Synthesis Of Nitrogen-doped Porous Carbon Materials For CO₂Adsorption

Currently among all kinds of adsorbents for CO2such as zeolites, metal oxides, silicon gels, metal organic frameworks, hydrotalcites and various porous carbons, porous carbons stand out for their impressive characteristics such as strong chemical and thermoldynamic stability, giant specific surface area, excellent cycling and selective adsorption performance, being cheap and green. And because porous carbons are easy to be modified on the surface, in-situ doping or secondary doping method is often applied to introduce nitrogen element or alkali metal oxides (MgO, CaO and so on), which contributes to the CO2adsorption performance of porous adsorbents via base-acid interaction between alkali functional groups and CO2molecules.In our research F127and magnesium citrate were used respectively as soft and hard template, PF resin or UF resin as carbon source, melamine and urea as nitrogen source to synthesis nitrogen-doped porous carbons or MgO/N-doped porous carbons. The samples were characterized by SEM, XRD, N2physical adsorption, elemental analysis and infrared microspectrography, and adsorption of CO2on the samples under different temperatures were investigated.The main results are given as follows:1) Porous carbons prepared using F127as soft template, urea or melamine as nitrogen source, phenol formaldehyde resin as carbon source not only contained small mesopores with an average diameter of about2nm which are fit for CO2but also were rich in nitrogen element which were proved to exist in the form of basic amino groups. The samples were also tested as CO2adsorbents under15℃,25℃,50℃and75℃. The result showed that when the molar rate of melamine against phenol was2, the specific surface area of the sample was189m2/g, the average pore diameter was2.1nm, the nitrogen elemental concentration was9.19%and the CO2adsorption capacity under15℃reached as high as147mg/g.2) Nitrogen-doped porous carbons were obtained after washing with diluted HC1MgO/nitrogen-doped porous carbons prepared employing magnesium citrate as hard template, urea-formaldehyde resin as both carbon and nitrogen source. The specific surface area of porous carbons containing MgO reached249m2/g at most with CO2adsorption capacity under15℃up to104mg/g while samples obtained after removing MgO boasts of the highest surface area of1501m/g with an average pore diameter of2.9nm, total pore volume of0.8cm3/g and the highest CO2adsorption capacity under15℃being146mg/g.3) After comparing CO2adsorption capacity of different samples, we come to a safe conclusion that specific surface areas, average pore diameters, concentration of basic nitrous groups and MgO have great impact on CO2adsorption capacity. The higher the specific surface area, the concentration of basic nitrous groups and MgO are, the closer the pore diameter is to0.7nm and the lower the temperature is, the higher the CO2adsorption capacity is.