Chemical immobilization of amino acids into robust metal–organic framework for efficient SO 2 removal

Efficient Electrochemical Lead Detection by a Histidine-Grafted Metal-Organic Framework MOF-808 Electrode Material

As the excessive presence of heavy metals in the environment significantly affects human health, it becomes necessary to develop efficient, selective, and sensitive methods for their detection. In this study, a novel electrochemical sensor for the detection of Pb2+ ions is described. The proposed sensor is based on a glassy carbon electrode (GCE) modified by a thin film of histidine-grafted metal-organic framework (MOF-808-His). The MOF-808 was obtained solvothermally, and then postsynthetically modified by substituting the coordinated acetate with histidinate. By electrochemistry, the MOF-808-His-modified GCE demonstrated high charge selectivity, while electrochemical impedance spectroscopy (EIS) and kinetic studies gave a lower charge transfer resistance (4196 Ω) and a better standard heterogeneous electron transfer rate constant (1.80 × 10-5 cm s-1) on MOF-808-modified GCE. These results indicated a swift and direct electron transfer rate from [Fe(CN)6]3-/4- to the electrode surface. Using square wave anodic stripping voltammetry (SWASV), the rapid and highly sensitive determination of Pb2+ was achieved on MOF-808-His-modified GCE. By optimizing the accumulation-detection parameters including pH of the detection medium, deposition time and potential, and concentration, a remarkable limit of detection (LoD, based on a signal-to-noise ratio of 3) of (1.12 × 10-10 ± 0.10 × 10-10) mol L-1 was obtained, with a sensitivity of (9.6 ± 0.1) μA L μmol-1. After interference and stability studies, the MOF-808-His-modified GCE was applied to the detection of Pb2+ in a tap water sample with a concentration of 10 μmol L-1 Pb2+.

Efficient Separation of Trace SO2 from SO2/CO2/N2 Mixtures in a Th-Based MOF

The emission of sulfur dioxide (SO₂) from flue gases is harmful since trace SO₂ impairs human health and the natural environment. Therefore, developing new metal organic frameworks (MOFs) to capture this toxic molecule is of great importance in flue gas desulfurization. In this work, we synthesized a new MOF, namely, ECUT-Th-60, which consists of two distinct channels (3.0 Å × 4.1 Å and 2.3 Å × 4.8 Å). It shows SO₂ uptakes of around 2.5 mmol/g at 0.1 kPa and 3.35 mmol/g at 1 bar, which are higher than those of CO₂ and N₂ under identical conditions. Both simulated and experimental breakthrough tests proved that ECUT-Th-60 can separate trace SO₂ from SO₂/CO₂ mixtures. Impressively, complete separation of SO₂ from SO₂/CO₂/N₂ mixtures under both dry and humid conditions was also proved in ECUT-Th-60, predicting its potential application in flue gas desulfurization.

Zirconium Metal Organic Framework-Based Hybrid Sensors with Chiral and Luminescent Centers Fabricated by Postsynthetic Modification for the Detection and Recognition of Tryptophan Enantiomers

By immobilizing the chiral center l-histidine (l-His) into a Zr-based metal-organic framework (MOF) through post-synthetic ligand exchange, a chiral compound MOF-His has been prepared. On this basis, MOF-His is hybridized with Eu³⁺ ions to obtain the final responsive compound Eu@MOF-His. It is worth noting that the bifunctional material exhibits enantioselective luminescence properties for tryptophan enantiomers. The experimental results demonstrate that tryptophan enantiomers can effectively quench the red-light emission of Eu³⁺ ions, and also, the quenching rates are various, which may originate from the differences in the interaction between analytes and chiral recognition sites. In addition, Eu@MOF-His can realize the sensing of tryptophan enantiomers in serum. Concurrently, the compound possesses reusability, high sensitivity, and fast response speed, which means that it has the potential to serve as an excellent fluorescent sensor for detecting and identifying tryptophan enantiomers.

Multi-Level Computational Screening of in Silico Designed MOFs for Efficient SO2 Capture

SO₂ presence in the atmosphere can cause significant harm to the human and environment through acid rain and/or smog formation. Combining the operational advantages of adsorption-based separation and diverse nature of metal-organic frameworks (MOFs), cost-effective separation processes for SO₂ emissions can be developed. Herein, a large database of hypothetical MOFs composed of >300,000 materials is screened for SO₂/CH₄, SO₂/CO₂, and SO₂/N₂ separations using a multi-level computational approach. Based on a combination of separation performance metrics (adsorption selectivity, working capacity, and regenerability), the best materials and the most common functional groups in those most promising materials are identified for each separation. The top bare MOFs and their functionalized variants are determined to attain SO₂/CH₄ selectivities of 62.4-16899.7, SO₂ working capacities of 0.3-20.1 mol/kg, and SO₂ regenerabilities of 5.8-98.5%. Regarding SO₂/CO₂ separation, they possess SO₂/CO₂ selectivities of 13.3-367.2, SO₂ working capacities of 0.1-17.7 mol/kg, and SO₂ regenerabilities of 1.9-98.2%. For the SO₂/N₂ separation, their SO₂/N₂ selectivities, SO₂ working capacities, and SO₂ regenerabilities span the ranges of 137.9-67,338.9, 0.4-20.6 mol/kg, and 7.0-98.6%, respectively. Besides, using breakdowns of gas separation performances of MOFs into functional groups, separation performance limits of MOFs based on functional groups are identified where bare MOFs (MOFs with multiple functional groups) tend to show the smallest (largest) spreads.