Strong‐Base‐Assisted Synthesis of a Crystalline Covalent Triazine Framework with High Hydrophilicity via Benzylamine Monomer for Photocatalytic Water Splitting

Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF‐HUST‐A1 with a benzylamine‐functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF‐HUST‐A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200 μmol g^?1 h^?1). Photocatalytic overall water splitting is achieved by depositing dual co‐catalysts in CTF‐HUST‐A1, with H₂ evolution and O₂ evolution rates of 25.4 μmol g^?1 h^?1 and 12.9 μmol g^?1 h^?1 in pure water without using sacrificial agent.     

Surface-Degenerate Semiconductor Photocatalysis for Efficient Water Splitting without Sacrificial Agents via a Reticular Chemistry Approach

The production of green hydrogen through photocatalytic water splitting is crucial for a sustainable hydrogen economy and chemical manufacturing. However, current approaches suffer from slow hydrogen production (<70 μmol ⋅ g_cat⁻¹ ⋅ h⁻¹) due to the sluggish four-electrons oxygen evolution reaction (OER) and limited catalyst activity. Herein, we achieve efficient photocatalytic water splitting by exploiting a multifunctional interface between a nano-photocatalyst and metal–organic framework (MOF) layer. The functional interface plays two critical roles: (1) enriching electron density directly on photocatalyst surface to promote catalytic activity, and (2) delocalizing photogenerated holes into MOF to enhance OER. Our photocatalytic ensemble boosts hydrogen evolution by ≈100-fold over pristine photocatalyst and concurrently produces oxygen at ideal stoichiometric ratio, even without using sacrificial agents. Notably, this unique design attains superior hydrogen production (519 μmol ⋅ g_cat⁻¹ ⋅ h⁻¹) and apparent quantum efficiency up to 13-fold and 8-fold better than emerging photocatalytic designs utilizing hole scavengers. Comprehensive investigations underscore the vital role of the interfacial design in generating high-energy photoelectrons on surface-degenerate photocatalyst to thermodynamically drive hydrogen evolution, while leveraging the nanoporous MOF scaffold as an effective photohole sink to enhance OER. Our interfacial approach creates vast opportunities for designing next-generation, multifunctional photocatalytic ensembles using reticular chemistry with diverse energy and environmental applications.     

Covalent Triazine Frameworks via a Low‐Temperature Polycondensation Approach

Covalent triazine frameworks (CTFs) are normally synthesized by ionothermal methods. The harsh synthetic conditions and associated limited structural diversity do not benefit for further development and practical large‐scale synthesis of CTFs. Herein we report a new strategy to construct CTFs (CTF‐HUSTs) via a polycondensation approach, which allows the synthesis of CTFs under mild conditions from a wide array of building blocks. Interestingly, these CTFs display a layered structure. The CTFs synthesized were also readily scaled up to gram quantities. The CTFs are potential candidates for separations, photocatalysis and for energy storage applications. In particular, CTF‐HUSTs are found to be promising photocatalysts for sacrificial photocatalytic hydrogen evolution with a maximum rate of 2647 μmol h⁻¹ g⁻¹ under visible light. We also applied a pyrolyzed form of CTF‐HUST‐4 as an anode material in a sodium‐ion battery achieving an excellent discharge capacity of 467 mAh g⁻¹.     

Isolated Electron Trap-Induced Charge Accumulation for Efficient Photocatalytic Hydrogen Production

The solar-driven evolution of hydrogen from water using particulate photocatalysts is considered one of the most economical and promising protocols for achieving a stable supply of renewable energy. However, the efficiency of photocatalytic water splitting is far from satisfactory due to the sluggish electron-hole pair separation kinetics. Herein, isolated Mo atoms in a high oxidation state have been incorporated into the lattice of Cd_0.5Zn_0.5S (CZS@Mo) nanorods, which exhibit photocatalytic hydrogen evolution rate of 11.32 mmol g⁻¹ h⁻¹ (226.4 μmol h⁻¹; catalyst dosage 20 mg). Experimental and theoretical simulation results imply that the highly oxidized Mo species lead to mobile-charge imbalances in CZS and induce the directional photogenerated electrons transfer, resulting in effectively inhibited electron-hole recombination and greatly enhanced photocatalytic efficiency.     

