Study on the Stability, Evolution of Physicochemical Properties, and Postsynthesis of Metal–Organic Frameworks in Bubbled Aqueous Ozone Solution

Abstract

Metal–organic frameworks (MOFs) are highly promising in many areas. Their application and postsynthesis under strong oxidative environments are emerging. However, the stability, physicochemical property evolution, and possible postmodification and postsynthesis of MOFs in strong oxidative solutions are largely unknown. In this paper, the behaviors of a series of MOFs in bubbled aqueous ozone (O3) solutions are studied. The chosen MOFs are categorized into trimesic type including MIL-101­(Fe) and MIL-96­(Al); terephthalic type including MOF-74­(Co), UiO-66­(Zr), MIL-53­(Al), and MIL-101­(Cr); and imidazole type including ZIF-67­(Co) and ZIF-8­(Zn), based on the ligand structure. The intrinsic stability and evolution of the physicochemical properties of these MOFs during aqueous O3 treatment are elucidated using structural, morphological, textural, thermal, and spectroscopic analyses. Several stable, metastable, and instable MOFs are identified. The critical parameters that determine the stability and capability for postsynthesis of these MOFs in aqueous O3 solutions are discussed. The stability follows the general order of trimesic-type > terephthalic-type ≫ imidazole-type MOFs because of the distinct antioxidation capability of the ligands. The effects of the ligand, metal cation, and their coordination number on stability are discussed. MIL-100­(Fe), MIL-96­(Al), and MOF-74­(Co) are stable in aqueous O3. UiO-66­(Zr), MIL-53­(Al), and MIL-101­(Cr) are metastable that their porosity, particle size, and crystallinity can be postmodified. ZIF-67­(Co) and ZIF-8­(Zn) are instable and can be gradually and completely disassembled. Their particle size and morphology and surface groups can be tuned by controlling the treatment time. Postsynthesis of metal hydroxides from ZIF-67­(Co) and gradual release of dissolved zinc ion from ZIF-8­(Zn) are achievable. The stable MIL-96­(Al) shows promising performance in catalytic ozonation for degrading 4-nitrophenol, and the α-Co­(OH)2 derived from treating ZIF-67­(Co) shows highly promising performance in the electrocatalytic oxygen evolution reaction (OER).

Near-infrared light induced adsorption–desorption cycle for VOC recovery by integration of metal–organic frameworks with graphene oxide nanosheets

“…For pure MIL-101, two strong peaks at 1639 and 1423 cm −1 correspond to the asymmetric stretching vibration and symmetric stretching vibration of the carboxyl group, respectively. 32,35 As expected, it was observed that all GO@MIL-101 nanocomposites have a similar spectrum to the MIL-101. Nevertheless, two peaks assigned to the CO bond of GO nanosheets couldn't be observed in the FT-IR spectra of GO@MIL-101 nanocomposites, which would result from the formation of a coordination bond between the GO layers and Cr site of MIL-101.…”

“…For MIL-101, the bands at 1702, 1648, 1596 and 1560 cm −1 were attributed to the typical stretching vibration of the COO − groups, while the bands at 1513 and 1450 cm −1 were assigned to aromatic CC stretching vibration within the MIL-101 framework. 32,35 After ethyl acetate adsorption onto the 5% GO@MIL-101 nanocomposite, the COO − asymmetric stretching vibration at 1638 cm −1 and the COO − symmetric stretching vibration at 1567 cm −1 were gradually red shifted to 1634 cm −1 and 1569 cm −1 , respectively, while two bands at 1598 and 1696 cm −1 gradually became weak and then totally disappeared. Meanwhile, a new band at 1729 cm −1 belonging to the CO stretching vibration of ethyl acetate emerged, and its intensity was raised as the adsorption time was prolonged.…”

Catalytic ozone decomposition and adsorptive VOCs removal in bimetallic metal-organic frameworks

“…The stability issue is especially outstanding for MOF-type catalysts since a large number of MOFs have been proven unstable even in ambient air 46 . In the last few years, a few MOFs showing high stability in water, even under harsh acidic or basic conditions, have been reported, whereas there are very little knowledge about the stability of MOFs when exposed to O 3 -containing air [47][48][49][50][51][52] . The high hydrolytic stability of PCN-250 MOFs has been well documented in the literature 53 .…”

Metal–organic framework (MOF) facilitated highly stretchable and fatigue-resistant ionogels for recyclable sensors

“…The MIL-100 was synthesized according to the previously reported method. 63 Briefly, FeCl 3 Á6H 2 O (4.04 g, 10 mmol), H 3 BTC (1.89 g, 9 mmol), and deionized water (6 mL) were mixed by sonication for 10 min and moved into a 25 mL round bottom flask with a reflux condenser. The round bottom flask was reacted at 95 1C for 12 h. The product was obtained by centrifugation after cooling down and washed with deionized water and ethanol three times.…”