Z‐Scheme 2D/2D Heterojunction of Black Phosphorus/Monolayer Bi2WO6 Nanosheets with Enhanced Photocatalytic Activities

Black phosphorus (BP), a star‐shaped two‐dimensional material, has attracted considerable attention owing to its unique chemical and physical properties. BP shows great potential in photocatalysis area because of its excellent optical properties; however, its applications in this field have been limited to date. Now, a Z‐scheme heterojunction of 2D/2D BP/monolayer Bi₂WO₆ (MBWO) is fabricated by a simple and effective method. The BP/MBWO heterojunction exhibits enhanced photocatalytic performance in photocatalytic water splitting to produce H₂ and NO removal to purify air; the highest H₂ evolution rate of BP/MBWO is 21042 μmol g^?1, is 9.15 times that of pristine MBWO and the NO removal ratio was as high as 67 %. A Z‐scheme photocatalytic mechanism is proposed based on monitoring of ^.O₂^?, ^.OH, NO₂, and NO₃^? species in the reaction. This work broadens applications of BP and highlights its promise in the treatment of environmental pollution and renewable energy issues.     

Z‐Scheme Photocatalytic Water Splitting on a 2D Heterostructure of Black Phosphorus/Bismuth Vanadate Using Visible Light

Spontaneously solar‐driven water splitting to produce H₂ and O₂, that is, the conversion of solar energy to chemical energy is a dream of mankind. However, it is difficult to make overall water splitting feasible without using any sacrificial agents and external bias. Drawing inspiration from nature, a new artificial Z‐scheme photocatalytic system has been designed herein based on the two‐dimensional (2D) heterostructure of black phosphorus (BP)/bismuth vanadate (BiVO₄). An effective charge separation makes possible the reduction and oxidation of water on BP and BiVO₄, respectively. The optimum H₂ and O₂ production rates on BP/BiVO₄ were approximately 160 and 102 μmol g^?1 h^?1 under irradiation of light with a wavelength longer than 420 nm, without using any sacrificial agents or external bias.     

Van der Waals Heterostructures Comprised of Ultrathin Polymer Nanosheets for Efficient Z‐Scheme Overall Water Splitting

Inspired by natural photosynthesis, Z‐scheme photocatalytic systems are very appealing for achieving efficient overall water splitting. Developing metal‐free Z‐scheme photocatalysts for overall water splitting, however, still remains challenging. The construction of polymer‐based van der Waals heterostructures as metal‐free Z‐scheme photocatalytic systems for overall water splitting is described using aza‐fused microporous polymers (CMP) and C₂N ultrathin nanosheets as O₂‐ and H₂‐evolving catalysts, respectively. Although neither polymer is able to split pure water using visible light, a 2:1 stoichiometric ratio of H₂ and O₂ was observed when aza‐CMP/C₂N heterostructures were used. A solar‐to‐hydrogen conversion efficiency of 0.23 % was determined, which could be further enhanced to 0.40 % by using graphene as the solid electron mediator to promote the interfacial charge‐transfer process. This study highlights the potential of polymer photocatalysts for overall water splitting.     

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.     

Efficient Solar Light Harvesting CdS/Co9S8 Hollow Cubes for Z‐Scheme Photocatalytic Water Splitting

Hollow structures with an efficient light harvesting and tunable interior component offer great advantages for constructing a Z‐scheme system. Controlled design of hollow cobalt sulfide (Co₉S₈) cubes embedded with cadmium sulfide quantum dots (QDs) is described, using hollow Co(OH)₂ as the template and a one‐pot hydrothermal strategy. The hollow CdS/Co₉S₈ cubes utilize multiple reflections of light in the cubic structure to achieve enhanced photocatalytic activity. Importantly, the photoexcited charge carriers can be effectively separated by the construction of a redox‐mediator‐free Z‐scheme system. The hydrogen evolution rate over hollow CdS/Co₉S₈ is 134 and 9.1 times higher than that of pure hollow Co₉S₈ and CdS QDs under simulated solar light irradiation, respectively. Moreover, this is the first report describing construction of a hollow Co₉S₈ based Z‐scheme system for photocatalytic water splitting, which gives full play to the advantages of light‐harvesting and charges separation.     

