Supported polytertiary amines: highly efficient and selective SO2 adsorbents

Triple Templates Directed Synthesis of Nitrogen-Doped Hierarchically Porous Carbons from Pyridine Rich Monomer as Efficient and Reversible SO2 Adsorbents

Herein, a variety of 2,6-diaminopyridine (DAP) derived nitrogen-doped hierarchically porous carbon (DAP-NHPC-T) prepared from carbonization-induced structure transformation of DAP-Zn-SiO2-P123 nanocomposites are reported, which are facilely prepared from solvent-free co-assembly of block copolymer templates P123 with pyridine-rich monomer of DAP, Zn(NO3)2 and tetramethoxysilane. In the pyrolysis process, P123 and SiO2 templates promote the formation of mesoporous and supermicroporous structures in the DAP-NHPC-T, while high-temperature volatilization of Zn contributed to generation of micropores. The DAP-NHPC-T possess large BET surface areas (≈956-1126 m2 g-1), hierarchical porosity with micro-supermicro-mesoporous feature and high nitrogen contents (≈10.44-5.99 at%) with tunable density of pyridine-based nitrogen sites (≈5.99-3.32 at%), exhibiting good accessibility and reinforced interaction with SO2. Consequently, the DAP-NHPC-T show high SO2 capacity (14.7 mmol g-1, 25 °C and 1.0 bar) and SO2/CO2/N2 IAST selectivities, extraordinary dynamic breakthrough separation efficiency and cycling stability, far beyond any other reported nitrogen-doped metal-free carbon. As verified by in situ spectroscopy and theoretical calculations, the pyridine-based nitrogen sites of the DAP-NHPC-T boost SO2 adsorption via the unique charge transfer, the adsorption mechanism and reaction model have been finally clarified.

Development and Characterization of Polyethylenimine-Infiltrated Mesoporous Silica Foam Pellets for CO2 Capture

Polyethylenimine (PEI) has been shown to be promising for direct air capture (DAC) of carbon dioxide and has potential for commercial scale-up globally. Laboratory scale processes include multiple steps, such as mixing, solvent extraction, vacuum application, sonication, and various flushes and activation steps. It is critical to properly control these operating parameters to achieve higher capture capacity as a result of the optimized material configuration. This study adopts previously published pelletization processes for PEI-infiltrated mesoporous foam silica (mesoporous silica foam) to uncover the adsorption mechanisms and optimize the associated fabrication steps, such as sonication, to achieve higher sorbent productivity. A high capture capacity was achieved at 46 °C for 75 wt % PEI loading (2.27 mmol/g) followed by PEI_MSF 70 (1.81 mmol/g) and PEI_MSF 80 (1.44 mmol/g). As part of the optimization, sonication parameters of frequency, amplitude, and time were modified for PEI_MSF 75 sorbent, which resulted in the highest uptake capacity of 3.04 mmol/g (sonicated at 40 kHz and a wave amplitude of 50% for 30 s). These preliminary results would tend to prove that sonication energy affects carbon capture capacity, although there is still a lack of understanding regarding the exact underlying mechanism, suggesting the need for further investigation. It is important to note that the present work is focused on the adsorption mechanisms and not desorption or durability of the capture performance. Ongoing research addresses these factors. This paper is intended to establish baseline DAC behavior of a promising capture medium and begins probing the optimization spectrum by considering the effects of sonication energy on adsorption. Ongoing work intends to address potential abbreviations of the full range of process steps and furthers the understanding of kinetics by considering the desorption and resorption attributes.

