Synergistic Enhancement Of Structural Defect And Metallic Nanopaticle On G-C₃N₄ Photocatalytic Performance

With the rapid development of society,energy shortage and environmental pollution have become two major problems in the world today.In particular,persistent pollutants that cannot be naturally decomposed for a long time in water seriously threaten the balance of the ecosystem.As a type of renewable energy,solar energy has attracted wide attention from scientists all over the world because of its rich,clean,and safe advantages,among which the conversion and utilization of solar energy through photocatalytic technology to achieve the efficient degradation of pollutants in water is a research work with academic value and application prospect.Graphite phase carbon nitride（g-C₃N₄）is a favored semiconductor because of its suitable band gap,excellent thermal and chemical stability,simple preparation,and non-toxicity and harmlessness.However,g-C₃N₄ prepared by traditional methods（such as calcination）severely limits a further application in the field of photocatalysis due to its small specific surface area,low visible-light utilization and high recombination rate of photogenerated electrons and holes.Aiming at above issues,researchers have proposed a variety of strategies to increase the photocatalytic activity of g-C₃N₄.This thesis is devoted to improving the photocatalytic performance of g-C₃N₄ by regulating the structural defect and loading noble metallic nanoparticles（NPs）,and its detailed research contents are listed as follow:（1）By using melamine and ascorbic acid as raw materials,porous g-C₃N₄ nanosheets（pg-C₃N₄）with larger specific surface area were obtained via high-temperature calcination method.And then Au/pg-C₃N₄ composite photocatalyst was prepared by sodium citrate reduction method to load Au NPs.Compared with traditional g-C₃N₄,Au/pg-C₃N₄ has the increased visible-light absorption range,and enlarged specific surface area that provides more active sites for the photocatalytic reaction.Meanwhile,the heterojunction between Au NPs and pg-C₃N₄ could reduce the photogenerated electron-hole recombination.Au/pg-C₃N₄showed excellent photocatalytic activity for the degradation of two organic dyes,rhodamine B and amaranth,and the degradation rate was increased by 3.9 and 5.7 times,respectively.（2）By utilizing the molecular structure characteristics of urea precursor,the modified g-C₃N₄ with the doping of oxygen atom and cyano group（COCN）was prepared by calcinating the mixture of urea and ascorbic acid at high temperature.And then Ag NPs were in-situ grown onto COCN（Ag/COCN）by sodium borohydride reduction method.Combining the synergistic effect of structural defect,localized surface plasmon resonance effect and heterojunction,Ag/COCN composite photocatalyst has the advantages of narrow band gap,wide light absorption range and fast charge separation rate,realizing the efficient degradation of sulfamethoxazole（SMX）.By optimizing Ag NPs loaded amount,10%-Ag/COCN exhibited outstanding catalytic activity under simulated sunlight radiation,along with the degradation efficiency up to 99.9%within 20 min,which is among the best results reported thus far for the photocatalytic degradation of SMX.