Overall photosynthesis of H2O2 by an inorganic semiconductor

Pyridine-Based Covalent Organic Frameworks with Pyridyl-Imine Structures for Boosting Photocatalytic H2O2 Production via One-Step 2e- Oxygen Reduction

Bipyridine-based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one-step two-electron (2e-) route to a two-step 2e- oxygen reduction pathway. In this work, we introduce 3,3'-bipyridine units into imine-based COF skeletons, creating a pyridyl-imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine-like architecture can effectively suppress the two-step 2e- ORR process at the single imine-nitrogen site, facilitating a more efficient one-step 2e- pathway. Consequently, the optimized pyridyl-imine COF (PyIm-COF) exhibits a remarkable H2O2 production rate of up to 5850 μmol h-1 g-1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Recent developments in photocatalytic production of hydrogen peroxide

Hydrogen peroxide (H2O2), an environmentally friendly strong oxidant and energy carrier, has attracted widespread attention in photocatalysis. Artificial photosynthesis of H2O2 using water and oxygen as raw materials, solar energy as an energy source, and semiconductor materials as catalysts is considered a promising technology. In the past few decades, encouraging progress has been made in the photocatalytic production of H2O2. Therefore, we summarize the research achievements in this field in recent years. This review first briefly introduces the reaction pathway, detection techniques and evaluation metrics. Then, the recent advances in photocatalysts are highlighted. Furthermore, the existing challenges and possible solutions in this field are presented. At last, we look forward to the future development direction of this field. This review provides valuable insights and guidance for efficient photocatalytic H2O2 production.

Oxygen-Centered Organic Radicals-Involved Unified Heterogeneous Self-Fenton Process for Stable Mineralization of Micropollutants in Water

Removing organic micropollutants from water through photocatalysis is hindered by catalyst instability and substantial residuals from incomplete mineralization. Here, a novel water treatment paradigm, the unified heterogeneous self-Fenton process (UHSFP), which achieved an impressive 32% photon utilization efficiency at 470 nm, and a significant 94% mineralization of organic micropollutants-all without the continual addition of oxidants and iron ions is presented. In UHSFP, the active species differs fundamentally from traditional photocatalytic processes. One electron acceptor unit of photocatalyst acquires only one photogenerated electron to convert into oxygen-centered organic radical (OCOR), then spontaneously completing subsequent processes, including pollutant degradation, hydrogen peroxide generation, activation, and mineralization of organic micropollutants. By bolstering electron-transfer capabilities and diminishing catalyst affinity for oxygen in the photocatalytic process, the generation of superoxide radicals is effectively suppressed, preventing detrimental attacks on the catalyst. This study introduces an innovative and cost-effective strategy for the efficient and stable mineralization of organic micropollutants, eliminating the necessity for continuous chemical inputs, providing a new perspective on water treatment technologies.

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.

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.

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.

ZnS/C Dual-Quantum-Dots Heterostructural Nanofibers for High-Performance Photocatalytic H2O2 Production

Constructing heterostructures of dual quantum-dots (QDs) is a promising way to achieve high performance in photocatalysis, but it still faces substantial synthetic challenges. Herein, we developed an in situ transformation strategy to coassemble ZnS QDs and C QDs into dual-quantum-dot heterostructural nanofibers (ZnS/C-DQDH). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results revealed the formation of strong Zn-O-C bonds at the interface between ZnS QDs and C QDs, improving the separation efficiency of photogenerated charge carriers. The ZnS/C-DQDH demonstrated remarkable photocatalytic activity in H2O2 production, with generation rates of 2896.4 μmol gcat-1 h-1 without sacrificial agents and 9879.3 μmol gcat-1 h-1 with ethanol as the sacrificial agent, significantly higher than the QD counterparts and surpassed state-of-the-art photocatalysts. Moreover, due to the nanofibrous feature, ZnS/C-DQDH demonstrated excellent stability and facile recyclability. This work provides a facile and large scalable method to gain dual-quantum-dot heterostructures and a promising alternative for photocatalytic H2O2 production.

