Triazine Units Research Articles

Facile preparation of perylene imide based supramolecular structure with strong internal electric-field for enhancing photocatalytic nitrogen fixation

Rational regulating supramolecular structure with built-in electric field is a promising tactic to improve the separation of charge carriers and photocatalytic nitrogen fixation efficiency. However, those synthetic procedures are complicated, time-consuming, and low-scale preparation. Here, we reported a simple tactic to prepare perylene diimide (PDI)-triazine-based supramolecular using the solution-dispersed supramolecular self-assembly method. The PDI-triazine-based supramolecular obtains an outstanding nitrogen fixation rate and near IR yield in pure water, which was about 10 times higher than that of pristine PDI. The DFT calculation and experiment reveal that embeds triazine units reasonably regulated the HOMO and LOMO band and the absorption properties, which guaranteed the PDIMA enable to absorb the near IR light and activate the N2 molecule. Moreover, the adjustable face-to-face arrangement of π–π stacking and intrinsic molecular dipole is conducive to the construction of built-in electric field, resulting in high carrier separation efficiency. This study provides a facile strategy to incorporate foreign groups for enhancing photocatalytic efficiency over organic-based supramolecular.

Porous Fe, N co-doped carbon with high electrocatalytic oxygen reduction reaction performance in Zn-air battery

Non-Pt electrocatalysts for oxygen reduction reactions (ORR) have been developed using metal and nitrogen co-doped carbon electrocatalysts. However, challenges remain regarding the porosity of the catalyst, distribution of active sites, and the easy aggregation of the metal components. Herein, we report a bottom-up preparation strategy to obtain a porous ethynyl-linked conjugated microporous polymer (CMP) precursor containing triazine units and bipyridine, ensuring high N content and coordination with Fe 3+ . The Fe doped CMP is then carbonization into a Fe, N co-doped nanoporous carbon material (BPCMP-Fe-800), which can be taken as the electrocatalyst in ORR. BPCMP-Fe-800 catalyst exhibits electrocatalytic performance dominated by 4e − transfer mechanism with the onset potential of 0.97 V, half-wave potential of 0.85 V, and higher kinetic current density of 11.3 mA cm −2 (0.8 V). In addition, when applied as cathode electrocatalyst in zinc-air batteries, BPCMP-Fe-800 displays more competitive power density (179.5 mW cm −2 ) and specific capacity (790.5 mAh g −1 ) compared with Pt/C. Our study demonstrates a general and facile approach for porous Fe, N co-doped carbon with the potential as alternatives to Pt catalysts for efficient ORR catalytic performances and provides new insights of multi-atom catalysts for other energy conversion related catalytic reactions.

A new nitrogen rich porous organic polymer for ultra-high CO2 uptake and as an excellent organocatalyst for CO2 fixation reactions

The steady increase in the carbon dioxide (CO2) concentration in the atmosphere is causing serious environmental threats like global warming and climate change. Thus to mitigate this issue, suitable adsorbent cum catalyst for high CO2 capture and its fixation to reactive organics is very much essential. In this context, we have synthesized a new porous cross-linked organic polymer DAT-1 through the radical polymerization of divinylbenzene, triallylamine and 2,4,6-tris(allyloxy)− 1,3,5-triazine. DAT-1 possesses high degree of flexibility, with exceptionally large BET surface area (1105 m2g−1) along with bimodal porosity. Furthermore, due to the presence of triazine unit along with tertiary amine moieties inside the porous architecture of DAT-1 with very rich in basic N-sites could make it as an excellent adsorbent for the unprecedented CO2 capture (73.3 mmol g−1 at 30 bar pressure / 273 K). Further, it exhibits excellent catalytic activity for the conversion of simple terminal epoxides to bio-derived sterically hindered epoxides to cyclic carbonate by utilizing carbon dioxide as C1 resource. Basicity associated with N-rich sites at the surface of the high surface area porous organic polymer is responsible for record CO2 capture and its excellent catalytic activity for the CO2 fixation on epoxides for the synthesis of value added cyclic carbonates.

Effect of Nitrogen Atom Introduction on the Photocatalytic Hydrogen Evolution Activity of Covalent Triazine Frameworks: Experimental and Theoretical Study.

