Metal-insulator-semiconductor photoelectrodes for enhanced photoelectrochemical water splitting.

Photoelectrochemical (PEC) water splitting provides a scalable and integrated platform to harness renewable solar energy for green hydrogen production. The practical implementation of PEC systems hinges on addressing three critical challenges: enhancing energy conversion efficiency, ensuring long-term stability, and achieving economic viability. Metal-insulator-semiconductor (MIS) heterojunction photoelectrodes have gained significant attention over the last decade for their ability to efficiently segregate photogenerated carriers and mitigate corrosion-induced semiconductor degradation. This review discusses the structural composition and interfacial intricacies of MIS photoelectrodes tailored for PEC water splitting. The application of MIS heterostructures across various semiconductor light-absorbing layers, including traditional photovoltaic-grade semiconductors, metal oxides, and emerging materials, is presented first. Subsequently, this review elucidates the reaction mechanisms and respective merits of vacuum and non-vacuum deposition techniques in the fabrication of the insulator layers. In the context of the metal layers, this review extends beyond the conventional scope, not only by introducing metal-based cocatalysts, but also by exploring the latest advancements in molecular and single-atom catalysts integrated within MIS photoelectrodes. Furthermore, a systematic summary of carrier transfer mechanisms and interface design principles of MIS photoelectrodes is presented, which are pivotal for optimizing energy band alignment and enhancing solar-to-chemical conversion efficiency within the PEC system. Finally, this review explores innovative derivative configurations of MIS photoelectrodes, including back-illuminated MIS photoelectrodes, inverted MIS photoelectrodes, tandem MIS photoelectrodes, and monolithically integrated wireless MIS photoelectrodes. These novel architectures address the limitations of traditional MIS structures by effectively coupling different functional modules, minimizing optical and ohmic losses, and mitigating recombination losses.

Crystalline Olefin-Linked Chiral Covalent Organic Frameworks as a Platform for Asymmetric Catalysis.

The construction of olefin-linked chiral covalent organic frameworks (COFs) with high crystallinity is highly desirable while remains great challenge due to the poor reversibility of the formation reaction for the olefin linkages during the in situ structural self-healing process. Herein, we successfully synthesized two sets of enantiomeric olefin-linked COFs. The chiral catalytic groups are uniformly distributed on the pore walls of COFs, resulting in the full exposure of catalytic sites to the reactants in asymmetric catalysis. The as-prepared (R)/(S)-CCOF8 exhibits excellent catalytic performance with exceeding 99 % enantiomeric excess in the enantioselective electrophilic amination reaction. Moreover, the heterogeneous chiral catalysts are conveniently recycled and could maintain the performance after ten catalytic cycles. Our findings expand the scope to construct stable and crystalline chiral COFs for the asymmetric catalysis.

Modulating Skeletons of Covalent Organic Framework for High-Efficiency Gold Recovery.

Covalent organic frameworks (COFs) have attracted considerable attention as adsorbents for capturing and separating gold from electronic wastes. To enhance the binding capture efficiency, constructing hydrogen-bond nanotraps along the pore walls was one of the most widely adopted approaches. However, the development of absorbing skeletons was ignored due to the weak binding ability of the gold salts (Au). Herein, we demonstrated skeleton engineering to construct highly efficiently absorbs for Au capture. The strong electronic donating feature of diarylamine units enhanced the electronic density of binding sites (imine-linkage) and thus resulted in high capacities over 1750 mg g-1 for all three COFs. Moreover, the absorbing performance was further improved via the ionization of diarylamine units. The ionic COF achieved 90 % of the maximal adsorption capacity, 1.63 times of that from the charge-neutral COF within ten minutes, and showed remarkable uptakes of 1834 mg g-1 , exceptional selectivity (97.45 %) and cycling stability. The theoretical calculation revealed the binding sites altering from imine bonds to ionic amine sites after ionization of the frameworks, which enabled to bind the AuCl4 - via coulomb force and contributed to enhanced absorbing kinetics. This work inspires us to design molecular/ionic capture based on COFs.

Mesoporous Vinylene-Linked Covalent Organic Frameworks with Heteroatom-Tuned Crystallinity and Photocatalytic Behaviors.

