Theoretical Research Of Photocatalysis Based On Low-Dimensional Carbon Compounds And Carbon Nitride

Photocatalysis has great potential in obtaining new pollution-free renewable energy sources,chemical feedstock synthesis,and pollutant degradation,and thus has become a hot spot for current research in physics and chemistry.However,the application of photocatalysis has high requirements on the band edge position and band gap of catalyst energy bands,which makes us need a deeper understanding of band engineering in photocatalysts.In this paper,the application of energy band engineering in low-dimensional materials is investigated for photocatalytic overall water splitting and nitrogen fixation through first-principles calculations and design effective catalysts for each.Our research covers the following three main aspects:（1）Based on the Kohn-Lutinger effective mass theory,a single boron atom is intrduced into g-C₃N₅ and adjusted the level of impurity states by adjusting the doping sites to obtain a photocatalytic total hydrolysis catalyst with both high redox ability and wide light absorption range.At the same time,the impurity state effectively separates photogenerated electrons and holes in space.（2）The traditional Kohn-Lutinger effective mass theory relies only on the projected density of states of the substitution atoms to predict impurity levels,which is not sufficient.The impurity atom can change electrostatic potential gradient and polarity,then significantly affect the spatial electron density around the substituted atom,which further adjusts the impurity level position of P doped g-C₃N₅.The band edge of doped structures can stride the potential requirements of POWS.Furthermore,the doping strategy also enhances the polarity and surface dipole of the catalyst,promoting the adsorption and subsequent splitting of water molecules.（3）A new N₂ immobilization strategy is proposed by the direct formation of*N₂^-excited states on diamond clusters decorated with metal-free boron.The surface-doped B atom promotes the adsorption of N₂ while inhibiting the adsorption of H⁺.Under the irradiation of photons with an energy of only 4 e V,the valence electrons of the doped diamond clusters are directly excited to theπ^*orbitals of*N₂,which not only further improves the selectivity but also forms*N₂^-excited states with sufficient lifetime（10 ns）for the free N₂,which requires photons with an energy of 11eV to do so.