The construction of high-performance photocatalyst has always been explored. Covalent organic frameworks (COFs), especially keto-amine-linked COFs, have many advantages, such as adjustable bandgaps, π-π stacking structure, excellent response ability to visible light, high specific surface area, high mobility of carrier carriers, good physical and chemical stability, and so on, showing strong potential applications in photocatalytic solar energy conversion and hydrogen production. Two analogous covalent triazine frameworks (CTFs), T3H-CTF and T3N-CTF, have been synthesized via Schiff-base condensation reactions between 2,4,6-trihydroxybenzene-1,3,5-tricarbalehyde (MOP) and the corresponding triazine-based aromatic amines under solvothermal condition. For T3N-CTF, the peripheral aromatic linker to the central triazine unit was the pyridine unit, instead of the benzene unit in the T3H-CTF unit. T3N-CTF had a hydrogen production rate (HPR) of 6485.05 μmol g-1 h-1 , much higher than that of T3H-CTF (2028.06 μmol g-1 h-1 ). Accordingly, T3N-CTF had a much higher apparent quantum yield (AQY) of 12.2 % than that of T3H-CTF (4.12 %) at 405 nm. The experimental and theoretical results showed that the extended light absorption range, enlarged surface area, and enhanced separation and transportation efficiencies of charge carriers of T3N-CTF compared with T3H-CTF were uniformly induced by the introduction of peripheral nitrogen atoms into the skeleton of former CTF, which eventually boosted the visible-light induced hydrogen evolution reaction (HER). The work suggests a new method for enhancing the intrinsic HER activity by modulating the electronic features of the conjugated COFs by the introduction of pyridinic N atoms.

Understanding of water desalination in two-dimensional porous membrane via molecular dynamics

To explore energy-efficient two-dimensional porous materials for water desalination is an urgent demand for rational utilization of water and sustainable development. In addition, how the pore hydrophilicity influencing the desalination performance remains elusive. Basing on molecular dynamics (MD) simulations, we herein proposed ultrathin membranes of 2D covalent organic frameworks (COFs) with triazine units that are competent to reject ions efficiently while giving access to high water permeability. The ordered porous structure of these two COFs membranes (CTF-FUM and TPMA) enable nearly 100% salt rejection and show remarkable higher water permeation (∼57.2 and ∼ 48.1 L cm−2 day−1 MPa−1, respectively) over 3 magnitude compared to commercial TFC membranes (∼0.03 L cm−2 day−1 MPa−1). As a further step, the influence of layer number on membrane desalination performance was discussed to understand the underlying mechanisms. Compared to TPMA multilayer, it was found that CTF-FUM multilayer with hydrophobic pore shows less water permeability and higher transport resistance, and even has no obvious water transport through the 8-layer membrane. This MD simulation work gives a microscopic insight into 2D COF membranes on desalination and suggests that TPMA multilayer might be a promising membrane material for desalination applications.

Tuning the Interlayer Interactions of 2D Covalent Organic Frameworks Enables an Ultrastable Platform for Anhydrous Proton Transport

AbstractThe development of effective, stable anhydrous proton‐conductive materials is vital but challenging. Covalent organic frameworks (COFs) are promising platforms for ion and molecule conduction owing to their pre‐designable structures and tailor‐made functionalities. However, their poor chemical stability is due to weak interlayer interactions and intrinsic reversibility of linkages. Herein, we present a strategy for enhancing the interlayer interactions of two‐dimensional COFs via importing planar, rigid triazine units into the center of C3‐symmetric monomers. The developed triazine‐core‐based COF (denoted as TPT‐COF) possesses a well‐defined crystalline structure, ordered nanochannels, and prominent porosity. The proton conductivity was ≈10 times those of non‐triazinyl COFs, even reaching up to 1.27×10−2 S cm−1 at 160 °C. Furthermore, the TPT‐COF exhibited structural ultrastability, making it an effective proton transport platform with remarkable conductivity and long‐term durability.

Tuning the Interlayer Interactions of 2D Covalent Organic Frameworks Enables an Ultrastable Platform for Anhydrous Proton Transport.