Owing to its prominent π-delocalization and stability, vinylene linkage holds great merits in the construction of covalent organic frameworks (COFs) with promising semiconducting properties. However, carbon-carbon double bond formation reaction always exhibits relatively low reversibility, unfavorable for the formation of high crystalline frameworks through self-error correction and assembling processes. In this work, we report a heteroatom-tuned strategy to build up a series of two-dimensional (2D) vinylene-linked COFs by Knoevenagel condensation of an electron-deficient methylthiazolyl-based monomer with different triformyl substituted (hetero-)aromatic derivatives. The resulting COFs show high-quality periodic mesoporous structures with high surface areas. Embedding heteroatoms into the backbones enables significantly improving their crystallinity, and finely tailoring their semiconducting structures. Upon visible light stimulation, one of the as-prepared COFs with donor-π-acceptor structure could deliver a nearly seven-fold increase in the catalytic activity of hydrogen generation as compared with the other two. Meanwhile, in combination with high crystallinity and the matched conduction band energy level, such kind of COFs can be able to selectively generate singlet oxygen and superoxide radicals in a high ratio of up to 30:1, allowing for catalyzing aerobic thioanisole oxidation in distinctly tunable activities through the substituent electronic effect of the substrates.

Hexatopic Vertex-Directed Approach to Vinylene-Linked Covalent Organic Frameworks with Heteroporous Topologies.

A D3h-symmetric hexatopic monomer was first prepared by attaching the three-fold ditopic moiety 2,6-dimethylpyridine to the meta-positions of a phenyl ring. It was further condensed at its six pyridylmethyl carbons with linear ditopic aromatic dialdehydes, resulting in two vinylene-linked COFs with heteroporous topologies, as revealed by powder X-ray diffraction (PXRD), nitrogen sorption, and pore-size distribution analyses, as well as transmission electron microscopy (TEM) image. The linear- and cross-conjugations, respectively, arising from the 2,6-linked pyridines and meta-linked phenylenes in the hexatopic nodes rendered the resultant COFs with well-patterned π-delocalization, allowing for efficiently catalyzing the bromination of aromatic derivatives with the pore-size-dependent conversion yields and regioselectivity under the irradiation of green light.

Synthesis of Vinylene-Linked Covalent Organic Frameworks by Monomer Self-Catalyzed Activation of Knoevenagel Condensation.

Reticular chemistry based on thermodynamically controlled linking modes and numerous organic building blocks has constituted versatile crystalline frameworks in molecular-level precision. However, vinylene-linked covalent organic frameworks (COFs) are still quite far from flexible tailoring in either their structures or topologies, due to the lack of monomers with sufficient activities. Herein, we establish a strategy to synthesize vinylene-linked COFs via Knoevenagel condensation between a tetratopic monomer 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP) and linear aromatic dialdehydes in a mixed solvent of benzoic anhydride and benzoic acid. Mechanistic investigation suggests that the condensation was promoted by a pyridine self-catalyzed benzoylation upon the cleavage of benzoic anhydride solvent molecules. The layered structures of the resultant COFs are highly crystallized into orthorhombic lattices with vertically aligned AA stacking modes, delivering high surface areas up to 1560 m2 g-1. The π-extended conjugated skeletons comprising para-bipyridyl units and vinylene linkages endow these COFs with substantial semiconducting properties, releasing visible-light-stimulated catalytic activity in water-splitting hydrogen evolution with a rate as high as 3230 µmol g-1 h-1.

Heteroatom-Embedded Approach to Vinylene-Linked Covalent Organic Frameworks with Isoelectronic Structures for Photoredox Catalysis.

Embedding heteroatoms into the main backbones of polymeric materials has become an efficient tool for tailoring their structures and improving their properties. However, owing to comparatively harsh heteroatom-doping conditions, this has rarely been explored in covalent organic frameworks (COFs). Herein, upon aldol condensation of a trimethyl-substituted pyrylium salt with a tritopic aromatic aldehyde, a two-dimensional oxonium-embedded COF with vinylene linkages was achieved, which was further converted to a neutral pyridine-cored COF by in situ replacement of oxonium ions with nitrogen atoms under ammonia treatment. The two heteroatom-embedded COFs are conceptually isoelectronic with each other, featuring similar geometric structures but different electronic structures, rendering them capable of catalyzing the visible-light-promoted multi-component synthesis of tri-substituted pyridine derivatives with good recyclability.

2,4,6-Trimethylpyridine-Derived Vinylene-Linked Covalent Organic Frameworks for Confined Catalytic Esterification.

