Research Of Electronic Structure And Photocatalytic Property Of G-C₃N₄:Experiment And Simulation

The graphitic carbonic nitride（g-C₃N₄）as a fascinating polymeric organic semiconductor has been widely researched due to its promising electronic and optical property,and g-C₃N₄ with excellent thermal and chemical stability has been considered as a potential metal-free photocatalysts for some photocatalytic redox reactions:splitting water,pollutant degradation,etc.However,the drawbacks of g-C₃N₄ have restricted its practical application,such as the large intrinsic band gap,the small specific surface area,low visible light response,rapid photogenerated e^-/h⁺recombination,etc.Thus,it is important to improve the g-C₃N₄ based photocatalysts efficiency.（1）g-C₃N₄ was prepared by the mtthod of thermal condensation,and the photocatalytic efficiency of prepared samples was adjusted by changing the amount of tripolycyanic acid.XRD,FT-IR,UV-vis,XPS,etc were used to characterize the crystal structure,chemical state,electronic structure and optical properties of the samples.Results show that the absorption edge of the 1:2-g-C₃N₄ red shift,and the intensity of visible light response was enhanced.More over,1:2-g-C₃N₄ also has a more effective separation efficiency of photogenerated electron-hole pairs.Under visible irradiation,the efficiencies of pollutant degradation and splitting water into H₂are almost 4.5 and 2.2 times higher than that of g-C₃N₄,respectively.（2）Doping is an effective means to modify the electronic behavior of materials by forming new chemical bonds and relaxing the surrounding chemical bonds.With the aid of first principle studies,the effects of a series of nonmetal dopants on the structure,thermodynamic,electronic,catalytic active sites and optical performances have been investigated.It was found that the changes of parameter a and film thickness h of monolayer g-C₃N₄ were caused by relaxed chemical bonds,especially for the newly formed C-NM bonds,it also affects the electronic structures.The band gap values were altered less than±0.14 eV.The optical absorption edges of all doped systems show red-shift 10-75 nm.Thus doping NM elements can alter the visible light response.It is believed that the H,B,O,S,F and As dopants can enhance the photocatalytic efficiency.（3）During the process of hydrogen generation via photocatalytic water splitting,solute ions may be adsorbed on the surface of monolayer g-C₃N₄,modifying its electronic and optical performances,as well as it redox ability due to chemical bond relaxation,and bond relaxation can alter the electronic structure of materials.With the aid of first principles calculations,we investigated the properties of monolayer g-C₃N₄with a series of NM ions adsorbed on its surface.The obtained results showed that,except C and N ions with high coverage rates,the other NM ions can be adsorbed on the surface of monolayer g-C₃N₄,and the systems are mosre stable with a lower coverage rate of NM ions.The newly formed chemical bonds NM-C,NM-N can alter the electronic structure of C,N atoms,which also lead to the change of the CB and VB by relaxing the associated C-N bonds.H,B,N,Si,O,P,As and lower rate halogen can enhance the efficient of photocatalytic splitting water.