Study On The Adsorption Mechanism Of CO₂ And Toluene Based On Organic Nitrogen-doped Bimass Porous Activated Carbon

Atmospheric pollution and global warming have become new challenges for people,both in terms of volatile organic compounds（VOCs）and carbon dioxide（CO₂）in the air,posing a great threat to human health and ecological environment.Therefore,the development of green and non-polluting solid adsorbents to reduce the concentration of VOCs and CO₂ in the atmosphere has become an important research topic in the field of energy and environment.Porous activated carbon is a new type of adsorption material with broad application prospects.It has the the characteristics of well-developed pores,large specific surface area,abundant surface functional groups and easy preparation.The heteroatom modification based on nitrogen-doped can greatly improve the adsorption properties of carbon materials by enhancing the polarity of carbon surface.Organic nitrogen that can be extracted from plants or other biomass are widely used as nitrogen sources for carbon material modification due to their inexpensive and environmentally friendly characteristics.How to prepare adsorbent with high nitrogen content and developed pores at the same time,and to clarify the mechanism of its physical and chemical properties on the adsorption process deserves further in-depth discussion.In this paper,biomass eucalyptus bark was used as carbon source,and urea and chitosan were modified as organic nitrogen sources to prepare a series of nitrogen-doped porous carbon materials respectively,and the adsorption process of CO₂ and toluene was studied.The main research contents and results are as follows:（1）Using eucalyptus bark as carbon source and urea as nitrogen source,nitrogen-doped porous activated carbon materials（NPCs）were successfully synthesized by hydrothermal-chemical activation method.The prepared carbon materials show large specific surface area(1114～1734 m²·g^-1),developed total pore volume(0.56～1.48 m³·g^-1)and abundant nitrogen content（2.03～3.80wt%）.The CO₂ static adsorption experiment was carried out with these carbons as adsorbent.Among them,NPC700 showed the largest CO₂ adsorption capacity,with adsorption capacities of 4.20 mmol/g（1 bar,25℃）and 6.98 mmol/g（1 bar,0℃）,respectively.Combined with adsorption experiment and molecular simulation calculation,the research shows that the nitrogen functional groups on the surface of carbon materials play a crucial contribution on CO₂ adsorption capacity at relative low pressure（0～0.16 bar）.In the case of relative high pressure（0.16～1 bar）,narrow micropore volume determins the CO₂ uptake capacity.（2）Using eucalyptus bark as carbon source and chitosan as nitrogen source,nitrogen-doped porous activated carbon materials（CPCs）were prepared by pre-carbonization combined with chemical activation method.The characterization results show that the porous carbon materials CPCs have high specific surface area(838～1495 m²·g^-1),large total pore volume(0.46～0.71 m³·g^-1)and rich nitrogen content（1.21～3.33wt%）.Using CPCs as adsorbents,the static adsorption experiments of CO₂ and toluene were carried out respectively.The results of CO₂ adsorption experiment on CPCs showed that the main factor affecting the CO₂ adsorption capacity at relative low pressure（0～0.16 bar）was nitrogen-containing functional groups.At relative high pressure（0.16～1 bar）,the narrow micropore volume determined the CO₂ adsorption performance.The results of toluene adsorption experiment showed that under the adsorption conditions of 25℃and 4 k Pa,the adsorption capacity of CPCs for toluene gradually increased with the increase of activation temperature.Among them,the sample CPC800 has the largest toluene adsorption capacity,which is 4.37 mmol/g.It is indicated that higher activation temperature can improve the specific surface area and pore volume structure of carbon materials,which provides more adsorption sites for the adsorption of toluene.In addition,specific surface area and micropore volume play a major role in promoting the adsorption of toluene by porous carbon materials,and nitrogen-containing functional groups are secondary factor in promoting the adsorption of toluene.The adsorption energy and adsorption equilibrium distance between different functionalized graphene and toluene were calculated by GCMC molecular simulation.The results show that the introduction of nitrogen-containing functional groups strengthens the interaction between carbon surface and toluene molecules,thus promoting the adsorption capacity of toluene on CPCs.