Direct glyphosate soil monitoring at the triazine-based covalent organic framework with the theoretical study of sensing principle

Covalent organic frameworks (COFs) are emerging as promising sensing materials due to their controllable structure and function properties, as well as excellent physicochemical characteristics. Here, specific interactions between a triazine-based COF and a mass-used herbicide - glyphosate (GLY) have been utilized to design a disposable sensing platform for GLY detection. This herbicide has been extensively used for decades, however, its harmful environmental impact and toxicity to humans have been recently proven, conditioning the necessity for the strict control and monitoring of its use and its presence in soil, water, and food. Glyphosate is an organophosphorus compound, and its detection in complex matrices usually requires laborious pretreatment. Here, we developed a direct, miniaturized, robust, and green approach for disposable electrochemical sensing of glyphosate, utilizing COF's ability to selectively capture and concentrate negatively charged glyphosate molecules inside its nanopores. This process generates the concentration gradient of GLY, accelerating its diffusion towards the electrode surface. Simultaneously, specific COF-glyphosate binding catalyses the oxidative cleavage of the C-P bond and, together with pore nanoconfinement, enables sensitive glyphosate detection. Detailed sensing principles and selectiveness were scrutinized using DFT-based modelling. The proposed electrochemical method has a linear working range from 0.1 μM to 10 μM, a low limit of detection of 96 nM, and a limit of quantification of 320 nM. The elaborated sensing approach is viable for use in real sample matrices and tested for GLY determination in soil and water samples, without pretreatment, preparation, or purification. The results showed the practical usefulness of the sensor in the real sample analysis and suggested its suitability for possible out-of-laboratory sensing.

Two-dimensional diamine-linked covalent organic frameworks for CO2/N2 capture and separation: theoretical modeling and simulations

Two-dimensional covalent organic frameworks (2D-COFs) with diamine-based linkers have been designed and investigated for CO2/N2 gaseous mixture adsorption and separation via a systematic theoretical study by combining density functional theory (DFT) calculations and force field-based molecular dynamics (MD) simulations. We explored the adsorption sites and adsorption energies of CO2/N2 on 2D-COFs. The gas uptake capacity, adsorption isotherms, permeability, and selectivity were simulated based on an improved formulation of force fields for mixture separation in post-combustion conditions. This theoretical approach provided atomistic understanding and quantitative description of intermolecular interactions governing the physisorption dynamics of the considered systems. The results suggest that 2D-COFs investigated in this study are competitive with other 2D materials for carbon capture and separation and can be considered as alternative molecular sieving materials offering efficient and rapid separation and adsorption of different molecules.

In Silico Discovery of Covalent Organic Frameworks for Carbon Capture

We screen a database of more than 69 000 hypothetical covalent organic frameworks (COFs) for carbon capture using parasitic energy as a metric. To compute CO₂-framework interactions in molecular simulations, we develop a genetic algorithm to tune the charge equilibration method and derive accurate framework partial charges. Nearly 400 COFs are identified with parasitic energy lower than that of an amine scrubbing process using monoethanolamine; more than 70 are better performers than the best experimental COFs and several perform similarly to Mg-MOF-74. We analyze the effect of pore topology on carbon capture performance to guide the development of improved carbon capture materials.

Exceptionally Stable Microporous Organic Frameworks with Rigid Building Units for Efficient Small Gas Adsorption and Separation

