Photocatalytic CO2 reduction represents a promising strategy for solar-to-fuel conversion, yet its mechanistic validity and visible-light performance remain widely debated. Niobium pentoxide (Nb2O5) has emerged as a distinctive oxide platform for CO2 reduction owing to its delocalized 4d-derived conduction band, tunable Nb4+–Vo defect states, and band-edge positions compatible with multi-electron CO2 reduction and oxidative half-reactions. Unlike previous reviews that primarily focus on material modifications, this work provides a comprehensive outline of Nb2O5-based photocatalytic systems adopted for CO2 reduction. The review was introduced by a concise discussion of Nb2O5 core merits as a potent catalyst for CO2 reduction. Then, the CO2 reduction process was discussed from thermodynamic, kinetic, and mechanistic perspectives. Afterwards, we critically analyzed how morphology and bandgap engineering, controlled defect engineering, heterojunction formation, and cocatalyst integration can modulate charge-carrier dynamics, CO2 adsorption, intermediate stabilization, and product selectivity. In addition, a theoretical insight based on density functional theory (DFT) calculations was conveyed to unravel the structure-activity interplay and reaction mechanism of CO2 conversion over Nb2O5-based photocatalytic systems. Finally, current limitations and outlooks are provided to motivate future studies on developing Nb2O5-based photocatalysts with adequate reactivity, selectivity, and stability.

The biosynthesis of volatile organic compound (VOC) signaling is essential for plant adaptation under disease stress. However, the efficient identification of VOCs remains a significant challenge. In this study, we engineered a biomimetic colorimetric sensor array by integrating stimulus-responsive dyes into a highly porous threedimensional covalent organic framework (3D COF), which is coupled with artificial intelligence analysis. These 3D COF@dye sensors exhibit high surface areas and interconnected large channels, facilitating highly sensitive colorimetric sensing of VOCs. The resultant platform demonstrated markedly enhanced sensitivity towards target VOCs, with detection limits ranging from 0.081 to 0.95 ppm. Furthermore, AI-assisted information fusion and perceptual analysis considerably improved the accuracy of VOC sensing processes, enabling direct visualization and classification of VOCs with >= 95% accuracy within 24 h of inoculation. This design, which leverages molecular recognition capabilities, amplifies host-guest interactions, thereby facilitating the differentiation of VOCs by their polarity, size, and shape. The platform effectively distinguished VOCs emitted by Botrytis cinerea, Alternaria solani, and Phytophthora infestans. Our findings provide a generalizable platform of intelligent, nano-enabled sensors for precision agriculture and non-invasive plant health monitoring.

ConspectusA persistent obstacle in heterogeneous photocatalysis is the rapid recombination of photogenerated electrons and holes, a consequence of the strong Coulombic attraction between carriers within conventional semiconductors. This intrinsic limitation significantly constrains the efficiency of solar-to-chemical conversion processes. Heterojunction engineering has therefore become a central strategy for promoting charge separation by coupling semiconductors with complementary electronic structures. Such systems typically outperform their single-component analogues because the interfacial electronic configuration promotes directional charge migration and suppresses bulk recombination losses.Within this context, S-scheme heterojunctions (SH) offer a mechanistically robust framework that reconciles efficient carrier separation with strong redox capability. An S-scheme couples a reduction photocatalyst (RP) and an oxidation photocatalyst (OP) in a staggered configuration. Under illumination, electrons in the OP selectively recombine with holes in the RP, while the high-energy electrons in the RP and high-energy holes in the OP are spatially retained and directed to catalytic sites. This selective recombination preserves redox power, enhances charge utilization, and accelerates surface reactions.Since introducing the S-scheme concept in 2019 with the WO3/g-C3N4 system supported by in situ irradiated X-ray photoelectron spectroscopy (ISIXPS)─we have expanded its material scope across multiple dimensional architectures, including perovskite materials, semiconducting quantum dots (QDs), conjugated polymers (CP), metal-organic frameworks (MOFs), and covalent-organic frameworks (COFs). To validate the S-scheme mechanism, elucidate charge transfer dynamics, and resolve reaction mechanisms, we have employed an array of state-of-the-art characterization techniques, such as light-irradiated Kelvin probe force microscopy (KPFM), in situ electron paramagnetic resonance (EPR), in situ X-ray absorption spectroscopy (XAS), and femtosecond-transient absorption spectroscopy (fs-TAS).Our most recent efforts focus on composition tuning, defect modulation, and interfacial bonding engineering to optimize the separation and lifetime of photogenerated carriers. Through these strategies, we aim to reinforce the internal electric field, regulate band bending, and precisely control charge flow pathways, ultimately maximizing photocatalytic efficiency. This Account provides a concise yet comprehensive overview of the evolution of SH, with emphasis on the design principles and advanced characterization techniques developed and adopted by our group. We summarize key strategies for engineering SH tailored for enhanced charge carrier separation and highlight their applications in major photocatalytic reactions. Finally, we outline promising future directions for the field.

