Crystalline Covalent Organic Frameworks with Tailored Linkages for Photocatalytic H2 Evolution

Visible light-driven triazine-based S-scheme COF-TpTt@BiOBr heterojunction with oxygen vacancy for enhanced photocatalytic pollutants removal and hydrogen production

S-scheme heterojunction is an effective tactic to improve photocatalytic property. But few studies on constructing heterojunction with BiOBr and covalent organic frameworks (COFs) are available. Herein, a novel series of COF-TpTt@BiOBr S-scheme heterojunctions with oxygen vacancies (OVs) were constructed via solvothermal method. COF-TpTt@BiOBr-10% showed enhanced photocatalytic performance under visible light. Pollutants (such as Methyl Orange (MO), methylene blue (MB), Rhodamine B (RhB), tetracycline (TC) and Levofloxacin hydrochloride (LEV)) can be efficiently degraded and the photocatalytic H2 generation rate reached 10828.075 μmol g-1 h-1, which was 12.4 and 8.5 times of COF-TpTt and BiOBr. In addition, 3,3',5,5'-tetramethylbenzidine (TMB) oxidation experiment showed it has excellent molecular oxygen activation capacity. Furthermore, the S-scheme heterojunction charge transfer mechanism was proved by density functional theory (DFT) calculations. Under the influence of internal electric field, energy band bending and Coulomb force, e- and h+ were efficiently separated and transferred. The formation of S-scheme heterojunction and generation of multiple free radicals assured the high redox activity of COF-TpTt@BiOBr-10% photocatalytic system. This study strengthened our deep understanding of S-scheme heterojunction charge transfer mechanism and offered a new way for high efficient hydrogen energy production.

Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Evolution

Covalent organic frameworks (COFs) are considered advanced class materials due to their exotic structural and optical properties. The abundance of starting monomers with variable linkage motifs may give rise to multiple conformations in either 2D or 3D fashion. Tailoring of the abovementioned properties has facilitated the application of COFs in a wide range of applications, which are strongly correlated with energy conversion schemes. Having a crystalline porous character and a large set of donor-acceptor combinations, COFs are expected to make huge impact in photocatalytic processes. In this Review, we present the recent advances in the development of semiconducting COF-based systems towards the photocatalytic hydrogen peroxide evolution. An overview is given about the effect of various parameters on the photocatalytic performance, such as charge transfer tuning, wettability by chemical functionalization, topology, porosity and crystallinity. Various challenges are discussed, and constructive insights are given for the development of highly functional COF-based photocatalysts for H2O2 evolution.

Fluorination-mediated polarization engineering in block copolymers for enhanced photocatalytic hydrogen evolution

Porous polymers have emerged as promising candidates for photocatalytic hydrogen evolution, but their structural rigidity and crosslinking pose significant challenges, often leading to charge recombination and inadequate water/polymer interfaces. This study introduces novel block copolymers (BCPs) comprising a rigid pyrene core and various fluorinated benzene structures coupled with flexible diethyl ether-based hydrophilic units. By computationally predicting monomer structures and dipoles, the relationship between structure and function in these BCPs is examined, particularly focusing on local charge delocalization. Four fluorinated block copolymers (F-BCPs), sharing identical π-conjugated skeletons but differing in the positions and quantities of fluorine atoms on the benzene rings, are explored. Experimental and theoretical analyses reveal that fine-tuning fluorination induces local charge polarization and delocalization. Notably, Py-DE-2F, with fluorination at two ortho positions on benzene, exhibits a remarkable hydrogen evolution rate of 77.68 μmol/h under visible light (λ > 420 nm) without any co-catalyst, surpassing other F-BCPs by an order of magnitude. These results underscore the potential of utilizing fluorination-mediated polarization engineering for developing advanced metal-free polymer photocatalysts.

A superlattice interface and S-scheme heterojunction for ultrafast charge separation and transfer in photocatalytic H2 evolution

The rapid recombination of photoinduced charge carriers in semiconductors fundamentally limits their application in photocatalysis. Herein, we report that a superlattice interface and S-scheme heterojunction based on Mn0.5Cd0.5S nanorods can significantly promote ultrafast charge separation and transfer. Specifically, the axially distributed zinc blende/wurtzite superlattice interfaces in Mn0.5Cd0.5S nanorods can redistribute photoinduced charge carriers more effectively when boosted by homogeneous internal electric fields and promotes bulk separation. Accordingly, S-scheme heterojunctions between the Mn0.5Cd0.5S nanorods and MnWO4 nanoparticles can further accelerate the surface separation of charge carriers via a heterogeneous internal electric field. Subsequent capture of the photoelectrons by adsorbed H2O is as fast as several picoseconds which results in a photocatalytic H2 evolution rate of 54.4 mmol·g-1·h-1 without any cocatalyst under simulated solar irradiation. The yields are increased by a factor of ~5 times relative to control samples and an apparent quantum efficiency of 63.1% at 420 nm is measured. This work provides a protocol for designing synergistic interface structure for efficient photocatalysis.

