Advances in Metal-Organic Frameworks for the Removal of Chemical Warfare Agents: Insights into Hydrolysis and Oxidation Reaction Mechanisms

Abstract

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal-organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large surface areas enable superior adsorption, reactivity, and catalytic abilities, making them ideal for capturing and decomposing target species. Moreover, the tunable networks of MOFs allow customization of their chemical functionalities, making them practicable in personal protective equipment and adjustable to dynamic environments. This review paper focuses on experimental and computational studies investigating the removal of CWAs by MOFs, specifically emphasizing the removal of nerve agents (GB, GD, and VX) via hydrolysis and sulfur mustard (HD) via selective photooxidation. Among the different MOFs, zirconium-based MOFs exhibit extraordinary structural stability and reusability, rendering them the most promising materials for the hydrolytic and photooxidative degradation of CWAs. Accordingly, this work primarily concentrates on exploring the intrinsic catalytic reaction mechanisms in Zr-MOFs through first-principles approximations, as well as the design of efficient degradation strategies in the aqueous and solid phases through the establishment of Zr-MOF structure-property relationships. Recent progress in the tuning and functionalization of MOFs is also examined, aiming to enhance practical CWA removal under realistic battlefield conditions. By providing a comprehensive overview of experimental findings and computational insights, this review paper contributes to the advancement of MOF-based strategies for the destruction of CWAs and highlights the potential of these materials to address the challenges associated with chemical warfare.

Keywords: Zr-MOFs; chemical warfare agent; computational research; degradation; hydrolysis; metal-organic framework; oxidation; reaction mechanism.

Figure 1

Representative examples of CWAs discussed in this work and their commonly used, less toxic simulants [16]. Reprinted with permission from ref. [16]. Copyright 2020 American Chemical Society.

Scheme 1

Detoxification/hydrolysis pathway of CWAs. (a) Nerve agent GD; (b) nerve agent VX; (c) vesicant agent HD [1,6,17]. Reprinted with permission from ref. [1] and reproduced with permission from refs. [6,17]. Copyright 2021 American Chemical Society, 2017 Elsevier, and 2016 Wiley-VCH, respectively.

Figure 2

Adsorption isotherms for water in different types of nanoporous adsorbents near room temperature. IUPAC classification of adsorption isotherm types (left) and adsorption patterns with respect to hydrophilicity (right) [50,59,60,61]. Reprinted with permission from ref. [60] (left) and from refs. [50,59] (right). Copyright 2019 Royal Society of Chemistry, 2014 American Chemical Society, and 2008 Elsevier, respectively.

Scheme 2

Mechanistic scheme for hydrolysis of organophosphorus nerve agents and their simulants on Zr^IV-MOFs. (a) Reaction with nucleophilic attack by displaced -OH₂ and monodentate product binding on metal nodes (example using DMNP) [75]. (b) Reaction with nucleophilic attack by adjacent -OH and bidentate product binding on metal nodes [73]. Reprinted with permission from ref. [75] (left) and ref. [73] (right). Copyright 2021 Royal Society of Chemistry and 2020 American Chemical Society, respectively.

Figure 3

Free energies and enthalpies for hydrolysis of sarin on Zr^IV-MOFs. (a) Reaction on hydrated metal nodes. (b) Reaction on dehydrated metal nodes [74]. Reprinted with permission from ref. [74]. Copyright 2018 American Chemical Society.

Figure 4

Degradation rates of VX in various aqueous-phase Zr-MOFs. (a) Pure water solution. (b) NEM buffer solution [90]. Reprinted with permission from ref. [90]. Copyright 2017 American Chemical Society.

Figure 5

Properties of Zr-based reactive materials exposed to water in the solid phase. (a) Water adsorption isotherms at room temperature; (b) comparison of GD degradation performances at t = 5 min according to pretreatment conditions of 0, 60, and 80% RH [71]. Reprinted with permission from ref. [71]. Copyright 2019 Elsevier.

Scheme 3

Proposed mechanism for the oxidation of CEES by singlet oxygen (¹O₂) [35]. Reprinted with permission from ref. [35]. Copyright 2016 Royal Chemical Society.

Figure 6

(a) Schematic representation of Br-BDP@NU-1000; (b) Zr₆ node of NU-1000, with SALI-displaceable aqua and hydroxy ligands shown in green; (c) structure of organic linker of NU-1000, (d) H- BDP, and (e) Br-BDP [99]. Reprinted with permission from ref. [99]. Copyright 2017 American Chemical Society.

Figure 7

Kinetic profiles for catalytic oxidation of HD in H₂O₂ ethanol solution using different materials as catalysts under standard room lighting [108].

Figure 8

Total (gray) and projected (red, green, blue, and yellow) density of states of UiO-66(Zr), UiO-66(Ti), and UiO-66(Ce). The energy is expressed with respect to the Fermi energy (E_F = 0) [109]. Reprinted with permission from ref. [109]. Copyright 2018 American Chemical Society.