Construction of Ultrathin S-Scheme Heterojunctions of Single Ni Atom Immobilized Ti-MOF and BiVO4 for CO2 Photoconversion of nearly 100% to CO by Pure Water

Na-Ru bimetallic functional sites promote photo-driven CO2 directed conversion into CH4

Recently, there has been a significant increase in interest in using photocatalysis for the energy conversion of polluting gases. In this research, sodium and ruthenium bimetallic functional sites co-modified bismuth tungstate (Ru/Na-Bi2WO6) nanoflower photocatalyst was synthesized via the hydrothermal method. The CO2 reduction products on the Bi2WO6 substrate were CO (1.66 μmol/g/h, 68 %) and CH4 (0.78 μmol/g/h, 32 %). After optimization, a significant change in the CO2 products of the Bi2WO6-based composite material was observed, with CO (0.61 μmol/g/h, 3.6 %) and CH4 (16.1 μmol/g/h, 96.4 %). Results showed that the dominance of CH4 as the main product in the Ru/Na-BWO system is attributed to the effective doping of Na, which generates impurity energy levels composed of oxygen vacancies, lowering the conduction band position of Bi2WO6, thereby suppressing CO generation, and enhancing CH4 selectivity by changing the CO2 activation pathway. The remarkable performance is ascribed to the synergized adsorption and activation of CO2 by the tandem Na+ sites and Ru0 sites. Specifically, the doped Na+ sites play a major role in promoting the adsorption CO2 molecules, while the Ru0 sites play a dominant role in facilitating the activation of the intermediates.

g-C3N4 as ballistic electron transport "Tunnel" in CsPbBr3-based ternary photocatalyst for gas phase CO2 reduction

Perovskite CsPbBr3 quantum dot shows great potential in artificial photosynthesis, attributed to its outstanding optoelectronic properties. Nevertheless, its photocatalytic activity is hindered by insufficient catalytic active sites and severe charge recombination. In this work, a CsPbBr3@Ag-C3N4 ternary heterojunction photocatalyst is designed and synthesized for high-efficiency CO2 reduction. The CsPbBr3 quantum dots and Ag nanoparticles are chemically anchored on the surface of g-C3N4 sheets, forming an electron transfer tunnel from CsPbBr3 quantum dots to Ag nanoparticles via g-C3N4 sheets. The resulting CsPbBr3@Ag-C3N4 ternary photocatalyst, with spatial separation of photogenerated carriers, achieves a remarkable conversion rate of 19.49 μmol·g-1·h-1 with almost 100 % CO selectivity, a 3.13-fold enhancement in photocatalytic activity as compared to CsPbBr3 quantum dots. Density functional theory calculations reveal the rapid CO2 adsorption/activation and the decreased free energy (0.66 eV) of *COOH formation at the interface of Ag nanoparticles and g-C3N4 in contrast to the g-C3N4, leading to the excellent photocatalytic activity, while the thermodynamically favored CO desorption contributes to the high CO selectivity. This work presents an innovative strategy of constructing perovskite-based photocatalyst by modulating catalyst structure and offers profound insights for efficient CO2 conversion.

Enhancing photocatalytic CO2 reduction with TiO2-based materials: Strategies, mechanisms, challenges, and perspectives

The concentration of atmospheric CO2 has exceeded 400 ppm, surpassing its natural variability and raising concerns about uncontrollable shifts in the carbon cycle, leading to significant climate and environmental impacts. A promising method to balance carbon levels and mitigate atmospheric CO2 rise is through photocatalytic CO2 reduction. Titanium dioxide (TiO2), renowned for its affordability, stability, availability, and eco-friendliness, stands out as an exemplary catalyst in photocatalytic CO2 reduction. Various strategies have been proposed to modify TiO2 for photocatalytic CO2 reduction and improve catalytic activity and product selectivity. However, few studies have systematically summarized these strategies and analyzed their advantages, disadvantages, and current progress. Here, we comprehensively review recent advancements in TiO2 engineering, focusing on crystal engineering, interface design, and reactive site construction to enhance photocatalytic efficiency and product selectivity. We discuss how modifications in TiO2's optical characteristics, carrier migration, and active site design have led to varied and selective CO2 reduction products. These enhancements are thoroughly analyzed through experimental data and theoretical calculations. Additionally, we identify current challenges and suggest future research directions, emphasizing the role of TiO2-based materials in understanding photocatalytic CO2 reduction mechanisms and in designing effective catalysts. This review is expected to contribute to the global pursuit of carbon neutrality by providing foundational insights into the mechanisms of photocatalytic CO2 reduction with TiO2-based materials and guiding the development of efficient photocatalysts.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

