The effect of enantioselective chiral covalent organic frameworks and cysteine sacrificial donors on photocatalytic hydrogen evolution

COF nanotubes/2D nanosheets heterojunction for superior photocatalytic bactericidal activity even at low concentration and weak light

Microbial fouling is a huge nuisance to equipment operation and human health. Two-dimensional (2D) photocatalytic materials such as g-C3N4, WSe2, and Ti3C2Tx, show immense potential for solar-driven eradication of microbial fouling. However, limited photon absorption and rapid photogenerated electron-hole recombination curtail their photocatalytic efficiency and availability, resulting in the necessity to operate at high concentration and strong light. Herein, three kinds of covalent organic frameworks (COF) nanotubes/2D nanosheets heterojunctions (COF-x) were flexibly constructed by in-situ growing COF nanotubes on g-C3N4, WSe2, and Ti3C2Tx nanosheet substrates via one-pot method. The internal electric field at the COF-x coupling interface enhanced the separation and migration of photogenerated charge pairs, contributing to the antimicrobial reactive oxygen species (ROS) produced by COF-x, which was 2.8-270 times more efficient than those of nanosheets. The bactericidal effect enhanced from 34.13 %∼41.68 % of pure nanosheets to over 99.86 % of COF-x at an ultra-low concentration of 2 µg/mL and a weak visible light of 15 mW/cm2. At a low concentration of 20 µg/mL, the bactericidal rate of COF-x achieved nearly 100 % within 6 h. COF-x also showed exceptional environmental stability and antimicrobial properties under heat, light, acid, alkali, and aqueous conditions, offering a new perspective in photocatalytic antimicrobial/antifouling.

Constructing asymmetric D'-A-D" imine covalent organic frameworks to optimize exciton effect and enhance photocatalytic reduction of U(VI)

Imine-based covalent organic frameworks (COFs) exhibit high exciton binding energies due to their weaker electronic delocalization. Herein, we report an asymmetric ternary imine COF (NCOF-3) bridged by D2 h and C2 h units, which is synthesized via an aldol-type condensation reaction mediated by amine monomers. Compared to symmetric NCOF-1 and NCOF-2, the asymmetric architecture of NCOF-3 maximizes interlayer interactions, leading to enhance crystallinity. Moreover, by incorporating two electron-donating units into the triazine framework, an asymmetric D'-A-D'' topological structure is formed, which facilitates the forward dissociation of photogenerated excitons, achieving a high carrier separation efficiency. Temperature-dependent fluorescence spectroscopy reveals that NCOF-3 possesses a smaller exciton binding energy (40.15 meV) compared to those of symmetric imine-based COFs. Under illumination conditions, NCOF-3 exhibits uranium removal capacity of 1084 mg g-1, significantly surpassing those of binary COFs containing imine bonds. Additionally, anti-interference experiments demonstrate that NCOF-3 maintains a uranium removal efficiency of over 90 % even in the presence of excess competing metal ions, confirming its high selectivity. Density functional theory (DFT) calculations indicate that lattice dipole asymmetry plays crucial roles in reducing the electronic bandgap of NCOF-3. This work highlights the importance of designing and fabricating imine-based COFs with dipole asymmetry of the connecting components to effectively manipulate the internal charge distribution, ultimately enhancing photocatalytic activity.

Homochiral versus Racemic 2D Covalent Organic Frameworks

The synthesis of homochiral two-dimensional covalent organic frameworks (2D COFs) from chiral π-conjugated building blocks is challenging, as chiral units often lead to misaligned stacking interactions. In this work, we introduce helical chirality into 2D COFs using configurationally stable enantiopure and racemic [5]helicenes as linkers in the backbone of 2D [5]HeliCOFs as powders and films. Through condensation with 1,3,5-triformylbenzene (TFB) or 1,3,5-triformylphloroglucinol (TFP), our approach enables the efficient formation of a set of homochiral and racemic 2D [5]HeliCOFs. The resulting carbon-based crystalline and porous frameworks exhibit distinct structural features and different properties between homochiral and racemic counterparts. Propagation of helical chirality into the backbone of the crystalline frameworks leads to the observation of advanced chiroptical properties in the far-red visible spectrum, along with a less compact structure compared with the racemic frameworks. Homogeneous thin films of [5]HeliCOFs disclosed photoluminescent properties arising from the controlled growth of highly ordered π-conjugated lattices. The present study offers insight into general chiral framework formation and extends the Liebisch-Wallach rule to 2D COFs.

Dual Modification of Metal-Organic Frameworks for Exceptional High Piezo-Photocatalytic Hydrogen Production

Metal-organic frameworks (MOFs) face significant challenges in photocatalysis due to severe carrier recombination. Here, a novel approach is presented that incorporates ─NH2 groups and Cu ions onto MOFs with a MIL-125 skeleton, forming NH2-MIL-125 and Cu-NH2-MIL-125. This modification effectively enhances the polarity of MOFs, evidenced by significantly increased d33 values (from 1.69 to 26.21 pm/V) and notable higher dipole moments (from 6.60 to 25.99 D). Notably, it's the first demonstration of boosting MOFs piezoelectricity via a dual modulation strategy. Moreover, the polarity can be further amplified by ultrasonic vibration based on the positive piezoelectric effect, which is justified by in situ Raman spectra, COMSOL simulations, and DFT calculations, by taking into account the applied pressure. The positive impact of introduced piezoelectric effect in facilitating charge separation and transfer of Cu-NH2-MIL-125, proved by enhanced current response. Consequently, through coupling piezocatalysis and photocatalysis, the H2 production rate of Cu-NH2-MIL-125 can be significantly enhanced to ≈2884.2 µmol·g-1·h-1, 2.76 and 9.92 times higher than that of NH2-MIL-125 and MIL-125, respectively, ranking first in all reported MOF-based piezo-photocatalysts. This research demonstrates the prospective opportunity for alleviating the severe carriers recombination problem for MOFs through the implantation of piezoelectric field driving force.

Bayesian Optimized Crystallization of a Hydroxamate-Functionalized Covalent Organic Framework for Enhanced Uranyl Uptake

To address the synthetic challenge of covalent organic frameworks (COFs), especially those with interfering functional groups, a Bayesian optimization (BO) centered approach is developed and implemented. Specifically, the crystallinity index for a well-known TAPB-PDA COF is improved by ≈80% via a one-round proof-of-concept BO. For a more complicated task toward the preparation of hydroxamate-functionalized TpPa COF, where improvement of both crystallinity and selectivity (against a crystalline byproduct) is needed, an efficient protocol comprising 6 BO iterations (with 5 experiments each) from an initial 64-experiment dataset is successfully developed. The functional COF, namely SUM-99 (SUM = Sichuan University Materials), with enhanced crystallinity, is subsequently demonstrated to be an effective, reversible, and selective sorbent for aquatic uranyl uptake. The importance of improved crystallinity, reflecting the power of BO, is showcased by a 23.7% increase in uranyl adsorption capacity. Therefore, the BO protocol and toolkit is presented for the efficient evolution of COF synthetic conditions, toward higher crystallinity and enhanced performances for downstream applications.