Visible light to the second near-infrared light-harvesting donor-acceptor1-donor-acceptor2-type terpolymers for boosted photocatalytic hydrogen evolution via dual-sulfone-acceptor engineering

Developing visible to near-infrared light-absorbing conjugated polymer photocatalysts is crucial for enhancing solar energy utilization efficiency, as most conjugated organic polymers only absorb light in the visible range. In this work, we firstly developed a novel thiophene S,S-dioxide (TDO) monomer with the stronger electron-withdrawing character, and then prepared a series of donor-acceptor1-donor-acceptor2-type (D-A1-D-A2-type) conjugated terpolymers (THTDB-1-THTDB-5) by statistically adjusting the molar ratio of two sulfone-based acceptor monomers, dibenzothiophene-S,S-dioxide (BTDO, A1) and TDO (A2). These terpolymers demonstrate a gradually expanding absorption range from visible light to the second near-infrared (Vis-to-NIR-II) region with the gradual increase of the TDO contents in the polymer skeleton, showcasing excellent absorption properties and efficient light-capturing capabilities. The optimized D-A1-D-A2 polymer photocatalyst THTDB-4 exhibits a high hydrogen evolution rate of 21.27 mmol g-1 h-1 under visible light without any co-catalyst. The dual-sulfone-acceptor engineering offers a viable approach for developing efficient the longer Vis-to-NIR-II light-harvesting polymer photocatalysts.

Modulating β-Keto-enamine-Based Covalent Organic Frameworks for Photocatalytic Atom-Transfer Radical Addition Reaction

The atom-transfer radical addition (ATRA) reaction simultaneously forges carbon-carbon and carbon-halogen bonds. However, frequently-used photosensitizers such as precious transition metal complexes, or organic dyes have limitations in terms of their potential toxicity and recyclability. Three β-ketoenamine-linked covalent organic frameworks (COFs) from 1,3,5-triformylphloroglucinol and 1,4-phenylenediamines with variable transient photocurrent and photocatalytic activity have been prepared. A COF bearing electron-deficient Cl atoms displayed the highest photocatalytic activity toward the ATRA reaction of polyhalogenated alkanes to give halogenated olefins under visible light at room temperature. This heterogeneous photocatalyst exhibited good functional group tolerance and could be recycled without significant loss of activity.

Expanding Olefin-Linked Covalent Organic Frameworks toward Selective Photocatalytic Oxidation of Organic Sulfides

Olefin-linked covalent organic frameworks (COFs) have exhibited great potential in visible-light photocatalysis. In principle, expanding fully conjugated COFs can facilitate light absorption and charge transfer, leading to improved photocatalysis. Herein, three olefin-linked COFs with the same topology are synthesized by combining 2,4,6-trimethyl-1,3,5-triazine (TMT) with 1,3,5-triformylbenzene (TFB), 1,3,5-tris(4-formylphenyl)benzene (TFPB), and 1,3,5-tris(4-formylphenylethynyl)benzene (TFPEB), namely, TMT-TFB-COF, TMT-TFPB-COF, and TMT-TFPEB-COF, respectively. From TMT-TFB-COF to TMT-TFPB-COF, expanding phenyl rings provides only limited expansion for π-conjugation due to the steric effect of structural twisting. However, from TMT-TFPB-COF to TMT-TFPEB-COF, the insertion of acetylenes eliminates the steric effect and provides more delocalized π-electrons. As such, TMT-TFPEB-COF exhibits the best optoelectronic properties among these three olefin-linked COFs. Consequently, the photocatalytic performance of TMT-TFPEB-COF is much better than those of TMT-TFB-COF and TMT-TFPB-COF on the oxidation of organic sulfides into sulfoxides with oxygen. The desirable reusability and substrate compatibility of the TMT-TFPEB-COF photocatalyst are further confirmed. The selective formation of organic sulfoxides over TMT-TFPEB-COF under blue light irradiation proceeds via both electron- and energy-transfer pathways. This work highlights a rational design of expanding the π-conjugation of fully conjugated COFs toward selective visible-light photocatalysis.

