Diaminopropane-Functionalized Metal-Organic Frameworks with Controllable Diamine Loss and One-Channel Flipped CO2 Adsorption Mode

Abstract

Diamine-functionalized metal-organic frameworks (MOFs) based on Mg2(dobpdc) (dobpdc4-=4,4'-dioxidobihyenyl-3,3'-dicarboxylate) are considered promising CO2 adsorbents owing to their characteristic stepwise adsorption behavior. However, the high temperatures required for CO2 desorption from diamine-Mg2(dobpdc)-based adsorbents induce gradual diamine loss. Additionally, the existence of an exotic CO2 adsorption mode remains experimentally unanswered. Herein, we present CO2 adsorbents obtained by functionalizing Mn2(dobpdc) with a series of diaminopropane derivatives. The low regeneration energies of these adsorbents allow for CO2 desorption at temperatures lower than those reported for Mg-based analogs. Our first-principles density functional theory calculations indicated that the bond strength between the diamine and Mn ions in Mn2(dobpdc) is greater than that between the diamine and Mg ions in Mg2(dobpdc). This stronger bonding prevents diamine loss even at high temperatures and enables efficient regeneration. Additionally, the computational and experimental results showed that MOFs functionalized with primary-tertiary diamine exhibit unique one-channel flipped adsorption structures that have not been previously observed. Our findings provide valuable insights into the role of metal ions in diamine loss for the future development of efficient amine-based CO2 adsorbents.