Insights into the proton-enhanced mechanism of hexavalent chromium removal by amine polymers in strong acid wastewater: Reduction of hexavalent chromium and sequestration of trivalent chromium

Adsorption is a green technology of treating heavy metal-contaminated strong acid wastewaters for the recycling of heavy metal and reuse of strong acid. Herein, three amine polymers (APs) with different alkalinities and electron donating abilities were prepared to investigate the adsorption-reduction processes of Cr(VI). It was found that the removal of Cr(VI) was controlled by the concentration of -NRH+ on the surface of APs at pH > 2, which relies on the alkalinity of APs. However, the high concentration of NRH+ significantly facilitated the adsorption of Cr(VI) on the surface of APs and accelerated the mass transfer between Cr(VI) and APs at strong acid environment (pH ≤ 2). More importantly, the reduction of Cr(VI) was enhanced at pH ≤ 2, due to the high reduction potential of Cr(VI) (E ≥ 0.437). The ratio of reduction to adsorption (α) of Cr(VI) was above 0.70, and the proportion of Cr(III) bonding on Ph-AP excessed 67.6 %. Finally, a proton-enhanced mechanism of Cr(VI) removal was verified by analyzing FTIR and XPS spectra as well as constructing DFT model. This study provides a theoretical basis for the removal of Cr(VI) in the strong acid wastewater.

Reactivity of the Intramolecular Vicinal Group-13/P- and B/Group-15-Based Frustrate Lewis Pairs with Sulfur Dioxide: Mechanistic Insight from DFT

The emission of SO2 gas by industrialized societies contributes to the occurrence of acid rain in natural environments. In this study, we put forward a theoretical investigation into the capture reactions of SO2. Our analysis centers on the energy profiles of intramolecular 1,2-cyclohexylene-bridged FLP-associated molecules. We will particularly examine the reactions involving G13/P-based (with G13 denoting Group 13 element) and B/G15-based (with G15 representing Group 15 element) FLP-associated molecules. Except for Tl/P-FLP, B/N-FLP, and B/Bi-FLP, our theoretical examinations indicate that the remaining six FLP-associated molecules, namely G13'/P-FLP (G13' = B, Al, Ga, and In) and B/G15 ' -FLP (G15' = P, As, and Sb), can easily undergo SO2 capture reactions due to their energetic feasibility. Particularly, our theoretical findings suggested that 1,2-cyclohexylene-bridged Al/P-FLP, Ga/P-FLP, B/As-FLP, and B/Sb-FLP are capable of undergoing a reversible reaction and returning to the initial reactant state. Our theoretical evidence indicates that the G13-G15 bond length in the 1,2-cyclohexylene-linked G13/G15-FLP can serve as a basis for evaluating the free activation barrier associated with its reaction with SO2. Two theoretical methods, namely, the frontier molecular orbital theory and the energy decomposition analysis-natural orbitals of chemical valence approach, are utilized to investigate the electronic structure and bonding nature of the reactions under consideration. Moreover, the analyses based on the activation strain model revealed that it is the geometrical deformation energies of G13/G15-FLP, which is the key factor that greatly influences the activation barriers of such SO2 capture reactions. Further, our theoretical computations indicate that such capturing reactions of SO2 by intramolecular 1,2-cyclohexylene-linked G13/G15-based FLP-type molecules obey the Hammond postulate.

Recent Progress in the Integration of CO2 Capture and Utilization

CO₂ emission is deemed to be mainly responsible for global warming. To reduce CO₂ emissions into the atmosphere and to use it as a carbon source, CO₂ capture and its conversion into valuable chemicals is greatly desirable. To reduce the transportation cost, the integration of the capture and utilization processes is a feasible option. Here, the recent progress in the integration of CO₂ capture and conversion is reviewed. The absorption, adsorption, and electrochemical separation capture processes integrated with several utilization processes, such as CO₂ hydrogenation, reverse water-gas shift reaction, or dry methane reforming, is discussed in detail. The integration of capture and conversion over dual functional materials is also discussed. This review is aimed to encourage more efforts devoted to the integration of CO₂ capture and utilization, and thus contribute to carbon neutrality around the world.