Photocatalysis provides a viable approach to address critical global challenges of energy scarcity and environmental pollution. Significantly, one-dimensional (1D) nanomaterials (e.g., nanorods, nanowires, nanofibers, nanotubes, and nanobelts) have attracted great attention in the field of photocatalysis owing to their inherent structural advantages such as directional charge transport pathways, high aspect ratio, and abundant exposed active surface sites. Nevertheless, the inherent issue including rapid photogenerated carrier recombination and low apparent quantum efficiency continue to hinder practical implementation of 1D scaffolds. To overcome these limitations, step-scheme (S-scheme) heterojunctions have been strategically constructed using 1D nanomaterials as fundamental building blocks, demonstrating superior charge separation and enhanced photocatalytic properties. In this review, we comprehensively summarized recent advances in the design and implementation of 1D-based S-scheme photocatalysts for targeted applications in sustainable energy conversion, and environmental remediation. The review was introduced by a historical development of the S-scheme charge transfer model and the typical charge transfer mechanism, followed by a comprehensive summary of the preparation approaches and characterization techniques of 1D-based S-scheme systems. Subsequently, a detailed discussion of the recent advances in 1D S-scheme heterojunction photocatalysts for various applications are provided and the implications of the S-scheme charge transfer mechanism on promoting the catalytic activity are elucidated. Finally, the prospects for the development of 1D-based S-scheme heterojunction photocatalysts are presented.

Recycling spent mushroom substrate (SMS) has gained significant attention owing to the environmental pollution caused by its improper disposal. Inspired by the "circular economy" concepts, this work addresses environmental pollution from SMS by transforming it into activated carbon (ACs) and integrating it with a Schiff-based covalent organic framework (COF) and a carbon nitride (g-C3N4) to create a COF/g-C3N4/ACs composite. The composite demonstrated excellent adsorption capacity (250 mg & sdot;g-1) for RhB, following pseudo-second-order kinetics and the Langmuir model, it also can degrade 100 %-RhB under light irradiation for 60 min. The COF/g-C3N4/ACs composite exhibited remarkable stability and reusability, offering a sustainable approach for SMS valorization and multifunctional material design.

The rapid recombination of photoinduced charge carriers in semiconductors remains a significant challenge for their practical application in photocatalysis. This study presents the design of a step-scheme (S-scheme) heterojunction composed of carbon nitride (g-C3N4) and nickel-based metal-organic framework (Ni-MOF) to achieve enhanced charge separation. The establishment of an S-scheme charge transfer configuration at the interface of the Ni-MOF/g-C3N4 heterostructure plays a pivotal role in enabling efficient charge carrier separation, and hence, high CO2 photoreduction efficiency with a CO evolution rate of 1014.6 µmol g-1 h-1 and selectivity of 95% under simulated solar illumination. CO evolution represents an approximately 3.7-fold enhancement compared to pristine Ni-MOF. Density functional theory (DFT) calculations, supported by in situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) experimental results, confirmed the establishment of a well-defined and strongly bonded interface, which improves the charge transfer and separation following the S-scheme mechanism. This study sheds light on MOF-based S-scheme heterojunctions as fruitful and selective alternatives for practical CO2 photoreduction.