Fully Conjugated 2D sp2 Carbon-Linked Covalent Organic Frameworks for Photocatalytic Overall Water Splitting

Covalent organic frameworks (COFs) hold great promise for solar-driven hydrogen production. However, metal-free COFs for photocatalytic overall water splitting remain elusive, primarily due to challenges in simultaneously regulating their band structures and catalytic sites to enable concurrent half-reactions. Herein, two types of π-conjugated COFs containing the same donor-acceptor structure are constructed via Knoevenagel condensation and Schiff base reaction to afford cyanovinylene- and imine-bridged COFs, respectively. The difference in the linkage leads to a remarkable difference in their photocatalytic activity toward water splitting. The 2D sp2 carbon-linked COF exhibits notable activity for photocatalytic overall water splitting, which can reach an apparent quantum efficiency of 2.53% at 420 nm. In contrast, the 2D imine-linked COF cannot catalyze the overall water-splitting reaction. Mechanistic investigations reveal that the cyanovinylene linkage is essential in modulating the band structure and promoting charge separation in COFs, thereby enabling overall water splitting. Moreover, it is further shown that crystallinity substantially impacts the photocatalytic performance of COFs. This study represents the first successful example of developing metal-free COFs with high crystallinity for photocatalytic overall water splitting.

Covalent Organic Frameworks: Cutting-Edge Materials for Carbon Dioxide Capture and Water Harvesting from Air

The implacable rise of carbon dioxide (CO2 ) concentration in the atmosphere and acute water stress are one of the central challenges of our time. Present-day chemistry is strongly inclined towards more sustainable solutions. Covalent organic frameworks (COFs), attributable to their structural designability with atomic precision, functionalizable chemical environment and robust extended architectures, have demonstrated promising performances in CO2 trapping and water harvesting from air. In this Review, we discuss the major developments in this field as well as sketch out the opportunities and shortcomings that remain over large-scale COF synthesis, device engineering, and long-term performance in real environments.

Rational Design of Vinylene-Linked Covalent Organic Frameworks for Modulating Photocatalytic H2 Evolution

Vinylene-linked covalent organic frameworks (COFs) have attracted enormous attention for photocatalytic H2 evolution from water because of their fully conjugated structures, high chemical stabilities, and enhanced charge-carrier mobilities. In this work, two novel vinylene-linked COFs with tuned cyano contents were successfully synthesized and then employed as photocatalysts for H2 generation. Notably, the photocatalytic H2 production rate of the COF with the higher cyano content reached 73 μmol h-1 under visible light irradiation, which is 2.4 times higher than that with the lower content (30 μmol h-1 ). Both the experimental and computational results demonstrated that the rational design incorporating cyano groups into COF skeletons could precisely tune the corresponding energy levels, expand the visible-light absorption, and improve the photoinduced charge separation. This work not only provides a simple method for modulating the photocatalytic activities of COFs at the molecular level, but also affords interesting insights into the relationship between their structures and photocatalytic performance.

Recent advances in glucose-oxidase-based nanocomposites for diabetes diagnosis and treatment

Glucose oxidase (GOx) has attracted a lot of attention in the field of diabetes diagnosis and treatment in recent years owing to its inherent biocompatibility and glucose-specific catalysis. GOx can effectively catalyze the oxidation of glucose in the blood to hydrogen peroxide (H2O2) and glucuronic acid and can be used as a sensitive element in biosensors to detect blood glucose concentrations. Nanomaterials based on the immobilization of GOx can significantly improve the performance of glucose sensors through, for example, reduced electron tunneling distance. Moreover, various insulin-loaded nanomaterials (e.g., metal-organic backbones, and mesoporous silica nanoparticles) have been developed for the control of blood glucose concentrations based on GOx catalytic chemistry. These nano-delivery carriers are capable of releasing insulin in response to GOx-mediated changes in the microenvironment, allowing for a rapid return of the blood microenvironment to a normal state. Therefore, glucose biosensors and insulin delivery vehicles immobilized with GOx are important tools for the diagnosis and treatment of diabetes. This paper reviews the characteristics of various GOx-based nanomaterials developed for glucose biosensing and insulin-responsive release as well as research progress, and also highlights the current challenges and opportunities facing this field.