Three microporous organic frameworks (hereafter denoted as MPOF-Ads) based on a rigid adamantane core have been successfully synthesized via Sonogashira-Hagihara polycondensation coupling in high yields, 83.7-94.6%. The obtained amorphous MPOF-Ads networks have high Brunauer-Emmett-Teller surface areas (up to 737.3 m² g^-1), narrow pore size distribution (0.95-1.06 nm), and superior thermal (the initial decomposition temperature T_5% under an N₂ atmosphere can reach 410 °C) and chemical stability (no apparent degradation in common organic solvents or strong acid/base solutions after 7 days). At 273 K and 1.0 bar, these MPOF-Ads networks present good uptake capacities for small gas molecules (13.9 wt % CO₂ and 1.66 wt % CH₄) for which the presence of high surface area, predominant microporosity, and narrow pore size distribution are beneficial. In addition, the as-prepared MPOF-Ads networks possess moderate isosteric heats for CO₂ (Q_st = 19.5-30.3 kJ mol^-1) and show desired CO₂/N₂ and CO₂/CH₄ selectivity (36.3-38.4 and 4.1-4.3 based on Henry's law and 17.88-24.92 and 4.24-5.70 based on ideal adsorbed solution theory, respectively). With the demonstrated properties, the synthesized MPOF-Ads networks display potential for small gas storage and separation that can be used in harsh environments because of their superior physical and chemical stability.

Discrete boronate ester ladders from the dynamic covalent self-assembly of oligo(phenylene ethynylene) derivatives and phenylenebis(boronic acid)

Reversible boronate ester chemistry enables the controlled, dynamic self-assembly of olig(phenylene ethynylene)s into highly conjugated ladder frameworks.

Competitive Adsorption of Methanol-Acetone on Surface Functionalization (-COOH, -OH, -NH2, and -SO3H): Grand Canonical Monte Carlo and Density Functional Theory Simulations

The capture and separation properties of surface-functionalized activated carbons (AC-Rs, R= -COOH, -OH, -NH₂, and -SO₃H) for the methanol-acetone mixture were investigated for the first time by grand canonical Monte Carlo simulation (GCMC) and density functional theory (DFT). The effects of surface functional groups and structural characteristics of AC-Rs on the adsorption and separation behaviors of methanol and acetone were clarified. The surface functional group with strong electron-donating or electron-accepting capacity (i.e., -NH₂, -OH, and -SO₃H) was a crucial factor for the methanol-acetone capture and separation performance at the lower pressure range, and the accessible surface area was found to be another determinative factor. AC-NH₂ with the relatively large accessible surface area (4497 m²/g) exhibited an efficient capture performance for the single component (15.7 mol/kg for methanol and 6.7 mol/kg for acetone) and the highest methanol/acetone selectivity (∼23) at 0.02 kPa. At high pressures, the surface functionalization and available pore volume of AC-Rs played pivotal roles in the adsorptive separation process. This study provided mechanistic insights on how the surface functional groups affected the capture and separation properties of ACs, which would further provide a rational alternative strategy in the preparation and synthesis of ACs for the effective gas mixture separation.

A computational study on the tunability of woven covalent organic frameworks for photocatalysis

We show that the visible light absorption of COF-505 is tunable via altering central metal ions or the dihedral angle between two adjacent ligand groups by first-principles calculations. We also found that positively charged COF-505 with Pd(ii) exhibits appreciable O–H activation of the adsorbed H₂O.

Lithium doping on 2D squaraine-bridged covalent organic polymers for enhancing adsorption properties: a theoretical study

A Li-modified squaraine-involved 2D COF material exhibits enhanced CO₂ adsorption and separation properties.

CO2adsorption and separation in covalent organic frameworks with interlayer slipping

In layered COFs, slipping results in non-monotonous variation in CO₂adsorption and higher uptakes were found near a slipping distance of 10 Å.

Highly efficient enrichment of N-linked glycopeptides using a hydrophilic covalent-organic framework

A highly specific enrichment method for N-linked glycopeptides was successfully developed using a hydrophilic covalent-organic framework with excellent binding capacity, stability and reusability.

