Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible-Light-Driven CO2 Photoreduction

Structure-phase transformation of bismuth oxide to BiOCl/Bi24O31Cl10 shoulder-by-shoulder heterojunctions for efficient photocatalytic removal of antibiotic

Developing heterojunction photocatalyst with well-matched interfaces and multiple charge transfer paths is vital to boost carrier separation efficiency for photocatalytic antibiotics removal, but still remains a great challenge. In present work, a new strategy of chloride anion intercalation in Bi2O3 via one-pot hydrothermal process is proposed. The as-prepared Ta-BiOCl/Bi24O31Cl10 (TBB) heterojunctions are featured with Ta-Bi24O31Cl10 and Ta-BiOCl lined shoulder-by-shouleder via semi-coherent interfaces. In this TBB heterojunctions, the well-matched semi-coherent interfaces and shoulder-by-shoulder structures provide fast electron transfer and multiple transfer paths, respectively, leading to enhanced visible light response and improved photogenerated charge separation. Meanwhile, a type-II heterojunction for photocharge separation has been obtained, in which photogenerated electrons are drove from the CB (conduction band) of Ta-Bi24O31Cl10 to the both of bilateral empty CB of Ta-BiOCl and gathered on the CB of Ta-BiOCl, while the photogenerated holes are left on the VB (valence band) of Ta-Bi24O31Cl10, effectively hindering the recombination of photogenerated electron-hole pairs. Furthermore, the separated electrons can effectively activate dissolved oxygen for the generation of reactive oxygen species (·O2-). Such TBB heterojunctions exhibit remarkably superior photocatalytic degradation activity for tetracycline hydrochloride (TCH) solution to Bi2O3, Ta-BiOCl and Ta-Bi24O31Cl10. This work not only proposes a Ta-BiOCl/Bi24O31Cl10 shoulder-by-shoulder micro-ribbon architectures with semi-coherent interfaces and successive type-II heterojunction for highly efficient photocatalytic activity, but offers a new insight into the design of highly efficient heterojunction through phase-structure synergistic transformation strategy.

Charge self-regulation over in-plane two-dimensional/two-dimensional hetero-cocatalyst for robust photocatalytic hydrogen generation

The rationally designing and constructing atomic-level heterointerface of two-dimensional (2D) chalcogenides is highly desirable to overcome the sluggish H2O-activation process toward efficient solar-driven hydrogen evolution. Herein, a novel in-plane 2D/2D molybdenum disulfide-rhenium disulfide (ReS2-MoS2) heterostructure is well-designed to induce the charge self-regulation of active site by forming electron-enriched Re(4-δ)+ and electron-deficient S(2-δ)- sites, thus collectively facilitating the activation of adsorbed H2O molecules and its subsequent H2 evolution. Furthermore, the obtained in-plane heterogenous ReS2-MoS2 nanosheet can powerfully transfer photoexcited electrons to inhibit photocarrier recombination as observed by advanced Kelvin probe measurement (KPFM), in-situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient absorption spectroscopy (fs-TAS). As expected, the obtained ReS2-MoS2/TiO2 photocatalyst achieves an outperformed H2-generation rate of 6878.3 μmol h-1 g-1 with visualizing H2 bubbles in alkaline/neutral conditions. This work about in-plane 2D/2D heterostructure with strong free-electron interaction provides a promising strategy for designing novel and efficient catalysts for various applications.

Theoretical investigation of 2D/2D van der Waals SbPO4/BiOClxBr1-x heterojunctions for photocatalytic water splitting

Bismuth halogenoxide (BiOX)-based heterojunctions have garnered considerable attention recently due to their potential to enhance photocatalytic performance. However, the predominant focus on II-type heterojunctions has posed challenges in achieving the requisite band edge positions for efficient water splitting. In this investigation, stable van der Waals SbPO4/BiOClxBr1-x heterojunctions were constructed theoretically by using density-functional theory (DFT). Our findings demonstrate that SbPO4 can modulate the formation of Z-scheme heterojunctions with BiOClxBr1-x. The structural properties of BiOX were preserved, while reaching excellent photocatalytic capabilities with high redox capacities. Further investigation unveiled that the band edge positions of the heterojunctions fully satisfy the oxidation-reduction potential of water. Moreover, these heterojunctions exhibit notable absorption efficiency in the visible range, with absorption increasing as x decreases. Our research provides valuable theoretical insights for the experimental synthesis of high-performance BiOX-based photocatalysts for water splitting, leveraging the unique properties of SbPO4. These insights contribute to the advancement of clean energy technology.