The Keto-Switched Photocatalysis of Reconstructed Covalent Organic Frameworks for Efficient Hydrogen Evolution

The keto-switched photocatalysis of covalent organic frameworks (COFs) for efficient H2 evolution was reported for the first time by engineering, at a molecular level, the local structure and component of the skeletal building blocks. A series of imine-linked BT-COFs were synthesized by the Schiff-base reaction of 1, 3, 5-benzenetrialdehyde with diamines to demonstrate the structural reconstruction of enol to keto configurations by alkaline catalysis. The keto groups of the skeletal building blocks served as active injectors, where hot π-electrons were provided to Pt nanoparticles (NPs) across a polyvinylpyrrolidone (PVP) insulting layer. The characterization results, together with density functional theory calculations, indicated clearly that the formation of keto-injectors not only made the conduction band level more negative, but also led to an inhomogeneous charge distribution in the donor-acceptor molecular building blocks to form a strong intramolecular built-in electric field. As a result, visible-light photocatalysis of TP-COFs-1 with one keto group in the skeletal building blocks was successfully enabled and achieved an impressive H2 evolution rate as high as 0.96 mmol g-1  h-1 . Also, the photocatalytic H2 evolution rates of the reconstructed BT-COFs-2 and -3 with two and three keto-injectors were significantly enhanced by alkaline post-treatment.

Zwitterionic and Hydrophilic Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution

Developing effective synthetic strategies as well as broadening functionalities for zwitterionic materials that comprise moieties with equimolar cationic and anionic groups still remains a huge challenge. Herein, we develop two zwitterionic vinylene-linked covalent organic frameworks (Zi-VCOF-1 and Zi-VCOF-2) that are a type of novel hydrophilic material. Zi-VCOF-1 and Zi-VCOF-2 are obtained directly through the convenient Knoevenagel condensation of new sulfonic-pyridinium zwitterionic monomers with aromatic aldehyde derivatives. This is the first report on zwitterionic COFs being constructed by the bottom-up functionalization approach from predesigned zwitterionic monomers. Both Zi-VCOFs exhibit a high photocatalytic hydrogen evolution rate (HER) because of their appropriate optical property and outstanding hydrophilicity. Specifically, Zi-VCOF-1 and Zi-VCOF-2 show photocatalytic HER of 13,547 and 5057 μmol h-1 g-1, respectively. Interestingly, the photocatalytic HER of Zi-VCOF-1 is about 2.68 times of that of Zi-VCOF-2, although they differ by only one methyl group in sulfonic-pyridinium zwitterionic pairs. The photocatalytic HER of Zi-VCOF-1 is not only the highest in the vinylene-linked COFs but also outstanding among the most reported COFs. This is the first application of zwitterionic COFs for photocatalytic hydrogen evolution, which would open a new frontier in zwitterionic COFs and be helpful for the design of other photocatalytic materials.

Thiadiazole-Derived Covalent Organic Framework Macroscopic Ultralight Aerogel

Shaping covalent organic frameworks (COFs) into macroscopic objects for practical application remains a huge challenge. Herein, a new thiadiazole-derived COF macroscopic ultralight aerogel (NNS-VCOF) was prepared through acid-catalyzed aldol condensation between 2,5-dimethyl-1,3,4-thiadiazole and a tritopic aromatic aldehyde derivative. NNS-VCOF aerogel shows extremely low density (ca. 0.020 g cm^-3), excellent mechanical properties (compression modulus of 16.65 kPa), thermal insulation properties (low thermal conductivity of 0.03270 W m^-1 K^-1 at 25 °C), and flame retardancy (quickly self-extinguishing after ignition) due to its three-dimensional sponge-like architecture and special nitrogen heterocyclic framework. To our delight, NNS-VCOF aerogel not only can be used as an outstanding macroscopic material but also shows efficient photocatalytic hydrogen evolution properties in a powder state because of the superhydrophilicity and appropriate optical properties.

