Multi-Elements Doped Porous Carbons:Preparation,Gas Adsorption And Separation

The effective separation of mixtures is widely demanded in many fields such as chemicals,energy,and daily life.However,the traditional separation based on thermal processes such as rectification and fractional liquefaction has a relatively high cost problem due to its huge energy consumption.In addition,there are many problems in the separation process of selective impurity elimination based on chemical reaction,such as high equipment investment and high catalyst price.Therefore,in recent years,the cost-effective selective adsorption separation based on porous materials has been widely recognized as a new direction of green separation,which has the advantages of material recyclability,simple equipment,low cost and high selectivity.Therefore,the development of low-cost,highly selective porous adsorbents appears to be of great scientific and practical industrial value.The porous material has the advantages of rich composition,strong modification,high specific surface area and adjustable pore structure.Among them,porous carbon materials have attracted more attention because of their low cost,high specific surface area,good thermal/chemical stability,adjustable pore structure and easy regeneration.It is well known that for gas adsorption,microporous materials can exhibit optimal performance,while the microporous-mesoporous-macroporous hierarchical pore structure can significantly improve mass transfer during separation,thereby improving dynamic separation ability.In addition,heteroatom doping can improve the intrinsic polarity of carbon-based skeleton and construct more active adsorption sites,which is an effective means to significantly change and enhance the adsorption activity of porous materials.Therefore,combined with the urgent demand for porous carbon materials in the field of adsorption separation,this paper prepared a series of carbon-based porous materials and studied their gas adsorption separation performance.The specific contents are as follows:?1?Heteroatom doped carbon quantum dots were prepared by microwave assisted process using citric acid,urea,thiourea as carbon and hetero atom sources.The preparation method of various materials was explored and optimized,which provided a reliable basis for the subsequent preparation of high specific surface area porous carbon materials.Furthermore,the semiconductor properties of doped carbon quantum dots are further characterized.The doped carbon quantum dots undergo significant luminescence peak shift,which confirms that the doping of surface heteroatoms greatly affects the electronic structure of carbon materials.?2?Using carbon nanotubes doped with heteroatoms,a series of multi-element doped?O/N/S?porous carbon materials with high specific surface area and large porosity were constructed by chemical activation.The O/N/S co-doped porous carbon prepared at 800°C has a high specific surface area and a large porosity.Here,the chemical composition and pore structure information were characterized in detail by various means such as BET,XPS and TEM,and the hydrogen adsorption performance was evaluated in depth.It can be seen from the test that the porous carbon prepared by us has the microporous-mesoporous-macroporous composite hierarchical structure characteristics,and the porous carbon?CT-800?has the highest volume H₂ adsorption at 77 K,which can reach 267.3 cm³ g^-1.More importantly,a series of s-type and n-type doped carbon models were constructed to clarify the influence of heteroatoms on the adsorption of H₂ molecules by studying the adsorption mechanism.The interaction between H₂ and the adsorption carrier was mainly generated through the interaction of van der Waals forces.?3?Taking natural cellulose as raw material,nitrogen doped cellulose-based porous carbon materials were obtained by means of low-temperature dissolution and normal temperature mixing,high-temperature carbonization and other methods.The experimental results show that the porous carbon?CL-2-600?prepared by the low-temperature cellulose dissolution strategy has relatively low CO₂ absorption but high CO₂/N₂ selectivity?253?.More notably,we tested the regenerative capacity of CL-2-600 using breakthrough experiments and found that the sample was fully regenerated under relatively mild conditions and was a good capture of CO₂ gas.