Covalent Organic Frameworks for CO2 Capture

As an emerging class of porous crystalline materials, covalent organic frameworks (COFs) are excellent candidates for various applications. In particular, they can serve as ideal platforms for capturing CO2 to mitigate the dilemma caused by the greenhouse effect. Recent research achievements using COFs for CO2 capture are highlighted. A background overview is provided, consisting of a brief statement on the current CO2 issue, a summary of representative materials utilized for CO2 capture, and an introduction to COFs. Research progresses on: i) experimental CO2 capture using different COFs synthesized based on different covalent bond formations, and ii) computational simulation results of such porous materials on CO2 capture are summarized. Based on these experimental and theoretical studies, careful analyses and discussions in terms of the COF stability, low- and high-pressure CO2 uptake, CO2 selectivity, breakthrough performance, and CO2 capture conditions are provided. Finally, a perspective and conclusion section of COFs for CO2 capture is presented. Recent advancements in the field are highlighted and the strategies and principals involved are discussed.

Periodic Mesoporous Organosilica Nanocubes with Ultrahigh Surface Areas for Efficient CO₂ Adsorption

Ultrahigh surface area single-crystals of periodic mesoporous organosilica (PMOs) with uniform cubic or truncated-cubic morphology and organic/inorganic components homogeneously distributed over the whole frameworks have successfully been prepared by a sol-gel surfactant-templating method. By tuning the porous feature and polymerization degree, the surface areas of the obtained PMO nanocubes can reach as high as 2370 m²/g, which is the highest for silica-based mesoporous materials. The ultrahigh surface area of the obtained PMO single crystals is mainly resulted from abundant micropores in the mesoporous frameworks. Furthermore, the diameter of the nanocubes can also be well controlled from 150 to 600 nm. The materials show ultrahigh CO₂ adsorption capacity (up to 1.42 mmol/g at 273 K) which is much higher than other porous silica materials and comparable to some carbonaceous materials. The adsorption of CO₂ into the PMO nanocubes is mainly in physical interaction, therefore the adsorption-desorption process is highly reversible and the adsorption capacity is much dependent on the surface area of the materials. Moreover, the selectivity is also very high (~11 times to N₂) towards CO₂ adsorption.

Channel-wall functionalization in covalent organic frameworks for the enhancement of CO2 uptake and CO2/N2 selectivity

Two structurally similar groups with one being CO₂-philic but the other not were anchored into the channel walls of 2D COFs. The decreased surface area of COFs undoubtedly decreased CO₂ adsorption if too many functional groups were introduced.

Hydroquinone and Quinone-Grafted Porous Carbons for Highly Selective CO2 Capture from Flue Gases and Natural Gas Upgrading

Hydroquinone and quinone functional groups were grafted onto a hierarchical porous carbon framework via the Friedel-Crafts reaction to develop more efficient adsorbents for the selective capture and removal of carbon dioxide from flue gases and natural gas. The oxygen-doped porous carbons were characterized with scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. CO2, CH4, and N2 adsorption isotherms were measured and correlated with the Langmuir model. An ideal adsorbed solution theory (IAST) selectivity for the CO2/N2 separation of 26.5 (298 K, 1 atm) was obtained on the hydroquinone-grafted carbon, which is 58.7% higher than that of the pristine porous carbon, and a CO2/CH4 selectivity value of 4.6 (298 K, 1 atm) was obtained on the quinone-grafted carbon (OAC-2), which represents a 28.4% improvement over the pristine porous carbon. The highest CO2 adsorption capacity on the oxygen-doped carbon adsorbents is 3.46 mmol g(-1) at 298 K and 1 atm. In addition, transient breakthrough simulations for CO2/CH4/N2 mixture separation were conducted to demonstrate the good separation performance of the oxygen-doped carbons in fixed bed adsorbers. Combining excellent adsorption separation properties and low heats of adsorption, the oxygen-doped carbons developed in this work appear to be very promising for flue gas treatment and natural gas upgrading.

A triazine-based covalent organic polymer for efficient CO2 adsorption

A new triazine functionalized hexagonally ordered covalent organic polymer (TRITER-1) with a high BET surface area (716 m² g⁻¹) has been synthesized via the Schiff-base condensation reaction between a triamine and terephthaldehyde. TRITER-1 shows an excellent CO₂ uptake capacity of 58.9 wt% at 273 K and 5 bar pressure.

