多孔有机骨架:基于傅氏烷基化反应的合成与气体吸附性质

通过傅氏烷基化反应成功地合成了基于四苯锗烷构筑单元的多孔有机骨架材料PAF-9。用红外光谱,粉末X射线衍射,固体核磁共振,热重分析和低温氮气吸附-脱附表征了PAF-9材料的微结构与孔道性质。表征数据表明PAF-9具有非常高的热稳定性和化学稳定性,同时具有较高的比表面积。该PAF材料的BET比表面积为334 m²·g^-1。此外,得到的PAF材料对二氧化碳具有较好的吸附能力。     

多孔有机骨架:基于傅氏烷基化反应的合成与气体吸附性质

通过傅氏烷基化反应成功地合成了基于四苯锗烷构筑单元的多孔有机骨架材料PAF-9。用红外光谱,粉末射X线衍射,固体核磁共振,热重分析和低温氮气吸附-脱附表征了PAF-9材料的微结构与孔道性质。表征数据表明PAF-9具有非常高的热稳定性和化学稳定性,同时具有较高的比表面积。该PAF材料的BET比表面积为334m²·g^-1。此外,得到的PAF材料对二氧化碳具有较好的吸附能力。     

Construction of a Stable Crystalline Polyimide Porous Organic Framework for C2H2/C2H4 and CO2/N2 Separation

Utilization of porous materials for gas capture and separation is a hot research topic. Removal of acetylene (C₂H₂) from ethylene (C₂H₄) is important in the oil refining and petrochemical industries, since C₂H₂ impurities deactivate the catalysts and terminate the polymerization of C₂H₄. Carbon dioxide (CO₂) emission from power plants contributes to global climate change and threatens the survival of life on this planet. Herein, 2D crystalline polyimide porous organic framework PAF-120, which was constructed by imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular 1,3,5-tris(4-aminophenyl)benzene, showed significant thermal and chemical stability. Low-pressure gas adsorption isotherms revealed that PAF-120 exhibits good selective adsorption of C₂H₂ over C₂H₄ and CO₂ over N₂. At 298 K and 1 bar, its C₂H₂ and CO₂ selectivities were predicted to be 4.1 and 68.7, respectively. More importantly, PAF-120 exhibits the highest selectivity for C₂H₂/C₂H₄ separation among porous organic frameworks. Thus PAF-120 could be a suitable candidate for selective separation of C₂H₂ over C₂H₄ and CO₂ over N₂.     

Alkylation of phenol with olefins in the presence of catalysts based on mesoporous aromatic frameworks

Mesoporous polyaromatic frameworks (PAFs) based on tetraphenylmethane were obtained and modified with sulfonic acid groups. The compounds were characterized by solid-state ¹³C NMR and IR spectroscopy, low-temperature nitrogen adsorption-desorption, and transmission electron microscopy. The acidities of the PAF-1-SO₃H and PAF-2-SO₃H samples determined by titration were 3.99 mmol g^–1 and 0.91 mmol g^–1, respectively. The catalytic activity of PAF-SO₃H for alkylation of phenol with linear terminal olefins was investigated. The reaction products were isomeric monoalkylphenols (C-alkylates), and alkyl phenyl ethers (O-alkylates).     