Smartphone-Controlled Portable Photoelectrochemical Biosensor Exploiting Chirality-Resolved Ratiometric Sensing Strategy: A Proof of Concept

Integrating ratiometric photoelectrochemical (PEC) strategy with a smartphone-based portable biosensor to build a bioanalysis device is usually subject to large-volume space-resolved facilities and is picky about the polarity or excitation wavelength of the photoactive materials. Herein, a chirality-resolved ratiometric portable PEC biosensor on a platform rich in crystalline-amorphous interfaces addresses this issue. Concretely, the crystalline Bi2WO6 bulk phase/amorphous BiOBr surfaces with Bi2S3 nanoparticles attached (a-BWO-s) platform and the paired photoactive markers with specific chirality Fe3O4@Ag-l-(and d-)histidine are integrated on the portable biosensor. Since the crystalline-amorphous interfaces of a-BWO-s exhibit considerable photocurrent signals. In the meantime, with the increase of targeted analytes' NSE concentration, the PEC performance of the markers shows an opposite trend in different chiral electron donors. So that double photocurrent signals can be output to realize the ratiometric sensing strategy, which furnishes an innovative universal strategy for bioanalysis. Unlike the other typical ratiometric PEC sensing strategies, this research proposes the first ratiometric PEC biosensor based on diverse chiral chemical environments. Generally speaking, this paper provides direction for the design of a chirality-resolved ratiometric sensing strategy and brings a unique new perspective to explore in practical analysis.

Cyclic Trinuclear Units Based Covalent Metal-Organic Frameworks for Gold Recovery

The development of porous solids for gold recovery is highly desired from both an economical and environmental point of view; however, the design of solid adsorbents with high overall performance is still challenging. Herein, we designed three copper(I) cyclic trinuclear units, Cu(I)-CTUs, based covalent metal-organic frameworks (CMOFs) by networking metal clusters with dynamic covalent linkages. These CMOFs deliver a high gold adsorption capacity of 3687 mg g-1, ultra-fast adsorption kinetics (i.e., removal efficiency > 99% within 20 s), excellent selectivity and reusability. In addition, they can be readily used for gold extraction from e-waste. Owing to the rich redox properties of Cu-CTUs, these CMOFs show three sorption mechanisms including adsorption, chemical reduction and photocatalytic reduction. Interestingly, the gold-loaded CMOFs can be used as catalysts for hydration of alkynes to ketones with high yields (e.g., up to ∼ 95% for 6 examples).

Programming Covalent Organic Frameworks for Photocatalysis: Investigation of Synthesis Methods

Covalent organic frameworks (COFs) are crystalline, porous materials with exceptional potential as high-performance photocatalysts for applications such as hydrogen and hydrogen peroxide production. In this study, we systematically evaluates various synthesis methods to optimize the preparation of COFs, specifically targeting enhanced photocatalytic activity. Four different synthetic strategies including solvothermal synthesis, microwave synthesis, ultrasonic synthesis, and mechanochemical synthesis were explored to prepare TAPT-COF with identical molecular structures. Although all methods produced COFs with comparable crystallinity, porosity, and light absorption capacity, their photocatalytic efficiencies in hydrogen and hydrogen peroxide production varied significantly. Notably, the mechanochemical method, which involves ball milling to disrupt interlayer interactions and produce COF nanosheets, exhibited the highest photocatalytic performance, particularly in the COF-BM-30 min sample. This difference highlights the importance of morphology in photocatalytic activity. Our findings shed light on the impact of synthesis methods on COF properties and provide valuable guidance for molecular strategy development and industrial applications in photocatalysis.

Construction of C4-Spirocyclic Chiral Covalent Organic Frameworks Via Asymmetric Multicomponent Povarov Reaction for Enantioselective Sensing

Although many chiral covalent organic frameworks (CCOFs) have been synthesized, the rapid development of this field has been severely restricted by the limitations of CCOFs synthesis methods and the scarcity of their chiral structural unit types. Herein we report, for the first time, the construction of C4-spirocyclic CCOFs via the asymmetric multicomponent Povarov reaction under ambient conditions. The obtained C4-spiro-(2S, 4R)-TMTT-COF can be as a novel chiral fluorescent sensor to discriminate D/L-PAL enantiomers. This finding will provide a simple and universal method for constructing CCOFs with novel chiral structural groups and might open new insights into the construction of the CCOFs featuring multiple distinct types of carbon chiral centers.

Xantphos-Cu-Decorated Covalent Organic Frameworks for C─H Arylation through Sensitized Electron Transfer

The isoindolinone scaffold is an important structural motif found in a wide range of naturally occurring and synthetic biologically active compounds. However, the synthesis of isoindolinone derivatives typically requires multi-step procedures or the use of palladium-based catalysts, which are often hampered by low reaction yields and high costs. Recently, covalent organic frameworks (COFs)-emerging crystalline and porous materials-have gained considerable attention for their applications in various organic transformations, particularly in C─H functionalization, cross-coupling and redox reactions. Although COFs have been extensively studied for photocatalysis, the development of sustainable heterogeneous catalysts using low-cost transition metal-based photosensitizers is still in its early stages. Herein, a strategy is presented to incorporate a copper-Xantphos complex with a tetrahedral Cu(I) geometry into a crystalline and porous COF matrix. This modification enables unprecedented simultaneous electron and energy transfer efficiency during photocatalysis. The Cu-Xantphos coordinated COF exhibits potent photocatalytic activity for the synthesis of isoindolinone derivatives via C─Br and C─H bond cleavage followed by C─C bond formation. In addition, the catalyst shows excellent recyclability as it can be rejuvenated by reintroducing the Cu-Xantphos complex after multiple photocatalytic cycles-highlighting its potential as a sustainable and cost-effective solution for valuable organic transformations.

Ground-state charge transfer in single-molecule junctions covalent organic frameworks for boosting photocatalytic hydrogen evolution

Ground-state charge transfer plays a vital role in improving the photocatalytic performance of D-A type covalent organic frameworks. However, limited studies have explored the modulation of photocatalytic performance in COFs-based photocatalysts through ground-state charge transfer. Here we show the formation of extremely intense ground-state charge transfer via a unique covalent bonding approach. We transform three-dimensional stacked COF-based S-scheme heterojunctions (FOOCOF-PDIU) into co-planar single-molecule junctions (FOOCOF-PDI). This co-planar single-molecule junction structure exhibits strong ground-state charge transfer compared to the traditional randomly stacked heterojunctions and individual COFs. Ground-state charge transfer induces charge redistribution and dipole moment formation, which enhances the built-in electric field intensity in single-molecule junctions. This enhanced built-in electric field promotes exciton dissociation and charge separation, resulting in improved photocatalytic efficiency. Therefore, a stable molecule-decorated COF with broad light absorption has been successfully obtained, whose hydrogen evolution rate can reach 265 mmol g-1 h-1. This work opens an avenue for exploiting photocatalytic mechanisms in COFs based on ground-state charge transfer effects.

