Theoretical Design And Performance Study Of Two-Dimensional Carbon Based Composite Photocatalytic Materials

Clean hydrogen production by photocatalysis is considered as an effective means to solve the current energy crisis.As one of the hottest materials in the field of two-dimensional materials,graphene fails to be used as an efficient photocatalyst due to its zero band gap characteristics.The carbon based materials obtained by the modification of the graphene not only retain their original excellent properties,but also improve some unfavorable defects.Therefore,they have potential applications in the field of photocatalysis.In recent years,with the continuous expansion of the depth and breadth of material simulation calculations,first-principles calculation has also developed into an important tool for calculating and analyzing material properties.In this paper,van der Waals heterojunctions are constructed from carbon-based materials.On the basis of the first-principles calculation,the types of heterojunctions,electronic structures,interface effects and photocatalytic activity are comprehensively analyzed.The purpose is to explore efficient photocatalysts with stable structure and excellent performance that can be used for photocatalytic decomposition of water to produce hydrogen.The main contents are as follows:（1）Study on photocatalytic properties of heterojunction formed by wide band gap semiconductors（SiC and GaN）and redox graphene oxide（RGO）:Based on the analysis of electronic structure and interface characteristics,it is concluded that Si C/RGO composite is a type-I heterojunction,which is a potential long-life optoelectronic material.Ga N/RGO composite is an ideal type-II heterojunction for photocatalytic splitting of water for hydrogen production.Thanks to its structural characteristics,the recombination of photogenerated electrons and holes is limited,which greatly improves the photocatalytic performance of the heterojunction.Moreover,the band gap of Ga N/RGO heterojunction of 1.92 e V not only ensures the absorption of visible light,but also ensures that the redox potential of water can be crossed when p H=0,which is an important condition for realizing photocatalytic splitting of water for hydrogen production.In addition,the oxidation reaction and reduction reaction occur at a relatively synchronous rate,which speeds up the occurrence rate of the entire reaction and further improves the efficiency of photocatalysis.（2）Study on photocatalytic properties of C₃N/WS₂ heterojunction formed by carbon based two-dimensional semiconductor（C₃N）and two-dimensional transition metal dihalide compounds:The thermodynamic stability,dynamic stability and mechanical stability of the heterojunction are proved by molecular dynamics simulation,phonon dispersion spectrum and calculation of elastic constants.The electronic structure,interface effect and bader charge quantitative analysis are combined to determine that C₃N/WS₂ composite is a type-Z heterojunction,and has good light absorption performance in the visible range.According to the characteristics of charge transfer and separation in Z-type heterojunction,although the band gap of C₃N/WS₂ heterojunction is relatively small（<1.23e V）,it also can perfectly realize total water splitting from p H=0 to p H=7.Carrier mobility and exciton binding energy can also prove that the heterojunction owns good photocatalytic performance.In addition,the calculation of overpotential（0.83V）shows that C₃N/WS₂ heterojunction has excellent oxygen evolution ability,which is expected to become a new efficient photocatalyst.