| Graphitic carbon nitride(g-C3N4),a two-dimensional material that is promising for application in the fields of biology and photocatalysis and becomes one of the focused topics in recent years,and it has received tremendous attention from researchers in the fields of chemistry,materials,biology,and physics.In this thesis,I will focus on the structure-modification of g-C3N4 and study the photocatalytic performance by analyzing the physical and chemical properties.In the first chapter,I will firstly give a brief review on the recent development of the study on g-C3N4,including the development history,the structure,the synthesis methods,the applications and the modification for improved performance for applications.Then,I will introduce three main works,including:(i)The urea and dicyandiamide are respectively selected as precursors to fabricate g-C3N4,giving rise to the g-C3N4 structures with different morphologies,as a consequent,g-C3N4 with different morphologies exhibit obvious different photocatalytic activities.The study found that g-C3N4 prepared with urea as a precursor has good photocatalytic performance,while g-C3N4 prepared with dicyandiamide as a precursor shows weaker photocatalytic activity.A variety of physical and chemical characterization methods are used to reveal the influence of its inherent basic structure and basic properties on the photocatalytic performance.(ii)A simple,facile and effective method to simultaneously hydrogenate and exfoliate g-C3N4 through high concentration sulfuric acid treatment.The hydrogenation mechanism of g-C3N4 is explained experimentally and it is further revealed in detail by molecular structure dynamics as well as the corresponding electronic structure evolutions.Different from the pristine g-C3N4 that is flat in basal plane,the energetically favored hydrogenation structure of g-C3N4 possesses the corrugated fluctuation plane.The hydrogenated structure with wider bandgap has also been explained experimentally and theoretically.Finally,it is found that the photocatalytic performance of g-C3N4 is dramatically enhanced once the crystal structure is hydrogenated.The enhanced photocatalytic performance is mainly attributed to the hydrogenation caused spatial charge separation due to the redistribution of charge density in both valence band maximum and conduction band minimum.The revealing of spatial charge separation provides insight into the deep understanding of hydrogenation mechanism of g-C3N4,which is critically significant for designing lightefficient photocatalysis.(ⅲ)Furthermore,I prepared ultra-fine Ag nanoparticles(Ag-NP)and the Ag-NPs have been well incorporated with g-C3N4 to form composite materials through special process technology.Various physical and chemical tools have been conducted to characterize various basic parameters of the composite structure.By careful analyzing the characteristics of the composite structure,the mechanism of dramatically improved photocatalytic activity of Ag incorporated g-C3N4 composite have been revealed.The preparation of composite structure to modify the performance of g-C3N4 system helps to expand the development of g-C3N4 in a wider range of applications.Finally,this thesis makes a summary.Studies on the different structures obtained by preparing g-C3N4 with different precursors have different photocatalytic activities,revealing that the slight change of the microstructure of g-C3N4 can lead to obvious differences in photocatalytic activity.This study introduced chemical modification and physical modification of g-C3N4 for improving its photocatalytic performance.The study found that the chemical modification of the surface hydrogenation process of gC3N4 and the physical modification combined with Ag nanoparticles can achieve a significant increase in photocatalytic activity.This study will contribute to a deeper basic understanding of g-C3N4 and pave the way for expanding its applications. |
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