Cu2O/2D COFs Core/Shell Nanocubes with Antiphotocorrosion Ability for Efficient Photocatalytic Hydrogen Evolution

A Z-scheme photoelectrochemical biosensing platform based on Cu2O-sensitized hollow covalent organic frameworks for sensitive microcystin-LR detection

Photoactive materials play a crucial role in enhancing the sensitivity of photoelectrochemical (PEC) biosensors. In this work, we developed a highly sensitive Z-scheme PEC biosensing platform based on Cu2O-sensitized hollow structured covalent organic frameworks (HCOF-OMe) microspheres for the detection of microcystin-LR (MC-LR). The HCOF-OMe photoelectrode with enhanced PEC response can be sensitized by Cu2O nanocubes through the formation of a Z-scheme system, enabling the construction of a signal-on PEC biosensing platform. To amplify the detection signal, a homogeneous biosensing strategy was employed by integrating a DNA walker nanomachine-assisted CRISPR/Cas12a system. A DNA walker nanomachine was assembled on streptavidin-modified magnetic bead (MB) and initially locked by MC-LR aptamer. Upon MC- LR recognition, the walker DNA was allowed to hybridize with support DNA, exposing cleavage sites for the nicking endonuclease Nb.BbvCI, which can release the activator strand to trigger the trans-cleavage ability of CRISPR/Cas12a. As a result, Cu2O nanocubes were released from the MB-ssDNA-Cu2O complex and subsequently loaded on the HCOF-OMe photoelectrode, significantly improving the PEC signals. This enabled the sensitive assay of MC-LR over a wide linear range of 1.0 × 10-5-100 μg/L with a low detection limit of 4.6 × 10-6 μg/L. The proposed biosensing platform is highly versatile and can be extended to detect other environmental pollutants or biological disease markers.

Unassisted Switchable Dual-Photoelectrode Devices Utilizing p-n Carbon Quantum Dots as "Semiconductor Electrolytes": Optimization Between H2O2 and Solar Electricity Production

Switchable self-driven photoelectrochemical (PEC) devices are developed to boost H2O2 or electricity generation under visible-light illumination, in which p-n type carbon quantum dots (N-CQDs) is applied as conceptually-new "semiconductor electrolytes". The N-CQDs contains N-dopants, and both negatively- and positively-charged surface groups. This allows N-CQDs to act as the electrolyte and to interact with both a BiVO4 photoanode and a Cu2O photocathode. In a two-compartment cell with a separating membrane, N-CQDs can dynamically form p-n heterojunctions with the photoanode or the photocathode, facilitating charge separation. In this setup, the fine-tuned electronic structure of N-CQDs promotes the two-electron reactions with water or O2 to produce H2O2, achieving a rate of 28 µm min-1 and Faradic efficiency exceeding 80%. Switching into a one-compartment cell, N-CQDs promotes four-electron charge transfer and stabilizes the photoelectrodes, giving electricity output for over 120 h. This control over electron transfer, selectivity, and durability cannot be achieved using traditional electrolytes.

Shining Light on Hydrogen: Solar-Powered Catalysis with Transition Metals

Artificial photosynthesis offers a promising pathway to address environmental challenges and the global energy crisis by converting solar energy into storable chemical fuels such as hydrogen. Among various photocatalysts, transition metal-based materials have garnered significant attention due to their tunable crystal phase, morphology, surface active sites, and other key properties. This review provides a comprehensive overview of recent advances in transition metal-based photocatalysts for hydrogen production, with a particular focus on modification strategies and their underlying mechanisms. By systematically classifying these materials, this work highlights effective approaches for enhancing their catalytic performance, including structural engineering, electronic modulation, and interfacial optimization. Furthermore, this work discusses the fundamental principles governing these modifications, offering deeper insights into their roles in charge separation, surface reactions, and stability. Finally, this work outlines future research directions and key challenges in the rational design of highly efficient transition metal-based photocatalysts for sustainable hydrogen production.

