Preparation And Catalytic Properties Of Graphitic Carbon Nitride-based Nanocatalysts

The most effective methods to solve the energy crisis and environmental pollution mainly include the production of hydrogen energy from water by solar energy and the elimination of environmental pollutants.As one of the most widely used technologies in the fields of energy and environment,nanocatalysis technology gets a lot of attention.At present,most of the preparation methods of nanocatalysts are complex and expensive.It is urgent to find a low-cost nanocatalyst which is easily prepared.Among a variety of nanomaterials,graphitic carbon nitride?g-C₃N₄?,has the advantages of non-toxicity,low cost,extraordinary stability and easy preparation,becomes the hot material in the field of nanocatalysis.In addition,g-C₃N₄ exhibits a wide range of light response??450 nm?due to a narrow band gap of ?2.7 eV,which is usually used as a photocatalyst in the field of photocatalysis.In this dissertation,we take g-C₃N₄ as the research subject,by means of noble metal deposition,microstructure control and element doping,the performances of g-C₃N₄-based materialsin photocatalytic hydrogen production and degradation of pollutants have been greatly improved.The main results are listed as follows:?1?Ultrathin porous g-C₃N₄ nanosheets?CNS?have been synthesized by thermal oxidation etching of bulk g-C₃N₄?CNB?.Compared with CNB,CNS possess a larger surface area of 234.65 m² g^-1,good dispersity in water and a high electron transfer rate.As a co-catalyst,ultra-small Pt nanoparticles?Pt NPs?are loaded on the surface of CNS.It is found that changing the loading method of Pt NPs in the preparation step remarkably alters the efficiency for hydrogen production.The Pt/CNS-CR photocatalyst fabricated by the chemical reduction?CR?method shows a much higher efficiency for H₂ evolution from water splitting,compared to the Pt/CNS-PR photocatalyst obtained by the loading of Pt NPs by the traditional photo-reduction?PR?method.The valence states of the Pt element in the Pt/CNS-CR and Pt/CNS-PR nanocomposites have been analyzed by X-ray photoelectron spectroscopy,respectively.At the same time,the effects of the loading amount of Pt and different sacrificial reagents on the photocatalytic H₂ generation activity have also been systematically investigated.?2?Ultrathin porous g-C₃N₄ nanosheets?g-C₃N₄-NS?are used as a carrier,with gold nanoparticles?Au NPs?being anchored on its surface.As a comparison,2D TiO₂ nanosheets?TiO₂-NS?,graphene oxide nanosheets?GO-NS?and bulk g-C₃N₄?g-C₃N₄-B?are also chosen as the carriers for immobilization of Au NPs.Au NPs supported on different carriers are served as catalysts for the reduction of 4-nitrophenol?4-NP?.The results show that the rate constant of 2.0% Au/g-C₃N₄-NS nanocatalyst is 11.4 and 42.1 times higher than that of 2.0% Au/TiO₂-NS and 2.0% Au/GO-NS nanocatalysts,respectively.2.0% Au/g-C₃N₄-NS show an excellent catalytic activity for converting 4-NP.The as-prepared 2.0% Au/g-C₃N₄-NS nanocatalyst also exhibit a good catalytic performance in the reduction of 2-nitrophenol?2-NP?and 3-nitrophenol?3-NP?.?3?With thioacetamide?TAA?as a sulfur source,the cellular S-doped g-C₃N₄ nanotube nanocatalyst?SCNB-18?is obtained by a one-step hydrothermal method.The introduction of S expands the visible light absorption range of g-C₃N₄,and the cellular morphology increases the specific surface area of nanocatalyst.Moreover,the microstructure and photoelectric properties for the samples have also been characterized.The catalytic performance of SCNB-18 is evaluated by photocatalytic hydrogen production and degradation of pollutants.The results show that SCNB-18 nanocatalyst exhibits an excellent photocatalytic performance and cyclic stability.