Covalent Triazine-based Frameworks Research Articles

Fluorinated, Sulfur-Rich, Covalent Triazine Frameworks for Enhanced Confinement of Polysulfides in Lithium-Sulfur Batteries.

Lithium-sulfur battery represents a promising class of energy storage technology owing to its high theoretical energy density and low cost. However, the insulating nature, shuttling of soluble polysulfides and volumetric expansion of sulfur electrodes seriously give rise to the rapid capacity fading and low utilization. In this work, these issues are significantly alleviated by both physically and chemically restricting sulfur species in fluorinated porous triazine-based frameworks (FCTF-S). One-step trimerization of perfluorinated aromatic nitrile monomers with elemental sulfur allows the simultaneous formation of fluorinated triazine-based frameworks, covalent attachment of sulfur and its homogeneous distribution within the pores. The incorporation of electronegative fluorine in frameworks provides a strong anchoring effect to suppress the dissolution and accelerate the conversion of polysulfides. Together with covalent chemical binding and physical nanopore-confinement effects, the FCTF-S demonstrates superior electrochemical performances, as compared to those of the sulfur-rich covalent triazine-based framework without fluorine (CTF-S) and porous carbon delivering only physical confinement. Our approach demonstrates the potential of regulating lithium-sulfur battery performances at a molecular scale promoted by the porous organic polymers with a flexible design.

A thiophene-containing covalent triazine-based framework with ultramicropore for CO2 capture

In this work, a 2D covalent triazine-based framework was prepared by using 1,3-dicyanobenzo[c]thiophene (DCBT) as monomer to effectively capture CO2. The resulting CTF-DCBT was characterized by FT-IR, XPS, PXRD, elemental analysis, SEM, TEM, and N2 adsorption-desorption. The results indicate that CTF-DCBT is partially crystalline and has ultramicropore (6.5 Å) as well as high heteroatom contents (11.24 wt% and 12.61 wt% for N and S, respectively). In addition, the BET surface area and total pore volume of CTF-DCBT are 500 m2/g and 0.26 cm3/g, respectively. CTF-DCBT possesses excellent thermal stability (450 °C) and chemical stability towards boiling water, 4 M HCl, and 1 M NaOH. The CO2 adsorption capacity of CTF-DCBT is 37.8 cm3/g at 1 bar and 25 °C. After six adsorption–desorption cycles, there is no obvious loss of CO2 uptake observed. Due to the ultramicropore and high heteroatom contents, CTF-DCBT has high isosteric heats of adsorption for CO2 and high selectivities of CO2 over N2 and CH4. At 25 °C, the CO2/N2 and CO2/CH4 selectivities are 112.5 and 10.3, respectively, which are higher than those of most POFs. Breakthrough curves indicate that CTF-DCBT could effectively separate CO2/N2 and CO2/CH4 mixtures.

Ultramicroporous carbon with extremely narrow pore distribution and very high nitrogen doping for efficient methane mixture gases upgrading

It is notably challenging to fabricate heavily heteroatom-doped porous carbonaceous materials with narrow ultramicropore size distributions for highly effective mixed-gas separation. In this study, new carbon-based materials with narrow ultramicropore size (<7 Å) distributions (>95%) and high N doping contents (>10 at%) are fabricated through the pyrolysis of a perchloro-substituted porous covalent triazine-based framework (ClCTF). In particular, the sample prepared at 650 °C (ClCTF-1-650) possesses the highest ultramicropores content (98%) and large N content (12 at%) and demonstrates a very high CH4 and CO2 capacity, as well as a low N2 uptake under ambient conditions. The extraordinarily high CH4/N2 and CO2/N2 selectivities correlate with both the ideal adsorption solution theory (IAST) method and performed dynamic separation experiments (breakthrough experiments). The results reported in this study far exceed the CH4/N2 and CO2/N2 selectivities of previously reported carbon-based adsorbents including various nitrogen-doped ones. These results are believed to be associated with the unusually high N content, as well as the suitably narrow ultramicropore size distribution. This report introduces a new pathway to design porous absorbents with precisely controlled ultramicropores for gas separation.

