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Covalent heptazine frameworks (CHFs) are widely utilized in the recent years as potential photocatalysts. However, their limited conjugated structures, low crystallinity and small surface areas have limited the practical photocatalysis performance. Along this line, we report herein the synthesis of a kind of mixed crystalline CHF (m-CHF-1) with built-in heterojunction structure, which can efficiently catalyze the formic acid dehydrogenation by visible light driven photocatalysis. The m-CHF-1 is synthesized from 2,5,8-triamino-heptazine and dicyanobenzene (DCB) in the molten salts, in which DCB plays as organic molten co-solvent to promote the rapid and ordered polymerization of 2,5,8-triamino-heptazine. The m-CHF-1 is formed by embedding phenyl-linked heptazine (CHF-Ph) units in the poly(heptazine imide) (PHI) network similar to doping. The CHF-Ph combined with PHI form an effective type II heterojunction structure, which promote the directional transfer of charge carriers. And the integration of CHF-Ph makes m-CHF-1 have smaller exciton binding energy than pure PHI, the charge carriers are more easily dissociated to form free electrons, resulting in higher utilization efficiency of the carriers. The largest hydrogen evolution rate reaches a value of 42.86 mmol h-1 g-1 with a high apparent quantum yield of 24.6% at 420 nm, which surpasses the majority of other organic photocatalysts.
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Covalent organic frameworks (COFs) with a periodic network of permanent porosity and ordered structures have witnessed enormous potential in many applications. However, the synthesis of COFs with controllable morphologies under mild conditions remains a critical issue. Herein, we report a novel strategy to synthesize ß-ketoenamine-linked COFs by emulsion polymerization via phase transfer catalysis for the first time. This new approach employs commercially available pyridinium surfactants as emulsifiers for emulsion polymerization, which function as both catalysts and morphological regulators. By controlling the interfacial interaction in the emulsion, the TpPa-COF can be prepared into different morphologies, i.e., spheres, bowls, and fibers. Furthermore, the COF emulsion can be directly used to prepare a film by applying an electric field, providing a new route to prepare COF films. This phase transfer catalysis method also allows the synthesis of the TpPa-COF on a gram scale. The strategy is fast, facile, and effective in improving the morphology and particle size, providing a prospective route for the green preparation of functional COFs.
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The development of heteroaromatic conjugated porous polymers (H-CPPs) have received enormous research interests, because of the important functional roles of the heteroatoms in photocatalysis and proton conduction. However, due to the synthetic challenges deriving from the stable structures, the structural diversity and synthetic methods of them are still limited. Herein, a new type of H-CPPs, covalent pyrimidine frameworks (CPFs), via an efficient tandem polycondensation reaction between aldehyde, acetyl, and amidine monomers is reported. The resulting CPFs are bridged by pyrimidine units, rich of nitrogen atoms and can be structurally regulated on demand. The CPFs are shown to be active photocatalysts for hydrogen evolution from methanol via a photo-thermo-catalysis process, achieving an excellent hydrogen evolution rate of 5282.8 µmol h-1 g-1 . The CPFs can be further processed into a mixed matrix membrane, displaying an excellent proton conductivity of 1.30 × 10-2 S cm-1 at 413 K under anhydrous condition.
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Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF-HUST-A1 with a benzylamine-functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF-HUST-A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200â µmol g-1 h-1 ). Photocatalytic overall water splitting is achieved by depositing dual co-catalysts in CTF-HUST-A1, with H2 evolution and O2 evolution rates of 25.4â µmol g-1 h-1 and 12.9â µmol g-1 h-1 in pure water without using sacrificial agent.
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Porous organic polymers (POPs) have enormous applications in various fields and thus have received a lot of research attention in recent decades. Numerous synthetic methods have been developed, but mild synthesis conditions and fast polymerization rate are highly desired. Herein, high porous POPs with high surface areas from aromatic vinyl monomers by using acid catalysis method is reported. The polymerization is ultrafast and could be accomplished even in 5 min at room temperature. Furthermore, the surface area can be tuned by using various acid catalysts and controlling the reaction time. Due to the high surface area, these POPs show promising adsorption of carbon dioxide and hydrogen, respectively. Furthermore, the large π-system of the building block and high surface area of the POPs also make them show potential applications in photocatalytic hydrogen evolution as well as promising catalyst support for metal nanoparticles.
