The Synthesis,characterization And Photocatalytic Properties Of Carbon Nitride Based Catalyst

The energy crisis and environmental pollution are two serious problems that humans face in the process of sustainable development.The development of semiconductor photocatalytic materials and photocatalytic technique brought new opportunities and challenges for solving the energy and environmental problems.g-C₃N₄ material has attracted much attention in the field of photocatalysis due to its non-toxic,inexpensive,excellent thermal and chemical stability and easy to prepare.However,g-C₃N₄ has some disadvantages such as small surface area and low quantum efficiency,both of which lead to low photocatalytic activity.This dissertation focuses on synthesis,characterization and photocatalytic properties of carbon nitride based catalyst.Specific research contents are shown as follows.1.Well dispersed TiO₂ nanoparticles were successfully grown in-situ on graphitic carbon nitride?g-C₃N₄?nanosheets through a facile hydrothermal method.The resultant TiO₂/g-C₃N₄ nanocomposites exhibit remarkably higher photocatalytic efficiency under visible light irradiation as compared to pure g-C₃N₄.The optimal composite with 30 wt% TiO₂ demonstrates highest photocatalytic activity,which can degrade 97% Rhodamine B?RhB?after reaction for 40 min.The enhanced photocatalytic activity induced by the in-situ grown TiO₂ nanoparticles is attributed to the interfacial transfer of photogenerated electrons between g-C₃N₄ and TiO₂,which leads to effective charge separation of g-C₃N₄.The photocatalytic mechanism for the TiO₂/g-C₃N₄ composites under visible light is tentatively proposed,and validated through the experiment.The corresponding research indicates that the free radicals of h+ and ·O2-are the major reactive species in the TiO₂/g-C₃N₄ reaction system.2.A series of P-doped g-C₃N₄?P-CN?samples have been prepared using urea?CO?NH₂?2?and diammonium hydrogen phosphate??NH4?2HPO4?as precursors by a simple thermal condensation method.The surface morphologies and structures of the as-prepared samples were characterized by X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,UV-Vis diffuse reflection spectra?UV-Vis DRS?and N2 adsorption-desorption isotherms,respectively.The visible light photocatalytic property was demonstrated for photodegradation of RhB solution,and the photocatalytic mechanism for the P-CN samples under visible light was tentatively proposed.The corresponding results indicate that C atoms in g-C₃N₄ are replaced by P atoms,which modify the surface morphologies and electronic structures.The as-prepared P-CN samples show remarkably higher photocatalytic efficiency than pure g-C₃N₄ for RhB degradation under visible light irradiation.3%P-CN sample demonstrates the highest photocatalytic activity,which degrades 96.8% RhB after reaction for 30 min.The replacement of P to C atoms in g-C₃N₄ makes the surface of P-CN in an electron-rich state.Furthermore,the research indicates the conduction band of P-CN shifts to more negative values,which improves the reduction performance of photoelectron.The electrons in conduction band of P-CN reduce O₂ to ·O₂-in the reaction system,so that the photocatalytic property are improved significantly.3.Magnetic Fe₃O₄/CdS/g-C₃N₄ composites were successfully fabricated via an “in situ” precipitation-deposition method.The magnetization curve of Fe₃O₄/CdS/g-C₃N₄ composite demonstrates that the products prepared had an excellent magnetic sensitivity.The as-prepared Fe₃O₄/CdS/g-C₃N₄ samples show remarkably higher photocatalytic efficiency than pure g-C₃N₄ and CdS for RhB degradation under visible light irradiation.Fe₃O₄/0.4CdS/0.6g-C₃N₄ sample demonstrates the highest photocatalytic activity,which degrades 97.1% RhB after reaction for 15 min.The enhancement in photocatalytic activity should be assigned to the effective separation and transfer of photogenerated chargesis between g-C₃N₄ and CdS.·O₂-and h+ are the major reactive species for the Fe₃O₄/CdS/g-C₃N₄ reaction system.