Influence of Acid Modulators on MIL-53(Al) Formation on the Surface of Aluminum Nanocrystals

Metal-organic framework (MOF) coatings around metal nanoparticles (MNPs) offer a promising route to create multifunctional composite materials, but controlling MOF growth on metal surfaces remains challenging. In this study, we investigate aluminum nanocrystals as both a metal-ion source and a template for MOF growth, enabled by the dissolution of their native oxide layer in an etching acid that also serves as a modulator of MOF formation. In the presence of terephthalic acid, we validate that MOF coatings crystallize as MIL-53(Al) on the surface of the nanoparticles (i.e., core-shell MNP@MOF structures), as confirmed by grazing-incidence X-ray diffraction analysis. We determined that the final heterostructure composition depends on the modulator identity, modulator concentration, solvent composition, and reaction time. Stronger modulation favors MIL-53(Al) formation but at the cost of Al dissolution. These findings provide insight into the competing roles of acid additives in MOF formation on MNP surfaces, establishing design principles that can potentially be generalized to other composites featuring MNP@MOF structures.