Exciton binding energy has been regarded as a crucial parameter for mediating charge separation in polymeric photocatalysts. Minimizing the exciton binding energy of the polymers can increase the ...yield of charge‐carrier generation and thus improve the photocatalytic activities, but the realization of this approach remains a great challenge. Herein, a series of linear donor–acceptor conjugated polymers has been developed to minimize the exciton binding energy by modulating the charge‐transfer pathway. The results reveal that the reduced energy loss of the charge‐transfer state can facilitate the electron transfer from donor to acceptor, and thus, more electrons are ready for subsequent reduction reactions. The optimized polymer, FSO‐FS, exhibits a remarkable photochemical performance under visible light irradiation.
Modulating the charge‐transfer pathway in a series of linear donor–acceptor conjugated polymers controls their ability to minimize the exciton binding energy. A low exciton binding energy promotes the photoreaction for artificial photosynthesis
Electron transfer is the rate‐limiting step in photocatalytic water splitting. Viologen and its derivatives are able to act as electron‐transfer mediators (ETMs) to facilitate the rapid electron ...transfer from photosensitizers to active sites. Nevertheless, the electron‐transfer ability often suffers from the formation of a stable dipole structure through the coupling between cationic‐radical‐containing viologen‐derived ETMs, by which the electron‐transfer process becomes restricted. Herein, cyclic diquats, a kind of viologen‐derived ETM, are integrated into a 2,2′‐bipyridine‐based covalent organic framework (COF) through a post‐quaternization reaction. The content and distribution of embedded diquat‐ETMs are elaborately controlled, leading to the favorable site‐isolated arrangement. The resulting materials integrate the photosensitizing units and ETMs into one system, exhibiting the enhanced hydrogen evolution rate (34600 μmol h−1 g−1) and sustained performances when compared to a single‐module COF and a COF/ETM mixture. The integration strategy applied in a 2D COF platform promotes the consecutive electron transfer in photochemical processes through the multi‐component cooperation.
Viologen‐derived electron‐transfer mediators (ETMs) are integrated into a 2,2′‐bipyridine‐containing covalent organic framework (COF) by a controllable post‐synthetic method. The site‐isolated ETM modules cooperate well with photosensitizer modules on the platform of COFs for enhanced electron‐transfer ability, thereby remarkably promoting the photocatalytic H2 evolution performance (34600 μmol h−1 g−1) from water splitting.
Large-scale photochemical synthesis of high value chemicals under mild conditions is an ideal method of green chemical production. However, a scalable photocatalytic process has been barely reported ...due to the costly preparation, low stability of photosensitizers and critical reaction conditions required for classical photocatalysts. Here, we report the merging of flow chemistry with heterogeneous photoredox catalysis for the facile production of high value compounds in a continuous flow reactor with visible light at room temperature in air. In the flow reactor system, polymeric carbon nitrides, which are cheap, sustainable and stable heterogeneous photocatalysts, are immobilized onto glass beads and fibers, demonstrating a highly flexible construction possibility for devices of the photocatalytic materials. As an example of the production of high value chemicals, important chemical structures such as cyclobutanes, which are basic building blocks for many pharmaceutical compounds, like magnosalin, are synthesized in flow with high catalytic efficiency and stability.
A simple structural design principle and band position alignment of conjugated microporous polymers for enhanced photocatalytic efficiency is presented. The valence and conduction band positions of ...the polymer networks can be fine‐tuned by altering the substitution positions on the centered phenyl unit to match the required redox potential of the catalytic reactions under visible light.
The search for metal‐free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic ...photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron‐withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one‐ or three‐dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h−1 were observed by employing the linear polymer based on a phenyl‐benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.
Bring to light: Conjugated polybenzothiadiazoles were introduced as a new family of organic photocatalysts for H2 evolution from water in the presence of electron donors with visible‐light irradiation. The molecular engineering of the electron‐withdrawing benzothiadiazole unit on the phenyl unit allows the construction of either one‐ or three‐dimensional polybenzothiadiazoles, and the effect of the structure on the photocatalytic H2 evolution activity was investigated.
