落叶松基氮掺杂泡沫炭的制备及其CO_(2)吸附性能研究

Preparation and CO_(2)Adsorption Performance of Larch-based N-doped Carbon Foam

以落叶松木屑为原料,尿素为氮源,采用苯酚液化-物理发泡-活化工艺制备了落叶松基氮掺杂泡沫炭。通过SEM、XRD、XPS、TG和N_(2)吸附-脱附等温线对材料的形貌、表面化学性质和孔结构进行表征,并测试了材料的CO_(2)吸附容量和CO_(2)/N_(2)吸附选择性,考察了氮掺杂量及活化温度对CO_(2)吸附性能的影响。研究结果表明:泡沫炭材料具有石墨层无序堆积的晶型结构,其无序性随着活化温度的升高而提高,氮掺杂会使其孔泡尺寸变小并降低其热稳定性;氮掺杂泡沫炭主要为微孔结构,微孔孔容占比最高可达95.83%。在活化温度为900℃、尿素掺杂量为4、6和8 g的条件下制备氮掺杂泡沫炭(NCF-4-900、NCF-6-900和NCF-8-900)的微孔孔径主要集中在0.50、0.81和1.26 nm,介孔孔径集中在3.85 nm左右;材料的掺杂氮以3种形式存在,活化温度为700和800℃时主要为吡啶型氮(N-6)和吡咯型氮(N-5);当活化温度达到900℃时部分N-5和N-6转化为热稳定性更好的四元型氮(N-Q),其中吡咯型氮含量最高;随着活化温度的升高,材料的CO_(2)吸附容量提高,在25℃和100 kPa下NCF-8-900具有最高的吸附容量(3.19 mmol/g)和CO_(2)/N_(2)吸附选择性(118.63)。

Larch-based N-doped carbon foam was prepared with larch sawdust as carbon source and urea as nitrogen source via phenol liquefaction-physical foaming-activation method.Morphology,surface chemical properties and pore structure of the prepared carbon foams were analyzed by SEM,XRD,XPS,TG and N_(2) adsorption-desorption isotherm.CO_(2)adsorption capacity and CO_(2)/N_(2) adsorption selectivity of the materials were tested as well.Effects of nitrogen doping and activation temperature on CO_(2)adsorption performance were investigated.The results showed that carbon foam had the crystal structure of disordered stacking of graphene layers,and its disorder increased with the rise of activation temperature.Nitrogen doping reduces the size of cell and thermal stability.Nitrogen-doped carbon foam exhibited typical microporous structure with the maximum micropore content of 95.83%.The microporous pore size of nitrogen-doped carbon foams(NCF-4-900,NCF-6-900 and NCF-8-900)which were prepared under the conditions of activation temperature of 900℃and urea doping amounts of 4,6 and 8 g were mainly concentrated at 0.50,0.81 and 1.26 nm,and the mesoporous pore size was concentrated in about 3.85 nm.The materials contained 3 types of nitrogen and they were mainly pyridine nitrogen(N-6)and pyrrole nitrogen(N-5)when the activation temperatures were 700 and 800℃.With the activation temperature reaching 900℃,some N-5 and N-6 were transformed into quaternary nitrogen(N-Q)with better thermal stability,and pyrrolic N was dominant.CO_(2)adsorption capacity increased with the rise of activation temperature.NCF-8-900 had the highest adsorption capacity(up to 3.19 mmol/g at 25℃and 100 kPa)and excellent CO_(2)/N_(2) adsorption selectivity of 118.63.