Knoevenagel condensation is a powerful tool for the construction of vinylene-linked covalent organic frameworks. Herein, we established a concise approach to vinylene-linked COFs by Knoevenagel condensation at the multi-methyl groups of a pyridine ring through in situ formation of an N-acyl pyridinium cation in the presence of various acylating reagents. Following this strategy, two vinylene-linked COFs were constructed using 2,4,6-trimethylpyridine and multi-aldehyde-substituted aromatic derivatives as monomers. The resultant COFs are highly crystalline and assembled into hexagonal lattices with specific surface areas as large as 1915 m2 g-1 (vs. 1972 m2 g-1 of the theoretical value). The stable and abundant pyridine-decorated regular nanochannels within the COFs allow for catalyzing the esterification of several pharmaceutical intermediates with distinct spatially confined selectivity and recyclability, representing an environmentally friendly catalytic organic transformation.

Synthesis of Ionic Vinylene-Linked Covalent Organic Frameworks through Quaternization-Activated Knoevenagel Condensation.

We developed a simple approach to synthesizing ionic vinylene-linked two-dimensional covalent organic frameworks (COFs) through a quaternization-promoted Knoevenagel condensation at three aromatic methyl carbon atoms of N-ethyl-2,4,6-trimethylpyridinium halide with multitopic aromatic aldehyde derivatives. The resultant COFs exhibited a honeycomb-like structure with high crystallinity and surface areas as large as 1343 m2 g-1 . The regular shape-persistent nanochannels and the positively charged polymeric frameworks allowed the COFs to be uniformly composited with linear polyethylene oxide and lithium salt, displaying ionic conductivity as high as 2.72×10-3  S cm-1 .

Vinylene-Bridged Two-Dimensional Covalent Organic Frameworks via Knoevenagel Condensation of Tricyanomesitylene.

Vinylene-bridged covalent organic frameworks (COFs) have shown great potential for advanced applications because of their high chemical stability and intriguing semiconducting properties. Exploring new functional monomers available for the reticulation of vinylene-bridged COFs and establishing effective reaction conditions are extremely desired for enlarging the realm of this kind of material. In this work, a series of vinylene-bridged two-dimensional (2D) COFs are synthesized by Knoevenagel condensation of tricyanomesitylene with ditopic or tritopic aromatic aldehydes. With use of appropriate secondary amines as catalysts, high-crystalline vinylene-bridged COFs were achieved, exhibiting long-range ordered structures, well-defined nanochannels, high surface areas (up to 1231 m2 g-1), and excellent photophysical properties. Under a low loading amount and short reaction time, they enable aerobic photocatalytic transformation of arylboronic acids to phenols with high efficiency and excellent recyclability. This work demonstrates a new functional monomer, tricyanomesitylene, feasible for the general synthesis of vinylene-bridged COFs with potential application in photocatalytic organic transformation, which instigates further research on such kind of material.

Intranasal Vaccination With Multiple Virulence Factors Promotes Mucosal Clearance of Streptococcus suis Across Serotypes and Protects Against Meningitis in Mice.

BACKGROUND: Streptococcus suis is an emerging zoonotic agent. Its natural habitat is the tonsils, which are the main portals of S. suis entry into the bloodstream of pigs. The remarkable variability of the bacteria and complex pathogenic mechanisms make the development of a vaccine a difficult task. METHOD: Five conserved virulence factors involved in critical events of S. suis pathogenesis were combined and used as an intranasal vaccine (V5). The effect of V5 was investigated with intranasal and systemic challenge models. RESULTS: V5 induced antibody and T-cell responses at the mucosal site and systemically. The immunity promoted clearance of S. suis from the nasopharynx independent of S. suis serotypes and reduced lethality after systemic challenge with S. suis serotype 2. Moreover, mice that survived sepsis from intravenous infection developed meningitis, whereas none of these mice showed neuropathological symptoms after V5 receipt. CONCLUSION: Intranasal immunization with multiple conserved virulence factors decreases S. suis colonization at the nasopharynx across serotypes and inhibits the dissemination of the bacteria in the host. The protective mucosal immunity effects would potentially reduce the S. suis reservoir and prevent S. suis disease in pigs.

Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity.

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D3h -symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C54 N6 -COF) via Knoevenagel condensation with another D3h -symmetric monomer 2,4,6-tris(4'-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C2v -symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C52 N6 -COF). The octupolar conjugated characters of g-C54 N6 -COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C52 N6 -COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C54 N6 -COF enabled the two-half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 µmol h-1 g-1 and H2 evolution rate of 2518.9 µmol h-1 g-1 . Such values are among the highest of state-of-the-art COF photocatalysts.