Hydrogen peroxide (H2O2) is one of the 100 most important chemicals used extensively in bleaching, disinfection, and synthetic chemistry industries. It is currently used as a fuel in direct fuel cells. The current H2O2 production relies on the harsh anthraquinone oxidation approach. Photocatalytic H2O2 production is a more favorable alternative from environmental, sustainability, and economic viewpoints. The process requires water and molecular oxygen as inputs and sunlight as the sole power source. Despite these merits, the practical application of this technology remains challenging. The most common bottlenecks are the photocatalyst's inadequacy, uphill thermodynamics, sluggish process kinetics, and competitive and backward reactions. This paper discusses these limitations and highlights the proposed perspectives to improve the efficiency and selectivity, aiming to pave the way toward large-scale H2O2 photogeneration.

Photocatalytic CO2 conversion into energy-rich fuels offers a sustainable route to address global energy and environmental challenges. However, achieving high activity and selectivity under visible light remains a key limitation. In this study, a 3D hierarchical Nb2O5 nanoflower photocatalyst dual-doped with vanadium (V), nitrogen (N), and sensitized with carbon (designated NVNBOC) is synthesized via a two-step hydrothermal process followed by calcination. The incorporation of dual metal and non-metal dopants, in combination with carbon sensitization, yielded a strong synergistic effect, significantly enhancing both photocatalytic performance and selectivity. Under visible-light irradiation, the NVNBOC catalyst achieved a remarkable methane (CH4) production rate of 78.32 mu molg-1h-1, approximately 12 times higher than that of pristine Nb2O5, with an outstanding CH4 selectivity of 97.10%. In-situ DRIFTS results revealed that the NVNBOC photocatalyst facilitates a stepwise CO2 reduction pathway, involving key intermediates such as *HCOO-, *CHO, and *CH3O, ultimately leading to full CH4 generation. These findings demonstrate the pivotal role of dual dopant engineering in enhancing light utilization, charge separation, and intermediate stabilization, providing a promising approach for advancing visible-light-driven photocatalytic CO2 reduction toward practical clean energy applications.

S-scheme heterojunctions have become a hot topic in photocatalysis. Copper (Cu) compounds are a versatile family of photocatalytic materials, including oxides (CuO, Cu2O), binary oxides (CuBi2O4, CuFe2O4), sulfides (CuxS, (1 ≤ x ≤ 2)), selenides (CuSe), phosphides (Cu3P), metal organic frameworks (MOFs), etc. These materials are characterized by narrow bandgaps, large absorption coefficients, and suitable band positions. To further increase the efficiency of photoinduced charge separation, Cu-based photocatalytic materials are widely integrated into S-scheme heterojunctions and exploited for the hydrogen evolution reaction (HER), CO2 reduction, H2O2 generation, N2 fixation, and pollutant degradation. This review comprehensively discusses recent progress in Cu-based S-scheme heterojunctions, and highlights their considerable potential for targeted applications in sustainable energy conversion, environmental remediation, and beyond. The fundamentals of S-scheme charge transfer, the design principles and verification tools are summarized. Then, the review describes the Cu-based photocatalytic materials, categorized according to their chemical composition, and their integration in S-scheme heterojunctions for photocatalytic applications. In particular, the implications of the S-scheme charge transfer mechanism on promoting the catalytic activity of selected systems are analyzed. Finally, current limitations and outlooks are provided to motivate future studies on developing novel and advanced Cu-based S-scheme photocatalysts with high performance and studying the underlying photocatalytic mechanisms.

The photocatalytic conversion of carbon dioxide (CO2) into valuable products holds great promise from environmental and economic perspectives. However, current photocatalytic materials still exhibit unsatisfactory efficiency. In this study, a notably efficient step-scheme (S-scheme) heterojunction was developed by combining the Co-MOFs with carbon nitride nanosheets (g-C3N4). The electrostatic interaction between these components not only facilitates the exfoliation of g-C3N4 layers but also enhances the stability of the photocatalyst structure. The optimal heterojunction Co-CN4 photocatalyst achieved a significantly enhanced CO production rate of 16.1 mu mol g- 1 h- 1, which is 4.7 times higher than that of pure g-C3N4. This improved activity is ascribed to the enhanced light absorption and mitigated charge carrier recombination. Density functional theory (DFT) computations in conjunction with experimental observations elucidate the establishment of a close contact interface. Additionally, electron paramagnetic resonance (EPR) and in situ X-ray photoelectron spectroscopy (XPS) characterization unveil the electron transfer pathway of Co-CN4 during photocatalytic CO2 conversion. This study offers valuable insights into the design of S-scheme photocatalysts for enhancement of CO2 photoreduction.

