Fabrication And Study Of Graphitic Carbon Nitride?g-C₃N₄?-Based Photo-catalysts For Water Splitting Under Visible-Light

Since the pioneering research by Honda and Fujishima on photo-catalytic water splitting in 1972,great efforts have been devoted to explore efficient and sustainable photocatalysts for industrial applications.Hitherto,the advances of photocatalytic materials for hydrogen evolution are still restricted by some critical factors:utilization of visible light,chemical stability and cost.Recently,graphitic carbon nitride?g-C₃N₄?has emerged as a promising organic semiconductor photocatalyst to drive water splitting under visible light owning to its proper band structure,superior physicochemical stability and high abundance.Thus far,many strategies have been explored to boost its photocatalytic performance,such as nanostructure design for modifying the surface and textural structures,heteroatom doping?e.g.,B,S,P,I?and copolymerization for tuning its optoelectronic properties,and coupling with other?semi-?conductors for facilitating charge separation.In this paper,holey g-C₃N₄nanosheets,multiple doped g-C₃N₄ and g-C₃N₄-based ternary homojunction were successfully fabricated and their photocatalytic performance were carefully investigated by hydrogen evolution from water.The main studies are listed in following three aspects:1.Fabrication of holey g-C₃N₄ nanosheets and investigation on their photocatalytic hydrogen evolution performance.Few-layered holey g-C₃N₄ nanosheets?CNS?were fabricated by simply introducing a piece of nickel foam over the precursors during the heating process.The as-prepared CNS with unique structural advantages exhibited superior photocatalytic water splitting activity than bulk g-C₃N₄?BCN?under visible light??31 fold?.Its outstanding photocatalytic performance originated from the high specific surface area and mesoporous structure,which endows CNS with more active sites,efficient exciton dissociation and prolonged charge carrier lifetime.Moreover,the obvious up-shift of the conduction band leads to a larger thermodynamic driving force for photocatalytic proton reduction.This methodology not only had the advantages for the direct and green synthesis of g-C₃N₄ nanosheets,but also paved a new avenue to modify the textural of g-C₃N₄ for advanced applications.2.Fabrication of multiple doped g-C₃N₄ and investigation on their photocatalytic hydrogen evolution performance.An in-situ multiple heteroelements?sodium,oxygen and iodide?doping strategy based on molten-salt-assisted route was developed to prepare a green-colored carbon nitride?GCN?.The as-prepared GCN yielded 25.5 times higher H₂ evolution rate than that of bulk polymeric carbon nitride under visible light.Experimental characterization data demonstrated that the GCN delivered an increased hydrophilicity,specific surface area and negative shift of the conduction band.As confirmed by time-resolved PL spectra,DMPO spin-trapping EPR analysis and so on,the excellent activity was dominantly ascribed to the greatly enhanced hydrophilicity,and subsequently efficient interfacial charge transfer and hydrogen liberation.This work highlighted the importance of surface modulation through multiple earth-abundant elements incorporation for the designing of advanced and practical photocatalysts.3.Construction of g-C₃N₄-based ternary homojunction and investigation on their photocatalytic hydrogen evolution performance.A cyano and cyanamide co-modified g-C₃N₄?CN-KSCN/NH₄Cl?was realized by an in-situ synthesis strategy of introducing KSCN and NH₄Cl during the polymerization of melamine for modulating the structure and exciton properties of the corresponding g-C₃N₄.As a result,the CN-KSCN/NH₄Cl sample exhibits striking enhanced visible-light photocatalytic hydrogen evolution performance in comparison with reference samples,especially bulk g-C₃N₄?17.8times higher?.The excellent activity should be ascribing to the accelerated exciton dissociation after introducing these two types of functional parts,and hence giving rise to the significant enhancement of hot carrier generation.This work not only provides a new avenue for rational design of polymeric photocatalysts,but also deepen the mechanistic understanding of excitonic regulation.