Semiconducting 2D Triazine-Cored Covalent Organic Frameworks with Unsubstituted Olefin Linkages.

Establishing an sp2-carbon-bonding pattern is one of the efficient accesses to various organic semiconducting materials. However, the less-reversible carbon-carbon bond formation makes it still challenging to spatially construct a well-defined organic framework with π-extended two-dimensional (2D) structure through solution process. Here, a Knoevenagel condensation approach to synthesize two new 2D covalent organic frameworks (COFs) connected by unsubstituted carbon-carbon double bond linkages through activating the methyl carbons of a 2,4,6-trimethyl-1,3,5-triazine monomer is presented. The resulting sp2-carbon-linked triazine-cored 2D sheets are vertically stacked into high-crystalline honeycomb-like structures, endowing this kind of COF with extended π-delocalization, tunable energy levels, as well as high surface areas, regular open channels, and chemical stabilities. On the other hand, their microfibrillar morphologies allow for the facile manipulation of thin films as photoelectrodes without additive. Accordingly, such kinds of COF-based photoelectrodes exhibit photocurrents up to ∼45 µA cm-2 at 0.2 V vs RHE as well as rapid charge transfer rates, in comparison with imine-linked COF-based photoelectrodes. In addition, both COFs are applicable for conducting photocatalytic hydrogen generation from water splitting by visible-light irradiation.

An Olefin-Linked Covalent Organic Framework as a Flexible Thin-Film Electrode for a High-Performance Micro-Supercapacitor.

Developing effective synthetic strategies as well as enriching functionalities for sp2 -carbon-linked covalent organic frameworks (COFs) still remains a challenge. Now, taking advantage of a variant of Knoevenagel condensation, a new fully conjugated COF (g-C34 N6 -COF) linked by unsubstituted C=C bonds was synthesized. Integrating 3,5-dicyano-2,4,6-trimethylpyridine and 1,3,5-triazine units into the molecular framework leads to the enhanced π-electron communication and electrochemical activity. This COF shows uniform nanofibrous morphology. By assembling it with carbon nanotubes, a flexible thin-film electrode for a micro-supercapacitor (MSC) can be easily obtained. The resultant COF-based MSC shows an areal capacitance of up to 15.2 mF cm-2 , a high energy density of up to 7.3 mWh cm-3 , and remarkable rate capability. These values are among the highest for state-of-the-art MSCs. Moreover, this device exhibits excellent flexibility and integration capability.

Asymmetric Boron-Cored Aggregation-Induced Emission Luminogen with Multiple Functions Synthesized through Stepwise Conversion from a Symmetric Ligand.

Multifunction luminogens have emerged as promising candidates in high-performance sensor and imaging systems. Concise approaches to the synthesis of such molecules are urgently required both for fundamental research and technological applications. In this study, a new symmetric ligand of di(2-hydroxyphenyl)phthalazine with multiple binding sites around a phthalazine unit was readily synthesized, which could be converted efficiently into an asymmetric luminogen (OBN-DHPP) through the formation of oxygen-boron-nitrogen bonding. This molecule has a twistable π-extended backbone with a tetracoordinated boron core bearing two bulky phenyl groups, giving it abundant optical properties including a large Stokes shift piezochromism and aggregation-induced emission enhancement. Importantly, the presence of a free phenolic hydroxyl group in the backbone of OBN-DHPP enables the incorporation of various functional moieties into the asymmetric luminogen. As an example, polyethylene glycol (PEG)-modified luminogen (OBN-DHPP-PEG45) was synthesized. In the aqueous medium, OBN-DHPP-PEG45 could self-assemble into spherical nanoparticles with low cytotoxicity and excellent emission performance as well as high solubility. The results of flow cytometry and fluorescence microscopy reveal that these nanoparticles could be internalized successfully by HeLa cells, demonstrating their potential application in bioimaging.

Toll-like Receptors 2 and 4-Mediated Reciprocal Th17 and Antibody Responses to Group A Streptococcus Infection.

