Preparation,Modification And Photocatalytic Properties Of G-C₃N₄ Nanometer Materials

The stability and development of human society need the support of energy.At present,fossil fuels still occupy an extremely high proportion of the energy used and the demand is increasing.However,these fossil fuels are rapidly decreasing and facing exhaustion.In the process of using fossil energy for energy,a lot of waste is produced,which causes damage to the environment.Photocatalysis can complete a series of complex chemical reactions under light through semiconductor nanomaterials,which is expected to be one of the effective ways to solve environmental problems and provide green and sustainable energy.With solar energy as the driving force and photocatalyst,a variety of catalytic reactions can be carried out,such as water decomposition,CO₂ reduction,pollutant degradation,organic synthesis,bacterial disinfection and so on.Since carbon nitride（g-C₃N₄）of graphite phase was first used as a photocatalyst for H₂ generation in 2009,g-C₃N₄ has attracted extensive attention and been studied in many aspects.Its unique properties make it a potential photocatalyst.In this paper,a doughnut-like hollow g-C₃N₄ nanoring material（CMU-500）was prepared by means of a simple hot polymerization method calcining the white spherical macromolecular intermediate.The results of XRD,XPS,SEM and TEM indicated that the materials with weak crystallinity of graphite carbon nitride of three-dimensional hollow structure were synthesized.Compared with the（100）and（002）crystal surfaces of typical g-C₃N₄ materials prepared by traditional methods,only the weak（002）crystal surfaces of CMU-500 were presented.The specific surface area of CMU-500 was up to 92 m²/g.The three-dimensional structure with two-dimensional lamination promotes the separation efficiency of carriers and improves the absorption efficiency of visible light,which is more conducive to improving the photocatalytic performance of the material.Under visible light irradiation,rhodamine B（RhB）and potassium dichromate Cr（VI）were used as pollutant models to analyze the photocatalytic performance of CMU-500 materials.In the RhB degradation experiment,the degradation efficiency of CMU-500 can reach 100%in 10minutes.In the Cr（VI）reduction experiment,CMU-500 can also completely reduce Cr（VI）within 15 minutes.And under visible light,the performance of photocatalytic decomposition of aquatic hydrogen was tested,and the hydrogen generation rate reached 2260μmol g^-1 h^-1,showing excellent photocatalytic performance.The catalytic performance efficiency of the catalyst did not decrease significantly in the fourth cycle test.Because g-C₃N₄ has its own inherent defects,such as the low separation efficiency of photogenic carriers,the composition of different semiconductors into heterojunction is beneficial to reduce the composition rate of photogenic electron hole pairs.We used p-type Co₃O₄ to compound with n-type g-C₃N₄,and prepared p-n heterojunction Co₃O₄/g-C₃N₄composite by adding（CH₃COO）₂Co to the spherical precursor.According to the results of ICP,SEM,XRD and XPS,Co₃O₄ was successfully attached to carbon graphite nitride despite its low content.The photocurrent response and impedance tests show that the composite material Co₃O₄/g-C₃N₄ can inhibit the recombination of photogenerated electron hole pairs and improve the separation efficiency.Under visible light,the reduction of Cr（VI）and degradation of tetracycline efficiency of the composite materials were greatly improved,which were 6.7 times and 5.8 times higher than that of g-C₃N₄ without doping Co₃O₄,respectively,with good cyclic stability.