Structure-property relationships for covalent triazine-based frameworks: The effect of spacer length on photocatalytic hydrogen evolution from water

Covalent triazine-based frameworks (CTFs) are a subclass of conjugated microporous polymers (CMPs) that can be used as organic photocatalysts for photocatalytic hydrogen evolution from water. Seven materials with varied spacer units from phenylene to quarterphenylene were synthesized, either by trifluoromethanesulfonic acid (TfOH) catalysis from nitriles or by Suzuki-Miyaura polycondensation. The photocatalytic performance under visible light of all materials was systematically studied in the presence of a hole-scavenger, showing that both synthesis routes produce CTFs with similar hydrogen evolution rates (HER), but different optical properties. The highest hydrogen evolution rate in the cyclotrimerized series was found for CTF-2 with an apparent quantum yield of 1.6% at 420 nm in a mixture of water and triethanolamine with a platinum co-catalyst. Based on (TD-)DFT calculations, the highest performance was expected for CTF-1 and this discrepancy is explained by a trade-off between increased light absorption and decreased thermodynamic driving force.

Environmentally benign and economic synthesis of covalent triazine-based frameworks

Covalent triazine-based frameworks (CTFs) are important microporous materials with a wide range of applications. Here, we demonstrate an environmentally benign and economic synthetic pathway to CTFs. The monomers used for CTFs, aromatic nitriles, were obtained by cyanation using nontoxic potassium hexacyanoferrate(II) in place of commonly used toxic cyanides. Then, the CTFs were synthesized by trimerization of the corresponding cyano monomers in molten zinc chloride. A series of CTFs was synthesized, and the highest Brunauer-Emmett-Teller surface area measured in this series was 2404 m2/g. Among the synthesized CTFs, CTFDCP exhibited excellent CO2 adsorption properties, with a CO2 uptake of 225 mg/g at 0 °C.

From covalent triazine-based frameworks to N-doped porous carbon/reduced graphene oxide nanosheets: efficient electrocatalysts for oxygen reduction

Based on covalent triazine-based frameworks, N-doped porous carbon/rGO nanosheets are prepared which exhibit excellent performance toward oxygen reduction.

Mechanochemical synthesis of porous organic materials

In this mini-review, we wish to summarise the recent advances on the design of polymers of intrinsic microporosity, covalent–organic frameworks, covalent triazine-based frameworks, ordered mesoporous polymers, and ordered mesoporous carbonsviamechanochemical synthesis.

Two linkers are better than one: enhancing CO2 capture and separation with porous covalent triazine-based frameworks from mixed nitrile linkers

By combining two different nitrile building blocks a synergistic increase in the CO2 uptake in the mixed-nitrile CTFs over the single-nitrile CTFs could be achieved.

Graphene-coupled nitrogen-enriched porous carbon nanosheets for energy storage

Nitrogen-enriched porous carbon nanosheets (G-PCs) are prepared through the pyrolysis of graphene-coupled covalent triazine-based frameworks (G-CTFs), which exhibit excellent energy storage performance.

Evolution of the formation of a covalent triazine-based framework catalyzed by p-toluenesulfonic acid monohydrate

A highly porous CTF-1 was prepared using an organic acid with medium acidity as the catalyst and the evolution of the crystalline structure throughout the catalyzed route was studied.

Rapid exfoliation of layered covalent triazine-based frameworks into N-doped quantum dots for the selective detection of Hg2+ions

A layered covalent triazine-based framework was rapidly cut into N-doped quantum dots by using piranha solution and was used to detect Hg2+ions.

Silica gel microspheres decorated with covalent triazine-based frameworks as an improved stationary phase for high performance liquid chromatography

A new stationary phase for high performance liquid chromatography (HPLC) applications based on silica gel microspheres decorated with covalent triazine-based frameworks (CTF–SiO2) composite has been reported here. In this new hybrid material, sheet-like covalent triazine-based frameworks (CTF) were grown onto the supporting silica spheres, in order to achieve improved chromatographic separation and selectivity. The new material was characterized by infrared spectroscopy, elemental analysis and thermogravimetric analysis. The chromatographic performance and retention mechanism of the new stationary phase were investigated in reversed-phase mode and compared against standard C18 and cyano-modified silica (CN–SiO2) columns. A variety of different probe molecules were analyzed, including mono-substituted benzenes, polycyclic aromatic hydrocarbons, phenols, anilines and bases. The synergism of triazine and aromatic moieties provided several different retention mechanisms, thus improving the selectivity in the CTF–SiO2 composite. The good column packing properties of the uniform silica microspheres combined with the separation ability of the CTF frameworks make the new CTF–SiO2 material a potentially useful stationary phase for the analysis of complex samples.

