Probing the role of O-containing groups in CO₂ adsorption of N-doped porous activated carbon

Abstract

Porous activated carbons (PACs) are promising candidates to capture CO through physical adsorption because of their chemical stability, easy-synthesis, cost-effectiveness and good recyclability. However, their low CO adsorption capacity, especially low CO/N selectivity, has limited their practical applications. In this work, an optimized PAC with a large specific surface area, a small micropore size, and a large micropore volume has been synthesized by one-step carbonization/activation of casein using KCO as a mild activation agent. It showed a remarkably enhanced CO adsorption capacity as high as 5.78 mmol g and an excellent CO/N selectivity of 144 (25 °C, 1 bar). Based on DFT calculations and experimental results, the coexistence of adjacent pyridinic N and -OH/-NH species was proposed for the first time to make an important contribution to the ultra-high CO adsorption performance, especially CO/N selectivity. This work provides effective guidance to design PAC adsorbents with high CO adsorption performance. The content of pyridine N combined with -OH/-NH was further elevated by additional nitrogen introduction, resulting in a further enhanced CO adsorption capacity up to 5.96 mmol g (25 °C, 1 bar). All these results suggest that, in addition to the well-defined pore structure, pyridinic N with neighboring OH or NH species played an important role in enhancing the CO adsorption performance of PACs, thus providing effective guidance for the rational design of CO adsorbents.

Carbon nanoflake hybrid for biohydrogen CO 2 capture: Breakthrough adsorption test

“…Currently, the best pore size for CO 2 capture is still debatable; small pores are the best structures because of their high total surface area, but they are at risk of pore blockage. Wang et al concluded that a high‐surface‐area macroporous framework sorbent with extremely high microporosity contributes to excellent CO 2 adsorption at relatively low pressure . Isahak et al discussed that mesopores are better than micropores because the latter undergo pore blockage, particularly after amine impregnation .…”

“…For example, N doping at high temperatures is better than the conventional low‐temperature amine impregnation because the latter is exposed to degradation factors during high‐temperature CO 2 adsorption. The base group is also important for hydrogen bonding between CO 2 and N‐friendly neighboring H atom (pyridinic N) because it promotes CO 2 capture by acting as a good Lewis base and interacts with the acidic CO 2 readily …”

“…Wang et al concluded that a high-surface-area macroporous framework sorbent with extremely high microporosity contributes to excellent CO 2 adsorption at relatively low pressure. 24 Isahak et al discussed that mesopores are better than micropores because the latter undergo pore blockage, particularly after amine impregnation. 25 In addition to optimizing the pore structure, the basicity of adsorbent must be increased through Lewis base addition because CO 2 is acidic.…”

“…The base group is also important for hydrogen bonding between CO 2 and Nfriendly neighboring H atom (pyridinic N) because it promotes CO 2 capture by acting as a good Lewis base and interacts with the acidic CO 2 readily. 24,28 Few general approaches have been reported for Ndoped carbon material preparation with high surface area and N density. These methods have been collected by Gong et al as physical and chemical activation using acids (nitric acid), alkalis (potassium hydroxide), and other etching materials (water and CO 2 ).…”

Great Location: About Effects of Surface Bound Neighboring Groups for Passive and Active Fine-Tuning of CO2 Adsorption Properties in Carbon Capture Materials

“…Wang et al studied the influence of coexisting pyridinic nitrogen species with adjacent OH/NH2 species and found that these neighboring groups play an important role in enhancing the capture performance of porous organic polymers. [6] Bloch et al showed a first example of NG interactions with other functional groups. [7] They used an indole carrying a second functional group to investigate the interplay between the secondary amine of the indole and the second functional group.…”