Engineering of Ultra-Thin Layer of MIL-125(Ti) Nanosheet\Zn-Tetracarboxy-Phthalocyanine S-Scheme Heterojunction as Photocatalytic CO2 Reduction Catalyst

Metal-organic frameworks (MOFs) with ultrathin 2D structure have attracted remarkable attention in photocatalytic application owing to the accessibility of abundant active sites on the surface. But high charge recombination results in poor photocatalytic activity. Herein, the synthesis of ultrathin MIL-125(Ti) nanosheets is reported with a thickness of 1.3 nm through a simple chemical reaction route of precursor solution aging and subsequent solvothermal process for photocatalytic CO2 production. The maximal CO evolution rate achieves 200.8 µmol g-1 h-1, which is prominently higher than that (78.6 µmol g-1 h-1) of the bulk MIL-125(Ti) counterpart. Furthermore, the structurally stable Zn (II) tetracarboxy phthalocyanine (ZnTcPc) molecules assembly on ultrathin MIL-125(Ti) nanosheet (NS) to form MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction through the strong interaction between the Ti3+ in MIL-125(Ti) and the COOH in ZnTcPc. The introduction of ZnTcPc greatly extends light absorption range and increases charge separation rate. The experimental and density functional theory calculation results validate that the MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction can favor CO2 adsorption and effectively depress the formation energy of the intermediates, achieving a high CO evolution rate of 450.8 µmol g-1 h-1. This work provides a strategy of engineering 2D MOF-based heterostructure systems for photocatalytic application.

Solar-Driven Conversion of CO2 to C2 Products by the 3d Transition Metal Intercalates of Layered Lead Iodides

Photocatalytic CO2 reduction to high-value-added C2+ products presents significant challenges, which is attributed to the slow kinetics of multi-e- CO2 photoreduction and the high thermodynamic barrier for C-C coupling. Incorporating redox-active Co2+/Ni2+ cations into lead halide photocatalysts has high potentials to improve carrier transport and introduce charge polarized bimetallic sites, addressing the kinetic and thermodynamic issues, respectively. In this study, a coordination-driven synthetic strategy is developed to introduce 3d transition metals into the interlamellar region of layered organolead iodides with atomic precision. The resultant bimetallic halide hybrids exhibit selective photoreduction of CO2 to C2H5OH using H2O vapor at the evolution rates of 24.9-31.4 µmol g-1 h-1 and high selectivity of 89.5-93.6%, while pristine layered lead iodide yields only C1 products. Band structure calculations and photoluminescence studies indicate that the interlayer Co2+/Ni2+ species greatly contribute to the frontier orbitals and enhance exciton dissociation into free carriers, facilitating carrier transport between adjacent lead iodide layers. In addition, Bader charge distribution calculations and in situ experimental spectroscopic studies reveal that the asymmetric Ni-O-Pb bimetallic catalytic sites exhibit intrinsic charge polarization, promoting C-C coupling and leading to the formation of the key *OC-CHO intermediate.

Synergistic effect of Ag@CN with BiVO4 in a unique Z-type heterojunction for enhancing photoelectrochemical water splitting performance

In the realm of photoelectrochemical technology, the enhancement of photogenerated charge carrier separation is pivotal for the advancement of energy conversion performance. Carbon nitride (CN) is established as a photocatalytic material with significant potential and exhibits unique advantages in addressing the issue of rapid recombination of photogenerated carriers. This study utilized an efficient in situ doping method that combined Mo,W-doped BiVO4 (Mo,W:BVO) with silver-loaded CN (Ag@CN), yielding an all-solid-state Mo,W:BVO/Ag@CN heterostructure that effectively augments the separation efficiency of electron-hole pairs. Through the annealing process, Ag@CN was uniformly coated within the Mo,W:BVO thin film, significantly enlarging the interface contact area to enhance visible light absorption and photogenerated carrier movement. The results of the photoelectrochemical tests showed that the Mo,W:BVO/Ag@CN heterostructure had the highest photocurrent and charge transfer efficiency, which were 6.4 times and 3.6 times higher respectively than those of the unmodified Mo,W:BVO. Our research elucidates the interactions within all-solid-state Z-scheme heterojunctions, outlining strategic approaches for crafting innovative and superior photocatalytic systems.