Three-layered nanoplates and amorphous/crystalline interface synergism boost CO2 photoreduction on bismuth oxychloride nanospheres

Structural features like 3D nano-size, ultrathin thickness and amorphous/crystalline interfaces play crucial roles in regulating charge separation and active sites of photocatalysts. However, their co-occurrence in a single catalyst and exploitation in photocatalytic CO2 reduction (PCR) remains challenging. Herein, nano-sized bismuth oxychloride spheres (BiOCl-NS) confining three-layered nanoplates (∼2.2 nm ultrathin) and an amorphous/crystalline interface are exclusively developed via intrinsic engineering for an enhanced sacrificial-reagent-free PCR system. The results uncover a unique synergism wherein the three-layered nanoplates accelerate electron-hole separation, and the amorphous/crystalline interface exposes electron-localized active sites (Bi-Ovac-Bi). Consequently, BiOCl-NS exhibit efficient CO2 adsorption and activation with the lowering of rate-determining-step energy barriers, leading to remarkable CO production (102.72 μmol g-1 h-1) with high selectivity (>99%), stability (>30 h), and apparent quantum efficiency (0.51%), outperforming conventional counterparts. Our work provides a facile structural engineering approach for boosting PCR and offers distinct synergism for advancing diverse materials.

In Situ Etching-Hydrolysis Strategy To Construct an In-Plane ZnIn2S4/In(OH)3 Heterojunction with Enhanced CO2 Photoreduction Performance

The in-plane heterojunctions with atomic-level thickness and chemical-bond-connected tight interfaces possess high carrier separation efficiency and fully exposed surface active sites, thus exhibiting exceptional photocatalytic performance. However, the construction of in-plane heterojunctions remains a significant challenge. Herein, we prepared an in-plane ZnIn2S4/In(OH)3 heterojunction (ZISOH) by partial conversion of ZnIn2S4 to In(OH)3 through the addition of H2O2. This in situ oxidation etching-hydrolysis approach enables the ZISOH heterojunction to not only preserve the original nanosheet morphology of ZnIn2S4 but also form an intimate interface. Moreover, generated In(OH)3 serves as an electron-accepting platform and also promotes the adsorption of CO2. As a result, the heterojunction exhibits a remarkably enhanced performance for photocatalytic CO2 reduction. The production rate and selectivity of CO reach 1760 μmol g-1 h-1 and 78%, respectively, significantly higher than those of ZnIn2S4 (842 μmol g-1 h-1 and 65%). This work puts forward a feasible and facile approach to construct in-plane heterojunctions to enhance the photocatalytic performance of two-dimensional metal sulfides.

Enriching surface-ordered defects on WO3 for photocatalytic CO2-to-CH4 conversion by water

Defect engineering has been widely applied in semiconductors to improve photocatalytic properties by altering the surface structures. This study is about the transformation of inactive WO3 nanosheets to a highly effective CO2-to-CH4 conversion photocatalyst by introducing surface-ordered defects in abundance. The nonstoichiometric WO3-x samples were examined by using aberration-corrected electron microscopy. Results unveil abundant surface-ordered terminations derived from the periodic {013} stacking faults with a defect density of 20.2%. The {002} surface-ordered line defects are the active sites for fixation CO2, transforming the inactive WO3 nanosheets into a highly active catalyst (CH4: O2 = 8.2: 16.7 μmol h-1). We believe that the formation of the W-O-C-W-O species is a critical step in the catalytic pathways. This work provides an atomic-level comprehension of the structural defects of catalysts for activating small molecules.

Surface-surface contacted direct Z-scheme TiO2-BiVO4-PI heterostructure for enhanced photoelectrocatalytic degradation of bisphenols under solar driven

