Design Of New Low-dimensional Materials Based On Nitrogen-heterocyclic Carbene And Theoretical Study On Their Optoelectronic And Catalytic Properties

Low-dimensional carbon materials have received extensive attention from researchers in the field of materials due to their unique structures and excellent properties.According to the dimension,low-dimensional carbon materials can be divided into:zero-dimensional,one-dimensional,two-dimensional carbon materials.Its representative materials are fullerenes with cage-like structure;carbon nanotubes with hollow cylindrical shape and graphene with a single-layer regular hexagonal lattice structure.These low-dimensional carbon materials show broad application prospects in optoelectronic devices,energy storage,photocatalysis and other fields due to their excellent electrical,optical,and mechanical properties,but there are still many challenges.The properties of materials are often determined by their structure,so modifying the structure of low-dimensional materials is an important means to improve their properties and expand their applications.Compared with other materials,the properties of low-dimensional materials are easier to control.Generally,operations such as vacancy and doping can change or even optimize the properties of materials.In this paper,we designed a series of novel low-dimensional carbon materials based on Nitrogen-heterocyclic carbenes,and investigated their structural stability,electronic properties and optical properties through first-principles calculations.Secondly,we explored the application of new two-dimensional carbon material adsorbed transition metal structure in the field of catalytic nitrogen reduction.The specific work and main discussion contents are as follows:（1）Based on the combination of classical five-membered Nitrogen-heterocyclic carbenes（NHCs）and low-dimensional carbon materials（zero-dimensional fullerenes,one-dimensional carbon nanotubes,two-dimensional graphene）,a series of novel Nitrogen-heterocyclic carbene low-dimensional carbons materials were designed.The giantπ-conjugation and steric hindrance of low-dimensional carbon materials jointly stabilize NHCs in low-dimensional carbon materials.The thermodynamic stability of Nitrogen-heterocyclic carbene low-dimensional carbon materials is linearly related to the nitrogen content in the unit cell.The binding energy is between-0.56 eV and-1.24 eV,which is lower than that of g-C₃N₄,indicating that the designed material is thermodynamically stable.The results of dynamic calculations show that the one-dimensional and two-dimensional Nitrogen-heterocyclic carbene carbon materials are very stable at 300K,and the atomic configuration of the two-dimensional nitrogen-containing heterocyclic carbene carbon material is still well maintained at 700K.In terms of electronic properties,the energy band gap of the designed materials is between 0 and 1.74 eV,that is,from metals to semiconductors.The differential charge calculation results show that the NHCs in the designed materials still have lone pair electrons of NHC molecule,and can adsorb C atoms,Fe atoms,CO molecules and BH₃molecules,indicating that the designed material not only maintains the classical properties of NHC molecules.characteristics,and showed new amphiprotic characteristics.In terms of optical properties,these Nitrogen-heterocyclic carbene low-dimensional carbon materials break the isotropic limit of graphene and exhibit the advantages of anisotropy.（2）We explored the performance of two-dimensional Nitrogen-heterocyclic carbene carbon materials in catalytic nitrogen reduction.The two-dimensional Nitrogen-heterocyclic carbene carbon materials show obvious spin polarization after adsorbing Fe atoms.Therefore,the electrocatalytic nitrogen reduction ability of the two-dimensional system adsorbed Fe structure was investigated.The results of free energy change for electrocatalytic nitrogen reduction show that the free energy barrier of the structure after iron adsorption is only 0.66 eV in the far path of nitrogen reduction,so the two-dimensional Nitrogen-heterocyclic carbene carbon material after anchoring Fe can be used as a catalyst with good catalytic ability for the reduction of nitrogen molecules.Subsequently,the catalysts were extended to 3d,4d,5d transition metal atom-doped two-dimensional structures,and their catalytic performances as heterogeneous catalysts for electrocatalytic nitrogen reduction were systematically investigated.Our results show that the two-dimensional Nitrogen-heterocyclic carbene carbon materials doped with Ti,V,Mn,and Nb have a good ability to activate nitrogen molecules,and the step diagram of the free energy change of electrocatalytic nitrogen reduction shows that Ti,V,Mn,and Nb doped two-dimensional systems have potential as electrocatalytic nitrogen reduction catalysts with potential barriers of 0.81,0.75,0.81,and 0.62 eV,respectively,which provide a powerful route for the green production of ammonia.