Preparation Of Modified Graphite-Carbon Nitride Based Composite Photocatalysts And Their Performance In Visible Light Degradation Of Pollutants

With the development of social economy,environmental pollution problems have come one after another,among which water pollution problems are closely related to human health.The sewage problems caused by persistent organic pollutants such as dyes and antibiotics have seriously threatened people’s living environment and health.Among the many wastewater treatment technologies,photocatalytic degradation technology has received widespread attention because of its green,simple,efficient and easy recycling advantages.Due to its unique structure,widely available precursors and excellent physicochemical stability,g-C₃N₄ has attracted much attention.However,the small specific surface area of g-C₃N₄ obtained by conventional thermal polymerization cannot provide more effective reactive sites and the photoavailability is also affected;meanwhile,its photogenerated electron-hole pairs will compound rapidly and the short photogenerated charge lifetime limits the photocatalytic reaction activity.Therefore,some modification means are urgently needed to enhance the photocatalytic ability of g-C₃N₄.The specific surface area of g-C₃N₄ can be improved by morphology modulation to increase the surface active sites and light utilization rate;semiconductor compounding technology can extend the lifetime of photogenerated carriers in g-C₃N₄ and inhibit the complexation of photogenerated electron-hole pairs;elemental doping and defect engineering can change the electronic structure of g-C₃N₄ to broaden the light response range,thus improving the photocatalytic efficiency.Based on this,we propose to prepare g-C₃N₄-based composites with high photocatalytic activity by using melamine as the main raw material,and investigate its degradation ability of organic pollutants and explore the photocatalytic degradation mechanism through modification methods such as morphology modulation,semiconductor compounding and element doping.The main studies are as follows:（1）Two g-C₃N₄ materials（CNx and CN）were prepared from melamine using KOH etching technique and acid exfoliation strategy,and silver-ear-shaped g-C₃N₄-based homojunction photocatalysts（CNx/CN）were prepared by self-assembly of CNx and CN.The samples were characterized by XRD,FTIR,SEM and PL to analyze their crystal structure,microscopic morphology and optical properties,and their photocatalytic degradation ability was evaluated mainly by degrading methylene blue dye（MB）.The results show that the homojunction structure integrates the advantages of CNx and CN,allowing CNx/CN to possess fold and cavity structures,enhancing the light utilization as well as providing more surface active sites;the homojunction construction inhibits the complexation of photogenerated electron-hole pairs.The photocatalytic activity of CNx/CN homojunction photocatalyst was thus enhanced.94.2%photodegradation efficiency of CNx/CN for MB was achieved at 140 min;the degradation efficiency of CNx/CN for MB still exceeded 80%after four cycles;it also showed excellent practicality,and the catalytic effect for MB configured with school pond water as solvent still reached 93.7%.（2）Tubular g-C₃N₄（TCN）was prepared using urea and melamine via a precursor reforming strategy,and the in situ growth of TiO₂ on the TCN surface was achieved by hydrothermal-calcination method using tetrabutyl titanate as the titanium source,resulting in the tubular g-C₃N₄（TCN/TiO₂）heterojunction photocatalyst loaded with TiO₂.The samples were characterized by XRD,FTIR,SEM,TEM and UV-vis to analyze their crystal structure,microscopic morphology and optical properties,and their photocatalytic degradation ability was evaluated mainly by degrading MB dyes and tetracycline（TC）antibiotics.The results showed that:the light absorption intensity of the composites was enhanced,the number of photogenerated carriers was increased and the photocatalytic activity was improved due to the visible light driving of TCN.the photodegradation efficiency of TCN/TiO₂ for MB reached 96.6%at 60 min;the photodegradation efficiency for TC reached 100%at 30 min;and it still had 90%catalytic effect after four cycles.The prepared TCN/TiO₂ has a broader prospect in practical applications.