Atomically dispersed antimony on carbon nitride for the artificial photosynthesis of hydrogen peroxide

Enhancing Photosynthesis Efficiency of Hydrogen Peroxide by Modulating Side Chains to Facilitate Water Oxidation at Low-Energy Barrier Sites

Hydrogen peroxide (H2O2) is a crucial oxidant in advanced oxidation processes. In situ, photosynthesis of it in natural water holds the promise of practical application for water remediation. However, current photosynthesis of H2O2 systems primarily relies on oxygen reduction, leading to limited performance in natural water with low dissolved oxygen or anaerobic conditions found in polluted water. Herein, a novel photocatalyst based on conjugated polymers with alternating electron donor-acceptor structures and electron-withdrawing side chains on electron donors is introduced. Specifically, carbazole functions as the electron donor, triazine serves as the electron acceptor, and cyano acts as the electron-withdrawing side chain. Notably, the photocatalyst exhibits a remarkable solar-to-chemical conversion of 0.64%, the highest reported in natural water. Furthermore, even in anaerobic conditions, it achieves an impressive H2O2 photosynthetic efficiency of 1365 µmol g-1 h-1, surpassing all the reported photosynthetic systems of H2O2. This remarkable improvement is attributed to the effective relocation of the water oxidation active site from a high-energy carbazole to a low-energy acetylene site mediated by the side chains, resulting in enhanced O2 or H2O2 generation from water. This breakthrough offers a new avenue for efficient water remediation using advanced oxidation technologies in oxygen-limited environments, holding significant implications for environmental restoration.

Emerging single-atom catalysts in the detection and purification of contaminated gases

Single atom catalysts (SACs) show exceptional molecular adsorption and electron transfer capabilities owing to their remarkable atomic efficiency and tunable electronic structure, thereby providing promising solutions for diverse important processes including photocatalysis, electrocatalysis, thermal catalysis, etc. Consequently, SACs hold great potential in the detection and degradation of pollutants present in contaminated gases. Over the past few years, SACs have made remarkable achievements in the field of contaminated gas detection and purification. In this review, we first provide a concise introduction to the significance and urgency of gas detection and pollutant purification, followed by a comprehensive overview of the structural feature identification methods for SACs. Subsequently, we systematically summarize the three key properties of SACs for detecting contaminated gases and discuss the research progress made in utilizing SACs to purify polluted gases. Finally, we analyze the enhancement mechanism and advantages of SACs in polluted gas detection and purification, and propose strategies to address challenges and expedite the development of SACs in polluted gas detection and purification.

Noble-Metal-Free Single- and Dual-Atom Catalysts for Artificial Photosynthesis

Artificial photosynthesis enables direct solar-to-chemical energy conversion aimed at mitigating environmental pollution and producing solar fuels and chemicals in a green and sustainable approach, and efficient, robust, and low-cost photocatalysts are the heart of artificial photosynthesis systems. As an emerging new class of cocatalytic materials, single-atom catalysts (SACs) and dual-atom catalysts (DACs) have received a great deal of current attention due to their maximal atom utilization and unique photocatalytic properties, whereas noble-metal-free ones impart abundance, availability, and cost-effectiveness allowing for scalable implementation. This review outlines the fundamental principles and synthetic methods of SACs and DACs and summarizes the most recent advances in SACs (Co, Fe, Cu, Ni, Bi, Al, Sn, Er, La, Ba, etc.) and DACs (CuNi, FeCo, InCu, KNa, CoCo, CuCu, etc.) based on non-noble metals, confined on an arsenal of organic or inorganic substrates (polymeric carbon nitride, metal oxides, metal sulfides, metal-organic frameworks, carbon, etc.) acting as versatile scaffolds in solar-light-driven photocatalytic reactions, including hydrogen evolution, carbon dioxide reduction, methane conversion, organic synthesis, nitrogen fixation, hydrogen peroxide production, and environmental remediation. The review concludes with the challenges, opportunities, and future prospects of noble-metal-free SACs and DACs for artificial photosynthesis.

Machine Learning-Assistant Colorimetric Sensor Arrays for Intelligent and Rapid Diagnosis of Urinary Tract Infection

Urinary tract infections (UTIs), which can lead to pyelonephritis, urosepsis, and even death, are among the most prevalent infectious diseases worldwide, with a notable increase in treatment costs due to the emergence of drug-resistant pathogens. Current diagnostic strategies for UTIs, such as urine culture and flow cytometry, require time-consuming protocols and expensive equipment. We present here a machine learning-assisted colorimetric sensor array based on recognition of ligand-functionalized Fe single-atom nanozymes (SANs) for the identification of microorganisms at the order, genus, and species levels. Colorimetric sensor arrays are built from the SAN Fe1-NC functionalized with four types of recognition ligands, generating unique microbial identification fingerprints. By integrating the colorimetric sensor arrays with a trained computational classification model, the platform can identify more than 10 microorganisms in UTI urine samples within 1 h. Diagnostic accuracy of up to 97% was achieved in 60 UTI clinical samples, holding great potential for translation into clinical practice applications.

Rationally Designed Cyclooctatetrathiophene-Based Porous Aromatic Frameworks (COTh-PAFs) for Efficient Photocatalytic Hydrogen Peroxide Production

Constructing stable and efficient photocatalysts for H2O2 production is of great importance and is challenging. In this study, the synthesis of three photoactive cyclooctatetrathiophene (COTh)-based porous aromatic frameworks (COTh-PAFs) in an alternating donor-acceptor (D-A) fashion is presented. In combination with a triazine-derived electron acceptor, PAF-363 exhibits high efficiency for the photosynthesis of H2O2 with production rates of 11733 μmol g-1 h-1(with sacrificial agent) and 3930 μmol g-1 h-1 (without sacrificial agent) from water and oxygen under visible light irradiation. Experimental results and theoretical calculations reveal that the charge transfer positions and the O2 adsorption sites in PAF-363 are both concentrated on COTh fragments, which facilitate the H2O2 production through the oxygen reduction reaction (ORR) pathway. This work highlights that the rational design of COTh-PAFs with consideration of D-A direction, charge transfer positions, and O2 adsorption sites provides a feasible access to efficient H2O2 production photocatalysts.

Enhancing photocatalytic H2O2 production with Au co-catalysts through electronic structure modification

Gold-based co-catalysts are a promising class of materials with potential applications in photocatalytic H2O2 production. However, current approaches with Au co-catalysts show limited H2O2 production due to intrinsically weak O2 adsorption at the Au site. We report an approach to strengthen O2 adsorption at Au sites, and to improve H2O2 production, through the formation of electron-deficient Auδ+ sites by modifying the electronic structure. In this case, we report the synthesis of TiO2/MoSx-Au, following selective deposition of Au onto a MoSx surface which is then further anchored onto TiO2. We further show that the catalyst achieves a significantly increased H2O2 production rate of 30.44 mmol g-1 h-1 in O2-saturated solution containing ethanol. Density functional theory calculations and X-ray photoelectron spectroscopy analysis reveal that the MoSx mediator induces the formation of electron-deficient Auδ+ sites thereby decreasing the antibonding-orbital occupancy of Au-Oads and subsequently enhancing O2 adsorption. This strategy may be useful for rationally designing the electronic structure of catalyst surfaces to facilitate artificial photosynthesis.

