Controllable Preparation Asphaltene Based Carbon Nanosheet And Its Adsorption Of CO₂

The morphology and size of functional carbon materials are the key factors that affect their physical properties and practical applications.The porous carbon nanosheet has great potential application in gas adsorption separation,catalysis,energy storage and other fields for its nanoscale thickness,ultra-high surface-to-volume ratio,unique electron transport performance,excellent chemical and thermal stability,and easy modification,etc.Therefore,the controllable preparation of nano-sheet porous carbon materials and the optimization of their application performance are the current research hotspots of carbon materials.In this paper,the coal tar asphaltenes were used as carbon precursors,according to their molecular structure and composition characteristics,the thermal condensation behavior of asphaltenes?ASP?under acid catalysis is studied;Then the asphaltene based carbon nanosheet with different morphology were prepared by salt bath method,assembly method and in-situ template method based on the thermochemical properties of asphaltene polymers.The structural and surface chemical properties,formation mechanism of the lamellar structure by different preparation methods and the evolution of their chemical composition and morphology during the carbonization process were explored by SEM,EDS elemental analysis,FT-IR,nitrogen isothermal adsorption and other characterization methods.The CO₂ adsorption performance of the asphaltene based carbon nanosheet was investigated.And the main conclusions are as follows:1.The specific surface area of the carbon nanosheet prepared by salt melt method was 327 m²·g^-11 when the ratio of C:N:LiCl/KCl was 1:1:9.In accordance with this ratio,different carbon nanosheet using ASP and ASP?O?as carbon sources were obtained.The influence factors on the preparation of carbon nanosheets were investigated such as nitric acid oxidation,temperature and time in salt melt process.The results showed that the sample prepared by ASP was amorphous carbon and its specific surface area was very small,while the sample prepared by ASP?O?showed a good sheet structure.Furthermore,the morphology of the carbon nanosheets varied due to the different conditions in salt melt process.The sample ASP?O?-150/400/600-1h and KOH were activated at a ratio of 1:1,and the asphaltene based carbon nanosheet ASP?YY?-KOH with a specific surface area of 1717 m²?g^-11 was obtained.The specific surface area of the sample after KOH activation was 5.25 times greater than that before activation,and its microporosity also increased by 24.3%.The adsorption capacity of CO₂ of ASP?YY?-KOH was increased from 2.20mmol?g^-11 to 3.88 mmol?g^-11 after activation,which was 18.8 times that of N₂.2.ASP?O-6h?and ASP?O-8h?were crystallize and coagulate with urea and KOH in H₂O and THF,respectively,then activated and self-assembled to form asphaltene based carbon nanosheet at 800?.The lamellar morphologies formed with different solvents were quite different.When THF was used as solvent,the prepared carbon nanosheets had a smaller sheet size because the carbon precursor can be uniformly dispersed in it.In addition,the samples?ASP?O-8h?-K/U-H₂O,ASP?O-6h?-K/U-H₂O,ASP?O-8h?-K/U-THF and ASP?O-6h?-K/U-THF?prepared by self-assembled generally had a large specific surface area and pore volume,and their microporosity was so high that their adsorption capacity for CO₂ reached 3.95 mmol?g^-1,3.27 mmol?g^-1,3.86mmol?g^-11 and 3.73 mmol?g^-1,respectively.3.Asphaltene based carbon nanosheet was prepared by using ASP?O?as carbon source,g-C₃N₄ nanosheet as soft template,KOH as activator at different ratios of 1:2:1 and 1:2:1.2.Thereinto,g-C₃N₄ nanosheet was produced by pyrolysis of urea.The specific surface area of the two samples prepared by template method at different ratios was 1981 m²?g^-11 and 1330 m²?g^-1,respectively.Due to a large amount of NH₃ produced in urea pyrolysis process,the nitrogen content of the two samples reached 6.88 wt%and 3.55 wt%.The high specific surface area and high nitrogen content of the asphaltene based carbon nanosheet gave them excellent CO₂ adsorption performance with adsorption capacities of5.17 mmol?g^-11 and 4.32 mmol?g^-1,respectively.