Construction of TiO2/CuPc Heterojunctions for the Efficient Photocatalytic Reduction of CO2 with Water

Utilizing solar energy for photocatalytic CO2 reduction is an attractive research field because of its convenience, safety, and practicality. The selection of an appropriate photocatalyst is the key to achieve efficient CO2 reduction. Herein, we report the synthesis of TiO2/CuPc heterojunctions by compositing CuPc with TiO2 microspheres via a hydroxyl-induced self-assembly process. The experimental investigations demonstrated that the optimal TiO2/0.5CuPc photocatalyst exhibited a significantly enhanced CO2 photoreduction rate up to 32.4 μmol·g-1·h-1 under 300 W xenon lamp irradiation, which was 3.7 times that of the TiO2 microspheres alone. The results of photoelectrochemical experiments indicated that the construction of the heterojunctions by introducing CuPc effectively promoted the separation and transport of photogenerated carriers, thus enhancing the catalytic effect of the photocatalyst.

Electron Localization-Triggered Proton Pumping Toward Cu Single Atoms for Electrochemical CO2 Methanation of Unprecedented Selectivity

Slow multi-proton coupled electron transfer kinetics and unexpected desorption of intermediates severely hinder the selectivity of CO2 methanation. In this work, a one-stone-two-bird strategy of pumping protons and improving adsorption configuration/capability enabled by electron localization is developed to be highly efficient for CH4 electrosynthesis over Cu single atoms anchored on bismuth vacancies of BiVO4 (Bi1-xVO4─Cu), with superior kinetic isotope effect and high CH4 Faraday efficiency (92%), far outperforming state-of-the-art electrocatalysts for CO2 methanation. Control experiments and theoretical calculations reveal that the bismuth vacancies (VBi) not only act as active sites for H2O dissociation but also induce electron transfer toward Cu single-atom sites. The VBi-induced electron localization pumps *H from VBi sites to Cu single atoms, significantly promoting the generation and stabilization of the pivotal intermediate (*CHO) for highly selective CH4 electrosynthesis. The metal vacancies as new initiators show enormous potential in the proton transfer-involved hydrogenative conversion processes.

Metal-organic framework heterojunctions for photocatalysis

Heterojunctions combining two photocatalysts of staggered conduction and valence band energy levels can increase the photocatalytic efficiency compared to their individual components. This activity enhancement is due to the minimization of undesirable charge recombination by the occurrence of carrier migration through the heterojunction interface with separated electrons and holes on the reducing and oxidizing junction component, respectively. Metal-organic frameworks (MOFs) are currently among the most researched photocatalysts due to their tunable light absorption, facile charge separation, large surface area and porosity. The present review summarizes the current state-of-the-art in MOF-based heterojunctions, providing critical comments on the construction of these heterostructures. Besides including examples showing the better performance of MOF heterojunctions for three important photocatalytic processes, such as hydrogen evolution reaction, CO2 photoreduction and dye decolorization, the focus of this review is on describing synthetic procedures to form heterojunctions with MOFs and on discussing the experimental techniques that provide evidence for the operation of charge migration between the MOF and the other component. Special attention has been paid to the design of rational MOF heterojunctions with small particle size and controlled morphology for an appropriate interfacial contact. The final section summarizes the achievements of the field and provides our views on future developments.

2D Atomic Layers for CO2 Photoreduction

Artificial photosynthesis can convert carbon dioxide into high value-added chemicals. However, due to the poor charge separation efficiency and CO2 activation ability, the conversion efficiency of photocatalytic CO2 reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO2 reduction performance. In this review, the basic principle of CO2 photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth-based materials, MXene, metal-organic framework, and metal-free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO2 reduction are prospected.