Background: The role of Toll-like receptors (TLRs) in adaptive immunity is incompletely understood. Recurrent human infections by group A streptococcus (GAS) and associated autoimmune conditions suggest that the immunity to GAS is intricately regulated and that TLRs may be involved in the regulation. Methods: This study investigated adaptive mucosal immune responses to GAS in TLR2-/- and TLR4-/- mice with an intranasal infection model. Results: Flow cytometric analyses of nasal-associated lymphoid tissue (NALT) cells showed that robust T helper 17 (Th17) cell responses to GAS in wild-type (WT) mice were reduced in TLR2-/- mice by 50%. Conversely, antibody levels and follicular T and B cells in the germinal center of NALT were significantly higher in TLR2-/- than in WT mice. However, antibody response to soluble antigens coimmunized with GAS was similar in WT and TLR2-/- mice. Moreover, the adaptive clearance of GAS in TLR2-/- mice was as efficient as in WT mice, whereas it was significantly impaired in TLR4-/- mice in which antibody responses were significantly lower than in WT mice. Conclusions: Activation of TLR2 by GAS is responsible for massive Th17 activation and deficient antibody response, which may increase predisposition to GAS-related autoimmunity and reduce protection efficiency.

syn-BN-heteroacene cored conjugated oligomers with finely tuned blue-violet luminescent properties.

Initiated by the effective dibromination of syn-BN-heteroacenes, a series of BN-containing conjugated oligomers was successfully synthesized upon transition-metal-catalyzed cross coupling. Their electronic structures can be finely tailored through varying the fused backbone or terminal substituents, endowing them with tunable luminescent properties within blue-violet regions.

3D Crown Ether Covalent Organic Framework as Interphase Layer toward High-Performance Lithium Metal Batteries.

The practical application of lithium (Li) metal batteries is inhibited by accumulative Li dendrites and continuous active Li consumption during cycling, which results in a low Coulombic efficiency and short lifetime. Constructing artificial solid-electrolyte interphase (SEI) layer in Li anode, such as 2D covalent organic frameworks (COFs), is an effective strategy to restrain the formation of Li dendrites and improve cycling performance. However, the exploration of 3D COFs as protecting layers is rarely reported, because of the preconception that the interconnect pores in 3D COFs eventually cause Li dendrites in disordered direction. 3D crown ether-based COF with ffc topology as interphase layer, in which the crown ether units are arranged in parallel and vertical orientation along the electrode, is demonstrated. The strong coupling effect between the crown ether and Li+ accelerates Li+ diffusion kinetics and enables homogeneous Li+ flux, resulting in a high Li+ transference number of 0.85 and smooth Li deposition in 3D direction. Li/COF-Cu cells display a lower Li-nucleation overpotential (17.4 mV) and high average Coulombic efficiency of ≈98.6% during 340 cycles with COF incorporation. This work gives a new insight into designing COFs for energy storage systems.

3D network with channel excitation and knowledge distillation for action recognition.

Modern action recognition techniques frequently employ two networks: the spatial stream, which accepts input from RGB frames, and the temporal stream, which accepts input from optical flow. Recent researches use 3D convolutional neural networks that employ spatiotemporal filters on both streams. Although mixing flow with RGB enhances performance, correct optical flow computation is expensive and adds delay to action recognition. In this study, we present a method for training a 3D CNN using RGB frames that replicates the motion stream and, as a result, does not require flow calculation during testing. To begin, in contrast to the SE block, we suggest a channel excitation module (CE module). Experiments have shown that the CE module can improve the feature extraction capabilities of a 3D network and that the effect is superior to the SE block. Second, for action recognition training, we adopt a linear mix of loss based on knowledge distillation and standard cross-entropy loss to effectively leverage appearance and motion information. The Intensified Motion RGB Stream is the stream trained with this combined loss (IMRS). IMRS surpasses RGB or Flow as a single stream; for example, HMDB51 achieves 73.5% accuracy, while RGB and Flow streams score 65.6% and 69.1% accuracy, respectively. Extensive experiments confirm the effectiveness of our proposed method. The comparison with other models proves that our model has good competitiveness in behavior recognition.

Fusogenic metallosupramolecular brush vesicles.

The electrostatic combination of a cationic metallosupramolecular polyelectrolyte (Fe-MSP) with sulfonate-terminated polymers leads to the formation of metallosupramolecular brushes (MSBs). The resulting MSBs can self-assemble into vesicular structures in chloroform/methanol (v/v = 1:1) mixture solvents. The rigid-rod Fe-MSP chain has to bend for the formation of the vesicles, which accompanies the presence of a lateral tension and thus induces a spontaneous vesicle fusion with an hour-scale fusion time. For this much longer fusion process, the arrow-like protrusion, stalk-like intermediate, and hemifusion diaphragm are clearly observed by transmission electron microscopy. The complete fusion into larger vesicles significantly releases the lateral tension.