Integrating Humidity-Resistant and Colorimetric COF-on-MOF Sensors with Artificial Intelligence Assisted Data Analysis for Visualization of Volatile Organic Compounds Sensing

Direct visualization and monitoring of volatile organic compounds (VOCs) sensing processes via portable colorimetric sensors are highly desired but challenging targets. The key challenge resides in the development of efficient sensing systems with high sensitivity, selectivity, humidity resistance, and profuse color change. Herein, a strategy is reported for the direct visualization of VOCs sensing by mimicking human olfactory function and integrating colorimetric COF-on-MOF sensors with artificial intelligence (AI)-assisted data analysis techniques. The Dye@Zeolitic Imidazolate Framework@Covalent Organic Framework (Dye@ZIF-8@COF) sensor takes advantage of the highly porous structure of MOF core and hydrophobic nature of the COF shell, enabling highly sensitive colorimetric sensing of trace number of VOCs. The Dye@ZIF-8@COF sensor exhibits exceptional sensitivity to VOCs at sub-parts per million levels and demonstrates excellent humidity resistance (under 20-90% relative humidity), showing great promise for practical applications. Importantly, AI-assisted information fusion and perceptual analysis greatly promote the accuracy of the VOCs sensing processes, enabling direct visualization and classification of seven stages of matcha drying processes with a superior accuracy of 95.74%. This work paves the way for the direct visualization of sensing processes of VOCs via the integration of advanced humidity-resistant sensing materials and AI-assisted data analyzing techniques.

Chiral Inorganic Nanomaterial-Based Diagnosis and Treatments for Neurodegenerative Diseases

Chiral nanomaterials are widely investigated over recent decades due to their biocompatibility and unique chiral effects. These key properties have significantly promoted the rapid development of chiral nanomaterials in bioengineering and medicine. In this review, the basic principles of constructing chiral nanomaterials along with the latest progress in research are comprehensively summarized. Then, the application of chiral nanomaterials for the diagnosis of neurodegenerative diseases (NDDs) is systematically described. In addition, the significant potential and broad prospects of chiral nanomaterials in the treatment of NDDs are highlighted from several aspects, including the disaggregation of neurofibrils, the scavenging of reactive oxygen species, regulation of the microbial-gut-brain axis, the elimination of senescent cells, and the promotion of directed differentiation in neural stem cells. Finally, a perspective of the challenges and future development of chiral nanomaterials for the treatment of NDDs is provided.

Impact of Postsynthetic Modification on the Covalent Organic Framework (COF) Structures

Covalent organic frameworks (COFs) have emerged as a versatile class of materials owing to their well-defined crystalline structures and inherent porosity. In the realm of COFs, their appeal lies in their customizable nature, which can be further enhanced by incorporating diverse functionalities. Postsynthetic modifications (PSMs) emerge as a potent strategy, facilitating the introduction of desired functionalities postsynthesis. A significant challenge in PSM pertains to preserving the crystallinity and porosity of the COFs. In this study, we aim to investigate the intricate interplay between PSM strategies and the resulting crystalline and porous structures of the COFs. The investigation delves into the diverse methodologies employed in PSMs, to elucidate their distinct influences on the crystallinity and porosity of the COFs. Through a comprehensive analysis of recent advancements and case studies, the study highlights the intricate relationships among PSM parameters, including reaction conditions, precursor selection, and functional groups, and their impact on the structural features of COFs. By understanding how PSM strategies can fine-tune the crystalline and porous characteristics of COFs, researchers can harness this knowledge to design COFs with tailored properties for specific applications, contributing to the advancement of functional materials in diverse fields. This work not only deepens our understanding of COFs but also provides valuable insights into the broader realm of PSM strategies for other solid materials.

Manipulating p-π Resonance through Methoxy Group Engineering in Covalent Organic Frameworks for an Efficient Photocatalytic Hydrogen Evolution

Kinetic factors frequently emerge as the primary constraints in photocatalysis, exerting a critical influence on the efficacy of polymeric photocatalysts. The diverse conjugation systems within covalent organic frameworks (COFs) can significantly impact photon absorption, energy level structures, charge separation and migration kinetics. Consequently, these limitations often manifest as unsatisfactory kinetic behavior, which adversely affects the photocatalytic activity of COFs. To address these challenges, we propose a methoxy (-OMe) molecular engineering strategy designed to enhance charge carrier kinetics and mitigate mass transfer resistance. Through strategic modulation of the position and quantity of -OMe units, we can effectively manipulate the p-π conjugation, thereby enhancing charge separation and migration. Moreover, COFs enriched with -OMe moieties exhibit enhanced mass transfer dynamics due to the hydrophilic nature of methoxy groups, which facilitate the diffusion of reactants and products within the porous structure. This approach is hypothesized to drive an efficient photocatalytic hydrogen evolution reaction.

The Structural Regulation of Photosensitive Unit and Conjugation in COFs for Efficient Photocatalytic H2 Evolution

The photosensitive unit and conjugation play a significant role in   photocatalytic performance of covalent organic frameworks (COFs). In this work, a series of COFs that introduced the phenyl phenanthridine as photosensitive unit with different planarity of linkages were synthesized and the common regulation between them for photocatalysis hydrogen evolution reaction (HER) was also studied. The results indicate that DHTB-PPD, with 2/3 planarity linkages (β-ketoenamine/imine is 2/3) and the phenyl phenanthridine as building blocks, shows the narrowest bandgap and the strongest charge separation efficiency. Therefore, it shows the highest H2 production rate of 12.13 mmol g-1 h-1. The optimal photocatalytic efficiency of DTHB-PPD can be attributed to the combined effect of the photosensitive unit and the long-range ordering of the COF skeleton. According to The Density Functional Theory (DFT), the O site on β-ketoamine is the most possible H2 generation site, but the photocatalytic efficiency of TP-PPD, with the highest skeletal conjugation and the highest proportion of β-ketoamine is not the most efficient photocatalyst, indicating that the long-range ordering of COFs is important on photocatalytic performance. Thus, these findings provide valuable guidance for the structural design of COFs photocatalysts.

Targeted anchoring of Cu sites in imine-based covalent organic frameworks as catalytic centers for efficient Li-CO2 batteries

Lithium-carbon dioxide (Li-CO2) batteries have attracted much attention due to their high theoretical energy density and reversible CO2 reduction/evolution process. However, the wide bandgap insulating discharge product Li2CO3 is difficult to decompose, leading to large polarization or even death of the battery, thus seriously hindering the practical application of Li-CO2 batteries. The properties of covalent organic framework (COF) materials, which can support the construction of multiphase catalytic systems, have great potential in the fields of CO2 enrichment and electrocatalytic reduction. In this paper, the excellent redox properties of transition metal were utilized to introduce Cu metal into an imine-based COF to form Cu-O,N sites as the active sites for CO2 oxidation and reduction. The electrochemical performance of the Cu sites in Li-CO2 batteries was investigated, and the prepared batteries were able to cycle stably at a current density of 200 mA g-1 for more than 1100 h. COF structural sites can be anchored by metal Cu sites to form Cu-O,N active centers for CO2 oxidation and reduction processes. This study provides a new approach for the development of lithium CO2 batteries towards more stable and stable.

