| As one of the most important elements in living organisms,nitrogen is one of the basic components of nucleic acids and amino acids,which is essential for life on earth.Nitrogen（N2）molecule is the main existence form of nitrogen.Due to its stable chemical properties,it cannot be used by organisms directly and the natural nitrogen fixation cannot meet the needs of human social development.Therefore,artificial nitrogen fixation is the most important way to solve the current dilemma.The photocatalytic nitrogen fixation technology uses sunlight as the driving force to catalyze the artificial nitrogen fixation reaction,which not only greatly saves energy,but is also environmentally friendly and pollution-free.It is a new technology with great development prospects under the current background of energy saving and emission reduction.Carbon nitride（CN）has become one of the most ideal photocatalytic nitrogen fixation materials due to its simple preparation method,low cost and easy availability of raw materials,and easy adjustment of the band gap.However,the current application of carbon nitride materials in artificial nitrogen fixation still faces some difficulties,such as low visible light utilization efficiency and easy recombination of photogenerated carriers.In order to further improve the catalytic efficiency of carbon nitride,this research modified the carbon nitride material from the molecular level,successfully controlled the electronic structure and energy band position of the material,promoted the migration of photogenerated carriers,and further inhibited the photogenerated carrier recombination.Therefore it improves the photocatalytic nitrogen fixation efficiency of carbon nitride materials.The specific research content are as follows:（1）The construction of 2D/2D MnO2-x/g-C3N4 Z-type heterojunction and its photocatalytic nitrogen fixation performance.The Z-type heterojunction is constructed between MnO2-x and CN through the redox pair of Mn,which consumes the electrons in the conduction band of MnO2-x and the holes in the valence band of 2D CN,so that more electrons can stay in the 2D CN.On the conduction band,nitrogen is reduced to produce ammonia.And the corresponding nitrogen fixation efficiency reaches 225mmol g-1 h-1,which is more than twice that of 2D CN.（2）The construction of Fe-doped CN system and its photocatalytic nitrogen fixation performance.The intermediate is prepared by a simple hydrothermal reaction,and then calcined in a muffle furnace under air conditions to obtain a yellow Fe-doped thin-layer carbon nitride.The prepared material has a thin porous tubular structure,which is beneficial to improve the utilization rate of light.After doping,the electronic structure of CN has changed significantly,the adsorption capability of N2 was enhanced.Consequently,the photo-generated electrons and holes of the doped material are inhibited from recombination and the migration rate of photoinduced carriers has been improved,and its nitrogen fixation efficiency has been increased to 647mmol g-1 h-1,which is more than 6 times higher than the nitrogen fixation performance of CN.（3）The construction of Mo-doped CN system and its photocatalytic nitrogen fixation performance.Using sodium molybdate as raw material,Mo-doped CN was synthesized by simple hydrothermal calcination.The material exhibits a porous foam morphology.In the DRS spectra,the absorption band edge of Mo-doped thin layer CN was observed a slight blue shift,indicating that the band structure of the material has changed,the band gap has become larger,and the photocatalytic redox ability has been promoted.In addition,the Mo-doped thin layer CN improves the migration efficiency of photogenerated carriers effectively,inhibits the recombination of photogenerated carriers in the semiconductor,and improves the photocatalytic nitrogen fixation efficiency of the material significantly.The nitrogen fixation performance of Mo-doped CN has been improved to 479mmol g-1 h-1. |
