Synergistic Effects of Water and SO₂ on Degradation of MIL-125 in the Presence of Acid Gases

Abstract

The behavior of metal−organic frameworks (MOFs) in the presence of acid gases may be decisive in their suitability for industrial applications. In this study, MIL-125 and MIL-125-NH 2 were investigated with SO 2 exposure in dry, humid, and aqueous environments. MIL-125 was found to be unstable in both humid and aqueous acidic environments, while MIL-125-NH 2 was stable under these exposure conditions, showing no change in textural properties or visual degradation, as observed through SEM. Both materials were stable in the presence of water and dry SO 2 , suggesting that the reaction of these molecules to form an acidic species is likely a key factor in the degradation of MIL-125. In situ IR experiments confirmed the presence of sulfite species, supporting the hypothesis that the presence of an acidic sulfur species likely leads to the degradation of the MIL-125 structure. Computational investigation of several potential reaction mechanisms in MIL-125 indicated reactions involving the bisulfite ion are favored over reactions with water or SO 2 . DFT simulations support the observation that MIL-125-NH 2 is stable in humid conditions, as all reactions are less favorable with the functionalized framework compared to the unfunctionalized framework. This combined experimental and computational study advances the fundamental understanding of MOF degradation mechanisms during acid gas exposure.

Imaging Beam‐Sensitive Materials by Electron Microscopy

“…The defects, in terms of either point defects, cluster defects, dislocations, stacking faults, or grain boundaries, are usually associated with locally modulated coordination environment,135 dangling bonds,136,137 and largely weakened framework stiffness,138 and account for the drastically increased beam sensitivity of materials 25,139. Susi et al observed that the nitrogen doping into graphene and single‐wall carbon nanotube (SWCNT) introduces noticeable knock‐on damage under 80 kV, which should have not existed in corresponding pristine structures 25.…”

Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study

“…MOFs have many excellent properties that are different from those of traditional porous and crystal materials, such as nanoscale controlled pore structure, high surface area, and metal-organic ligand combination diversity, etc. Correspondingly, MOF has a variety of potential applications in many fields, including gas separation and storage, [1][2][3][4] catalysis, [5][6][7] biochemistry 8 and so on. Especially, many investigations have demonstrated that MOF materials are promising catalysts in photocatalysis.…”

“…Especially, many investigations have demonstrated that MOF materials are promising catalysts in photocatalysis. 5,6,[9][10][11][12][13][14][15][16] As one of the most popular MOF, 1,[5][6][7] the titanium-based MIL-125 can catalyze the oxidation of alcohols to aldehydes under the UV irradiation, indicating that MIL-125 is an active photocatalyst. 10 However, because of the large optical band gap (3.6 eV), 10 MIL-125 is only active under UV irradiation.…”

Nanometric MIL-125-NH2 Metal–Organic Framework as a Potential Nerve Agent Antidote Carrier

“…Nevertheless, this structure possesses physicochemical properties required in the biomedical field, specifically: (i) a significant porosity ( S BET = 1130 m 2 g −1 and tetragonal or octahedral cavities of ca. 6.1 and 12.5 Å, respectively, accessible through micropores of 5–7 Å (see Figure 1 b) able to host important loadings of different molecules [ 29 , 30 ]; (ii) very good chemical stability in water and organic solvents [ 31 , 32 ]; (iii) the presence of –NH 2 moieties, able to establish hydrogen bonds with guest molecules (e.g., 2-PAM); and (iv) an a priori biocompatible character, associated with the inert biological behavior of titanium (rat oral 50% lethal dose ( LD 50 ) = 464 and > 2000 mg kg −1 for TiCl 4 and TiO 2 , respectively [ 33 , 34 ]) and the low toxicity of the ligand (50% inhibitory concentration (IC 50 ) in HeLa and J774 cells = 600 and 20 μg mL −1 , respectively) [ 35 ]. To date, the only bio-application of MIL-125-NH 2 was recently proposed by Wang et al [ 36 ], who developed a MIL-125-NH 2 -hemoglobin nanoconjugate.…”