Evaluation of the Stability of Diamine-Appended Mg2(dobpdc) Frameworks to Sulfur Dioxide

Diamine-appended Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are a promising class of CO₂ adsorbents, although their stability to SO₂─a trace component of industrially relevant exhaust streams─remains largely untested. Here, we investigate the impact of SO₂ on the stability and CO₂ capture performance of dmpn-Mg₂(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine), a candidate material for carbon capture from coal flue gas. Using SO₂ breakthrough experiments and CO₂ isobar measurements, we find that the material retains 91% of its CO₂ capacity after saturation with a wet simulated flue gas containing representative levels of CO₂ and SO₂, highlighting the robustness of this framework to SO₂ under realistic CO₂ capture conditions. Initial SO₂ cycling experiments suggest dmpn-Mg₂(dobpdc) may achieve a stable operating capacity in the presence of SO₂ after initial passivation. Evaluation of several other diamine-Mg₂(dobpdc) variants reveals that those with primary,primary (1°,1°) diamines, including dmpn-Mg₂(dobpdc), are more robust to humid SO₂ than those featuring primary,secondary (1°,2°) or primary,tertiary (1°,3°) diamines. Based on the solid-state ¹⁵N NMR spectra and density functional theory calculations, we find that under humid conditions, SO₂ reacts with the metal-bound primary amine in 1°,2° and 1°,3° diamine-appended Mg₂(dobpdc) to form a metal-bound bisulfite species that is charge balanced by a primary ammonium cation, thereby facilitating material degradation. In contrast, humid SO₂ reacts with the free end of 1°,1° diamines to form ammonium bisulfite, leaving the metal-diamine bond intact. This structure-property relationship can be used to guide further optimization of these materials for CO₂ capture applications.

Schematic Design of Metal-Free NHC-Mediated Sequestering and Complete Conversion of SO2 to Thiocarbonyl S-Oxide Derivatives at Room Temperature

The sequestering and complete conversion of SO₂ to valuable chemicals in a metal-free pathway is highly demanded. The recent success of SO₂ fixation by N-heterocyclic carbenes instigated further studies in this regard. Previous reports were confined within the carbene-SO₂ reaction mechanism and the stability of oxathiirane S-oxide derivatives. The complete conversion of captured SO₂ to precious chemicals was not studied. The present inquisition has accomplished the scarcity of the earlier studies. It is observed that in the presence of an excess amount of carbene, the registered SO₂ is converted to the ketone derivative and thiocarbonyl S-oxide derivative. An electronic level investigation of these reactions is carried out. From the change of the molecular orbitals along the reaction path, it is concluded that the reaction between the oxathiirane S-oxide derivative and carbene follows a frog's hunting mechanism.

SO2 Capture Using Porous Organic Cages

We report the first experimental investigation of porous organic cages (POCs) for the demanding challenge of SO2 capture. Three structurally related N-containing cage molecular materials were studied. An imine-functionalized POC (CC3) showed modest and reversible SO2 capture, while a secondary-amine POC (RCC3) exhibited high but irreversible SO2 capture. A tertiary amine POC (6FT-RCC3) demonstrated very high SO2 capture (13.78 mmol g-1 ; 16.4 SO2 molecules per cage) combined with excellent reversibility for at least 50 adsorption-desorption cycles. The adsorption behavior was investigated by FTIR spectroscopy, 13 C CP-MAS NMR experiments, and computational calculations.

Capture of Acidic Gases from Flue Gas by Deep Eutectic Solvents

Up to now, many kinds of deep eutectic solvents (DESs) were investigated for the capture of acidic gases from flue gases. In this review, non-functionalized and functionalized DESs, including binary and ternary DESs, for SO2, CO2 and NO capture, are summarized based on the mechanism of absorption, physical interaction or chemical reaction. New strategies for improving the absorption capacity are introduced in this review. For example, a third component can be introduced to form a ternary DES to suppress the increase in viscosity and improve the CO2 absorption capacity. DESs, synthesized with halogen salt hydrogen bond acceptors (HBAs) and functionalized hydrogen bond donors (HBDs), can be used for the absorption of SO2 and NO with high absorption capacities and low viscosities after absorption, due to physicochemical interaction between gases and DESs. Emphasis is given to introducing the absorption capacities of acidic gases in these DESs, the mechanism of the absorption, and the ways to enhance the absorption capacity.

