Robust 4d-5f Bimetal-Organic Framework for Efficient Removal of Trace SO2 from SO2/CO2 and SO2/CO2/N2 Mixtures

Metal-organic frameworks (MOFs) toward SO2 detection

Developing technology that can precisely monitor specific air pollutants in diverse settings is essential to control emissions and ensure safe exposure limits are not exceeded. Metal-organic frameworks (MOFs) are crystalline organic-inorganic hybrid materials, which are promising candidates for SO2 detection. Their chemically mutable periodic structure confers outstanding surface area, thermal stability, and a well-defined pore distribution. Moreover, MOFs have exhibited extraordinary performance for SO2 capture. Therefore, research has focused on their possible applications for SO2 sequestration due to the selective and robust chemical and physical interactions of SO2 molecules within MOFs. The variable SO2 affinity presented by MOFs enables the adsorption mechanism and preferential adsorption sites to be resolved. However, for MOF-based SO2 detection, selective SO2 capture at shallow partial pressure (0.01-0.1 bar) is required. Thus, capturing SO2 at low concentration is crucial for SO2 detection, where textural properties of MOFs, mainly the pore-limiting diameter, are essential to achieve selective detection. In this review, we discuss the fundamental aspects of SO2 detection in MOFs, providing a step-by-step methodology for SO2 detection in MOFs. We hope this review can provide valuable background around SO2 detection in MOFs and inspire further research within this new and exciting field.

Molecular Simulation Insights into Acid Gas Interactions within Ni-Based Fluorinated Square-Pillared Metal-Organic Framework

The increasing prominence of metal-organic frameworks (MOFs) in gas separation technologies has sparked significant interest in their application in flue gas treatment. Nevertheless, the adsorption of acidic gases in MOFs presents significant challenges owing to their complex interactions with the framework. The adsorption interactions of acidic gases and their mixtures with [Ni(1,4-pyrazine)2(AlF5)]n (ALFFIVE-Ni-Pyr) are explored while considering the flexibility of the framework. Using grand canonical Monte Carlo simulations, guest-host interactions are evaluated, focusing on gas loading, whereas molecular dynamics simulations highlight the structural dynamics induced by guest molecules within the framework. Density functional theory calculations further confirm the interactions between acidic gases and the framework. A significantly higher adsorption capacity for SO2 than for CO2 and NO2 is shown in results, particularly in gas mixtures, highlighting the adaptability of the framework and its superior performance for acidic gas separation. This study aims to contribute to advancements in gas separation processes and provide valuable insights into the optimization of MOFs for industrial applications.

Cost-Effective Synthesis of Carbazole-Based Nanoporous Organic Polymers for SO2 Capture

Sulfur dioxide (SO2), a pervasive air pollutant, poses significant environmental and health risks, necessitating advanced materials for its efficient capture. Nanoporous organic polymers (NOPs) have emerged as promising candidates; however, their development is often hindered by high synthesis temperatures, complex precursors, and limited SO2 selectivity. Herein, we report a room-temperature, cost-effective synthesis of carbazole-based nanoporous organic polymers (CNOPs) using 1,3,5-trioxane and paraldehyde, offering a significant advancement over traditional Friedel-Crafts alkylation methods. The resulting CNOPs exhibit a high surface area of up to 842 m2·g-1 and feature ultramicroporous structures optimized for SO2 adsorption. At 298 K and 1 bar, the CNOPs demonstrated SO2 adsorption capacities of up to 9.39 mmol·g-1. Ideal adsorbed solution theory (IAST) calculations revealed outstanding selectivities of 105 for SO2/CO2 and 6139 for SO2/N2 mixtures, supported by breakthrough experiments demonstrating superior separation performance. This work not only provides a straightforward synthetic route for CNOPs but also offers valuable insights into the design and development of porous materials tailored for enhanced SO2 capture, addressing critical environmental and health challenges.

