Preparation And Properties Of G-C₃N₄ Based Composite Photocatalytic Materials

In recent years,organic dyes have been widely used in production and life,resulting in serious water pollution problems due to the unreasonable discharge of waste and liquid waste.Therefore,seeking an effective method to remove residual organic dyes from water resources has become a research hotspot.Among them,semiconductor photocatalytic technology is widely used in wastewater treatment due to its advantages of simplicity,efficiency,low cost,and green.Among many semiconductor photocatalytic materials,graphitic carbon nitride（g-C₃N₄）is favored for its rich raw materials,simple manufacturing process,strong physical and chemical stability,and unique crystal structure.However,the photocatalytic efficiency of unmodified g-C₃N₄is limited by its low specific surface area,rapid electron hole recombination rate,and relatively insufficient visible light utilization capabilities.Therefore,researchers are committed to studying the modification of g-C₃N₄to prepare materials with excellent photocatalytic performance.Currently,there are approximately four methods for modification,namely,morphology control,element doping,noble metal deposition,and heterojunction construction.In this thesis,the methods of P element doping,composite SnS,and Ag metal deposition were successively used to modify g-C₃N₄.By exploring the preparation method,doping ratio,reaction temperature,reaction time,and other factors,the optimal preparation conditions were obtained,and finally,photocatalytic materials with excellent photocatalytic performance were obtained.At the same time,the stability and recyclability of the material were determined through multiple recycling experiments.Finally,through active species capture experiments,a possible photodegradation mechanism of Rhodamine B（Rh B）by photocatalytic materials was proposed.The specific content is as follows:（1）Using ammonium dihydrogen phosphate and urea as raw materials,a series of P-g-C₃N₄photocatalysts were prepared by thermal polymerization.The effects of doping ratio,heating rate,calcination temperature,and calcination time on the photocatalytic properties of the materials were investigated.The results showed that the photocatalytic activity of the0.7%P-g-C₃N₄photocatalyst prepared by mixing 0.07 g of ammonium dihydrogen phosphate and 9.93 g of urea at a heating rate of 5℃/min to 600℃for 2 hours was the strongest.After60 minutes of irradiation with a 19 W LED lamp,the degradation rate of Rh B（10 mg/L）in a solution with a photocatalyst concentration of 1 g/L was 91.34%,and the degradation rate constant k was 0.04216 min^-1,5.23 times that of g-C₃N₄(k=0.00806 min^-1).After the fifth use of the cycle,the degradation rate of Rh B by P-g-C₃N₄can still reach 87%.The active species capture experiment showed that the main active substances for photodegradation of Rh B were·O₂^-and h⁺radicals.（2）Using SnCl₂.2H₂O,Na₂S.9H₂O,and P-g-C₃N₄as raw materials,a series of SnS/P-g-C₃N₄composite photocatalytic materials were prepared by precipitation method in an acidic environment.The effects of composite ratio,tin source to sulfur source ratio,and reaction time on the photocatalytic performance of the materials were investigated.The results showed that when the SnS composite ratio reached 10 wt%,the molar ratio of tin source to sulfur source was 1:3,and the reaction time was 3 hours,the SnS/P-g-C₃N₄composite photocatalytic material obtained had the best performance.After 180 minutes of irradiation with a 19 W LED lamp,the degradation rate of Rh B（10 mg/L）in a solution with a photocatalyst concentration of 0.3 g/L was 97.42%,and the degradation rate constant k was0.01848 min^-1,which were 1.95 and 9.99 times the reaction rate constants of pure P-g-C₃N₄(k=0.0095 min^-1)and pure SnS(k=0.00185 min^-1),respectively.After the fifth use of the cycle,the degradation rate of Rh B by SnS/P-g-C₃N₄can still reach 90%.The active species capture experiment showed that the main active substances for photodegradation of Rh B were·O₂^-and h⁺radicals,indicating the formation of a Z-scheme heterostructure.（3）Based on the previous two parts of experiments,a series of Z-scheme Ag/SnS/P-g-C₃N₄composite photocatalytic materials were prepared using a simple photoreduction method.After experimental analysis,it was found that when the loading ratio of Ag nanoparticles reached 0.0054 wt%,the Ag/SnS/P-g-C₃N₄composite photocatalytic material prepared after 3 hours of photoreduction had the best performance.After 120 minutes of irradiation with a 19 W LED lamp,the degradation rate of Rh B（10 mg/L）in a solution with a photocatalyst concentration of 0.3 g/L was 98%,and the degradation rate constant k was 0.03104 min^-1,which was 3.27,16.78,and 2.32 times higher than that of pure P-g-C₃N₄reaction rate constant(k=0.0095 min^-1),pure SnS reaction rate constant(k=0.00185 min^-1),and SnS/P-g-C₃N₄composite photocatalytic material(k=0.0134 min^-1).Through recycling experiments,it was found that the material has high stability and strong recyclability.Active species capture experiments have shown that the main active substance for photodegradation of Rh B is·O₂^-free radical.