Photocatalytic CO 2 conversion into energy‐rich fuels offers a sustainable route to address global energy and environmental challenges. However, achieving high activity and selectivity under visible light remains a key limitation. In this study, a 3D hierarchical Nb 2 O 5 nanoflower photocatalyst dual‐doped with vanadium (V), nitrogen (N), and sensitized with carbon (designated NVNBOC) is synthesized via a two‐step hydrothermal process followed by calcination. The incorporation of dual metal and non‐metal dopants, in combination with carbon sensitization, yielded a strong synergistic effect, significantly enhancing both photocatalytic performance and selectivity. Under visible‐light irradiation, the NVNBOC catalyst achieved a remarkable methane (CH 4 ) production rate of 78.32 µmol·g −1 ·h −1 , approximately 12 times higher than that of pristine Nb 2 O 5 , with an outstanding CH 4 selectivity of 97.10%. In‐situ DRIFTS results revealed that the NVNBOC photocatalyst facilitates a stepwise CO 2 reduction pathway, involving key intermediates such as *HCOO − , *CHO, and *CH 3 O, ultimately leading to full CH 4 generation. These findings demonstrate the pivotal role of dual dopant engineering in enhancing light utilization, charge separation, and intermediate stabilization, providing a promising approach for advancing visible‐light‐driven photocatalytic CO 2 reduction toward practical clean energy applications.

Post-synthetic modification (PSM) offers a promising approach for tailoring the compositional, structural, and electronic properties of covalent organic frameworks (COFs), thereby enhancing their exciton dissociation ability and facilitating charge transfer. The effectiveness of these approaches is largely compromised by the harsh conditions, complexity, and alteration of the original structure. Therefore, developing a facile yet effective PSM for modulating COFs' properties without altering the original geometry and/or structure is a challenge. By introducing a phosphazene moiety, ca. hexachlorocyclotriphosphazene (CP), as a donor scaffold, we fabricated a CP-modified triazine-based COF (TDCP COF) with a donor-acceptor (D-A) configuration, via a facile one-step PSM method, and used it for photocatalytic conversion of O2 into H2O2. The resultant TDCP COF with D-A characteristic and substantial intramolecular dipole moment displays a facilitated exciton dissociation and charge transfer. The modified TDCP COF not only provides more favorable adsorption sites for O2 molecules, but also manipulates the O2 activation pathways through multiple mechanisms into •O2- and singlet oxygen (1O2). Benefiting from these features, the TDCP COF exhibited a three times higher H2O2 production rate compared to TD. This work sheds light on a facile yet effective PSM strategy for the development of highly efficient COFs applied for various applications, including photocatalysis, organic solar cells, drug delivery, and gas separation.

The construction of crystalline/amorphous g-C3N4 homojunctions presents a versatile strategy to obtain all-organic homojunction photocatalysts with better interface matching and lower interface charge carrier movement resistance for optimized photocatalytic activity. However, the process entails a complex multi-step workup, which compromises its feasibility. To overcome this challenge, this work provided an innovative Na2CO3-induced crystallinity modulation strategy to construct a Na-doped crystalline/amorphous g-C3N4 S-scheme homojunction photocatalyst in a single step. The approach involves the initial pre-assembling of melamine and cyanuric acid molecules, and subsequent introduction of Na2CO3 before the calcination. Na2CO3 plays key roles to induce in-situ crystallinity modulation during the calcination and as a source for Na-doping. The prepared g-C3N4 S-scheme homojunction photocatalyst demonstrated a prominent H2O2-production rate of 444.6 mu molL-1h-1, which is 6.1-fold higher than that of bulk g-C3N4. The enhanced activity was attributed to the synergistic effect of charge carrier separation induced by the S-scheme homojunction system, and the optimized interfacial H2O2 generation kinetics. The latter was fostered by the Na-doping. This study provides an innovative approach for the one-step construction of g-C3N4 S-scheme homojunction and its integration in photocatalytic applications. Published by Elsevier B.V. All rights reserved.

