Dual-State heptanuclear metal cluster-based MOF materials: Open Metal Sites Enhanced Acetylene/Ethylene Separation and Coordinated Water-Driven Propylene /Propane Kinetics

Abstract

In cluster-based MOF materials, although clusters with open metal sites (OMSs) play a critical role in separation processes，excessively strong OMSs can lead to a large amount of co-adsorption with the counterpart gases and result in reduced selectivity.Coordinated water molecules can not only results in atomic-level differences in pore size, but also can significantly affect the binding forces between the host frameworks and guest molecules. Herein, we report a methyl-modified heptanuclear cluster-based MOF, Ni7Me, constructed from inexpensive organic linkers under pure water conditions. Two guest-free materials, Ni7Me-80 (with coordinated water) and Ni7Me-200 (with OMSs), were synthesized to investigate the separation properties and mechanisms for C2H2/C2H4 and C3H6/C3H8 mixtures. Dynamic breakthrough tests showed that both Ni7Me-80 and Ni7Me-200 could achieve clean separation of binary C2H2/C2H4 mixtures (5/95 v/v), yielding high-purity C2H4 (>99.9%). Grand canonical Monte Carlo (GCMC) simulations revealed that the enhanced adsorption and separation performance of Ni7Me-200, compared to Ni7Me-80, is primarily due to differences in the interaction forces between C2 molecules and the framework, independent of the OMSs. Notably, Ni7Me-80 exhibited thermodynamically driven adsorption for C3H6, while showing kinetic behaviour for C3H8 adsorption. This unique property enabled effective separation of C3H6 and C3H8, as demonstrated by dynamic permeation tests. Stability tests further showed that Ni7Me has exceptional air and boiling water stability.