The development of effective, stable anhydrous proton-conductive materials is vital but challenging. Covalent organic frameworks (COFs) are promising platforms for ion and molecule conduction owing to their pre-designable structures and tailor-made functionalities. However, their poor chemical stability is due to weak interlayer interactions and intrinsic reversibility of linkages. Herein, we present a strategy for enhancing the interlayer interactions of two-dimensional COFs via importing planar, rigid triazine units into the center of C3 -symmetric monomers. The developed triazine-core-based COF (denoted as TPT-COF) possesses a well-defined crystalline structure, ordered nanochannels, and prominent porosity. The proton conductivity was ≈10 times those of non-triazinyl COFs, even reaching up to 1.27×10-2 S cm-1 at 160 °C. Furthermore, the TPT-COF exhibited structural ultrastability, making it an effective proton transport platform with remarkable conductivity and long-term durability.

Boosting lithium ions inserting onto aromatic ring by extending conjugation of triazine-based porous organic frameworks for lithium-ion batteries

Conjugated polymeric materials characterized by chemical cost benefit, environmental friendliness and richness at the molecular design, are considered as promising electrode materials for LIBs. However, their relatively low capacity, poor structural stability, and sluggish ion/electron diffusion kinetics remain the obstacles and deep exploration of their electrochemical mechanisms are also urgently needed. Here, two triazine-based porous polymeric frameworks with tunable conjugated structures are fabricated and their electrochemical behaviors are explored in-depth to further probe the mechanisms of lithium ions inserting onto aromatic rings. Based on the ex-situ experimental analysis and theoretical calculations, the intercalation of lithium ions is a stepwise process for triazine and benzene units, and the polymer with extended conjugation structures could involve 12 lithium ions intercalation with a high capacity of 1497.6 mAh g-1 after 150 cycles at 100 mA g−1. Furthermore, the full cells also elicit the potential of the ToF-2 as a readily processable anode material with the commercially tested LiCoO2 as cathode.

Polarization Engineering of Covalent Triazine Frameworks for Highly Efficient Photosynthesis of Hydrogen Peroxide from Molecular Oxygen and Water.

Two-electron oxygen photoreduction to hydrogen peroxide (H2 O2 ) is seriously inhibited by its sluggish charge kinetics. Herein, a polarization engineering strategy is demonstrated by grafting (thio)urea functional groups onto covalent triazine frameworks (CTFs), giving rise to significantly promoted charge separation/transport and obviously enhanced proton transfer. The thiourea-functionalized CTF (Bpt-CTF) presents a substantial improvement in the photocatalytic H2 O2 production rate to 3268.1µmol h-1 g-1 with no sacrificial agents or cocatalysts that is over an order of magnitude higher than unfunctionalized CTF (Dc-CTF), and a remarkable quantum efficiency of 8.6% at 400nm. Mechanistic studies reveal the photocatalytic performance is attributed to the prominently enhanced two-electron oxygen reduction reaction by forming endoperoxide at the triazine unit and highly concentrated holes at the thiourea site. The generated O2 from water oxidation is subsequently consumed by the oxygen reduction reaction (ORR), thereby boosting overall reaction kinetics. The findings suggest a powerful functional-groups-mediated polarization engineering method for the development of highly efficient metal-free polymer-based photocatalysts.

Covalently grafting conjugated porous polymers to MXene offers a two-dimensional sandwich-structured electrocatalytic sulfur host for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have received increasing attention due to their high energy density (2600 W h kg−1) as well as the low cost and nontoxicity of sulfur. However, sluggish conversion kinetics and the notorious shuttle effect of the polysulfides present in sulfur cathodes hinder the practical use of Li–S batteries. Herein, an electrocatalytic sulfur host with a two-dimensional (2D) sandwich structure is synthesized and found to display excellent properties for overcoming the noted challenges. The electrocatalytic sulfur host is prepared by covalently grafting a conjugated microporous polymer (CMP) to MXene nanosheets and denoted as CMP-M. The CMP component features triazine and benzothiophene units and thus the constituent heteroatoms endow CMP-M with a plethora of chemisorption sites to capture various polysulfides. The MXene component provides an electrocatalytic template to construct the 2D sandwich composite and can facilitate charge transfer while accelerating polysulfide conversion. Li–S cells prepared using CMP-M as sulfur hosts are found to exhibit a number of outstanding performance metrics including a high specific capacity (i.e., 1402 mA h g−1 at 0.1C), an outstanding rate capability (i.e., 610 mA h g−1 at 4C), and a low capacity decay (from an initial value of 730 to 550 after 1000 cycles at 2C, corresponding to 0.025% per cycle). The methodology presented herein offers a universal approach for constructing electrocatalytic 2D composites that are useful not only in Li–S batteries but also in other contemporary energy technologies.