Spaced Double Hydrogen Bonding in an Imidazole Poly Ionic Liquid Composite for Highly Efficient and Selective Photocatalytic Air Reductive H2O2 Synthesis

Photocatalytic oxygen reductive H2O2 production is a promising approach to alternative industrial anthraquinone processes while suffering from the requirement of pure O2 feedstock for practical application. Herein, we report a spaced double hydrogen bond (IC-H-bond) through multi-component Radziszewski reaction in an imidazole poly-ionic-liquid composite (SI-PIL-TiO2) and levofloxacin hydrochloride (LEV) electron donor for highly efficient and selective photocatalytic air reductive H2O2 production. It is found that the IC-H-bond formed by spaced imino (-NH-) group of SI-PIL-TiO2 and carbonyl (-C=O) group of LEV can switch the imidazole active sites characteristic from a covered state to a fully exposed one to shield the strong adsorption of electron donor and N2 in the air, and propel an intenser positive potential and more efficient orbitals binding patterns of SI-PIL-TiO2 surface to establish competitive active sites for selectivity O2 chemisorption. Moreover, the high electron enrichment of imidazole as an active site for the 2e- oxygen reduction ensures the rapid reduction of O2. Therefore, the IC-H-bond enables a total O2 utilization and conversion efficiency of 94.8 % from direct photocatalytic air reduction, achieving a H2O2 production rate of 1518 μmol/g/h that is 16 and 23 times compared to poly-ionic-liquid composite without spaced imino groups (PIL-TiO2) and TiO2, respectively.

Photochemical tuning of dynamic defects for high-performance atomically dispersed catalysts

Developing active and stable atomically dispersed catalysts is challenging because of weak non-specific interactions between catalytically active metal atoms and supports. Here we demonstrate a general method for synthesizing atomically dispersed catalysts via photochemical defect tuning for controlling oxygen-vacancy dynamics, which can induce specific metal-support interactions. The developed synthesis method offers metal-dynamically stabilized atomic catalysts, and it can be applied to reducible metal oxides, including TiO2, ZnO and CeO2, containing various catalytically active transition metals, including Pt, Ir and Cu. The optimized Pt-DSA/TiO2 shows unprecedentedly high photocatalytic hydrogen evolution activity, producing 164 mmol g-1 h-1 with a turnover frequency of 1.27 s-1. Furthermore, it generates 42.2 mmol gsub-1 of hydrogen via a non-recyclable-plastic-photoreforming process, achieving a total conversion of 98%; this offers a promising solution for mitigating plastic waste and simultaneously producing valuable energy sources.

Surface Engineered Single-atom Systems for Energy Conversion

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

Keto-anthraquinone covalent organic framework for H2O2 photosynthesis with oxygen and alkaline water

Hydrogen peroxide photosynthesis suffers from insufficient catalytic activity due to the high energy barrier of hydrogen extraction from H2O. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework which is able to directly synthesize H2O2 (4784 μmol h-1 g-1 at λ > 400 nm) from oxygen and alkaline water (pH = 13) in the absence of any sacrificial reagents. The strong alkalinity resulted in the formation of OH-(H2O)n clusters in water, which were adsorbed on keto moieties within the framework and then dissociated into O2 and active hydrogen, because the energy barrier of hydrogen extraction was largely lowered. The produced hydrogen reacted with anthraquinone to generate anthrahydroquinone, which was subsequently oxidized by O2 to produce H2O2. This study ultimately sheds light on the importance of hydrogen extraction from H2O for H2O2 photosynthesis and demonstrates that H2O2 synthesis is achievable under alkaline conditions.

Weak-Field Electro-Flash Induced Asymmetric Catalytic Sites toward Efficient Solar Hydrogen Peroxide Production

Borocarbonitride (BCN), in a mesoscopic asymmetric state, is regarded as a promising photocatalyst for artificial photosynthesis. However, BCN materials reported in the literature primarily consist of symmetric N-[B]3 units, which generate highly spatial coupled electron-hole pairs upon irradiation, thus kinetically suppressing the solar-to-chemical conversion efficiency. Here, we propose a facile and fast weak-field electro-flash strategy, with which structural symmetry breaking is introduced on key nitrogen sites. As-obtained double-substituted BCN (ds-BCN) possesses high-concentration asymmetric [B]2-N-C coordination, which displays a highly separated electron-hole state and broad visible-light harvesting, as well as provides electron-rich N sites for O2 affinity. Thereby, ds-BCN delivers an apparent quantum yield of 7.6% at 400 nm and a solar-to-chemical conversion efficiency of 0.3% for selective 2e-reduction of O2 to H2O2, over 4-fold higher than that of the traditional calcined BCN analogue and superior to the metal-free C3N4-based photocatalysts reported so far. The weak-field electro-flash method and as-induced catalytic site symmetry-breaking methodologically provide a new method for the fast and low-cost fabrication of efficient nonmetallic catalysts toward solar-to-chemical conversions.

Large-Scale Continuous and In Situ Photosynthesis of Hydrogen Peroxide by Sulfur-Functionalized Polymer Catalyst for Water Treatment

Photocatalytic H2 O2 generation system based on polymer catalyst receives increasing attention in recent years; however, the insufficient charge separation efficiency and low oxygen adsorption/activation capacity severely limit their potential application. In this study, a sulfur (C=S) functionalized polymer catalyst is reported through a green water-mediated and catalyst-free multi-component reactions (MCRs) route. The sulfur functional group endows the polymer with a suitable energy band and facilitates the separation of photogenerated electron-hole pair. The reported polymer achieves a high H2 O2 production efficiency (3132 μmol g-1  h-1 ) in pure water without oxygen aeration. To demonstrate their potential in in situ wastewater treatment, a panel reactor system (20×20 cm) is constructed for large-scale production of H2 O2 , which realizes continuous degradation of emerging pollutants including antibiotics and bisphenol A under natural sunlight irradiation condition. The H2 O2 utilization efficiency of the photo-self-Fenton system using in situ generated H2 O2 is found 7.9 times higher than that of the traditional photo-Fenton system. This study offers new insights in green synthesis and design of functional polymer photocatalyst, and demonstrates the feasibility of panel reactor system for large-scale continuous H2 O2 photocatalytic production and water treatment.

Guiding the Driving Factors on Plasma Super-Photothermal S-Scheme Core-Shell Nanoreactor to Enhance Photothermal Catalytic H2 Evolution and Selective CO2 Reduction

Light-induced heat has a non-negligible role in photocatalytic reactions. However, it is still challenging to design highly efficient catalysts that can make use of light and thermal energy synergistically. Herein, the study proposes a plasma super-photothermal S-scheme heterojunction core-shell nanoreactor based on manipulation of the driving factors, which consists of α-Fe2 O3 encapsulated by g-C3 N4 modified with gold quantum dots. α-Fe2 O3 can promote carrier spatial separation while also acting as a thermal core to radiate heat to the shell, while Au quantum dots transfer energetic electrons and heat to g-C3 N4 via surface plasmon resonance. Consequently, the catalytic activity of Au/α-Fe2 O3 @g-C3 N4 is significantly improved by internal and external double hot spots, and it shows an H2 evolution rate of 5762.35 µmol h-1 g-1 , and the selectivity of CO2 conversion to CH4 is 91.2%. This work provides an effective strategy to design new plasma photothermal catalysts for the solar-to-fuel transition.

