Efficient Preparation And Modification Of Graphite-like Carbon Nitride Nano-photocatalyst With High Specific Surface Area

Graphite phase carbon nitride（g-C₃N₄）has excellent photocatalytic performance,strong hydrophilicity,affordability,and environmental friendliness,making it the most promising photocatalytic material in the field of photocatalysis.The path of using g-C₃N₄ to catalyze visible light driven water splitting to prepare clean energy fuel hydrogen is considered one of the most environmentally friendly ways to obtain green energy.In this paper,g-C₃N₄ was taken as the research object.In order to solve the key problems such as low specific surface area,less exposure of active site,high recombination rate of photogenerated carriers,narrow absorption range of visible light,and low yield,the research goal of improving the photocatalytic hydrogen production performance and yield of graphite phase carbon nitride was achieved by optimizing the precursor and thermal polymerization process in the traditional method of urea thermal polymerization to prepare g-C₃N₄.At the same time,diffractometer,photoelectron spectroscopy,infrared and ultraviolet spectroscopy,scanning electron microscope,transmission electron microscopy and photocatalysis analyzer were used to study the physical,chemical,optical and photocatalytic properties vary with the amount of L-aspartic acid（LAA）introduced into the precursor;on the other hand,the influence of the mass ratio of urea and melamine in the precursor on the preparation yield,physical,chemical,optical,and photocatalytic hydrogen production performance of g-C₃N₄ products was studied.Submicron short tubular oxygen doped graphitic carbon nitride was successfully prepared by conventional thermal polymerization using urea as precursor and L-aspartic acid as modifier.An appropriate amount of L-aspartic acid（LAA）promotes the formation of submicron short tubular oxygen doped graphitic carbon nitride from urea precursor,improves the specific surface area and porosity of graphite phase carbon nitride,expands the optical absorption range,and improves the photocatalytic hydrogen production efficiency.Under visible light irradiation,the rate of LAA/C₃N₄photocatalytic decomposition of water to produce hydrogen first increased and then decreased with the increase of L-aspartic acid content.When the amount of LAA introduced is 8 mg,the specific surface area of obtained product 8-LAA/C₃N₄is 59.34 m² g^-1,and the pore volume is 0.29 cm³ g^-1.The photocatalytic hydrogen evolution rate is as high as 3.11 mmol g^-1 h^-1,which is 311 times that of undoped g-C₃N₄.Under high oxidation etching conditions of high temperature salt spray in a mixed solution of Na Cl and KCl,a lower amount of LAA promotes the formation of urea precursors into graphite phase nitride carbon co doped with Na⁺,K⁺and O with better semiconductor optical and photocatalytic properties.The thickness,specific surface area and pore volume of LAA/Na/K/C₃N₄ nanosheets first decrease and then increase with the increase of L-aspartic acid content.Under visible light irradiation,the rate of photocatalytic water decomposition to hydrogen production first increases and then decreases with the increase of L-aspartic acid content.When the introduction amount of L-aspartic acid is 2 mg,the specific surface area of 2-LAA/Na/K/C₃N₄ is 61.18 m² g^-1,and the pore volume is0.30 cm³ g^-1.Under the synergistic effect of Na⁺,K⁺and O co doping,the photocatalyst shows the best photocatalytic activity,and the photocatalytic hydrogen evolution rate is as high as 10.99 mmol g^-1 h^-1,which is 1100 times as that of undoped g-C₃N₄,3.53 times as that of 8-LAA/C₃N₄,and 1.65times as that of Na/K/C₃N₄.Under the conditions of thermal polymerization,the mass ratio of melamine to urea has a significant impact on the yield,morphology,specific surface area,and photocatalytic hydrogen production performance of g-C₃N₄ nanosheets.Melamine promotes the formation of g-C₃N₄nanosheets with higher yield from urea precursor.With the further increase of melamine addition,although the yield continues to increase,the specific surface area,porosity,and photocatalytic performance of the material all decrease accordingly.When the addition amount of melamine is 3 g and the content of urea is 9 g,the graphite phase carbon nitride material（3U1M）exhibits the highest specific surface area of 40.74 m² g^-1 and pore volume of 0.23 cm³ g^-1.The 3U1M photocatalyst has the most excellent photocatalytic activity,and its H₂ production is 1.3 times that of g-C₃N₄ prepared with pure urea as the precursor.