Competitive Reactivity of SO2 and NO2 with N-Heterocyclic Carbene: A Mechanistic Study

Recent DFT based molecular engineering to obtain stable oxathiirane S-oxide derivatives evokes the recommencement of the use of carbenes for the sequestering of SO₂, which has been kept separate so far. Carbene is one of the key chemicals for the sequestering of various premier greenhouse gases like CO₂, CO, N₂O, etc. In this respect, a comparative study of the reactivity of carbenes with variant greenhouse gases is highly demanding. The present investigation is engrossed in the comparative reactivity of SO₂ and NO₂ with carbenes. All three selected carbenes are highly susceptible to SO₂ and NO₂. Through an immaculate mechanistic study, we are able to corroborate that the end product of the carbene-SO₂ reaction is an adduct which has a preferable structure having a six-membered ring with hydrogen bonding instead of ketone and SO with higher thermodynamic stability than the corresponding oxathiirane S-oxide derivative. Carbene reacts with NO₂ to form a stable carbene N, N-dioxide derivative which forms vibrationally excited oxaziridine N-oxide which rapidly dissociates to form a ketone derivative. The formation of carbene S, S-dioxide and carbene N, N-dioxide is a barrierless process. The dissociation of oxaziridene N-oxide is also a barrierless process.

An investigation into the adverse effects of O2, SO2, and NOx on polyethyleneimine functional CO2 adsorbents

In this study, we investigated the influence of O2, SO2, and NOx on branched and linear polyethyleneimine (PEI) functional silica CO2 adsorbents (BPEI-SiO2 and LPEI-SiO2, respectively). O2 was much more likely to oxidize BPEI-SiO2, compared with LPEI-SiO2, to form C=O and C=N groups and led to a 23.0% decrease in the CO2 adsorption capacity after 990 min of cumulative contact with 10% O2. In contrast, LPEI-SiO2 lost only approximately 3.6% of its CO2 adsorption capacity, although O2 oxidized LPEI-SiO2 to form C=O groups. SO2 can cause severe degradation of BPEI-SiO2 and LPEI-SiO2 by forming heat-stable NH3+—and/or NH2+—containing adducts and by promoting the formation of urea linkages. After cumulative contact with 10, 50, and 200 ppm SO2 for 990 min, BPEI-SiO2 lost 18.2%, 61.4%, and 89.0% of its CO2 adsorption capacity, and LPEI-SiO2 lost 18.5%, 60.6%, and 78.5% of its CO2 adsorption capacity, respectively. NO2 at 10 ppm and NO at 200 ppm caused almost no loss in CO2 adsorption capacity after cumulative contact for 990 min, but both led to degradation of adsorbents. NO2 can cause irreversible formation of NH3+—and/or NH2+—containing adducts, acid products, N-nitro compounds (N–NO2), C-nitroso compounds (C–N=O), and C-nitro (C–NO2) compounds, and can promote the formation of urea linkages. NO can lead to the formation of NH3+—and/or NH2+—containing adducts and N-nitroso (N–N = O) compounds.

Significantly promoted SO2 uptake by the mixture of N-methylated ethylene imine polymer and 1-ethyl-3-methylimidazolium tetrazolate

A novel class of hybrid solvents (mEIP:Tetz) comprising of N-methylated ethylene imine polymer (mEIP) and 1-ethyl-3-methylimidazolium tetrazolate ([Emim][Tetz]) were developed for the highly efficient and reversible capture of SO₂. The synergistic interactions rather than simple mixing between mEIP and [Emim][Tetz] were confirmed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations. Besides, it was experimentally demonstrated that mEIP:Tetz mixtures exhibited improved kinetics for SO₂ absorption, and the production of viscous solids were completely eliminated, compared with using mEIP alone. More significantly, an exceedingly high solubility of 0.308 g SO₂·g^-1 absorbent in 2mEIP:8Tetz was received for trapping SO₂ from simulated flue gas containing 2000 ppm SO₂, which was much higher than most of the results reported in previous literatures under the same conditions. Finally, the absorption and desorption mechanisms were proposed according to the results of FTIR and ¹H NMR analysis.

