Covalent organic frameworks (COFs) have recently emerged as a new generation of porous polymers combining molecular functionality with the robustness and structural definition of crystalline solids. ...Drawing on the recent development of tailor-made semiconducting COFs, we report here on a new COF capable of visible-light driven hydrogen generation in the presence of Pt as a proton reduction catalyst (PRC). The COF is based on hydrazone-linked functionalized triazine and phenyl building blocks and adopts a layered structure with a honeycomb-type lattice featuring mesopores of 3.8 nm and the highest surface area among all hydrazone-based COFs reported to date. When illuminated with visible light, the Pt-doped COF continuously produces hydrogen from water without signs of degradation. With their precise molecular organization and modular structure combined with high porosity, photoactive COFs represent well-defined model systems to study and adjust the molecular entities central to the photocatalytic process.
Nanosheets of a crystalline 2D carbon nitride were obtained by ionothermal synthesis of the layered bulk material poly(triazine imide), PTI, followed by one-step liquid exfoliation in water. ...Triazine-based nanosheets are 1-2 nm in height and afford chemically and colloidally stable suspensions under both basic and acidic conditions. We use solid-state NMR spectroscopy of isotopically enriched, restacked nanosheets as a tool to indirectly monitor the exfoliation process and carve out the chemical changes occurring upon exfoliation, as well as to determine the nanosheet thickness. PTI nanosheets show significantly enhanced visible-light driven photocatalytic activity toward hydrogen evolution compared to their bulk counterpart, which highlights the crucial role of morphology and surface area on the photocatalytic performance of carbon nitride materials.
Covalent organic frameworks (COFs) have emerged as a new class of crystalline porous polymers displaying molecular tunability combined with structural definition. Here, a series of three conjugated, ...photoactive azine‐linked COFs based on pyrene building blocks which differ in the number of nitrogen atoms in the peripheral aromatic units is presented. The structure of the COFs is analyzed by combined experimental and computational physisorption as well as quantum‐chemical calculations, which suggest a slipped‐stacked arrangement of the 2D layers. Photocurrents of up to 6 µA cm−2 with subsecond photoresponse times are measured on thin film samples for the first time. While all COFs are capable of producing hydrogen from water, their efficiency increases significantly with decreasing number of nitrogen atoms. The trending activities are rationalized by photoelectrochemical measurements and quantum‐chemical calculations which suggest an increase in the thermodynamic driving force with decreasing nitrogen content to be the origin of the observed differences in hydrogen evolution activities.
A series of three conjugated pyrene‐based azine‐linked covalent organic frameworks (COFs) which differ in the number of nitrogen atoms in the peripheral aromatic units is presented. All COFs are photoactive and produce photocurrents up to 6 µA cm−2 as thin films. The decreasing hydrogen evolution activity with decreasing nitrogen content points to an oxidative quenching mechanism.
A new dimension: The doping of amorphous poly(triazine imide) (PTI) through ionothermal copolymerization of dicyandiamide with 4‐amino‐2,6‐dihydroxypyrimidine (4AP) results in triazine‐based carbon ...nitrides with increased photoactivity for water splitting compared to crystalline poly(triazine imide) (PTI/Li+Cl−, see picture) and melon‐type carbon nitrides. This family of carbon nitride semiconductors has potential as low‐cost, environmentally clean photocatalysts for solar fuel production.
Redox active electrode materials derived from organic precursors are of interest for use as alternative cathodes in Li batteries due to the potential for their sustainable production from renewable ...resources. Here, a series of organic networks that either contain triazine units or are derived from triazine-containing precursors are evaluated as cathodes versus Li metal anodes as possible active materials in Li batteries. The role of the molecular structure on the electrochemical performance is studied by comparing several materials prepared across a range of conditions allowing control over functionality and long-range order. Well-defined structures in which the triazine unit persists in the final material exhibit very low capacities at voltages relevant for cathode materials (<10 mA·h g–1). Relatively high, reversible capacity (around 150 mA·h g–1) is in fact displayed by amorphous materials with little evidence of triazine functionality. This result directly contradicts previous suggestions that the triazine unit is responsible for charge storage in this family of materials. While the gently sloping discharge and charge profiles suggest a capacitive-type mechanismfurther confirmed by the trend of increasing capacity with increasing surface areaelectron paramagnetic resonance (EPR) spectroscopy studies show that the materials exhibiting higher capacities also display substantial EPR signals, potentially implicating unpaired spins in a charge storage mechanism that could involve charge transfer.
