Abstract
Three novel silver-based metal-organic frameworks materials, which were synthesized from either 3-phosphono or 4-phosphonobenzoic acid and silver nitrate, are reported. The novel hybrids were synthesized under hydrothermal conditions; the pH of the reaction media was controlled by adding different quantities of urea thereby producing different topologies. Compound 1 (Ag3(4-PO3-C6H4-COO)), synthesized in the presence of urea, exhibits a compact 3D structure in which both phosphonic acid and carboxylic acid functional groups are linked to the silver-based inorganic network. Compound 2 (Ag(4-PO3H-C6H4-COOH)), which was synthesized at lower pH (without urea), has a layered structure in which only the phosphonic acid functional groups from 4-phosphonobenzoic acid moieties are linked to the silver inorganic network; the carboxylic acid groups being engaged in hydrogen bonds. Finally, material 3 (Ag(3-PO3H-C6H4-COOH)) was synthesized from 3-phosphonobenzoic acid and silver nitrate without urea. This material 3 features a layered structure exhibiting carboxylic acid functional groups linked via hydrogen bonds in the interlayer space. After the full characterization of these materials (single X-ray structure, IR, TGA), their ability to release silver salts in aqueous environment was measured. Silver release, determined in aqueous solution by cathodic stripping voltammetry, shows that the silver release capacity of these materials is dependent on the topology of the hybrids. The more compact structure 1 is extremely stable in water with only trace levels of silver ions being detected. On the other hand, compounds 2 and 3, in which only the phosphonic acid functional groups were bonded to the inorganic network, released larger quantities of silver ions into aqueous solution. These results which were compared with the silver release of the previously described compound 4 (Ag6(3-PO3-C6H4-COO)2). The results clearly show that the release capacity of silver-based metal organic framework can be tuned by modifying their topology which, in the present study, is governed by the regio-isomer of the organic precursor and the synthetic conditions under which the hybrids are prepared.
Highlights
Hybrid organic-inorganic materials have been extensively studied for their potential application in magnetism1, luminescence2,3, catalysis4 and gas storage5
At low pH, materials in which only the phosphonic acid functional groups were bonded to the inorganic network were produced while, at higher pH, the two functional groups were linked to the inorganic network producing 3D structures
With the aim of following our previous study reporting the ability of compound 4, (Ag6(4-PO3-C6H4-COO)2), to release silver ions and to act as an efficient bactericidal material,30 we investigated whether the chemoselectivity principle, previously observed with copper, -based materials, could be applied to silver-based hybrids
Summary
Hybrid organic-inorganic materials have been extensively studied for their potential application in magnetism, luminescence, catalysis and gas storage. Hydrothermal synthesis of Ag6(3-PO3-C6H4-COO)2 [4] by microwave heating In a TFM insert of 100 mL capacity, 3 equivalents of silver nitrate salt (AgNO3, 0.201g, 1.2 mmol), 1 equivalent of 3-phosphonobeinzoic acid (3-PO(OH)2-C6H4-COOH, 0.08 g, 0.4 mmol) and 1.5 equivalents of urea (CO(NH2)2, 0.035g, 0.6 mmol) were dissolved in 15 mL of distilled water This insert was placed in a CEM MARS 5 microwave oven and heated from room temperature to 140°C over 1 hour, heated for 3 hours at 140°C and allowed to air cool to room temperature.
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