Study On SO₂ Adsorption Characteristics On The Surface Of Nitrogen-doped Activated Carbon

Activated carbon is widely used in environmental pollution control due to its strong adsorption performance and economic and environmental protection characteristics.Among the environmental pollution problems,air pollution is the most serious problem,and it is also the most closely related to human production and life,and SO2 is one of the most harmful pollutants.The activated carbon is modified by chemical means,and the molecular structure model of activated carbon is constructed to explain the relationship between the adsorbate and the structure of the adsorbent from the molecular level,which provides a new idea for in-depth exploration of the adsorption performance of activated carbon.The current activated carbon model focuses more on the reduction of activated carbon morphology,but ignores the reduction of chemical and physical properties.Therefore,the simulation study of carbon behavior also has certain limitations.In this paper,based on X-ray photoelectron spectroscopy scanning,element analysis and BET pore size analysis,a molecular structure model of porous activated carbon was constructed.Use Perl script programming to realize the editing of functional groups and the addition of nitrogen-containing functional groups.On this basis,the adsorption position and adsorption state of SO2 on the surface of the graphite crystallite layer,and the migration law in the pore structure are explained from the perspective of molecular simulation.First,the two activated carbons(coal-based activated carbon and coconut shell-based activated carbon)were modified at different temperatures(450℃ and 950℃),and then X-ray photoelectron spectroscopy,element analysis,and BET nitrogen isotherm adsorption and desorption.The physical and chemical properties of activated carbon before and after modification were characterized.The activation of urea has no obvious effect on the formation of the pore structure of activated carbon.Urea activation can effectively increase the nitrogen content on the surface of activated carbon.After activation,the proportion of pyridine nitrogen on the surface of coconut shell-based activated carbon increased.Due to the higher oxygen content in coal-based activated carbon,the content of oxidized nitrogen-containing functional groups is higher(such as pyridine nitrogen oxide and pyrrole nitrogen oxide).450℃ is better than 950℃ to increase the content of nitrogen-containing functional groups on the surface of activated carbon with urea.Compared with the activation temperature of 950℃,the surface nitrogen content of activated carbon at 450℃ rises more(1.32%).After the homogeneous activated carbon is treated at the same temperature,the desulfurization capacity of the urea activated group is higher than that of the activated carbon without urea activation.The best performance in the adsorption experiment was coconut shell-based activated carbon activated by urea at 450℃.Combining the X-ray photoelectron spectroscopy scan and the calculation results of BET and NLDFT in the experimental stage,the activated carbon molecular structure model was reconstructed,and the simulated adsorption of SO2 was performed on it.The adsorption sites and adsorption state of SO2 on the surface of activated carbon were investigated.The saturated adsorption capacity of sulfur dioxide of the simulated coconut shell-based activated carbon doped with nitrogen is 0.204mg/g,which is higher than the activated carbon without nitrogen(0.2mg/g).The saturated adsorption capacity of the same simulated coal-based activated carbon with nitrogen added is increased from 0.223mg/g to 0.226mg/g.The adsorption energy of a single sulfur dioxide molecule on the surface of the simulated coconut shell-based activated carbon is about-69.25kJ/mol,and the average adsorption distance is about 3.81 A;the adsorption energy on the surface of the simulated coal-based activated carbon is about-72kJ/mol,the average adsorption after activation.The distance is reduced from 3.95 A to 3.75 A.The uneven surface of the graphite microcrystalline layer and the edges of the graphite microcrystalline layer are easy to provide the best adsorption sites for sulfur dioxide molecules.Sulfur dioxide molecules tend to be adsorbed on pore structures with pore diameters around 15A.