Few-Layer Fullerene Network for Photocatalytic Pure Water Splitting into H2 and H2O2

A few-layer fullerene network possesses several advantageous characteristics, including a large surface area, abundant active sites, high charge mobility, and an appropriate band gap and band edge for solar water splitting. Herein, we report for the first time that the few-layer fullerene network shows interesting photocatalytic performance in pure water splitting into H₂ and H₂O₂ in the absence of any sacrificial reagents. Under optimal conditions, the H₂ and H₂O₂ evolution rates can reach 91 and 116 μmol g⁻¹ h⁻¹, respectively, with good stability. This work demonstrates the novel application of the few-layer fullerene network in the field of energy conversion.     

An Amine-Functionalized Zirconium Metal–Organic Polyhedron Photocatalyst with High Visible-Light Activity for Hydrogen Production

Metal–organic polyhedra (MOPs) are promising candidates for many potential applications; however, their use as photocatalysts for hydrogen production has yet to be developed. Herein, the photocatalytic performance of a water-stable Zr-MOP, ZrT-1-NH₂, was evaluated, for the first time, through photocatalytic hydrogen evolution under visible-light irradiation. ZrT-1-NH₂ shows clearly enhanced photocatalytic activity (510.42 μmol g⁻¹ h⁻¹) for hydrogen production, in comparison with that of other homogeneous crystalline materials. If platinum nanoparticles were introduced into the photocatalytic system, the hydrogen production efficiency of ZrT-1-NH₂ could be further improved. For ZrT-1-NH₂, the conspicuous improvement in photocatalysis can be attributed to efficient electron–hole separation, targeted electron transfer, and excellent recombination suppression. Furthermore, ZrT-1-NH₂ shows excellent stability during photocatalytic hydrogen evolution over five continuous runs. This work illustrates that MOP-based photocatalysts hold promise for broad applications in the domain of clean energy.     

Toward photocatalytic hydrogen generation over BiVO_4 by controlling particle size

Owing to excellent light absorption and high activity fo r oxygen evolution,monoclinic bismuth vanadate(BiVO_4) is regarded as an ideal candidate for photocatalytic water splitting.However,its application is limited by the large particle size in micrometer scale,as well as the slightly positive conduction band.In this work,we successfully synthesized nano-BiVO_4 with particle size ranged from 27 nm to 57 nm by wet chemical method based on electrostatic spinning method.Unlike bulk BiVO_4,the nano-sized BiVO_4 possesses the ability to generate hydrogen by water splitting,and the activity could reach up to1.66 μmol h~(-1) g~(-1) with the assistance of Pt.The enhanced activity is mainly attributed to the improvements resulted from reduced particle size,which includes elevated conduction band,enlarged specific surface area and promoted charge separation.This work provides a simple method for synthesizing photocatalyst with small particle size and high yield.     

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water

Constructing a powerful photocatalytic system that can achieve the carbon dioxide (CO₂) reduction half-reaction and the water (H₂O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust −C=C− bond linkages. The charge-separation ability of viCOF-bpy-Re is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge-separation enables the photogenerated electron–hole pairs, followed by an intramolecular charge-transfer process, to form photogenerated electrons involved in CO₂ reduction and photogenerated holes that participate in H₂O oxidation simultaneously. The viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g⁻¹ h⁻¹ with about 100 % selectivity) and oxygen (O₂) evolution (90.2 μmol g⁻¹ h⁻¹) among all the porous catalysts in CO₂ reduction with H₂O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure–function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.     