2D/2D Heterojunction of BiOBr/BiOI Nanosheets for In Situ H2 O2 Production and Activation toward Efficient Photocatalytic Wastewater Treatment

The presence of toxic organic pollutants in aquatic environments poses significant threats to human health and global ecosystems. Photocatalysis that enables in situ production and activation of H2 O2 presents a promising approach for pollutant removal; however, the processes of H2 O2 production and activation potentially compete for active sites and charge carriers on the photocatalyst surface, leading to limited catalytic performance. Herein, a hierarchical 2D/2D heterojunction nanosphere composed of ultrathin BiOBr and BiOI nanosheets (BiOBr/BiOI) is developed by a one-pot microwave-assisted synthesis to achieve in situ H2 O2 production and activation for efficient photocatalytic wastewater treatment. Various experimental and characterization results reveal that the BiOBr/BiOI heterojunction facilitates efficient electron transfer from BiOBr to BiOI, enabling the one-step two-electron O2 reduction for H2 O2 production. Moreover, the ultrathin BiOI provides abundant active sites for H2 O2 adsorption, promoting in situ H2 O2 activation for •O2 - generation. As a result, the BiOBr/BiOI hybrid exhibits excellent activity for pollutant degradation with an apparent rate constant of 0.141 min-1 , which is 3.8 and 47.3 times that of pristine BiOBr and BiOI, respectively. This work expands the range of the materials suitable for in situ H2 O2 production and activation, paving the way toward sustainable environmental remediation using solar energy.

Rejoint of Carbon Nitride Fragments into Multi-Interfacial Order-Disorder Homojunction for Robust Photo-Driven Generation of H2 O2

Photocatalytic technology based on carbon nitride (C3 N4 ) offers a sustainable and clean approach for hydrogen peroxide (H2 O2 ) production, but the yield is severely limited by the sluggish hot carriers due to the weak internal electric field. In this study, a novel approach is devised by fragmenting bulk C3 N4  into smaller pieces (CN-NH4 ) and then subjecting it to a directed healing process to create multiple order-disorder interfaces (CN-NH4 -NaK). The resulting junctions in CN-NH4 -NaK significantly boost charge dynamics and facilitate more spatially and orderly separated redox centers. As a result, CN-NH4 -NaK demonstrates outstanding photosynthesis of H2 O2 via both two-step single-electron and one-step double-electron oxygen reduction pathways, achieving a remarkable yield of 16675 µmol h-1  g-1 , excellent selectivity (> 91%), and a prominent solar-to-chemical conversion efficiency exceeding 2.3%. These remarkable results surpass pristine C3 N4 by 158 times and outperform previously reported C3 N4 -based photocatalysts. This work represents a significant advancement in catalyst design and modification technology, inspiring the development of more efficient metal-free photocatalysts for the synthesis of highly valued fuels.

Single Zn Atoms with Acetate-Anion-Enabled Asymmetric Coordination for Efficient H2 O2 Photosynthesis

Exploring unique single-atom sites capable of efficiently reducing O2 to H2 O2 while being inert to H2 O2 decomposition under light conditions is significant for H2 O2 photosynthesis, but it remains challenging. Herein, we report the facile design and fabrication of polymeric carbon nitride (CN) decorated with single-Zn sites that have tailorable local coordination environments, which is enabled by utilizing different Zn salt anions. Specifically, the O atom from acetate (OAc) anion participates in the coordination of single-Zn sites on CN, forming asymmetric Zn-N3 O moiety on CN (denoted as CN/Zn-OAc), in contrast to the obtained Zn-N4 sites when sulfate (SO4 ) is adopted (CN/Zn-SO4 ). Both experimental and theoretical investigations demonstrate that the Zn-N3 O moiety exhibits higher intrinsic activity for O2 reduction to H2 O2 than the Zn-N4 moiety. This is attributed to the asymmetric N/O coordination, which promotes the adsorption of O2 and the formation of the key intermediate *OOH on Zn sites due to their modulated electronic structure. Moreover, it is inactive for H2 O2 decomposition under both dark and light conditions. As a result, the optimized CN/Zn-OAc catalyst exhibits significantly improved photocatalytic H2 O2 production activity under visible light irradiation.

Triple-Phase Photocatalytic H2O2 Production on a Janus Fiber Membrane with Asymmetric Hydrophobicity

Photocatalytic O2 reduction is an intriguing approach to producing H2O2, but its efficiency is often hindered by the limited solubility and mass transfer of O2 in the aqueous phase. Here, we design and fabricate a two-layered (2L) Janus fiber membrane photocatalyst with asymmetric hydrophobicity for efficient photocatalytic H2O2 production. The top layer of the membrane consists of superhydrophobic polytetrafluoroethylene (PTFE) fibers with a dispersed modified carbon nitride (mCN) photocatalyst. Amphiphilic Nafion (Naf) ionomer is sprayed onto this layer to modulate the microenvironment and achieve moderate hydrophobicity. In contrast, the bottom layer consists of bare PTFE fibers with high hydrophobicity. The elaborate structural configuration and asymmetric hydrophobicity feature of the optimized membrane photocatalyst (designated as 2L-mCN/F-Naf; F, PTFE) allow most mCN to be exposed with gas-liquid-solid triple-phase interfaces and enable rapid mass transfer of gaseous O2 within the hierarchical membrane, thus increasing the local O2 concentration near the mCN photocatalyst. As a result, the optimized 2L-mCN/F-Naf membrane photocatalyst shows remarkable photocatalytic H2O2 production activity, achieving a rate of 5.38 mmol g-1 h-1 under visible light irradiation.

Efficient Photosynthesis of Hydrogen Peroxide by Cyano-Containing Covalent Organic Frameworks from Water, Air and Sunlight

The insufficient exciton (e- -h+ pair) separation/transfer and sluggish two-electron water oxidation are two main factors limiting the H2 O2 photosynthetic efficiency of covalent organic frameworks (COFs) photocatalysts. Herein, we present an alternative strategy to simultaneously facilitate exciton separation/transfer and reduce the energy barrier of two-electron water oxidation in COFs via a dicyano functionalization. The in situ characterization and theoretical calculations reveal that the dicyano functionalization improves the amount of charge transfer channels between donor and acceptor units from two in COF-0CN without cyano functionalization to three in COF-1CN with mono-cyano functionalization and four in COF-2CN with dicyano functionalization, leading to the highest separation/transfer efficiency in COF-2CN. More importantly, the dicyano group activates the neighbouring C atom to produce the key *OH intermediate for effectively reducing the energy barrier of rate-determining two-electron water oxidation in H2 O2 photosynthesis. The simultaneously enhanced exciton separation/transfer and two-electron water oxidation in COF-2CN result in high H2 O2 yield (1601 μmol g-1  h-1 ) from water and oxygen without using sacrificial reagent under visible-light irradiation. COF-2CN can effectively yield H2 O2 in water with wide pH range, in different real water samples, in scaled-up reactor under natural sunlight irradiation, and in continuous-flow reactor for consecutively producing H2 O2 solution for water decontamination.

Atomically isolated Sb(CN)3 on sp2-c-COFs with balanced hydrophilic and oleophilic sites for photocatalytic C-H activation

Activation of carbon-hydrogen (C-H) bonds is of utmost importance for the synthesis of vital molecules. Toward achieving efficient photocatalytic C-H activation, our investigation revealed that incorporating hydrophilic C≡N-Sb(CN)3 sites into hydrophobic sp2 carbon-conjugated covalent organic frameworks (sp2-c-COFs) had a dual effect: It simultaneously enhanced charge separation and improved generation of polar reactive oxygen species. Detailed spectroscopy measurements and simulations showed that C≡N-Sb(CN)3 primarily functioned as water capture sites, which were not directly involved in photocatalysis. However, the potent interaction between water molecules and the Sb(CN)3-modified framework notably enhanced charge dynamics in hydrophobic sp2-c-COFs. The reactive species ·O2- and ·OH (ad) subsequently combined with benzyl radical, leading to the formation of benzaldehyde, benzyl alcohol, and lastly benzyl benzoate. Notably, the Sb(CN)3-modified sp2-c-COFs exhibited a 54-fold improvement in reaction rate as compared to pristine sp2-c-COFs, which achieved a remarkable 68% conversion rate for toluene and an 80% selectivity for benzyl benzoate.

