Flexible-Rigid Aluminum-Organic frameworks with Ultra-Fine Pore-Environment regulation for benchmark acetylene storage and purification

Rational regulation of functional groups on the pore surface of robust aluminum metal–organic framework (CAU-10-H) from amino (–NH2), hydrazino (–N2H3), to azido (–N3) continuously control their framework rigidity-flexibility together with ultra-fine pore-size change in the scale of 0.1–0.5 Å. Benefited from the rigid architecture and suitable pore environments, CAU-10-NH2 exhibits a supreme acetylene (C2H2) storage density (473 g/L) exceeding the values of liquid C2H2 (393 g/L) and all reported MOF adsorbents under ambient conditions. Different from CAU-10-H/NH2/N2H3, CAU-10-N3 exhibited temperature-dependent flexible stepwise adsorption behaviors for C2H2 with azido groups as the guest-sensitive gate, having highest storage capacity (106 cm3 cm−3) and second-high storage density (405 g/L) among these materials. Notably, compared with other C2-hydrocarbon and CO2 molecules, only C2H2 can open the azido door at 298 K, and thus effectively enhancing their separation selectivity with top-level uptake ratios for C2H2/C2H4 (2.65) and C2H2/CO2 (2.93), which are further supported by the practical fixed-bed breakthrough curves and theoretical simulations. Such a rational combination of rigidity and flexibility breaks new ground in MOF chemistry and sets a benchmark for acetylene storage and purification.