Multifunctional Nitrogen‐Doped Carbon Nanodots for Photoluminescence,Sensor, and Visible‐Light‐Induced H2 Production

Herein, multifunctional N‐doped carbon nanodots (NCNDs) were prepared through the one‐step hydrothermal treatment of yeast. Results show that the NCNDs can be used as a new photocatalyst to drive the water‐splitting reaction under UV light. Moreover, the NCNDs can efficiently catalyze the hydrogen evolution reaction. Under visible‐light irradiation, Eosin Y‐sensitized NCNDs exhibit excellent activity for hydrogen evolution. The hydrogen evolution rate of NCNDs (without any modification and co‐catalyst) reaches 107.1 μmol h^?1 (2142 μmol g^?1 h^?1). When Pt is loaded on the NCNDs, the hydrogen evolution rate reaches 491.2 μmol h^?1 (9824 μmol g^?1 h^?1) under visible‐light irradiation. In addition, the NCNDs show excellent fluorescent properties and can be applied as a fluorescent probe for the sensitive and selective detection of Fe³⁺.     

Noble‐Metal‐Free Janus‐like Structures by Cation Exchange for Z‐Scheme Photocatalytic Water Splitting under Broadband Light Irradiation

Z‐scheme water splitting is a promising approach based on high‐performance photocatalysis by harvesting broadband solar energy. Its efficiency depends on the well‐defined interfaces between two semiconductors for the charge kinetics and their exposed surfaces for chemical reactions. Herein, we report a facile cation‐exchange approach to obtain compounds with both properties without the need for noble metals by forming Janus‐like structures consisting of γ‐MnS and Cu₇S₄ with high‐quality interfaces. The Janus‐like γ‐MnS/Cu₇S₄ structures displayed dramatically enhanced photocatalytic hydrogen production rates of up to 718 μmol g⁻¹ h⁻¹ under full‐spectrum irradiation. Upon further integration with an MnO_x oxygen‐evolution cocatalyst, overall water splitting was accomplished with the Janus structures. This work provides insight into the surface and interface design of hybrid photocatalysts, and offers a noble‐metal‐free approach to broadband photocatalytic hydrogen production.     

Consecutive Charging of a Perylene Bisimide Dye by Multistep Low-Energy Solar-Light-Induced Electron Transfer Towards H2 Evolution

A photocatalytic system containing a perylene bisimide (PBI) dye as a photosensitizer anchored to titanium dioxide (TiO₂) nanoparticles through carboxyl groups was constructed. Under solar-light irradiation in the presence of sacrificial triethanolamine (TEOA) in neutral and basic conditions (pH 8.5), a reaction cascade is initiated in which the PBI molecule first absorbs green light, giving the formation of a stable radical anion (PBI^.−), which in a second step absorbs near-infrared light, forming a stable PBI dianion (PBI²⁻). Finally, the dianion absorbs red light and injects an electron into the TiO₂ nanoparticle that is coated with platinum co-catalyst for hydrogen evolution. The hydrogen evolution rates (HERs) are as high as 1216 and 1022 μmol h⁻¹ g⁻¹ with simulated sunlight irradiation in neutral and basic conditions, respectively.     

Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting

Solar-driven water splitting to produce clean and renewable hydrogen offers a green strategy to address the energy crisis and environmental pollution. Heterostructure catalysts are receiving increasing attention for photocatalytic hydrogen generation. ZnO/ZnS/CdS and ZnO/CdS heterostructures have been successfully designed and prepared according to two different strategies. By introducing a heterointerface layer of ZnS between ZnO and CdS, a Z scheme charge-transfer channel was promoted and achieved superior photocatalytic performance. A highest hydrogen generation rate of 156.7 μmol g⁻¹ h⁻¹ was achieved by precise control of the thickness of the heterointerface layer and of the CdS shell. These findings demonstrated that heterostructures are promising catalysts for solar-driven water splitting, and that heterointerface engineering is an effective way to improve the photocatalytic properties of heterostructures.     