Sp2 carbon-conjugated covalent organic frameworks for efficient photocatalytic degradation and visualized pH detection

The design and fabrication of versatile covalent organic frameworks (COFs) with multiple properties for diverse applications is highly desirable. Here, the difunctional COFs material g–C18N3–COF was prepared and modified to be applied for efficient photocatalytic degradation of Rhodamine B (RhB) and pH detection, respectively. Owing to the triazine unit which was suitable for photocatalyst construction, g–C18N3–COF was sensitive to visible light and exhibited excellent photocatalysis capability toward RhB. Specially, the photocatalytic degradation of RhB with a high concentration of 300 ppm using g–C18N3–COF reached equilibrium within 6 h. Moreover, g–C18N3–COF was further grown in-situ onto the filter paper to generate a novel composite material g–C18N3–COF@Paper with bright yellow fluorescence. g–C18N3–COF@Paper could visualize the pH detection by remarkable changes in its fluorescent intensity and color in the range of pH value from 1 to 5, on account of the protonation of the nitrogen atoms from the triazine ring in g–C18N3–COF. The triazine-based sp2 carbon-conjugated g–C18N3–COF, respectively, used as photocatalyst and sensor in this work offers a new strategy to construct the versatile COFs material, facilitating the application of functional COFs in the environmental protection field.

High-efficiency photoreduction of CO2 to solar fuel on alkali intercalated Ultra-thin g-C3N4 nanosheets and enhancement mechanism investigation

The visible-light photocatalytic reduction of CO2 becomes a vital breakthrough to alleviate the greenhouse effect and achieve carbon neutrality. In this paper, ultrathin g-C3N4 nanosheets of 1.74 nm were constructed, and K+ was successfully doped between layers. The yields of CO and CH4 are 1.65 μmol·g−1·h−1 and 0.15 μmol·g−1·h−1, which are 4.70 and 7.27 times higher than the original g-C3N4, respectively. The ultra-thin nano-lamellar structure shortens the carrier transmission distance, and the intercalation of K+ not only promotes the electron transport between g-C3N4 layers but also changes the original hybrid mode of the catalytic system, thus shortening the band gap and adjusting the energy band structure.In addition, the CO2 adsorption center of the K+ intercalated g-C3N4 is transferred from the coordinated carbon atom to the center of the triazine unit, and the binding energy is obviously increased, which strengthens the CO2 adsorption. Finally, through in-situ DRIFT characterization, it is speculated that the reaction enhancement mechanism is that the modified catalyst promotes the adsorption and activation of CO2, resulting in the production of more intermediates, especially more hydrocarbon intermediates, which is more conducive to the photocatalytic reduction of CO2.

Triazine-Based Conjugated Microporous Polymers With Different Linkage Units for Visible Light-Driven Hydrogen Evolution.

Conjugated microporous polymers (CMPs), as a kind of two-dimensional material, have attracted extensive attention due to their advantages in visible light–driven photocatalytic splitting of water for hydrogen evolution. However, improving the microstructure and electronic structure of the material to enhance their photocatalytic performance for hydrogen evolution remains a challenge. We designed and reported two analogous CMPs including CMP-1 and CMP-2 that contain triazine and dibenzothiophene-S,S-dioxide units, which were prepared by Pd-catalyzed Suzuki-Miyaura coupling reaction. The main difference of two CMPs is that the triazine units are connected to benzene unit (CMP-1) or thiophene unit (CMP-2). Both of the CMPs exhibit excellent light capture capability, and compared with CMP-2, CMP-1 has faster separation rates and lower recombination rates for the charge carriers (electron/hole), and then, a higher hydrogen evolution rate was obtained from water decomposition reaction. We find the H2 production rate of CMP-1 can be up to 9,698.53 μmol g−1h −1, which is about twice of that of CMP-2. This work suggests that molecular design is a potent method to optimize the photocatalytic performance toward hydrogen evolution of the CMPs.

