Microstructure Manipulation And Visible-light Catalytic Activity Intensification Of G-C₃N₄-based Photocatalytic Materials

Harvesting solar energy to trigger the semiconductor photocatalysis has great potential to solve the growing worldwide energy and environment crisis.The photocatalysts are motivated to generate active electrons and holes,further achieving the redox reaction.With booming interest in earth-abundant and intrinsic visible-light response photocatalysts for potential solar conversion,enormous attention has been paid to graphite-like carbon nitride?g-C₃N₄?in recent years because of its unique properties.g-C₃N₄ possesses a band gap of?2.7 eV,which enables a visible-light-active photocatalysis.Currently,due to a majority of charge carriers are lost by recombination and a low light-harvesting capacity,the solar energy conversion efficiency of pristine g-C₃N₄ is still low?quantum efficiency is around 0.1%at 420–460 nm?.This paper carried out a systematic and in-depth study on the materials preparation,micro-structure manipulation,heterojuntion construction and the performance intensification of g-C₃N₄-based photocatalysts,aiming at solving some key issues in g-C₃N₄ research and development.First,a facile approach is developed to synthesize the g-C₃N₄/TiO₂ nanosheet by combining the biomimetic mineralization of TiO₂ with the delamination of bulk g-C₃N₄,which exhibits 3 times higher degradation efficiency for dyes than g-C₃N₄under visible light.Based on this work,a triple g-C₃N₄/TiO₂/Ag photocatalyst was further designed to extend the visible light spectra.Second,inspired by the hierarchical structure and excellent performance of thylakoids,multi-shell g-C₃N₄nanocapsules were synthesized by using multi-shell SiO₂ nanospheres as hard template.The resultant triple-shell g-C₃N₄ nanocapsules display superior H₂-generation activity to the single-shell and double-shell counterparts owing to the excellent visible-light harvesting and electron transfer properties.Third,a three-dimensional?3D?porous g-C₃N₄/graphene oxide aerogel?CNGA?has been prepared by the hydrothermal co-assembly of g-C₃N₄ and GO nanosheets,in which g-C₃N₄ act as photocatalyst,and GO support the 3D framework and promote the electron transfer simultaneously.In CNGA,the highly interconnected porous network renders numerous pathways for rapid mass transport and multi-reflection of incident light;meanwhile the large planar interface between g-C₃N₄ and GO nanosheets increases electron transfer rate.Consequently,the optimized CNGA sample could reduce CO₂ into CO with a high yield of 23 mmol g^-1?within 6 h?,exhibiting about2.3-fold increment compared to pure g-C₃N₄.Fourth,a tubular g-C₃N₄/g-C₃N₄ isotype heterojunction?TCNH?photocatalyst was designed for cooperative manipulation of the oriented transfer of photogenerated electrons and holes to pursue high catalytic performance.The differences in electronic band structures of g-C₃N₄?cyanuric acid and melamine?and g-C₃N₄?urea?ensure the optimal matching between conductive band and valence band levels.TCNH exhibits the outstanding photocatalytic activity for H₂ production and pollutant elimination.Hopefully,the above studies could offer some methodological and theoretical basis for the design of high activity,stability and visible-light response photocatalysts,meanwhile,offer some reference for the exploitation of g-C₃N₄ photocatalysts and their composite materials.