Metal-organic framework-based S-scheme heterojunction photocatalysts

Photocatalysis is a promising technology to resolve energy and environmental issues, where the design of high-efficiency photocatalysts is the central task. As an emerging family of photocatalysts, semiconducting metal-organic frameworks (MOFs) with remarkable features have demonstrated great potential in various photocatalytic fields. Compared to MOF-based photocatalysts with a single component, construction of S-scheme heterojunctions can render MOFs with enhanced charge separation, redox capacity and solar energy utilization, and thus improved photocatalytic performance. Herein, an overview of the recent advances in the design of MOF-based S-scheme heterojunctions for photocatalytic applications is provided. The basic principle of S-scheme heterojunctions is introduced. Then, three types of MOF-based S-scheme heterojunctions with different compositions are systematically summarized including MOF/non-MOF, MOF-on-MOF and MOF-derived heterojunctions. Afterwards, the enhanced performances of MOF-based S-scheme heterojunctions in hydrogen production, CO2 reduction, C-H functionalization, H2O2 production and wastewater treatment are highlighted. Lastly, the current challenges and future prospects regarding the design and applications of MOF-based S-scheme heterojunctions are discussed to inspire the further development of this emerging field.

Construction of 2D S-Scheme Heterojunction Photocatalyst

Semiconductor photocatalytic technology holds immense promise for converting sustainable solar energy into chemically storable energy, with significant applications in the realms of energy and the environment. However, the inherent issue of rapid recombination of photogenerated electrons and holes hinders the performance of single photocatalysts. To overcome this challenge, the construction of 2D S-scheme heterojunction photocatalysts emerges as an effective strategy. The deliberate design of dimensionality ensures a substantial interfacial area; while, the S-scheme charge transfer mechanism facilitates efficient charge separation and maximizes redox capabilities. This review commences with a fresh perspective on the charge transfer mechanism in S-scheme heterojunctions, followed by a comprehensive exploration of preparation methods and characterization techniques. Subsequently, the recent advancements in 2D S-scheme heterojunction photocatalysts are summarized. Notably, the mechanism behind activity enhancement is elucidated. Finally, the prospects for the development of 2D S-scheme photocatalysts are presented.

Electrospinning Photocatalysis Meet In Situ Irradiated XPS: Recent Mechanisms Advances and Challenges

Producing solar fuels over photocatalysts under light irradiation is a considerable way to alleviate energy crises and environmental pollution. To develop the yields of solar fuels, photocatalysts with broad light absorption, fast charge carrier migration, and abundant reaction sites need to be designed. Electrospun 1D nanofibers with large specific areas and high porosity have been widely used in the efficient production of solar fuels. Nevertheless, it is challenging to do in-depth mechanism research on electrospun nanofiber-based photocatalysts since there are multiple charge transfer routes and various reaction sites in these systems. Here, the basic principles of electrospinning and photocatalysis are systemically discussed. Then, the different roles of electrospun nanofibers played in recent research to boost photocatalytic efficiency are highlighted. It is noteworthy that the working principles and main advantages of in situ irradiated photoelectron spectroscopy (ISI-XPS), a new technique to investigate migration routes of charge carriers and identify active sites in electrospun nanofibers based photocatalysts, are summarized for the first time. At last, a brief summary on the future orientation of photocatalysts based on electrospun nanofibers as well as the perspectives on the development of the ISI-XPS technique are also provided.

Boron Dopant Modulated Electron Localization of Tin Oxide for Efficient Electrochemical CO2 Reduction to Formate

Sn-based electrocatalysts have great economic potential in the reduction of CO2 to HCOOH, while they still suffer from low current density, dissatisfactory selectivity, and poor stability. Inspired by electronic modification engineering, boron-doped SnO2 nanospheres (B-SnO2 ) are successfully synthesized to achieve high-efficiency CO2 reduction reaction (CO2 RR). It is found that the introduction of boron dopants can increase the number of active sites and facilitate the formation of the electron-rich Sn sites in its structure, thus enhancing the activation of CO2 molecules and reducing the energy barrier of *OCHO intermediates on the SnO2 surface. Thus, the B-doped SnO2 electrocatalyst exhibits a remarkable FEHCOOH above 90% within a broad potential window of -0.7 to -1.3 V versus reversible hydrogen electrode (RHE) (600 mV) and obtains the maximum value of 95.1% (the partial current density of HCOOH is 42.35 mA cm-2 ) at -1 V versus RHE. In conclusion, this work provides a novel strategy for optimizing the intrinsic properties of electrocatalysts for CO2 RR by the method of tuning the electronic structure.

