Three-dimensional covalent organic frameworks with nia nets for efficient separation of benzene/cyclohexane mixtures

The synthesis of three-dimensional covalent organic frameworks with highly connected building blocks presents a significant challenge. In this study, we report two 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the good performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications.

Numerical analysis of the porous structure of spherical activated carbons obtained from ion-exchange resins

This paper presents the results of an analysis of the porous structure of spherical activated carbons obtained from cation-exchange resin beads subjected to ion exchange prior to activation. The study investigated the effects of the type of cation exchange resin, the concentration of potassium cations in the resin beads and the temperature of the activation process on the adsorption properties of the resulting spherical activated carbons. The numerical clustering-based adsorption analysis method and the quenched solid density functional theory were used to analyse the porous structure of spherical activated carbons. Based on original calculations and unique analyses, complex relationships between preparation conditions and the porous structure properties of the obtained spherical activated carbons were demonstrated. The results of the study indicated the need for simultaneous analyses using advanced methods for the analysis of porous structures, i.e., the numerical clustering-based adsorption analysis method and the quenched solid density functional theory. This approach allows a reliable and precise determination of the adsorption properties of the materials analysed, including, among other things, surface heterogeneities, and thus an appropriate selection of production conditions to obtain materials with the expected adsorption properties required for a given industrial process.

Precise Modulation of Carbon Activity Sites in Metal-Free Covalent Organic Frameworks for Enhanced Oxygen Reduction Electrocatalysis

Metal-free carbon-based materials have gained recognition as potential electrocatalysts for the oxygen reduction reaction (ORR) in new environmentally-friendly electrochemical energy conversion technologies. The presence of effective active centers is crucial for achieving productive ORR. In this study, we present the synthesis of two metal-free dibenzo[a,c]phenazine-based covalent organic frameworks (DBP-COFs), specifically JUC-650 and JUC-651, which serve as ORR electrocatalysts. Among them, JUC-650 demonstrates exceptional catalytic performance for ORR in alkaline electrolytes, exhibiting an onset potential of 0.90 V versus RHE and a half-wave potential of 0.72 V versus RHE. Consequently, JUC-650 stands out as one of the most outstanding metal-free COF-based ORR electrocatalysts report to date. Experimental investigations and density functional theory calculations confirm that modulation of the frameworks' electronic configuration allows for the reduction of adsorption energy at the Schiff-base carbon active sites, leading to more efficient ORR processes. Moreover, the DBP-COFs can be assembled as excellent air cathode catalysts for zinc-air batteries (ZAB), rivaling the performance of commercial Pt/C. This study provides valuable insights for the development of efficient metal-free organoelectrocatalysts through precise regulation of active site strategies.

Ab Initio Screening of Divalent Cations for CH4, CO2, H2, and N2 Separations in Chabazite Zeolite

The efficient separation and adsorption of critical gases are, more than ever, a major focus point in important energy processes, such as CH4 enrichment of biogas or natural gas, CO2 separation and capture, and H2 purification and storage. Thanks to its physicochemical properties, cation-exchanged chabazite is a potent zeolite for such applications. Previous computational screening investigations have mostly examined chabazites exchanged with monovalent cations. Therefore, in this contribution, periodic density functional theory (DFT) calculations in combination with dispersion corrections have been used for a systematic screening of divalent cation exchanged chabazite zeolites. The work focuses on cheap and readily available divalent cations, Ca(II), Mg(II), and Zn(II), Fe(II), Sn(II), and Cu(II) and investigates the effect of the cation nature and location within the framework on the adsorption selectivity of chabazite for specific gas separations, namely, CO2/CH4, N2/CH4, and N2/H2. All the cationic adsorption sites were explored to describe the diversity of sites in a typical experimental chabazite with a Si/Al ratio close to 2 or 3. The results revealed that Mg-CHA is the most promising cation for the selective adsorption of CO2. These predictions were further supported by ab initio molecular dynamics simulations performed at 300 K, which demonstrated that the presence of CH4 has a negligible impact on the adsorption of CO2 on Mg-CHA. Ca(II) was found to be the most favorable cation for the selective adsorption of H2 and CO2. Finally, none of the investigated cations were suitable for the preferential capture of N2 and H2 in the purification of CH4 rich mixtures. These findings provide valuable insights into the factors influencing the adsorption behavior of N2, H2, CH4, and CO2 and highlight the crucial role played by theoretical calculations and simulations for the optimal design of efficient adsorbents.

