L-lysine-assisted synthesis of gismondine and chabazite nanozeolites for direct air capture of CO2

Abstract

The search for more efficient and selective solid adsorbents towards carbon capture, particularly in trace CO2 concentration, remains a significant challenge. Here, we present the synthesis of nanocrystalline sodium gismondine (Na-GIS) with Si/Al = 2.5 and potassium chabazite (K-CHA) zeolites with Si/Al = 2.0 using L-lysine as a crystal growth inhibitor. Na-GIS nanozeolites were found to show a CO2 uptake as high as 0.70 mmol g−1 under direct air capture (DAC) conditions (i.e., 298 K and 400 ppm CO2), about 18 times greater than that of microcrystalline Na-GIS, together with high adsorbent stability. Such behavior was also observed for Na-CHA nanozeolites, although the extent of increase (0.47 vs 0.13 mmol g−1) was smaller compared to the microcrystalline counterpart. This study demonstrates that the introduction of nanocrystallinity into small-pore zeolites without losing intrinsic microporosity is a viable route to the development of more efficient zeolite-based DAC adsorbents.