2D covalent organic frameworks for photosynthesis of α-trifluoromethylated ketones from aromatic alkenes

Photoactive two-dimensional covalent organic frameworks (2D-COFs) have recently emerged as a promising platform for efficient solar to chemical energy conversion. The photosynthesis of α-trifluoromethylated ketones, which is an important access to various fluorine-containing compounds, is rarely reported in heterogeneous photocatalytic systems. Herein, we report two 2D-COFs constructed from the electron-deficient triazine and electron-rich benzotrithiophene units with imine and amide linkages for the photosynthesis of α-trifluoromethylated ketones. The novel triazine-based COFs showed good activity, broad substrate flexibility and recyclability under visible-light irradiation, which is much superior to the classical pyrene-based COFs. Density functional theory calculations revealed that the triazine-based COFs have intrinsically lower carrier recombination tendency and can produce more intermediates •CF3, resulting in higher catalytic efficiency. This research will contribute to the rational design of photoactive COFs and facilitate the development of fluorine chemistry.

Foldable Detergents for Membrane Protein Study: Importance of Detergent Core Flexibility in Protein Stabilization.

Membrane proteins are of biological and pharmaceutical significance. However, their structural study is extremely challenging mainly due to the fact that only a small number of chemical tools are suitable for stabilizing membrane proteins in solution. Detergents are widely used in membrane protein study, but conventional detergents are generally poor at stabilizing challenging membrane proteins such as G protein-coupled receptors and protein complexes. In the current study, we prepared tandem triazine-based maltosides (TZMs) with two amphiphilic triazine units connected by different diamine linkers, hydrazine (TZM-Hs) and 1,2-ethylenediamine (TZM-Es). These TZMs were consistently superior to a gold standard detergent (DDM) in terms of stabilizing a few membrane proteins. In addition, the TZM-Es containing a long linker showed more general protein stabilization efficacy with multiple membrane proteins than the TZM-Hs containing a short linker. This result indicates that introduction of the flexible1,2-ethylenediamine linker between two rigid triazine rings enables the TZM-Es to fold into favourable conformations in order to promote membrane protein stability. The novel concept of detergent foldability introduced in the current study has potential in rational detergent design and membrane protein applications.

Effective design and synthesis of donor-acceptor covalent triazine polymers with boosted photocatalytic performance for Cr(VI) reduction

Two new donor–acceptor covalent triazine polymers (CTPs), namely Th-Trz (JOU-6) and Th-Ph-Trz (JOU-7), containing electron-donating thieno[2,3-b]thiophene (Th) units and electron-withdrawing triazine (Trz) units have been successfully constructed (Ph = benzene ring). The unique conjugated structure of the CTPs invokes wide absorption range and high charge transfer efficiency. Because of these advantages, the as-prepared CTPs are highly effective photocatalysts for Cr(VI) reduction. It is found that high acid concentration in the photocatalytic system may assist the protonation of triazine groups in CTPs, which not only can enhance their adsorption ability for Cr2O72−, but also can promote their charge transfer ability. Another important finding is that compared with JOU-6, JOU-7 shows more efficient charge separation owing to the introduction of benzene ring between the donor and acceptor units, inducing a spatial separation of photogenerated electrons and holes, and thereby giving a better photocatalytic performance. The spatial charge distribution of the CTPs was also investigated by theoretical calculation based on molecular orbital theory. Fascinatingly, Cr(VI) and organic pollutions can be simultaneously removed by JOU-7 without any sacrificial agents, oxidizer, or acid. This work provides a valuable strategy for the design and construction of effective photocatalysts for the removal of pollutants in wastewater.