Thermal degradation study of phenolphthalein polycarbonate

Phenolphthalein polycarbonate underwent complicated thermal degradation which included random scission, rearrangement, hydrolysis, Friedel-Crafts acylation, and cross-linking. The carbonate group and lactone ring were both susceptible to thermal deterioration. Kinetic parameters were determined from the dynamic TGA thermograms. During early stages of degradation the measured reaction order was nearly 1, which suggested a random chain scission mechanism. The measured activation energy was 42.6 kcal/mol, compared with 41.2 kcal/mol calculated from isothermal aging. The Arrhenius preexponential constant was 3.09 × 10¹¹ min^?1. Below 80% weight residue the plot of fractional weight against 1/T revealed that complicated reactions with different activation energies occurred simultaneously and resulted in a final overlap of TGA curves for different heating rates indicative of cross-linking and a lower preexponential constant. The reaction order changed and kept increasing in the last stages of degradation. Pyrolysis of this polymer was performed at 350°C under vacuum, followed by GC-mass spectroscopic identification of products. The volatile products (17.5%) contained CO₂, CO, O₂, H₂O, phenol, fluorenone, diphenyl carbonate, xanthone, anthraquinone, 2-hydroxylanthraquinone, 2-benzoxyanthraquinone, phenolphthalein, and trace amounts of benzoxyphenol and hydroquinone; the other 82.5% of products was insoluble gel. Functional group changes were examined by Fourier transform infrared spectroscopy (FT-IR). Lactone, carbonate, and aromatic absorptions decreased during degradation. Increasing absorptions at 1739, 1728, 1280–1200, and 1138–1075 cm^?1 were believed to result from aromatic ester (1728 cm^?1) and phenyl aromatic ester (1739 cm^?1) cross-linkages ortho to the aromatic ether group (increases at 1155 cm^?1 and 1280–1200 cm^?1). Existence of 2-hydroxyanthraquinone and xanthone contained in the crosslinked polymer matrix were also detected. Mechanisms for random scission, rearrangement, Friedel-Crafts acylation, hydrolysis, and cross-linking were suggested.     

Synthesis of porous aromatic framework with Friedel–Crafts alkylation reaction for CO_2 separation

A novel porous aromatic framework, PAF-8, derived from tetraphenylsilane as basic building unit, was successfully synthesized via Friedel–Crafts alkylation reaction. This PAF material had high thermal stability as well as high surface area(785 m~2g~(-1)) calculated from the Brunauer–Emmett–Teller(BET)model. Meanwhile, PAF-8 possessed high performances in gas sorption and especially for CO_2 separation.     

Continuous Porous Aromatic Framework Membranes with Modifiable Sites for Optimized Gas Separation

Continuous microporous membranes are widely studied for gas separation, due to their low energy premium and strong molecular specificity. Porous aromatic frameworks (PAFs) with their exceptional stability and structural flexibility are suited to a wide range of separations. Main-stream PAF-based membranes are usually prepared with polymeric matrices, but their discrete entities and boundary defects weaken their selectivity and permeability. The synthesis of continuous PAF membranes is still a major challenge because PAFs are insoluble. Herein, we successfully synthesized a continuous PAF membrane for gas separation. Both pore size and chemistry of the PAF membrane were modified by ion-exchange, resulting in good selectivity and permeance for the gas mixtures H₂/N₂ and CO₂/N₂. The membrane with Br^? as a counter ion in the framework exhibited a H₂/N₂ selectivity of 72.7 with a H₂ permeance of 51844 gas permeation units (GPU). When the counter ions were replaced by BF₄^?, the membrane showed a CO₂ permeance of 23058 GPU, and an optimized CO₂/N₂ selectivity of 60.0. Our results show that continuous PAF membranes with modifiable pores are promising for various gas separation situations.     

Enzymatic Electrosynthesis of Glycine from CO2 and NH3

Enzymatic electrosynthesis has gained more and more interest as an emerging green synthesis platform, particularly for the fixation of CO₂. However, the simultaneous utilization of CO₂ and a nitrogenous molecule for the enzymatic electrosynthesis of value-added products has never been reported. In this study, we constructed an in vitro multienzymatic cascade based on the reductive glycine pathway and demonstrated an enzymatic electrocatalytic system that allowed the simultaneous conversion of CO₂ and NH₃ as the sole carbon and nitrogen sources to synthesize glycine. Through effective coupling and the optimization of electrochemical cofactor regeneration and the multienzymatic cascade reaction, 0.81 mM glycine was yielded with a highest reaction rate of 8.69 mg L⁻¹ h⁻¹ and faradaic efficiency of 96.8 %. These results imply a promising alternative for enzymatic CO₂ electroreduction and expand its products to nitrogenous chemicals.     

