Facile synthesis of hydrophobic amine-functionalized silica aerogel with low regeneration temperature and long-term stability for efficient direct air capture

The objective of this research is to develop an adsorbent with long-term stability for direct air capture of CO 2 (DAC) under humid conditions. Silica aerogel with amine and methyl hybridized (SA-AM) was synthesized to achieve long-term stability and high CO 2 adsorption performance under humid conditions. SA-AM-M with a moderate precursor concentration exhibited well-developed nanostructure and hydrophobicity, achieving a specific surface area of 306 m 2 /g and a water contact angle of 133°. The CO 2 adsorption capacity of SA-AM-M is 0.97 and 1.14 mmol/g at 25 °C with dry and humid 400 ppm CO 2 , respectively. The CO 2 adsorption capacity mainly depends on the temperature, and lower temperature leads to higher CO 2 adsorption capacity in the range of 5–45 °C. The average adsorption rate shows a positive dependency with gas flow rate, indicating that the working capacity can be improved by increasing gas flow rate significantly. SA-AM-M exhibited the lowest regeneration temperature (65 °C) among reported adsorbents for DAC. The diminishment of CO 2 adsorption capacity is only 35 % after the long-term aging for equivalent 18 months at 25 °C and 65 % relative humidity. This study smoothly combines two different functional groups within the silica aerogel, offering significant guidance towards the development of durable aerogels with high performance for practical DAC.