Design And Synthesis Of N-doped Microporous Carbon Materials And Their CO2 Adsorption Performance

The massive exploitation of fossil fuels has severely damaged the environment in which human beings live.The use of fossil fuel generates huge amount of CO2emission,which is a major component of greenhouse gases causing global climate changes and threats to human.Therefore,the reduction of CO2 emission becomes a global target.Carbon capture and storage(CCS)technology has become the focus of research.One of its cores is to find ideal adsorbents,which possess the advantages of large adsorption capacity,high physical and chemical stability,high selectivity,and strong recycling ability.In recent years,a range of porous materials with wide chemical compositions have been studied because of their large specific surface area,high pore volume and good CO2 capture performance.Among them,porous carbonaceous materials have gained wide interest and much progress in CO2 adsorption.However,the adsorption capacity and selectivity of the traditional activated carbonsare yet to be improved.In this thesis,we focus on N-doped porous carbonaceous materials for CO2 adsorption.In order to take the advantages of carbon materials and to overcome some of its demerits,we have proposed the solvent-free synthesis of highly microporous and highly N-doped carbonaceous materials.The pore structure,surface chemical properties of the resultant materials have been adjusted and their CO2 adsorption performance under different conditions has been studied with the correlations between pore structure and surface chemical properties and adsorption capacity and selectivity established.Theresultant N-doped microporous carbonaceous adsorbents show high capacity,high electivity and excellent cyclic capability for CO2 capture.The main research contents and results of the thesis are as follows.(1)In order to improve the issues of low microporosity,low N content and the use of large amount of solvents in the synthesis process for conventional porous carbonaceous materials,we proposed the solvent-free one-step reaction activation method.The key concept of the method is the use of bases to react with amphoteric amino acids and subsequently in-situ activate their derivatives.Typically,arginine and other amphipathic amino acids can react with alkaline molecules such as potassium hydroxide in a solvent-free condition to achieve a uniform mixing.In the process of in situ polymerization and activation,potassium hydroxide can not only act as a pore-forming agent,but also act as a shield agent of carboxyl group so as to better retain the N sites and create rich micropores,even pure microporous materials.This method that use of acid-base reaction and in-situ activation had a good universality.We have used a variety of amino acids and a variety of alkaline activators,and ultimately have obtained a series of carbonaceous adsorbents with high micropore ratios,high N contents and high performance for CO2 capture.(2)The structure and property of the obtained materials were well characterized.The skeleton of the materialswere a carbonaceous material similar to an organic polymer.The microporosity occupancy was as high as 100%in most cases,and the nitrogen content was as high as 16.9 wt%.The pore sizes of the materials were distributed between the super-micropores(0.8?1 nm)and ultra-micropores(<0.8 nm),with the 0.57 nm micropores as the most abundant ones.They obtained materials showhigh CO2 adsorption performance,that is,the adsorption capacity can reach 4.17 mmol/g,and the CO2/N2 selectivity can reach 150.(3)We adjusted the physicochemical property,surface composition,and microporosity ratio of the resulting materials by adjusting the amount of activator and the activation temperature.We investigated the relationship between the N content and micropore occupancy and the CO2 adsorption capacity and CO2/N2 selectivity.The N atom can help to capture more CO2,which is a key factor in determining the selectivity of CO2/N2.At the same time,the micropore volume is another decisive factor for CO2/N2selectivity.(4)By changing the activation temperature,N-containing microporous/mesoporous carbon materials with a specific surface area of up to 2686 m2 g-1 can be obtained,which can be applied to an electrochemical supercapacitor.It showed a good double layer capacitance behavior.At a current density of 0.5 A/g,the capacitance can reach 210 F/g with a good rate performance.(5)For the first time,we reported the useof the deoxynucleic acids with very high theoretical nitrogen content as the precursors and the mesoporous silica SBA-15 as the mesoporous template to successfully prepare ordered mesoporous carbon nitrides.the synthesis is based on a facile solvent-free assembly method.The carbon nitride materialscanbe expected to be used in the CO2 adsorption and other fields.