碳化多孔有机骨架制备氮掺杂多孔碳及其气体吸附研究

Preparation of N-doped Porous Carbon from Porous Organic Framework for Gas Sorption

通过简单的一步碳化方法,以含氮的多孔有机骨架JUC-Z2为碳前驱物制备出氮掺杂多孔碳材料.与原始JUC-Z2材料相比,制备的多孔碳材料显示出明显提高的气体吸附量和增强的吸附焓.其中JUC-Z2-900的CO2吸附量高达113 cm3·g-1,H2吸附量也达到246 cm3·g-1,超过了大部分报道的多孔材料.尤其是JUC-Z2-900的CH4吸附量在273 K,1 bar下高达60 cm3·g-1,据我们所知,这一值为目前报道材料的最高值.除此之外,样品还显示出选择性吸附CO2的能力,273 K下,JUC-Z2-900的CO2/N2的选择性高达10,CO2/H2的选择性也高达66.另外,样品具有很高的热稳定性,有望应用在碳捕获和清洁能源储存等领域.

In this report, a series of N-doped porous carbon materials were successfully prepared from nitrogen-containing porous organic framework JUC-Z2. Compared to original JUC-Z2, the carbonized samples show obviously enhanced gas uptake and isosteric heats of adsorption(Qst for short). Among the carbonized samples, JUC-Z2-900 shows high CO2 uptake of 113 cm3·g-1 at 273 K and 1 bar and H2 sorption of 246 cm3·g-1 at 77 K and 1 bar, surpassing most reported porous materials. Especially for CH4 sorption, a large sorption amount of 60 cm3·g-1 could be achieved at 273 K and 1 bar. To our best knowledge, this value is comparable to the highest among all the porous materials reported to date. Apart from high gas uptake, the carbon materials also show selective adsorption ability. At 273 K, JUC-Z2-900 shows a high CO2/N2 adsorption selectivity of 10 and CO2/H2 adsorption selectivity of 66. Raman spectra showed two Raman shifts, the G-band at 1590 cm-1is associated with the E2 g mode of graphite, whereas the D-band centered at around 1360 cm-1 is attributed to the D-band of disordered carbon, corresponding to the defect-induced mode. The intensity of D-band is higher than G-band, indicating a low degree of graphitization. This is also confirmed by powder X-ray diffraction results. X-ray Photoelectron Spectroscopy(XPS) results indicate the nitrogen content is 3.26 wt%, 2.88 wt% and 2.19 wt% for JUC-Z2-700, JUC-Z2-800 and JUC-Z2-900 respectively. Though the nitrogen content decreased after carbonization, the gas sorption increased greatly. This can be attributed to the increased heat of adsorption of the carbonized samples. First, the narrow pore size after carbonization is beneficial for gas storage. Reports indicate that by tuning the pore sizes to around the kinetic diameter of CO2, it may be possible to increase the number of double or multiple interactions between the adsorbed CO2 and the pore walls. Second, the all-carbon-scaffold networks also benefit the gas-adsorbent interaction. Last but not the least, the N-doped framework also devote the high gas uptake. Besides the high gas uptake, the carbon materials exhibit high thermal stabilities and could be stable up to 500 ℃. Based on the above results, the carbon materials show great potential in the fields of CO2 capture and clean energy storage.