Zeolite@Metal-organic framework core-shell synthesized from the aluminum of the zeolite with accessible internal surface for CO2 adsorption

Combining the rigid microporosity of zeolites with the more versatile structures of metal–organic frameworks (MOFs) seeks to obtain a synergistic effect of both materials. Starting from a low cost and industrially produced zeolite, as it is zeolite NaA (with the LTA type structure), we show that it is possible to crystallize a MOF as shell onto it by only using an aqueous solution of terephthalic acid (H₂BDC). Unlike other zeolite-MOF hybrids reported in the literature, the crystallized MOF only uses the aluminum from the zeolite and may share in turn some aluminum atoms with the inorganic zeolite core, therefore it consists solely of zeolitic Al and BDC. Depending on the pretreatment of the zeolite and the synthesis conditions (pH, time, linker ratio), the crystalline zeolite core is maintained or converted into an amorphous aluminosilicate. Thus, it is possible to retain a part of the adsorption properties of the parent zeolite without degrading its structure through the two fundamental strategies of pH control and previous calcination of the zeolite. The resulting core–shell material, designated as LTA@Al-BDC, combines the zeolite microporosity and molecular sieving properties with the MOF that crystallizes as high aspect ratio sheets which, together with its hydrophobicity, favors the contact with polymeric materials. In addition, being zeolite 4A (NaA) affinity towards CO₂ been probed, the resulting LTA@Al-BDC material constitutes a prominent candidate towards CO₂ separation.