Bisphenols (BPs) are a series of widely used endocrine disruptors, which potentially harm the environment and human health. In this work, a novel Z-scheme TiO2-BiVO4-PI heterostructure was synthesized, characterized, and used for the simulated sunlight-driven photoelectrocatalytic degradation of BPs. Due to the existence of surface-surface contacted direct Z-scheme between BiVO4 and PI, holes were concentrated on the valence band of BiVO4 and electrons were concentrated on the conduction band of PI, resulting in a stronger redox activity. All six BPs exhibited appreciable degradation following the order of bisphenol A (BPA, 93.5%) > bisphenol B (BPB, 92.7%) > bisphenol AP (BPAP, 85.6%) > bisphenol F (BPF, 75.9%) > bisphenol AF (BPAF, 69.8%) > bisphenol S (BPS, 39.2%), within 120 min under the optimal condition. In the process of degradation, superoxide radicals (·O2-) and hydroxyl radicals (·OH) played dominant roles, and the intermediates of BPs degradation were mainly formed via the substituent shedding or C-C bond breaking of phenol ring, hydroxylation, and ring opening of phenol ring. The ECOSAR program was used to analyze the changes in the toxicity of the intermediates, and it was proved that the toxicity showed a decrease trend during the degradation process. This study provides a Z-scheme mechanism for TiO2-BiVO4-PI, which can degrade BPs and reduce their toxicity effectively.

Surface and interface engineering of BiOCl nanomaterials and their photocatalytic applications

BiOCl materials have received much attention because of their unique optical and electrical properties. Still, their unsatisfactory catalytic performance has been troubling researchers, limiting the application of BiOCl-based photocatalysts. Therefore, many researchers have studied the adjustment of BiOCl-based materials to enhance photocatalytic efficiency. This review focuses on surface and interface engineering strategies for boosting the photocatalytic performance of BiOCl-based nanomaterials, including forming oxygen vacancy defects, constructing metal/BiOCl, and the fabrication of semiconductor/BiOCl nanocomposites. The photocatalytic applications of the above composites are also concluded in photodegradation of aqueous pollutants, photocatalytic NO removal, photo-induced H2 production, and CO2 reduction. Special emphasis has been given to the modification methods of BiOCl and photocatalytic mechanisms to provide a more detailed understanding for researchers in the fields of energy conversion and materials sciences.

Strain-Induced Surface Interface Dual Polarization Constructs PML-Cu/Bi12O17Br2 High-Density Active Sites for CO2 Photoreduction

The insufficient active sites and slow interfacial charge transfer of photocatalysts restrict the efficiency of CO2 photoreduction. The synchronized modulation of the above key issues is demanding and challenging. Herein, strain-induced strategy is developed to construct the Bi-O-bonded interface in Cu porphyrin-based monoatomic layer (PML-Cu) and Bi12O17Br2 (BOB), which triggers the surface interface dual polarization of PML-Cu/BOB (PBOB). In this multi-step polarization, the built-in electric field formed between the interfaces induces the electron transfer from conduction band (CB) of BOB to CB of PML-Cu and suppresses its reverse migration. Moreover, the surface polarization of PML-Cu further promotes the electron converge in Cu atoms. The introduction of PML-Cu endows a high density of dispersed Cu active sites on the surface of PBOB, significantly promoting the adsorption and activation of CO2 and CO desorption. The conversion rate of CO2 photoreduction to CO for PBOB can reach 584.3 μmol g-1, which is 7.83 times higher than BOB and 20.01 times than PML-Cu. This work offers valuable insights into multi-step polarization regulation and active site design for catalysts.

Design of ultrathin CoAl-LDHs/ZnIn2S4 with strong interfacial bonding and rich oxygen vacancies for highly efficient hydrogen evolution activity

Designing a semiconductor-based heterostructure photocatalyst is very important way to enhance the hydrogen production activity. Here, a novel 2D/2D CoAl-LDHs/ZnIn2S4 S-scheme heterostructure with an ultrathin structure was synthesized by electrostatic attraction between CoAl-LDHs and ZnIn2S4 nanosheets. The presence of oxygen vacancies in the monolayer CoAl-LDHs nanosheet promotes the formation of Co-SX bonds, which serve as charge transfer channels at the interface of the CoAl-LDHs/ZnIn2S4 heterostructure. The ultrathin CoAl-LDHs/ZnIn2S4 exhibits broadened light absorption in the near-infrared range due to the occurrence of Co-SX chemical bonds. The CoAl-LDHs/ZnIn2S4 with a mass ratio of 1:2 demonstrated the highest photocatalytic hydrogen evolution activity (1563.64 μmol g-1 h-1) under the simulated sunlight, which is 4.6 and 9.7 times than that of the ZnIn2S4 and CoAl-LDHs/ZnIn2S4(bulk), respectively. The enhanced photocatalytic activity of ultrathin 2D/2D CoAl-LDHs/ZnIn2S4 should attributed to the shorter carriers path that benefit from the ultrathin structure and the quicker photogenerated charge transfer and the S-scheme migration pathway accelerated by the charge channel of Co-SX bonds. These new ideas should be inspiring for the design and construction of heterostructures for higher photocatalytic hydrogen evolution activity.

