Confined Mg2+-Directed Interfacial Evolution of Primary Structural Units of Mg-MOF-74 on Platelet Clinoptilolite for CO2/CH4, CH4/N2, and CO2/N2 Separations

Abstract

Controlling MOF nucleation on zeolite surfaces remains challenging when metal ions are freely supplied in solution, often resulting in poorly regulated interfaces. Herein, Mg2+-exchanged platelet clinoptilolite (Mg-PCP) was used as a confined metal source to direct the in situ growth of Mg-MOF-74-related sol–gel species (primary structural units, abbreviated as PSUs) without adding external Mg2+ salts. Using 2,5-dihydroxyterephthalic acid (DHTA) as a ligand, the structure features of the prepared PSU@Mg-PCPs revealed the progressive evolution of the disordered Mg-DHTA coordination species into locally ordered, unsaturated Mg-MOF-74-related interfacial subunits, accompanied by gradual interfacial roughening and coordination ordering. The evolving interfaces regulated the adsorption and separation behaviors of CO2, CH4, and N2. At 298 K, PSU@Mg-PCP-10 exhibited apparent CO2/CH4 and CO2/N2 separation factors of 24.23 and 15.01, respectively, higher than those of Mg-PCP (7.83 and 9.01). Meanwhile, PSU@Mg-PCP-180 achieved the highest CO2 uptake of 1.60 mmol g−1 at 273 K. Grand canonical Monte Carlo simulations indicated that the separation behaviors originated from the combined effects of micropore blockage and preferential CO2 adsorption at Mg2+ sites and newly formed interfacial regions. This confined-metal-source strategy provides a metal-efficient route for tailoring zeolite–MOF interfaces and tuning gas-separation performance.