Room-temperature synthesis of nanometric and luminescent silver-MOFs

Abstract

Three silver-MOFs were prepared using an optimized, room-temperature methodology starting from AgNO₃ and dicarboxylate ligands in water/ethanol yielding <b>Ag</b> _<b>2</b> <b>BDC</b>, <b>Ag</b> _<b>2</b> <b>NDC</b> (<b>UAM-1</b>), and <b>Ag</b> _<b>2</b> <b>TDC</b> (<b>UAM-2</b>) at 38%-48% (BDC, benzenedicarboxylate; NDC, 1,8-naphthalene-dicarboxylate; TDC, p-terphenyl-4,4″-dicarboxylate). They were characterized by PXRD/FT-IR/TGA/photoluminescence spectroscopy, and the former two by SEM. These materials started decomposing at 330°C, while showing stability. The crystal structure of <b>UAM-1</b> was determined by PXRD, DFT calculations, and Rietveld refinement. In general, the structure was 3D, with the largest Ag-O bond interlinking 2D layers. The FT-IR spectra revealed 1450 and 1680 bands (cm^-1) of asymmetrically stretching aniso-/iso-bidentate -COO in coordination with 2/3-Ag atoms, accompanied by Ag-O bands at 780-740 cm^-1, all demonstrating the network formation. XRD and SEM showed nanometric-scale crystals in <b>Ag₂BDC</b>, and <b>UAM-1</b> developed micrometric single-stranded/agglomerated fibrillar particles of varying nanometric widths. Luminescence spectroscopy showed emission by <b>Ag₂BDC</b>, which was attributed to ligand-to-metal or ligand-to-metal-metal transitions, suggesting energy transfer due to the short distance between adjacent BDC molecules. <b>UAM-1</b> and <b>UAM-2</b> did not show luminescence emission attributable to ligand-to-metal transition; rather, they presented only UV emission. The stabilities of <b>Ag₂BDC</b> and <b>UAM-1</b> were evaluated in PBS/DMEM/DMEM+FBS media by XRD, which showed that they lost their crystallinity, resulting in AgCl due to soft-soft (Pearson's principle) affinity.