Effect of the Surfactant on the Synthesis of Metal-Organic Framework Structures ^†

Abstract

The beginnings of metal-organic frameworks (MOF) chemistry were established by Yaghi et al., in the 1990s. 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 1990s it has been reported different synthetic routes (e.g., hydro-solvothermal synthesis, microwave and ultrasound-assisted synthesis, mechanochemistry, microemulsion synthesis, and 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.