Polarization-Sensitive Photodetector Based on High Crystallinity Quasi-1D BiSeI Nanowires Synthesized via Chemical Vapor Deposition

Bismuth chalcohalides (BiSeI and BiSI), a class of superior light absorbers, have recently garnered great attention owing to their promise in constructing next-generation optoelectronic devices. However, to date, the photodetection application of bismuth chalcohalides is still limited due to the challenge in controllable preparation. Herein, the synthesis of large-scale quasi-1D BiSeI nanowires via chemical vapor deposition growth is reported. By precisely tuning the growth temperature and the Se supply, it can effectively control the growth thermodynamics and kinetics of BiSeI crystal, and thus achieve high purity quasi-1D BiSeI nanowires with high crystal quality, uniform diameter, and tunable domain length. Theory and optical characterizations of the quasi-1D BiSeI nanowires reveal an indirect bandgap of 1.57 eV with prominent optical linear dichroism. As a result, the quasi-1D BiSeI nanowire-based photodetector demonstrates a broadband photoresponse (400-800 nm) with high responsivity of 5880 mA W-1 , fast response speed of 0.11 ms and superior air stability. More importantly, the photodetector displays strong polarization sensitivity (anisotropic ratio = 1.77) under the 532 nm light irradiation. This work will provide important guides to the synthesis of other quais-1D metal chalcohalides and shed light on their potential in constructing novel multifunctional optoelectronic devices.

High-Crystallinity BiOCl Nanosheets as Efficient Photocatalysts for Norfloxacin Antibiotic Degradation

Semiconductor photocatalysts are essential materials in the field of environmental remediation. Various photocatalysts have been developed to solve the contamination problem of norfloxacin in water pollution. Among them, a crucial ternary photocatalyst, BiOCl, has attracted extensive attention due to its unique layered structure. In this work, high-crystallinity BiOCl nanosheets were prepared using a one-step hydrothermal method. The obtained BiOCl nanosheets showed good photocatalytic degradation performance, and the degradation rate of highly toxic norfloxacin using BiOCl reached 84% within 180 min. The internal structure and surface chemical state of BiOCl were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared spectroscopy (FTIR), UV-visible diffuse reflectance (UV-vis), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectra (XPS), and photoelectric techniques. The higher crystallinity of BiOCl closely aligned molecules with each other, which improved the separation efficiency of photogenerated charges and showed high degradation efficiency for norfloxacin antibiotics. Furthermore, the obtained BiOCl nanosheets possess decent photocatalytic stability and recyclability.

Two-dimensional lateral anatase-rutile TiO2 phase junctions with oxygen vacancies for robust photoelectrochemical water splitting

Exploiting the photoelectrode materials with broad solar light response, high-efficient separation of photogenerated charges and abundant active sites is extremely vital yet enormously challenging. Herein, an innovative two-dimensional (2D) lateral anatase-rutile TiO₂ phase junctions with controllable oxygen vacancies perpendicularly aligned on Ti mesh is presented. Our experimental observations and theoretical calculations corroborate explicitly that the 2D lateral phase junctions together with three-dimensional arrays not only exhibit the high-efficient photogenerated charges separation guaranteed by the build-in electric field at the side-to-side interface, but also furnish enriching active sites. Moreover, the interfacial oxygen vacancies generate new defect energy levels and serve as electron donors, hence extending visible light response and further accelerating the separation and transfer of photogenerated charges. Profiting from these merits, the optimized photoelectrode yield a pronounced photocurrent density of 1.2 mA/cm² at 1.23 V vs. RHE with Faradic efficiency of 100%, which is approximately 2.4 times larger than that of pristine 2D TiO₂ nanosheets. Furthermore, the incident photon to current conversion efficiency (IPCE) of the optimized photoelectrode is also boosted within both ultraviolet and visible light regions. This research is envisioned deliver the new insight in developing the novel 2D lateral phase junctions for PEC applications.