Enhancing Photocatalytic Antibiotics Mineralization and Water Oxidation via Constructing Interfacial Electric Field in Plate-on-Plate BiOCl/WO3 Photocatalysts

Two-dimensional materials and related plate-on-plate interfacial heterostructures offer great flexibility for integrating different atomic layers, providing an attractive scheme for the construction of built-in electric fields in photocatalysts. Here, we developed an interfacial engineering strategy to construct well-interfaced plate-on-plate BiOCl/WO₃ heterojunctions for general enhanced photocatalytic oxidation reactions. BiOCl/WO₃ heterojunctions exhibited significant enhancements in oxygen evolution and antibiotic degradation, with a rate of 9.5 times and 14.7 times higher than that of WO₃. This enhancement is attributed to the well lattice matching contact surface of WO₃ {020} plane with BiOCl {001} plane, which integrates a strong built-in electric field induced by Bi-O chemically bonds, providing atomically fast transport channels for electrons. These findings offer new guidelines for designing interfacial structures for high-performance oxidative photocatalysts and provide insights into the underlying interfacial carrier transport mechanisms.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production

Photocatalytic water splitting into H₂ is the most economic and environmentally friendly strategy for H₂ production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H₂ production. The photocatalytic H₂ production performance of optimized COF/CN composites can reach up to 449.64 μmol·h^-1, which is approximately 5 times that of pure CN (89.08 μmol·h^-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e^--h⁺ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

Zn (II) Porphyrin Built-in D-A Covalent Organic Framework for Efficient Photocatalytic H2 Evolution

Covalent organic frameworks (COFs) with donor-acceptor (D-A) units are credible photocatalysts for their per-designed structure, inherent porosity, large surface area, splendid stability and so forth. Developing COFs with an excellent photocatalytic efficiency for hydrogen evolution is of a great significance in alleviating the energy crisis. Herein, a D-A type imine-linked crystalline Zn-Por-TT COF was fabricated successfully via the co-polymerization of electron-deficient Zinc (II) 5,10,15,20-tetrakis(para-aminophenyl) porphyrin (Zn-TAPP), and electron-rich thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT). Profiting from the D-A complex structure, the obtained Zn-Por-TT COF showcases an excellent photocatalytic activity with a hydrogen evolution rate of 8200 μmol/g/h, while the Zn-TAPP monomer presents practically no capacity for the generation of hydrogen under identical conditions. In addition, the counterparts Por-TT COF and COF-366-Zn were employed to illustrate the enhancement of the photocatalytic performance by metal catalytic sites and D-A structures. In addition, the counterparts Por-TT COF and COF-366-Zn were employed to illustrate the enhancement of metal catalytic sites and D-A structures for the photocatalytic performance.

Enzyme-Responsive COF-Based Thiol-Targeting Nanoinhibitor for Curing Bacterial Infections

Pathogen infections impose severe challenges in clinical practice, especially for patients infected with antibiotic-resistant microbes. The thioredoxin (Trx) system in Gram-positive bacteria serves as an ideal antimicrobial target for novel medicine design due to the structural differences from corresponding system in mammals. However, a backup thiol-dependent antioxidant glutathione (GSH) system limits the effectiveness of drugs in many Gram-negative bacteria. Herein, we synthesize a thiol-targeting nanoinhibitor based on an enzyme-responsive covalent organic framework (COF) coloaded with silver nanoparticles (AgNPs) and ebselen (EBS) (Ag-TA-CON@EBS@PEG) to exert synergistic antibacterial effects. Since azoreductase can dissociate the enzyme-responsive COF, we adopt this strategy to achieve the accurate release of EBS and Ag⁺ at infection sites. Our research identifies that the functionalized nanoinhibitor shows excellent bactericidal performance for Gram-positive and Gram-negative bacteria in vitro and exhibits low toxicity to normal cells. Besides, the nanoinhibitor presents favorable biocompatibility, anti-inflammatory property, and effective wound healing ability in mice. This paper provides a promising clinical strategy for synergistic antibacterial therapy and enhanced wound healing properties via an optimized combination of the targeted nanomedicines with an intelligent drug conveying platform.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

Photocatalytic Anaerobic Dehydrogenation of Alcohols over Metal Halide Perovskites: A New Acid-Free Scheme for H2 Production

Photocatalytic H₂ evolution from haloid acid (HX) solution by metal halide perovskites (MHPs) has been intensively investigated; however, the corrosive acid solution severely restricts its practical operability. Therefore, developing acid-free schemes for H₂ evolution using MHPs is highly desired. Here, we investigate the photocatalytic anaerobic dehydrogenation of alcohols over a series of MHPs (APbX₃, A = Cs⁺, CH₃NH₃⁺ (MA), CH(NH₂)₂⁺ (FA); X = Cl^-, Br^-, I^-) to simultaneously produce H₂ and aldehydes. Via the coassembly of Pt and rGO nanosheets on MAPbBr₃ microcrystals, the optimal MAPbBr₃/rGO-Pt reaches a H₂ evolution rate of 3150 μmol g^-1 h^-1 under visible light irradiation (780 nm ≥ λ ≥ 400 nm), which is more than 105-fold higher than pure MAPbBr₃ (30 μmol g^-1 h^-1). The present work not only brings new ample opportunities toward photocatalytic H₂ evolution but also opens up new avenues for more effective utilization of MHPs in photocatalysis.

