Mixed polyamines promotes CO₂ adsorption from air

The deployment of large-scale direct air capture (DAC) technology relies on the development of energy-efficient and cost-effective CO₂ capture materials. The high desorption temperature of the current DAC adsorbents, especially the supported polyamines, is undesirable. In this work, the "mixed-polyamines" concept was adopted to prepare class 1 adsorbents by impregnating both tetraethylenepentamine (TEPA) and diethanolamine (DEA) into the mesoporous SBA-15. The synergy of TEPA and DEA influences the reaction mechanism between CO₂ and amines sites, resulting in higher amine efficiency and lower regeneration temperature. Moreover, CO₂ adsorption and desorption kinetics are enhanced by the introduction of hydroxyl groups from DEA. The desorption process of solid polyamines-loaded adsorbents fits well with the Avrami model under ultra-dilute CO₂ concentrations. SBA-15 loaded mixed polyamine with a weight ratio of TEPA to DEA equaling to 4 shows a maximum CO2adsorption amount of 1.93 mmol/g at 400 ppm CO2and 25 °C, a fast adsorption rate of 1.82 mmol/(g·h), and a desorption rate of 0.26 mmol/(g·min) at 80 °C within the first 5 min, which is believed to be a promising DAC adsorbent for practical application.