pK_a-Directed Incorporation of Phosphonates into MOF-808 via Ligand Exchange: Stability and Adsorption Properties for Uranium

Abstract

We report a class of pK a -directed, precise incorporation of phosphonate ligands into a zirconium-based metal−organic framework (Zr-MOF), MOF-808, via ligand exchange. By replacing of formate ligands with methylphosphonic acid (MPA), ethanephosphonic acid (EPA), and vinylphosphonic acid (VPA), whose pK a values are slightly higher than that of the benzenetricarboxylic acid (BTC) linker in MOF-808, daughter MOFs can be synthesized without controlling the stoichiometric amounts of added MPA. The methylphosphonate MOFs (808-MPAs) demonstrate high porosities, with only small changes in the pore diameter and specific surface area when compared with the parent MOF-808. PXRD patterns and structure refinements indicate the expansion of the lattice for all MOFs after decorating with methylphosphonate ligands. The XPS spectra reveal a charge redistribution of the Zr 6 node after ligand exchange. FTIR and 31 P MAS NMR spectra, combined with DFT calculation, suggest that the methylphosphonate ligand is connected to the Zr 6 node as CH 3 P(O)(OZr)(OH) species with an accessible acidic P−OH group. Besides, 808-MPAs demonstrate excellent chemical stability in concentrated HCl, concentrated HNO 3 , hot water, and 0.2 mol/L trifluoroacetic acid solutions. Impressively, 808-MPAs show ultrafast adsorption performance for uranyl ions using the ion-exchange property of P−OH sites in their cavity environment, with an equilibrium time of 10 min, much quicker than the previous adsorbents. The present study demonstrates a series of important proof-of-concept examples of the pK a -directed Zr-MOFs with tunable phosphonate-terminated ligands, which can extend to other phosphonate-functionalized Zr-based framework platforms in the near future.

Phosphorylation of Guar Gum/Magnetite/Chitosan Nanocomposites for Uranium (VI) Sorption and Antibacterial Applications

“…On the other side, Pal et al [79] reported the isoelectric point of GG close to 2.2: GG in acidic conditions may be considered neutral, while in mild acid conditions the biopolymer turns negatively charged. The first ionization constant of phosphonic acids depends on the side chain bound to phosphorus; however, for short chains the pK a values are close to 2.4 [80]. It means that GG and phosphonate groups have similar acid behavior, while chitosan is bringing base properties (associated with amine groups).…”

Computational determination of coordination structure impact on adsorption and acidity of pristine and sulfated MOF-808

“…We also note that the experimentally measured lattice constants might be affected by residual water within the MOF-808 framework. 11,31 Therefore, we examined the effect of water on physical properties of MOF-808. Several water-containing models were constructed by adding water molecules to the tetrahedral cage of model I and then re-optimized using DFT methods in CP2K.…”

Multivariate Modulation of the Zr MOF UiO‐66 for Defect‐Controlled Combination Anticancer Drug Delivery

“…1.2 % (w/w) incorporation with minimal DCA leakage, as determined by ICP‐OES, postsynthetic loading of drugs containing metal‐binding units resulted in partial or total displacement of DCA (Table S1), as determined by 1 H NMR spectroscopic analysis of acid‐digested samples, suggesting their loading occurs through attachment to the Zr positions (subsequently detaching DCA ) rather than pore storage (see SI, Section S3.1 for full characterisation). AL loading resulted in a complete structural change, likely due to the affinity of its phosphonate groups for Zr inducing breakdown, again confirming the competing coordination of the drugs. As such, this postsynthetic process was not considered viable for multiple drug loading.…”

“…1 DCA per 3 BDC) whilst IBU/DCA@UiO‐66 showed a smaller degree of incorporation of IBU (2.9 mol % compared to BDC) due to its higher p K a , and similarly ≈37 mol % of DCA . Alendronate had the highest incorporation, again likely representative of its ditopicity and the Zr‐phosphonate affinity, as AL/DCA@UiO‐66 contained 38.1 mol % (ca. 1 AL per 2.5 BDC), suggesting its possible role as a linker, and 18.8 mol % of DCA (ca.…”