Fabrication Of Element-Doped G-C₃N₄ Photocatalyst For Hydrogen Production

The shortage of energy resources and environmental pollution are huge challenges to the sustainable development of today’s society.Hydrogen is a green and environmentally friendly energy carrier and high-density fuel.Solar photocatalytic hydrogen production is considered as a green and sustainable hydrogen production technology.Graphite-phase carbon nitride（g-C₃N₄）has the advantages of low cost,easy synthesis,high chemical stability and narrow and adjustable electronic energy band structure.It is a promising photocatalyst for hydrogen production.However,the photocatalytic efficiency of traditional g-C₃N₄ is still very low,mainly because the recombination rate of photogenerated electrons and holes is fast,and the visible light utilization efficiency is low.Therefore,it is very important to study efficient photocatalysts with high visible light utilization and rapid photo-generated electron-hole separation based on g-C₃N₄.In this thesis,two g-C₃N₄ photocatalysts were prepared by means of phosphorus and iron doping respectively,which improved the photocatalytic hydrogen production activity.The g-C₃N₄ photocatalysts with different P doping amounts（PCNx）were prepared by using melamine as carbon and nitrogen precursor and using sodium hypophosphite as phosphorus source.Structural characterization showed that P mainly existed in the skeleton structure of g-C₃N₄ in the form of P-N bonds.P-doping increased the specific surface area of g-C₃N₄,changed the electronic band structure of g-C₃N₄,formed a doped energy level,broadened the response range of visible light,and the photogenerated carriers were separated more effectively and could migrate to the surface of the catalyst faster to participate in the reaction.The photocatalytic hydrogen production activity test showed that in the absence of the precious Pt cocatalyst,the hydrogen production rate of PCN2 catalyst with the best performance under visible light reached 360.4μmol h^-1 g^-1,which was 120 times that of the reference sample BCN catalyst.After supporting the Co O_x cocatalyst on PCN2,the visible light catalytic hydrogen productions performance could be further enhanced,which was 16.6 times that of Pt/BCN.The stability experiment results showed that Co O_x/PCN2 could still maintain stable photocatalytic hydrogen production performance in the experiment of6 cycles totaling 18 hours.Using ferrous gluconate which was organic iron source and melamine as raw materials,Fe-doped g-C₃N₄（FCNx）was synthesized by one-step calcining.Structural characterization showed that Fe doping had no obvious effect on the morphology of g-C₃N₄.Fe species existed in g-C₃N₄ in the state of Fe³⁺and were connected to nitrogen atoms through Fe-N bonds.Compared with the original g-C₃N₄,Fe doping significantly reduced the band gap,broadened the visible light response range,and the separation and migration rate of photogenerated carriers was also enhanced.Visible light photocatalytic hydrogen production experiments showed that the hydrogen evolution rate of the optimal catalyst Pt/FCN2 reached 646.02μmol h^-1 g^-1,which was 17.5 times that of unmodified Pt/g-C₃N₄.The results of the stability experiment showed that Pt/FCN2 could still maintain a stable performance of photocatalytic hydrogen production in the experiment of 4 cycles totaling 12 hours.