Diacetylene-bridged covalent organic framework as crystalline graphdiyne analogue for photocatalytic hydrogen evolution

Graphdiyne (GDY) alone as a photocatalyst is unsatisfactory because of its low crystallinity, limited regulation of the band gap, weak photogenerated charge separation, etc., and heterojunctioning with other materials is necessary to activate the photocatalytic activity of GDY. Through elaborate design, a diacetylene-rich linker (S2) was prepared and employed to construct a crystalline and structurally well-defined GDY-like covalent organic framework (COF, namely S2-TP COF) which merges the merits of both COF and GDY to boost the photocatalytic hydrogen evolution reaction (HER). By theoretical prediction on the donor-acceptor (D-A) pair, two other monoacetylene-bridged COFs (S1-TP COF and S3-TP COF) were prepared for comparison. Exhibiting enhanced separation and suppressed recombination of photogenerated excitons, Pt-photodeposited S2-TP COF showed a higher HER rate (10.16 mmol g-1 h-1) than the other two non-GDY-like COFs (3.71 and 1.13 mmol g-1 h-1). A joint experimental-theoretical study suggests that the appropriate D-A structure for photogenerated charge separation and diacetylene motif as the adsorption site are the key reasons for the boosted HER. This work opens a new avenue for the rational design of COFs as GDY mimics for photocatalytic application.

Covalent Organic Framework Stabilized Single CoN4Cl2 Site Boosts Photocatalytic CO2 Reduction into Tunable Syngas

Solar carbon dioxide (CO2) reduction provides an attractive alternative to producing sustainable chemicals and fuel. However, the construction of a highly active photocatalyst was challenging because of the rapid charge recombination and sluggish surface CO2 reduction. Herein, a unique Co-N4Cl2 single site was fabricated by loading Co species into the 2,2'-bipyridine and triazine-containing covalent organic framework (COF) for CO2 conversion into syngas under visible light irradiation. The resulting champion catalyst TPy-COF-Co enabled a record-high CO production rate of 426 mmol g-1 h-1, associated with the unprecedented turnover number (TON) and turnover frequency (TOF) of 2095 and 1607 h-1, respectively. The catalyst also exhibited favorable recycling performance and widely adjustable syngas production (CO/H2 ratio: 1.8 : 1-1 : 16). A systematical investigation including operando synchrotron X-ray absorption fine structure (XAFS) spectroscopy, in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and theoretical calculation indicated that the triazine-based COF framework promoted the charge transfer towards the single Co-N4Cl2 sites that greatly promoted the CO2 activation by lowering the energy barrier of *COOH generation, facilitating the CO2 transformation. This work highlights the great potential of the molecular regulation of COF-derived single-atom catalysts to boost CO2 photoreduction efficiency.

Surface Engineering of 2D Metal-Porphyrin Metal-Organic Frameworks Z-Scheme Heterostructure for Boosting and Stable Photocatalytic Hydrogen Evolution

How to improve the stability and activity of metal-organic frameworks is an attractive but challenging task in energy conversion and pollutant degradation of metal-organic framework materials. In this paper, a facile method is developed by fabricating titanium dioxide nanoparticles (TiO2 NPs) layer on 2D copper tetracarboxylphenyl-metalloporphyrin metal-organic frameworks with zinc ions as the linkers (ZnTCuMT-X, "Zn" represented zinc ions as the linkers, the first "T" represented tetracarboxylphenyl-metalloporphyrin (TCPP), "Cu" represented the Cu2+ coordinated into the porphyrin macrocycle, "M" represented metal-organic frameworks, the second "T" represented TiO2 NPs layer, and "X" represented the added volume of n-tetrabutyl titanate (X = 100, 200, 300 or 400)). It is found that the optimized ZnTCuMT-200 showed greatly and stably enhanced H2 generation, which is ≈28.2 times and 47.0 times as high as those of the original ZnTCuM and TiO2, respectively. Combined with the results of free radical capture, X-ray photoelectron spectra (XPS), electron spin resonance (ESR), and theoretical calculation, a direct Z-scheme electron transfer mechanism is achieved to fully explain the enhanced photocatalytic performance. It demonstrates that facilely designing Z-scheme heterostructures based on porphyrin MOFs modified with an inorganic semiconductor layer can be an advantageous strategy for enhancing the stability and activity of photocatalytic hydrogen evolution.

The photocatalytic wastewater hydrogen production process with superior performance to the overall water splitting

The utilization of a cost-free sacrificial agent is a novel approach to significantly enhance the efficiency of photocatalytic hydrogen (H2) production by water splitting. Wastewater contains various organic pollutants, which have the potential to be used as hole sacrificial agents to promote H2 production. Our studies on different pollutants reveals that not all pollutants can effectively promote H2 production. However, when using the same pollutants, not all photocatalysts achieved a higher H2 evolution rate than pure water. Only when the primary oxidizing active species of the photocatalyst are •OH radicals, which are generated by photogenerated holes, and when the pollutants are easily attacked and degraded by •OH radicals, can the production of H2 be effectively promoted. It is noteworthy that the porous brookite TiO2 photocatalyst exhibits a significantly higher H2 evolution rate in Reactive Red X-3B and Congo Red, reaching as high as 26.46 mmol⋅g-1⋅h-1 and 32.85 mmol⋅g-1 ⋅h-1, respectively, which is 2-3 times greater than that observed in pure water and is 10 times greater than most reported studies. The great significance of this work lies in the potential for efficient H2 production through the utilization of wastewater.

Construction of 2D/2D Pd Metallene/COFs System with Strong Internal Electric Field for Outstanding Solar Energy Photocatalysis

Due to the severe recombination of charge carriers, the photocatalytic activity of covalent organic frameworks (COFs) materials is limited. Herein, through simple ultrasound and stirring processes, the Pd metallene (Pde) is successfully combined with 2D COFs to form Pde/TpPa-1-COF (Pde/TPC) composites. Obviously, a strong internal electric field (IEF) is successfully formed in Pde/TPC hybrid materials, which significantly boosts the separation of photogenerated charges. In addition, the matched 2D structure of the two materials can also lead to electronic coupling effects, plentiful active sites, and shortened carrier migration paths. Thus, the Pde/TPC hybrid materials own extraordinary carrier separation ability with a longer carriers lifetime (3.3 ns for Pde/TPC and 2.7 ns for TPC), which can be proved series of photoelectrochemical and spectroscopic tests. Benefiting from the formation of IEF and the matched 2D structure, the 8% Pde/TPC demonstrates the highest photocatalytic H2 evolution efficiency, with H2 production rate reaching up to 5.85 mmol g-1 h-1, which is over 25 times greater than that of pristine COFs, also exceeding that of many reported COFs-based photocatalysts. This research provides new perspectives and innovative approaches to further research on enhancing the internal electric field of COFs to promote their photocatalytic performance.

A Protocol for Unveiling the Nature of Photocatalytic Hydrogen Evolution Reactions: True Water Splitting or Sacrificial Reagent Acceptorless Dehydrogenation?

Photocatalytic water splitting for hydrogen evolution is a highly topical subject in academic research and a promising approach for sustainable fuel production from solar energy. Due to the mismatched energy diagram of the photosensitizer (especially semiconductor-based materials where band-edge engineering is not trivial) and the redox potential of the half-reactions of water splitting, photocatalytic H2 generation from water splitting is usually accelerated by the addition of hole scavengers, i.e. sacrificial reagents such as alcohols, amines, and thiols. However, the source of the protons of the evolved H2 is often neglected, and it is questionable whether such systems are really water splitting. Here, we discuss recent reports on sacrificial reagent-assisted photocatalytic water splitting and present our recent findings, which showcase that the sacrificial reagent in the investigated photocatalytic water splitting systems inherently undergoes acceptorless dehydrogenation, with H2O serving as the proton shuttle, the amount of which doesn't change during the course of the reaction.