Dynamic in-situ reconstruction of active site circulators for photo-Fenton-like reactions

Developing efficient and stable heterogeneous catalysts for the continuous activation of oxidants is crucial to mitigating the global water resource crisis. Guided by computational predictions, this research achieved this goal through the synthesis of a modified graphitic carbon nitride with enhanced catalytic activity and stability. Its intrinsic activity was further amplified by dynamic in-situ reconstruction using the I-/I3- redox mediator system during photoreactions. Impressively, this reconstructed catalyst demonstrated the capability for at least 30 regeneration cycles while maintaining high purification efficacy. The mechanism underlying the in-situ reconstruction of active sites for periodate functionalization was elucidated through theoretical calculations, coupled with semi-in-situ X-ray photoelectron spectroscopy (XPS) and electrochemical analyses. The system's capacity to detoxify recalcitrant pollutants was demonstrated through successful Escherichia coli cultivation and Zebrafish embryo experiments. The economic feasibility and environmental impacts are quantitatively assessed by the Electrical Energy per Order (EE/O) metric and Life Cycle Assessment (LCA), confirming the system's scalability and applicability in real-world scenarios. This dual-site constrained interlayer insertion, and controllable in-situ catalyst reconstruction achieve durable robustness of the photocatalyst, paving the way for the development of sustainable catalytic water purification technologies.

Co-Atomic Interface Minimizing Charge Transfer Barrier in Polytypic Perovskites for CO2 Photoreduction

Heterojunctions, known for their decent separation of photo-generated electrons and holes, are promising for photocatalytic CO2 reduction. However, a significant obstacle in traditional post-assembled heterojunctions is the high interfacial barrier for charge transfer caused by atomic lattice mismatch at multiphase interfaces. Here, as research prototypes, the study creates a lattice-matched co-atomic interface within CsPbBr3-CsPb2Br5 polytypic nanocrystals (113-125 PNs) through the proposed in situ hybrid strategy to elucidate the underlying charge transfer mechanism within this unique interface. Compared to CsPbBr3 nanocrystals, the 113-125 PNs exhibit a remarkable 3.6-fold increase in photocatalytic CO2 reduction activity (173.3 µmol-1 g-1 within 5 h). Furthermore, Kelvin probe force microscopy results reveal an increase in the built-in electric field within this lattice-matched co-atomic interface from 43.5 to 68.7 mV, providing a stronger driving force for charge separation and directional migration. Additionally, ultrafast transient absorption spectroscopy uncovers the additional charge carrier transfer pathways across this lattice-matched co-atomic interface. Thus, this unique co-atomic interface significantly promotes the interfacial electronic coupling and mitigates the charge transfer barrier, thus facilitating efficient charge separation and transfer. These insights underscore the importance of interfacial structure in heterojunction design and comprehending the intricate interplay between interface and carrier dynamics.

A novel aptasensor integrating the DNA rolling nanomachine and Tb/COF/KB as dual signal amplifiers for kanamycin detection in foods

A novel aptasensor for the detection of kanamycin (KNM) was developed based on dual signal amplification through nanomaterials and DNA rolling machines. Firstly, a composite consisting of the covalent organic framework (COF), ketjen black (KB) and toluidine blue (Tb), was synthesized for signal generation. Tb molecules were loaded into the composite and combined with AuNPs to serve as tracer label. Secondly, the wDNA-loaded Fe3O4 magnetic beads (wDNA@MBs) as the DNA walking legs, with cleavage by Mg2+-driven DNAzyme, the DNA walking legs can move along the sDNA-decorated MBs surface, converting the target KNM into numerous output DNA strand, achieving sensitive amplification. With a low detection limit of 0.66 fM and a wide linear dynamic range from 10 fM to 100 nM, this aptasensor showed good results in the detection of KNM in real samples. Therefore, we envision it can provide a useful method for KNM detection in actual samples.

Regulating coordination environment in metal-organic Framework@Cuprous oxide Core-Shell catalyst for Promoting electrocatalytic oxygen evolution reaction

As a kind of promising oxygen evolution reaction (OER) catalysts, metal-organic frameworks (MOF) are often constrained by their inherent poor electroconductivity and structural instability. In this study, we developed a mono-dispersed zeolitic imidazolate framework-67@cuprous oxide (ZIF-67@Cu2O) core-shell catalyst via in-situ growth method for highly efficient alkaline OER. The ZIF-67@Cu2O shows an excellent OER activity with a low overpotential of 254 mV at 10 mA cm-2 and Tafel slope of 87.9 mV·dec-1 in 1.0 M KOH. Furthermore, the ZIF-67@Cu2O also shows a high turnover frequency (TOF) of 0.166 s-1 at 1.60  V vs. RHE and long-term stability for 160 h at a high current density of 100 mA cm-2. The unique core-shell structure with the Cu2O core linked with ZIF-67 shell through interfacial di-oxygen bridge improves the structural stability, enhances the charge transfer, and provides more active sites. Moreover, the interfacial coordination structure was regulated from Co-N4 to Co-N2O2 which elevates the valence of Co sites and optimizes the adsorption free energy of oxygen-containing intermediates, thus improving the electrocatalytic OER performance. This work could propose the way for designing novel MOF-based nanomaterials and developing desirable and robust heterogeneous OER catalysts.