Quasi-Three-Dimensional Cyclotriphosphazene-Based Covalent Organic Framework Nanosheet for Efficient Oxygen Reduction

Metal-free carbon-based materials are considered as promising oxygen reduction reaction (ORR) electrocatalysts for clean energy conversion, and their highly dense and exposed carbon active sites are crucial for efficient ORR. In this work, two unique quasi-three-dimensional cyclotriphosphazene-based covalent organic frameworks (Q3CTP-COFs) and their nanosheets were successfully synthesized and applied as ORR electrocatalysts. The abundant electrophilic structure in Q3CTP-COFs induces a high density of carbon active sites, and the unique bilayer stacking of [6 + 3] imine-linked backbone facilitates the exposure of active carbon sites and accelerates mass diffusion during ORR. In particular, bulk Q3CTP-COFs can be easily exfoliated into thin COF nanosheets (NSs) due to the weak interlayer π-π interactions. Q3CTP-COF NSs exhibit highly efficient ORR catalytic activity (half-wave potential of 0.72 V vs. RHE in alkaline electrolyte), which is one of the best COF-based ORR electrocatalysts reported so far. Furthermore, Q3CTP-COF NSs can serve as a promising cathode for Zn-air batteries (delivered power density of 156 mW cm-2 at 300 mA cm-2). This judicious design and accurate synthesis of such COFs with highly dense and exposed active sites and their nanosheets will promote the development of metal-free carbon-based electrocatalysts.

Piezochromism in Dynamic Three-Dimensional Covalent Organic Frameworks

Piezochromic materials with pressure-dependent photoluminescence tuning properties are important in many fields, such as mechanical sensors, security papers, and storage devices. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials (CPMs) with structural dynamics and tunable photophysical properties, are suitable for designing piezochromic materials, but there are few related studies. Herein, we report two dynamic three-dimensional COFs based on aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ) chromophores, termed JUC-635 and JUC-636 (JUC = Jilin University China), and for the first time, study their piezochromic behavior by diamond anvil cell technique. Due to the various luminescent groups, JUC-635 has completely different solvatochromism and molecular aggregation behavior in the solvents. More importantly, JUC-635 with AIE effect exhibits a sustained fluorescence upon pressure increase (~3 GPa), and reversible sensitivity with high-contrast emission differences (Δλem = 187 nm) up to 12 GPa, superior to other CPMs reported so far. Therefore, this study will open a new gate to expand the potential applications of COFs as exceptional piezochromic materials in pressure sensing, barcoding, and signal switching.

Topological Isomerism in Three-Dimensional Covalent Organic Frameworks

Although isomerism is a typical and significant phenomenon in organic chemistry, it is rarely found in covalent organic framework (COF) materials. Herein, for the first time, we report a controllable synthesis of topological isomers in three-dimensional COFs via a distinctive tetrahedral building unit under different solvents. Based on this strategy, both isomers with a dia or qtz net (termed JUC-620 and JUC-621) have been obtained, and their structures are determined by combining powder X-ray diffraction and transmission electron microscopy. Remarkably, these architectures show a distinct difference in their porous features; for example, JUC-621 with a qtz net exhibits permanent mesopores (up to ∼23 Å) and high surface area (∼2060 m² g^-1), which far surpasses those of JUC-620 with a dia net (pore size of ∼12 Å and surface area of 980 m² g^-1). Furthermore, mesoporous JUC-621 can remove dye molecules efficiently and achieves excellent iodine adsorption (up to 6.7 g g^-1), which is 2.3 times that of microporous JUC-620 (∼2.9 g g^-1). This work thus provides a new way for constructing COF isomers and promotes structural diversity and promising applications of COF materials.