Chelated Ion-Exchange Strategy toward BiOCl Mesoporous Single-Crystalline Nanosheets for Boosting Photocatalytic Selective Aromatic Alcohols Oxidation

The photoresponse and photocatalytic efficiency of bismuth oxychloride (BiOCl) are greatly limited by rapid recombination of photogenerated carriers. The construction of porous single-crystal BiOCl photocatalyst can effectively alleviate this issue and provide accessible active sites. Herein, a facile chelated ion-exchange strategy is developed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) using acetic acid and ammonia solution respectively as chelating agent and ionization promoter. The strong chelation between acetate ions and Bi³⁺ ions introduces acetate ions into the precipitated product to exchange with Cl^- ions, resulting in large lattice mismatch, strain release, and formation of void-like mesopores. The prepared BiOCl MSCN photocatalyst exhibits excellent catalytic performance with 99% conversion and 98% selectivity for oxidation of benzyl alcohol to benzaldehyde and superior general adaptability for various aromatic alcohols. The theoretical calculations and characterizations confirm that the superior performance is mainly attributed to the abundant oxygen vacancies, plenty of accessible adsorption/active sites and fast charge transport path without grain boundaries.

Moiré Superlattice Structure in Two-Dimensional Catalysts: Synthesis, Property and Activity

Two-dimensional (2D) layered materials have been widely used as catalysts due to their high specific surface area, large fraction of uncoordinated surface atoms, and high charge carrier mobility. Moiré superlattice emerges in 2D layered materials with twist angle or lattice mismatch. By manipulating the moiré superlattice structure, 2D layered materials present modulated electronic band structure, topological edge states, and unconventional superconductivity which are tightly associated with the performance of catalysts. Hence, engineering moiré superlattice structures are proposed to be an important technology in modifying 2D layered materials for improved catalytic properties. However, currently, the investigation of moiré superlattice structure in a catalytic application is still in its infancy. This perspective starts with the discussion of structural features and fabrication strategy of 2D materials with moiré superlattice structure. Afterward, the catalytic applications, including electrocatalytic and photocatalytic applications, are summarized. In particular, the promotion mechanism of the catalytic performance caused by the moiré superlattice structure is proposed. Finally, the perspective is concluded by outlining the remaining challenges and possible solutions for the future development of 2D materials with moiré superlattice structure towards the catalytic applications.

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

Assembling different 2D nanomaterials into heterostructures with strong interfacial interactions presents a promising approach for novel artificial photocatalytic materials. Chemically implementing the 2D nanomaterials' construction/stacking modes to regulate different interfaces can extend their functionalities and achieve good performance. Herein, based on different fundamental principles and photochemical processes, multiple construction modes (e.g., face-to-face, edge-to-face, interface-to-face, edge-to-edge) are overviewed systematically with emphasis on the relationships between their interfacial characteristics (e.g., point, linear, planar), synthetic strategies (e.g., in situ growth, ex situ assembly), and enhanced applications to achieve precise regulation. Meanwhile, recent efforts for enhancing photocatalytic performances of 2D/2D heterostructures are summarized from the critical factors of enhancing visible light absorption, accelerating charge transfer/separation, and introducing novel active sites. Notably, the crucial roles of surface defects, cocatalysts, and surface modification for photocatalytic performance optimization of 2D/2D heterostructures are also discussed based on the synergistic effect of optimization engineering and heterogeneous interfaces. Finally, perspectives and challenges are proposed to emphasize future opportunities for expanding 2D/2D heterostructures for photocatalysis.

One-pot construction of highly efficient TaON/Bi2O3/S-BiOCl ternary photocatalysts: Simultaneously integrating type-Ⅰ with Z-scheme junctions for improved visible light-driven removal of organic pollutants

Bismuth oxychloride (BiOCl) has appeared as a popular candidate in photocatalysis field but is plagued by its poor visible light harvesting and low carriers-flow steering inherited from wide band gap. Integration of doping and heterojunction engineering into the bulk has proven to be an optimal and generally applied method for enabling excellent photocatalytic activity. Nevertheless, the previous reported BiOCl-based photocatalysts fabricated by the above strategies are still suffered from harsh synthesis process, poor interface stability and narrow application area. Here, we introduce a facile one-pot hydrothermal strategy to achieve in-situ growth of TaON as a medium on the surface of Bi₂O₃ and S-doped BiOCl (denoted as S-BiOCl) for constructing ternary TaON/Bi₂O₃/S-BiOCl heterostructures, which were obtained by the simultaneous coprecipitation and ripening process. Current investigation suggests that such a unique TaON/Bi₂O₃/S-BiOCl exhibits a relatively much higher photocatalytic activity for visible light-driven removal of rhodamine B (RhB), tetracycline (TC) and tetracycline hydrochloride (TC-HCl) than those of hybrid Bi₂O₃/S-BiOCl and pristine S-BiOCl. It is ascribed to the synergetic effect on the introduction of S dopant level in BiOCl lattice as well as the construction of intimate double heterointerfaces among Bi₂O₃, TaON and S-BiOCl, which endows the TaON/Bi₂O₃/S-BiOCl photocatalysts with considerable advantages for highly elevating photocatalytic performances, such as the intensive optical absorption, high redox potential as well as high-efficient photocharge separation originated from type-I and Z-scheme pathways. This work delivers novel insights for design and one-pot preparation of high-active BiOX (X = Cl, Br and I)-based photocatalysts towards organic dye and antibiotic removal in the future research.

