Ambient and sub-ambient temperature direct air CO2 capture (DAC) by novel supported in situ polymerized amines

Abstract

With the dramatic increase in CO₂ emissions over the last few decades and the subsequent increase in global temperatures leading to climate change, substantial efforts have been directed towards the development of materials designed for the direct capture of CO₂ from the atmosphere, a process known as direct air capture (DAC). DAC stands out as one of the primary negative emission technologies (NETs) expected to play a pivotal role in achieving negative CO₂ emissions. However, most of the reported sorbent performances have been focused on ambient temperatures (around 25 °C) or higher, specifically under dry conditions, with very few exceptions. This limitation has posed a significant obstacle to the widespread deployment of DAC, as a substantial portion of the world experiences sub-ambient temperatures and non-zero humidity levels. In this study, we evaluate the in situ cationic ring-opening polymerization of three different 2-oxazolines monomers initiated by CPTMS or IPTMS, which are chemically tethered to mesoporous silica foam (MSF) and large-pore alumina-silica (LPAlSi) supports, and their performance for CO₂ capture under various conditions. Among all combinations of supports, initiators, and monomers, the MSF–C–EtOX sorbent demonstrated exceptional utilization of the support, initiator, and monomer properties, resulting in superior CO₂ uptakes under various conditions. The optimum adsorption temperature under dry conditions was found to be 40 °C, achieving a CO₂ uptake of 1.72 mmol g⁻¹. Further testing under sub-ambient dry adsorption conditions at −20 °C showed a CO₂ capacity of 0.80 mmol g⁻¹. The introduction of moisture significantly enhanced CO₂ uptakes, reaching 2.45 mmol g⁻¹ at 20 °C. Under humid conditions, the sorbent exhibited robust performance at low temperatures, with CO₂ uptakes of 1.88 and 1.40 mmol g⁻¹ at 0 °C and −20 °C, respectively. Importantly, the sorbent demonstrated stable cycling capacity over 50 and 10 cycles under dry and humid conditions, respectively. The findings presented in this study suggest that supported in situ polymerized amines are promising materials for DAC under ambient-temperature and low-temperature conditions. There are additional prospects for fine-tuning these materials to facilitate the large-scale implementation of DAC facilities under diverse environmental conditions.