Acidic medium synthesis of zeolites - an avenue to control the structure-directing power of organic templates

This paper deals with the extension of the synthesis field of microporous zeolite-type materials and types of organic structure-directing agents (OSDA) that can be used to promote their crystallization. The highly hydrophilic hexamethylenetetramine (urotropine), with its C/N ratio = 1.5, which is unusual to act as a structure-directing agent in the crystallization of open-framework silica polymorphs, is used to exemplify the novelty of the employed approach. Namely, the protonation of urotropine in an acidic fluorine-containing medium transforms it into a very efficient OSDA that yields dodecasil 3C (MTN-type). This novel synthesis also allows gaining insights into OSDA-framework interactions in the MTN-type structure. The comprehensive ²⁹Si and ¹⁹F MAS NMR indicate a small number of point defects of the framework T sites and the multiple bonding of F^- ions to Si in a disordered manner. Based on this finding, a unit cell model has been generated using Monte Carlo simulation and validated with Rietveld refinement using experimental powder X-ray diffraction data. In the model, protonated urotropine cations are located in the center of the big hexakaidecahedral [5¹²6⁴] cages at full occupancy with random orientations. The charge balance is provided by the disordered F^- ions.

Three-Dimensional Triptycene-Functionalized Covalent Organic Frameworks with hea Net for Hydrogen Adsorption

Owing to the finite building blocks and difficulty in structural identification, it remains a tremendous challenge to elaborately design and synthesize three-dimensional covalent organic frameworks (3D COFs) with predetermined topologies. Herein, we report the first two cases of 3D COFs with the non-interpenetrated hea net, termed JUC-596 and JUC-597, by using the combination of tetrahedral and triangular prism building units. Due to the presence of triptycene functional groups and fluorine atoms, JUC-596 exhibits an exceptional performance in the H₂ adsorption up to 305 cm³  g^-1 (or 2.72 wt%) at 77 K and 1 bar, which is higher than previous benchmarks from porous organic materials reported so far. Furthermore, the strong interaction between H₂ and COF materials is verified through the DFT theoretical calculations. This work represents a captivating example of rational design of functional COFs based on a reticular chemistry guide and demonstrates its promising application in clean energy storage.

Gating Effects for Ion Transport in Three-Dimensional Functionalized Covalent Organic Frameworks

The development of bioinspired nano/subnano-sized (<2 nm) ion channels is still considered a great challenge due to the difficulty in precisely controlling pore's internal structure and chemistry. Herein, for the first time, we report that three-dimensional functionalized covalent organic frameworks (COFs) can act as an effective nanofluidic platform for intelligent modulation of the ion transport. By strategic attachment of 12-crown-4 groups to the monomers as ion-driver door locks, we demonstrate that gating effects of functionalized COFs can be activated by lithium ions. The obtained materials exhibit an outstanding selective ion transmission performance with a high gating ratio (up to 23.6 for JUC-590), which is among the highest values in metal ion-activated solid-state nanochannels reported so far. Furthermore, JUC-590 offers high tunability, selectivity, and recyclability of ion transport proved by the experimental and simulated studies.

Dissolution Behavior and Varied Mesoporosity of Zeolites by NH4 F Etching

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH₄ F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano- and sub-nano scales. At the nano-scale, the hidden mosaics of zeolite structure predetermine the spatio-temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub-nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites.

Defect Sites in Zeolites: Origin and Healing

This paper deals with the synthesis conditions-defect formation relationship in zeolites. Silicalite-1 (MFI-type) is used as a model material. Samples synthesized from a system with high basicity (at 100 °C), a system with moderate basicity (at 150 °C), and a fluoride-containing system in neutral medium (at 170 °C) are compared. Well-crystallized materials with sizes ≈0.1, 1-10, and 30-40 µm are obtained. The samples are analyzed by complementary methods providing information on the short- and long-range order in the zeolite framework. A strong correlation between the number of point defects in the zeolite framework and preparation conditions is established. Silicalite-1 synthesized under mild synthesis conditions from a highly basic system exhibits a larger number of framework defects and thus low hydrophobicity. Further, the calcined samples are subjected to aluminum and silicon incorporation by postsynthesis treatment. The Al/Si incorporation in the zeolite framework and its impact on the physicochemical properties is studied by XRD, TEM/SEM, solid-state NMR, FTIR, and thermogravimetric analyses. The defects healing as a function of the number of point defects in the initial material and zeolite crystal size is evaluated. The results of this study will serve for fine-tuning zeolite properties by in situ and postsynthesis methods.

Ethane oxidative dehydrogenation with CO2 on thiogallates

The CO2-assisted oxidative dehydrogenation of ethane (ODH-CO2) attracts a lot of research interest since it combines greenhouse gas utilization with the production of valuable chemicals.

