Preparation Of C₃N₅ Material Loaded With Co-catalyst And Their Visible-Light-Induced Hydrogen Production Performance

Semiconductor-based photocatalytic hydrogen production is of great importance to solve the global energy crisis and environmental pollution.Especially,the development of new wide visible light absorbing semiconductor materials and noble-metal-free cocatalysts are the hotspots of current research.Among series of semiconductor materials,novel metal-free carbon nitride（i.e.C₃N₄）has attracted numerous attentions in the past decade,but its photocatalytic performance is limited by the wide band-gap and low photogenerated carriers separation efficiency.Recently,it has been reported novel N-rich C₃N₅possess narrower band gap and higher photocatalytic activity than conventional C₃N₄,which is promising in the field of photocatalytic hydrogen production in consideration of its facial preparation,low cost and environmentally friendly properties.However,there are few reports on C₃N₅,and the systematic research on its photocatalytic hydrogen production performance,photogenerated carrier separation and surface active site construction are still lacked,which is not conducive to the development and research of this type of new carbon nitride.Thus,on one hand,this dissertation conducts a systematic study on the photocatalytic hydrogen production performance of Pt loaded C₃N₅,and explores the influencing factors afford to its higher performance than that of traditional C₃N₄;On the other hand,nickel-based non-noble metal cocatalysts are loaded on C₃N₅ to improve the separation efficiency of photogenerated carriers and serve as reactive sites,and then further improve the photocatalytic hydrogen evolution activity.It is hoped that this research will provide new insights for the development and application of carbon nitride-based photocatalysts.The main research contents of this dissertation are as follows:1.Taking 3-amino-1,2,4-triazole as the raw material,C₃N₅ was synthesized by heat treatment at 500℃,and Pt nanoparticles were deposited on the material’s surface by chemical reduction method with NaBH₄.The photocatalytic hydrogen evolution performance of the material was comprehensively researched,and compared with traditional C₃N₄.The results reveal that the photocatalytic hydrogen evolution rate of C₃N₅ is～2.2 times that of C₃N₄ with 1.0wt% Pt as co-catalyst.It has good long-term stability of photocatalytic hydrogen production and high apparent quantum yield（AQY）,where the AQY at 420nm is 28.65%.Combining the results of DRS,PL and photo-current,it is found that C₃N₅ has a lower band gap and a wider visible light absorption range,as well as faster photo-generated e^-/h⁺separation efficiency.On the other hand,through thermogravimetric analysis and in-situ DRIFTS analysis,it is found that C₃N₅ adsorbs more H₂O molecules,which is also beneficial to promote the occurrence of surface water reduction reactions.This result provides new insights for the comparison research on the photocatalytic hydrogen production performance of different carbon nitride materials.2.Considering that the noble metal Pt as a scarce resource is not conducive to practical applications,three different nickel-based cocatalysts（Ni、S-Ni（OH）₂ and Ni_xS_y）are loaded on C₃N₅ by in-situ chemical deposition and in-situ hydrothermal methods to develop Ni-based non-noble-metal co-catalysts aiming to replace Pt,and enhance the photocatalytic hydrogen production activity of C₃N₅.The successful loading of the Ni-based cocatalysts on the C₃N₅ material are confirmed by XRD,HRTEM,SEM and XPS characterizations.The photocatalytic hydrogen production test proves that the photocatalytic hydrogen production activity of C₃N₅ material are significantly improved after the Ni-based cocatalysts are loaded.Under visible light irradiation,the enhancing effect of the three cocatalysts on the photocatalytic hydrogen production of C₃N₅ follows the order of Ni_xS_y>S-Ni（OH）₂>Ni.Under the optimal conditions,the photocatalytic hydrogen evolution rate of 1.0wt% S-Ni（OH）₂-C₃N₅ is 1450μmol/h,and the AQY at 420nm is 30.86%,which is comparable to the afore mentioned Pt-C₃N₅.The photocatalytic hydrogen evolution rate of 3.0wt% Ni_xS_y-C₃N₅ reaches 1595μmol/h,and the AQY at 420nm is 37.02%,which is higher than that of Pt-C₃N₅.The results of EPR,PL,photocurrent and EIS show that the photo-generated carrier separation efficiency of C₃N₅ are greatly enhanced after Ni-based cocatalysts are loaded,which further improves the photocatalytic hydrogen production performance of the composite material.This research provides a reference for the design of low-cost and highly efficient carbon nitride-based composite photocatalytic materials,which is conducive to promote the breakthrough of solar to hydrogen energy conversion efficiency.