Surface Engineering of 2D Metal-Porphyrin Metal-Organic Frameworks Z-Scheme Heterostructure for Boosting and Stable Photocatalytic Hydrogen Evolution

How to improve the stability and activity of metal-organic frameworks is an attractive but challenging task in energy conversion and pollutant degradation of metal-organic frameworks materials. In this paper, we developed a facile method by fabricating TiO2 nanoparticles (NPs) layer on 2D copper tetracarboxylphenyl-metalloporphyrin metal-organic frameworks (MOFs) with Zn2+ as the linkers (ZnTCuMT-X, "Zn" represented Zn2+ as the linkers, the first "T" represented tetracarboxylphenyl-metalloporphyrin (TCPP), "Cu" represented the Cu2+ coordinated into the porphyrin macrocycle, "M" represented MOFs, the second "T" represented TiO2 NPs layer, and "X" represented the added volume of n-tetrabutyl titanate (X = 100, 200, 300 or 400)). It was found that the optimized ZnTCuMT-200 showed greatly and stably enhanced H2 generation, which was about 28.2 times and 47.0 times as high as those of the original metalloporphyrin MOFs and TiO2, respectively. Combined with the results of free radical capture, X-ray photoelectron spectra, electron spin resonance and theoretical calculation, a direct Z-scheme electron transfer mechanism was achieved to fully explain the enhanced photocatalytic performance. It demonstrates that facilely designing Z-scheme heterostructures based on porphyrin MOFs modified with inorganic semiconductor layer could be an advantageous strategy for enhancing the stability and activity of photocatalytic hydrogen evolution.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Material Engineering Strategies for Efficient Hydrogen Evolution Reaction Catalysts

Water electrolysis, a key enabler of hydrogen energy production, presents significant potential as a strategy for achieving net-zero emissions. However, the widespread deployment of water electrolysis is currently limited by the high-cost and scarce noble metal electrocatalysts in hydrogen evolution reaction (HER). Given this challenge, design and synthesis of cost-effective and high-performance alternative catalysts have become a research focus, which necessitates insightful understandings of HER fundamentals and material engineering strategies. Distinct from typical reviews that concentrate only on the summary of recent catalyst materials, this review article shifts focus to material engineering strategies for developing efficient HER catalysts. In-depth analysis of key material design approaches for HER catalysts, such as doping, vacancy defect creation, phase engineering, and metal-support engineering, are illustrated along with typical research cases. A special emphasis is placed on designing noble metal-free catalysts with a brief discussion on recent advancements in electrocatalytic water-splitting technology. The article also delves into important descriptors, reliable evaluation parameters and characterization techniques, aiming to link the fundamental mechanisms of HER with its catalytic performance. In conclusion, it explores future trends in HER catalysts by integrating theoretical, experimental and industrial perspectives, while acknowledging the challenges that remain.

Analyte-Induced Specific Regulation of Light-Responsive COF-Cu Nanozyme Activity for Ultrafast Thiram Colorimetric Sensing

A light-responsive covalent-organic framework (COF) nanozyme, which integrates the advantages of the COF structure and light-stimulated nanozyme catalysis, is a class of sensing star materials with wide application prospects. However, the sensing methods based on light-responsive COF nanozymes are relatively single at present. Therefore, it is necessary to develop new sensing strategies to broaden its application in chemical sensing and achieve highly efficient detection. Here, a Cu2+-modified COF composite material (TpDA-Cu) was rationally designed. The addition of Cu significantly inhibits the excellent light-responsive nanozyme activity of TpDA itself. However, because of the restoration of the enzyme activity by thiram (Tr) and the oxidase mimic activity of the newly formed Cu/Tr complex, TpDA-Cu/Tr exhibits stronger light-responsive nanozyme activity. Enzyme kinetic data show that compared with TpDA, TpDA-Cu/Tr has a larger Vmax value, which can achieve efficient catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). In addition, the strong coordination effect of Tr and TpDA-Cu also plays a key role in achieving ultrafast, sensitive, and selective colorimetric detection of Tr. This work develops a dual activity regulation strategy of light-responsive COF nanozymes based on analyte induction and provides a new perspective for the application of light-responsive COF nanozymes in the field of sensing.

Chiral Inorganic Polar BaTiO3/BaCO3 Nanohybrids with Spin Selection for Asymmetric Photocatalysis

Chirality-dependent photocatalysis is an emerging domain that leverages unique chiral light-matter interactions for enabling asymmetric catalysis driven by spin polarization induced by circularly polarized light selection. Herein, we synthesize chiral inorganic polar BaTiO3/BaCO3 nanohybrids for asymmetric photocatalysis via a hydrothermal method employing chiral glucose as a structural inducer. When excited by opposite circularly polarized light, the same material exhibits significant asymmetric catalysis, while enantiomers present an opposite polarization preference. More importantly, the preferred circularly polarized light undergoes reversal with reversal of the CD signal. Systematic experimental results demonstrate that more photogenerated carriers are generated in chiral semiconductors under suitable circularly polarized light irradiation, including more spin-polarized electrons, which inhibits the recombination of electron-hole pairs and promotes the activation of oxygen molecules into reactive oxygen species, thus inducing this asymmetric photocatalytic feature. This study provides valuable insights for the development of highly efficient polarization-sensitive chiral perovskite nanostructures as promising candidates for next-generation, multifunctional chiral device applications.

Novel Top-Down Synthesis of Covalent Organic Frameworks for Uranyl Ion Capture

Seeking novel synthetic methodology to further promote the preparation of covalent organic frameworks (COFs) has long been our pursuit but remains a challenging task. Herein, we report a new protocol, a top-down approach for facile synthesis of COFs. Interestingly, our top-down route can impressively generate extended COFs by reticular chemistry which cannot be accessed by the commonly used bottom-up synthesis route. Notably, our top-down method also has outstanding advantages in achieving what we are pursuing in COFs, such as heteropores and multiple components. The current findings not only dramatically reduce the difficulty of COF synthesis but also are generally applicable for the synthesis of complicated COFs constructed from different building blocks and linkages.

Enhancing photocatalytic performance of covalent organic frameworks via ionic polarization

Covalent organic frameworks have emerged as a thriving family in the realm of photocatalysis recently, yet with concerns about their high exciton dissociation energy and sluggish charge transfer. Herein, a strategy to enhance the built-in electric field of series β-keto-enamine-based covalent organic frameworks by ionic polarization method is proposed. The ionic polarization is achieved through a distinctive post-synthetic quaternization reaction which can endow the covalent organic frameworks with separated charge centers comprising cationic skeleton and iodide counter-anions. The stronger built-in electric field generated between their cationic framework and iodide anions promotes charge transfer and exciton dissociation efficiency. Moreover, the introduced iodide anions not only serve as reaction centers with lowered H* formation energy barrier, but also act as electron extractant suppressing the recombination of electron-hole pairs. Therefore, the photocatalytic performance of the covalent organic frameworks shows notable improvement, among which the CH3I-TpPa-1 can deliver an high H2 production rate up to 9.21 mmol g-1 h-1 without any co-catalysts, representing a 42-fold increase compared to TpPa-1, being comparable to or possibly exceeding the current covalent organic framework photocatalysts with the addition of Pt co-catalysts.

