Solvent-Free And One-Step Synthesis Of Porous Carbon Materials With Ultra-High Nitrogen Contents For SO₂ Capture

At present,traditional industries play an important role in the social economy.These industries include oil and gas extraction and coal chemical industry.As is known to all,the products of these industries have been closely related to human life and have made human society develop rapidly.However,human beings have to face a series of social problems caused by the operation of these industries,such as the over-consumption of non-renewable energy,the pollution of industrial wastewater and the emission of industrial exhaust.Among them,the global environmental damage caused by industrial exhaust emissions has seriously threatened the survival of human beings.SO₂ is a toxic gas with highly corrosive and acidic,and its emission will cause serious environmental problems such as acid rain and haze.At the same time,SO₂ is also an important industrial raw material.Therefore,the development of efficient and selective SO₂ adsorbents has far-reaching social significance.Porous carbon materials are widely used in the fields of catalysis,energy,batteries and adsorption due to their high specific surface area,adjustable pore structure,excellent mechanical and chemical stability and outstanding thermal conductivity.It is worth pointing out that porous carbon materials are abundant in source and low in cost.In addition,nitrogen-doped porous carbon materials are considered to be an efficient SO₂ adsorbent due to the abundant lewis alkaline sites on the surface.However,there are two main challenges in preparing nitrogen-doped porous carbon:（1）it is difficult to achieve high nitrogen doping due to the high temperature of the porous carbon material;（2）it is difficult to control the pore size distribution of nitrogen-doped porous carbon materials.In order to overcome the above challenges,a series of nitrogen-doped porous carbon was successfully constructed by solvent-free and one-step method that were using the rich and low-cost glucose as carbon source and nitrogen-rich urea,melamine and g-C₃N₄ as nitrogen source.These specific works are as follows:First,in chapter 2 we propose urea as a nitrogen source.Urea is a cheap industrial product,rich in nitrogen,and it produces a large number of nitrogen-containing gases in the pyrolysis process.These nitrogen-containing gases are not only good nitrogen dopants,but also efficient pore forming agents.Therefore,the nitrogen contents of the porous carbon prepared in chapter 2 is up to 11.5～17.4 wt.%,and its pore size distribution is mainly concentrated in 0.6～0.9 run.In addition,the gas adsorption experiment shows that the nitrogen-doped microporous carbon capture SO₂ has high efficiency,selectivity and excellent recycling performance.Secondly,in chapter 3,we propose to use melamine as a nitrogen source.On the one hand,because melamine is rich in nitrogen contents,on the other hand,because melamine is an intermediate product in the pyrolysis process of urea.During the pyrolysis of melamine,lamellar g-C₃N₄ was generated at 500～600 ℃,and lamellar g-C₃N₄ further guided the formation of lamellar graphene.When the pyrolysis temperature reached 600～700℃,a large number of layered g-C₃N₄ volatilized nitrogen-containing gases were used as nitrogen dopants to make layered graphene curl and form mesoporous framework.It is worth pointing out that GMF-30 prepared in chapter 3 has an IAST selectivity of up to 23.4 and 724.5 for SO₂/CO2 and SO₂/N2 mixtures when the SO₂ mole fraction ratio is 0.1.The quantum calculation results further confirm that the nitrogen-doped mesoporous carbon has an ultra-high selectivity for SO₂ in SO₂/CO2 and SO₂/N2 mixtures.Finally,in chapter 4,we successfully prepared nitrogen-doped porous carbon with rich mesoporous morphology by using g-C₃N₄ as nitrogen dopants and soft templates.The fourth chapter shows that with the increase of mass ratio of nitrogen source to carbon source,it is helpful to the formation of flake morphology of porous carbon materials.In addition,the nitrogen-doped mesoporous carbon prepared in chapter 4 has ultrahigh pore volume（2.18～2.83 cm3·g-1）.Furthermore,the adsorption capacity of GC-4 on SO₂ at 273 K and 100 kPa is as high as 18.7 mmol·g-1.In summary,a series of nitrogen-doped porous carbon with narrow pore spacing distribution was successfully constructed by simple and green synthesis method in this paper,and confirmed that nitrogen-doped porous carbon has high efficiency and selectivity for SO₂ capturing.