Sulfur dioxide removal: An overview of regenerative flue gas desulfurization and factors affecting desulfurization capacity and sorbent regeneration

Numerous mitigation techniques have been incorporated to capture or remove SO₂ with flue gas desulfurization (FGD) being the most common method. Regenerative FGD method is advantageous over other methods due to high desulfurization efficiency, sorbent regenerability, and reduction in waste handling. The capital costs of regenerative methods are higher than those of commonly used once-through methods simply due to the inclusion of sorbent regeneration while operational and management costs depend on the operating hours and fuel composition. Regenerable sorbents like ionic liquids, deep eutectic solvents, ammonium halide solutions, alkyl-aniline solutions, amino acid solutions, activated carbons, mesoporous silica, zeolite, and metal-organic frameworks have been reported to successfully achieve high SO₂ removal. The presence of other gases in flue gas, e.g., O₂, CO₂, NOx, and water vapor, and the reaction temperature critically affect the sorption capacity and sorbent regenerability. To obtain optimal SO₂ removal performance, other parameters such as pH, inlet SO₂ concentration, and additives need to be adequately governed. Due to its high removal capacity, easy preparation, non-toxicity, and low regeneration temperature, the use of deep eutectic solvents is highly feasible for upscale utilization. Metal-organic frameworks demonstrated highest reported SO₂ removal capacity; however, it is not yet applicable at industrial level due to its high price, weak stability, and robust formulation.

Triplexed Tracking Labile Sulfur-Containing Species on a Single-Molecule "Nezha" Sensor

Sulfur-containing species (SCS), especially sulfur dioxide-relevant species, play an essential role in ecological balance. Owing to the intrinsically labile and mobile characteristics of SCS, it is still considered to be an insurmountable challenge for multiplexed tracking dynamics of SCS with distinct molecular structure, valence state, and condensed state. To address this key problem, we proposed herein alternative versatile single-molecule sensors (VSMs) that intramolecularly integrate high affinity target-guided multiple recognition units into a single sensory molecule, clarified as molecular Nezha available in triplexed responses to gaseous sulfur dioxide, liquid sulfur trioxide, and aqueous bisulfite through ubiquitous charge transfer and nucleophilic addition. High-performance molecular Nezha remarkably facilitated promising applications in a quantitative visualization of SCS on lab-on-paper and tracking the dynamics transformation of SCS as well comprehensive evaluation of multiphase adsorption science of SCS on an advanced Zeolitic imidazolate framework-8 (ZIF-8).

Methylated Poly(ethylene)imine Modified Capacitive Micromachined Ultrasonic Transducer for Measurements of CO2 and SO2 in Their Mixtures

A gravimetric gas detection device based on surface functionalized Capacitive Micromachined Ultrasound Transducers (CMUTs) was designed, fabricated and tested for detection of carbon dioxide (CO₂) and sulfur dioxide (SO₂) mixtures in nitrogen. The created measurement setup of continuous data collection, integrated with an in-situ Fourier Transform Infrared (FT-IR) spectroscopy, allows for better understanding of the mechanisms and molecular interactions with the sensing layer (methylated poly(ethylene)imine) and its need of surface functionalization for multiple gas detection. During experimentation with CO₂ gases, weak molecular interactions were observed in spectroscopy data. Linear sensor response to frequency shift was observed with CO₂ concentrations ranging from 0.16 vol % to 1 vol %. Moreover, the Raman and FT-IR spectroscopy data showed much stronger SO₂ and the polymer interactions, molecules were bound by stronger forces and irreversibly changed the polymer film properties. However, the sensor change in resonance frequency in the tested region of 1 vol % to 5 vol % SO₂ showed a linear response. This effect changed not only the device resonance frequency but also affected the magnitude of electroacoustic impedance which was used for differentiating the gas mixture of CO₂, SO₂, in dry N₂.