The step-scheme (S-scheme) heterojunction has garnered significant interest due to its exceptional efficiency in spatially separating photogenerated charge carriers for their potent participation in photoredox reactions. However, the restricted interfacial contact between the two catalysts compromised the charge transport process, resulting in low photocatalytic efficiency. Here, a copper-based metal-organic framework (Cu-MOF) and graphitic carbon nitride (g-C3N4) S-scheme heterojunction with intimate interfacial contact was synthesized for CO2 photoreduction. The developed S-scheme heterojunction demonstrated a superior photocatalytic CO2 reduction with CO and CH4 rates of 6.9 and 6.7 mu mol g-1 h-1, significantly higher than those of pristine components. The S-scheme charge transfer mechanism was validated using in situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Besides, the photogenerated charge dynamics are investigated by femtosecond transient absorption spectroscopy (fs-TAS). Compared to pure g-C3N4, Cu-MOF/gC3N4 S-scheme heterojunction has an additional ultrashort lifetime (4.7 ps), representing the interfacial electron transfer at g-C3N4/Cu-MOF interface, following the S-scheme charge transfer mechanism. Experimental results demonstrate that rational construction of MOF-based S-scheme heterojunctions not only facilitates the effective separation of photogenerated charges, but also elaborates novel systems for improved CO2 photoreduction.

Semiconductor photocatalysis presents a promising route to convert solar energy into storable fuels and tackle global energy and environmental challenges. However, its efficiency is often hindered by rapid electron-hole recombination. Covalent organic frameworks (COFs)-a class of crystalline, porous organic polymers-offer exceptional potential for photocatalysis owing to their precisely tunable structures and distinctive physicochemical properties, yet their performance remains limited by intrinsic charge recombination. To overcome this limitation, the construction of S-scheme heterojunctions has been proposed as a promising strategy to enhance charge separation while maintaining strong redox capabilities. This review begins by presenting a comprehensive perspective on the development and scientific significance of S-scheme heterojunctions. It then systematically summarizes the design principles and synthetic strategies of COFs, followed by an in-depth discussion of the fabrication methods and principles of COF-based S-scheme heterojunctions. Furthermore, advanced characterization techniques that enable precise elucidation of charge migration pathways within these heterostructures are highlighted. The review also provides a comprehensive overview of recent applications of COF-based S-scheme photocatalysts, including hydrogen evolution, carbon dioxide reduction, environmental remediation, hydrogen peroxide production, and others. Finally, current challenges and future perspectives are discussed to inspire continued innovation in the development of high-performance S-scheme photocatalytic systems.

In this work, a physical adsorption strategy including three steps of “turning waste into treasure-removal of pollutants-adsorption mechanism” have been provided to solve the environmental problems caused by spent mushroom substrate and organic pollution simultaneously. A series of environment-friendly Zn2+ modified activated carbon (AC) with adequate adsorption capacity are prepared by using spent mushroom substrate as raw material. X-Ray Diffraction results indicate weak graphitization of Zn2+ modified AC sample during the calcination process. FTIR results indicate that the AC adsorbents are inevitably entailed with abundant surface functional groups. Zn2+ modified AC calcinated at 600 °C (Zn-AC-600) has the bigger BET surface area of 450 m2·g−1 and excellent adsorption property, it can remove about 95, 75, and 88% of Rhodamine B, Amoxicillin and Cefixime after 120 min adsorption process. While the maximal adsorption capacity qmax for Rhodamine B, Amoxicillin and Cefixime towards Zn-AC-600 sample is about 202, 123, and 130 mg·g−1, respectively. The adsorption process of all pollutants is found to match well with the pseudo-second-order kinetics. Zeta potential measurements reveal that Zn-AC-600 is negatively charged (-23.5 mV), which can absorb Rhodamine B, Amoxicillin, and Cefixime by electrostatic attraction. This work may provide an effective strategy toward beneficial recycling of spent mushroom substrate wastes and remove pollutants from water.