Converting formaldehyde in methanol with MoO2 under irradiation: A pollution-free strategy for cleaning air

Direct photocatalytic reduction of toxic formaldehyde (HCHO) in value-added chemicals and fuels is promising because that not only abates the environmental pollution, but also solves the energy shortage. Herein, self-supported MoO2 and MoO3 nanoparticles growing on Mo meshes were comparatively applied to the photocatalytic conversion of HCHO. Under UV-visble lights, MoO2 reduces HCHO in methanol (CH3OH) while MoO3 oxidizes HCHO in carbon oxide and water. Their contrary photocatalytic capacities were revealed. Compared with MoO3, the lower work function of MoO2 enables an electron-rich interface, realizing a complete reduction of 30 ppm HCHO to CH3OH in 30 min. Theoretical calculations clarify that a large number of delocalized electrons on MoO2 attracts HCHO molecule and activates its CO bond, facilitating subsequent hydrogenation and reduction of HCHO to CH3OH. As for MoO3, the wider bandgap and higher potential of valence band govern the photocatalytic oxidation of HCHO.

Embedding electronic perpetual motion into single-atom catalysts for persistent Fenton-like reactions

In our quest to leverage the capabilities of the emerging single-atom catalysts (SACs) for wastewater purification, we confronted fundamental challenges related to electron scarcity and instability. Through meticulous theoretical calculations, we identified optimal placements for nitrogen vacancies (Nv) and iron (Fe) single-atom sites, uncovering a dual-site approach that significantly amplified visible-light absorption and charge transfer dynamics. Informed by these computational insights, we cleverly integrated Nv into the catalyst design to boost electron density around iron atoms, yielding a potent and flexible photoactivator for benign peracetic acid. This exceptional catalyst exhibited remarkable stability and effectively degraded various organic contaminants over 20 cycles with self-cleaning properties. Specifically, the Nv sites captured electrons, enabling their swift transfer to adjacent Fe sites under visible light irradiation. This mechanism accelerated the reduction of the formed "peracetic acid-catalyst" intermediate. Theoretical calculations were used to elucidate the synergistic interplay of dual mechanisms, illuminating increased adsorption and activation of reactive molecules. Furthermore, electron reduction pathways on the conduction band were elaborately explored, unveiling the production of reactive species that enhanced photocatalytic processes. A six-flux model and associated parameters were also applied to precisely optimize the photocatalytic process, providing invaluable insights for future photocatalyst design. Overall, this study offers a molecule-level insight into the rational design of robust SACs in a photo-Fenton-like system, with promising implications for wastewater treatment and other high-value applications.

Magnetic Field Enhanced Oxygen Reduction Reaction via Oxygen Diffusion Speedup

The mass-transfer of oxygen in liquid phases (including in the bulk electrolyte and near the electrode surface) is a critical step to deliver oxygen to catalyst sites (especially immersed catalyst sites) and use the full capacity of oxygen reduction reaction (ORR). Despite the extensive efforts of optimizing the complex three-phase reaction interfaces to enhance the gaseous oxygen transfer, strong limitations remain due to oxygen's poor solubility and slow diffusion in electrolytes. Herein, a magnetic method for boosting the directional hydrodynamic pumping of oxygen toward immersed catalyst sites is demonstrated which allows the ORR to reach otherwise inaccessible catalytic regions where high currents normally would have depleted oxygen. For Pt foil electrodes without forced oxygen saturation in KOH electrolytes, the mass-transfer-limited current densities can be improved by 60% under an external magnetic field of 435 mT due to the synergistic effect between bulk- and surface-magnetohydrodynamic (MHD) flows induced by Lorentz forces. The residual magnetic fields are further used at the surface of magnetic materials (such as CoPt alloys and Pt/FeCo heterostructures) to enhance the surface-MHD effect, which helps to retain part of the ORR enhancement permanently without applying external magnetic fields.

Halogen-Modulated 2D Coordination Polymers for Efficient Hydrogen Peroxide Photosynthesis under Air and Pure Water Conditions

H2 O2 is a widely used eco-friendly oxidant and a potential energy carrier. Photocatalytic H2 O2 production from water and O2 is an ideal approach with the potential to address the current energy crisis and environmental issues. Three zig-zag two-dimensional coordination polymers (2D CPs), named CuX-dptz, were synthesized by a rapid and facile method at room temperature, showing preeminent H2 O2 photoproduction performance under pure water and open air without any additives. CuBr-dptz exhibits a H2 O2 production rate high up to 1874 μmol g-1  h-1 , exceeding most reported photocatalysts under this condition, even comparable to those supported by sacrificial agents and O2 . The coordination environment of Cu can be modulated by halogen atoms (X=Cl, Br, I), which in turn affects the electron transfer process and finally determines the reaction activity. This is the first time that 2D CPs have been used for photocatalytic H2 O2 production in such challenging conditions, which provides a new pathway for the development of portable in situ H2 O2 photosynthesis devices.

Promoting Piezocatalytic H2 O2 Production in Pure Water by Loading Metal-Organic Cage-Modified Gold Nanoparticles on Graphitic Carbon Nitride

Piezocatalytic hydrogen peroxide (H2 O2 ) production is a green synthesis method, but the rapid complexation of charge carriers in piezocatalysts and the difficulty of adsorbing substrates limit its performance. Here, metal-organic cage-coated gold nanoparticles are anchored on graphitic carbon nitride (MOC-AuNP/g-C3 N4 ) via hydrogen bond to serve as the multifunctional sites for efficient H2 O2 production. Experiments and theoretical calculations prove that MOC-AuNP/g-C3 N4 simultaneously optimize three key parts of piezocatalytic H2 O2 production: i) the MOC component enhances substrate (O2 ) and product (H2 O2 ) adsorption via host-guest interaction and hinders the rapid decomposition of H2 O2 on MOC-AuNP/g-C3 N4 , ii) the AuNP component affords a strong interfacial electric field that significantly promotes the migration of electrons from g-C3 N4 for O2 reduction reaction (ORR), iii) holes are used for H2 O oxidation reaction (WOR) to produce O2 and H+ to further promote ORR. Thus, MOC-AuNP/g-C3 N4 can be used as an efficient piezocatalyst to generate H2 O2 at rates up to 120.21 μmol g-1  h-1 in air and pure water without using sacrificial agents. This work proposes a new strategy for efficient piezocatalytic H2 O2 synthesis by constructing multiple active sites in semiconductor catalysts via hydrogen bonding, by enhancing substrate adsorption, rapid separation of electron-hole pairs and preventing rapid decomposition of H2 O2 .

Large electronegativity differences between adjacent atomic sites activate and stabilize ZnIn2S4 for efficient photocatalytic overall water splitting

Photocatalytic overall water splitting into hydrogen and oxygen is desirable for long-term renewable, sustainable and clean fuel production on earth. Metal sulfides are considered as ideal hydrogen-evolved photocatalysts, but their component homogeneity and typical sulfur instability cause an inert oxygen production, which remains a huge obstacle to overall water-splitting. Here, a distortion-evoked cation-site oxygen doping of ZnIn2S4 (D-O-ZIS) creates significant electronegativity differences between adjacent atomic sites, with S1 sites being electron-rich and S2 sites being electron-deficient in the local structure of S1-S2-O sites. The strong charge redistribution character activates stable oxygen reactions at S2 sites and avoids the common issue of sulfur instability in metal sulfide photocatalysis, while S1 sites favor the adsorption/desorption of hydrogen. Consequently, an overall water-splitting reaction has been realized in D-O-ZIS with a remarkable solar-to-hydrogen conversion efficiency of 0.57%, accompanying a ~ 91% retention rate after 120 h photocatalytic test. In this work, we inspire an universal design from electronegativity differences perspective to activate and stabilize metal sulfide photocatalysts for efficient overall water-splitting.