Directed Electron Delivery from a Pb-Free Halide Perovskite to a Co(II) Molecular Catalyst Boosts CO2 Photoreduction Coupled with Water Oxidation

The development of high-performance photocatalytic systems for CO₂ reduction is appealing to address energy and environmental issues, while it is challenging to avoid using toxic metals and organic sacrificial reagents. We here immobilize a family of cobalt phthalocyanine catalysts on Pb-free halide perovskite Cs₂AgBiBr₆ nanosheets with delicate control on the anchors of the cobalt catalysts. Among them, the molecular hybrid photocatalyst assembled by carboxyl anchors achieves the optimal performance with an electron consumption rate of 300±13 μmol g⁻¹ h⁻¹ for visible-light-driven CO₂-to-CO conversion coupled with water oxidation to O₂, over 8 times of the unmodified Cs₂AgBiBr₆ (36±8 μmol g⁻¹ h⁻¹), also far surpassing the documented systems (<150 μmol g⁻¹ h⁻¹). Besides the improved intrinsic activity, electrochemical, computational, ex-/in situ X-ray photoelectron and X-ray absorption spectroscopic results indicate that the electrons photogenerated at the Bi atoms of Cs₂AgBiBr₆ can be directionally transferred to the cobalt catalyst via the carboxyl anchors which strongly bind to the Bi atoms, substantially facilitating the interfacial electron transfer kinetics and thereby the photocatalysis.     

Single‐Site Active Cobalt‐Based Photocatalyst with a Long Carrier Lifetime for Spontaneous Overall Water Splitting

An active and stable photocatalyst to directly split water is desirable for solar‐energy conversion. However, it is difficult to accomplish overall water splitting without sacrificial electron donors. Herein, we demonstrate a strategy via constructing a single site to simultaneously promote charge separation and catalytic activity for robust overall water splitting. A single Co₁‐P₄ site confined on g‐C₃N₄ nanosheets was prepared by a facile phosphidation method, and identified by electron microscopy and X‐ray absorption spectroscopy. This coordinatively unsaturated Co site can effectively suppress charge recombination and prolong carrier lifetime by about 20 times relative to pristine g‐C₃N₄, and boost water molecular adsorption and activation for oxygen evolution. This single‐site photocatalyst exhibits steady and high water splitting activity with H₂ evolution rate up to 410.3 μmol h⁻¹ g⁻¹, and quantum efficiency as high as 2.2 % at 500 nm.     

Graphene Oxide-Assisted Covalent Triazine Framework for Boosting Photocatalytic H2 Evolution

Covalent triazine frameworks (CTFs) with two-dimensional structures have exhibited promising visible-light-induced H₂ evolution performance. However, it is still a challenge to improve their activity. Herein, we report π-conjugation-linked CTF-1/GO for boosting photocatalytic H₂ evolution. The CTF-1/GO hybrid material was obtained by a facile low-temperature condensation of 1,4-dicyanobenzene in the presence of GO. The results of photocatalytic H₂ evolution indicate that the optimum hybrid, CTF-1/GO-3.0, exhibited an H₂ evolution rate of 2262.4 μmol ⋅ g⁻¹ ⋅ h⁻¹ under visible light irradiation, which was 9 times that of pure CTF-1. The enhanced photocatalytic performance could be attributed to the fact that GO in CTF-1/GO hybrids not only acts as an electron collector and transporter like a “bridge” to facilitate the separation and transfer of photogenerated charges but also shortens the electron migration path due to its thin sheet layer uniformly distribution over CTF-1. This work could help future development of novel conjugated CTF-based composite materials as high-efficiency photocatalyst for photocatalysis.     