Synergistically-mediated highly-efficient visible-light-driven hydrogen evolution activity using Ohmic/Schottky-type dual-junctions and sulfur vacancy

Enabling highly-efficient multiplex-optimization photocatalysts is critical to overcome the bottlenecks of hydrogen evolution reaction efficiency and photostability. Herein, novel CoS/Sv-ZnIn2S4/MoS2 composites are successfully synthesized through an in situ technique. Taking advantage of the synergistic effect of sulfur vacancy, Schottky-type MoS2/Sv-ZnIn2S4 junction and Ohmic-type CoS/Sv-ZnIn2S4 junction, the light absorption, electron/hole separation efficiency, charge transfer rate and hydrogen reduction reaction dynamic can be significantly enhanced. As a result, an impressive photocatalytic hydrogen evolution rate of 18.43 mmol g-1 h-1 is achieved under the visible-light irradiation. Furthermore, apparent quantum efficiencies of 72.14 % and 9.91 % are also achieved under 350 and 420 nm monochromatic light irradiation. This work presents an in situ perspective to design multiplex-optimization photocatalytic system for highly-efficient hydrogen production.

Surface Sulfurization of Cubic Cu2O to Form Cu2S Nanostructure-Decorated Catalysts for Light-Enhanced Electrocatalytic H2 Evolution and Photocatalytic CO2 Reduction

Developing highly efficient bifunctional catalysts for electrocatalysis and photocatalysis suffers from sluggish charge transfer and poor photo-to-electric conversion rate. Herein, micro-sized Cu2O cubes were initially prepared for subsequent transformation into Cu2O@Cu2S core-shell structures by a slight surface sulfurization. The formation of nanostructured Cu2S thin layer at Cu2O surface can endow an immediate charge separation and migration under light irradiation, leading to high surface photovoltages (SPV, 18-30 mV). As a result, the as-prepared Cu2O@Cu2S catalysts exhibited reduced overpotentials (η, only 86 mV is required for the optimized sample to achieve a current density of 10 mA cm-2) for H2 evolution with good cycling stability in electrocatalytic water splitting. Meanwhile, a high methane (CH4) production rate of 30.3 μmol h-1 g-1 can be delivered from the optimized Cu2O@Cu2S sample when used for photocatalytic CO2 reduction. This work has provided a strategy to prepare bifunctional catalysts with improved photoelectric properties for photo/electrocatalytic applications.

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.

Defect Engineering Enhancing Piezoelectric Catalytic Activity of Covalent Organic Framework Matrix Composites for Uranium Removal

Piezoelectric catalysis is an emerging green strategy, but the existing piezoelectric heterostructures are not sufficient in performance for catalytic reduction of low-reduction potential uranium under harsh conditions. This study innovatively employs a defect heterogeneous engineering strategy, wherein covalent organic frameworks (COFs) are grown in situ on the surface of zinc oxide (ZnO) via Schiff base reactions, and defects are introduced into the COF shell layer via imine exchange reactions to construct D-COF@ZnO for piezoelectric catalytic uranium removal. The comprehensive study shows that defect heterogeneous engineering increases the asymmetry induced polarization of the material to promote charge redistribution, and thus significantly improves the activity of piezoelectric catalysis. In addition, defect engineering optimizes the nanosize of D-COF@ZnO to expose a richer array of active sites, resulting in ultra-fast U(VI) removal kinetics and ultra-high removal capacity. In the actual nuclear wastewater settings, D-COF@ZnO demonstrates outstanding selective removal efficacy for uranium, manifesting its considerable application potential and efficiency superiority. This strategy holds profound implications for facilitating the application of piezoelectric catalytic technology in environmental protection domains such as uranium removal, manifesting its considerable potential and value.

Defect-Induced Atomical Zn-O/N-C Bonding Promotes Efficient Charge Transfer in S-Scheme Interface for Bubble Level Solar Hydrogen Production

Establishing efficient and clear atomic-level charge transfer channels presents a significant challenge in the design of effective photocatalysts. A sound strategy has been developed herein involving the construction of defect-induced heterostructures that create chemical bonds serving as charge transfer channels at the heterojunction interface. In situ XPS, alongside theoretical calculations, demonstrates the successful construction of Zn-O/N-C as atomic charge transfer channels. Our findings reveal that the introduction of zinc vacancies (VZn) reduces the carrier transport activation energy (CTAE) from 155.2 meV for ZIS/CN to 128.7 meV for VZn-ZIS/CN. Consequently, the optimal VZn-ZIS/CN achieves a high hydrogen evolution rate of 22.26 mmol g-1 h-1 without Pt as a cocatalyst, which is approximately 57 times greater compared to that of ZIS/CN. Notably, hydrogen is generated at bubble levels under natural sunlight. This work provides insights into the mechanisms by which defect-induced heterostructure building strategies can introduce chemical bonds at the heterojunction interface.