Atmospheric Spectroscopy and Photochemistry at Environmental Water Interfaces

The air-water interface is ubiquitous in nature, as manifested in the form of the surfaces of oceans, lakes, and atmospheric aerosols. The aerosol interface, in particular, can play a crucial role in atmospheric chemistry. The adsorption of atmospheric species onto and into aerosols modifies their concentrations and chemistries. Moreover, the aerosol phase allows otherwise unlikely solution-phase chemistry to occur in the atmosphere. The effect of the air-water interface on these processes is not entirely known. This review summarizes recent theoretical investigations of the interactions of atmosphere species with the air-water interface, including reactant adsorption, photochemistry, and the spectroscopy of reactants at the water surface, with an emphasis on understanding differences between interfacial chemistries and the chemistries in both bulk solution and the gas phase. The results discussed here enable an understanding of fundamental concepts that lead to potential air-water interface effects, providing a framework to understand the effects of water surfaces on our atmosphere.

SO2-Resistant Amine-Containing CO2 Adsorbent with a Surface Protection Layer

Amine-containing solids are promising adsorbents for CO₂ capture, but they suffer from irreversible poisoning by the highly acidic SO₂ in flue gas. Here, we demonstrate a facile strategy to inhibit SO₂ poisoning. We first prepared an amine-containing adsorbent by impregnating polyethyleneimine (PEI) into porous silica. The PEI located at the external surface of the adsorbent was selectively alkylated with epoxide so that amines were fully converted to tertiary amines. As opposed to that onto primary and secondary amines, SO₂ adsorption onto tertiary amines is fully reversible. Therefore, during the flue gas adsorption, SO₂ is reversibly captured by the tertiary-amine-rich layer and then desulfurized CO₂ is adsorbed onto PEI beneath this layer. The resultant adsorbent showed insignificant loss of CO₂ adsorption capacity (8.52%) even after 1000 CO₂ adsorption-desorption cycles in the presence of 50 ppm SO₂, whereas conventional PEI/silica showed severe capacity loss (65.1%) due to irreversible SO₂ poisoning.

Stability of amine-functionalized CO2 adsorbents: a multifaceted puzzle

This review focuses on important stability issues facing amine-functionalized CO2 adsorbents, including amine-grafted and amine-impregnated silicas, zeolites, metal-organic frameworks and carbons. During the past couple of decades, major advances were achieved in understanding and improving the performance of such materials, particularly in terms of CO2 adsorptive properties such as adsorption capacity, selectivity and kinetics. Nonetheless, to pave the way toward commercialization of adsorption-based CO2 capture technologies, in addition to other attributes, adsorbent materials should be stable over many thousands of adsorption-desorption cycles. Adsorbent stability, which is of utmost importance as it determines adsorbent lifetime and operational costs of CO2 capture, is a multifaceted issue involving thermal, hydrothermal, and chemical stability. Here we discuss the impact of the adsorbent physical and chemical properties, the feed gas composition and characteristics, and the adsorption-desorption operational parameters on the long-term stability of amine-functionalized CO2 adsorbents. We also review important insights associated with the underlying deactivation pathways of the adsorbents upon exposure to high temperature, oxygen, dry CO2, sulfur-containing compounds, nitrogen oxides, oxygen and steam. Finally, specific recommendations are provided to address outstanding stability issues.