Covalent organic frameworks (COFs) have recently emerged as a new generation of porous polymers combining molecular functionality with the robustness and structural definition of crystalline solids. ...Drawing on the recent development of tailor-made semiconducting COFs, we report here on a new COF capable of visible-light driven hydrogen generation in the presence of Pt as a proton reduction catalyst (PRC). The COF is based on hydrazone-linked functionalized triazine and phenyl building blocks and adopts a layered structure with a honeycomb-type lattice featuring mesopores of 3.8 nm and the highest surface area among all hydrazone-based COFs reported to date. When illuminated with visible light, the Pt-doped COF continuously produces hydrogen from water without signs of degradation. With their precise molecular organization and modular structure combined with high porosity, photoactive COFs represent well-defined model systems to study and adjust the molecular entities central to the photocatalytic process.
A new hydrazone-based covalent organic framework has been developed as a photocatalyst for visible-light induced hydrogen production.
Towards Mesostructured Zinc Imidazolate Frameworks Junggeburth, Sebastian C.; Schwinghammer, Katharina; Virdi, Kulpreet S. ...
Chemistry : a European journal,
February 13, 2012, Letnik:
18, Številka:
7
Journal Article
Recenzirano
The transfer of supramolecular templating to the realm of metal–organic frameworks opens up new avenues to the design of novel hierarchically structured materials. We demonstrate the first synthesis ...of mesostructured zinc imidazolates in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), which acts as a template giving rise to ordered lamellar hybrid materials. A high degree of order spanning the atomic and mesoscale was ascertained by powder X‐ray diffraction, electron diffraction, as well as solid‐state NMR and IR spectroscopy. The metrics of the unit cells obtained for the zinc methylimidazolate and imidazolate species are a=(11.43±0.45), b=(9.55±0.35), c=(27.19±0.34) Å, and a=(10.98±0.90), b=(8.95±0.95), c=(26.33±0.34) Å, respectively, assuming orthorhombic symmetry. The derived structure model is consistent with a mesolamellar structure composed of bromine‐terminated zinc (methyl)imidazolate chains interleaved with motionally rigid cationic surfactant molecules in an all‐trans conformation. The hybrid materials exhibit unusually high thermal stability up to 300 °C, at which point CTAB is lost and evidence for a thermally induced transformation into poorly crystalline mesostructures with larger feature sizes is obtained. Treatment with ethanol effects the extraction of CTAB from the material, followed by facile transformation into pure microporous ZIF‐8 nanoparticles within minutes, thus demonstrating a unique transition from a mesostructure into a microporous zinc imidazolate.
The structural analogy between microporous ZIFs and zeolites has been demonstrated to also hold for mesostructured silica materials on the one hand, and mesostructured imidazolate frameworks (MIFs) on the other (see figure). Comprehensive characterization of the obtained MIF materials gives evidence of a lamellar hybrid structure composed of bromine‐terminated zinc imidazolate chains, which are sandwiched by cationic surfactant layers.
Eine neue Dimension: Dotiertes amorphes Poly(triazinimid) (PTI), das durch ionothermale Copolymerisation von Dicyandiamid mit 4‐Amino‐2,6‐dihydroxypyrimidin (4AP) hergestellt wurde, zeigt eine höhere ...Photoaktivität für die Wasserspaltung als kristallines Poly(triazinimid) (PTI/Li+Cl−) und Melon (siehe Bild). Diese neue Familie von Kohlenstoffnitrid‐Halbleitern hat Potenzial für die Entwicklung kostengünstiger Photokatalysatoren für die solare Brennstofferzeugung.
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