In situ Construction of Single-Atom Electronic Bridge on COF to Enhance Photocatalytic H2 Production

Photocatalytic hydrogen production is one of the most valuable technologies in the future energy system. Here, we designed a metal-covalent organic frameworks (MCOFs) with both small-sized metal clusters and nitrogen-rich ligands, named COF-Cu3TG. Based on our design, small-sized metal clusters were selected to increase the density of active sites and shorten the distance of electron transport to active sites. While another building block containing nitrogen-rich organic ligands acted as a node that could in situ anchor metal atoms during photocatalysis and form interlayer single-atom electron bridges (SAEB) to accelerate electron transport. Together, they promoted photocatalytic performance. This represented the further utilization of Ru atoms and was an additional application of the photosensitizer. N2-Ru-N2 electron bridge (Ru-SAEB) was created in situ between the layers, resulting in a considerable enhancement in the hydrogen production rate of the photocatalyst to 10.47 mmol g-1 h-1. Through theoretical calculation and EXAFS, the existence position and action mechanism of Ru-SAEB were reasonably inferred, further confirming the rationality of the Ru-SAEB configuration. A sufficiently proximity between the small-sized Cu3 cluster and the Ru-SAEB was found to expedite electron transfer. This work demonstrated the synergistic impact of small molecular clusters with Ru-SAEB for efficient photocatalytic hydrogen production.

Synergistic Linker and Linkage of Covalent Organic Frameworks for Enhancing Gold Capture

The tunable pore walls and skeletons render covalent organic frameworks (COFs) as promising absorbents for gold (Au) ion. However, most of these COFs suffered from low surface areas hindering binding sites exposed and weak binding interaction resulting in sluggish kinetic performance. In this study, COFs have been constructed with synergistic linker and linkage for high-efficiency Au capture. The designed COFs (PYTA-PZDH-COF and PYTA-BPDH-COF) with pyrazine or bipyridine as linkers showed high surface areas of 1692 and 2076 m2 g‒1, providing high exposed surface areas for Au capture. In addition, the Lewis basic nitrogen atoms from the linkers and linkages are easily hydronium, which enabled to fast trap Au via coulomb force. The PYTA-PZDH-COF and PYTA-BPDH-COF showed maximum Au capture capacities of 2314 and 1810 mg g-1, higher than other reported COFs. More importantly, PYTA-PZDH-COF are capable of rapid adsorption kinetics with achieving 95% of maximum binding capacity in 10 min. The theoretical calculation revealed that the nitrogen atoms in linkers and linkages from both COFs are simultaneously hydronium, and then the protonated PYTA-PZDH-COF are more easily binding the AuCl4 ‒, further accelerating the binding process. This study gives the a new insight to design COFs for ion capture.

Recent Advances in the Utilization of Chiral Covalent Organic Frameworks for Asymmetric Photocatalysis

The use of light energy to drive asymmetric organic transformations to produce high-value-added organic compounds is attracting increasing interest as a sustainable strategy for solving environmental problems and addressing the energy crisis. Chiral covalent organic frameworks (COFs), as porous crystalline chiral materials, have become an important platform on which to explore new chiral photocatalytic materials due to their precise tunability, chiral structure, and function. This review highlights recent research progress on chiral COFs and their crystalline composites, evaluating their application as catalysts in asymmetric photocatalytic organic transformations in terms of their structure. Finally, the limitations and challenges of chiral COFs in asymmetric photocatalysis are discussed, with future opportunities for research being identified.

Linear oligo(phenylenevinylene)-based covalent organic frameworks

Covalent organic frameworks (COFs) incorporating oligo(phenylenevinylene) units have shown promise in enhancing photocatalytic hydrogen evolution. This study presents a series of linear oligo(phenylenevinylene)-based COFs with various ratios of β-ketoenamine to imine linkages. The COFs-950-OMe are crystalline, exhibiting higher surface area compared to amorphous COFs-950, due to the introduction of methoxy side groups.

Engineering spin-dependent catalysts: chiral covalent organic frameworks with tunable electroactivity for electrochemical oxygen evolution

The chiral-induced spin selectivity (CISS) effect offers promising prospects for spintronics, yet designing chiral materials that enable efficient spin-polarized electron transport remains challenging. Here, we report the utility of covalent organic frameworks (COFs) in manipulating electron spin for spin-dependent catalysis via CISS. This enables us to design and synthesize three three-dimensional chiral COFs (CCOFs) with tunable electroactivity and spin-electron conductivity through imine condensations of enantiopure 1,1'-binaphthol-derived tetraaldehyde and tetraamines derived from 1,4-benzenediamine, pyrene, or tetrathiafulvalene skeletons. The CISS effect of CCOFs is verified by magnetic conductive atomic force microscopy. Compared with their achiral analogs, these CCOFs serve as efficient spin filters, reducing the overpotential of oxygen evolution and improving the Tafel slope. Particularly, the diarylamine-based CCOF showed a low overpotential of 430 mV (vs reversible hydrogen electrode) at 10 mA cm-2 with long-term stability comparable to the commercial RuO2. This enhanced spin-dependent OER activity stems from its excellent redox-activity, good electron conductivity and effective suppression effect on the formation of H2O2 byproducts.

A photothermal assisted zinc-air battery cathode based on pyroelectric and photocatalytic effect

Zinc-air battery as one of the new generations of battery system, its theoretical specific energy is as high as 1086 Wh kg-1, specific capacity up to 820 mAh/g, and zinc has the advantages of environmental friendliness, resource abundance, low cost and good safety, so it has attracted much attention. However, due to its slow reaction kinetic process, zinc-air battery will produce a large charging overpotential usually up to 2 V, it is far beyond the theoretical voltage of 1.65 V, so reducing the overpotential of zinc-air batteries is extremely necessary, and the most common way to solve this problem is to use excellent catalyst cathode to improve the oxygen reduction and oxygen evolution kinetics of zinc-air batteries. So we developed a new photothermal assisted zinc-air battery system with Hollow carbon nanosphere@poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)@CdS(HCN@PVTC@CdS) photocathode, the pyroelectric and photocatalysis effect can effectively promote the reaction kinetics and reduce the reaction overpotential. With the pyroelectric and photocatalysis synergistic effect, the zinc-air has displayed a high discharge potential of 1.33 V and a low charging potential of 1.5 V with good cycle stability. This multi-assist technology with built-in electric and light fields paves the way for the development of high-performance zinc-air batteries and other energy storage systems.