Engineering Nanoporous Polyaminal Networks for Superior SO2 Capture and Selectivity

Designing adsorbent materials with high SO2 adsorption capacities and selectivity remains a significant challenge in flue gas desulfurization. This work focuses on developing two nitrogen-rich nanoporous polyaminal networks (NPANs), which demonstrate promising capabilities for SO2 adsorption and separation. Two nitrogen-rich nanoporous polyaminal networks, NPAN-5 and NPAN-6, were synthesized via a one-pot method using thiophene-2,5-dicarbaldehyde and furan-2,5-dicarbaldehyde with 1,4-bis(2,4-diamino-1,3,5-triazine)-benzene, respectively. The Brunauer-Emmett-Teller (BET) specific surface areas of NPANs range from 838 to 956 m2·g-1. At 298 K and pressures of 0.1 and 1.0 bar, NPAN-5, featuring thiophene units, demonstrates a SO2 adsorption uptake of 5.14 and 9.63 mmol·g-1, respectively, surpassing many previously reported materials. Furthermore, at room temperature, NPAN-6, containing furan moieties, exhibits unprecedented selectivity for SO2 over CO2 and N2, with ratios reaching up to 78 and 9321, respectively. Dynamic breakthrough experiments reveal that NPANs effectively separate SO2 from a ternary gas mixture comprising SO2, CO2, and N2 at concentrations of 0.2, 10, and 89.8%, respectively. Notably, NPAN-6 achieves a prolonged SO2 retention time of 218 min·g-1 and a saturation adsorption uptake of 0.42 mmol·g-1. The remarkable SO2 adsorption capacities and selectivities demonstrated by these nitrogen-rich nanoporous polyaminal networks underscore their potential to revolutionize industrial flue gas desulfurization.

Highly Selective SO2 Capture by Triazine-Functionalized Triphenylamine-Based Nanoporous Organic Polymers

The emissions of sulfur dioxide (SO2) from combustion exhaust gases pose significant risks to public health and the environment due to their harmful effects. Therefore, the development of highly efficient adsorbent polymers capable of capturing SO2 with high capacity and selectivity has emerged as a critical challenge in recent years. However, existing polymers often exhibit poor SO2/CO2 and SO2/N2 selectivity. Herein, we report two triazine-functionalized triphenylamine-based nanoporous organic polymers (ANOP-6 and ANOP-7) that demonstrate both good SO2 uptake and high SO2/CO2 and SO2/N2 selectivity. These polymers were synthesized through cost-effective Friedel-Crafts reactions using cyanuric chloride, 3,6-diphenylaminecarbazole, and 2,2',7,7'-tetrakis(diphenylamino)-9,9'-spirobifluorene. The resultant ANOPs are composed of triazine and triphenylamine units and feature an ultramicroporous structure. Remarkably, ANOPs exhibit impressive adsorption capacities for SO2, with uptakes of approximately 3.31-3.72 mmol·g-1 at 0.1 bar, increasing to 9.52-9.94 mmol·g-1 at 1 bar. The static adsorption isotherms effectively illustrate the ability of ANOPs to separate SO2 from SO2/CO2 and SO2/N2 mixtures. At 298 K and 1 bar, ANOP-6 shows outstanding selectivity toward SO2/CO2 (248) and SO2/N2 (13146), surpassing all previously reported triazine-based nanoporous organic polymers. Additionally, dynamic breakthrough tests demonstrate the superior separation properties of ANOPs for SO2 from an SO2/CO2/N2 mixture. ANOPs exhibit a breakthrough time of 73.1 min·g-1 and a saturated SO2 capacity of 0.53 mmol·g-1. These results highlight the exceptional adsorption properties of ANOPs for SO2, indicating their promising potential for the highly efficient capture of SO2 from flue gas.

Feasible bottom-up development of conjugated microporous polymers (CMPs) for boosting the deep removal of sulfur dioxide

A pain-point for material development is that computer-screened structures are usually difficult to realize in experiments. Herein, considering that linkages are crucial for building functional nanoporous polymers with diverse functionalities, we develop an efficient approach for constructing target-specific conjugated microporous polymers (CMPs) based on screening feasible polymerization pathways. Taking the deep removal of SO2 from a SO2/CO2 mixture as the specific target, we precisely screen the linkages and fabricate different CMPs by manipulating the porosity and hydrophobicity. Based on the optimized Buchwald-Hartwig amination, the obtained CMPs can achieve SO2/CO2 selectivity as high as 113 and a moderate Qst of 30 kJ mol-1 for feasible regeneration. Furthermore, the potential of CMPs for practical SO2/CO2 separation is demonstrated through continued breakthrough tests. The SO2 binding sites are consistent with the screening results and proved by in situ Fourier transform infrared spectroscopy and grand canonical Monte Carlo simulation, providing solid feasibility for synthesis realizability for future boosts of task-specific CMPs.