Iron oxide-promoted photochemical oxygen reduction to hydrogen peroxide (H2O2)

Hydrogen peroxide (H2O2) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safe operation, storage and transportation. The photochemical production of H2O2 serves as a promising alternative to the waste- and energy-intensive anthraquinone process. Following the 12 principles of Green Chemistry, we demonstrate a facile and general approach to sustainable catalyst development utilizing earth-abundant iron and biobased sources only. We developed several iron oxide (FeOx) nanoparticles (NPs) for successful photochemical oxygen reduction to H2O2 under visible light illumination (445 nm). Achieving a selectivity for H2O2 of >99%, the catalyst material could be recycled for up to four consecutive rounds. An apparent quantum yield (AQY) of 0.11% was achieved for the photochemical oxygen reduction to H2O2 with visible light (445 nm) at ambient temperatures and pressures (9.4-14.8 mmol g-1 L-1). Reaching productivities of H2O2 of at least 1.7 ± 0.3 mmol g-1 L-1 h-1, production of H2O2 was further possible via sunlight irradiation and in seawater. Finally, a detailed mechanism has been proposed on the basis of experimental investigation of the catalyst's properties and computational results.

Efficient and stable visible-light-driven Z-scheme overall water splitting using an oxysulfide H2 evolution photocatalyst

So-called Z-scheme systems permit overall water splitting using narrow-bandgap photocatalysts. To boost the performance of such systems, it is necessary to enhance the intrinsic activities of the hydrogen evolution photocatalyst and oxygen evolution photocatalyst, promote electron transfer from the oxygen evolution photocatalyst to the hydrogen evolution photocatalyst, and suppress back reactions. The present work develop a high-performance oxysulfide photocatalyst, Sm2Ti2O5S2, as an hydrogen evolution photocatalyst for use in a Z-scheme overall water splitting system in combination with BiVO4 as the oxygen evolution photocatalyst and reduced graphene oxide as the solid-state electron mediator. After surface modifications of the photocatalysts to promote charge separation and redox reactions, this system is able to split water into hydrogen and oxygen for more than 100 hours with a solar-to-hydrogen energy conversion efficiency of 0.22%. In contrast to many existing photocatalytic systems, the water splitting activity of the present system is only minimally reduced by increasing the background pressure to 90 kPa. These results suggest characteristics suitable for applications under practical operating conditions.

Identification of the Contributing Factors to the Photoelectric Conversion Efficiency for Hematite Photoanodes by Using Machine Learning

Hematite has gained significant attention in the field of photocatalysis as one of the most promising materials for the photoanode of photoelectrochemical (PEC) water splitting due to visible light absorption and the abundance of availability. However, its performance improvement process suffers from a serious bottleneck due to "sample variation" and "inactivity". However, the physical origin of them has not yet been elucidated. To address these issues, we have developed a machine learning (ML) strategy using a combination of various analytical data of hematite photoanodes to discern "active/inactive" and identify the dominant factors. For the demonstration purpose of the ML strategy, we picked up one of the dominant factors, the interfacial resistivity between hematite and FTO, which has not generally been explored as a first candidate in the improvement of photocatalytic materials. The operational parameters for the sample preparation were optimized to modify the selected physical property. Along with the improvement of the selected resistivity, we found that the other dominant descriptors related to the properties of bulk hematite and the surface facet were also modified and help improve the PEC performance.

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 .

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.