Triggering the Channel-Sulfur Sites in 1T'-ReS2 Cocatalyst toward Splendid Photocatalytic Hydrogen Generation

Electron density manipulation of active sites in cocatalysts is of great essential to realize the optimal hydrogen adsorption/desorption behavior for constructing high-efficient H2 -evolution photocatalyst. Herein, a strategy about weakening metal-metal bond strength to directionally optimize the electron density of channel-sulfur(S) sites in 1T' Re1- x Mox S2 cocatalyst is clarified to improve their hydrogen adsorption strength (S─H bond) for rapid H2 -production reaction. In this case, the ultrathin Re1- x Mox S2 nanosheet is in situ anchored on the TiO2 surface to form Re1- x Mox S2 /TiO2 photocatalyst by a facial molten salt method. Remarkably, numerous visual H2 bubbles are constantly generated on the optimal Re0.92 Mo0.08 S2 /TiO2 sample with a 10.56 mmol g-1  h-1 rate (apparent quantum efficiency is about 50.6%), which is 2.6 times higher than that of traditional ReS2 /TiO2 sample. Density functional theory and in situ/ex situ X-ray photoelectron spectroscopy results collectively demonstrate that the weakened Re─Re bond strength via Mo introduction can induce the formation of unique electron-deficient channel-S sites with suitable electron density, which yield thermoneutral S─H bonds to realize superior interfacial H2 -generation performance. This work provides fundamental guidance on purposely optimizing the electronic state of active sites by manipulating the intrinsic bonding structure, which opens an avenue for designing efficacious photocatalytic materials.

Embedding CsPbBr3 Quantum Dots into an In2O3 Nanotube for Selective Photocatalytic CO2 Reduction to Hydrocarbon Fuels

Halide perovskite quantum dots (QDs) are one of the most prospective candidates for photocatalytic CO2 reduction, but their photocatalytic performances are far from satisfactory due to structural instability and severe charge recombination. In this study, we demonstrated a CsPbBr3 QDs/In2O3 hierarchical nanotube (CPB/IO) for efficient CO2 conversion, in which CsPbBr3 QDs were well-dispersed on the In-MOF-derived In2O3 nanotube by a facile self-assembly process. The optimized CPB/IO catalyst displayed an enhanced photocatalytic CO2 performance with a (CO + CH4) generation rate of 16.37 μmol·g-1·h-1 upon simulated solar illumination without a photosensitizer and sacrificial agent, which is 3.59 times stronger than that of pristine CsPbBr3 QDs (4.56 μmol·g-1·h-1). Besides, the modified CsPbBr3 QD catalyst exhibited an obvious increase of CH4 selectivity and excellent stability after four cycles. The unique zero-dimensional (0D)/one-dimensional (1D) heterostructure and matching band potentials between CsPbBr3 and In2O3 supply an intimate interfacial contact, numerous active sites, and effective charge transfer for CO2 photoreduction. This work can inspire the formation of novel halide-perovskite-involving photocatalysts for solar fuel formation.

Enlarging the Ni-O Bond Polarizability in a Phosphorene-Hosted Metal-Organic Framework for Boosted Water Oxidation Electrocatalysis

The emerging lattice-oxygen oxidation mechanism (LOM) presents attractive opportunities for breaking the scaling relationship to boost oxygen evolution reaction (OER) with the direct OLattice-*O interaction. However, currently the LOM-triggering rationales are still debated, and a streamlined physicochemical paradigm is extremely desirable for the design of LOM-defined OER catalysts. Herein, a Ni metal-organic framework/black phosphorene (NiMOF/BP) heterostructure is theoretically profiled and constructed as a catalytic platform for the LOM-derived OER studies. It is found that the p-type BP host can enlarge the Ni-O bond polarizability of NiMOF through the Ni-O bond stretching and Ni valence declining synergically. Such an enlarged bond polarizability will in principle alleviate the lattice oxygen confinement to benefit the LOM pathway and OER performance. As a result, the optimized NiMOF/BP catalyst exhibits promising OER performance with a low overpotential of 260 mV at 10 mA cm-2 and long-term stability in 1 M KOH electrolyte. Both experiment and calculation results suggest the activated LOM pathway with a more balanced step barrier in the NiMOF/BP OER catalyst. This research puts forward Ni-O bond polarizability as the criterion to design LOM-scaled electrocatalysts for water oxidation.

