The Enhancement Of The Photo-induced Charge Separation And Visible Light Photocatalytic No Purification Of G-C₃N₄

As a harmful gas of air pollution,low concentration of NO is difficult to remove completely by traditional methods.Semiconductor photocatalytic technology can utilize solar energy to degrade nitric oxide with a low concentration of PPb level.This environmentally friendly technology is sustainable,clean-energy,high efficiency without secondary pollution.Graphitic carbon nitride?g-C₃N₄?,an inexpensive metal-free visible-light photocatalyst,has great potential for applications to environmental cleanup.However,the photocatalytic efficiency of g-C₃N₄ is limited because its recombination rate of photogenerated electrons and holes is high.Therefore,it is studied in this paper how to promote the separation of charge carriers and improve the photocatalytic performance of NO degradation.To enhance the separation of charge carriers,three modified methods are presented such as the construction of type I and type II g-C₃N₄/g-C₃N₄ metal-free isotype heterostructures,the decoration of g-C₃N₄ nanosheets with Pd nanoparticles and La³⁺-doped carbon nitride.The as-prepared samples are systematically characterized by XRD,SEM,TEM,XPS,FT-IR,BET,UV-vis DRS,PL,ESR,SPV,photocurrent,impedance spectroscopy and so on.The characterization above contributes to the analyses of microstructure,charge carriers separation,radical species and NO photocatalytic performance for g-C₃N₄.The research conclusions are as follows.?1?Type I and type II g-C₃N₄/g-C₃N₄ metal-free isotype heterostructures:Easily available composite precursors such as melamine and urea?dicyandiamide and urea?are used and thermally treated in situ creating type I?type II?g-C₃N₄/g-C₃N₄ metal-free isotype heterostructures.With different transfer paths of charge carriers,the intrinsic drawback of fast charge recombination can be overcome by type I and type II g-C₃N₄/g-C₃N₄ heterostructures.For the removal of ppb-level NO in air,the type I andtype II g-C₃N₄-based heterostructures demonstrate highly enhanced photocatalytic activity and stability in comparison with pure g-C₃N₄,which can be directly ascribed to the promoted charge separation and the limited fast charge recombination.?2?g-C₃N₄ nanosheets decorated with Pd nanoparticles: g-C₃N₄ nanosheets decorated with Pd nanoparticles?C₃N₄-Pd?are prepared and demonstrated from the different photocatalytic behaviors of C₃N₄-Pd in the oxidation and reduction reaction.C₃N₄-Pd displays highly enhanced photocatalytic activity in oxidation removal of NO because Pd nanoparticles?NPs?can shuttle the photoexcited electrons from g-C₃N₄ and the Schottky barrier formed between g-C₃N₄ and Pd NPs can prevent the reverse electron flow from Pd to g-C₃N₄.While the photo-oxidation of NO is greatly improved,the photocatalytic reduction of CO2 is significantly inhibited,which can be ascribed to the decreased reducibility of the electrons in g-C₃N₄ caused by the transfer of photogenerated electrons from g-C₃N₄ to Pd NPs.The present work can provide new perspectives not only for degradation of pollutants,but also for photocatalytic applications in hydrogen or oxygen production,organic synthesis and solar cell.?3?La³⁺-doped amorphous carbon nitride photocatalyst:With urea and lanthanum carbonate as precursor,La³⁺-doped amorphous carbon nitride is prepared by thermal polymerization.With the increase of La2?CO3?3,C₃N₄ gradually turns into amorphization.During the heat treatment,CO32-can attack the hydrogen bonding between C₃N₄ layers and destroy the ordered interlayer melon strands,which makes amorphous carbon nitride short-range ordered and long-range disordered.Amorphization with band tails or local states can shorten the band gap and improve the visible light utilization.At the same time,the internal defects from amorphism and La³⁺dopant can capture photogenerated electrons or holes,promote charge separation,increase the production of ·O2-and ·OH radicals,and enhance the photocatalytic activity.In addition,La³⁺-doped amorphous carbon nitride is beneficial to the adsorption of NO2-intermediate,improving the photocatalytic oxidizability of NO.