Study On Luminescence And Photocatalysis Properties Of Carbon Nitride Synthesized Via Microwave Heating Method

Due to the low density,stable chemical property,good biocompatibility,moderate band gap and metal free composition,graphite carbon nitride（g-C₃N₄）has been widely applied in many fields such as photocatalysis,sensors,catalyst carriers,etc.However,g-C₃N₄prepared by the traditional thermal condensation method possesses many disadvantages covering long preparation time,complex process and low yield.The microwave heating method is a simple,fast and efficient synthesis approach to overcome these shortcomings.Therefore,this paper focuses on the effect of process parameters of high-energy microwave method on the preparation of g-C₃N₄ samples.Besides,their electrochemiluminescence characteristics,photocatalytic performances and application in sensing were studied.In this paper,g-C₃N₄ with different structures were prepared by high-energy microwave method by changing the types of microwave absorbers and precursors.A variety of analysis and test methods were used to characterize and analyze its morphology,structure and properties.The electrochemiluminescence and photocatalytic performance were studied.Then,photoluminescence and electrochemiluminescence sensors for Cu²⁺ions were constructed based on the prepared material.The details are as follows:（1）The hollow spherical g-C₃N₄ was synthesized by using melamine as precursor,carbon fiber and metal iron powder as microwave absorbers via a rapid,efficient and environmentally friendly microwave heating technology.When the amount of iron powder is 1wt.%and 3wt.%,the synthesized samples showed hollow spherical structure.Compared with the pure g-C₃N₄,3Fe-g-C₃N₄ had better dispersion and stability in water,so it can be better film-forming on the glassy carbon electrode.Besides,3Fe-g-C₃N₄ had faster electron transfer rate,resulting the increase of ECL intensity 28.4 times higher than pure g-C₃N₄.This makes a good foundation for the following detection for the target ions.In addition,the photocatalytic properties of these samples were also studied.The degradation efficiency of Rh B by 3Fe-g-C₃N₄ was the highest.The degradation rate reached up to 95.21%within 30 minutes.（2）3Fe-g-C₃N₄ samples were used to prepare carbon nitride nanosheets（g-C₃N₄-NS）with a diameter of 20～40 nm and a thickness of 1.5～2 nm via an ultrasonic method.Fluorescence and electrochemiluminescence sensors for Cu²⁺detection were constructed by using g-C₃N₄-NS.The detection limit of Cu²⁺concentration by fluorescence method can reach 1 n M.Afterwards,the intensities of different Cu²⁺concentrations were measured by electrochemiluminescence method.It is found that it had a good linear relationship in the concentration range of 0～100 n M,and its detection limit was estimated to be 0.2 n M.（3）By means of the hydrothermal treatment of melamine and the subsequent microwave heating,sodium-doped g-C₃N₄ nanotubes were obtained.This approach utilized a self-assemble between melamine and cyanuric acid in the Na OH solution to form Na-doped melamine cyanaurate supramolecular intermediate.Then the supramolecular intermediate was heated under direct microwave irradiation with carbon fibers which were acted as microwave absorbents.It was found that the precursor with rod like structure tends to retain its one-dimensional structure.However,the different concentration of Na OH in the hydrothermal process directly affected the content of melamine and supramolecular aggregates in the self-assembly process,resulting in a difference in the aspect ratio of nanotubes.When melamine was treated with 0.50 M Na OH solution in the hydrothermal process,the product（0.50Na-g-C₃N₄）had better ECL emission intensity after being made into cathode and anode.Compared with g-C₃N₄,the ECL emission intensity increased by 23.8 and 20.4 times,respectively.In addition,the photocatalytic activity of Rh B was also studied.The product（0.25Na-g-C₃N₄）,which was treated with 0.25 M Na OH solution in the hydrothermal process,had the highest degradation efficiency,and Rh B was degraded by 91.43%in 20 minutes.