Covalent Triazine-based Frameworks Research Articles

Hierarchical porous MOF/CTF hybrid frameworks used as protection against acidic harmful gases

Benefiting from the structural diversity, high porosity, controllable pore and functional design, porous organic frameworks (POPs) are attracting great attention in adsorption areas. In particular, metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs) have exhibited fascinating potential in gas adsorption. However, in practical application, because the dominant micropores are unfavorable to the transport and diffusion of gas molecules, coupled with the unstable structure stemmed from weak coordination bonds, MOFs are restricted, while COFs are limited by the lack of sufficient active sites. The complementary advantages between MOFs and COFs provide ideas for designing novel hybrid frameworks. Here, a covalent triazine-based framework (CTF) was chosen as skeleton to in situ synthesize Zr-MOF-NH2, constructing an interpenetrated MOF/CTF hybrid. Further, Cu2+ ions were introduced to endow the hybrid with more active centers, resulting in a hierarchical porous Zr-MOF-NH2/CTF-Cu2+. The synergistic effect between MOF and CTF, coupled with Cu2+ active centers, endows the Zr-MOF-NH2/CTF-Cu2+ hybrid with exceptional adsorption performance for harmful acidic gases. The adsorption capacities of Zr-MOF-NH2/CTF-Cu2+ for SO2 and NO2 are 39.3 mg g−1 and 27.3 mg g−1, which are 2.6 and 3.1 times as high as that of Zr-MOF-NH2, respectively. Meanwhile, the breakthrough times of Zr-MOF-NH2/CTF-Cu2+ for SO2 and NO2 are 252.8 and 187.6 min, which are approximately 1.9 and 2.3 times as long as that of pristine MOF, respectively.

In-situ construction of AgI nanoparticle-decorated covalent triazine-based frameworks heterojunction with enhanced photocatalytic performance for the degradation of persistent organic pollutants

In this paper, a multitude of novel CTF-1/AgI (CTFA-x) type-Ⅱ heterojunction were fabricated by in-situ growth approach based on the stable covalent triazine-based framework CTFs. 2D CTF-1 with sufficient nitrogen sites anchored AgI to its matrix, supporting ample active sites for CTFA to degrade ciprofloxacin (CIP) in aqueous solution. The structural and physicochemical characteristic of the CTFA products were explored by TEM, XRD, XPS, FT-IR, BET and PL characterization. The respective roles and synergistic effects of AgI and CTF-1 are discussed. Benefiting from this unique structure, the CTF-1/AgI with the mass ratio of 1:1 (CTFA-50) demonstrated the highest photocatalytic capacity and showed a degradation efficiency of more than 90 % against CIP after 120 min under simulated sunshine irradiation. Compared to pure AgI and CTF-1, the apparent rate constant for the CIP photodegradation of CTFA-50 (0.0153 min−1) was found to be 6.7 and 8.5 times greater. The CTFA-50 catalyst possessed good structural stability and broad-spectrum applicability, and had the ability to efficiently degrade various stubborn organic matters including tetracycline (87.97 %), 2-sec-butyl-4,6-dinitrophenol (63.42 %), bisphenol A (68.22 %), rhodamine B (98.62 %), methyl orange (70.25 %), methylene blue (63.27 %). As demonstrated by the results of the radical trapping tests and EPR analysis, the photodegradation process of CIP was mostly mediated by •O2– and h+. In view of the LC/MS findings, all reaction intermediates could be determined and a reasonable photocatalytic mechanism was proposed.

Covalent triazine-based frameworks – switching selectivity in HMF photooxidation

Switching the HMF photooxidation pathway is possible by tailoring the CTF photocatalyst.

A pyrrolo[3,2-b]pyrrole core containing a covalent triazine-based framework (CTF) for photocatalytic H2 production

We report herein a novel pyrrolo[3,2-b]pyrrole core containing CTF and its Pd NP or Pt NP incorporation for efficient H2 production under visible light irradiation.

Single-site cobalt catalyst embedded in a covalent triazine-based framework (CTF) for photocatalytic CO2 reduction

Single-site Co-embedded CTF-TPE exhibits high photocatalytic CO2 conversion to CO with a production rate of 945 μmol g−1 h−1.

Selective anchoring of Pt NPs on covalent triazine-based frameworks via in situ derived bridging ligands for boosting photocatalytic hydrogen evolution.