Spin-related excited-state phenomena in photochemistry

The spin of electrons plays a vital role in chemical reactions and processes, and the excited state generated by the absorption of photons shows abundant spin-related phenomena. However, the importance of electron spin in photochemistry studies has been rarely mentioned or summarized. In this review, we briefly introduce the concept of spin photochemistry based on the spin multiplicity of the excited state, which leads to the observation of various spin-related photophysical properties and photochemical reactivities. Then, we focus on the recent advances in terms of light-induced magnetic properties, excited-state magneto-optical effects and spin-dependent photochemical reactions. The review aims to provide a comprehensive overview to utilize the spin multiplicity of the excited state in manipulating the above photophysical and photochemical processes. Finally, we discuss the existing challenges in the emerging field of spin photochemistry and future opportunities such as smart magnetic materials, optical information technology and spin-enhanced photocatalysis.

Linkage-Mixed Covalent Organic Frameworks Synthesized by a Liquid-Solid Two-Phase Strategy for Photoenhanced Uranium Extraction

Synthesizing COFs with hybrid linkage coupling with both reversible and irreversible natures remains a challenging issue. Herein, we report the synthesis of two rare COFs constructed by both reversible and irreversible linkages through a liquid-solid two-phase strategy. A systematic study reveals a one-pot, two-step reaction mechanism for the two COFs, the first step being a reversible Schiff base reaction and the second step being an irreversible Knoevenagel reaction. Interestingly, this hybrid linkage COF is found to show an outstanding photoenhanced uranium extraction performance. The results not only provide a general and green approach to develop the linkage chemistry of COFs but also enrich the synthesis toolboxes and application of COFs.

Elaborate Modulating Binding Strength of Intermediates via Three-component Covalent Organic Frameworks for CO2 Reduction Reaction

The catalytic performance for electrocatalytic CO2 reduction reaction (CO2RR) depends on the binding strength of the reactants and intermediates. Covalent organic frameworks (COFs) have been adopted to catalyze CO2RR, and their binding abilities are tuned via constructing donor-acceptor (DA) systems. However, most DA COFs have single donor and acceptor units, which caused wide-range but lacking accuracy in modulating the binding strength of intermediates. More elaborate regulation of the interactions with intermediates are necessary and challenge to construct high-efficiency catalysts. Herein, the three-component COF with D-A-A units was first constructed by introducing electron-rich diarylamine unit, electron-deficient benzothiazole and Co-porphyrin units. Compared with two-component COFs, the designed COF exhibit elevated electronic conductivity, enhanced reducibility, high efficiency charge transfer, further improving the electrocatalytic CO2RR performance with the faradic efficiency of 97.2 % at -0.8 V and high activity with the partial current density of 27.85 mA cm-2 at -1.0 V which exceed other two-component COFs. Theoretical calculations demonstrate that catalytic sites in three-component COF have suitable binding ability of the intermediates, which are benefit for formation of *COOH and desorption of *CO. This work offers valuable insights for the advancement of multi-component COFs, enabling modulated charge transfer to improve the CO2RR activity.

One-Dimensional Covalent Organic Framework-Based Multilevel Memristors for Neuromorphic Computing

Memristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one-dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF-4,4'-methylenedianiline (MDA) and COF-4,4'-oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF-ODA film, a built-in electric field between the COF-TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF-based memristors to achieve energy-efficient and high-density memory devices.

Solvent Effects on Metal-free Covalent Organic Frameworks in Oxygen Reduction Reaction

Binding water molecules to polar sites in covalent organic frameworks (COFs) is inevitable, but the corresponding solvent effects in electrocatalytic process have been largely overlooked. Herein, we investigate the solvent effects on COFs for catalyzing the oxygen reduction reaction (ORR). Our designed COFs incorporated different kinds of nitrogen atoms (imine N, pyridine N, and phenazine N), enabling tunable interactions with water molecules. These interactions play a crucial role in modulating electronic states and altering the catalytic centers within the COFs. Among the synthesized COFs, the one with pyridine N atoms exhibits the highest activity, with characterized by a half-wave potential of 0.78 V and a mass activity of 0.32 A mg-1, which surpass those from other metal-free COFs. Theoretical calculations further reveal that the enhanced activity can be attributed to the stronger binding ability of *OOH intermediates to the carbon atoms adjacent to the pyridine N sites. This work sheds light on the significance of considering solvent effects on COFs in electrocatalytic systems, providing valuable insights into their design and optimization for improved performance.

Donor-acceptor moiety functionalized covalent organic frameworks for boosting charge separation and H2 photogeneration

Covalent organic frameworks (COFs) have a broad prospect to be used as a photocatalytic platform to convert solar energy into valuable chemicals due to their tunable structures and rich active catalytic sites. However, constructing COFs with tuned sp2-carbon donor-acceptor moiety remains an enormous challenge. Herein, we synthesized two new fully π-conjugated cyano-ethylene-linked COFs containing benzotrithiophene as functional group by Knoevenagel polycondensation reaction. The accetpor 2,2'-bipyridine unit in BTT-BpyDAN-COF skeleton favored the formation of a intermolecular specific electron transport pathway with the donor benzotrithiophene, and thereby promoted charge separation and transfer efficiency. Specifically, a donor-acceptor (D-A) type BTT-BpyDAN-COF exhibited high hydrogen evolution rate of 10.1 mmol g-1h-1 and an excellent apparent quantum efficiency of 4.83 % under visible light irradiation.

Hierarchically Porous Covalent Organic Frameworks: Synthesis Methods and Applications

Covalent organic frameworks (COFs) with high porosity have garnered considerable interest for various applications owing to their robust and customizable structure. However, conventional COFs are hindered by their narrow pore size, which poses limitations for applications such as heterogeneous catalysis and guest delivery that typically involve large molecules. The development of hierarchically porous COF (HP-COF), featuring a multi-scale aperture distribution, offers a promising solution by significantly enhancing the diffusion capacity and mass transfer for larger molecules. This review focuses on the recent advances in the synthesis strategies of HP-COF materials, including topological structure design, in-situ templating, monolithic COF synthesis, defect engineering, and crystalline self-transformation. The specific operational principles and affecting factors in the synthesis process are summarized and discussed, along with the applications of HP-COFs in heterogeneous catalysis, toxic component treatment, optoelectronics, and the biomedical field. Overall, this review builds a bridge to understand HP-COFs and provides guidance for further development of them on synthesis strategies and applications.

Photoenzymatic CO2 Reduction Dominated by Collaborative Matching of Linkage and Linker in Covalent Organic Frameworks

Artificial photoenzymatic systems based on covalent organic frameworks (COFs) provide an interesting platform for converting CO2 to value-added fuels. However, the dual roles of COFs as photocatalysts and enzyme hosts showcase contradictory preferences for structures, which poses a great challenge for their rational design. Herein, we report the collaborative matching of linkages and linkers in COFs on their ability to exert both photocatalytic activity and enzyme loading, which has been neglected until now. The linkage-dependent linker regulation pattern was elucidated, and the optimal match showed a record-breaking apparent quantum efficiency at 420 nm for photocatalytic cofactor regeneration of 13.95% with a high turnover frequency of 5.3 mmol g-1 h-1, outperforming other reported crystalline framework photocatalysts. Moreover, theoretical calculations and experiments revealed the mechanism underlying the effects of matching the linkage and linker on exciton dissociation and charge migration in photocatalysis. This newfound understanding enabled the construction of COFs with both high photoactivity and large pores closer in size to the formate dehydrogenase, achieving high loading capacity and a suitable confinement effect. Remarkably, the artificial photoenzymatic system constructed according to optimal linkage-linker matching exhibited highly efficient CO2 reduction, yielding formic acid with a specific activity as high as 1.46 mmol g-1 catalyst h-1 and good reusability, paving the way for sustainable CO2 conversion driven by visible light.

