Microwave Plasma Material Modification And Diagnosis

Low-temperature plasma has many applications in industrial production due to its special properties.The ionized gas mass generated by the discharge contains a large number of high-energy particles and reactive groups,which gives it special advantages in material modification,biomedicine,thin film deposition,etc.In material modification,the advantages of low temperature,high efficiency and low loss make low temperature plasma material modification a hot research topic,one of the representatives is the application of photocatalyst modification.Efficient photocatalytic decomposition of aquatic hydrogen and degradation of pollutants are important means to cope with the tight energy demand and environmental pollution,which is in line with the current green trend of the times.In this paper,the following studies are done for low-temperature plasma catalyst modification and the diagnosis of the modification process:We propose a modification method based on microwave plasma technology using graphite-phase carbon nitride as the research object.Highly reactive plasma was generated in a mixed H₂+CO₂ atmosphere for the rapid treatment of carbon nitride,and finally carbon nitride nanosheets with mesoporous structure and carboxyl defects were obtained.Analysis of the subsequent characterization results revealed that the electronic structure and active sites were significantly improved,and the separation efficiency of photogenerated carriers was also enhanced while keeping the main structure of carbon nitride intact.The hydrogen production rate using the modified carbon nitride was increased from the original 1.68mmol·h^-1g^-1 to 8.53mmol·h^-1g^-1.This demonstrates the potential and operability of the low-temperature plasma approach in improving the carboxylate defects and mesoporous structure of carbon nitride,which provides a new idea for the modification of other catalysts.On the basis of the above study,we carried out the study of doubly modified carbon nitride.By using CO₂ plasma to treat the mixed powder of carbon nitride and copper sulfate pentahydrate,we successfully prepared the dual modified carbon nitride with single copper atoms and carboxyl defects,which is difficult to achieve by conventional methods.The presence of carboxyl defects and single copper atoms in the material structure was verified by XPS and other characterization results and spherical differential electron microscopy,respectively.The double modification resulted in a5.5times and 16.5times increase in the efficiency of carbon nitride photocatalytic degradation of Rh B and hydrogen production,respectively,which was attributed to the synergistic complementation of copper atoms and carboxyl groups.It was also found that the length of plasma treatment time also affected the modification effect.In the above plasma modification process,because the complex working conditions make the traditional probe diagnostic method no longer applicable,we developed a microstrip antenna diagnostic electron density to study the plasma state and modification mechanism during the modification process.Based on the correlation between plasma density,relative equivalent permittivity and antenna S11 parameters,plasma density diagnosis can be achieved by the microstrip antenna.Through simulation and experimental results,we found that the temperature during the discharge process also affects the diagnostic effect,so the temperature variable needs to be introduced to correct the results.In addition,the initial resonant frequency is related to the antenna structure and needs to be set according to the approximate range of the actual plasma density.