The efficient and stable production of hydrogen (H2) through Pt-containing photocatalysts remains a great challenge. Herein, we develop an effective strategy to selectively and uniformly anchor Pt NPs (∼1.2 nm) on a covalent triazine-based framework photocatalyst via in situ derived bridging ligands. Compared to Pt/CTF-1, the obtained Pt/AT-CTF-1 exhibits a considerable photocatalytic H2 evolution rate of 562.9 μmol g-1 h-1 under visible light irradiation. Additionally, the strong interaction between the Pt NPs and in situ derived bridging ligands provides remarkable stability to Pt/AT-CTF-1. Experimental investigations and photo/chemical characterization reveal the synergy of the in situ derived bridging ligands in Pt/AT-CTF-1, which can selectively anchor the Pt NPs with homogeneous sizes and efficiently improve the transmission of charge carriers. This work provides a new perspective toward stabilizing ultrasmall nanoclusters and facilitating electron transfer in photocatalytic H2 evolution materials.

All-in-one strategy to construct bifunctional covalent triazine-based frameworks for simultaneous extraction of per- and polyfluoroalkyl substances and polychlorinated naphthalenes in foods

Per- and polyfluoroalkyl substances (PFASs) and polychlorinated naphthalenes (PCNs) are of growing concern due to their toxic effects on the environment and human health. There is an urgent need for strategies to monitor and analyze the coexistence of PFASs and PCNs, especially in food samples at trace levels, to ensure food safety. Herein, a novel β-cyclodextrin (β-CD) derived fluoro-functionalized covalent triazine-based frameworks named CD-F-CTF was firstly synthesized. This innovative framework effectively combines the porous nature of the covalent organic framework and the host-guest recognition property of β-CD enabling the simultaneous extraction of PFASs and PCNs. Under the optimal conditions, a simple and rapid method was developed to analyze PFASs and PCNs by solid-phase extraction (SPE) based simultaneous extraction and stepwise elution (SESE) strategy for the first time. When coupled with liquid chromatography−tandem mass spectrometry (HPLC−MS/MS) and gas chromatography−tandem mass spectrometry (GC−MS/MS), this method achieved impressive detection limits for PFASs (0.020 −0.023 ng/g) and PCNs (0.016 −0.075 ng/g). Furthermore, the excellent performance was validated in food samples with recoveries of 76.7–107 % (for PFASs) and 78.0–108 % (for PCNs). This work not only provides a simple and rapid technique for simultaneous monitoring of PFASs and PCNs in food and environmental samples, but also introduces a new idea for the designing novel adsorbents with multiple recognition sites.

Boosting photocatalytic H2 evolution on UIO-66-NH2/covalent triazine-based frameworks composites by constructing a covalent heterojunction.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been proved as efficient catalysts for photocatalytic hydrogen (H2) evolution, thanks to their tunable functionalities, permanent porosity, excellent visible light response, and physicochemical stability. Herein, a series of photocatalysts (termed NUBC) was fabricated by loading different amounts of Zr-UiO-66-NH2 (NU) onto a benzoic acid-modified covalent triazine-based framework (BC) based on post-synthetic covalent modification. The resulting NUBC catalysts exhibited a type-II Z-scheme heterojunction structure formed via the amide covalent bonds between the amine groups on NU and carboxyl groups on BC. The optimal loading of NU on BC is 30 wt.% (30NUBC) and the corresponding photocatalytic H2 evolution rate was 378 μmol h-1 g-1, almost 445 and 2 times than that of NU and BC, respectively. The synergistic effect between the type-II Z-scheme heterojunctions and amide bonds was conducive to boosting visible light harvesting and facilitating charge transportation and separation. Furthermore, the prepared NUBC catalysts show great reusability and stability. Overall, this work sheds light on the design of novel MOF/COF hybrid materials and provides a systematic exploration of their photocatalytic H2 evolution properties.

New Mechanism via Dichlorocarbene Intermediate for Activated Carbon-Mediated Reductive Dechlorination of Carbon Tetrachloride by Sulfide in Aqueous Solutions.

