Enhanced adsorption efficiency through materials design for direct air capture over supported polyethylenimine

Until recently, carbon capture and sequestration (CCS) was regarded as the most promising technology to address the alarming increase in the concentration of anthropogenic CO₂ in the atmosphere. There is now an increasing interest in carbon capture and utilization (CCU). In this context, the capture of CO₂ from air is an ideal solution to supply pure CO₂ wherever it is needed. Here, we describe innovative materials for direct air capture (DAC) with unprecedented efficiency. Pol-yethylenimine (PEI) was supported on PME, which is an extralarge-pore silica (pore-expanded MCM-41) with its internal surfaces fully covered by a uniform layer of readily accessible C₁₆ chains from cetyltrimethylammonium (CTMA⁺) cations. The CTMA⁺ layer plays a key role in enhancing the amine efficiency toward dry or humid ultradilute CO₂ (400 ppm CO₂/N₂) to unprecedented levels. At the same PEI content, the amine efficiency of PEI/PME was two to four times higher than that of the corresponding calcined mesoporous silica loaded with PEI or with different combinations of C₁₆ chains and PEI. Under humid conditions, the amine efficiency of 40 wt % PEI/PME reached 7.31 mmol_CO2/g_PEI, the highest ever reported for any supported PEI in the presence of 400 ppm CO₂. Thus, amine accessibility, which reflects both the state of PEI dispersion and the adsorption efficiency, is intimately associated with the molecular design of the adsorbent.