Constructing Heterogeneous Photocatalysts Based on Carbon Nitride Nanosheets and Graphene Quantum Dots for Highly Efficient Photocatalytic Hydrogen Generation

Although graphitic carbon nitride nanosheets (CNs) with atomic thickness are considered as promising materials for hydrogen production, the wide band gap (3.06 eV) and rapid recombination of the photogenerated electron-hole pairs impede their applications. To address the above challenges, we synergized atomically thin CNs and graphene quantum dots (GQDs), which were fabricated as 2D/0D Van der Waals heterojunctions, for H₂ generation in this study. The experimental characterizations indicated that the addition of GQDs to the π-conjugated system of CNs can expand the visible light absorption band. Additionally, the surface photovoltage spectroscopy (SPV) confirmed that introducing GQDs into CNs can facilitate the transport of photoinduced carriers in the melon chain, thus suppressing the recombination of charge carriers in body. As a result, the H₂ production activity of the Van der Waals heterojunctions was 9.62 times higher than CNs. This study provides an effective strategy for designing metal-free Van der Waals hetero-structured photocatalysts with high photocatalytic activity.

The Organic Bromide Sources Adjusting the Shape and Band Structures of BiOBr Nanosheets for Enhanced Photodegradation Performances of BPA

Bismuth oxybromide (BiOBr) nanosheets were prepared by employing organic bromide sources. In the presence of organic bromide sources, the effects of different conditions on the band structure, shape, size, and light responses of BiOBr nanosheets were examined. The reaction conditions, including different types of organic bromide sources, solvent, concentration, temperature, and time, were examined regarding the formation of BiOBr nanosheets. Then, the photocatalytic performances of different BiOBr nanosheets were also examined. Especially, the BiOBr nanosheets obtained from the addition of over 2 mmol of tetramethyl ammonium bromide (TMAB) in mannitol or EG at a higher temperature and longer reaction time showed superior photocatalytic activity. The enhanced photocatalytic performance of bisphenol A over these BiOBr nanosheets was achieved within 50 min due to efficient charge transfer and separation.

Two-dimensional ultrathin metal-based nanosheets for photocatalytic CO2 conversion to solar fuels

Artificially simulated photosynthesis has created substantial curiosity as the majority of efforts in this arena have been aimed to upsurge solar fuel efficiencies for commercialization. The layered inorganic 2D nanosheets offer considerably higher tunability of their chemical surface, physicochemical properties and catalytic activity. Despites the intrinsic advantages of such metal-based materials viz., metal oxides, transition metal dichalcogenides, metal oxyhalides, metal organic frameworks, layered double hydroxide, MXene's, boron nitride, black phosphorous and perovskites, studies on such systems are limited for applications in photocatalytic CO₂ reduction. The role of metal-based layers for CO₂ conversion and new strategies such as surface modifications, defect generation and heterojunctions to optimize their functionalities are discussed in this review. Research prospects and technical challenges for future developments of layered 2D metal-based nanomaterials are critically discussed.

Thin In-Plane In2 O3 /ZnIn2 S4 Heterostructure Formed by Topological-Atom-Extraction: Optimal Distance and Charge Transfer for Effective CO2 Photoreduction