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.

Pyrene-based covalent organic frameworks (PyCOFs): a review

Recently, pyrene-based covalent organic frameworks (PyCOFs) have aroused great interest because the large planar structure of the pyrene unit could effectively enhance the interlayer π-π interaction and promote the separation and migration of carriers, significantly improving the crystallinity and photoelectrical properties of PyCOFs. Since the first PyCOF-containing boroxate linkage was reported in 2008 by the Yaghi group, many PyCOFs with different kinds of linkages have been reported, exhibiting great potential applications in different fields such as adsorption/separation, chemical sensing, catalysis, energy storage, etc. However, as far as we know, the reviews related to PyCOFs are rare, although PyCOFs have been widely reported to show promising applications. Thus, it is right time and important for us to systematically summarize the research advance in PyCOFs, including the synthesis with different linkages and applications. Moreover, the prospects and obstacles facing the development of PyCOFs are discussed. We hope that this review will provide new insights into PyCOFs that can be explored for more attractive functions or applications.

Constructing Stable Nitrogen-Rich Core-Shell CdS@MC for Photocatalytic Reduction of U(VI) in Air without Sacrificial Agent

Photocatalytic reduction of uranium from U(VI) to U(IV) has been recognized as an effective treatment method for uranium wastewater. However, most photocatalysts have to be reduced under inert gas and sacrificial agent. Here, a class of nitrogen-rich core-shell photocatalysts (CdS@MC) with high stability was successfully prepared by modifying CdS with melamine and cyanuric chloride condensation. When the initial concentration of U(VI) was 100 mg/L and the solid-liquid ratio was 0.2 g/L, the removal of U(VI) by CdS@MC without sacrificial agent under air could reached 95%. The removal rate was still above 80% after five cycles with good stability and good removal rate of U(VI) at high salt concentration. CdS@MC not only efficiently generates electrons for photocatalytic reduction of U(VI), but also generates H2O2 from O2, which then reacts with uranyl ions to produce metastudtite. This study provides a new direction for the study of efficient uranium removal photocatalysts without sacrificial agent in air environment.

Large Scale Synthesis of a Stable Prefunctionalized Silver Nanocluster

Due to the stability issue, It is difficult to prepare a silver nanocluster bearing functional sites, especially at a large scale. We report the synthesis and structure of a stable silver nanocluster bearing multiple surface aldehyde groups [Ag21(Ph2PO2)10(p-CHOPhC≡C)6]SbF6, which allows for postsynthesis modification such as surface functionalization through aldimine condensation to give homochiral clusters. Remarkably, the preparation of this cluster can be done in ~90 % high yield at gram scale, which facilitates further studies and potential applications. Through DFT calculations and geometric structure analysis, the high stability of this cluster is attributed to the geometric closure and electronic structure. This is the first time that an effective one-pot method has been developed to synthesize functional silver nanoclusters in high yield. The title cluster will be useful in the development of a variety of cluster-based materials.

2D Porphyrin-Based Covalent-Organic Framework/PEG Composites: A Rational Strategy for Photocatalytic Hydrogen Evolution

Two-dimensional porphyrin-based covalent-organic frameworks (2D-por-COFs) have gained significant attention as attractive platforms for efficient solar light conversion into hydrogen production. Herein, it is found that introducing transition metal zinc and polyethylene glycol (PEG) into 2D-por-COFs can effectively improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rate of ZnPor-COF is 2.82 times higher than that of H2Por-COF. Moreover, ZnPor-COF@PEG has the highest photocatalytic hydrogen evolution efficiency, which is 1.31 and 3.7 times that of pristine ZnPor-COF and H2Por-COF, respectively. The filling of PEG makes the layered structure of COFs more stable. PEG reduces the distortion and deformation of the carbon skeleton after the experiment of photocatalytic hydrogen evolution. The layered stacking and crystallization of 2D-por-COFs are also enhanced. Meanwhile, the presence of PEG also accelerates the transfer of excited electrons and enhances the photocatalytic hydrogen evolution activity. This strategy will provide valuable insights into the design of 2D-por-COFs as efficient solid photocatalysts for solar-driven hydrogen production.

