Chemical Warfare Agents Detoxification Properties of Zirconium Metal–Organic Frameworks by Synergistic Incorporation of Nucleophilic and Basic Sites

The development of protective self-detoxifying materials is an important societal challenge to counteract risk of attacks employing highly toxic chemical warfare agents (CWAs). In this work, we have developed bifunctional zirconium metal–organic frameworks (MOFs) incorporating variable amounts of nucleophilic amino residues by means of formation of the mixed ligand [Zr6O4(OH)4(bdc)6(1–x)(bdc-NH2)6x] (UiO-66-xNH2) and [Zr6O4(OH)4(bpdc)6(1–x)(bpdc-(NH2)2)6x] (UiO-67-x(NH2)2) systems where bdc = benzene-1,4-dicarboxylate; bdc-NH2= benzene-2-amino-1,4-dicarboxylate; bpdc = 4,4′-biphenyldicarboxylate; bpdc-(NH2)2= 2,2′-diamino-4,4′-biphenyldicarboxylate and x= 0, 0.25, 0.5, 0.75, 1. In a second step, the UiO-66-xNH2and UiO-67-x(NH2)2systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiOtBu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH2@LiOtBuand UiO-67-x(NH2)2@LiOtBumaterials. The results show that the combination of pre and postsynthetic modifications on these MOF series gives rise to fine-tuning of the catalytic activity toward the hydrolytic degradation of both simulants and real CWAs in unbuffered aqueous solutions. Indeed, UiO-66-0.25NH2@LiOtBuis able to hydrolyze both CWAs simulants (diisopropylfluorophosphate (DIFP), 2-chloroethylethylsulfide (CEES), and real CWAs (soman (GD), sulfur mustard (HD)) quickly in aqueous solution. These results are related to a suitable combination of robustness, nucleophilicity, basicity, and accessibility to the porous framework.