Preparation Of Heteroatom Doped Graphitic Carbon Nitride And Its Photocatalytic Activity

Photocatalytic technology,as a low energy consumption environmental protection technology,has a wide application prospect in solving energy shortage and environmental pollution.The traditional photocatalytic technology is mainly focused on the study of ultraviolet photocatalytic technology.The utilization rate of sunlight is too low.The traditional photocatalytic materials have some disadvantages,such as poor stability,low carrier mobility and high preparation cost,which greatly restrict the further development of photocatalytic technology.Graphitic carbon nitride（abbreviated to CN）,as a new type of non-metallic organic polymer semiconductor,has shown obvious advantages in photocatalytic technology in recent years.However,the application of CN in photocatalysis is limited to a certain extent due to its insufficient spectral response and easy recombination of photogenerated electron and hole pairs.In this paper,CN was modified by heteroatom doping.Tellurium（Te）doped CN photocatalyst（TeCN）and sulfur（S）,gadolinium（Gd）double-doped CN photocatalyst（SCN/Gd）were prepared respectively.The photocatalysts were used in visible-light photocatalytic nitrogen fixation and visible-light photocatalytic degradation of sulfamethazine（SMR）,respectively.The main research contents and conclusions are as follows:1.The Te doped CN photocatalyst（TeCN）was synthesized by hydrothermal method and high-temperature calcination using melamine and tellurium powder as precursors.The photocatalytic performance of TeCN in visible-light nitrogen fixation was studied.The results show that the introduction of Te enlarges the specific surface area of CN,broadens its spectral response range and inhibits the combination of photogenerated electrons and holes on the surface of the catalyst.The midgap states and nitrogen vacancies produced by Te doping have significant effects on the enhancement of photocatalytic nitrogen fixation activity.At the same time,the valence state changes between Te⁶⁺,Te⁴⁺and Te⁰ in TeCN catalyst further promoted the nitrogen fixation activity.Among them,1.0%TeCN catalyst（the mass ratio of tellurium to melamine is 1.0%）shows the best photocatalytic nitrogen fixation effect,which is 7.2 times as high as CN.Besides,1.0%TeCN catalyst not only has high visible-light photocatalytic nitrogen fixation activity,but also has good photocatalytic stability.2.The S,Gd double-doped CN photocatalyst（SCN/Gd）was prepared by one-step copolymerization and used for the photocatalytic degradation of antibiotic SMR.The results show that with the doping of S and Gd atoms,CN was successfully striped into thin sheets,the specific surface area of the catalyst increased significantly which provided more adsorption and reaction sites for photocatalytic reaction.At the same time,the absorption region of the modified SCN/Gd catalyst shows red-shift,which broadened the absorption range of the catalyst to sunlight.In addition,the synergistic effect of S and Gd atoms effectively inhibits the recombination of photogenerated electron hole pairs and improves the mobility of photogenerated carriers.Under visible light irradiation,SCN/Gd-0.1 catalyst（the amount of GdCl₃?6H₂O is 0.10 g）shows the best degradation efficiency,which was 62%and52%higher than that of CN and sulfur-doped CN（SCN）,respectively.The capture experiments shows that superoxide radical（?O₂^-）was the main active species for photocatalytic degradation of SMR by SCN/Gd-0.1.