Covalent Organic Frameworks Meet Titanium Oxide

In order to expand the applicability of materials and improve their performance, the combined use of different materials has increasingly been explored. Among these materials, inorganic-organic hybrid materials often exhibit properties superior to those of single materials. Covalent organic frameworks (COFs) are famous crystalline porous materials constructed by organic building blocks linked by covalent bonds. In recent years, the combination of COFs with other materials has shown interesting properties in diverse fields, and the composite materials of COFs and TiO2 have been investigated more and more. These two outstanding materials are combined through covalent bonding, physical mixing, and other methods and exhibit excellent performance in various fields, including photocatalysis, electrocatalysis, sensors, separation, and energy storage and conversion. In this Review, the current preparation methods and applications of COF-TiO2 hybrid materials are introduced in detail, and their future development and possible problems are discussed and prospected, which is of great significance for related research. It is believed that these interesting hybrid materials will show greater application value as research progresses.

New insight into the effects of p-benzoquinone on photocatalytic reduction of Cr(VI) over Fe-doped g-C3N4

It is of great significance to establish an effective method for removing Cr(VI) from wastewater. Herein, Fe-doped g-C3N4 (namely Fe-g-C3N4-2) was synthesized and then employed as photocatalyst to conduct the test of Cr(VI) reduction. Notably, the embedding of Fe ion in g-C3N4 can offer the Fe2+/Fe3+ redox couples, so reducing the interfacial resistance of charge transfer and suppressing the recombination of photogenerated electrons and holes. The impurity energy levels will form in g-C3N4 after the introduction of Fe ion, thereby boosting the light absorption capacity of catalyst. Thus, Fe-g-C3N4-2 showed good performance in photocatalytic Cr(VI) reduction, and the reduction efficiency of Cr(VI) can reach 39.9% within 40 min. Different with many previous studies, current work unexpectedly found that the addition of p-benzoquinone (BQ) can promote the Cr(VI) reduction, and the reduction efficiency of Cr(VI) over Fe-g-C3N4-2 was as high as 93.2% in the presence of BQ (1.5 mM). Further analyses showed that BQ can be reduced to hydroquinone (HQ) by photogenerated electrons, and UV light can also directly induce BQ to generate HQ by using H2O as the hydrogen donor. The HQ with reducing ability can accelerate the Cr(VI) reduction. In short, current work shared some novel insights into photocatalytic Cr(VI) reduction in the presence of BQ. Future research should consider possible reactions between photogenerated electrons and BQ. For the UV-induced photocatalysis, the suitability of BQ as the scavenger of O2•‒ must be given carefully consideration.

Design and synthesis of broadband absorption covalent organic framework for efficient artificial photocatalytic amine coupling

Developing highly active materials that efficiently utilize solar spectra is crucial for photocatalysis, but still remains a challenge. Here, we report a new donor-acceptor (D-A) covalent organic framework (COF) with a wide absorption range from 200 nm to 900 nm (ultraviolet-visible-near infrared light). We find that the thiophene functional group is accurately introduced into the electron acceptor units of TpDPP-Py (TpDPP: 5,5'-(2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]pyrrole-1,4-diyl)bis(thiophene-2-carbaldehyde), Py: 1,3,6,8-tetrakis(4-aminophenyl)pyrene) COFs not only significantly extends its spectral absorption capacity but also endows them with two-photon and three-photon absorption effects, greatly enhancing the utilization rate of sunlight. The selective coupling of benzylamine as the target reactant is used to assess the photocatalytic activity of TpDPP-Py COFs, showing high photocatalytic conversion of 99% and selectivity of 98% in 20 min. Additionally, the TpDPP-Py COFs also exhibit the universality of photocatalytic selective coupling of other imine derivatives with ~100% conversion efficiency. Overall, this work brings a significant strategy for developing COFs with a wide absorption range to enhance photocatalytic activity.

Metal-Organic Frameworks-Derived Nanocarbon Materials and Nanometal Oxides for Photocatalytic Applications

Harnessing low-density solar energy and converting it into high-density chemical energy through photocatalysis has emerged as a promising avenue for the production of chemicals and remediation of environmental pollution, which contributes to alleviating the overreliance on fossil fuels. In recent years, metal-organic frameworks (MOFs) have gained widespread application in the field of photocatalysis due to their photostability, tunable structures, and responsiveness in the visible light range. However, most MOFs exhibit relatively low response to light, limiting their practical applications. MOFs-derived nanomaterials not only retain the inherent advantages of pristine MOFs but also show enhanced light adsorption and responsiveness. This review categorizes and summarizes MOFs-derived nanomaterials, including nanocarbons and nanometal oxides, providing representative examples for the synthetic strategies of each category. Subsequently, the recent research progress on MOFs-derived materials in photocatalytic applications are systematically introduced, specifically in the areas of photocatalytic water splitting to H2, photocatalytic CO2 reduction, and photocatalytic water treatment. The corresponding mechanisms involved in each photocatalytic reaction are elaborated in detail. Finally, the review discusses the challenges and further directions faced by MOFs-derived nanomaterials in the field of photocatalysis, highlighting their potential role in advancing sustainable energy production and environmental remediation.