Although activated carbon (AC) is widely used as an adsorbent and barrier for contaminated sediment remediation, little attention has been paid to its mediation effects on reductive dechlorination of chlorinated solvents by commonly presenting sulfide. Here, we reported that highly porous, graphitized AC (250 mg L-1) suspended in deoxygenated aqueous solutions could increase the pseudo-first-order rate constant of sulfide-induced dechlorination of carbon tetrachloride (CCl4) by more than 1 order of magnitude. Carbon disulfide (CS2) was the only main product, with no production of chloroform or dichloromethane. The minimum promotion of CCl4 reduction observed with electro-conductive but nonporous graphite and a microporous but electro-insulative resin (XAD-4) indicates that graphitic carbons and micropores both play key roles in AC-mediated dechlorination of CCl4 by sulfide. The detection of dichlorocarbene (:CCl2) by free radical trapping experiments combined with the high suitability of the Langmuir-Hinshelwood model led us to propose a new mediation mechanism: CCl4 molecules adsorbed within the deep regions of AC micropores formed by graphitic carbons accept two electrons transferred from sulfide to form :CCl2, which is impeded from hydrolysis and hydrogenolysis by the hydrophobic micropore and further reacts with sulfide to generate CS2. Consistently, the production of :CCl2 was very low when AC was replaced with graphite or XAD-4. The proposed mechanism was further validated by the enhanced mediation effects of another two carbonaceous materials (template-synthesized mesoporous carbon and covalent triazine-based framework) that are electro-conductive and have well-developed micropore structures. These findings highlight the importance of pore properties of carbonaceous materials as mediators or catalysts for reductive dechlorination reactions and shed light on the development of coupled adsorption-reaction systems for remediation.

Highly dispersed Pd nanoclusters supported on covalent triazine-based frameworks for highly efficient aryl nitro reduction and Ullmann coupling

The feasible preparation of Pd catalysts, one of the most widely used catalysts, with high performance and easy recovery still remains the greatest challenge. Covalent triazine-based frameworks (CTFs), by virtue of strong covalent linkages and abundant nitrogen atoms, have been deemed as a central subclass of porous supports for nano-functional materials including metal nanocatalysts. Herein, a series of CTFs have been prepared by ionothermal synthesis followed by rearrangement at higher temperatures (500–900 °C). The CTF-immobilized nano-Pd(0) catalysts with different particle size distributions (<0.5, 1.35 ± 0.93, 2.21 ± 1.43, 3.80 ± 1.33, 6.10 ± 3.23 nm) were then prepared by simply suspension impregnation-in-situ reduction. Among them, the smallest and highly dispersed Pd nanoclusters (Pd/CTF-600) exhibited excellent activity and outstanding recyclability in aryl nitro reduction and Ullmann coupling. The study provides a new insight for the preparation of high-performance metal nano-catalysts that could enable efficient chemical transformations.

High pressure and high temperature phase transformations of covalent triazine-based frameworks

A monolithic two-dimensional (2D) biphenyl-linked triazine-based framework (CTF-2) showing merely slight crystallinity was prepared by Lewis acid-promoted polymerisation of 4,4′-biphenyldicarbonitrile in liquid TiCl4 at moderate temperature to avoid unwanted carbonization. The transformations of CTF-2 induced by high pressure (up to 60 GPa) and temperature (up to 2400 K) were studied by IR and in situ Raman spectroscopy as well as TEM microscopy. In contrast to graphitic C3N4 materials, CTF-2 exhibits high optical density and reduced fluorescence at high pressure, allowing laser-induced sample heating. Spectral data show the formation of sp3 hybridised carbon atoms and triazine ring distortion in CTF-2 material at pressures above 17 GPa. According to the pressure Raman effect, the bulk modulus of the high-pressure phase of CTF-2 (high-pressure phase CTF-2) was found to be 570 ± 10 GPa, which is a typical value for superhard carbon materials. Structural studies revealed nitrogen preservation in the specimen after high-pressure treatment and stability of the disordered sp3 states of the high-pressure phase CTF-2 in the quenched specimen. This behaviour is quite different from that of the quenched disordered sp3 states of high pressure pure carbon phases, which convert to the sp2 state at pressures below 3–7 GPa.

Covalent triazine-based monolayer with dual application in sensing and delivery of mercaptopurine anticancer drug: a periodic DFT study

The mercaptopurine (MP) molecule's interaction with the pristine covalent triazine-based framework (CTF) was evaluated in the gas and the water medium. The S1 structure is the most stable form of MP/CTF complexes, with the Eads of −0.532 and −0.385 eV in the gas and water medium, respectively. The adsorption behaviour of the MP/CTF nanostructures is further discussed using band structure and partial density of state analyses. The MP drug adsorption reduced the band gap energy of the desired monolayer in the range of 47 to 71% for the studied complexes. The adsorbed drug on the surface of the CTF substrate can be released in the adjacency of tumour cells, and the therapeutic operation is carried out on the target cells. The recovery time indicates the suitability of the desired CTF as a carrier of the MP drug in drug delivery applications.