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction

Photoconversion of CO2 and H2 O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton-coupled electron transfer (PCET), a slow C-C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi2 WO6 (BP/BWO) was constructed for photocatalytic CO2 reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO2 reduction, with a yield of 61.3 μmol g-1  h-1 for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi-O-P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C-C coupling. In addition, the substitution of BA oxidation for H2 O oxidation can further enhance the photocatalytic performance of CO2 reduction to C2 H5 OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO2 photoconversion to C2 H5 OH based on cooperative photoredox systems.

A π-Conjugated Van der Waals Heterostructure Between Single-Atom Ni-Anchored Salphen-Based Covalent Organic Framework and Polymeric Carbon Nitride for High-Efficiency Interfacial Charge Separation

Semiconductor-based heterostructures have exhibited great promise as a photocatalyst to convert solar energy into sustainable chemical fuels, however, their solar-to-fuel efficiency is largely restricted by insufficient interfacial charge separation and limited catalytically active sites. Here the integration of high-efficiency interfacial charge separation and sufficient single-atom metal active sites in a 2D van der Waals (vdW) heterostructure between ultrathin polymeric carbon nitride (p-CN) and Ni-containing Salphen-based covalent organic framework (Ni-COF) nanosheets is illustrated. The results reveal a NiN2 O2 chemical bonding in NiCOF nanosheets, leading to a highly separated single-atom Ni sites, which will function as the catalytically active sites to boost solar fuel production, as confirmed by X-ray absorption spectra and density functional theory calculations. Using ultrafast femtosecond transient adsorption (fs-TA) spectra, it shows that the vdW p-CN/Ni-COF heterostructure exhibits a faster decay lifetime of the exciton annihilation (τ = 18.3 ps) compared to that of neat p-CN (32.6 ps), illustrating an efficiently accelerated electron transfer across the vdW heterointerface from p-CN to Ni-COF, which thus allows more active electrons available to participate in the subsequent reduction reactions. The photocatalytic results offer a chemical fuel generation rate of 2.29 mmol g-1 h-1 for H2 and 6.2 µmol g-1 h-1 for CO, ≈127 and three times higher than that of neat p-CN, respectively. This work provides new insights into the construction of a π-conjugated vdW heterostructure on promoting interfacial charge separation for high-efficiency photocatalysis.

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.

Atomically Dispersed ZnN5 Sites Immobilized on g-C3 N4 Nanosheets for Ultrasensitive Selective Detection of Phenanthrene by Dual Ratiometric Fluorescence

Ultrasensitively selective detection of trace polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHE) is critical but remains challenging. Herein, atomically dispersed Zn sites on g-C₃ N₄ nanosheets (sZn-CN) are constructed by thermal polymerization of a Zn-cyanuric acid-melamine supramolecular precursor for the fluorescence detection of PHE. A high amount (1.6 wt%) of sZn is grafted in the cave of CN with one N vacancy in the form of unique Zn(II)N₅ coordination. The optimized sZn-CN achieves a wide detection range (1 ng L^-1 to 5 mg L^-1 ), ultralow detection limit (0.35 ng L^-1 , with 5-order magnitude improvement over CN), and ultrahigh selectivity toward PHE even among typical PAHs based on the built PHE-CN dual ratiometric fluorescence method. By means of in situ Fourier transform infrared spectroscopy, time-resolved absorption and fluorescence spectroscopy, and theoretical calculations, the resulting superior detection performance is attributed to the favorable selective adsorption of PHE on as-constructed atomic Zn(II)N₅ sites via the ionic cation-π interactions (Zn^δ+ C₂ ^δ- type), and the fluorescence quenching is dominated by the inner filter effect (IFE) from the multilayer adsorption of PHE at low concentrations, while it is done by the protruded photogenerated electron-transfer process, as well as IFE from the monolayer adsorption of PHE at ultralow concentration.