Assuntos
Hidrocarbonetos Aromáticos/química , Polímeros/química , Compostos de Vinila/química , Catálise , Concentração de Íons de Hidrogênio , Estrutura Molecular , Tamanho da Partícula , Polimerização , Porosidade , Propriedades de SuperfícieRESUMO
Soluble porous organic polymers (SPOPs) are currently the subject of extensive investigation due to the enhanced processability compared to insoluble counterparts. Here, a new concept for the construction of SPOPs is presented, which combines the unique topological structure of hyperbranched polymers with rigid building blocks. By using this facile, one-step strategy, a class of novel SPOPs which possess surface areas up to 646 m2 g-1 have been synthesized. The extended π-conjugated backbone affords the polymers bright fluorescence under UV irradiation. Interestingly, after dissolution in a suitable solvent that was slowly evaporated, the polymers retain a large extent of porosity. The SPOPs are potential candidates for gas storage and separation, photovoltaic, and biological applications. In particular, due to the presence of an internal porous structure and open conformations, they show high drug loading efficiency (1.91 g of ibuprofen per gram), which is considerably higher than conventional porous organic polymers.
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Polímeros/química , Adsorção , Fluorescência , Estrutura Molecular , Tamanho da Partícula , Porosidade , Solubilidade , Propriedades de Superfície , Raios UltravioletaRESUMO
Covalent triazine frameworks (CTFs) with aromatic triazine linkages have recently received increasing interest for various applications because of their rich nitrogen content and high chemical stability. Owing to the strong aromatic C=N bond and high chemical stability, only a few CTFs are crystalline, and most CTFs are amorphous. Herein we report a new general strategy to give highly crystalline CTFs by inâ situ formation of aldehyde monomers through the controlled oxidation of alcohols. This general strategy allows a series of crystalline CTFs with different monomers to be prepared, which are shown to have higher thermal stability and enhanced performance in photocatalysis as compared with the less crystalline or amorphous CTFs. This open-system approach is very simple and convenient, which presents a potential pathway to large-scale industrial production of crystalline CTFs.
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Covalent triazine frameworks (CTFs) are normally synthesized by ionothermal methods. The harsh synthetic conditions and associated limited structural diversity do not benefit for further development and practical large-scale synthesis of CTFs. Herein we report a new strategy to construct CTFs (CTF-HUSTs) via a polycondensation approach, which allows the synthesis of CTFs under mild conditions from a wide array of building blocks. Interestingly, these CTFs display a layered structure. The CTFs synthesized were also readily scaled up to gram quantities. The CTFs are potential candidates for separations, photocatalysis and for energy storage applications. In particular, CTF-HUSTs are found to be promising photocatalysts for sacrificial photocatalytic hydrogen evolution with a maximum rate of 2647â µmol h-1 g-1 under visible light. We also applied a pyrolyzed form of CTF-HUST-4 as an anode material in a sodium-ion battery achieving an excellent discharge capacity of 467â mAh g-1 .
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Porous carbon materials prepared from the porous organic polymers are currently the subject of extensive investigation. On the basis of their interesting applications, it is highly desirable to develop new synthetic methodologies to obtain carbon materials with controllable pore size and morphology. Herein, a facile synthesis of hollow microporous carbon spheres (HCSs) from hollow microporous organic capsules (HMOCs) with a good control over the pore morphology, hollow cavity, and the shell thickness is reported. The highly porous hollow carbon spheres are prepared by the pyrolysis of HMOCs-based microporous polymers. The synthetic parameters, such as hypercrosslinking and pyrolysis conditions, are optimized to modify the porous structures and the properties. The morphology and porosity as well as energy storage applications of the microporous structures HCSs, derived through a combination of divinylbenzene-crosslinking and micropore-generating hypercrosslinking, are discussed. These findings provide a new benchmark for fabricating well-defined HCSs with great promise for various applications.
