Effects Of Heterojunction On Photocatalyst Of Na TaO₃: La And Its Activity Of Photocatalytic Water Splitting

At present,the resources that human beings rely on for survival are constantly consumed,and severe energy shortage and environmental pollution are huge challenges facing human beings.Looking for clean,pollution-free and recyclable new energy has become one of the most important tasks for human.Hydrogen energy,as a secondary energy,has many advantages,such as clean,efficient,safe,storable,transportable,etc.Hydrogen energy has been widely considered as an ideal green energy without pollution in the new century.Therefore,it has been wildly concerned by scholars all over the world.At the same time,solar energy is widely distributing,clean and renewable.Therefore,using solar energy to decompose water to prepare H₂ and O₂ has attracted more and more attention as a potential system for clean hydrogen production,and using semiconductor catalyst to decompose water to produce hydrogen is one of the most ideal ways.Photocatalyst plays an important role in the process of photocatalytic water decomposition for hydrogen production.At present,it has been found that a large number of semiconductor photocatalysts can achieve one-step water decomposition,for example,SrTiO₃,KTaO₃,Na TaO₃ and etc.Perovskite NaTaO₃ has attracted much attention due to its strong photocatalytic water decomposition efficiency in the ultraviolet wavelength.In the case of ultraviolet irradiation,the electrons and holes of Na TaO₃ will be separated and reduced and oxidized with water to generatehydrogen and oxygen.However,NaTaO₃ doped with La can make the crystal surface appear orderly stepped structure,which is conducive to the separation of electrons and holes and improve the efficiency of photocatalytic.However,the traditional powder catalyst has the following disadvantages as follows.,Firstly,the powder photocatalyst needs to be dispersed in water to participate in the reaction during the process of photocatalytic.In this way,the catalyst dispersed in the upper layer can not only reduce the amount of hydrogen production when the light irradiates the catalyst in the bottom layer,but also is not convenient for recycling.Secondly,the gas produced in the process of photocatalytic water splitting is a mixture of hydrogen and oxygen.Finally,the hydrogen generation potential of the powder catalyst is close to the oxygen generation potential,and it is located on the surface of the catalyst,hence,the reverse reaction is more likely to occur,resulting in a lower efficiency of hydrogen generation.Therefore,based on the disadvantages and advantages of traditional powder photocatalyst,NaTaO₃ doped with La was chosen as the photocatalyst.Firstly,Ni/NiO/NaTaO₃: La thin film photocatalyst was prepared with Ni sheet as the substrate,and NiO was loaded on it by simple annealing to improve the efficiency of photocatalytic and solve the complex problem of NiO loading method.Secondly,in order to analyze the PN combination had a positive effect on the photocatalytic efficiency of Na TaO₃: La,Ti/TNT/N-P/NaTaO₃: La thin film photocatalyst based on Ti sheet was prepared to improve its photocatalytic efficiency.The specific research content is as follows:?1?Ta₂O₅,Na₂CO₃ and La₂O₃ were used as reaction materials.NaTaO₃: La powder photocatalyst was prepared by high temperature solid phase reaction.Then Ni sheet was used as substrate,and the Ni/NaTaO₃: La thin film photocatalyst was prepared by screen printing technology.Ni/NiO/NaTaO₃: La thin film photocatalyst was formed by annealing in air,and the influence of different annealing temperatures on the activity of photolysis water was investigated.The photocatalytic activity of Ni/NiO/NaTaO₃: La was 10.83 mol/h�cm²,which was twice that ofNi/NaTaO₃: La.In addition,according to the results,when the samples at 700 ?annealing,the highest activity of photocatalytic decomposition of water,show that the formation of the temperature on the NiO and light catalytic efficiency has the very important influence.?2?Ti O₂ nanotubes were prepared using Ti sheets as the substrate as the electron transport layer?TNT?.On this basis,n-type semiconductor Ti O₂ nanofilms?N?and p-type semiconductor NiO films?P?were prepared to form PN junction.Then NaTaO₃: La photocatalyst powder was processed by screen printing and annealed to form Ti/TNT/N-P/NaTaO₃: La thin film photocatalyst.The preparation of Ti O₂ nano-thin films was mainly based on sol gel as the precursor,and the method of spin coating was used to prepare dense nanocrystalline thin films,and the influence of different precursor concentration,spin coating speed and number of spin coating on n-layer Ti O₂ nano-thin films was explored to find the optimal conditions for the preparation of dense Ti O₂ thin films.NiO thin films were prepared by chemical water bath deposition,and the effects of different number of coating cycles on the photocatalytic efficiency of Ti/TNT/N-P/NaTaO₃: La thin films were investigated.The results show that when the number of coating layers were four,Ti/TNT/N-P/NaTaO₃: La thin film photocatalyst has the highest photocatalytic efficiency,and the gas production is 8.14 ?mol/h�cm².This is mainly because the n-type layer prepared by the four-layer rotary coating has better film formation and is more conducive to the formation of PN junction.Compared with photocatalytic efficiency of Ti/TNT/N-P/NaTaO₃: La,the photocatalytic efficiency of the latter is twice that of the former.It is observed that PN pair plays a positive role in photocatalyst.At the same time,hydrogen and oxygen can be generated with high efficiency on both sides of Ti substrate,which has solved the insufficiency of traditional powder photocatalyst.