Electron spin-polarization and spin lattices in the boron- and nitrogen-doped organic framework COF-5

Kagome spin lattice and half-metallicity can be achieved in a COF-5 framework by substitutional doping with nitrogen and boron atoms.

Microporous organic polymers for gas storage and separation applications

Microporous organic polymers (MOPs), an emerging class of functional porous materials featured with the pure organic component have been widely studied in recent years. These materials have potential uses in areas such as storage, separation, and catalysis. In this Perspective, we focused on the gas storage and separation of MOPs. The targeted design and synthesis of MOPs toward the enhancement of gas capacity and selectivity are discussed. Furthermore, special emphasis is given to the post-synthesis modification of MOPs which have been proved to be effective methods to accurately tune the desired properties.

Synergetic effect of carbon nanopore size and surface oxidation on CO2 capture from CO2/CH4 mixtures

We have studied the synergetic effect of confinement (carbon nanopore size) and surface chemistry (the number of carbonyl groups) on CO2 capture from its mixtures with CH4 at typical operating conditions for industrial adsorptive separation (298 K and compressed CO2-CH4 mixtures). Although both confinement and surface oxidation have an impact on the efficiency of CO2/CH4 adsorptive separation at thermodynamics equilibrium, we show that surface functionalization is the most important factor in designing an efficient adsorbent for CO2 capture. Systematic Monte Carlo simulations revealed that adsorption of CH4 either pure or mixed with CO2 on oxidized nanoporous carbons is only slightly increased by the presence of functional groups (surface dipoles). In contrast, adsorption of CO2 is very sensitive to the number of carbonyl groups, which can be examined by a strong electric quadrupolar moment of CO2. Interestingly, the adsorbed amount of CH4 is strongly affected by the presence of the co-adsorbed CO2. In contrast, the CO2 uptake does not depend on the molar ratio of CH4 in the bulk mixture. The optimal carbonaceous porous adsorbent used for CO2 capture near ambient conditions should consist of narrow carbon nanopores with oxidized pore walls. Furthermore, the equilibrium separation factor was the greatest for CO2/CH4 mixtures with a low CO2 concentration. The maximum equilibrium separation factor of CO2 over CH4 of ~18-20 is theoretically predicted for strongly oxidized nanoporous carbons. Our findings call for a review of the standard uncharged model of carbonaceous materials used for the modeling of the adsorption separation processes of gas mixtures containing CO2 (and other molecules with strong electric quadrupolar moment or dipole moment).

Synthesis of hierarchical porous carbon monoliths with incorporated metal-organic frameworks for enhancing volumetric based CO₂ capture capability

This work aims to optimize the structural features of hierarchical porous carbon monolith (HCM) by incorporating the advantages of metal-organic frameworks (MOFs) (Cu₃(BTC)₂) to maximize the volumetric based CO₂ capture capability (CO₂ capacity in cm³ per cm³ adsorbent), which is seriously required for the practical application of CO₂ capture. The monolithic HCM was used as a matrix, in which Cu₃(BTC)₂ was in situ synthesized, to form HCM-Cu₃(BTC)₂ composites by a step-by-step impregnation and crystallization method. The resulted HCM-Cu₃(BTC)₂ composites, which retain the monolithic shape and exhibit unique hybrid structure features of both HCM and Cu₃(BTC)₂, show high CO₂ uptake of 22.7 cm³ cm⁻³ on a volumetric basis. This value is nearly as twice as the uptake of original HCM. The dynamic gas separation measurement of HCM-Cu₃(BTC)₂, using 16% (v/v) CO₂ in N₂ as feedstock, illustrates that CO₂ can be easily separated from N₂ under the ambient conditions and achieves a high separation factor for CO₂ over N₂, ranging from 67 to 100, reflecting a strongly competitive CO₂ adsorption by the composite. A facile CO₂ release can be realized by purging an argon flow through the fixed-bed adsorber at 25 °C, indicating the good regeneration ability.