Towards a comprehensive understanding of mesoporosity in zeolite Y at the single particle level

A full understanding of zeolite mesoporosity is not trivial yet is necessary to understand and optimize the catalytic performance of zeolites. The present work reports an integrated approach for the...

Deadlocks of adenine ribonucleotide synthesis: evaluation of adsorption and condensation reactions in a zeolite micropore space

Herein, we report on adenine, d-ribose, and monophosphate adsorption/co-adsorption into the synthetic analog of the zeolite mineral mordenite followed by drying at 50 °C and thermal activation at 150 °C under an argon atmosphere.

Defect Formation, T-Atom Substitution and Adsorption of Guest Molecules in MSE-Type Zeolite Framework-DFT Modeling

We used computational modeling, based on Density Functional Theory, to help understand the preference for the formation of silanol nests and the substitution of Si by Ti or Al in different crystallographic positions of the MSE-type framework. All these processes were found to be energetically favorable by more than 100 kJ/mol. We suggested an approach for experimental identification of the T atom position in Ti-MCM-68 zeolite via simulation of infrared spectra of pyridine and acetonitrile adsorption at Ti. The modeling of adsorption of hydrogen peroxide at Ti center in the framework has shown that the molecular adsorption was preferred over the dissociative adsorption by 20 to 40 kJ/mol in the presence or absence of neighboring T-atom vacancy, respectively.

Unlocking the Potential of Hidden Sites in Faujasite: New Insights in a Proton Transfer Mechanism

Zeolite Y and its ultra-stabilized hierarchical derivative (USY) are the most widely used zeolite-based heterogeneous catalysts in oil refining, petrochemisty, and other chemicals manufacturing. After almost 60 years of academic and industrial research, their resilience is unique as no other catalyst displaced them from key processes such as FCC and hydrocracking. The present study highlights the key difference leading to the exceptional catalytic performance of USY versus the parent zeolite Y in a multi-technique study combining advanced spectroscopies (IR and solid-state NMR) and molecular modeling. The results highlight a hitherto unreported proton transfer involving inaccessible active sites in sodalite cages that contributes to the exceptional catalytic performance of USY.

Three-Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols

With excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal-free heterogeneous catalysts. Here, we report two 3D radical-based COFs (JUC-565 and JUC-566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom-up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal-free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h^-1 , which has exceeded other TEMPO-modified catalytic materials tested under similar conditions. These stable COF-based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

3D Hydrazone-Functionalized Covalent Organic Frameworks as pH-Triggered Rotary Switches

The property expansion of 3D functionalized covalent organic frameworks (COFs) is important for developing their potential applications. Herein, the first case of 3D hydrazone-decorated COFs as pH-triggered molecular switches is reported, and their application in the stimuli-responsive drug delivery system is explored. These functionalized COFs with hydrazone groups on the channel walls are obtained via a multi-component bottom-up synthesis strategy. They exhibit a reversible E/Z isomerization at various pH values, confirmed by UV-vis absorption spectroscopy and proton conduction. Remarkably, after loading cytarabine (Ara-C) as a model drug molecule, these pH-responsive COFs show an excellent and intelligent sustained-release effect with an almost fourfold increase in the Ara-C release at pH = 4.8 than at pH = 7.4, which will effectively improve drug-targeting. Thus, these results open a way toward designing 3D stimuli-responsive functionalized COF materials and promote their potential application as drug carriers in the field of disease treatment.

Adsorption of Toluene and Water over Cationic-Exchanged Y Zeolites: A DFT Exploration

In this study, density functional theory (DFT) calculations have been performed to investigate the adsorption mechanisms of toluene and water onto various cationic forms of Y zeolite (LiY, NaY, KY, CsY, CuY and AgY). Our computational investigation revealed that toluene is mainly adsorbed via π-interactions on alkalis exchanged Y zeolites, where the adsorbed toluene moiety interacts with a single cation for all cases with the exception of CsY, where two cations can simultaneously contribute to the adsorption of the toluene, hence leading to the highest interaction observed among the series. Furthermore, we find that the interaction energies of toluene increase while moving down in the alkaline series where interaction energies are 87.8, 105.5, 97.8, and 114.4 kJ/mol for LiY, NaY, KY and CsY, respectively. For zeolites based on transition metals (CuY and AgY), our calculations reveal a different adsorption mode where only one cation interacts with toluene through two carbon atoms of the aromatic ring with interaction energies of 147.0 and 131.5 kJ/mol for CuY and AgY, respectively. More importantly, we show that water presents no inhibitory effect on the adsorption of toluene, where interaction energies of this latter were 10 kJ/mol (LiY) to 47 kJ/mol (CsY) higher than those of water. Our results point out that LiY would be less efficient for the toluene/water separation while CuY, AgY and CsY would be the ideal candidates for this application.