Highly efficient Lewis acid catalytic activity of the tritylium ion at the node of a tensile organic framework

Tritylium salts have been used as Lewis acid catalysts in organic synthesis for a long time. In this work, we found that the Lewis acid catalytic activity of tritylium ions at the node of a tensile framework is significantly improved compared to that of the free tritylium salts. The tritylium-based framework, PAF-201 (PAF, porous aromatic framework), was prepared by acidification of a semi-rigid triphenylcarbinol-based parent framework, PAF-200. When PAF-200 was alternately exposed to HCl and NH₃ gas, a fast allochroic cycle was observed due to repeated formation of tritylium species. Interestingly, the pseudo-first-order reaction rate of a Povarov model reaction catalyzed by PAF-201 as a Lewis acid was ∼3.7 times and ∼4.7 times as those of tritylium tetrafluoroborate and tri(4-biphenyl)carbonium tetrafluoroborate, respectively. Theoretical calculations revealed that the tritylium ion at the node of PAF-201 has a quasi-planar structure. The transformation of triphenylcarbinol in PAF-200 to tritylium in PAF-201 can make the framework taut, and the rebounding force toward the tetrahedral structure is stored. This is favorable for tritylium to activate the imine substrate along with a deformation of the quasi-plane to tetrahedron. PAF-201 could be easily recycled at least three times without evident loss of catalytic activity. This work presents the catalytic activity of the tritylium ion under stress.

In this work, a tensile tritylium-based organic framework, PAF-201 was prepared. The Lewis acid catalytic ability of PAF-201 was significantly higher than that of tritylium tetrafluoroborate. This work presented the catalytic activity of the tritylium ion under stress.     

Synthesizing Interpenetrated Triazine-based Covalent Organic Frameworks from CO2

Crystalline triazine-based covalent organic frameworks (COFs) are aromatic nitrogen-rich porous materials. COFs typically show high thermal/chemical stability, and are promising for energy applications, but often require harsh synthesis conditions and suffer from low crystallinity. In this work, we propose an environmentally friendly route for the synthesis of crystalline COFs from CO₂ molecules as a precursor. The mass ratio of CO₂ conversion into COFs formula unit reaches 46.3 %. The synthesis consists of two steps; preparation of 1,4-piperazinedicarboxaldehyde from CO₂ and piperazine, and condensation of the dicarboxaldehyde and melamine to construct the framework. The CO₂-derived COF has a 3-fold interpenetrated structure of 2D layers determined by powder X-ray diffraction, high-resolution transmission electron microscopy, and select-area electron diffraction. The structure shows a high Brunauer–Emmett–Teller surface area of 945 m² g⁻¹ and high stability against strong acid (6 M HCl), base (6 M NaOH), and boiling water over 24 hours. Post-modification of the framework with oxone has been demonstrated to modulate hydrophilicity, and it exhibits proton conductivity of 2.5×10⁻² S cm⁻¹ at 85 °C, 95 % of relative humidity.     

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO₂ from flue gas or natural gas. Here, a typical metal-organic framework HKUST-1(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals (Li, Na and K) and they were further used to investigate their CO₂ adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction (XRD), thermo-gravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO₂ storage capacity of HKUST-1 doped with moderate quantities of Li⁺, Na⁺ and K⁺, individually, was greater than that of unmodified HKUST-1. The highest CO₂ adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST-1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO₂ than those of N₂. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO₂ after 10 cycles.     

Gas transport in TiO2 nanoparticle-filled poly(1-trimethylsilyl-1-propyne)

Titanium dioxide (TiO₂) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form nanocomposite films. Nanoparticle dispersion was investigated using atomic force microscopy and transmission electron microscopy. At low-particle loadings, nanoparticles were dispersed individually and in nanoscale aggregates. At high-particle loadings, some nanoparticles formed micron-sized aggregates. The gas transport and density exhibited a strong dependence on nanoparticle loading. At low-TiO₂ loadings, the composite density was similar to or slightly higher than that predicted by a two-phase additive model. However, at particle loadings exceeding approximately 7 nominal vol.%, the density was markedly lower than predicted, suggesting that the particles induced the creation of void space within the nanocomposite. For example, when the TiO₂ nominal volume fraction was 0.35, the polymer/particle composite density was 40% lower than expected based on a two-phase additive model for density. At low-nanoparticle loading, light gas permeability was lower than that of the unfilled polymer. At higher nanoparticle loadings, light gas permeability (i.e., CO₂, N₂, and CH₄) increased to more than four times higher than in unfilled PTMSP. At most, selectivity changed only slightly with particle loading.     