Constructing sulfur and oxygen super-coordinated main-group electrocatalysts for selective and cumulative H2O2 production

Direct electrosynthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction presents a burgeoning alternative to the conventional energy-intensive anthraquinone process for on-site applications. Nevertheless, its adoption is currently hindered by inferior H2O2 selectivity and diminished H2O2 yield induced by consecutive H2O2 reduction or Fenton reactions. Herein, guided by theoretical calculations, we endeavor to overcome this challenge by activating a main-group Pb single-atom catalyst via a local micro-environment engineering strategy employing a sulfur and oxygen super-coordinated structure. The main-group catalyst, synthesized using a carbon dot-assisted pyrolysis technique, displays an industrial current density reaching 400 mA cm-2 and elevated accumulated H2O2 concentrations (1358 mM) with remarkable Faradaic efficiencies. Both experimental results and theoretical simulations elucidate that S and O super-coordination directs a fraction of electrons from the main-group Pb sites to the coordinated oxygen atoms, consequently optimizing the *OOH binding energy and augmenting the 2e- oxygen reduction activity. This work unveils novel avenues for mitigating the production-depletion challenge in H2O2 electrosynthesis through the rational design of main-group catalysts.

Emerging Xene-Based Single-Atom Catalysts: Theory, Synthesis, and Catalytic Applications

In recent years, the emergence of novel 2D monoelemental materials (Xenes), e.g., graphdiyne, borophene, phosphorene, antimonene, bismuthene, and stanene, has exhibited unprecedented potentials for their versatile applications as well as addressing new discoveries in fundamental science. Owing to their unique physicochemical, optical, and electronic properties, emerging Xenes have been regarded as promising candidates in the community of single-atom catalysts (SACs) as single-atom active sites or support matrixes for significant improvement in intrinsic activity and selectivity. In order to comprehensively understand the relationships between the structure and property of Xene-based SACs, this review represents a comprehensive summary from theoretical predictions to experimental investigations. Firstly, theoretical calculations regarding both the anchoring of Xene-based single-atom active sites on versatile support matrixes and doping/substituting heteroatoms at Xene-based support matrixes are briefly summarized. Secondly, controlled synthesis and precise characterization are presented for Xene-based SACs. Finally, current challenges and future opportunities for the development of Xene-based SACs are highlighted.

High-Throughput Calculations for Screening d- and p-Block Single-Atom Catalysts toward Li2 S/Na2 S Decomposition Guided by Facile Descriptor beyond Brønsted-Evans-Polanyi Relationship

Single-atom catalysts (SACs) are promising cathode materials for addressing issues faced by lithium-sulfur batteries. Considering the ample chemical space of SACs, high-throughput calculations are efficient strategies for their rational design. However, the high throughput calculations are impeded by the time-consuming determination of the decomposition barrier (Eb ) of Li2 S. In this study, the effects of bond formation and breakage on the kinetics of SAC-catalyzed Li2 S decomposition with g-C3 N4 as the substrate are clarified. Furthermore, a new efficient and easily-obtained descriptor Li─S─Li angle (ALi─S─Li ) of adsorbed Li2 S, different from the widely accepted thermodynamic data for predicting Eb , which breaks the well-known Brønsted-Evans-Polanyi relationship, is identified. Under the guidance of ALi─S─Li , several superior SACs with d- and p-block metal centers supported by g-C3 N4 are screened to accelerate the sulfur redox reaction and fix the soluble lithium polysulfides. The newly identified descriptor of ALi─S─Li can be extended to rationally design SACs for Na─S batteries. This study opens a new pathway for tuning the performance of SACs to catalyze the decomposition of X2 S (X = Li, Na, and K) and thus accelerate the design of SACs for alkaline-chalcogenide batteries.

Cyano-Rich g-C3 N4 in Photochemistry: Design, Applications, and Prospects

Cyano-rich g-C3 N4 materials are widely used in various fields of photochemistry due to the very powerful electron-absorbing ability and electron storage function of cyano, as well as its advantages in improving light absorption, adjusting the energy band structure, increasing the polarization rate and electron density in the structure, active site concentration, and promoting oxygen activation ability. Notwithstanding, there is yet a huge knowledge break in the design, preparation, detection, application, and prospect of cyano-rich g-C3 N4 . Accordingly, an overall review is arranged to substantially comprehend the research progress and position of cyano-rich g-C3 N4 materials. An overall overview of the current research position in the synthesis, characterization (determination of their location and quantity), application, and reaction mechanism analysis of cyano-rich g-C3 N4 materials to provide a quantity of novel suggestions for cyano-modified carbon nitride materials' construction is provided. In view of the prevailing challenges and outlooks of cyano-rich g-C3 N4 materials, this paper will purify the growth direction of cyano-rich g-C3 N4 , to achieve a more in-depth exploration and broaden the applications of cyano-rich g-C3 N4 .

Defective ZnIn2S4 Nanosheets for Visible-Light and Sacrificial-Agent-Free H2O2 Photosynthesis via O2/H2O Redox

H2O2 photosynthesis has attracted great interest in harvesting and converting solar energy to chemical energy. Nevertheless, the high-efficiency process of H2O2 photosynthesis is driven by the low H2O2 productivity due to the recombination of photogenerated electron-hole pairs, especially in the absence of a sacrificial agent. In this work, we demonstrate that ultrathin ZnIn2S4 nanosheets with S vacancies (Sv-ZIS) can serve as highly efficient catalysts for H2O2 photosynthesis via O2/H2O redox. Mechanism studies confirm that Sv in ZIS can extend the lifetimes of photogenerated carriers and suppress their recombination, which triggers the O2 reduction and H2O oxidation to H2O2 through radical initiation. Theoretical calculations suggest that the formation of Sv can strongly change the coordination structure of ZIS, modulating the adsorption abilities to intermediates and avoiding the overoxidation of H2O to O2 during O2/H2O redox, synergistically promoting 2e- O2 reduction and 2e- H2O oxidation for ultrahigh H2O2 productivity. The optimal catalyst displays a H2O2 productivity of 1706.4 μmol g-1 h-1 under visible-light irradiation without a sacrificial agent, which is ∼29 times higher than that of pristine ZIS (59.4 μmol g-1 h-1) and even much higher than those of reported photocatalysts. Impressively, the apparent quantum efficiency is up to 9.9% at 420 nm, and the solar-to-chemical conversion efficiency reaches ∼0.81%, significantly higher than the value for natural synthetic plants (∼0.10%). This work provides a facile strategy to separate the photogenerated electron-hole pairs of ZIS for H2O2 photosynthesis, which may promote fundamental research on solar energy harvest and conversion.

Organic Molecule Bifunctionalized Polymeric Carbon Nitride for Enhanced Photocatalytic Hydrogen Peroxide Production

Modifying the polymeric carbon nitride (CN) with organic molecules is a promising strategy to enhance the photocatalytic activity. However, most previously reported works show that interchain embedding and edge grafting of the organic molecule can hardly be achieved simultaneously. Herein, we successfully synthesized organic molecule bifunctionalized CN (MBCN) through copolymerization of melon and sulfanilamide at a purposely elevated temperature of 550 °C. In MBCN, the edge grafted and interchain embedded benzene rings act as the electron-donating group and charge-transfer channel, respectively, rendering efficient photocatalytic H2 O2 production. The optimal MBCN exhibits a significantly improved non-sacrificial photocatalytic H2 O2 generation rate (54.0 μmol g-1  h-1 ) from pure water, which is 10.4 times that of pristine CN. Experimental and density functional theory (DFT) calculation results reveal that the enhanced H2 O2 production activity of MBCN is mainly attributed to the improved photogenerated charge separation/transfer and decreased formation energy barrier (▵G) from O2- to the intermediate 1,4-endoperoxide (⋅OOH). This work suggests that simultaneous formation of electron donating group and charge transfer channel via organic molecule bifunctionalization is a feasible strategy for boosting the photocatalytic activity of CN.

