Water induces crystal orientation during MIL-88A (Fe) growth: linking morphology with antibacterial activity

Metal-organic frameworks (MOFs) have emerged as promising materials for antimicrobial applications due to their tunable structure and chemical properties. In this work, the morphology of MIL-88A was systematically controlled by adjusting the molar proportion of the water relative to the iron precursor in a solvothermal synthesis approach, by ranging from the absence of water to a molar proportion of 1 : 9 from the salt to water. Increasing the water content induced a progressive morphological transition from rod-like to spindle-like and ultimately star-like architectures, as revealed in the SEM analysis. Structural characterization showed that the solvent composition influenced not only the morphology but also the crystallinity of MIL-88A, with changes in the dominant crystal planes observed by X-ray diffraction. Raman and FTIR analyses confirmed the formation of MIL-88A in all synthesized samples. Antibacterial assays against Escherichia coli and Staphylococcus aureus demonstrated that rod-like and spindle-like structures exhibit enhanced inhibitory activity, particularly at low concentrations (0.24-0.48 mg mL^-1), suggesting that morphology plays a key role in antimicrobial capacity. At higher concentrations (1.2 mg mL^-1), all morphologies displayed similar antibacterial performance, likely associated with iron-mediated oxidative damage to bacterial cells. These findings highlight the potential of MIL-88A as antibacterial agents by finely tuning morphology, suggesting its potential for applications requiring low material dosages, including antimicrobial coatings, food-contact materials, and biomedical-related systems.