Effect of the surfactant on the Synthesis of Metal-Organic Framework Structures

The beginnings of Metal-Organic Frameworks (MOFs) chemistry were established by Yaghi et al. in the 90s. They started a new promising field for which, depending on the nature of the organic functionality and metal−ligand coordination chemistry, diversity of MOFs in terms of their structures and chemical properties is virtually endless. Since the 90s it has been reported different synthetic routes (e.g. hydro-solvothermal synthesis, microwave and ultrasound-assisted synthesis, mechanochemistry, microemulsion synthesis, continuous flow production). Nevertheless, no control on the shape and size of the crystal was achieved in a proper way. The results obtained during this work demonstrates that the surfactant plays an important role in the MOF´s synthesis protocol, in particular, in those with Zeolitic Imidazolate Framework (ZIF-8) structure, by changing the former physico-chemical properties without altering their crystalline structure. That is, variations on surfactant´s properties lead to changes both in shape and size of MOFs without altering their intrinsic properties. Thus, this work is focused on the effect of two surfactants: Sodium Dodecyl Sulfate (SDS) and Hexadecyltrimethylammonium bromide (CTAB). In this sense, for each family of surfactant the influence of the surfactant tail chain length and the nature of their head group were investigated. For these studies, dynamic laser-light scattering (DLS), scanning electron microscopy (SEM) and powder X-Ray Diffraction (PXRD) were performed in order to characterize the physicochemical properties and the morphology of the obtained MOFs.

Acknowledgements: This work was supported by Agencia Estatal de Investigación (AEI) through Project MAT2016-80266-R, and Xunta de Galicia (Grupo de Referencia Competitiva ED431C 2018/26; Agrupación Estratégica en Materiales-AEMAT ED431E 2018/08). FEDER funds are also acknowledged.