A simple and portable vacuum assisted headspace solid phase microextraction device coupled to gas chromatography based on covalent organic framework/metal organic framework hybrid for simultaneous analysis of volatile and semi-volatile compounds in soil

Various microextraction methods have demonstrated a positive effect when assisted by vacuum. However, working with such systems is often laborious, they often require expensive and non-portable vacuum pumps, and may even suck off some sample vapor or solid particles during the evacuation process. To address these issues, a simple, and affordable vacuum-assisted headspace solid-phase microextraction (HS-SPME) device was developed in this study. The device, named In Syringe Vacuum-assisted HS-SPME (ISV-HS-SPME), utilizes an adjustable 40 mL glass syringe as a vacuum provider and sampling vessel. A new fiber coating, made from a hybrid of covalent triazine-based frameworks and metal-organic frameworks (COF/MOF), was prepared and characterized by Fourier transform infrared spectrometry, field emission scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, thermogravimetric analysis, and Brunauer–Emmett–Teller techniques for use in the ISV-HS-SPME. By optimizing parameters such as extraction temperature, extraction time, desorption temperature, desorption time, and, humidity using a simplex method, the ISV system was found to increase the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylenes (BTEX) in solid samples by up to 175%. The determinations were followed by GC-FID measurements. Compared to three commercially available fibers, the ISV-HS-SPME device with the COF/MOF (2DTP/MIL-101-Cr) fiber exhibited significantly higher peak areas for PAHs and BTEX. The linear dynamic ranges for BTEX and PAHs were 7.1–9000 ng g−1 and 0.23–9000 ng g−1, respectively, with limits of detection ranging from 2.1–5 ng g−1 for BTEX and 0.07–1.6 ng g−1 for PAHs. The relative standard deviation of the method was 2.6–7.8% for BTEX and 1.6–6.7% for PAHs. The ISV-HS-SPME was successfully used to simultaneously determine PAHs and BTEX in polluted soil samples with recoveries ranging from 80.4 to 108%.

Three-dimensional organization of pyrrolo[3,2-b]pyrrole-based triazine framework using nanostructural spherical carbon: enhancing electrochemical performance of materials for supercapacitors

Covalent triazine-based frameworks have attracted much interest recently due to their high surface area and excellent thermal and electrochemical stabilities. This study shows that covalently immobilizing triazine-based structures on spherical carbon nanostructures results in the organization of micro- and mesopores in a three-dimensional manner. We selected the nitrile-functionalized pyrrolo[3,2-b]pyrrole unit to form triazine rings to construct a covalent organic framework. Combining spherical carbon nanostructures with the triazine framework produced a material with unique physicochemical properties, exhibiting the highest specific capacitance value of 638 F g−1 in aqueous acidic solutions. This phenomenon is attributed to many factors. The material exhibits a large surface area, a high content of micropores, a high content of graphitic N, and N-sites with basicity and semi-crystalline character. Thanks to the high structural organization and reproducibility, and remarkably high specific capacitance, these systems are promising materials for use in electrochemistry. For the first time, hybrid systems containing triazine-based frameworks and carbon nano-onions were used as electrodes for supercapacitors.

Magnetically solid-phase extraction of diazinon and chlorpyrifos pesticides in vegetables using covalent triazine-based framework incorporated chitosan nanocomposite

Magnetically solid-phase extraction of diazinon and chlorpyrifos pesticides in vegetables using covalent triazine-based framework incorporated chitosan nanocomposite

A novel covalent triazine-based frameworks as photocatalysts for the degradation of dyes under visible light irradiation

This work reported a material with efficient degradation ability to dyes, providing an effective way to construct highly active metal-free photocatalysts for environmental remediation and energy conversion.

Synthesis of a Co-Nx type catalyst derived from the pyrolysis of a covalent triazine-based framework for oxygen reduction reaction

• A Co N C catalyst had been developed using an inexpensive and N -rich precursor. • The covalent triazine-based framework provided high density and evenly distributed M N C sites. • The HAT-CN-Co/C-800 catalyst showed the highest ORR activity close to Pt/C. The preparation of non-noble metal catalysts with performance in the oxygen reduction reaction (ORR) comparable or superior to platinum-based catalysts remains challenging. In the present study, hexaazatriphenylenehexacarbonitrile (HAT-CN), which is rich in both cyano groups and pyrazine units, was used as the precursor and then cyclotrimerized into a covalent triazine-based framework with a macrocyclic structure containing abundant complexation sites for transitional metal ions. Subsequently, a series of non-platinum Co N C type catalysts (HAT-CN-Co/C) were prepared, and then pyrolyzed at different temperatures (700 °C, 800 °C, and 900 °C). The pyrolysis treatment endowed the catalysts with activated Co-N x sites, large pore sizes and high specific surface areas, which can promote oxygen transfer and accelerate the ORR catalytic process. It is found that the catalyst (HAT-CN-Co/C-800) obtained from pyrolysis at 800 °C possessed the best ORR activity and followed the four- electrons transfer pathway; the onset potential of ORR was determined as 0.972 V vs reversible hydrogen electrode (RHE), very close to that of Pt/C (0.993 V vs RHE), and the half-wave potential (0.895 V vs RHE) was significantly higher than that of Pt/C (0.859 V vs RHE). Furthermore, the HAT-CN-Co/C-800 catalyst showed good durability (83.2 % current retention after 28000 s) and significant methanol tolerance with good application potential as a substitute for the platinum-based ORR catalyst in fuel cell.