K-N Bridge-Mediated charge separation in hollow g-C3N4 Frameworks: A bifunctional photocatalysts towards efficient H2 and H2O2 production

The development of bifunctional photocatalysts for enhancing hydrogen (H2) and hydrogen peroxide (H2O2) production from water is essential in addressing environmental and energy issues. However, the practical implementation of photocatalytic technology is still constrained by the inadequate separation of photo-generated charge carriers. Herein, potassium (K) atoms are introduced into the interlayers of graphitic carbon nitride (g-C3N4) with a hollow hexagonal structure (K-TCN) and are coordinated with N atoms in adjacent layers. The presence of K-N coordination serves as a layer bridge, facilitating the separation of charge carriers. The hollow hexagonal structure reduces the distance over which photogenerated electrons migrate to the surface, thereby enhancing the reaction kinetics. Consequently, the optimized K-TCN exhibits a dramatically improved photocatalytic H2 (941.6 μmol g-1h-1 with platinum (Pt) as the cocatalyst) and H2O2 (347.6 μmol g-1h-1) generation as compared to hollow g-C3N4 (TCN) and bulk g-C3N4 nanosheet (CN) without K-N bridge under visible light irradiation. The unique design holds promising potential for developing highly efficient bifunctional photocatalysts towards producing renewable fuels and value-added chemicals.

Photocatalytic H2O2 production from water and air using porous organic polymers

Producing hydrogen peroxide (H2O2) from H2O and O2 under visible light irradiation is a promising solar-to-chemical energy conversion technology. Hydrogen peroxide has versatile applications as a green oxidant and liquid energy carrier but has been produced through energy-intensive and complex anthraquinone processes. Herein, we report the rational design of efficient and stable porous organic polymer (POP) containing redox centers, anthraquinone photocatalyst (ANQ-POP) for solar H2O2 production. ANQ-POP is readily synthesized with stable dioxin-linkages via efficient one-pot, transition-metal-free nucleophilic aromatic substitution reactions between 1,2,3,4,5,6,7,8-octafluoro-9,10-anthraquinone (OFANQ) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP). Exhibiting a fibrillar morphology, ANQ-POP boasts a high surface area of 380 m2∙g-1 and demonstrates thermal stability. With 10 % ethanol, ANQ-POP yields an H2O2 production rate of 320 μmol g-1 under visible light irradiation. Moreover, ANQ-POP alone can efficiently produce H2O2 without any photosensitizers and cocatalysts. Density functional theory calculations reveal that the quinone groups of the anthraquinone moieties can serve as redox centers for H2O2 production under light irradiation. Furthermore, unlike most conventional photocatalysts, it can produce H2O2 using only water and air by catalyzing both oxygen reduction and evolution reactions under light irradiation. Our findings provide an efficient, eco-friendly pathway for photocatalytic production of H2O2 under mild reaction conditions using a dioxin-derived POP-based photocatalyst.

Pauling-Type Adsorption of O2 Induced by Heteroatom Doped ZnIn2 S4 for Boosted Solar-Driven H2 O2 Production

Breaking the trade-off between activity and selectivity has perennially been a formidable endeavor in the field of hydrogen peroxide (H2 O2 ) photosynthesis, especially the side-on configuration of oxygen (O2 ) on the catalyst surface will cause the cleavage of O-O bonds, which drastically hinders the H2 O2 production performance. Herein, we present an atomically heteroatom P doped ZnIn2 S4 catalyst with tunable oxygen adsorption configuration to accelerate the ORR kinetics essential for solar-driven H2 O2 production. Indeed, the spectroscopy characterizations (such as EXAFS and in situ FTIR) and DFT calculations reveal that heteroatom P doped ZnIn2 S4 at substitutional and interstitial sites, which not only optimizes the coordination environment of Zn active sites, but also facilitates electron transfer to the Zn sites and improves charge density, avoiding the breakage of O-O bonds and reducing the energy barriers to H2 O2 production. As a result, the oxygen adsorption configuration is regulated from side-on (Yeager-type) to end-on (Pauling-type), resulting in the accelerated ORR kinetics from 874.94 to 2107.66 μmol g-1  h-1 . This finding offers a new avenue toward strategic tailoring oxygen adsorption configuration by the rational design of doped photocatalyst.

Solar-to-H2 O2 Catalyzed by Covalent Organic Frameworks

Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H2 O2 ) photosynthesis in 2020. H2 O2 , serving as an environmental-friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs-based photocatalysts are developed with encouraging achievements in H2 O2 production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H2 O2 production. We first introduce the priorities of COFs in H2 O2 photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value-added chemicals not limited to H2 O2 .

Boosting photocatalytic hydrogen peroxide production by regulating electronic configuration of single Sb atoms via carbon vacancies in carbon nitrides

Single-atom catalysts supported on semiconductors can serve as active sites for efficient oxygen reduction to hydrogen peroxide (H2O2). However, researchers have long been puzzled by the lack of guidance on optimizing the performance of single-atom photocatalysts. In this study, we propose a versatile strategy that utilizes carbon vacancies to regulate the electronic configuration of antimony (Sb) atoms on carbon nitrides (C3N4). This strategy has been found to significantly enhance the photocatalytic production of H2O2. The H2O2 evolution rate of Sb single-atom on carbon vacancy-rich C3N4 (designated as Sb1/Cv-C3N4) is 5.369 mmol g-1h-1, which is 10.9 times higher than C3N4 alone. By combining experimental characterizations and density functional theory simulations, we reveal the strong electronic interaction between Sb atoms and carbon vacancy-rich C3N4. This interaction is capable for maintaining the electron-rich state of Sb atoms, facilitating efficient electron transfer to pauling-type absorbed oxygen, and ultimately enhancing the formation of *OOH intermediates. This innovative defect-engineering approach can manipulate the electronic configuration of single-atom catalysts, providing a new avenue to boost the photocatalytic oxygen reduction reaction towards H2O2 production.

Exploring the Roles of Single Atom in Hydrogen Peroxide Photosynthesis

This comprehensive review provides a deep exploration of the unique roles of single atom catalysts (SACs) in photocatalytic hydrogen peroxide (H2O2) production. SACs offer multiple benefits over traditional catalysts such as improved efficiency, selectivity, and flexibility due to their distinct electronic structure and unique properties. The review discusses the critical elements in the design of SACs, including the choice of metal atom, host material, and coordination environment, and how these elements impact the catalytic activity. The role of single atoms in photocatalytic H2O2 production is also analysed, focusing on enhancing light absorption and charge generation, improving the migration and separation of charge carriers, and lowering the energy barrier of adsorption and activation of reactants. Despite these advantages, several challenges, including H2O2 decomposition, stability of SACs, unclear mechanism, and low selectivity, need to be overcome. Looking towards the future, the review suggests promising research directions such as direct utilization of H2O2, high-throughput synthesis and screening, the creation of dual active sites, and employing density functional theory for investigating the mechanisms of SACs in H2O2 photosynthesis. This review provides valuable insights into the potential of single atom catalysts for advancing the field of photocatalytic H2O2 production.

