Study On Morphology Regulation And Photocatalytic Activity Of G-C₃N₄

The environmental problems caused by the excessive emission of CO₂ and the energy crisis caused by the burning of fossil fuels have greatly restricted the sustainable development of today's society.Photocatalytic technology has been considered as one of the most promising technologies to alleviate the energy crisis and environmental problems since the concept of photocatalysis was put forward in1972.In the photocatalytic reaction,the driving force is light energy.Because the solar light is composed of ultraviolet,visible and infrared rays?about 5,43 and 52%respectively?.TiO₂,as the representative of the traditional photocatalyst,can only be excited by ultraviolet light because of its larger band gap?3.2 eV?,which greatly limits its application in photocatalysis.As a new type of two-dimensional photocatalytic material in 2009,g-C3N4 with a band gap of 2.7 eV has caused great interest in photocatalytic application because of visible absorption ability and good chemical stability.In addition,because of its high conduction band position,g-C₃N₄is often used in many photocatalytic reduction reactions,such as photocatalytic H₂production and photocatalytic CO₂ reduction.However,pure g-C₃N₄ shows unsatisfactory catalytic performance due to its low light utilization efficiency,easy recombination of photogenerated carriers and a small number of photocatalytic reaction sites.On the one hand,the photocatalytic activity can be improved by loading noble metal cocatalyst to improve the separation efficiency of photogenerated carriers and provide abundant active sites for H₂ production.However,precious metals are so expensive that we should optimize the utilization of precious metals in photocatalytic systems.Therefore,on the other hand,because pure g-C₃N₄ is consist of bulk structure of multilayer stacking,the carrier transport ability between layers is poor and the effective area of contact reaction is greatly reduced,the photocatalytic reaction efficiency is limited.It is an effective method to control morphology by stripping it into nanosheet structure to reduce carrier composition between layers or to construct three-dimensional porous structure to enhance light absorption ability and increase reactant contact area.The main contents of this thesis are as follows:1.Using urea as raw material,g-C₃N₄ with few layers were successfully prepared by thermal oxygen etching and ultrasonic assisted stripping.Triethanolamine?TEOA?was used as sacrificial agent and H₂PtCl₆ aqueous solution was used as Pt precursor.To explore the influence factors of photodeposition of Pt and its effect on hydrogen production performance.It is found that the strong interaction between the sacrificial agent TEOA and the Pt precursor limits the effective photoreduction of Pt.This may be due to the formation of a new complex?precursor of new Pt?by the reaction of TEOA with Pt⁴⁺in H₂PtCl₆ aqueous solution.The complex has a high reduction potential and cannot be reduced to metal Pt by electron photoreduction from CNS conduction band.2.3D porous g-C₃N₄ was prepared by thermal polymerization of urea at high temperature,and then quenched in ice water immediately.Compared with the samples prepared by naturally cooling in air,the related characterization revealed that the crystal structure and basic skeleton of g-C₃N₄ were not destroyed.In addition,because of the advantages of the sample in morphology and structure,the sample has high optical absorption ability,photogenerated carrier separation efficiency,and the three-dimensional porous structure is conducive to the adsorption and mass transfer process of CO₂,it shows excellent photocatalytic CO₂ reduction performance.