A mixed-linker approach towards improving covalent triazine-based frameworks for CO2 capture and separation

Carbon dioxide separation and capture/sequestration are important problems not only in the context of global warming but also for optimization of industrial processes. Porous covalent triazine-based frameworks (CTFs) are a class of promising materials for adsorptive separation of CO2, which could be an effective alternative to chemisorption based approaches. We report nine novel CTFs based on mixed building-block approach, synthesized under ionothermal conditions (ZnCl2, 400 °C). Angular 1,3-bis(4-cyanophenyl)adamantane (Ad2), trigonal-pyramidal 1,3,5-tris(4-cyanophenyl)adamantane (Ad3) and tetrahedral 1,3,5,7-tetrakis(4-cyanophenyl)adamantane (Ad4) were processed together with the linear terephthalonitrile (L1) and 4,4'-biphenyl dicarbonitrile (L2) as well as the planar trigonal 1,3,5-benzenetricarbonitrile (L3) targeting maximization of surface area and void volume. The thermally (>500 °C) and acid stable CTFs showed a specific surface area (SBET) in the range of 747–1885 m2 g−1, with the highest surface area achieved for Ad4L2, reflecting the generally observed synergism of elongation of L-building blocks with branching of the Ad-building blocks. The CO2 uptake correlates empirically with the product of BET surface area, micropore volume fraction (V0.1/Vtot) and CO2-accessible micropore volume (Vmicro(CO2)). At low pressure (up to 1 bar) and 273 K, Ad2L1 - Ad4L3 adsorb significant amounts of CO2 (40–76 cm3 g−1) and CH4 (14–26 cm3 g−1), which are generally in line with other reported CTFs, proving the viability of the mixed building-block approach for continuous tuning of properties in the case of CTFs. The obtained CTFs exhibit good ideal selectivity in the range of 17–30 for CO2 over N2 (for a 85% N2/15% CO2 mixture at 273 K, 1 bar), and represent a prototypal ‘tunable’ series for efficient adsorption separations. Water vapour sorption by the novel CTS indicates that the adamantane based CTFs are largely hydrophobic.

Covalent triazine-based framework: A promising adsorbent for removal of perfluoroalkyl acids from aqueous solution

Perfluoroalkyl acids (PFAAs) are highly stable, persistent, and ubiquitous in the environment with significant concerns growing with regards to both human and ecosystem health. Due to the high stability to both biological and chemical attack, the only currently feasible approach for their removal from water is adsorbent technology. The main objective of this study was to assess a covalent triazine-based framework (CTF) adsorbent for removal from aqueous solutions of perfluoro C4, C6, and C8 carboxylates and sulfonates including the two C8s most commonly monitored, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Adsorption affinity and capacity were quantified and compared to three commonly used sorbents: pulverized microporous activated carbon, single-walled carbon nanotubes, and Amberlite IRA-400 anion-exchange resin. CTF adsorbent exhibited pronouncedly higher adsorption affinity and capacity of PFAAs than other test sorbents. The remarkably strong adsorption to CTF can be attributed to the favored electrostatic interaction between the protonated triazine groups on the inner wall of the hydrophobic CTF pore and the negatively charged head groups of the PFAAs intercalated between the CTF layers. The homogeneous, nanosized pores (1.2 nm) of CTF hindered adsorption of a large-sized dissolved humic acid, thus minimizing the suppression of PFAA adsorption. Additionally, regeneration of CTF was easily accomplished by simply raising pH > 11, which inhibited the electrostatic adsorptive interaction of PFAAs.

Covalent Triazine-Based Frameworks with Ultramicropores and High Nitrogen Contents for Highly Selective CO2 Capture.