Construction of Core-Shelled Covalent/Metal-Organic Frameworks for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is the half-reaction in zinc-air batteries and water splitting. Developing highly efficient catalysts toward OER is a challenge due to the difficulty of removing four electrons from two water molecules. Covalent organic frameworks (COFs) provide the new chance to construct the highly active catalysts for OER, because they have controlled skeletons, porosities, and well-defined catalytic sites. In this work, core-shell hybrids of COF and metal-organic frameworks (MOFs) have first demonstrated to catalyze the OER. The synergetic effects between the COF-shell and MOF-core render the catalyst with higher activity than those from the COF and MOF. And the catalyst achieved an overpotential of 328 mV, with a Tafel slope of 43.23 mV dec-1 in 1 m KOH. The theoretical calculation revealed that the high activity is from the Fe sites in the catalyst, which has suitable binding ability of reactant intermediate (OOH*), and thus contributed high activity. This work gives a new insight to designing COFs in electrochemical energy storage and conversion systems.

Low-temperature synthesis of porous organic polymers with donor-acceptor structure and β-ketoenamine for photocatalytic oxidative coupling of amines

In light of the widespread use of fossil fuels and the resulting environmental pollution, it is crucial to develop efficient photocatalysts for renewable energy applications that utilize visible light. Organic photocatalysts based on β-ketoenamine offer several advantages, including facile preparation, high stability, structural controllability, and excellent photovoltaic properties. However, in previous studies, the synthesis of porous organic polymers (POPs) often involved long, high-temperature processes. In this study, POPs with donor (D)-acceptor (A) structure were constructed by utilizing various branched bridging groups and 2,4,6-triformylphloroglucinol, across multiple temperature gradients. Through adjustments in hydrothermal temperature, we successfully synthesized a series of POPs with varying enol-keto structure ratios. Among these POPs, the dimethoxybenzidine-POPs (DMDPOPs) with methoxy electron-rich branched chains exhibited superior photovoltaic performance, electron transfer rate, and photocatalytic activity compared to the dihydroxybenzidine-POPs (DHDPOPs) with electron-deficient hydroxyl branched chains. Notably, DMDPOP-30 demonstrated outstanding performance, achieving a conversion rate of 98% within 3 h. Additionally, other POPs exhibited favorable conversions (90%), further confirming the feasibility of this synthetic approach. Moreover, the synthesis of DMDPOP-30 was achieved under mild conditions at room temperature, highlighting its significant potential for practical applications.

Nitrogen-Rich Triazine-Based Covalent Organic Frameworks as Efficient Visible Light Photocatalysts for Hydrogen Peroxide Production

Covalent organic frameworks (COFs) have been widely used in photocatalytic hydrogen peroxide (H2O2) production due to their favorable band structure and excellent light absorption. Due to the rapid recombination rate of charge carriers, however, their applications are mainly restricted. This study presents the design and development of two highly conjugated triazine-based COFs (TBP-COF and TTP-COF) and evaluates their photocatalytic H2O2 production performance. The nitrogen-rich structures and high degrees of conjugation of TBP-COF and TTP-COF facilitate improved light absorption, promote O2 adsorption, enhance their redox power, and enable the efficient separation and transfer of photogenerated charge carriers. There is thus an increase in the photocatalytic activity for the production of H2O2. When exposed to 10 W LED visible light irradiation at a wavelength of 420 nm, the pyridine-based TTP-COF produced 4244 μmol h-1 g-1 of H2O2 from pure water in the absence of a sacrificial agent. Compared to TBP-COF (1882 μmol h-1 g-1), which has a similar structure but lacks pyridine sites, TTP-COF demonstrated nearly 2.5 times greater efficiency. Furthermore, it exhibited superior performance compared to most previously published nonmetal COF-based photocatalysts.

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.