Due to the fast inference and good performance, discriminative learning methods have been widely studied in image denoising. However, these methods mostly learn a specific model for each noise level, ...and require multiple models for denoising images with different noise levels. They also lack flexibility to deal with spatially variant noise, limiting their applications in practical denoising. To address these issues, we present a fast and flexible denoising convolutional neural network, namely FFDNet, with a tunable noise level map as the input. The proposed FFDNet works on downsampled sub-images, achieving a good trade-off between inference speed and denoising performance. In contrast to the existing discriminative denoisers, FFDNet enjoys several desirable properties, including: 1) the ability to handle a wide range of noise levels (i.e., 0, 75) effectively with a single network; 2) the ability to remove spatially variant noise by specifying a non-uniform noise level map; and 3) faster speed than benchmark BM3D even on CPU without sacrificing denoising performance. Extensive experiments on synthetic and real noisy images are conducted to evaluate FFDNet in comparison with state-of-the-art denoisers. The results show that FFDNet is effective and efficient, making it highly attractive for practical denoising applications.
The construction of multi‐heteroatom‐doped metal‐free carbon with a reversibly oxygen‐involving electrocatalytic performance is highly desirable for rechargeable metal‐air batteries. However, the ...conventional approach for doping heteroatoms into the carbon matrix remains a huge challenge owing to multistep postdoping procedures. Here, a self‐templated carbonization strategy to prepare a nitrogen, phosphorus, and fluorine tri‐doped carbon nanosphere (NPF‐CNS) is developed, during which a heteroatom‐enriched covalent triazine polymer serves as a “self‐doping” precursor with C, N, P, and F elements simultaneously, avoiding the tedious and inefficient postdoping procedures. Introducing F enhances the electronic structure and surface wettability of the as‐obtained catalyst, beneficial to improve the electrocatalytic performance. The optimized NPF‐CNS catalyst exhibits a superb electrocatalytic oxygen reduction reaction (ORR) activity, long‐term durability in pH‐universal conditions as well as outstanding oxygen evolution reaction (OER) performance in an alkaline electrolyte. These superior ORR/OER bifunctional electrocatalytic activities are attributed to the predesigned heteroatom catalytic active sites and high specific surface areas of NPF‐CNS. As a demonstration, a zinc‐air battery using the NPF‐CNS cathode displays a high peak power density of 144 mW cm−2 and great stability during 385 discharging/charging cycles, surpassing that of the commercial Pt/C catalyst.
A nitrogen, phosphorus, and fluorine tri‐doped carbon nanosphere (NPF‐CNS) is fabricated from a heteroatom‐enriched covalent triazine polymer by a one‐pot self‐doping strategy. Due to its abundant and uniformly distributed heteroatom electrocatalytic active centers, the as‐developed NPF‐CNS can readily work as an oxygen reduction reaction/oxygen evolution reaction dual‐functional electrocatalyst for a high‐performance rechargeable zinc‐air battery.
For metal‐free, organic conjugated polymer‐based photocatalysts, synthesis of defined nanostructures is still highly challenging. Here, we report the formation of covalent triazine framework (CTF) ...nanoparticles via a size‐controllable confined polymerization strategy. The uniform CTF nanoparticles exhibited significantly enhanced activity in the photocatalytic formation of dibenzofurans compared to the irregular bulk material. The optoelectronic properties of the nanometer‐sized CTFs could be easily tuned by copolymerizing small amounts of benzothiadiazole into the conjugated molecular network. This optimization of electronic properties led to a further increase in observed photocatalytic efficiency, resulting in total an 18‐fold enhancement compared to the bulk material. Full recyclability of the heterogeneous photocatalysts as well as catalytic activity in dehalogenation, hydroxylation and benzoimidazole formation reactions demonstrated the utility of the designed materials.
Size‐controllable covalent triazine framework nanoparticles were synthesized through a confined polymerization strategy within silica capsules. They show a manifold increase in photocatalytic activity compared to the bulk system.
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