Exploitation of atomic-level principles to optimize the charge transfer on ultrathin 2D heterostructures is an emerging frontier in relieving the energy and environmental crisis. Herein, a facile "topological-atom-extraction" protocol is disclosed, i.e., selective extraction of Zn from ultrathin half-unit-cell ZnIn₂ S₄ (HZIS) can embed thin In₂ O₃ domain into 1.60 nm thick HZIS layer to create an atomically thin in-plane In₂ O₃ /HZIS heterostructure. Thanks to the optimal distance and capability of charge separation, the in-plane In₂ O₃ /HZIS heterostructure is among the best ZnIn₂ S₄ -based CO₂ reduction reaction (CRR) photocatalysts, and indeed demonstrates a significant increase (from 6.8- to 128-fold) in CO production rate compared with those of out-plane ZIS@In₂ O₃ and out-plane In₂ O₃ -HZIS_calcined heterostructures. Density Functional Theory simulation reveals that whereas the out-plane heterostructure has a much smaller ∆q of 0.2-0.25 e, the in-plane heterostructure with "zero distance contact" has an optimal ∆q of 1.05 e between In₂ O₃ and HZIS that induces remarkable charge redistribution on the in-plane heterojunction interface and creates local electric field confined within the ultrathin layer. The charge redistribution efficiently directs the charge-carrier separation in S-scheme photocatalytic system and endows long-lifetime carrier to CRR active HZIS. The findings demonstrate the strong versatility of engineering atomic-level heterojunctions for efficient catalysts design.

Insights into Dynamic Surface Bromide Sites in Bi4 O5 Br2 for Sustainable N2 Photofixation

Simulating photosynthesis has long been one of the ideas for realizing the conversion of solar energy into industrial chemicals. Heterogeneous N₂ photofixation in water is a promising way for sustainable production of ammonia. However, a mechanistic understanding of the complex aqueous photocatalytic N₂ reduction is still lacking. In this study, a light-dependent surface hydrogenation mechanism and light-independent protection of catalyst surface for N₂ reduction are revealed on ultrathin Bi₄ O₅ Br₂ (BOB) nanosheets, in which the creation and annihilation of surface bromine vacancies can be controlled via a surface bromine cycle. Our rapid scan in situ FT-IR spectra verify that photocatalytic N₂ reduction proceeds through an associative alternating mechanism on BOB surface with bromine vacancies (BrV-BOB). This work provides a new strategy to combine light-dependent facilitated reaction with light-independent regeneration of catalyst for advancing sustainable ammonia production.

Synergy between Palladium Single Atoms and Nanoparticles via Hydrogen Spillover for Enhancing CO2 Photoreduction to CH4

Selective photoreduction of carbon dioxide (CO₂ ) into carbon-neutral fuels such as methane (CH₄ ) is extremely desirable but remains a challenge since sluggish multiple proton-electron coupling transfer and various C₁ intermediates are involved. Herein, a synergistic function between single Pd atoms (Pd₁ ) and Pd nanoparticles (Pd_NPs ) on graphitic carbon nitride (C₃ N₄ ) for photocatalytic CO₂ methanation is presented. The catalyst achieves a high selectivity of 97.8% for CH₄ production with a yield of 20.3 µmol g_cat. ^-1 h^-1 in pure water. Mechanistic studies revealed that Pd₁ sites activated CO₂ , while Pd_NPs sites boosted water (H₂ O) dissociation for increased H* coverage. The H* produced by Pd_NPs migrate to the Pd₁ sites to promote multiple proton-electron coupling transfer via hydrogen spillover. Moreover, the adjacent Pd₁ and Pd_NPs effectively stabilized intermediates such as *CHO, thereby favoring the pathway for CH₄ production. This work provides a new perspective into the development of selective photocatalytic CO₂ conversion through the artful design of synergistic catalytic sites.

An efficient hydrogen evolution photocatalyst of Rh@Cr2O3 loaded PbMoO4 twenty-six facets polyhedron

Shape anisotropic semiconductor is advanced catalyst for resolving energy crises. However, modification studies are still needed to overcome its intrinsic disadvantages, such as the lack of active sites. For this...

Dynamic Active Sites in Bi5O7I Promoted by Surface Tensile Strain Enable Selective Visible Light CO2 Photoreduction

Surface defects with abundant localized electrons on bismuth oxyhalide catalysts are proved to have the capability to capture and activate CO₂. However, bismuth oxyhalide materials are susceptible to photocorrosion, making the surface defects easily deactivated and therefore losing their function as active sites. Construction of deactivation-resistant surface defects on catalyst is essential for stable CO₂ photoreduction, but is a universal challenge. In this work, the Bi₅O₇I nanotubes with surface tensile strain are synthesized, which are favorable for the visible light-induced dynamic I defects generation. The CO₂ molecules absorbed on I defects are constantly reduced by the incoming photogenerated electrons from I-deficient Bi₅O₇I nanotubes and the successive protonation of CO₂ molecules is thus highly promoted, realizing the selective CO₂ conversion process via the route of CO₂-COOH^--CO. The efficient and stable photoreduction of CO₂ into CO with 100% selectivity can be achieved even under visible light (λ >420 nm) irradiation benefited from the dynamic I defects as active sites. The results presented herein demonstrate the unique action mechanism of light-induced dynamic defects during CO₂ photoreduction process and provide a new strategy into rational design of deactivation-resistant catalysts for selective CO₂ photoreduction.