A quadruple-strategy of modification on carbon nitride boosts oxygen reduction for high performance photocatalytic hydrogen peroxide production

This paper reports a quadruple-strategy for material design, simultaneously applying morphology control, group modification, defect engineering and alkali metal doping to the design of catalysts, and successfully constructing irregular clusters of carbon nitride (pMNK-CN) with excellent photogenerated carrier separation performance and structural stability. The pMNK-CN is an irregular flower cluster-like morphology with a nanosheet structure on the surface, and the repolymerization process of the prepolymer in the microvoid of the metal salt gives it an open pore structure. With the help of essential characterization, it was confirmed that the heptazine unit in the backbone underwent partial decomposition due to the etching of metal salts at high temperatures, reducing the overall polymerization and introducing cyano and nitrogen vacancies. Meanwhile, the potassium ion embedded in the lattice can induce the growth of ordered structures and thus improve the short-range order. The pMNK-CN possesses a hydrogen peroxide production efficiency of 240.0 μmol·g-1·h-1 in pure water, which is 31 times higher than that of bulk carbon nitride. And the apparent quantum efficiencies of pMNK-CN in the 380 and 420 nm bands are 17.5 % and 14.8 % in the presence of isopropanol. The effects of each modification strategies on the electronic structure of carbon nitride were investigated using First-Principles, and it was demonstrated that the multiple modification strategies synergistically enhanced the optical absorption, photogenerated charge separation efficiency, and lowered the reaction energy barrier, thus greatly contributing to the oxygen reduction to hydrogen peroxide performance.

Developing Ni single-atom sites in carbon nitride for efficient photocatalytic H2O2 production

Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H2O2) is gaining popularity as a promising avenue of research. However, structural evolution mechanisms of catalytically active sites in the entire photosynthetic H2O2 system remains unclear and seriously hinders the development of highly-active and stable H2O2 photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H2O2 synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N3 sites dynamically transform into high-valent O1-Ni-N2 sites after O2 adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N2. Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H2O2 production activity and selectivity.

Molecular Heptazine-Triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Revealing the photocatalytic mechanism between various junctions and catalytic activities has become a hotspot in photocatalytic systems. Herein, an internal molecular heptazine/triazine (H/T) junction in crystalline carbon nitride (HTCN) is constructed and devoted to selective two-electron oxygen reduction reaction (2e- ORR) for efficient hydrogen peroxide (H2 O2 ) production. In-situ X-ray diffraction spectra under various temperatures authenticate the successful formation of molecular H/T junction in HTCN during the calcining process rather than physically mixing. The increased surface photovoltage and transient photovoltage signals, and the decreased exciton binding energy undoubtably elucidate that an obvious increasement of carrier density and diffusion capability of photogenerated electrons are realized over HTCN. Additionally, the analyses of in situ photoirradiated Kelvin probe force microscopy and femto-second transient absorption spectra reveal the successful construction of the strong internal built-in-electric field and the existence of the majority of long-lived shallow trapped electrons associated with molecular H/T junction over HTCN, respectively. Benefiting from these, the photocatalytic results exhibit an incredible improvement (96.5-fold) for H2 O2 production. This novel work provides a comprehensive understanding of the long-lived reactive charges in molecular H/T junctions for strengthening the driving-force for photocatalytic H2 O2 production, which opens potential applications for enhancing PCN-based photocatalytic redox reactions.

Ultrafast charge transfer in metal-free H2O2 photoproduction by anhydride modified g-C3N4

As a low-cost, low toxicity and metal-free catalyst with strong light absorption, graphitic carbon nitride (g-C3N4)-based materials have gained wide attention for efficient H2O2 photocatalysis. However, further investigation regarding the charge transfer process and reaction mechanism of H2O2 photoproduction remains to be completed. In this work, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTDA) modified g-C3N4 is synthesized through a facile one-step dehydration process, and the H2O2 photoproduction could reach 22.5 μmol within 8 hours. The proposed structure of g-BTDA is confirmed by FTIR, XPS and SEM studies. The transient absorption reveals a 20.88 ps charge transfer process caused by the electron withdrawing ability of the CO group, and a 2-electron oxygen reduction pathway is proposed. Our work represents a new strategy for efficient H2O2 photoproduction using easily acquired materials with future application potential.

Multifunctional carbon nitride nanoarchitectures for catalysis

Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.

Interfacial engineering of a vertically stacked graphene/h-BN heterostructure as an efficient electrocatalyst for hydrogen peroxide synthesis

Recently, it was reported that an in-plane graphene (G)/hexagonal boron nitride (h-BN) (G/h-BN) heterostructure provided the catalytic activity for H2O2 synthesis by the 2 e- oxygen reduction reaction (ORR). However, there are few reports on the vertically stacked G/h-BN heterostructure, which refers to the stacking of graphene domains on the surface of h-BN. Herein, a simulated chemical vapor deposition method is proposed for fabricating a heterostructure of abundant vertically stacked G/h-BN by in situ growing graphene quantum dots (GQDs) on porous h-BN sheets. The performance of our vertically stacked heterostructure catalyst is superior to that of reported carbon-based electrocatalysts under an alkaline environment, with an H2O2 selectivity of 90-99% in a wide potential range (0.35 V-0.7 V vs. RHE), over 90% faradaic efficiency, and high mass activity of 1167 mmol gcatalyst-1 h-1. The experimental results and density functional theory (DFT) simulation verified that the vertically stacked heterostructure exhibits an excellent catalytic performance for the 2 e- ORR, and the edge B atoms in the B-centered AB stacking model are the most active catalytic sites. This research adequately demonstrates the promising catalytic activity of the vertically stacked G/h-BN heterostructure and provides a facile route for fabricating other vertically stacked heterostructures.

Single-Atom Heterogeneous Catalysts: Human- and AI-Driven Platform for Augmented Designs, Analytics and Reality-Enabled Manufacturing

Heterogeneous catalysts with targeted functionality can be designed with atomic precision, but it is challenging to retain the structure and performance upon the scaled-up manufacturing. Particularly challenging is to ensure the "atomic economy", where every catalytic site is most gainfully utilized. Given the emerging synergistic integration of human- and artificial intelligence (AI)-driven augmented designs (AD), augmented analytics (AA), and augmented reality manufacturing (AM) platforms, this minireview focuses on single-atom heterogeneous catalysts (SAHCs) and examines the current status, challenges, and future perspectives of translating atomic-level structural precision and data-driven discovery to next-generation industrial manufacturing. We critically examine the atomistic insights into structure-driven SAHCs functionality and discuss the opportunities and challenges on the way towards the synergistic human-AI collaborative data-driven platform capable of monitoring, analyzing, manufacturing, and retaining the atomic-scale structure and functions. Enhanced by the atomic-level AD, AA, and AM, evolving from the current high-throughput capabilities and digital materials manufacturing acceleration, this synergistic human-AI platform is promising to enable atom-efficient and atomically precise heterogeneous catalyst production.

An Unlocked Two-Dimensional Conductive Zn-MOF on Polymeric Carbon Nitride for Photocatalytic H2 O2 Production

Developing highly efficient catalytic sites for O2 reduction to H2 O2 , while ensuring the fast injection of energetic electrons into these sites, is crucial for artificial H2 O2 photosynthesis but remains challenging. Herein, we report a strongly coupled hybrid photocatalyst comprising polymeric carbon nitride (CN) and a two-dimensional conductive Zn-containing metal-organic framework (Zn-MOF) (denoted as CN/Zn-MOF(lc)/400; lc, low crystallinity; 400, annealing temperature in °C), in which the catalytic capability of Zn-MOF(lc) for H2 O2 production is unlocked by the annealing-induced effects. As revealed by experimental and theoretical calculation results, the Zn sites coordinated to four O (Zn-O4 ) in Zn-MOF(lc) are thermally activated to a relatively electron-rich state due to the annealing-induced local structure shrinkage, which favors the formation of a key *OOH intermediate of 2e- O2 reduction on these sites. Moreover, the annealing treatment facilitates the photoelectron migration from the CN photocatalyst to the Zn-MOF(lc) catalytic unit. As a result, the optimized catalyst exhibits dramatically enhanced H2 O2 production activity and excellent stability under visible light irradiation.