Understanding the Fundamentals of Microporosity Upgrading in Zeolites: Increasing Diffusion and Catalytic Performances

Hierarchical zeolites are regarded as promising catalysts due to their well-developed porosity, increased accessible surface area, and minimal diffusion constraints. Thus far, the focus has been on the creation of mesopores in zeolites, however, little is known about a microporosity upgrading and its effect on the diffusion and catalytic performance. Here the authors show that the "birth" of mesopore formation in faujasite (FAU) type zeolite starts by removing framework T atoms from the sodalite (SOD) cages followed by propagation throughout the crystals. This is evidenced by following the diffusion of xenon (Xe) in the mesoporous FAU zeolite prepared by unbiased leaching with NH4 F in comparison to the pristine FAU zeolite. A new diffusion pathway for the Xe in the mesoporous zeolite is proposed. Xenon first penetrates through the opened SOD cages and then diffuses to supercages of the mesoporous zeolite. Density functional theory (DFT) calculations indicate that Xe diffusion between SOD cage and supercage occurs only in hierarchical FAU structure with defect-contained six-member-ring separating these two types of cages. The catalytic performance of the mesoporous FAU zeolite further indicates that the upgraded microporosity facilitates the intracrystalline molecular traffic and increases the catalytic performance.

3D Thioether-Based Covalent Organic Frameworks for Selective and Efficient Mercury Removal

Developing functionalized 3D covalent organic frameworks (3D COFs) is critical to broaden their potential applications. However, the introduction of specific functionality in 3D COFs remains a great challenge because most of the functional groups are not compatible with the synthesis conditions. Herein, for the first time 3D thioether-based COFs (JUC-570 and JUC-571) for mercury (Hg²⁺ ) removal from aqueous solution is reported. These 3D thioether-based COFs prepared by the bottom-up approach display high Hg²⁺ uptakes (972 mg g^-1 for JUC-570 and 970 mg g^-1 for JUC-571 at pH = 5), fast adsorption kinetics (distribution coefficient K_d value of 2.29 × 10⁷  mL g^-1 for JUC-570 and 2.07 × 10⁷  mL g^-1 for JUC-571), and favorable selectivity. In particular, JUC-570 is periodically decorated with isopropyl groups around imine bonds that markedly improve its chemical stability and effectively prevent the pore collapse, and thus endows high Hg²⁺ adsorption capacity (619 mg g^-1 ) and excellent cycle performance even at pH = 1. This study not only puts forward a new route to construct stable functionalized 3D COFs, but also promotes their potential applications in areas related to the environment.

Time-resolved dissolution elucidates the mechanism of zeolite MFI crystallization

Zeolite crystal growth mechanisms are not fully elucidated owing to their complexity wherein the formation of a particular zeolite can occur by more than one crystallization pathway. Here, we have conducted time-resolved dissolution experiments of MFI-type zeolite crystals in ammonium fluoride medium where detailed structural analysis allowed us to extrapolate and elucidate the possible mechanism of nucleation and crystal growth. A combination of electron and scanning probe microscopy shows that dissolution initiates preferentially at lattice defects and progressively removes defect zones to reveal a mosaic structure of crystalline domains within each zeolite crystal. This mosaic architecture evolves during the growth process, reflecting the changing conditions of zeolite formation that can be retroactively assessed during zeolite crystal dissolution. Moreover, a more general implication of this study is the establishment that dissolution can be used successfully as an ex situ technique to uncover details about crystal growth features inaccessible by other methods.