Symmetrical Localized Built-in Electric Field by Induced Polarization Effect in Ionic Covalent Organic Frameworks for Selective Imaging and Killing Bacteria

Photocatalytic materials are some of the most promising substitutes for antibiotics. However, the antibacterial efficiency is still inhibited by the rapid recombination of the photogenerated carriers. Herein, we design a cationic covalent organic framework (COF), which has a symmetrical localized built-in electric field due to the induced polarization effect caused by the electron-transfer reaction between the Zn-porphyrin unit and the guanidinium unit. Density functional theory calculations indicate that there is a symmetrical electrophilic/nucleophilic region in the COF structure, which results from increased electron density around the Zn-porphyrin unit. The formed local electric field can further inhibit the recombination of photogenerated carriers by driving rapid electron transfer from Zn-porphyrin to guanidinium under light irradiation, which greatly increases the yield of reactive oxygen species. This COF wrapped by DSPE-PEG2000 can selectively target the lipoteichoic acid of Gram-positive bacteria by electrostatic interaction, which can be used for selective discrimination and imaging of bacteria. Furthermore, this nanoparticle can rapidly kill Gram-positive bacteria including 99.75% of Staphylococcus aureus and 99.77% of Enterococcus faecalis at an abnormally low concentration (2.00 ppm) under light irradiation for 20 min. This work will provide insight into designing photoresponsive COFs through engineering charge behavior.

The prospect of CuxO-based catalysts in photocatalysis: From pollutant degradation, CO2 reduction, and H2 production to N2 fixation

The topic of photocatalysis and CuxO-based materials has been intertwined for quite a long time. Its relatively high abundance in the earth's crust makes it an important target for researchers around the globe. One of the properties exploited by researchers is its ability to exist in different oxidation states (Cu0, Cu+, Cu2+, and Cu3+) and its implications on photocatalytic efficiency improvement. Recently, they have been extensively used as photocatalytic materials for dye and pollutant degradation. However, it has almost reached saturation levels, therefore, currently, they are being mostly utilized for CO2 reduction and H2 evolution. Hence, this review will discuss the evolution (in application) of CuxO-based photocatalysts, relating to their past, present, and future. Moreover, photocatalytic efficiency improvement strategies such as doping, heterojunction formation, and carbonaceous construction with other materials will also be touched upon. Finally, the prospect of Cu2O-based photocatalysts will be discussed in the field of photocatalytic N2 fixation to ammonia. The significance of N2 chemisorption on photocatalysts to maximize ammonia production will also be given importance.

Comparative photocatalytic study of visible light driven BiVO4, Cu2O, and Cu2O/BiVO4 nanocomposite for degradation of antibiotic for wastewater treatment

Semiconductor-based photocatalysts have become increasingly used in the removal of pollutants from wastewater, especially antibiotics. A series of composite-based cuprous oxide and bismuth vanadate (Cu2O/BiVO4) composite-based photocatalysts were synthesized by using the chemical method. The structure of the Cu2O/BiVO4 composite was verified by using x-ray diffraction, scanning electron microscopy, photoluminescence, Fourier transform infrared spectroscopy, and UV-visible spectra. The degradation of methylene blue (MB) and tetracycline (TC) was investigated to check the photocatalytic activity of the Cu2O/BiVO4 composite series. The quantity of Cu2O was varied from 1% to 7% by weight to prepare the series of Cu2O/BiVO4 composites. The analysis of results verified that 5% Cu2O/BiVO4 exhibits an outstanding photocatalytic activity as compared to 1%, 3%, and 7% Cu2O/BiVO4, pure Cu2O, and pure BiVO4 under visible light irradiation. The optimum value of photocatalytic degradation achieved with 5% Cu2O/BiVO4 was 97% for MB dye and 95% for TC in 120 min, which is greater than the photocatalytic degradation of pure BiVO4 (MB 45% and TC 72%), pure Cu2O (MB 57% and TC 80%), 1% Cu2O/BiVO4 (MB 72% and TC 85%), 3% Cu2O/BiVO4 (MB 83% and TC 88%), and 7% Cu2O/BiVO4 (MB 87% and TC 91%). The stability and reusability of Cu2O/BiVO4 were also investigated. To check the major role of trapping in degradation, a trapping experiment was also performed by using three trapping agents: BQ, EDTA, and tBuOH. The results showed that Cu2O/BiVO4 exhibits an improved photocatalytic activity in the degradation of antibiotics in polluted water because the recombination rate of the electron-hole pair decreased and the surface area increased, which increased the active sites for redox reactions. Such a photocatalytic composite with high efficiency has various applications, such as energy production, environmental remediation, and water remediation.

