Morphology Modification of the Iron Fumarate MIL-88A Metal-Organic Framework Using Formic Acid and Acetic Acid as Modulators

Metal-organic frameworks (MOFs) are best known for their great structural diversity. The uniformity in the properties of MOFs is mainly governed by the size and morphology of the particles. In the present research, iron-MIL-88A was prepared by a modulator-assisted solvothermal method, and the role of modulating agents in the formation process of MOF particles was investigated. Acetic acid and formic acid were chosen as monoligand modulating agents. The changes in morphology and size distribution of the products were scrutinized by using SEM micrographs. Both modulators clearly interfered with the crystallization process through their attachment to the reactive sites. At low modulator content, the primary diamondlike characteristic morphology of the particles was preserved. While acetic acid mildly altered the morphology of the MOF and narrowed its particle-size distribution, formic acid drastically changed the morphology of the MOF particles to those resembling dendrites. The structural properties of the products were examined using XRD, FTIR, and TGA studies. Correct amounts of acetic acid improved the crystallinity of the product, while high contents of acetic acid greatly interfered with the formation process and had a paramount effect on the particle morphology evidenced by the decrease in the intensity of diffraction peaks.