Design strategies and mechanisms of g-C3N4-based photoanodes for photoelectrocatalytic degradation of organic pollutants in water

Emerging photoelectrocatalytic (PEC) systems integrate the advantages of photocatalysis and electrocatalysis and are considered as a promising technology for solving the global organic pollution problem in water environments. Among the photoelectrocatalytic materials applied for organic pollutant degradation, graphitic carbon nitride (CN) has the combined advantages of environmental compatibility, stability, low cost, and visible light response. However, pristine CN has disadvantages such as low specific surface area, low electrical conductivity, and high charge complexation rate, and how to improve the degradation efficiency of PEC reaction and the mineralization rate of organic matter is the main problem faced in this field. Therefore, this paper reviews the progress of various functionalized CN used for PEC reaction in recent years, and the degradation efficiency of these CN-based materials is critically evaluated. First, the basic principles of PEC degradation of organic pollutants are outlined. Then, engineering strategies to enhance the PEC activity of CN (including morphology control, elemental doping, and heterojunction construction) are focused on, and the structure-activity relationships between these engineering strategies and PEC activity are discussed. In addition, the important role of influencing factors on the PEC system is summarized in terms of mechanism, to provide guidance for the subsequent research. Finally, suggestions and perspectives are provided for the preparation of efficient and stable CN-based photoelectrocatalysts for practical wastewater treatment applications.

Regulating Relative Nitrogen Locations of Diazine Functionalized Covalent Organic Frameworks for Overall H2 O2 Photosynthesis

Nitrogen-heterocycle-based covalent organic frameworks (COFs) are considered promising candidates for the overall photosynthesis of hydrogen peroxide (H2 O2 ). However, the effects of the relative nitrogen locations remain obscured and photocatalytic performances of COFs need to be further improved. Herein, a collection of COFs functionalized by various diazines including pyridazine, pyrimidine, and pyrazine have been judiciously designed and synthesized for photogeneration of H2 O2 without sacrificial agents. Compared with pyrimidine and pyrazine, pyridazine embedded in TpDz tends to stabilize endoperoxide intermediate species, leading toward the more efficient direct 2e- oxygen reduction reaction (ORR) pathway. Benefiting from the effective electron-hole separation, low charge transfer resistance, and high-efficiency ORR pathway, an excellent production rate of 7327 μmol g-1  h-1 and a solar-to-chemical conversion (SCC) value of 0.62 % has been achieved by TpDz, which ranks one of the best COF-based photocatalysts. This work might shed fresh light on the rational design of functional COFs targeting photocatalysts in H2 O2 production.

Co-construction of oxygen doping and van der walls heterojunction in O-CB/ZnIn2S4 promoting photocatalytic production and activation of H2O2 for the degradation of antibiotics

The in situ production of H2O2 by photocatalysis have shown a sustainable strategy for water remediation, but the peroxide evolution capacity are still unsatisfactory. Herein, we ingeniously design oxygen-doped carbon black/zinc indium sulfide (O-CB/ZnIn2S4) composites for photocatalytic production and activation of H2O2 to degrade antibiotics. The rich oxygen dopants and van der walls heterojunction between O-CB and ZnIn2S4 promoted charge transfer, oxygen adsorption and reduction for peroxide generation. The optimized O-CB/ZnIn2S4-2 composites exhibited ultrahigh H2O2 production rate (1985 μmol/g/h) in pure water (pH=7) without sacrificial reagents and aeration assistance, which was 2 times, 3 times, and 12 times higher than CB/ZnIn2S4-2, ZnIn2S4 and O-CB, respectively. Additionally, O-CB/ZnIn2S4-2 composites exhibited considerable amount of OH of 30 μmol/L in 60 min, which was originated from the reduction of innergenerate-H2O2 by photogenerated electrons and direct photolysis. The degradation and quenching experiments shows that the innergenerate-H2O2 contributed to the rapid degradation and deep mineralization of tetracycline antibiotics(tetracycline, oxytetracycline, chlortetracycline hydrochloride). Moreover, intermediates analysis and toxicity estimation further confirm the significant mineralization and toxicity decrease during the degradation of oxytetracycline by O-CB/ZnIn2S4-2. The work provides deep insights into the crucial role of dopants and heterojunction in promoting H2O2 production and activation.

Promoting Solar-driven Hydrogen Peroxide Production over Thiazole-based Conjugated Polymers via Generating and Converting Singlet Oxygen

Solar-driven synthesis of hydrogen peroxide (H2 O2 ) from water and air provides a low-cost and eco-friendly alternative route to the traditional anthraquinone method. Herein, four thiazole-based conjugated polymers (Tz-CPs: TTz, BTz, TBTz and BBTz) are synthesized via aldimine condensation. BBTz exhibits the highest H2 O2 production rate of 7274 μmol g-1  h-1 in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in situ diffuse reflectance infrared Fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (1 O2 ). The generation of 1 O2 occurs through the oxidation of superoxide radical (⋅O2 - ) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz, which promotes charge separation and reduces the barrier for H2 O2 production. This work provides new insight into the mechanism of photocatalytic O2 reduction and the molecular design of superior single-polymer photocatalysts.

Shear Stress Triggers Ultrathin-Nanosheet Carbon Nitride Assembly for Photocatalytic H2O2 Production Coupled with Selective Alcohol Oxidation

Coupled photocatalysis without cocatalysts can maximize the utilization of photons and atoms, which puts forward higher demands on photocatalysts. Polymeric carbon nitride (CN) has become the most promising photocatalyst, but still suffers from major drawbacks of insufficient catalytic sites and low quantum efficiency. Herein, we report a fluid shear stress-assisted molecular assembly to prepare ultrathin-nanosheet-assembled acanthosphere-like CN (ASCN) with nitrogen vacancy (Nv) and carbonyl modification. Shear stress breaks the stacking interactions between layers and cuts the stacked structure into ultrathin layers, which are further reassembled into acanthosphere bundles driven by "centrifugal force". Benefitted greatly from the ultrathin nature that provides more exposed active sites and improves charge carrier separation, ASCN-3 exhibits a 20-fold higher activity than the bulk counterpart toward oxygen reduction to H2O2 coupled with 4-methoxybenzyl alcohol (4-MBA) oxidation to anisaldehyde (AA), with significantly increased turnover frequency (TOF) values (TOF: 1.69 h-1 for H2O2 and 1.02 h-1 for AA). Significantly, ASCN-3 exhibits 95.8% conversion for 4-MBA oxidation with nearly 100% selectivity. High apparent quantum yields of 11.7% and 9.3% at 420 nm are achieved for H2O2 photosynthesis and 4-MBA oxidation. Mechanism studies suggest that carbonyl induces holes concentrated at the neighboring melem unit to directly oxidize the Cα-H bond of 4-MBA to produce carbon radicals, and Nv as oxygen adsorption active site traps electrons to form a superoxide radical that further combines with the shed protons into H2O2. This work presents a simple physical method to break the layered stack of CN for creating hierarchical assembly for coupled photocatalysis.