U-Co Bimetallic-Organic Framework Showing a Helical 1D Pore Decorated by Abundant -CH3 Groups: Robust Nature under Acid, Base, and Water for High-Performance SO2 Removal

Constructing robust adsorbents for SO₂ removal remains a challenging issue. Herein, a U-Co bimetallic-organic framework, namely, ECUT-123, showing a helical 1D pore decorated by abundant -CH₃ groups, enables ultrahigh stability under acid, base, and water. This merit further supports its big potential for the removal of trace SO₂.

Analysis of SO2 Physisorption by Edge-Functionalized Nanoporous Carbons Using Grand Canonical Monte Carlo Methods and Density Functional Theory: Implications for SO2 Removal

Nanoporous carbons (NPCs) are ideal materials for the dry process of flue gas desulfurization (FGD) due to their rich pore structure and high specific surface area. To study the effect of edge-functionalized NPCs on the physisorption mechanism of sulfur dioxide, different functional groups were embedded at the edge of NPCs, and the physisorption behavior was simulated using the grand canonical Monte Carlo method (GCMC) combined with density functional theory (DFT). The results indicated that the insertion of acidic oxygenous groups or basic nitrogenous groups into NPCs could enhance the physisorption of SO₂. The influence of edge functionalization on the pore structure of NPCs is also analyzed. To further explore the interaction in the adsorption process, the van der Waals (vdW) interaction and electrostatic interaction between the SO₂ molecule and the basic structural unit (BSU) were investigated. Simulated results showed that edge functionalization had limited influence on vdW interaction and did not significantly change the distribution characteristics of vdW interaction. According to the study on electrostatic interaction, edge functionalization was found to promote inhomogeneity of the surface charge of the adsorbent, enhance the polarity of the adsorbent, and thus enhance the physisorption capacity of SO₂. More importantly, we provide an idea for studying the difference in adsorption capacity caused by different functional groups connected to carbon adsorbents.

Capture of toxic gases in MOFs: SO2, H2S, NH3 and NO x

MOFs are promising candidates for the capture of toxic gases since their adsorption properties can be tuned as a function of the topology and chemical composition of the pores. Although the main drawback of MOFs is their vulnerability to these highly corrosive gases which can compromise their chemical stability, remarkable examples have demonstrated high chemical stability to SO2, H2S, NH3 and NO x . Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. Thus, the interactions of such functional groups (coordinatively unsaturated metal sites, μ-OH groups, defective sites and halogen groups) with these toxic molecules, not only determines the capture properties of MOFs, but also can provide a guideline for the desigh of new multi-functionalised MOF materials. Thus, this perspective aims to provide valuable information on the significant progress on this environmental-remediation field, which could inspire more investigators to provide more and novel research on such challenging task.

A Robust Cage-Based Metal-Organic Framework Showing Ultrahigh SO2 Uptake for Efficient Removal of Trace SO2 from SO2/CO2 and SO2/CO2/N2 Mixtures

Removal of trace SO₂ from an SO₂-containing product is now receiving increasing attention. However, designing a robust porous adsorbent with high SO₂ adsorption capacity and good SO₂/CO₂ selectivity, as well as validity under humid conditions, is still a challenging task. Herein, we report a porous cage-based metal-organic framework, namely ECUT-111, which contains two distinct cages with apertures of 5.4 and 10.2 Å, respectively, and shows high a BET of up to 1493 m²/g and a pore volume of 0.629 cm³/g. Impressively, ECUT-111 enables an ultrahigh SO₂ uptake of up to 11.56 mmol/g, exceeding most reported top-performing adsorbents for such a use. More importantly, complete separation of trace SO₂ from SO₂/CO₂ and SO₂/CO₂/N₂ mixtures, especially under humid conditions, and excellent recycle use were observed for ECUT-111, suggesting its superior application in desulfurization of SO₂-containing products.