Abstract
(Two fluorinated ultra-microporous materials, NbOFFIVE-1-Ni and AlFFIVE-1-Ni with [NbOF5]2− and [AlF5]2− building block acting as inorganic pillars, respectively, result in much different adsorption behavior for CO2 and C2+. NbOFFIVE-1-Ni with confined pore space exhibit much higher CO2 uptake amount at low pressures, by contrast, AlFFIVE-1-Ni with potential open metal sites in pore spaces exhibit relatively larger pore volume, leading to enhanced C2H2 adsorption performance at low pressures and improved C2H2/C2H4 separation selectivity).
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•Stable fluorinated Metal Organic Frameworks with tunable structural properties.•Structural properties of MFFIVE-1-Ni with relation to C2+ adsorption were unveiled.•Substitution of Nb5+ by Al3+ led to improved separation for C2H2/C2H4:1/99 system.•NbOFFIVE-1-Ni shows unprecedented CO2/C2+ selectivity in favor of CO2.•Substitution of Nb5+ by Al3+ affects the mechanism involved in C2+ separations.
In this work, the reticular chemistry approach was implemented on a very stable ultra-microporous fluorinated MFFIVE-1-Ni MOFs to unveil the effect of subtle changes of the structure-employment of different fluorinated inorganic block on the adsorption of C2H2, C2H4 and CO2. A series of variable temperature single C2H2, C2H4 and CO2 adsorption isotherms and mixed gas adsorption column breakthrough experiments for different C2H2/C2H4 and CO2/C2H2 gas pair systems were carried out on the two isoreticular NbOFFIVE-1-Ni and AlFFIVE-1-Ni, containing respectively [NbOF5]2− and [AlF5]2− inorganic building blocks. The introduction of potential open metal site in a very confined pores led to favoring interaction of C2H2 but lowering the interaction with CO2, which resulted in enhancement of C2H2/C2H4 selectivity at low C2H2 concentration but a decrease in CO2/C2+ selectivity. The comparison of the C2H2/C2H4 and CO2/C2H2 separation performances with the structures of the MFFIVE-1-Ni MOFs provides useful information to shed light on the relationship between the structural features of this MOF platform and C2H2/C2H4 and CO2/C2H2 separation properties. This is a critical step in the wanted rational discovery/design of materials with enhanced performances for C2H2 recovery from C2H4 and CO2 at different concentration and having different level of input energy for recycling.