Highly efficient sorption and luminescence sensing of oxoanionic species by 8-connected alkyl-amino functionalized Zr 4+ MOFs

In the present study we provide the sorption properties of four 8-connected Zr 4+ MOFs with the general formula H 16 [Zr 6 O 16 (RNH-BDC) 4 ]·solvent (RNH-BDC 2− = 2-alkyl-amine-terephthalate; R = ethyl-, ET-MOF ; R = propyl-, PROP-MOF ; R = isobutyl-, SBUT-MOF ; R = n -butyl, BUT-MOF ) towards toxic Cr( vi ) and radionuclide-related ReO 4 − oxoanions. These MOFs represent superior sorbents for the removal of oxoanionic species, in terms of kinetics, sorption isotherms, selectivity and regeneration/reusability. The excellent sorption capability of the MOFs is due to a combination of surface and intra-framework sorption phenomena. The latter process proceeds via replacement of terminal water/hydroxyl ligands from the Zr 6 clusters and subsequent binding of oxonanions to the Zr 4+ centers, a fact that was proved via Rietveld PXRD analysis for the anion-loaded BUT-MOF . Importantly, BUT-MOF demonstrated an exceptional sorption capacity for Cr 2 O 7 2− (505 mg g −1 ) and was further utilized in a sorption column in the form of MOF/calcium alginate beads, displaying remarkable removal efficiency towards industrial (chrome-plating) wastewater. Furthermore, the luminescence Cr( vi ) sensing properties of BUT-MOF were explored in detail, presenting high sensitivity (detection limits as low as 9 ppb) and selectivity for these species against various competitive anions.