Study On Preparation And Modification Effects On Photocatalytic Activity Of Mesoporous G-C₃N₄

Photocatalysis is an ideal technology for environmental pollution control.As a new type of photocatalytic materials which is used for visible light,g-C3N4 has great potential in the degradation of organic pollutants.It is popular in the field of photocatalysis in recent years.However,the photocatalytic activity of g-C3N4 is undesirable,because of its small specific surface area and poor electron conductivity.In this paper,g-C3N4 with mesoporous structure was prepared to enhance its specific surface area.The surface modification of Ag particles and O doping were used to further modify g-C3N4 and enhance its photocatalytic activity.The specific research works are as follows:(1)The study of the preparation process of g-C3N4 with mesoporous structure(mpg-C3N4).g-C3N4 with mesoporous structure was prepared by using dicyandiamide and nano SiO2.The influence of the additive amount of SiO2 and the pH value of dicyandiamide pre-treatment on the specific surface area of g-C3N4 was discussed.The results showed that the best ratio of dicyandiamide and SiO2 is 1:1,and the best pH value of dicyandiamide pre-treatment is 3,the prepared mpg-C3N4 has the highest surface area.The degradation of methylene blue(MB)data showed that the photocatalytic activity of mpg-C3N4 is 4.98 times that of g-C3N4.(2)The study of influence of surface modification of metal Ag particles on photocatalytic activity of g-C3N4.The Ag/mpg-C3N4 composites were prepared by reduction method.The data of degradation of MB showed that Ag/mpg-C3N4 has the best photocatalytic activity when the Ag content is 3 wt.%,which is 2.89 times of mpg-C3N4.The reason of the enhancement of Ag modification was discussed by the first principles calculations.The surface cluster energy calculations showed that the Ag particles can stably exist on the g-C3N4 surface,and the large particles Ag are thermodynamically more stable.DFT calculations showed that the Ag 3d orbitals affect the electronic structure of g-C3N4,and the Ag modification promotes the separation of photogenerated carriers and enhances the photocatalytic activity.(3)The study of the influence of O doping on photocatalytic activity of g-C3N4.Oxalic acid was used as oxygen source to synthesis O/mpg-C3N4 composites.When the additive amount of oxalic acid was 40%,the degradation activity of O/mpg-C3N4 is 3.36 times of mpg-C3N4,The calculation results showed that O atoms can replace the N atoms in g-C3N4.After doping,the O 2p orbitals will appear in the band gap of g-C3N4,and appear below the Fermi level.As a result,the electron transition energy was reduced and the photocatalytic activity was enhanced.