An analysis of the effect of zirconium precursors of MOF-808 on its thermal stability, and structural and surface properties

Due to their thermal and chemical stability, zirconium-based metal-organic frameworks (Zr-MOFs) have been extensively studied in the literature. However, many details of the influence of preparation conditions are still unclear. Most papers tend to use one type of metallic precursor for synthesizing Zr-MOFs such as MOF-808. Therefore, as far as we know, a systematic analysis of the effect of zirconium precursors on the properties of MOF-808 has not been conducted. In this work, three different metallic precursors were employed, namely, zirconium chloride, zirconyl chloride, and zirconyl nitrate for synthesizing MOF-808 while keeping all other synthesis conditions constant. The results of the study indicated the following: (i) the nature of the zirconium precursor impacts the crystalline and porous structure of MOF-808. Particularly, the presence of structural water in the precursors seems to cause a detriment to these properties which resulted in an increase of the relative percentage of amorphicity of the materials as well as the formation of disorganized mesopores. (ii) In contrast to (i), the surface properties of the materials and their thermal stability under an air atmosphere were not altered by the use of the different precursors. All the materials exhibited a surface populated by free and uncoordinated carboxylates as well as inorganic zirconium structures corresponding to uncoordinated oxo-clusters. The ensemble of these findings contributes to a better understanding of the features that make MOFs interesting for diverse applications. Particularly, studies on defect engineering may benefit from the insight into surface chemistry provided in this contribution.