An adsorbate biased dynamic 3D porous framework for inverse CO2 sieving over C2H2.

ABSTRACT

Separating carbon dioxide (CO2) from acetylene (C2H2) is one of the most critical and complex industrial separations due to similarities in physicochemical properties and molecular dimensions. Herein, we report a novel Ni-based three-dimensional framework {[Ni4(µ3-OH)2(µ2-OH2)2(1,4-ndc)3](3H2O)}n (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å2), that perfectly matches with the molecular size of CO2 and C2H2. The dehydrated framework shows structural transformation, decorated with an unsaturated Ni(ii) centre and pendant oxygen atoms. The dynamic nature of the framework is evident by displaying a multistep gate opening type CO2 adsorption at 195, 273, and 298 K, but not for C2H2. The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO2 selectivity over C2H2, attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, in situ spectroscopic inspection, and selectivity approximations. In situ DRIFTS measurements and DFT-based theoretical calculations confirm CO2 binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.