Research On Novel Two-dimenstional Photocatalytic Materials Based On Stannum Triphosphide Monolayer

With the development of human beings,the demand for energy is increasing.However,the traditional methods of producing energy often cause great pollution to the environment,so it is imperative to develop clean energy sources.Photocatalytic of water splitting is a novel method to produce hydrogen and oxygen with zero pollution,regarding semiconductor material as catalyst,sunlight as power and water as raw stuff.So in recent years,it has been widely concerned by the reaserchers.Among the materials that can be used for photocatalysis,two-dimensional materials stand out by virtue of their excellent optical / electrical properties?such as ultra-high photocurrent density,the high IPCE,low recombination rate of photo generated carriers,etc.?.The purpose of this work is to improve the photocatalytic efficiency of two-dimensional materials and find novel photocatalytic materials with high photocatalytic efficiency.SnP₃ monolayer is a new type of two-dimensional semiconductor material,which has ultra-high infrared / visible light absorption capacity and carrier mobility.These properties are necessary for excellent photocatalytic materials.However,due to its small band gap,it is difficult to conduct overall photocatalytic decomposition of water,which limits the application of SnP₃ monolayer.In order to make SnP₃ be used in photocatalytic decomposition of water,its optical / electrical properties must be changed.Luckily,a large number of experimental and theoretical studies have proved that atomic doping and substitution can significantly change the geometry and electronic structure of materials,thus improving their optical / electrical properties.In this work,we use nitrogen atom to replace the phosphorus atom of SnP₃ monolayer,and study the optical / electrical properties of SnP₃ monolayer under different doping concentration and the ability of photocatalytic decomposition of water.The simulation results show that nitrogen atom doping can effectively adjust the band gap and work function,improve the reduction of catalytic efficiency caused by hydrogen electrode over potential,but still can not carry out overall photocatalytic water splitting.However,with the increase of nitrogen doping concentration,the electronic structure of SnP₃ monolayer is changing,which shows that there is still room for the improvement of the properties of SnP₃ monolayer.Follow the idea above,SnN₃ monolayer is proposed,and the comprehensive property simulation of this new material is carried out.The results show that SnN₃ monolayer has the ability of overall photocatalytic decomposition of water and maintains other excellent photoelectric properties of SnP₃ monolayer.It is a novel photocatalytic material that has never been found before.In order to confirm the possibility of the existence of this new material as much as possible,the stability simulation analysis of SnN₃ including phonon spectrum was carried out.The results show that SnN₃ monolayer has good energy stability,structural stability and thermodynamic stability,and it can exist stably in theory.In order to further study the photocatalytic performance of SnN₃ monolayer,the carrier mobility of SnN₃ monolayer was calculated.The results show that SnN₃ monolayer has much higher carrier mobility than SnP₃ monolayer.Then,the adsorption / desorption of water and hydrogen molecules on the surface of the material was simulated.It was found that SnN₃ monolayer has certain attraction and repulsion to water and hydrogen molecules,which is conducive to the occurrence of water decomposition reaction and the regeneration of photocatalyst.Finally,the Gibbs free energy change of water splitting on the surface of SnN₃ monolayer is calculated,and it is divided into three cases of "without light","light" and "light + electric field" for discussion.The results show that "light + 0.95 V electric field" is the theoretical condition for water decomposition reaction to proceed in the positive direction.In this study,the electronic structure,optical response and photocatalytic properties of pristine SnP₃,nitrogen doped SnP₃ and SnN₃ monolayers were studied theoretically by the first-principles calculations.