Synthesis,Characterization And Photocatalytic Hydrogen Production Performance Of Carbon Nitride Modified With Non-metallic Elements

Nowadays,the environmental pollution and energy consumption are becoming prominent problems worldwide,which needs to be solved urgently.Recently,photocatalytic hydrogen production has received widespread attention due to its advantages of high efficiency,safety,environmental-friendly and easy to operate.Among the many studied photocatalytic materials,graphitic carbon nitride（g-C₃N₄）has been widely researched due to its environmental-friendly preparation process,abundant yield and stable physicochemical properties.However,the bulk g-C₃N₄obtained by the well-known pyrolysis method has two major problems,the limited utilization of visible-light and the high recombination rate of photoexcitated carriers,which severely limits its application.Therefore,in this paper,g-C₃N₄was used as a research object to synthesize efficient photocatalytic materials with the enhanced visible-light response through strategies such as introduction of heteroelements and construction of heterojunctions.The main conclusions of the paper are as follow.（1）P-doped graphitic carbon nitride tubes（P-CNT）were successfully prepared from melamine（C₃H₆N₆）and disodium hydrogen phosphate dodecahydrate（Na₂HPO₄·12H₂O）via a pre-hydrothermal in combination with calcination process under nitrogen atmosphere.Mo S₂sample were prepared by hydrothermal method using ammonium molybdate[（NH₄）₆Mo₇O₂₄·4H₂O)]and thiourea[CS（NH）₂]as raw materials,and then 0.9P-CNT and Mo S₂were ultrasonically mixed by physical compounding method to gain the 0.9P-CNT/3MS heterojunction.The tubular structure and rough inner surface of P-CNT improved the specific surface area（SSA）of g-C₃N₄,increased the utilization of visible-light and provided more active sites for the hydrogen production reaction.In addition,the introduction of P element can effectively adjust the energy band structure of g-C₃N₄,increase the visible-light response range of g-C₃N₄and improve its hydrogen production performance.When the P-source input was 0.9 wt%of C₃H₆N₆,the as-prepared sample possessed the highest hydrogen production rate（HPR）of 2749.3μmol·h^-1·g^-1,which was 17.5times that of the bulk g-C₃N₄.The heterojunction can promote the separation and transport of carriers,reduce the quenching rate between them and enhance the photocatalytic hydrogen production performance.The results showed that0.9P-CNT/3MS had the highest HPR when the mass of Mo S₂was 3 wt%of0.9P-CNT,which was 38.6 and 2.2 times higher than that of the bulk g-C₃N₄and0.9P-CNT,respectively.（2）O-doped graphitic carbon nitride nanosheets（O-CNS）were prepared from urea[CO（NH）₂]and hydrogen peroxide（H₂O₂）via an ultrasonic in combination with calcination process under argon atmosphere,and the O-CNS possessed a larger SSA and decreased band-gap,which synergistically enhanced the hydrogen production performance of g-C₃N₄.When the amount of H₂O₂used was 65 m L,the prepared sample（65O-CNS）possessed the optimal HPR,which was 13.4 times higher than bulk g-C₃N₄.The 65O-CNS/5MS heterojunction was obtained by ultrasonically mixing 65O-CNS and Mo S₂through a physical compounding method.Heterojunction allowed carriers to migrate in the opposite directions and reduced the complexation between them.Then more photogenerated charges will be participated in the reduction reaction to release hydrogen and the 65O-CNS/5MS nanocomposites exhibited the enhanced hydrogen production performance.The results showed that65O-CNS/5MS had the optimal HPR when the mass of Mo S₂was 5 wt%of65O-CNS,which was 30.5 and 2.3 times higher than that of the bulk g-C₃N₄and65O-CNS,respectively.