Core–shell heterostructured composites of carbon nanotubes and imine-linked hyperbranched polymers as metal-free Li-ion anodes

Abstract An in situ Schiff-base condensation between p-phthalaldehyde (PPD) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) or 1,3,5-tris(4-aminophenyl)triazine (TAPT) was actualized in the presence of carbon nanotubes (CNTs), producing imine-linked hyperbranched poly(PPD-TAPB) and poly(PPD-TAPT)-coated CNTs (abbreviated as CNT@HBP-1 and CNT@HBP-2, respectively). Such quasi-1D core–shell heterostructures are interleaved to build robust 3D networks with porous internal channels, which are favorable for efficient electron transport and ion diffusion, exposing active sites, fast redox kinetics, and high electrochemical utilization. When used as Li-ion anodes, both CNT@HBP-1 and CNT@HBP-2 exhibit larger specific capacity, better rate performance, and higher cycling stability compared to their pure polymers. Furthermore, CNT@HBP-2 delivers higher reversible capacities of 351 mA h g−1 at 0.05 A g−1, and 81 mA h g−1 at 1.0 A g−1, respectively, compared to CNT@HBP-1 (335 and 56 mA h g−1). Besides, CNT@HBP-2 retains 268 mA h g−1 over 100 cycles at 0.1 A g−1, and 617 mA h g−1 in the 500th cycles at 0.5 A g−1, respectively, outperforming CNT@HBP-1 (155 and 256 mA h g−1). Further improvements in the electrochemical performance for CNT@HBP-2 relative to CNT@HBP-1 are attributable to the incorporation of additional redox-active triazine units into HBP-2. This work would unlock insights into the rational development of metal-free polymer-based electrodes for rechargeable batteries.

Fabrication of thiophene decorated side chain entanglement free COFs for highly regenerable mercury extraction

The accumulation of mercury in the food chain and environment is harmful to living beings. This raises the need for high affinity, reusable cost-efficient adsorbents for mercury. Herein, we report a side chain entanglement free hetero atom effect bearing covalent organic framework MTF prepared by integrating melamine and thiophene linker. The AA stacked MTF-2 was prepared via transformation strategy from its AB stacked MTF-1 congener. The MTF-1 and MTF-2 were comprehensively analyzed through PXRD, SEM, TEM, 13C CP/MAS, N2 sorption and mercury removal efficiency. The adsorption capacity of MTF-2 revealed a value of 540 mg g−1, which is greater than that of MTF-1 (328 mg g−1). The adsorption mechanism was studied through XPS, 13C CP/MAS and XAFS indicating probable coordination of Hg2+ with both the triazine and sulfur moieties in a cooperative manner. To demonstrate the role of aromatic triazine ring, the analogous aliphatic triaminoguanidine was selected and the removal efficiencies between triaminoguanidine-thiophene COF (TAG-TF) and MTF-2 were compared. It revealed that the triazine unit containing MTF-2 showed 2.2 times greater removal efficiency than TAG-TF. The results reveal the structure-performance relationship, where the high surface area and relatively ordered functional moieties both paly a synergistic role in efficient mercury adsorption.

Highly efficient thermally activated delayed fluorescence emitter based on the 5H-benzo[d]benzo[4,5]imidazo[1,2-a]imidazole donor

A donor–π-acceptor-type TADF emitter (BzITz) was designed and synthesized using 5H-benzo[d]benzo[4,5]imidazo[1,2-a]imidazole as a fused rigid electron donor and a benzonitrile merged triazine unit as an electron acceptor.

Fully Condensed Poly (Triazine Imide) Crystals: Extended π‐Conjugation and Structural Defects for Overall Water Splitting

AbstractConventional polymerization for the synthesis of carbon nitride usually generates amorphous heptazine‐based melon with an abundance of undesired structural defects, which function as charge carrier recombination centers to decrease the photocatalytic efficiency. Herein, a fully condensed poly (triazine imide) crystal with extended π‐conjugation and deficient structure defects was obtained by conducting the polycondensation in a mild molten salt of LiCl/NaCl. The melting point of the binary LiCl/NaCl system is around 550 °C, which substantially restrain the depolymerization of triazine units and extend the π‐conjugation. The optimized polymeric carbon nitride crystal exhibits a high apparent quantum efficiency of 12 % (λ=365 nm) for hydrogen production by one‐step excitation overall water splitting, owing to the efficient exciton dissociation and the subsequent fast transfer of charge carriers.