Hollow Core-Shell potassium Phosphomolybdate@Cadmium Sulfide@Bismuth sulfide Z-Scheme tandem heterojunctions toward optimized Photothermal-Photocatalytic performance

A hollow core-shell potassium phosphomolybdate (KMoP)@cadmium sulfide (CdS)@bismuth sulfide (Bi₂S₃) Z-scheme tandem heterojunction is fabricated by a simple hydrothermal strategy and kept in a water bath to continue the reaction. At the same time, the ternary structure combined Keggin-type polyoxometalate with two photosensitive sulfide semiconductors to form a stable hollow core-shell heterojunction. KMoP@CdS@Bi₂S₃ with a narrow band gap of ∼ 1.2 eV also has excellent photothermal performance, which may further promote photocatalytic efficiency. The hollow core-shell KMoP@CdS@Bi₂S₃ tandem heterojunction shows excellent H₂ production performance, Cr^VI reduction ability and photocatalytic degradation performance of highly toxic tetracycline (TC). Under visible light irradiation, the photocatalytic H₂ generation rate of the KMoP@CdS@Bi₂S₃ tandem heterojunction reaches 831 μmol h^-1, which is 103 times higher than that of pristine KMoP. The photocatalytic reduction efficiency of Cr^VI and degradation efficiency of TC are as high as 95.5 and 97.51%, ∼4 times higher than that of KMoP. The boosted photocatalytic performance can be ascribed to the formation of core-shell Z-scheme tandem heterojunctions favoring spatial charge separation and the narrow band gap, which extends the photoresponse to visible light/NIR regions. When TC and Cr^VI exist at the same time, the reduction efficiency of Cr^VI can be as high as 99.64% because the intermediate of TC degradation can promote the reduction of Cr^VI. In addition, the photocatalytic performance of the KMoP@CdS@Bi₂S₃ heterojunction remains nearly constant after 4 recycles, which indicates high stability. The design strategy may provide new insights for preparing other high-performance core-shell tandem heterojunction photocatalysts for solar energy conversion.

Highly Dispersed Pt Nanoparticle-Doped Mesoporous ZnO Photocatalysts for Promoting Photoconversion of CO2 to Methanol

Photoreduction of CO₂ is considered a challenge due to the lack of effective photocatalysts with wide-spectrum absorption, active charge separation dynamically, and CO₂ adsorption. Herein, mesoporous Pt/ZnO nanocomposites with different Pt percentages (0.5-2%) have been fabricated using the sol-gel process in the presence of a template for CO₂ photoreduction during visible-light exposure. Pt nanoparticles (NPs) deposited onto mesoporous ZnO with a considerable surface area can effectively promote charge mobility. The mesoporous 1.5% Pt/ZnO nanocomposite exhibits an optimal CH₃OH yield (668 μmol g^-1), which is 18.5-fold larger than that of mesoporous ZnO (36 μmol g^-1). The most photoactive material was the 1.5% Pt/ZnO nanocomposite, producing CH₃OH of 668 μmol g^-1, and the production rate of CH₃OH over the 1.5% Pt/ZnO nanocomposite (74.11 μmol g^-1 h^-1) was increased 20 times in comparison with ZnO NPs (3.72 μmol g^-1 h^-1). The enhancement of CO₂ photoreduction efficiency over Pt/ZnO nanocomposites was attributed to the formation of the heterojunction at the Pt/ZnO interface, promoting a lower resistance to charge transfer and a larger electron transfer to the conduction band. Mesoporous Pt/ZnO nanocomposites offer enhanced accessibility and a larger surface area. Such an unparalleled mesostructure provides a new framework for the construction and design of photoactive materials with high-efficiency photocatalysts.

Surface engraving engineering of polyhedral photocatalysts

Surface engraving engineering of polyhedral photocatalysts is overviewed based on synthetic strategies and engraved surface-related photocatalytic mechanisms. Some challenges and perspectives are also proposed.

A hydrolysis synthesis route for (001)/(102) coexposed BiOCl nanosheets with high visible light-driven catalytic performance

The (001)/(102) co-exposed BiOCl nanosheet shows good adsorption of cationic dyes and high visible light-driven catalytic performance.