Tetrathiafulvalene-based covalent organic frameworks for ultrahigh iodine capture

To safeguard the development of nuclear energy, practical techniques for capture and storage of radioiodine are of critical importance but remain a significant challenge. Here we report the synergistic effect of physical and chemical adsorption of iodine in tetrathiafulvalene-based covalent organic frameworks (COFs), which can markedly improve both iodine adsorption capacity and adsorption kinetics due to their strong interaction. These functionalized architectures are designed to have high specific surface areas (up to 2359 m2 g-1) for efficient physisorption of iodine, and abundant tetrathiafulvalene functional groups for strong chemisorption of iodine. We demonstrate that these frameworks achieve excellent iodine adsorption capacity (up to 8.19 g g-1), which is much higher than those of other materials reported so far, including silver-doped adsorbents, inorganic porous materials, metal-organic frameworks, porous organic frameworks, and other COFs. Furthermore, a combined theoretical and experimental study, including DFT calculations, electron paramagnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, reveals the strong chemical interaction between iodine and the frameworks of the materials. Our study thus opens an avenue to construct functional COFs for a critical environment-related application.

Relationship between the sexual abuser and the victim

Introduction

Although much of society believes that the sexual aggressor is unknown to the victim, this is not supported by the literature. In most cases, the rapist is a known, former or current intimate partner of the victim or even a family member.

Objectives

189 persons accused of perpetrators of sexual crimes and who were subject to forensic psychiatric evaluation for the period from January 2010 to December 2019 in the territory of Central Northern Bulgaria were examined.

Methods

The current research uses sociological methods to gather information - interviews, observations, research of forensic and medical documents,

Results

In the study group, 62% of the victims were known to the perpetrator of the sexual crime, 11% were part of the nuclear family and 8% were members of the extended family of the perpetrator.

Conclusions

Our data supports data from previous studies

Disclosure

No significant relationships.

Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio

Zeolite crystals offering a short diffusion pathway through the pore network are highly desired for a number of catalytic and molecule separation applications. Herein, we develop a simple synthetic strategy toward reducing the thickness along the b-axis of MFI-type crystals, thus providing a short diffusion path along the straight channel. Our approach combines preliminary aging and a fluoride-assisted low-temperature crystallization. The synthesized MFI crystals are in the micrometer-size range along the a- and c-axis, while the thickness along the b-axis is a few tens of nanometers. The synthesis parameters controlling the formation of platelike zeolite are studied, and the factors controlling the zeolite growth are identified. The synthesis strategy works equally well with all-silica MFI (silicalite-1) and its Al- and Ga-containing derivatives. The catalytic activity of platelike ZSM-5 in the methanol-to-hydrocarbons (MTH) reaction is compared with a commercial nanosized ZSM-5 sample, as the platelike ZSM-5 exhibits a substantially extended lifetime. The synthesis of platelike MFI crystals is successfully scaled up to a kilogram scale.

Cu- and Fe-speciation in a composite zeolite catalyst for selective catalytic reduction of NOx: insights from operando XAS

Cu-SAPO-34 (Cu-CZC) and Fe-mordenite (Fe-MOR) and their mechanical mixture (50 : 50) have been exhaustively investigated by means of operando X-ray absorption spectroscopy under NH₃-SCR conditions.

Two-Dimensional COF-Three-Dimensional MOF Dual-Layer Membranes with Unprecedentedly High H2/CO2 Selectivity and Ultrahigh Gas Permeabilities

Composite membranes embodying multilayered architecture have been on an uptrend to tap the synergy between different materials to attain new heights in gas separation performance. In the light of sustainable materials research, covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) have emerged as cutting-edge platforms for molecular-sieving membranes owing to their phenomenal surface areas, ultrahigh porosities, and precise control over chemical functionalities. In this study, we report for the first time a three-dimensional (3D) MOF-mediated strategy where a specially designed MOF film provides the binding sites along the vertical direction to anchor the two-dimensional (2D) COF structural building units. The strong chemical bonding between the 3D MOF and 2D COF provides a new outlook to fabricate 2D COF-based composite membranes. The π-stacked columns of 2D H₂P-DHPh COF that can contribute to direct pathways for gas transport render the resulting membrane incredibly promising for high-flux gas separation. Besides, the chemical synergy between the MOF and COF endows the thus-developed H₂P-DHPh COF-UiO-66 composite membrane with unprecedented H₂/CO₂ gas mixture selectivity (32.9) as well as ultrahigh H₂ (108 341.3 Barrer) and CO₂ permeabilities, which significantly outperform the present Robeson upper bound and polymer membranes hitherto reported.

