Study On Preparation And Performance Of G-C₃N₄ Based Photocatalyst

In recent years,photocatalytic technology has been widely studied for the treatment of pollutants in water.Ultraviolet light only accounts for 5%of solar energy.In order to efficiently utilize solar energy,the development of photocatalysts with high degradation performance under visible light has become a priority.G-C₃N₄ material can be used as photocatalyst for degradation of organic pollutants due to its non-toxic,easy preparation and good photocatalytic effect.However,as a photocatalytic material,g-C₃N₄ monomer has certain defects.For example,the block g-C₃N₄ prepared by conventional thermal polymerization has weak light response,resulting in a low utilization rate of visible light.Therefore,based on g-C₃N₄,this thesis improved its photocatalytic activity by modifying g-C₃N₄ and constructing semiconductor composite materials with matched semiconductors.The main research contents and results are as follows:（1）A cable-like photocatalyst Ti Bs@MCN based on Ti O₂ band（Ti Bs）and mesoporous g-C₃N₄（MCN）nanosheets was prepared by in-situ hydrothermal self-assembly method.The photocatalytic performance was evaluated by photocatalytic degradation tests of methyl orange（MO）and methylene blue（MB）of monomer and different proportions of Ti Bs@MCN under visible light.The results showed that the degradation rates of MB and MO were 86.7%and 98.8%,respectively.When the ratio of Ti Bs to MCN was 1:7（TMCN 1:7）under simulated visible light irradiation.TMCN 1:7 showed the best degradation effect,and its degradation rate constants were 0.066 min^-1（MO）and 0.031 min^-1（MB）,which were 10 times and 3 times of MCN,respectively.（2）Synthesis of tetracarboxyphenylporphinatoiron-sensitized g-C₃N₄ nanosheets（Fe TCPP@CNNS）was doped and modified by metal salt DMF to prepare tetracarboxyphenylporphinatoiron-sensitized g-C₃N₄ nanosheets（CNNS）with different amount of doping.The photocatalytic degradation performance of the prepared material was judged by the degradation rate of the pollutant p-nitrophenol（4-NP）.The study showed that under simulated visible light irradiation,the doping amount of Fe TCPP was 3%of the content of CNNS（3%Fe TCPP@CNNS）,showing a high degradation rate.The degradation rate of 4-NP reached 92.4%within 60 min,and the degradation rate constants were 0.037min^-1,which were more than 5 times that of CNNS.After 5 times of photodegradation experiments,3%Fe TCPP@CNNS can still maintain high degradation efficiency for pollutants,indicating that the photocatalytic composite has good photocatalytic efficiency and stability.·O₂^-was identified as the main active substance for photocatalytic degradation of 4-NP by activity capture experiment and the related mechanism was proposed.（3）CNNS@Bi₂WO₆ and Fe₃O₄@CNNS/Bi₂WO₆（FCB）composites were prepared by hydrothermal method,and the photocatalytic activity of the prepared materials was determined by the degradation properties of Rhodamine B（Rh B）and tetracycline（TC）.The composite prepared with proper content of Fe₃O₄@CNNS and Bi₂WO₆ exhibits wider absorption edge,expands the visible region and improves the utilization rate of light energy.The ternary composites prepared by Fe₃O₄@CNNS and Bi₂WO₆ microflower showed excellent photocatalytic degradation performance.The degradation rates of Rh B and TC by photocatalyst（7%-FCB）within 60 min were 94.5%and 91.5%,respectively.The degradation rate constants were 0.0424 min^-1 and 0.03499 min^-1,respectively.The stability and possible photocatalytic mechanism of the composite were determined by cyclic experiment and activity capture experiment.