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An electron-deficient copper(III) corrole was utilized for the construction of donor-acceptor conjugates with zinc(II) porphyrin (ZnP) as a singlet excited state electron donor, and the occurrence of photoinduced charge separation was demonstrated by using transient pump-probe spectroscopic techniques. In these conjugates, the number of copper corrole units was varied from 1 to 2 or 4 units while maintaining a single ZnP entity to observe the effect of corrole multiplicity in facilitating the charge-separation process. The conjugates and control compounds were electrochemically and spectroelectrochemically characterized. Computational studies revealed ground state geometries of the compounds and the electron-deficient nature of the copper(III) corrole. An energy level diagram was established to predict the photochemical events by using optical, emission, electrochemical, and computational data. The occurrence of charge separation from singlet excited zinc porphyrin and charge recombination to yield directly the ground state species were evident from the diagram. Femtosecond transient absorption spectroscopy studies provided spectral evidence of charge separation in the form of the zinc porphyrin radical cation and copper(II) corrole species as products. Rates of charge separation in the conjugates were found to be of the order of 10(10) â s(-1) and increased with increasing multiplicity of copper(III) corrole entities. The present study demonstrates the importance of copper(III) corrole as an electron acceptor in building model photosynthetic systems.
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By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions.
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Imidas/química , Indóis/química , Metais/química , Naftalenos/química , Compostos Organometálicos/química , Perileno/análogos & derivados , Polímeros/química , Elétrons , Isoindóis , Simulação de Dinâmica Molecular , Perileno/química , Difração de Raios XRESUMO
The construction of a new class of covalent TTF lattice by integrating TTF units into two-dimensional covalent organic frameworks (2D COFs) is reported. We explored a general strategy based on the C2 +C2 topological diagram and applied to the synthesis of microporous and mesoporous TTF COFs. Structural resolutions revealed that both COFs consist of layered lattices with periodic TTF columns and tetragonal open nanochannels. The TTF columns offer predesigned pathways for high-rate hole transport, predominate the HOMO and LUMO levels of the COFs, and are redox active to form organic salts that exhibit enhanced electric conductivity by several orders of magnitude. On the other hand, the linkers between the TTF units play a vital role in determining the carrier mobility and conductivity through the perturbation of 2D sheet conformation and interlayer distance. These results open a way towards designing a new type of TTF materials with stable and predesignable lattice structures for functional exploration.
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Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine π-conjugated skeletons with permanent nanopores, in sharp contrast to other porous materials that are not π-conjugated and with conventional conjugated polymers that are nonporous. As an emerging material platform, CMPs offer a high flexibility for the molecular design of conjugated skeletons and nanopores. Various chemical reactions, building blocks and synthetic methods have been developed and a broad variety of CMPs with different structures and specific properties have been synthesized, driving the rapid growth of the field. CMPs are unique in that they allow the complementary utilization of π-conjugated skeletons and nanopores for functional exploration; they have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas adsorption, heterogeneous catalysis, light emitting, light harvesting and electrical energy storage. This review describes the molecular design principles of CMPs, advancements in synthetic and structural studies and the frontiers of functional exploration and potential applications.
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In this work, a high-throughput screening strategy and density functional theory (DFT) are jointly employed to identify high-performance TM@g-C4N3 (TM = 3d, 4d, 5d transition metals) single-atom catalysts (SACs) for the oxygen reduction reaction (ORR). Comprehensive studies demonstrated that Cu@, Zn@, and Ag@g-C4N3 show high ORR catalytic activities under both acidic and alkaline conditions with favorable overpotentials (ηORR) of 0.70, 0.89, and 0.89 V, respectively; among them, Cu@g-C4N3 is the best candidate. The ORR follows a four-electron mechanism with the final product H2O/OH-. Cu@, Zn@, and Ag@g-C4N3 catalysts also exhibit good thermal (500 K) and electrochemical (0.93-3.14 V) stabilities. Cu@, Zn@, and Ag@g-C4N3 demonstrate superior activities with low ηORR due to its moderate adsorption strength of *OH. The ηORR and the Gibbs free energy changes of *OH (ΔG4(acidic)/ΔG4(alkaline)) resemble a volcano-type relationship under acidic/alkaline conditions, respectively. Additionally, the O-O bond length in *OOH emerged as an effective structural descriptor for rapidly identifying the promising electrocatalysts. This research provides valuable insights into the origin of the ORR activity on TM@g-C4N3 and offers useful guidance for the efficient exploration of high-performance catalyst candidates.
