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

Controllable Synthesis of Defective UiO-66 for Efficient Degradation and Detection of Ozone

Metal-organic framework (MOF) structures have gained significant attention for their exceptional catalytic performance in ozone degradation, even under high humidity conditions, which is attributed to the presence of unsaturated metal sites (MOF defects). However, the correlation between MOF defects and catalytic ozone remains ambiguous, and a general approach for the controllable synthesis of high-performance MOF structures is currently lacking. Herein, different defective UiO-66 materials with cluster or ligand defects were obtained by precisely controlling small molecular acid modulators. Their catalytic performance can be analyzed in real time through the specific cataluminescence (CTL) signal of ozone at the interface. The presence of ligand defects was found to be crucial for both catalytic degradation and luminescence of ozone, and the CTL signal exhibited a positive correlation with the endogenous hydroxyl group content in the material (R2 = 0.982), while external humidity further supplemented internal water molecules within the material. Furthermore, theoretical calculations were conducted to compare the adsorption behaviors of ozone on the defective UiO-66 under dry/wet conditions, leading to the proposal of two potential reaction pathways. Subsequently, UiO-66-DA with superior catalytic performance was employed to develop a highly efficient CTL sensor capable of accurately detecting ozone (LOD = 23.3 ppb). This study held significant value in elucidating the reaction site of ozone on MOFs and achieving optimal catalytic effects through the careful selection of modulators and humidity levels.

Three-Dimensional Neodymium Metal-Organic Framework for Catalyzing the Cyanosilylation of Aldehyde and the Synthesis of 2,3-Dihydroquinazolin-4(1H)-one Derivatives

In this work, a novel 3D lanthanide metal-organic framework (Ln-MOF) Nd-cdip (H₄cdip = 5,5'-carbonyldiisophthalic acid) was successfully synthesized, which could be used as an efficient heterogeneous catalyst for cyanosilylation and the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives at room temperature based on the Lewis acid sites in the channels of the MOF. Moreover, Nd-cdip had an excellent turnover number (500) for catalyzing cyanosilylation in no solvent condition. Nd-cdip could be reused in both of the above-mentioned reactions at least five times without a significant decrease in yield. The possible mechanism of cyanosilylation catalyzed by Nd-cdip was studied by using the luminescence properties of Tb-cdip, which has the same structure and functions as Nd-cdip. Furthermore, both reactions catalyzed by Nd-cdip were fitted to zero-order dynamics.

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

Ionogel-based flexible sensors are widely applied in wearable biomedical devices and soft robots. However, the abandoned ionic sensors are rapidly turning into e-waste. Here, we harness the porosity and the coordination of metal sites of metal-organic frameworks (MOFs) to develop physically crosslinked ionogels, which are composed of polymer chains that coordinate with the MOF metal sites. The covalent crosslinking of the host material transformed into reversible bond interactions that significantly enhance the mechanical properties of the MOF-ionogels. The obtained ionogels can endure an 11 000% stretch and exhibit Young's modulus and toughness of 58 MPa and 25 MJ m^-3, respectively. In addition, the fracture energy is as high as 125 kJ m^-2, outperforming most reported ionogels. Furthermore, the UiO-66-ionogels are fully recyclable and both the mechanical and electrical properties can be restored. The results of this work provide a new vision for the development of future "green" sensors.

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

Atmospheric ozone has long been a threat to human health, however, rational design of high-performance O₃-decomposition catalysts remains challenging. Herein, we demonstrate the great potential of a series of isomorphous bimetallic MOFs denoted as PCN-250(Fe₂M) (M = Co²⁺, Ni²⁺, Mn²⁺) in catalytic O₃ decomposition. Particularly, PCN-250(Fe₂Co) showed 100% O₃ removal efficiency for a continuous air flow containing 1 ppm O₃ over a wide humidity range (0 ‒ 80% RH) at room temperature. Mechanism studies suggested that the high catalytic performance originated from the introduction of open Co(II) sites as well as its porous structure. Additionally, at low pressures around 10 Pa, PCN-250(Fe₂Co) exhibited high adsorption capacities (89 ‒ 241 mg g^-1) for most VOCs, which are not only a class of hazardous air pollutants but also the precursor of O₃. This work opens up a new avenue to develop advanced air purification materials for O₃ and VOCs removal in one.

A novel 3D terbium metal-organic framework as a heterogeneous Lewis acid catalyst for the cyanosilylation of aldehyde

A novel 3D lanthanide(iii) metal-organic framework (MOF) (namely Tb-MOF), was synthesized by self-assembly from Tb(iii) ion nitrate and the rigid organic ligand H₂sbdc (H₂sbdc = 5,5-dioxo-5H-dibenzo[b,d]thiophene-3,7-dicarboxylic acid), and could work as an efficient heterogeneous catalyst for the cyanosilylation of aromatic aldehydes at room temperature. The obtained Tb-MOF has been characterized and analysed in detail by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and so on. The pores of Tb-MOF provided a microenvironment that was beneficial for the substrates to be close to the Lewis acid catalytic sites. The IR spectrogram and the fluorescence titration proved that the substrates could be activated inside the channel of Tb-MOF. The heterogeneous Tb-MOF catalyst with fine catalytic efficiency exhibited a high TON (TON = 460), and could be recycled at least three times without significantly reducing its activity.