Structural and Dynamic Analysis of Sulphur Dioxide Adsorption in a Series of Zirconium-Based Metal-Organic Frameworks

Metal-organic framework with pore contraction and modification by diethylammonium cations for record SO2/CO2 separation

A robust MOF with diethylammonium cations in its pores, enhances pore partitioning and modifies the environment, enabling selective and dense SO2 packing through hydrogen bonds. It achieves a reversible SO2 uptake with a high adsorption enthalpy and record IAST selectivity of 1182 for SO2/CO2 at 298 K and 1 bar.

APTES functionalization in SBA-15: the effect on SO2 capture and detection applications

The development of adsorbents for air pollutant remediation and effective monitoring is of interest. Then, the effect of the APTES functionalization ratio on the impact of the adsorption and detection of SO2 molecules was evaluated. The higher APTES functionalization material (SBA-15_6.1APTES) shows a high uptake of 1.15 mmol g-1 at 0.001 bar and 298 K. Fluorescence, time-resolved photoluminescence, and quantum yield experiments revealed a turn-on effect specifically for SO2 molecules, indicating high selectivity, suggesting host-to-guest energy transfer. Attractively, XPS measurement provided an understanding of the mechanism, suggesting hydrogen bonding and dipole-dipole interactions as the main interactions between SO2 molecules and SBA-15_6.1APTES. DFT calculations were performed to confirm these interactions. Furthermore, this study highlights the application of SBA-15 materials with different amino modifications for SO2 treatment and provides insight into the interaction mechanism using experimental techniques.

Porous Organic Polymers for Efficient and Selective SO2 Capture from CO2-rich Flue Gas

The quest for effective technologies to reduce SO2 pollution is crucial due to its adverse effects on the environment and human health. Markedly, removing a ppm level of SO2 from CO2-containing waste gas is a persistent challenge, and current technologies suffer from low SO2/CO2 selectivity and energy-intensive regeneration processes. Here using the molecular building blocks approach and theoretical calculation, we constructed two porous organic polymers (POPs) encompassing pocket-like structures with exposed imidazole groups, promoting preferential interactions with SO2 from CO2-containing streams. Markedly, the evaluated POPs offer outstanding SO2/CO2 selectivity, high SO2 capacity, and an easy regeneration process, making it one of the best materials for SO2 capture. To gain better structural insights into the notable SO2 selectivity of the POPs, we used dynamic nuclear polarization NMR spectroscopy (DNP) and molecular modelling to probe the interactions between SO2 and POP adsorbents. The newly developed materials are poised to offer an energy-efficient and environment-friendly SO2 separation process while we are obliged to use fossil fuels for our energy needs.

A robust aluminum-octacarboxylate framework with topology for selective capture of sulfur dioxide

The high structural diversity and porosity of metal-organic frameworks (MOFs) promote their applications in selective gas adsorption. The development of robust MOFs that are stable against corrosive SO2 remains a daunting challenge. Here, we report a highly robust aluminum-based MOF (HIAM-330) built on a 4-connected Al3(OH)2(COO)4 cluster and 8-connected octacarboxylate ligand with a (4,8)-connected scu topology. It exhibits a fully reversible SO2 uptake of 12.1 mmol g-1 at 298 K and 1 bar. It is capable of selective capture of SO2 over other gases (CO2, CH4, and N2) with high adsorption selectivities of 60, 330, and 3537 for equimolar mixtures of SO2/CO2, SO2/CH4, and SO2/N2, respectively, at 298 K and 1 bar. Breakthrough measurements verified the capability of HIAM-330 for selective capture of SO2 (2500 ppm) over CO2 or N2. High-resolution synchrotron X-ray powder diffraction of SO2 loaded HIAM-330 revealed the binding domains of adsorbed SO2 molecules and host-guest interactions.

Fabrication of Carboxylate-Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra-low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50-500 µg L-1 within 5 min. Moreover, the 2D nano-material exhibits ultra-high anti-interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

Solvent-Driven Dynamics: Crafting Tailored Transformations of Cu(II)-Based MOFs

Metal-organic frameworks (MOFs), a sort of crystalline porous coordination polymers composed of metal ions and organic linkers, have been intensively studied for their ability to take up nonpolar gas-phase molecules such as ethane and ethylene. In this context, interpenetrated MOFs, where multiple framework nets are entwined, have been considered promising materials for capturing nonpolar molecules due to their relatively higher stability and smaller micropores. This study explores a solvent-assisted reversible strategy to interpenetrate and deinterpenetrate a Cu(II)-based MOF, namely, MOF-143 (noninterpenetrated form) and MOF-14 (doubly interpenetrated forms). Interpenetration was achieved using protic solvents with small molecular sizes such as water, methanol, and ethanol, while deinterpenetration was accomplished with a Lewis-basic solvent, pyridine. Additionally, this study investigates the adsorptive separation of ethane and ethylene, which is a significant application in the chemical industry. The results showed that interpenetrated MOF-14 exhibited higher ethane and ethylene uptakes compared to the noninterpenetrated MOF-143 due to narrower micropores. Furthermore, we demonstrate that pristine MOF-14 displayed higher ethane selectivity than transformed MOF-14 from MOF-143 by identifying the "fraction of micropore volume" as a key factor influencing ethane uptake. These findings highlight the potential of controlled transformations between interpenetrated and noninterpenetrated MOFs, anticipating that larger MOF crystals with narrower micropores and higher crystallinity will be more suitable for selective gas capture and separation applications.

Modulator-Dependent Dynamics Synergistically Enabled Record SO2 Uptake in Zr(IV) Metal-Organic Frameworks Based on Pyrene-Cored Molecular Quadripod Ligand

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal-organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g-1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in isostructural Zr-TPA variants synthesized with different capping modulators (formate, acetate, benzoate, and trifluoroacetate, abbreviated as FA, HAc, BA, and TFA, respectively) through computational analyses. These analyses revealed unexpected SO2-induced modulator-node dynamics, resulting in transient chemisorption that enhanced synergistic SO2 sorption. Additionally, we conducted a proof-of-concept experiment demonstrating that the captured SO2 in Zr-TPA-FA can be converted in situ into a valuable pharmaceutical intermediate known as aryl N-aminosulfonamide, with a high yield and excellent recyclability. This highlights the potential of robust Zr-MOFs for storing SO2 in catalytic applications. In summary, this work contributes significantly to the development of efficient SO2 solid sorbents and advances our understanding of the molecular mechanisms underlying SO2 sorption in Zr-MOF materials.

The Role of Water in Carbon Dioxide Adsorption in Porphyrinic Metal-Organic Frameworks

Capturing and converting CO2 through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO2 concentrations. Porphyrinic Zr-based metal-organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO2 sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO2 into PCN-222 and PCN-223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration. A shift in CO2 sorption site and bending of the porphyrin macrocycle in response to humidity was observed, and CO2/H2O competition experiments revealed that the exchange of CO2 with H2O is pore-size dependent. Therefore, humidity and pore-size can be used to tune CO2 sorption, CO2 capacity, and light harvesting in porphyrinic MOFs, which are key factors for CO2 photoreduction.