Electroactive Covalent Organic Frameworks: Design, Synthesis, and Applications

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailorable compositions, porosities, functionalities, and intrinsic chemical stability. The incorporation of electroactive moieties in the structure transforms COFs into electroactive materials with great potential for energy-related applications. Herein, the recent advances in the design and use of electroactive COFs as capacitors, batteries, conductors, fuel cells, water-splitting, and electrocatalysis are addressed. Their remarkable performance is discussed and compared with other porous materials; hence, perspectives in the development of electroactive COFs are presented.

Expanding the Synthesis Field of High-Silica Zeolites

Aluminosilicate zeolites are synthesized under hydrothermal conditions in a basic/alkaline medium in the pH range between 9 and 14. The synthesis of MFI-type zeolite in an acidic medium is presented. The critical parameter determining the zeolite formation in an acidic medium was found to be the isoelectric point (IEP) of gel particles. MFI-type zeolite was synthesized above the isoelectric point of the employed silica source, where the silica species exhibit a negative charge and the paradigm of zeolite formation based on the electrostatic interaction with the positively charged template is retained. No zeolite formation is observed below the isoelectric point of silica. The impact of aluminum on the zeolite formation is also studied. The results of this study will serve to extend the synthesis field of high silica zeolites to the acidic medium and thus open new opportunities to control the zeolite properties.

Probing the Brønsted Acidity of the External Surface of Faujasite-Type Zeolites

We outline two methodologies to selectively characterize the Brønsted acidity of the external surface of FAU-type zeolites by IR and NMR spectroscopy of adsorbed basic probe molecules. The challenge and goal are to develop reliable and quantitative IR and NMR methodologies to investigate the accessibility of acidic sites in the large pore FAU-type zeolite Y and its mesoporous derivatives often referred to as ultra-stable Y (USY). The accessibility of their Brønsted acid sites to probe molecules (n-alkylamines, n-alkylpyridines, n-alkylphosphine- and phenylphosphine-oxides) of different molecular sizes is quantitatively monitored either by IR or ³¹ P NMR spectroscopy. It is now possible, for the first time to quantitatively discriminate between the Brønsted acidity located in the microporosity and on the external surface of large pore zeolites. For instance, the number of external acid sites on a Y (LZY-64) zeolite represents 2 % of its total acid sites while that of a USY (CBV760) represents 4 % while the latter has a much lower framework Si/Al ratio.

Nanosized zeolites as a gas delivery platform in a glioblastoma model

Approaches able to counteract, at least temporarily, hypoxia, a well-known factor of resistance to treatment in solid tumors are highly desirable. Herein, we report the use of nanosized zeolite crystals as hyperoxic/hypercapnic gas carriers for glioblastoma. First, the non-toxic profile of nanosized zeolite crystals in living animals (mice, rats and non-human primates) and in various cell types is presented. Second, the ability of the nanosized zeolites to act as a vasoactive agent for a targeted re-oxygenation of the tumor after intravenous injection is shown. As attested by an MRI protocol, the zeolites were able to increase oxygenation and blood volume specifically within the brain tumor whilst no changes in the healthy-non tumoral brain-were observed. The first proof of concept for the use of metal-containing nanosized zeolites as a tool for vectorization of hyperoxic/hypercapnic gases in glioblastoma is revealed.

Three-Dimensional Chemically Stable Covalent Organic Frameworks through Hydrophobic Engineering

The development of three-dimensional (3D) covalent organic frameworks (COFs) with high chemical stability is of critical importance for their practical use. In this work, it is demonstrated that the stability of 3D COFs can be improved by periodic decoration of isopropyl groups on their backbones. Owing to the strong hydrophobicity of the alkyl groups, the resultant COFs show high crystallinity, permanent pores, and exceptional stability in harsh environments, such as strong acids (3 m HCl or 3 m H₂ SO₄ for one week), a strong base (20 m NaOH for one week), and boiling water (100 °C for one month). Furthermore, these highly stable and hydrophobic COFs display excellent oil/water separation performance with >99 % separation efficiency over a wide pH range. This work demonstrates the use of alkyl decoration in 3D COFs to tune their chemical stability and expand their potential applications.