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 [ZrO(OH)(bdc)(bdc-NH)] (UiO-66-xNH) and [ZrO(OH)(bpdc)(bpdc-(NH))] (UiO-67-x(NH)) systems where bdc = benzene-1,4-dicarboxylate; bdc-NH= benzene-2-amino-1,4-dicarboxylate; bpdc = 4,4'-biphenyldicarboxylate; bpdc-(NH) = 2,2'-diamino-4,4'-biphenyldicarboxylate and x = 0, 0.25, 0.5, 0.75, 1. In a second step, the UiO-66-xNH and UiO-67-x(NH) systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiOBu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH@LiOBu and UiO-67-x(NH)@LiOBu 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-66-0.25NH@LiOBu 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.

UiO-66, MOF-808 and NU-1000 metal–organic frameworks exhibit a differentiated reactivity toward [Mg­(OMe)2(MeOH)2]4 related to their pore accessibility. Microporous UiO-66 remains unchanged while mesoporous MOF-808 and hierarchical micro/mesoporous NU-1000 materials yield doped systems containing exposed MgZr5O2(OH)6 clusters in the mesoporous cavities. This modification is responsible for a remarkable enhancement of the catalytic activity toward the hydrolytic degradation of P–F and P–S bonds of toxic nerve agents, at room temperature, in unbuffered aqueous solutions.

Heterometallic or mixed-metal Metal-Organic Frameworks (MOFs), incorporating two or more metal ions to the inorganic node of the frameworks, are increasingly gaining importance as a route to produce materials with increasing chemical and functional complexity. Heterometallic MOFs can offer important advantages over their homometallic counterparts to enable targeted modification of the adsorption properties, structural response, electronic structure or chemical reactivity of the framework. This field is still in its infancy likely due to the difficulties of controlling the formation of heterometallic nodes by direct synthesis. This restriction is even more acute in the case of titanium frameworks for which their challenging chemistry renders post-synthetic doping of preformed materials as the only route available. However, this often results in partial or non-homogeneous metal substitution in detriment of the potential benefits of controlling metal distribution at an atomic level toward performance improvement. We report the first family of heterometallic titanium frameworks that can be prepared by direct synthesis from metal precursors and trimesic acid. MUV-101 frameworks [TiM2(µ3-O)(O2CR)6X3] (M = Mg, Fe, Co, Ni; X = H2O, OH -, O 2-) combine mesoporosity with good chemical stability. We use these materials to exemplify the advantages of controlling metal distribution across the framework in heterogeneous catalysis by exploring their activity toward the degradation of a nerve agent simulant of Sarin gas. MUV-101(Fe) is the only pristine MOF capable of catalytic degradation of (diisopropyl-fluorophosphate) DIFP in non-buffered aqueous media without the presence of a basic/nucleophilic co-catalyst. Compared to MUV-101(Fe), other titanium heterometallic and homometallic MOFs as MUV-101(Mg, Co and Ni), MUV-10(Mn), MIL-100(Ti and Fe) or UiO-66(Zr), all display a poorer performance or are poisoned by the degradation products. The catalytic activity of MUV-101(Fe) cannot be explained only by the association of Ti(IV) and Fe(III) but to their synergistic cooperation. Our simulations suggest that the combination of Ti(IV) Lewis acid and Fe(III)-OH Brönsted base sites in this dual metal catalyst leads to a much lower energy barrier for more efficient degradation of DIFP in absence of a base. Overall, this mechanism resembles the activity of the metalloenzyme purple acid phosphatase that displays also bimetallic active sites.

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We report the controlled synthesis of thin films of p r o t o t y p i c a l z i r c o n i u m m e t a l − o r g a n i c f r a m e w o r k s [Zr 6 O 4 (OH) 4 (benzene-1,4-dicarboxylate-2-X) 6 ] (X = H, UiO-66 and X = NH 2 , UiO-66-NH 2 ) over the external surface of shaped carbonized substrates (spheres and textile fabrics) using a layer-by-layer method. The resulting composite materials contain metal−organic framework (MOF) crystals homogeneously distributed over the external surface of the porous shaped bodies, which are able to capture an organophosphate nerve agent simulant (diisopropylfluorophosphate, DIFP) in competition with moisture (very fast) and hydrolyze the P−F bond (slow). This behavior confers the composite material self-cleaning properties, which are useful for blocking secondary emission problems of classical protective equipment based on activated carbon.