Structural Regulation of Photocatalyst to Optimize Hydroxyl Radical Production Pathways for Highly Efficient Photocatalytic Oxidation

Ring-opening of phenol in wastewater is the pivotal step in photocatalytic degradation. The highly selective generation of catalytical active species (•OH) to facilitate this process presents a significant scientific challenge. Therefore, a novel approach for designing photocatalysts with single-atom containment in metal-covalent organic frameworks (M-COFs) is proposed. The selection of imine-linked COFs containing abundant N and O-chelate sites provides a solid foundation for anchoring metal atom. These dispersed metal atom possess rapid accumulation and transfer capabilities for photogenerated electrons, while the periodic π-conjugated structure in 2D-COFs establishes an effective platform. Additionally, the Lewis acid properties of imine bonds in COFs can enhance the adsorption capacity toward gases with Lewis base properties, such as O2 and N2 . It is demonstrated that the Pd2+ @Tp-TAPT, designed based on this concept, exhibits efficient oxygen adsorption and follows the reaction pathway of O2 →•O2 - →H2 O2 →•OH with high selectivity, thereby achieving completely degradation of refractory phenol through photocatalysis within 10 min. It is anticipated that the selective generation of catalytic active species via advanced material design concepts will serve as a significant reference for achieving precise material catalysis in the future.

Synergistic Enhancement of Photocatalytic H2 Evolution over NH2-MIL-125 Modified with Dual Cocatalyst

The construction of efficient photocatalysts for water splitting to enable H2 evolution is pivotal to alleviate energy issues and environmental concerns. In this work, carbon dots (CDs) were prepared by employing "green solvent" ionic liquids as carbon sources and then combined with Pt/NH2-MIL-125, resulting in the emergence of a high-efficiency photocatalyst termed CDs-Pt/NH2-MIL-125 for the first time. This composite photocatalyst exhibited outstanding photocatalytic activity in H2 production under visible light irradiation. Notably, the H2 production rate of CDs100-Pt/NH2-MIL-125 reaches up to 951.4 μmol/g/h, which was 3.1 times that of Pt/NH2-MIL-125. The characterization results indicate that CDs and Pt uniformly dispersed on the surface of NH2-MIL-125 and fabricated a synergistic compact structure, providing a high BET surface area (985 m2 g-1) and a suitable band gap. Furthermore, the distinctive embeddable-dispersed CDs and Pt, as dual cocatalyst, can harvest light and facilitate the transfer of photogenerated electrons, thereby significantly augmenting the exploitation of visible light. The plausible mechanism of photocatalytic H2 evolution over the CDs-Pt/NH2-MIL-125 catalyst was also discussed. This work introduces a promising strategy for designing high-performance CDs-MOFs-based photocatalysts, an innovative step toward achieving efficient photocatalytic water splitting for H2 production.

Synthesis of Chiral Triazine Frameworks for Enantiodiscrimination

Manipulation of the structure of covalent organic frameworks at the molecular level is an efficient strategy to shift their biological, physicochemical, optical, and electrical properties in the desired windows. In this work, we report on a new method to construct chiral triazine frameworks using metal-driven polymerization for enantiodiscrimination. The nucleophilic substitution reaction between melamine and cyanuric chloride was performed in the presence of PdCl2, ZnCl2, and CuCl2 as chirality-directing agents. Palladium, with the ability of planar complex formation, was able to assemble monomers in two-dimensions and drive the reaction in two directions, leading to a two-dimensional triazine network with several micrometers lateral size. Nonplanar arrangements of monomers in the presence of ZnCl2 and CuCl2, however, resulted in calix and bouquet structures, respectively. While 2D and bouquet structures showed strong negative and positive bands in the CD spectra, respectively, their calix counterparts displayed long-range weak negative bands. In spite of the ability of both calix and bouquet networks to load l-histidine 35 and 50% more than d-histidine from pure enantiomers, respectively, only calix counterparts were able to take up this enantiomer (78%) from the racemic mixture. The two-dimensional polytriazine network did not show any specific interactions with pure enantiomers or their racemic mixtures.

Blocking Accretion Enables Dimension Reduction of Metal-Organic Framework for Photocatalytic Performance

The evolution and formation process of two-dimensional metal-organic frameworks (MOFs) primarily arise from the anisotropic growth of crystals, leading to variations in photocatalytic performance. It is crucial to achieve a synergistic combination of anisotropic electron transfer direction and dimension reduction strategies. In this study, a novel approach that effectively blocks crystal growth accretion through the coordination of solvent molecules is presented, achieving the successful synthesis of impurity-free two-dimensional nanosheet Zn-PTC with exceptional hydrogen evolution reaction (HER) performance (15.4 mmol g-1  h-1 ). The structural and photophysical characterizations validate the successful prevention of crystal accretion, while establishing correlation between structural anisotropy and intrinsic charge transfer mode through transient spectroscopy. These findings unequivocally demonstrate that electron transfer along the [001] direction plays a pivotal role in the redox performance of nano-Zn-PTC. Subsequently, by coupling the photocatalytic performance and density functional theory (DFT) simulation calculations, the carrier diffusion kinetics is explored, revealing that effective dimension reduction along the ligand-to-metal charge transfer (LMCT) direction is the key to achieving superior photocatalytic performance.

Towards high-performance nonlinear optical materials through embedding a D-A system into β-ketoenamine-linked COFs

Two covalent organic framework (COF) films supported by a glass substrate were obtained by solvothermal reaction of an electron donor with electron acceptor 1,3,5-triformylbenzene (TF) or 2,4,6-triformylphloroglucinol (TFP), respectively. The TFP-BD film exhibits a nonlinear absorption coefficient of -3.01 × 105 cm GW-1. The TFP-BD film can aggregate electrons around the connected monomer through the D-A effect due to its highly polar and electronegative carbonyl oxygen atoms, thereby modulating the electronic structure of the COFs. This work provides a novel approach for the structural modulation of optical materials with strong nonlinearity.

Research Progress in Donor-Acceptor Type Covalent Organic Frameworks

Covalent organic frameworks (COFs) are new organic porous materials constructed by covalent bonds, with the advantages of pre-designable topology, adjustable pore size, and abundant active sites. Many research studies have shown that COFs exhibit great potential in gas adsorption, molecular separation, catalysis, drug delivery, energy storage, etc. However, the electrons and holes of intrinsic COF are prone to compounding in transport, and the carrier lifetime is short. The donor-acceptor (D-A) type COFs, which are synthesized by introducing D and A units into the COFs backbone, combine separated electron and hole migration pathway, tunable band gap and optoelectronic properties of D-A type polymers with the unique advantages of COFs and have made great progress in related research in recent years. Here, the synthetic strategies of D-A type COFs are first outlined, including the rational design of linkages and D-A units as well as functionalization approaches. Then the applications of D-A type COFs in catalytic reactions, photothermal therapy, and electronic materials are systematically summarized. In the final section, the current challenges, and new directions for the development of D-A type COFs are presented.