Rational Design of Aminopolymer for Selective Discrimination of Acidic Air Pollutants

Strong acidic gases such as CO₂, SO₂, and NO₂ are harsh air pollutants with major human health threatening factors, and as such, developing new tools to monitor and to quickly sense these gases is critically required. However, it is difficult to selectively detect the acidic air pollutants with single channel material due to the similar chemistry shared by acidic molecules. In this work, three acidic gases (i.e., CO₂, SO₂, and NO₂) are selectively discriminated using single channel material with precise moiety design. By changing the composition ratio of primary (1°), secondary (2°), and tertiary (3°) amines of polyethylenimine (PEI) on CNT channels, unprecedented high selectivity between CO₂ and SO₂ is achieved. Using in situ FT-IR characterizations, the distinct adsorption phenomenon of acidic gases on each amine moiety is precisely demonstrated. Our approach is the first attempt at controlling gas adsorption selectivity of solid-state sensor via modulating chemical moiety level within the single channel material. In addition, discrimination of CO₂, SO₂, and NO₂ with the single channel material solid-state sensor is first reported. We believe that this approach can greatly enhance air pollution tracking systems for strong acidic pollutants and thus aid future studies on selective solid-state gas sensors.

Adsorption of Carbonyl Sulfide on Propylamine Tethered to Porous Silica

Carbonyl sulfide (COS) reacts slowly with amines in the aqueous solutions used to absorb CO₂ from natural gas and flue gas and can also deactivate certain aqueous amines. The effects of COS on amines tethered to porous silica, however, have not been investigated before. Hence, the adsorption of COS on aminopropyl groups tethered to porous silica was studied using in situ IR spectroscopy. COS chemisorbed mainly and reversibly as propylammonium propylthiocarbamate ion pairs [R-NH(C═O)S^-+H₃N-R] under dry conditions. In addition, a small amount of another chemisorbed species formed slowly and irreversibly. Nevertheless, the CO₂ capacities of the adsorbents were fully retained after COS was desorbed.

Flying MOFs: polyamine-containing fluidized MOF/SiO2 hybrid materials for CO2 capture from post-combustion flue gas

Solid-state synthesis ensures a high loading and well-dispersed growth of a large collection of metal-organic framework (MOF) nanostructures within a series of commercially available mesoporous silica. This approach provides a general, highly efficient, scalable, environmentally friendly, and inexpensive strategy for shaping MOFs into a fluidized form, thereby allowing their application in fluidized-bed reactors for diverse applications, such as CO2 capture from post-combustion flue gas. A collection of polyamine-impregnated MOF/SiO2 hybrid sorbents were evaluated for CO2 capture under simulated flue gas conditions in a packed-bed reactor. Hybrid sorbents containing a moderate loading of (Zn)ZIF-8 are the most promising sorbents in terms of CO2 adsorption capacity and long-term stability (up to 250 cycles in the presence of contaminants: SO2, NO x and H2S) and were successfully prepared at the kilogram scale. These hybrid sorbents demonstrated excellent fluidizability and performance under the relevant process conditions in a visual fluidized-bed reactor. Moreover, a biochemically inspired strategy for covalently linking polyamines to MOF/SiO2 through strong phosphine bonds has been first introduced in this work as a powerful and highly versatile post-synthesis modification for MOF chemistry, thus providing a novel alternative towards more stable CO2 solid sorbents.

Ultrahigh and Selective SO2 Uptake in Inorganic Anion-Pillared Hybrid Porous Materials

The efficient capture of SO₂ is of great significance in gas-purification processes including flue-gas desulfurization and natural-gas purification, but the design of porous materials with high adsorption capacity and selectivity of SO₂ remains very challenging. Herein, the selective recognition and dense packing of SO₂ clusters through multiple synergistic host-guest and guest-guest interactions by controlling the pore chemistry and size in inorganic anion (SiF₆^2- , SIFSIX) pillared metal-organic frameworks is reported. The binding sites of anions and aromatic rings in SIFSIX materials grasp every atom of SO₂ firmly via S^δ+ ···F^δ- electrostatic interactions and O^δ- ···H^δ+ dipole-dipole interactions, while the guest-guest interactions between SO₂ molecules further promote gas trapping within the pore space, which is elucidated by first-principles density functional theory calculations and powder X-ray diffraction experiments. These interactions afford new benchmarks for the highly efficient removal of SO₂ from other gases, even if at a very low SO₂ concentration. Exceptionally high SO₂ capacity of 11.01 mmol g^-1 is achieved at atmosphere pressure by SIFSIX-1-Cu, and unprecedented low-pressure SO₂ capacity is obtained in SIFSIX-2-Cu-i (4.16 mmol g^-1 SO₂ at 0.01 bar and 2.31 mmol g^-1 at 0.002 bar). More importantly, record SO₂ /CO₂ selectivity (86-89) and excellent SO₂ /N₂ selectivity (1285-3145) are also achieved. Experimental breakthrough curves further demonstrate the excellent performance of these hybrid porous materials in removing low-concentration SO₂ .