Enhanced photocatalytic H2 evolution over covalent organic frameworks through an assembled NiS cocatalyst

Covalent organic frameworks (COFs) have been investigated in the field of photocatalysts for H₂ evolution because of their crystalline structure and diversity. However, most of them need the help of noble metals as co-catalysts to realize a high hydrogen evolution. Herein, we chose typical COFs as a platform and constructed NiSX-BD (X: weight fraction of NiS) composites by assembling NiS at room temperature. The NiS nanoparticles are shown to tightly adhere to the COFs surface. Under visible light irradiation (wavelength > 420 nm), the optimized sample with 3 wt% NiS loading exhibits a photocatalytic H₂ evolution rate of 38.4 μmol h⁻¹ (3840 μmol h⁻¹ g⁻¹), which is about 120 folds higher than that of the pure TpBD-COF and better than TpBD-COF/Pt with the same Pt loading (3 wt%). NiS3-BD shows stable hydrogen evolution in at least six consecutive cycle tests totaling 18 h. Further investigation reveals that the loaded NiS can facilitate the transfer of photogenerated electrons from TpBD-COF to the co-catalyst, leading to efficient and high photocatalytic activity. Combining the significant feature of COFs, this study opens up a feasible avenue to boost the photocatalytic H₂ performance by constructing the synergetic effects between COFs and cost-effective material.

We constructed a novel hybrid photocatalyst by assembling NiS through a milder method. Under visible light irradiation, controlled NiS/TpBD-COF composites can readily optimize photocatalytic performances without a noble cocatalyst.

Finding the Sweet Spot of Photocatalysis─A Case Study Using Bipyridine-Based CTFs

Covalent triazine frameworks (CTFs) are a class of porous organic polymers that continuously attract growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic framework structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far. Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows us to tailor the physicochemical features of the CTF materials, including the nitrogen content, the apparent specific surface area, and optoelectronic properties. Based on a comprehensive analytical investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as the specific surface area, band gap, charge separation, and surface wettability with water. The entirety of these parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER). The material with the optimal balance between optoelectronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol/(h·g) under visible light irradiation and in the presence of a platinum cocatalyst.

Molecular Dipole-Induced Photoredox Catalysis for Hydrogen Evolution over Self-Assembled Naphthalimide Nanoribbons

D-π-A type 4-((9-phenylcarbazol-3-yl)ethynyl)-N-dodecyl-1,8-naphthalimide (CZNI) with a large dipole moment of 8.49 D and A-π-A type bis[(4,4'-1,8-naphthalimide)-N-dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of a molecular dipole as the dominant mechanism for controlling charge separation of organic semiconductors. In aqueous solution, these two novel naphthalimides can self-assemble to form nanoribbons (NRs) that present significantly different traces of exciton dissociation dynamics. Upon photoexcitation of NINI-NRs, no charge-separated excitons (CSEs) are formed due to the large exciton binding energy, accordingly there is no hydrogen evolution. On the contrary, in the photoexcited CZNI-NRs, the initial bound Frenkel excitons are dissociated to long-lived CSEs after undergoing ultrafast charge transfer within ca. 1.25 ps and charge separation within less than 5.0 ps. Finally, these free electrons were injected into Pt co-catalysts for reducing protons to H₂ at a rate of ca. 417 μmol h^-1  g^-1 , correspondingly an apparent quantum efficiency of ca. 1.3 % can be achieved at 400 nm.

Simultaneous photocatalytic H2 generation and organic synthesis over crystalline-amorphous Pd nanocube decorated Cs3Bi2Br9

Cs3Bi2Br9 decorated with crystalline-amorphous Pd nanocubes as cocatalyst is reported to photocatalytically coproduce ca. 1400 μmol h−1 g−1 of H2 and benzaldehyde from the selective benzyl alcohol oxidation. This route...