Spatially Separated Photosystem II and a Silicon Photoelectrochemical Cell for Overall Water Splitting: A Natural–Artificial Photosynthetic Hybrid

Integrating natural and artificial photosynthetic platforms is an important approach to developing solar‐driven hybrid systems with exceptional function over the individual components. A natural–artificial photosynthetic hybrid platform is formed by wiring photosystem II (PSII) and a platinum‐decorated silicon photoelectrochemical (PEC) cell in a tandem manner based on a photocatalytic‐PEC Z‐scheme design. Although the individual components cannot achieve overall water splitting, the hybrid platform demonstrated the capability of unassisted solar‐driven overall water splitting. Moreover, H₂ and O₂ evolution can be separated in this system, which is ascribed to the functionality afforded by the unconventional Z‐scheme design. Furthermore, the tandem configuration and the spatial separation between PSII and artificial components provide more opportunities to develop efficient natural–artificial hybrid photosynthesis systems.     

Polymeric Carbon Nitride/Reduced Graphene Oxide/Fe2O3: All‐Solid‐State Z‐Scheme System for Photocatalytic Overall Water Splitting

The charge transfer between hydrogen evolution photocatalysts (HEPs) and oxygen evolution photocatalysts (OEPs) is the rate‐determining step that controls the overall performance of a Z‐scheme water‐splitting system. Here, we carefully design reduced graphene oxide (RGO) nanosheets for use as solid‐state mediators to accelerate the charge carrier transfer between HEPs (e.g., polymeric carbon nitride (PCN)) and OEPs (e.g., Fe₂O₃), thus achieving efficient overall water splitting. The important role of RGO could also be further proven in other PCN‐based Z‐systems (BiVO₄/RGO/PCN and WO₃/RGO/PCN), illustrating the universality of this strategy.     

Nanosized Functional MOFs Loading Ag/AgBr with Throughout‐Visible‐Light Absorption for High‐Efficiency Photocatalysis

Porous metal‐organic frameworks (MOFs) loading metal nanoparticles to form a composite photocatalyst demonstrated unique advantages. Modification of the electron donating group on the aromatic linkers of MOFs could increase the absorption range of light, thereby increasing the photocatalytic activity. In this study, we prepared a composite photocatalyst using a stable NH₂‐functionalized MOF (UiO‐66‐NH₂) to load semiconductor Ag/AgBr nanoparticles, and the resultant composites have intense optical absorption throughout visible light range. The greatly enhanced optical absorption and the unique hetero‐junction between Ag/AgBr and UiO‐66‐NH₂ render efficient separation and utilization of photogenerated electron‐hole pairs. Therefore, Ag/AgBr@UiO‐66‐NH₂ showed much more excellent photocatalytic activity, compared with unmodified UiO‐66 loading Ag/AgBr (Ag/AgBr@UiO‐66) and reported AgX@MOF catalysts. Moreover, the composite photocatalysts showed excellent stability during cycling experiment.     

Efficient Visible‐Light‐Driven Z‐Scheme Overall Water Splitting Using a MgTa2O6−xNy /TaON Heterostructure Photocatalyst for H2 Evolution

An (oxy)nitride‐based heterostructure for powdered Z‐scheme overall water splitting is presented. Compared with the single MgTa₂O_6?xN_y or TaON photocatalyst, a MgTa₂O_6?xN_y /TaON heterostructure fabricated by a simple one‐pot nitridation route was demonstrated to effectively suppress the recombination of carriers by efficient spatial charge separation and decreased defect density. By employing Pt‐loaded MgTa₂O_6?xN_y /TaON as a H₂‐evolving photocatalyst, a Z‐scheme overall water splitting system with an apparent quantum efficiency (AQE) of 6.8 % at 420 nm was constructed (PtO_x‐WO₃ and IO₃^?/I^? pairs were used as an O₂‐evolving photocatalyst and a redox mediator, respectively), the activity of which is circa 7 or 360 times of that using Pt‐TaON or Pt‐MgTa₂O_6?xN_y as a H₂‐evolving photocatalyst, respectively. To the best of our knowledge, this is the highest AQE among the powdered Z‐scheme overall water splitting systems ever reported.     