PEDOT/FeOOH/BiVO4 Nanohybrids with Excellent Photoelectric Performance Promoted by Photothermal Effects for the Ultrasensitive Detection of MicroRNA-375-3p

Herein, a novel photoactive poly(3,4-ethyl-enedioxythiophene) (PEDOT)/FeOOH/BiVO₄ nanohybrid with excellent photoelectrochemical (PEC) efficiency was assembled for the construction of an ultrasensitive biosensor for microRNA-375-3p (miRNA-375-3p) detection. In comparison with the traditional FeOOH/BiVO₄ photoactive composite, the PEDOT/FeOOH/BiVO₄ nanohybrids exhibited markedly enhanced photocurrent due to the promoted interfacial charge separation by PEDOT, which was used not only as an electron conductor but also as a localized photothermal heater to enhance the photogenerated carrier separation. Based on this PEDOT/FeOOH/BiVO₄ photoelectrode and an enzyme-free signal amplification strategy including a target-induced catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR), a PEC sensing platform for the detection of miRNA-375-3p was established, achieving a wide linear range from 1 fM to 10 pM with a low detection limit of 0.3 fM. Moreover, this work provides a general photocurrent enhancement strategy for the development of high-performing PEC biosensors for sensitive detection of biomarkers and early disease diagnosis.

Enhancing Built-in Electric Fields for Efficient Photocatalytic Hydrogen Evolution by Encapsulating C60 Fullerene into Zirconium-Based Metal-Organic Frameworks

High-efficiency photocatalysts based on metal-organic frameworks (MOFs) are often limited by poor charge separation and slow charge-transfer kinetics. Herein, a novel MOF photocatalyst is successfully constructed by encapsulating C₆₀ into a nano-sized zirconium-based MOF, NU-901. By virtue of host-guest interactions and uneven charge distribution, a substantial electrostatic potential difference is set-up in C₆₀ @NU-901. The direct consequence is a robust built-in electric field, which tends to be 10.7 times higher in C₆₀ @NU-901 than that found in NU-901. In the catalyst, photogenerated charge carriers are efficiently separated and transported to the surface. For example, photocatalytic hydrogen evolution reaches 22.3 mmol g^-1  h^-1 for C₆₀ @NU-901, which is among the highest values for MOFs. Our concept of enhancing charge separation by harnessing host-guest interactions constitutes a promising strategy to design photocatalysts for efficient solar-to-chemical energy conversion.

Ti-MOF single-crystals featuring an intracrystal macro-microporous hierarchy for catalytic oxidative desulfurization

For the first time, we demonstrate a Ti-MOF (Ti-metal organic framework) single-crystal featuring an intracrystal macro-microporous hierarchy (Hier-NTU-9) by a vapor-assisted polymer-templated method. This Hier-NTU-9 possesses macropores (100-1000 nm) derived from polymer templates and enhanced transport ability of bulky molecules, exhibiting almost double the desulfurization activity compared to the conventional NTU-9.

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF-8 Modified by Ni2+ Ions

The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework-8 (ZIF-8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF-8 carrier by using Ni²⁺ ions as anchor (ZIF-8@PEP-Ni). By contrast, the direct coating of PEP on the surface of ZIF-8 (ZIF-8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF-8@PEP-Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm^-2 , which is much lower than the 690 and 919 mV overpotential values of ZIF-8@PEP and PEP, respectively.

Functionalized MOF-Based Photocatalysts for CO2 Reduction

Metal-organic frameworks (MOFs) materials have become a research forefront in the field of photocatalytic CO₂ reduction attributed to their ultra-high specific surface area, adjustable structure, and abundant catalytic active sites. Particularly, MOFs can be facilely tuned to match CO₂ photoreduction by utilizing post-modification of metal nodes, functionalization of organic linkers, and combination with other active materials. Herein, the recent advances in the construction strategy of MOF-based photocatalysts materials for CO₂ reduction are highlighted. Some systematic modification strategies on MOF-based photocatalysts are also discussed, such as modification of metal sites and organic ligands, construction of heterojunction, introduction of single/dual-atom, and strain engineering. Finally, the future development directions of MOF-based photocatalysts in the field of CO₂ reduction are presented.