Amine-Functionalized Covalent Organic Framework for Efficient SO2 Capture with High Reversibility

Removing sulfur dioxide (SO2) from exhaust flue gases of fossil fuel power plants is an important issue given the toxicity of SO2 and subsequent environmental problems. To address this issue, we successfully developed a new series of imide-linked covalent organic frameworks (COFs) that have high mesoporosity with large surface areas to support gas flowing through channels; furthermore, we incorporated 4-[(dimethylamino)methyl]aniline (DMMA) as the modulator to the imide-linked COF. We observed that the functionalized COFs serving as SO2 adsorbents exhibit outstanding molar SO2 sorption capacity, i.e., PI-COF-m10 record 6.30 mmol SO2 g-1 (40 wt%). To our knowledge, it is firstly reported COF as SO2 sorbent to date. We also observed that the adsorbed SO2 is completely desorbed in a short time period with remarkable reversibility. These results suggest that channel-wall functional engineering could be a facile and powerful strategy for developing mesoporous COFs for high-performance reproducible gas storage and separation.

New Solid-Base Cu-MgO for CO2 Capture at 473 K and Removal of Nitrosamine

To fabricate a new solid base with high efficiency in the adsorption of CO₂ at 473 K and catalytic activity in the degradation of nitrosamines, magnesium oxalate and copper nitrate are mixed with the assistance of microwave irradiation followed by calcination to immobilize CuO among MgO particles. The binary solid base CuO-MgO is thus moderately reduced to form the Cu-inserted MgO composite with highly exposed strong basic sites, and it can capture 34.6 mg g^-1 of CO₂ in the harsh instantaneous adsorption at 473 K and keep a high strong basicity while trapping the CO₂ mixed with SO₂ and NO. Besides this, the new solid base exhibits high activity in the removal of volatile nitrosamine N-nitrosopyrrolidine (NPYR), for the first time expanding the application of solid bases to environmental catalysis.

In situ Formation of a Monodispersed Spherical Mesoporous Nanosilica-Torlon Hollow-Fiber Composite for Carbon Dioxide Capture

We describe a new template-free method for the in situ formation of a monodispersed spherical mesoporous nanosilica-Torlon hollow-fiber composite. A thin layer of Torlon hollow fiber that comprises silica nanoparticles was created by the in situ extrusion of a tetraethyl orthosilicate/N-methyl-2-pyrrolidone solution in a sheath layer and a Torlon polymer dope in a core support layer. This new method can be integrated easily into current hollow-fiber composite fabrication processes. The hollow-fiber composites were then functionalized with 3-aminopropyltrimethoxy silane (APS) and evaluated for their CO2 -capture performance. The resulting APS-functionalized mesoporous silica nanoparticles/Torlon hollow fibers exhibited a high CO2 equilibrium capacity of 1.5 and 1.9 mmol g(-1) at 35 and 60 °C, respectively, which is significantly higher than values for fiber sorbents without nanoparticles reported previously.

Improving SO2 capture by tuning functional groups on the cation of pyridinium-based ionic liquids

Novel pyridinium-based ionic liquids [NEt₂C₂Py][SCN], [C₄OPy][SCN] and [C₄CNPy][SCN] with high SO₂ gravimetric capacity were developed and the mechanism was discussed.

PEI@Mg2SiO4: an efficient carbon dioxide and nitrophenol compounds adsorbing material

PEI@Mg₂SiO₄: an efficient carbon dioxide and nitrophenol compounds adsorbing material.