Mildly oxidized porous covalent triazine frameworks with rapid and high adsorption capability for aqueous organic micropollutants

Two microporous and amorphous covalent triazine-based frameworks (CTFs) were synthesized by the low-temperature Friedel–Craft reaction using phenanthrene and anthracene as monomers, and cyanuric chloride as a linker. The synthesized CTFs were then further functionalized by mild oxidation to obtain CTF derivatives (CTF-OXs) with amide and imine groups. The functionalized derivatives showed excellent maximum adsorption capacities for bisphenol A (BPA), bisphenol S (BPS), and 2-naphthol (247, 249, and 376 mg g−1, respectively), which are aqueous organic micropollutants. The maximum adsorption capacities were estimated using the Langmuir and Jovanovic isotherm models, and the adsorption kinetics could be well fitted by the pseudo-second-order kinetics model. The extremely high association constants between the pollutants and the mildly oxidized CTFs surface, calculated by the Langmuir isotherm model, showed a 1:1 complex formation between micropollutants (BPA, BPS, and 2-naphthol) and CTF-OXs. This suggests excellent binding properties for the removal of the selected micropollutants at any concentration level. The thermodynamics parameters for the removal of BPA, BPS, and 2-naphthol showed the adsorption process is feasible and involves physisorption. Hence, CTF-OXs have significant potential for use as effective adsorbents for water decontamination.

Covalent triazine-based frameworks for efficient solid-phase microextraction of phthalic acid esters from food-contacted plastics

Owing to various health threats associated with phthalic acid esters (PAEs), this category of endocrine-disrupting compounds has attracted more and more public scrutiny. However, the efficient preconcentration of PAEs from complex food-contacted plastics still remains challenging. Herein, three covalent triazine-based frameworks (CTFs) were constructed by facile Friedel-Crafts reactions of cyanuric chloride (CC), with triptycene (TPC), fluorene (FL) and 1,3,5-triphenylbenzene (TPB), respectively. Three CTFs were then employed as solid-phase microextraction (SPME) coatings for the extraction of PAEs. Benefiting from the large surface area and high pore volume, the newly-synthesized CC-TPC based SPME method exhibited large enrichment factors (978-2210), low limits of detection (0.027-0.10ng g-1), satisfactory linear ranges (0.09-20ng g-1), acceptable repeatabilities (4.3-9.6%) and high relative recoveries (92.0-104.6%).

An Artificial Photosystem of Metal-Insulator-CTF Nanoarchitectures for Highly Efficient and Selective CO2 Conversion to CO.

It is of pivotal significance to explore robust photocatalysts to promote the photoreduction of CO2 into solar fuels. Herein, an intelligent metal-insulator-semiconductor (MIS) nano-architectural photosystem was constructed by electrostatic self-assembly between cetyltrimethylammonium bromide (CTAB) insulator-capped metal Ni nanoparticles (NPs) and covalent triazine-based frameworks (CTF-1). The metal-insulator-CTF composites unveiled a substantially higher CO evolution rate (1254.15 μmol g-1 h-1 ) compared with primitive CTF-1 (1.08 μmol g-1 h-1 ) and reached considerable selectivity (98.9 %) under visible-light irradiation. The superior photocatalytic CO2 conversion activity over Ni-CTAB-CTF nanoarchitecture could be attributed to the larger surface area, reinforced visible-light response, and CO2 capture capacity. More importantly, the Ni-CTAB-CTF nanoarchitecture endowed the photoexcited electrons on CTF-1 with the ability to tunnel across the thin CTAB insulating layer, directionally migrating to Ni NPs and thereby leading to the efficient separation of photogenerated electrons and holes in the photosystem. In addition, isotope-labeled (13 CO2 ) tracer results verified that the reduction products come from CO2 rather than the decomposition of the photocatalysts. This study opens a new avenue for establishing a highly efficient and selective artificial photosystem for CO2 conversion.