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Condensation of hydrazine with 1,3,6,8-tetrakis(4-formylphenyl)pyrene under solvothermal conditions yields highly crystalline two-dimensional covalent organic frameworks. The pyrene units occupy the vertices and the diazabutadiene (-CâN-NâC-) linkers locate the edges of rohmbic-shaped polygon sheets, which further stack in an AA-stacking mode to constitute periodically ordered pyrene columns and one-dimensional microporous channels. The azine-linked frameworks feature permanent porosity with high surface area and exhibit outstanding chemical stability. By virtue of the pyrene columnar ordering, the azine-linked frameworks are highly luminescent, whereas the azine units serve as open docking sites for hydrogen-bonding interactions. These synergestic functions of the vertices and edge units endow the azine-linked pyrene frameworks with extremely high sensitivity and selectivity in chemosensing, for example, the selective detection of 2,4,6-trinitrophenol explosive. We anticipate that the extension of the present azine-linked strategy would not only increase the structural diversity but also expand the scope of functions based on this highly stable class of covalent organic frameworks.
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Proton-conducting materials are essential to the emerging hydrogen economy. Covalent triazine frameworks (CTFs) are promising proton-conducting materials at high temperatures but need more effective sites to strengthen interaction for proton carriers. However, their construction and design in a concise condition are still challenges. Herein, we show a low temperature approach to synthesize CTFs via a direct cyclotrimerization of aromatic aldehyde using ammonium iodide as facile nitrogen source. Among the CTFs, the perfluorinated CTF (CTF-TF) was successfully synthesized with much lower temperature ( ≤ 160 °C) and open-air atmosphere. Due to the additional hydrogen-bonding interaction between fluorine atoms and proton carriers (H3PO4), the CTF-TF achieves a proton conductivity of 1.82 × 10-1 S cm-1 at 150 °C after H3PO4 loading. Moreover, the CTF-TF can be readily integrated into mixed matrix membranes, displaying high proton conduction abilities and good mechanical strength. This work provides an alternative strategy for rational design of proton conducting media.
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The merging of good crystallinity and high dispersibility into two-dimensional (2D) layered crystalline polymers (CPs) still represents a challenge because a high crystallinity is often accompanied by intimate interlayer interactions that are detrimental to the material processibility. We herein report a strategy to address this dilemma using rationally designed three-dimensional (3D) monomers and regioisomerism-based morphology control. The as-synthesized CPs possess layered 2D structures, where the assembly of layers is stabilized by relatively weak van der Waals interactions between C-H bonds other than the usual π-π stackings. The morphology and dispersibility of the CPs are finely tuned via regioisomerism. These findings shed light on how to modulate the crystallinity, morphology, and ultimate function of crystalline polymers using the spatial arrangements of linking groups.
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Under high temperature anhydrous conditions, it is still a formidable challenge to improve the performance of proton-conducting materials based on H3 PO4 and elucidate its proton conduction mechanism. Herein, a highly stable covalent triazine frameworks (CTFs) based on H3 PO4 is reported. The more pyridinic nitrogen CTFs contain, the higher proton conductivity is. Compared with H3 PO4 @CTF-L with less pyridinic nitrogen, H3 PO4 @CTF-H has a higher proton conductivity of 1.6×10-1 â S cm-1 at 150 °C under anhydrous conditions, which does not decay after about 18â months exposure in air. The high proton conductivity is associated with the formation and breaking of the activated Ntriazine â¯H+ â¯H2 PO4 - pairs by pyridinic nitrogen of CTFs. The outstanding long-term stability is mainly attributed to the ultra-strong triazine skeleton structure of CTFs.
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Photocatalytic oxidative organic reactions are important synthetic transformations, and research on reaction selectivity by reactive oxygen species (ROS) is significant. To date, however, there has rarely been any focus on the directed generation of ROSs. Herein, we report the first identification of tunable molecular oxygen activation induced by polymeric conjugation in nonmetallic conjugated microporous polymers (CMP). The conjugation between these can be achieved by the introduction of alkynyl groups. CMP-A with an alkynyl bridge facilitates the intramolecular charge mobility while CMP-D, lacking an alkynyl group enhances the photoexcited carrier build-up on the surface from diffusion. These different processes dominate the directed ROS generation of the superoxide radical (O2-) and singlet oxygen (1O2), respectively. This theory is substantiated by the different performances of these CMPs in the aerobic oxidation of sulfides and the dehydrogenative coupling of amines, and could provide insight into the rational design of CMPs for various heterogeneous organic photosynthesis.
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Oxigênio , Fotossíntese , Espécies Reativas de Oxigênio , Fenômenos Químicos , DifusãoRESUMO
[This retracts the article DOI: 10.1039/D1SC03970A.].