A Redox‐Mediator‐Free Solar‐Driven Z‐Scheme Water‐Splitting System Consisting of Modified Ta3N5 as an Oxygen‐Evolution Photocatalyst

Tantalum nitride (Ta₃N₅) modified with various O₂‐evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a redox‐mediator‐free Z‐scheme water‐splitting system. Ta₃N₅ was prepared by nitriding Ta₂O₅ powder under a flow of NH₃ at 1023–1223 K. The activity of Ta₃N₅ for water oxidation from an aqueous AgNO₃ solution as an electron acceptor without cocatalyst was dependent on the generation of a well‐crystallized Ta₃N₅ phase with a low density of anionic defects. Modification of Ta₃N₅ with nanoparticulate metal oxides as cocatalysts for O₂ evolution improved water‐oxidation activity. Of the cocatalysts examined, cobalt oxide (CoO_x) was found to be the most effective, improving the water‐oxidation efficiency of Ta₃N₅ by six to seven times. Further modification of CoO_x/Ta₃N₅ with metallic Ir as an electron sink allowed one to achieve Z‐scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle redox mediator in combination with Ru‐loaded SrTiO₃ doped with Rh as a H₂‐evolution photocatalyst.     

Semiconductor/Covalent‐Organic‐Framework Z‐Scheme Heterojunctions for Artificial Photosynthesis

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z‐scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z‐scheme photocatalysts combining water‐oxidation semiconductors (TiO₂, Bi₂WO₆, and α‐Fe₂O₃) with CO₂ reduction COFs (COF‐316/318) was synthesized and exhibited high photocatalytic CO₂‐to‐CO conversion efficiencies (up to 69.67 μmol g^?1 h^?1), with H₂O as the electron donor in the gas–solid CO₂ reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic‐semiconductor systems utilizing the Z‐scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor‐to‐COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO₂ reduction and holes in the semiconductor for H₂O oxidation, thus mimicking natural photosynthesis.     

Pigment–Acceptor–Catalyst Triads for Photochemical Hydrogen Evolution

In order to solve the problems of global warming and shortage of fossil fuels, researchers have been endeavoring to achieve artificial photosynthesis: splitting water into H₂ and O₂ under solar light illumination. Our group has recently invented a unique system that drives photoinduced water reduction through “Z‐scheme” photosynthetic pathways. Nevertheless, that system still suffered from a low turnover number (TON) of the photocatalytic cycle (TON=4.1). We have now found and describe herein a new methodology to make significant improvements in the TON, up to around TON=14–27. For the new model systems reported herein, the quantum efficiency of the second photoinduced step in the Z‐scheme photosynthesis is dramatically improved by introducing multiviologen tethers to temporarily collect the high‐energy electron generated in the first photoinduced step. These are unique examples of “pigment–acceptor–catalyst triads”, which demonstrate a new effective type of artificial photosynthesis.     

From Extended Nanofluidics to an Autonomous Solar‐Light‐Driven Micro Fuel‐Cell Device

Autonomous micro/nano mechanical, chemical, and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro‐power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage, and delivery to the sensor. Herein, we realized a solar‐light‐driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen fuel is then consumed by the μFC to generate electricity. Importantly, the by‐product water returns back to the photocatalytic μFG via recirculation loop without losses. Both devices rely on novel phenomena in extended‐nano‐fluidic channels that ensure ultra‐fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ca. 17.2 mWh cm⁻² at room temperature.     

Ligand‐Assisted Co‐Assembly Approach toward Mesoporous Hybrid Catalysts of Transition‐Metal Oxides and Noble Metals: Photochemical Water Splitting

A bottom‐up synthetic approach was developed for the preparation of mesoporous transition‐metal‐oxide/noble‐metal hybrid catalysts through ligand‐assisted co‐assembly of amphiphilic block‐copolymer micelles and polymer‐tethered noble‐metal nanoparticles (NPs). The synthetic approach offers a general and straightforward method to precisely tune the sizes and loadings of noble‐metal NPs in metal oxides. This system thus provides a solid platform to clearly understand the role of noble‐metal NPs in photochemical water splitting. The presence of trace amounts of metal NPs (≈0.1 wt %) can enhance the photocatalytic activity for water splitting up to a factor of four. The findings can conceivably be applied to other semiconductors/noble‐metal catalysts, which may stand out as a new methodology to build highly efficient solar energy conversion systems.     