Competitive permeation of gas and water vapour in high free volume polymeric membranes

Highly permeable glassy polymeric membranes based on poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) and a polymer of intrinsic porosity (PIM‐1) were investigated for water sorption, water permeability and the separation of CO₂ from N₂ under humid mixed gas conditions. The water sorption isotherms for both materials followed behavior indicative of multilayer adsorption within the microvoids, with PIM‐1 registering a significant water uptake at very high water activities. Analysis of the sorption isotherms using a modified dual sorption model which accounts for such multilayer effects gave Langmuir affinity constants more consistent with lighter gases than the use of the standard dual mode approach. The water permeability through PTMSP and PIM‐1 was comparable over the water activities studied, and could be successfully model ed through a dual mode sorption model with a concentration dependent diffusivity. The water permeability through both membranes as a function of temperature was also measured, and found to be at a minimum at 80 ° C for PTMSP and 70 °C for PIM‐1. This temperature dependence is a function of reducing water solubility in both membranes with increasing temperature countered by increasing water diffusivity. The CO₂ ‐ N₂ mixed gas permeabilities through PTMSP and PIM‐1 were also measured and model ed through dual mode sorption theory. Introducing water vapour further reduced both the CO₂ and N₂ permeabilities. The plasticization potential of water in PTMSP was determined and indicated water swelled the membrane increasing CO₂ and N₂ diffusivity, while for PIM‐1 a negative potential implied that water filling of the microvoids hampered CO₂ and N₂ diffusion through the membrane. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 719–728     

Adenine Components in Biomimetic Metal–Organic Frameworks for Efficient CO2 Photoconversion

Visible‐light driven photoconversion of CO₂ into energy carriers is highly important to the natural carbon balance and sustainable development. Demonstrated here is the adenine‐dependent CO₂ photoreduction performance in green biomimetic metal–organic frameworks. Photocatalytic results indicate that AD‐MOF‐2 exhibited a very high HCOOH production rate of 443.2 μmol g^?1 h^?1 in pure aqueous solution, and is more than two times higher than that of AD‐MOF‐1 (179.0 μmol g^?1h^?1) in acetonitrile solution. Significantly, experimental and theoretical evidence reveal that the CO₂ photoreduction reaction mainly takes place at the aromatic nitrogen atom of adenine molecules through a unique o‐amino‐assisted activation rather than at the metal center. This work not only serves as an important case study for the development of green biomimetic photocatalysts used for artificial photosynthesis, but also proposes a new catalytic strategy for efficient CO₂ photoconversion.     

Non-3d metal modulated zinc imidazolate frameworks for CO2 cycloaddition in simulated flue gas under ambient condition

Cycloaddition of CO₂ and epoxide into cyclic carbonate is one of the most efficient ways for CO₂ conversion with 100% atom-utilization. Metal–organic frameworks are a kind of potential heterogeneous catalysts, however, high temperature, high pressure, and high-purity CO₂ are still required for the reaction. Here, we report two new Zn(II) imidazolate frameworks incoporating MoO₄^2– or WO₄^2– units, which can catalyse cycloaddition of CO₂ and epichlorohydrin at room temperature and atomospheric pressure, giving 95% yield after 24 h in pure CO₂ and 98% yield after 48 h in simulated flue gas (15% CO₂ + 85% N₂), respectively. For comparison, the analogic Zn(II) imidazolate framework MAF-6 without non-3d metal oxide units showed 71% and 33% yields under the same conditions, respectively. The insightful modulation mechanisms of the MoO₄^2– unit in optimizing the electronic structure of Zn(II) centre, facilitating the rate-determined ring opening process, and minimizing the reaction activation energy, were revealed by X-ray photoelectron spectroscopy, temperature programmed desorption and computational calculations.     

CO2-catalyzed/promoted transformation of organic functional groups

Carbon dioxide is a cheap, non-toxic, abundant chemical and has been widely utilized in organic syntheses. Many new strategies have been developed using CO₂ as a C1 building block and highly utilizable chemicals have been synthesized out of it. On the other hand, CO₂-catalyzed or promoted reactions can also be important from an environmental and scientific point of view. These reactions avoid toxic chemicals, expensive catalysts and often occur under mild reaction conditions. In this review, we would like to draw a summary about organic functional group transformation reactions that are promoted or catalyzed by CO₂.     

Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism,Selective CO2 Capture,and Catalysis

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH₂?bdc)(bphz)_0.5]?DMF?H₂O}_n (NH₂?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd₂(COO)₄ secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd₂(μ‐OCO)₂ SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH₂ and ?N?N? functional groups. Both the frameworks are nonporous to N₂, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO₂ adsorption profile, whereas the second isomer shows a typical type I CO₂ profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO₂ among other gases (N₂, O₂, H₂, and Ar), which has been correlated to the specific interaction of CO₂ with the ?NH₂ and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH₂ group is the primary binding site for CO₂. The high heat of CO₂ adsorption (ΔH_ads=37.7 kJ mol^?1) in the oxo‐bridged isomer is realized by NH₂???CO₂/aromatic π???CO₂ and cooperative CO₂???CO₂ interactions. Further, postsynthetic modification of the ?NH₂ group into ?NHCOCH₃ in the second isomer leads to a reduced CO₂ uptake with lower binding energy, which establishes the critical role of the ?NH₂ group for CO₂ capture. The presence of basic ?NH₂ sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.     

Facile Synthesis of Ultrastable Porous Aromatic Frameworks by Suzuki–Miyaura Coupling Reaction for Adsorption Removal of Organic Dyes

Porous aromatic frameworks (PAFs) with robust structure, high stability, and high surface area have attracted intense interest from scientists in diverse fields. However, there are still very few reports on the adsorption of organic dyes by PAFs. In this work, four new PAFs have been facilely synthesized by the polymerization of a tetrahedral-shaped (four-node) monomer with a series of three-node monomers through Suzuki–Miyaura coupling reactions. All the obtained materials possess hierarchical porous structures and show high thermal and chemical stability. The Brunauer–Emmett–Teller (BET) surface areas of these PAFs were determined to be 857 m² g⁻¹ for PAF-111 , 526 m² g⁻¹ for PAF-112A , 725 m² g⁻¹ for PAF-112B , and 598 m² g⁻¹ for PAF-113 . Rhodamine B was selected as a model organic dye to test the adsorption capacities of the obtained PAF materials. PAF-111 showed a maximum adsorption capacity of 1666 mg g⁻¹ (167 wt %) for Rhodamine B, which is among the highest values reported to date for porous organic materials. It is noteworthy that PAF-111 could be reused in at least ten cycles under the adsorption conditions without any loss of adsorption capacity. Our study has revealed the great potential and advantages of PAFs as ultrastable adsorption materials for the removal of organic dyes.     

Isostructural NiII Metal–Organic Frameworks (MOFs) for Efficient Electrocatalysis of Oxygen Evolution Reaction and for Gas Sorption Properties

Design and synthesis of stable, active and cost-effective electrocatalyst for water splitting applications is an emerging area of research, given the depletion of fossil fuels. Herein, two isostructural Ni^II redox-active metal–organic frameworks (MOFs) containing flexible tripodal trispyridyl ligand ( L ) and linear dicarboxylates such as terephthalate (TA) and 2-aminoterphthalate (H₂NTA) are studied for their catalytic activity in oxygen evaluation reaction (OER). The 2D-layered MOFs form 3D hydrogen bonded frameworks containing one-dimensional hydrophilic channels that are filled with water molecules. The electrochemical studies reveal that MOFs display an efficient catalytic activity towards oxygen evolution reaction in alkaline conditions with an overpotential as low as 356 mV. Further, these 2D-MOFs exhibit excellent ability to adsorb water vapor (180–230 cc g⁻¹ at 273 K) and CO₂ (33 cc g⁻¹ at 273 K). The presence of hydrophilic functionality in the frameworks was found to significantly enhance the electrocatalytic activity as well as H₂O sorption.     

Composite Membranes Based on the Poly(1-trimethylsylyl-1-propine): Influence of the Porous Aromatic Frameworks Produced from the Friedel–Crafts Reaction and Introduced into the Polymer Matrix

Russian Journal of Applied Chemistry - The effect of particles of porous aromatic frameworks, synthesized by the Friedel–Crafts reaction (PAF-FC), introduced into matrix of glassy polymer...