Zeolitic metal azolate frameworks (MAFs) from ZnO/Zn(OH)2 and monoalkyl-substituted imidazoles and 1,2,4-triazoles: Efficient syntheses and properties

Acid–base neutralization reaction between monoalkyl-substituted azole derivatives and ZnO/Zn(OH)2 can be effectively activated by aqueous ammonia to synthesize a series of metal azolate frameworks (MAFs) including SOD-[Zn(mim)2] (MAF-4, Hmim = 2-methylimidazole), ANA-[Zn(eim)2] (MAF-5, Heim = 2-ethylimidazole), SOD-[Zn(mtz)2] (MAF-7, Hmtz = 3-methyl-1,2,4-triazole), dia-[Zn(mim)2] (MAF-31), qtz-[Zn(eim)2] (MAF-32), and dia-[Zn(etz)2] (MAF-33, Hetz = 3-ethyl-1,2,4-triazole). The porous zeolitic MAFs obtained by this reaction possess high stability and can be easily activated. Their high porosity, unique pore size/surface characteristic, and framework flexibility were demonstrated by gas and solvent vapor (water, methanol, and benzene) sorption measurements. The imidazolate frameworks MAF-4 and MAF-5 are highly hydrophobic adsorbents with exceptional organic/water selectivity, while the triazolate framework MAF-7 containing uncoordinated nitrogen donor on the pore surface exhibits higher sorption affinity and lower stability. Despite the very small aperture sizes (3.2–3.4 Å), the SOD frameworks can readily adsorb large organic molecules by temporary distortion of the structure.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Simple acid–base reaction is very efficient for large-scale synthesis of zinc MAFs. ► MAFs from the reaction have higher chemical stability compared with other methods. ► MAFs show unique pore size/surface characteristic and framework flexibility. ► MAF-4 and MAF-5 are suitable for removal of trace aromatic molecules from water.