Study On Photocatalytic Degradation Of Dyes By Modification Of G-C₃N₄ With Metal Nanoparticles

Photocatalytic degradation is considered to be one of the most promising technologies for environmental remediation and solar energy utilization,and has attracted more and more attention at present,and the technology has the potential for long-term development and is expected to gradually reduce environmental pollution.In this experiment,the graphite phase carbon nitride（g-C₃N₄,hereinafter referred to as CN）photocatalyst was successfully synthesized by calcination method under different precursors and calcination conditions,and g-C₃N₄was combined with copper nanoparticles（Cu NPs）and silver nanoparticles（Ag NPs）by two different composite methods,and ultrasonic composite photocatalysts（Cu-CN-Ult,Ag-CN-Ult）and in situ composite photocatalysts（Cu-CN-In,Ag-CN-In）were successfully synthesized.The samples were characterized by different characterization methods,and the effects of composite materials with different composite methods and different proportions on photocatalytic performance were discussed.The main tasks are as follows:（1）The three different precursors of urea,melamine and thiourea were calcined by the heat shrinkage method,and the CN was successfully prepared,and the characterization results showed that among the three precursors,the sample BET synthesized by urea had the largest specific surface area,which could reach 44.56 m²/g,which was about 5 to 6 times that of melamine and thiourea,and the synthesized sample kinetic fitting data met the quasi-first-level kinetic model.Taking urea as the precursor,10°C/min heating to 550°C heat preservation 4 h synthesis of catalyst CN-1,catalytic degradation of rhodamine B（Rh B）under simulated sunlight has good photocatalytic activity.（2）By adjusting the precursor and calcination conditions,the CN-1material with good activity was successfully prepared,and the Cu NPs were introduced by ultrasonic composite and in situ composite by using ultrasonic composite and in situ composite material,and the effects of the photodegradation effect of composite photocatalysts with different mass ratios were prepared.The results show that the introduction of Cu NPs increases the specific surface area of the composite material and effectively inhibits the recombination of photogenerated electrons and holes.Among them,ultrasonic composite has the largest absorption edge and the smallest bandgap energy,which can absorb more visible light.Under simulated sunlight,the photocatalytic performance of composite materials with different composite methods and different proportions was evaluated with Rh B as the target product.From the degradation rate point of view,the in situ composite catalyst Cu-CN-In（1）degradation of Rh B degradation rate is slightly higher,within 120min,the degradation rate can reach 97.69%;compared with the reaction rate constant of the two composite catalysts,it shows that the introduction of Cu NPs improves the reaction rate,of which Cu-CN-In（1）catalyst reaction rate constant is the largest;with good stability and recyclability,after 4 cycle recovery tests,the degradation rate can still reach 90.98%The active substances that play a major role in the photocatalytic degradation process are·O^2-and h⁺.（3）Using CN-1 as the substrate material,ultrasonic recombination and in situ recombination were used to introduce Ag NPs,and the Ag-CN-Ult and Ag-CN-In series catalysts were successfully synthesized,and the effects of photodegradation effects of composite photocatalysts with different mass ratios were explored.Through the experimental analysis of photocatalytic degradation,Ag-CN-Ult（0.1）and Ag-CN-In（1）catalysts had the best effect in their respective synthesis methods.The samples were characterized by XRD,XPS,BET,UV-Vis and PL,and the characterization results showed that the introduction of Ag NPs increased the specific surface area of g-C₃N₄,which could absorb a wider range of visible light and have higher electron transfer and separation efficiency.From the degradation rate and reaction rate constant,the two composite methods have better photocatalytic performance in situ:the reaction rate constants of Ag-CN-Ult（0.1）and Ag-CN-In（1）are 3.5 and 4.2 times that of CN,and the reaction rate is significantly accelerated,the reaction time is shortened to 60 min,and the degradation rate reaches 100%.And after four cycle recovery experiments,the degradation rate of Ag-CN-In（1）can still reach more than 91%,indicating that Ag-CN-In has excellent stability and cyclity;the active substances that play a major role in the photocatalytic degradation process are·O^2-and h⁺.