Controllable Construction Of Modified Carbon Nitride/Two-dimensional Titanium Carbide Schottky Photocatalytic Material And Enhancement Mechanism Of Hydrogen Production Performance

The use of semiconductor photocatalytic materials to convert sustainable solar energy into hydrogen energy offers an alternative to fossil fuel consumption.However,how to use photocatalytic decomposition of water to produce hydrogen remains a challenge.So far,many semiconductor materials with the ability to decompose water to produce hydrogen have been reported,but most of them have inherent defects such as secondary pollution,low specific surface area,poor charge migration capacity and high recombination rate of photogenerated electron-hole pairs,which lead to low efficiency of hydrogen production.therefore,it is very challenging to design novel and efficient photocatalytic hydrogen-producing composites.The results show that the best way to achieve high efficiency solar energy-hydrogen energy conversion is to make perfect interfacial composite?heterostructure construction?between nanomaterials with definite size and matching energy level band gap.Carbon nitride?g-C₃N₄?has the characteristics of visible light absorption,moderate band gap width,stable structure,etc.However,its low visible light utilization rate and poor charge transfer ability limit the photocatalytic hydrogen production capacity of g-C₃N₄.In this paper,Ti₃C₂,a two-dimensional material with good morphology,was firstly prepared and then compounded with protonized g-C₃N₄ in different ways to form Ti₃C₂/protonized g-C₃N₄composite with good interface contact.With metal conductivity,Ti₃C₂ can be used as a medium for photogenic carrier transmission in composite materials to improve the charge transmission capacity,thus enhancing the photocatalytic hydrogen production activity of protonated g-C₃N₄.The specific contents of the study are as follows:?1?MXene material has excellent structural stability,adjustable surface functional group and good conductivity.Therefore,it can be used as an excellent electron transfer medium in photocatalytic reactions to improve the photocatalytic performance of the catalyst.A new two-dimensional MXene material?Ti₃C₂?was prepared by HF etch,intercalation and ultrasonic stripping of MAX material?Ti₃AlC₂?to remove Al elements.The morphology and thickness of MXene films can be observed by SEM?TEM?AFM.Zeta potential measurements show that the surface potential is negative,which provides effective evidence for the construction of composite heterostructures in the later stage.?2?Protonation of graphite phase g-C3N4 with dilute hydrochloric acid?PCN?alters the surface electrical properties to make it positively charged,constructing the Ti₃C₂/PCN composite by electrostatic self-assembly method with negatively charged MXene materials.the results show that the protonation of carbon nitride cannot only change its surface electrical properties but also reduce its band gap to improve the utilization of visible light.Electrochemical property tests show that compared with pure carbon nitride,PCN's charge transfer ability is significantly improved and its charge transfer resistance is reduced,which is beneficial to the improvement of photocatalytic activity.According to the hydrogen production evaluation,the hydrogen yield of PCN was improved compared with that of pure carbon nitride,and was further increased when it was combined with Ti₃C₂ material.?3?Using the ultra-thin two-dimensional nanomaterial Ti₃C₂ as the construction platform,the protonated melamine?DCDA?and Ti₃C₂ were uniformly mixed,and the Ti₃C₂/PDCN photocatalytic composite material was constructed in situ by thermal polymerization.The results of SEM,TEM and AFM analysis results show that the composite material has good two-dimensional morphology and close contact interface.The evaluation and analysis of hydrogen production show that the hydrogen production of in-situ composites is much higher than that of pure carbon nitride composites synthesized by electrostatic self-assembly method,which may be more compact and more beneficial to charge transmission than the heterojunction constructed by electrostatic self-assembly method.The electrochemical properties of photocatalysis materials show that Ti₃C₂ materials play a good role in charge transfer in the composite system.Because of the excellent metal conductivity of Ti₃C₂,the electrons in the valence band of excited semiconductor materials can be quickly transferred to the conduction band and the reduction hydrogen production reaction can take place on the surface of Ti₃C₂ to reduce the recombination rate of electron holes,thus improving the photocatalytic activity of PDCN.