Thiophene-Containing Covalent Organic Frameworks for Overall Photocatalytic H2O2 Synthesis in Water and Seawater

H₂O₂ is a significant chemical widely utilized in the environmental and industrial fields, with growing global demand. Without sacrificial agents, simultaneous photocatalyzed H₂O₂ synthesis through the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) dual channels from seawater is green and sustainable but still challenging. Herein, two novel thiophene-containing covalent organic frameworks (TD-COF and TT-COF) were first constructed and served as catalysts for H₂O₂ synthesis via indirect 2e⁻ ORR and direct 2e⁻ WOR channels. The photocatalytic H₂O₂ production performance can be regulated by adjusting the N-heterocycle modules (pyridine and triazine) in COFs. Notably, with no sacrificial agents, just using air and water as raw materials, TD-COF exhibited high H₂O₂ production yields of 4060 μmol h⁻¹ g⁻¹ and 3364 μmol h⁻¹ g⁻¹ in deionized water and natural seawater, respectively. Further computational mechanism studies revealed that the thiophene was the primary photoreduction unit for ORR, while the benzene ring (linked to the thiophene by the imine bond) was the central photooxidation unit for WOR. The current work exploits thiophene-containing COFs for overall photocatalytic H₂O₂ synthesis via ORR and WOR dual channels and provides fresh insight into creating innovative catalysts for photocatalyzing H₂O₂ synthesis.     

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

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D_3h-symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C₅₄N₆-COF) via Knoevenagel condensation with another D_3h-symmetric monomer 2,4,6-tris(4′-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C_2v-symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C₅₂N₆-COF). The octupolar conjugated characters of g-C₅₄N₆-COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C₅₂N₆-COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C₅₄N₆-COF enabled the two-half reactions of photocatalytic water splitting with an average O₂ evolution rate of 51.0 μmol h⁻¹ g⁻¹ and H₂ evolution rate of 2518.9 μmol h⁻¹ g⁻¹. Such values are among the highest of state-of-the-art COF photocatalysts.     

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas-Liquid Interface of Microdroplets**

Solar-driven CO₂ reduction reaction (CO₂RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO₂RR efficiency at the abundant gas-liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO₃ ⋅ 0.33H₂O mediated by microdroplets reaches 2536 μmol h⁻¹ g⁻¹ (vs. 13 μmol h⁻¹ g⁻¹ in bulk phase), which is significantly superior to the previously reported photocatalytic CO₂RR in bulk phase reaction condition. Beyond the efficient delivery of CO₂ to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas-liquid interface of microdroplets essentially promotes the separation of photogenerated electron-hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO₂ reduction to fuel.     

Efficient One-Pot Microwave-Assisted Hydrothermal Synthesis of Nitrogen-Doped TiO2 for Hydrogen Production by Photocatalytic Water Splitting

Develop a photocatalyst system for solar energy conversion to electric energy or chemical energy is a topic of great interest for fundamental and practical importance. In this study, nitrogen-doped TiO₂ with high hydrogen production by photocatalytic water splitting were prepared by microwave-assisted hydrothermal method using titanium sulfate as precursor in the presence of urea. The nitrogen doped TiO₂ prepared in this study was pure anatase phase with a high surface area (372?m²?g^?1) and showed a very high hydrogen evolution rate of water splitting reaction under UV light irradiation (4,386?μmol?g^?1?h^?1) and visible light irradiation (185?μmol?g^?1?h^?1) which was about 15?times higher than commercial TiO₂ (Degussa P25).     

A Metal-Organic-Framework-Derived g-C3N4/α-Fe2O3 Hybrid for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

As one of the most efficient systems for photocatalytic hydrogen evolution, the Z-Scheme system, consisting of different semiconductors with a reversible donor–acceptor pair, has attracted great attention. Considering the non-toxicity and low cost of photocatalysts, a series of g-C₃N₄/α-Fe₂O₃ hybrids were rationally constructed based on the Z-Scheme mechanism for the first time, using a metal-organic framework template approach that can fine tune the compositions and properties of the hybrids. An optimized hybrid, g-C₃N₄/α-Fe₂O₃-2, exhibited prominent photocatalytic water splitting performance with a visible light response. Under irradiation of visible light (λ>420 nm), the hybrid shows a high durability and superior hydrogen production rate of 2066.2 μmol g⁻¹ h⁻¹ from water splitting, which is approximately three times greater than that of bulk g-C₃N₄ because of the effective separation of photo-excited charge carriers by two narrow band gap semiconductors, tightly coupled with the Z-Scheme structural feature.