Porous organic frameworks (POFs) are a class of porous materials composed of organic precursors linked by covalent bonds. The objective of this work is to develop POFs with both ultramicropores and high nitrogen contents for CO2 capture. Specifically, two covalent triazine-based frameworks (CTFs) with ultramicropores (pores of width <7 Å) based on short (fumaronitrile, FUM) and wide monomers (1,4-dicyanonaphthalene, DCN) were synthesized. The obtained CTF-FUM and CTF-DCN possess excellent chemical and thermal stability with ultramicropores of 5.2 and 5.4 Å, respectively. In addition, they exhibit excellent ability to selectively capture CO2 due to ultramicroporous nature. Especially, CTF-FUM-350 has the highest nitrogen content (27.64%) and thus the highest CO2 adsorption capacity (57.2 cc/g at 298 K) and selectivities for CO2 over N2 and CH4 (102.4 and 20.5 at 298 K, respectively) among all CTF-FUM and CTF-DCN. More impressively, as far as we know, the CO2/CH4 selectivity is larger than that of all reported CTFs and ranks in top 10 among all reported POFs. Dynamic breakthrough curves indicate that both CTFs could indeed separate gas mixtures of CO2/N2 and CO2/CH4 completely.

Covalent triazine-based frameworks (CTFs) from triptycene and fluorene motifs for CO2adsorption

Two microporous CTFs with triptycene (TPC) and fluorene (FL) have been synthesized through a mild AlCl3-catalyzed Friedel–Crafts reaction, with the highest surface area of up to 1668 m2g−1for non-ionothermal CTFs. CTF-TPC and CTF-FL show an excellent carbon dioxide uptake capacity of up to 4.24 mmol g−1at 273 K and 1 bar.

Sulfur-doped covalent triazine-based frameworks for enhanced photocatalytic hydrogen evolution from water under visible light

Sulfur-doped covalent organic frameworks were synthesized via a simple approach for enhanced photocatalytic hydrogen evolution from water under visible light.

Synthetic Control and Multifunctional Properties of Fluorescent Covalent Triazine-Based Frameworks.

Conjugated microporous polymers (CMPs), with the virtue of high porosity and optoelectronic activity, are attracting increasing research interest and have been used in various environmental and energy areas. Efficient synthesis and the exploitation of new functionalities are the research hotspots in the CMPs research area. Covalent triazine frameworks (CTFs) synthesized by CF3 SO3 H catalyzed trimerization reactions show properties quite alike to CMPs and this method avoids the use of noble metal catalysts. In this study, a series of novel fluorescent covalent triazine-based frameworks (F-CTFs) is prepared using different tetra-cyano compounds as the starting monomers. Both porosity and fluorescence properties of the F-CTFs can be adjusted by the monomer structure. Gas adsorption measurement reveals that F-CTF1 with the largest surface area of 896 m(2) g(-1) shows the highest CO2 uptake of 3.29 mmol g(-1) at 273 K and 1.13 bar among the polymers. Taking advantages of their large surface areas and strong fluorescence, these F-CTFs could be used as efficient chemical sensing agents for various nitroaromatic compounds as well.

Covalent Triazine-Based Frameworks as Visible Light Photocatalysts for the Splitting of Water.

Covalent triazine-based frameworks (CTFs) with a graphene-like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid-catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF-T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF-T1 exhibits excellent photocatalytic activity and stability for H2 evolution in the presence of platinum under visible light irradiation (λ ≥ 420 nm). The activity and stability of CTF-T1 are comparable to those of g-C3 N4 . Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular-level understanding of the inherent heterogeneous photocatalysis.

Three novel triazine-based materials with different O/S/N set of donor atoms: One-step preparation and comparison of their capability in selective separation of uranium

Cyanuric chloride was chosen as a core skeleton which reacted with desired linker molecules, urea, thiourea and thiosemicarbazide, to prepare three novel functional covalent triazine-based frameworks, CCU (O-donor set), CCTU (S-donor set) and CCTS (S, N-donor set) respectively, designed for selective adsorption of U(VI). The products have high nitrogen concentration (>30wt%), regular structure, relatively high chemical and thermal stability. Adsorption behaviors of the products on U(VI) were examined by batch experiments. CCU and CCTU can extract U(VI) from simulated nuclear industrial effluent containing 12 co-existing cations with relatively high selectivity (54.4% and 54.2%, respectively). Especially, effects of donor atoms O/S on adsorption were investigated, and the outcomes indicate that the difference in coordinating ability between the donor atoms is weakened in large conjugated systems, and the related functional groups with originally very strong coordination abilities may not be the best choice for the application in selective adsorption of uranium and also other metals. The as-proposed approach can easily be expanded into design and preparation of new highly efficient adsorbents for selective separation and recovery of uranium through adjusting the structures, types and amounts of functional groups of adsorbents by choosing suitable linkers.