Water‐Catalyzed Oxidation of Few‐Layer Black Phosphorous in a Dark Environment

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness‐dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light‐induced oxidation. Herein, we report a new degradation channel via water‐catalyzed oxidation of BP in the dark. When oxygen co‐adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus‐based devices.     

Boosting Photocatalytic Water Splitting: Interfacial Charge Polarization in Atomically Controlled Core–Shell Cocatalysts

Platinum is a commonly used cocatalyst for improved charge separation and surface reactions in photocatalytic water splitting. It is envisioned that its practical applications can be facilitated by further reducing the material cost and improving the efficacy of Pt cocatalysts. In this direction, the use of atomically controlled Pd@Pt quasi‐core–shell cocatalysts in combination with TiO₂ as a model semiconductor is described. As demonstrated experimentally, the electron trapping necessary for charge separation is substantially promoted by combining a Schottky junction with interfacial charge polarization, enabled by the three‐atom‐thick Pt shell. Meanwhile, the increase in electron density and lattice strain would significantly enhance the adsorption of H₂O onto Pt surface. Taken together, the improved charge separation and molecular activation dramatically boost the overall efficiency of photocatalytic water splitting.     

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.     

Unraveling the Interfacial Charge Migration Pathway at the Atomic Level in a Highly Efficient Z‐Scheme Photocatalyst

A highly efficient Z‐scheme photocatalytic system constructed with 1D CdS and 2D CoS₂ exhibited high photocatalytic hydrogen‐evolution activity of 5.54 mmol h^?1 g^?1 with an apparent quantum efficiency of 10.2 % at 420 nm. More importantly, its interfacial charge migration pathway was unraveled: The electrons are efficiently transferred from CdS to CoS₂ through a transition atomic layer connected by Co–S_5.8 coordination, thus resulting in more photogenerated carriers participating in surface reactions. Furthermore, the charge‐trapping and charge‐transfer processes were investigated by transient absorption spectroscopy, which gave an estimated charge‐separation yield of approximately 91.5 % and a charge‐separated‐state lifetime of approximately (5.2±0.5) ns in CdS/CoS₂. This study elucidates the key role of interfacial atomic layers in heterojunctions and will facilitate the development of more efficient Z‐scheme photocatalytic systems.     

Encapsulating Au‐Fe3O4 Nanodots into AIE‐active Supramolecular Assemblies: Ambient Visible‐light Harvesting “Dip‐Strip” Photocatalyst for C−C/C−N Bond Formation Reactions

The present study demonstrates the development of a supramolecular porous ensemble consisting of hetero‐oligophenylene derivative 6 and Au‐Fe₃O₄ nanodots. Supramolecular assemblies of AIE‐active hetero‐oligophenylene derivative 6 served as reactors for the generation of Au‐Fe₃O₄ nanodots. The as prepared supramolecular ensemble functioned as an efficient recyclable photocatalytic system for C(sp²)?H bond activation of anilines for the construction of quinoline carboxylates. Interestingly, the “dip catalyst” prepared by depositing PTh‐co‐PANI‐6: Au‐Fe₃O₄ nanodots on a filter paper served as a recyclable strip (up to 10 cycles) for C?C/C?N bond formation reaction.     

CdS/聚合物梯形产氢光催化剂及其原位光照电子转移机制

氢气是公认的洁净、高效、可再生的能源载体,有望替代目前广泛使用的化石燃料.太阳能光催化产氢是实现高效、低成本、可持续生产氢能的一种途径.然而,单一组分光催化剂的性能受限于光生电子-空穴的快速复合,并且不能同时满足宽的太阳光吸收范围和强的氧化还原能力的要求,因此需要构建异质结来增强光生载流子的分离并保持高效光吸收和强氧化...