Crystal-Size Effects on Carbon Dioxide Capture of a Covalently Alkylamine-Tethered Metal-Organic Framework Constructed by a One-Step Self-Assembly

To enhance the carbon dioxide (CO₂) uptake of metal-organic frameworks (MOFs), amine functionalization of their pore surfaces has been studied extensively. In general, amine-functionalized MOFs have been synthesized via post-synthetic modifications. Herein, we introduce a one-step construction of a MOF ([(NiL_ethylamine)(BPDC)]=MOF_NH2; [NiL_ethylamine]²⁺=[Ni(C₁₂H₃₂N₈)]²⁺; BPDC^2-=4,4′-biphenyldicarboxylate) possessing covalently tethered alkylamine groups without post-synthetic modification. Two-amine groups per metal centre were introduced by this method. MOF_NH2 showed enhanced CO₂ uptake at elevated temperatures, attributed to active chemical interactions between the amine groups and the CO₂ molecules. Due to the narrow channels of MOF_NH2, the accessibility to the channel of CO₂ is the limiting factor in its sorption behaviour. In this context, only crystal size reduction of MOF_NH2 led to much faster and greater CO₂ uptake at low pressures.