Controllable Synthesis And Photocatalytic Properties Of G-C₃N₄ Based Nanomaterials

Energy crisis and environmental pollution are two major problems in the sustainable development of contemporary society.As a kind of renewable energy,solar energy is the basis of sustainable development.Semiconductor photocatalysts can utilize clean,resource rich solar energy to produce hydrogen from water and degradation of environmental pollutants.In order to give full play to the advantages of photocatalyst in the development of new energy sources and environmental purification,the design and synthesis of novel and efficient photocatalytic materials is an outstanding and challenging subject in the field of photocatalysis.Graphite phase carbon nitride?g-C3N4?is a kind of organic semiconductor material,which has a good band gap and chemical stability.The relationship between the structure and photocatalytic activity of the photocatalysts was systematically studied by the controlled synthesis of the composite photocatalysts.In this paper,several kinds of the photocatalysts have been developed,which can further broaden the application of g-C3N4photocatalyst in the field of energy crisis mitigation and environmental pollution control.The main conclusions were summarized as follows:?1?AuPd/g-C3N4 photocatalysts were synthesized through introducing AuPd bimetallic nanoparticles by means of chemical reduction and heat treatment.The doping of AuPd nanoparitcles did not affect the morphology and structure of g-C3N4photocatalysts.The composite photocatalysts exhibited enhanced photocatalytic activity in the presence of small AuPd nanoparticles,and the highest efficiency was observed with0.5 wt%AuPd/g-C3N4 sample.The rate of photocatalytic hydrogen production reached326?mol·h^-1·g^-1.Based on the analysis of the surface photovoltage technique,the photoinduced electron transfer process at the heterojunction interface can be further understood.?2?PtCo nanoparticles cocatalyst decorated ultrathin 2D g-C3N4 nanosheet photocatalysts were successfully prepared with a solvthermal synthsis approach.In this study,the g-C3N4 nanosheets with high surface areas were synthesized by using HCl and NH3 gas as the template in the pyrolysis process of NH4Cl.Compared with Pt/g-C3N4photocatalyst,the photocatalytic activity of PtCo/g-C3N4 nanosheets photocatalysts has been greatly improved,and the hydrogen production rate is up to 960?mol·h^-1·g^-1.The unique structure of the binary alloy can inhibit the recombination of photogenerated electrons and holes,and improve the photocatalytic activity of hydrogen production.?3?g-C3N4 nanosheets were prepared by a facile bubble expanding process,and a new methodology with in-situ light and hydrogen reduction was adapted to synthesize AuPd/g-C3N4 composite photocatalyst.After optimization of the photocatalyst,the hydrogen production rate reached 2145?mol·h^-1·g^-1,about 6 times higher than that of sodium borohydride reduced AuPd AuPd/g-C3N4.HPO4^2-is more likely to act as a mediator and participates directly in the photocatalytic reaction,thus bring about a new proton reduction process:HPO4^2-instead of water is reduced by the photo-generated electrons and subsequently produce PO4^3-and H2 at the interface of metal-semiconductor catalysts.?4?Based on the analysis of the active species in the photocatalytic degradation of methyl orange dye by Co3O4/g-C3N4 and Ag@AgCl photocatalysts,the essence of photocatalytic process was investigated.The composite photocatalysts exhibited enhanced photocatalytic activity in the presence of small amounts of Co3O4 species.The results showed that the superoxide radical is the main active species in the composite samples.In the Ag@AgCl system,the surface plasmon resonance of Ag nanoparticles produces hot electrons,which promotes the photocatalytic degradation of organic compounds.The preparation method of Ag@AgCl heterojunction photocatalyst can provide a new idea for design and synthesis of new nanoscale devices.