Fluorination of Covalent Organic Framework Reinforcing the Confinement of Pd Nanoclusters Enhances Hydrogen Peroxide Photosynthesis

Metal-isolated clusters (MICs) physically confined on photoactive materials are of great interest in the field of photosynthesis of hydrogen peroxide (H2O2). Despite recent important endeavors, weak confinement of MICs in the reported photocatalytic systems leads to their low catalytic activity and stability. Herein, we report a new strategy of fluorinated covalent organic frameworks (COFs) to strongly confine Pd ICs for greatly boosting the photocatalytic activity and stability of H2O2 photosynthesis. Both experimental and theoretical results reveal that strong electronegative fluorine can increase the metal-support interaction and optimize the d-band center of Pd ICs, thus significantly enhancing the stability and activity of photocatalytic H2O2. An optimal TAPT-TFPA COFs@Pd ICs photocatalyst delivers a stable H2O2 yield rate of 2143 μmol h-1 g-1. Most importantly, the as-made TAPT-TFPA COFs@Pd ICs exhibit high catalytic stability over 100 h, which is the best among the reported materials.

Carbon Dots as an Electron Acceptor in the ZnIn2S4@MIL-88A Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

In this study, visible-light-responsive carbon dots (CDs)/ZnIn2S4@MIL-88A (C/ZI@ML) photocatalysts were successfully prepared through in situ loading CDs and ZnIn2S4 nanosheets on MIL-88A(Fe) to form a ternary heterojunction. The detailed characterization indicated that the two-dimensional ZnIn2S4 nanosheets were uniformly coated on the surface of MIL-88A(Fe), and ZnIn2S4/MIL-88A(Fe) exhibited enhanced photocatalytic hydrogen production performance (1259.63 μmol h-1 g-1) compared to that of pristine MIL-88A(Fe) and ZnIn2S4 under visible light illumination. After introduction of CDs into ZnIn2S4/MIL-88A(Fe), the C/ZI@ML catalyst remarkably enhanced the photocatalytic activity and the hydrogen evolution rate of 1C/ZI@ML was up to 3609.23 μmol g-1 h-1. The photoinduced charge carriers of C/ZI@ML can be efficiently separated and migrated because of the close contacted interface, synergistic effect, and suitable band structure. In combination with photoelectrochemical experiments and electron paramagnetic resonance spectra, a possible photocatalytic mechanism over C/ZI@ML was proposed. This work demonstrated a facile preparation method for fabricating efficient visible-light-driven heterojunction photocatalysts.

A Review on Cu2O-Based Composites in Photocatalysis: Synthesis, Modification, and Applications

Photocatalysis technology has the advantages of being green, clean, and environmentally friendly, and has been widely used in CO₂ reduction, hydrolytic hydrogen production, and the degradation of pollutants in water. Cu₂O has the advantages of abundant reserves, a low cost, and environmental friendliness. Based on the narrow bandgap and strong visible light absorption ability of Cu₂O, Cu₂O-based composite materials show infinite development potential in photocatalysis. However, in practical large-scale applications, Cu₂O-based composites still pose some urgent problems that need to be solved, such as the high composite rate of photogenerated carriers, and poor photocatalytic activity. This paper introduces a series of Cu₂O-based composites, based on recent reports, including pure Cu₂O and Cu₂O hybrid materials. The modification strategies of photocatalysts, critical physical and chemical parameters of photocatalytic reactions, and the mechanism for the synergistic improvement of photocatalytic performance are investigated and explored. In addition, the application and photocatalytic performance of Cu₂O-based photocatalysts in CO₂ photoreduction, hydrogen production, and water pollution treatment are discussed and evaluated. Finally, the current challenges and development prospects are pointed out, to provide guidance in applying Cu₂O-based catalysts in renewable energy utilization and environmental protection.

Recrystallization of 2D C-MOF Films for High-Performance Electrochemical Sensors

Two-dimensional (2D) conjugated metal-organic framework (c-MOF) films bring a completely new opportunity in the fields of catalysis, energy, and sensors, but preparing large-area continuous 2D c-MOF films remains a tremendous challenge. Here, we report a universal recrystallization strategy to synthesize large-area continuous 2D c-MOF films, revealing that the recrystallization strategy can significantly improve the electrochemical sensor sensitivity. Applying the 2D Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) c-MOF film as the active layer, the electrochemical sensor for glucose detection shows a high sensitivity of 20600 μA mM^-1 cm^-2, which is the best compared with the active materials reported previously. Most importantly, the as-made Cu₃(HHTP)₂ c-MOF-based electrochemical sensor possesses excellent stability. Overall, this work brings a brand-new universal strategy to prepare large-area continuous 2D c-MOF films for electrochemical sensors.