Juan M. Zamaro

Combination of MOFs and Zeolites for Mixed-Matrix Membranes

Mixed-matrix membranes (MMMs) were prepared by combinations of two different kinds of porous fillers [metal-organic frameworks (MOFs) HKUST-1 and ZIF-8, and zeolite silicalite-1] and polysulfone. In the search for filler synergy, the MMMs were applied to the separation of CO(2)/N(2), CO(2)/CH(4), O(2)/N(2), and H(2)/CH(4) mixtures and we found important selectivity improvements with the HKUST-1-silicalite-1 system (CO(2)/CH(4) and CO(2)/N(2) separation factors of 22.4 and 38.0 with CO(2) permeabilities of 8.9 and 8.4 Barrer, respectively).

Sonocrystallization of zeolitic imidazolate frameworks (ZIF-7, ZIF-8, ZIF-11 and ZIF-20)

Zeolitic imidazolate frameworks ZIF-7, ZIF-8, ZIF-11 and ZIF-20 have been synthesized by sonocrystallization. In general, crystals obtained at lower temperatures and shorter times are smaller and have a narrower size distribution than those achieved by conventional solvothermal synthesis. Moreover, crystallization curves have been calculated from the XRD patterns and the Gualtieris model has been applied to simulate the extent of crystallization as a function of time. According to the parameters calculated, for ZIF-8 the nucleation rate controls the synthesis reaction, while for ZIF-11 and ZIF-20 both growth and nucleation rates are similar.

Influence of the solvent in the synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals at room temperature.

The effect of the solvent on the synthesis process and on the nanocrystal characteristics of the zeolitic imidazolate framework-8 (ZIF-8) was investigated. A synthesis protocol at room temperature employing a series of aliphatic alcohols, water, dimethylformamide and acetone was employed. The results show that the solvent modifies the evolution of the reaction, altering the crystallization rates and nanocrystal sizes. Its hydrogen bond donation ability is the main factor that governs this effect. More precisely, the solvent modulates the formation of ZIF-8 nanocrystals with sizes in the range between 15 and 42 nm. When synthesized in alcohol and acetone, these nanocrystals form globular aggregates with sizes between 130 and 420 nm. In contrast, under the same synthesis conditions, when using water or dimethylformamide the ZIF phase is not developed. In alcohols other than methanol, the crystals develop pill-shaped morphologies with poorly defined facets. Moreover, a markedly fast growing kinetics is verified in these alcohols, leading to an ultra-fast crystallization of ZIF-8 in about 60s. These findings provide new information about the role of the solvent in the synthesis process of nanoZIF-8, which can be useful for controlling the crystallization rates and nanocrystal sizes of this material.

Insight into the crystal synthesis, activation and application of ZIF-20

The crystallization of the zeolitic imidazolate framework ZIF-20 has been tuned from the point of view of crystal size and aggregation by using rotation and seeding with a previously prepared material. In addition, the activation of ZIF-20 by solvent extraction has been found to be in correlation with the relative permittivity of the solvent. High permittivity solvents (acetone and methanol) extract more guest dimethylformamide but amorphize the structure, while those with low permittivity (n-pentane and chloroform) preserve the crystallinity of ZIF-20. The dispersion in commercial polysulfone of the small synthesized ZIF-20 particles obtained with low aggregation results in an improved O2-selective mixed matrix membrane (O2 permeability and O2/N2 selectivity being 1.0 (±0.0) Barrer and 6.7 (±0.5), respectively).