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

Abstract

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-xNH₂ and UiO-67-x(NH₂)₂ systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiO^tBu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH₂@LiO^tBu and UiO-67-x(NH₂)₂@LiO^tBu materials. 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@LiO^tBu is 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.