application due to their low utilization of solar energy and poor stability.Therefore,pursuing a new photocatalytic material with outstanding performance and excellent stability has become a new research hotspot in the field of photocatalysis.Owing to the specific electronic structure,remarkable stability and suitable conductive band and valence band positions,graphitic carbon nitride?g-C₃N₄?exhibits outstanding performance in diverse photocatalytic applications and has been considered as one of the most promising photocatalytic materials for the future application.However,the intrinsic drawbacks,such as narrow visible light responsive region,low specific surface area and fast recombination of photoinduced electrons and holes,seriously restrict its photocatalytic performance.This academic dissertation aimed at simultaneously optimizing the electronic band structure and increasing specific surface area of g-C₃N₄ by isochronously tuning its molecular defect structure and micro structure,then realizing the goal of improving its photocatalytic activity.In addition,with the purpose of providing crucial references for future research,this academic dissertation also investigated thoroughly the intrinsic relationships between the properties of materials and the catalysis.The detailed contents are listed as follows:?1?A novel porous defect-modified graphitic carbon nitride?P-DCN?with specific surface area up to 65.0 m² g^-1,was successfully fabricated by a facile one-step thermal polymerization of a freeze-dried crystalline mixture containing dicyandiamide?DCDA?and ammonium chloride?NH₄Cl?under nitrogen atmosphere.Results of characterizations show that both two types of defect?cyano group and nitrogen vacancy?and porous structure were simultaneously introduced into P-DCN framework.On the one hand,the implantation of defects can modulate the electronic band structure of P-DCN,thus improve its capability of visible light absorption and substantially decrease the recombination probability of photoinduced electrons and holes.On the other hand,the introduction of porous feature can not only increase the specific surface area of P-DCN,which provides more active sites for the reaction,but also be favorable for decreasing the transmission distance of charge carriers,thus facilitating charge carriers transfer from internal to surface.Moreover,the porous feature is also conducive to strengthening mass transfer.The as-synthesized P-DCN exhibits outstanding photocatalytic performance in the photocatalytic water splitting for H₂ production test,and its H₂ evolution rate reaches 20.9?mol h^-1.This value is 26 times higher than that of bulk g-C₃N₄.?2?Cyano groups?–C?N?decorated g-C₃N₄ nanosheets?DCNNS?was successfully prepared via thermally treating g-C₃N₄ nanosheets?CNNS?under N₂ atmosphere.The as-obtained material demonstrates higher performance than original CNNS in the test of molecular oxygen activation for superoxide radical?O₂·^-?production.Further investigation reveals that the introduction of–C?N can alter the electronic band structure of partial DCNNS,thus,a homojunction is constructed.Under the action of built-in electric field,electrons and holes can separately gather on the different districts of DCNNS,thus suppressing the recombination of photoinduced electrons and holes and increasing the number of free electrons.DCNNS exhibits higher performance than CNNS in the test of oxidative coupling reaction of amines to imines under visible light irradiation.The optimized catalyst demonstrates 2.4 times higher activity than CNNS.