Substandard discharge of industrial wastewater leads to abundant silver ions (Ag+) emission into water and soil, causing serious environmental threat. Precise and reliable detection of Ag+ is vital for environmental surveillance, while it remains a great challenge in complex actual environment. Herein, a lab-to-factory adoptable photoelectrochemical (PEC) approach for highly selective and sensitive detection of Ag+ in industrial wastewater has been first demonstrated. BiOI nanosheets (NSs) were prepared as photocathode and showed a spontaneous and selective ion-exchange process with Ag+ ions when it immersed into complicated industrial wastewater. The in situ generated AgI/Ag exhibits unique localized surface plasmonic resonance (LSPR) effect to modulate PEC signals for highly selective and sensitive Ag+ detection. As a result, the prepared photocathode delivers an ultralow detection limit (0.21 nM) and a broad linear range (up to 300 μM), outperforming most reported results. This work opens a feasible avenue for Ag+ monitoring in actual environment.

Electrocatalytic CO 2 reduction reaction (CO 2 RR) to multi-carbon products (C 2+ ) in acidic electrolyte is one of the most advanced routes for tackling our current climate and energy crisis. However, the competing hydrogen evolution reaction (HER) and the poor selectivity towards the valuable C 2+ products are the major obstacles for the upscaling of these technologies. High local potassium ions (K + ) concentration at the cathode's surface can inhibit proton-diffusion and accelerate the desirable carbon-carbon (C−C) coupling process. However, the solubility limit of potassium salts in bulk solution constrains the maximum achievable K + concentration at the reaction sites and thus the overall acidic CO 2 RR performance of most electrocatalysts. In this work, we demonstrate that Cu nanoneedles induce ultrahigh local K + concentrations (4.22 M) – thus breaking the K + solubility limit (3.5 M) – which enables a highly efficient CO 2 RR in 3 M KCl at pH=1. As a result, a Faradaic efficiency of 90.69±2.15 % for C 2+ (FE C2+ ) can be achieved at 1400 mA.cm −2 , simultaneous with a single pass carbon efficiency (SPCE) of 25.49±0.82 % at a CO 2 flow rate of 7 sccm.

The use of gas diffusion electrode (GDE) based flow cell can realize industrial-scale CO 2 reduction reactions (CO 2 RRs). Controlling local CO 2 and CO intermediate diffusion plays a key role in CO 2 RR toward multi-carbon (C 2+ ) products. In this work, local CO 2 and CO intermediate diffusion through the catalyst layer (CL) was investigated for improving CO 2 RR toward C 2+ products. The gas permeability tests and finite element simulation results indicated CL can balance the CO 2 gas diffusion and residence time of the CO intermediate, leading to a sufficient CO concentration with a suitable CO 2 /H 2 O supply for high C 2+ products. As a result, an excellent selectivity of C 2+ products ~ 79% at a high current density of 400 mA·cm −2 could be obtained on the optimal 500 nm Cu CL (Cu500). This work provides a new insight into the optimization of CO 2 /H 2 O supply and local CO concentration by controlling CL for C 2+ products in CO 2 RR flow cell.

The meticulous design of semiconductor photocatalysts has been known as the key to achieve a highly efficient and selective photocatalytic reaction toward solving the current environmental pollution and energy crisis. Recently, the combination of two or more semiconductors to form step-scheme (S-scheme) heterojunction photocatalysts has emerged as a rising star in photocatalysis due to their capability for optimizing the photogenerated charge carrier utilization and maximizing the reduction-oxidation potential of the photocatalytic system. Herein, this review summarizes and highlights the recent development of the S-scheme heterojunction photocatalysts. We first concisely compile the working mechanism of S-scheme photocatalysts, followed by discussing their characterization techniques. Then, we discuss and overview the applications of the S-scheme photocatalysts in water splitting, CO2 conversion, wastewater purification, H2O2 production, N-2 fixation and so on. Finally, we conclude this review with a brief discussion of significant challenges and future prospects in the development of S-scheme photocatalytic systems.