An Oxysulfide Photocatalyst Evolving Hydrogen with an Apparent Quantum Efficiency of 30 % under Visible Light

Photocatalytic water splitting is a simple means of converting solar energy into storable hydrogen energy. Narrow-band gap oxysulfide photocatalysts have attracted much attention in this regard owing to the significant visible-light absorption and relatively high stability of these compounds. However, existing materials suffer from low efficiencies due to difficulties in synthesizing these oxysulfides with suitable degrees of crystallinity and particle sizes, and in constructing effective reaction sites. The present work demonstrates the production of a Gd2 Ti2 O5 S2 (λ<650 nm) photocatalyst capable of efficiently driving photocatalytic reactions. Single-crystalline, plate-like Gd2 Ti2 O5 S2 particles with atomically ordered surfaces were synthesized by flux and chemical etching methods. Ultrafine Pt-IrO2 cocatalyst particles that promoted hydrogen (H2 ) and oxygen (O2 ) evolution reactions were subsequently loaded on the Gd2 Ti2 O5 S2 while ensuring an intimate contact by employing a microwave-heating technique. The optimized Gd2 Ti2 O5 S2 was found to evolve H2 from an aqueous methanol solution with a remarkable apparent quantum efficiency of 30 % at 420 nm. This material was also stable during O2 evolution in the presence of a sacrificial reagent. The results presented herein demonstrates a highly efficient narrow-band gap oxysulfide photocatalyst with potential applications in practical solar hydrogen production.

Cyano-Regulated Organic Polymers for Highly Efficient Photocatalytic H2 O2 Production in Various Actual Water Bodies

Photocatalytic production of H2 O2 has drawn significant attention in recent years, but the yield rate of current photocatalytic systems is still unsatisfactory. Moreover, the presence of various components in actual water bodies will consume the photogenerated charges and deactivate the catalyst, severely limiting the real applications of photocatalytic H2 O2 production. Herein, a cyano-modified polymer photocatalyst is synthesized by Knoevenagel condensation with subsequent thermal polymerization. The introduction of cyano group and sulfer (S), oxygen (O) elements modulates the microstructure and energy band of the polymer catalyst, and the cyano group sites can effectively adsorb and activate O2 , realizing the generation of H2 O2 in the two-step single-electron oxygen reduction process. The reported system achieves high H2 O2 generation rate up to 1119.2 µmol g-1 h-1 in various water bodies including tap water, river water, seawater, and secondary effluent. This simple and readily available catalyst demonstrates good anti-interference performance and pH adaptability in photocatalytic H2 O2 production in actual water bodies, and its photodegradation and sterilization applications are also demonstrated. This study offers new insights in developing polymer catalysts for efficient photocatalytic production of H2 O2 in various water bodies for practical application.

Realizing Unassisted Photo-Charging of Zinc-Air Batteries by Anisotropic Charge Separation in Photoelectrodes

Solar rechargeable zinc-air battery is a promising approach for capturing and storing intermittent solar energy through photoelectrochemical reactions. However, unassisted photo-charging of zinc-air batteries is challenging due to suboptimal carrier accumulation on photoelectrodes, resulting in sluggish reaction kinetics. Here, unassisted photo-charging of zinc-air battery is achieved by investigating anisotropic photogenerated charge separation on a series of representative semiconductors (ZnIn2 S4 , TiO2 , and In2 O3 ), among which the exceptional anisotropic charge separation on a ZnIn2 S4 photoelectrode is revealed based on anisotropic charge diffusion capabilities. The charge separation is facet-dependent, which is observed using Kelvin probe force microscopy, verifying a cause-and-effect relationship between the photo-charge accumulation on photoelectrodes and their photo-charging performance in zinc-air batteries. This work achieves an unassisted photo-charging current density of 1.9 mA cm-2 with a light-to-chemical energy conversion efficiency of 1.45%, highlighting the importance of anisotropic semiconductors for unassisted photo-charging of zinc-air batteries via efficient photogenerated charge separation.

Aurivillius-layered Bi2WO6 nanoplates with CoOx cocatalyst as high-performance piezocatalyst for hydrogen evolution

Developing a high-performance piezocatalyst that directly transforms mechanical energy into hydrogen is highly desirable in the field of new energy. Herein, the Aurivillius-layered Bi2WO6 (BWO) nanoplates are prepared through a hydrothermal reaction at a moderate temperature of 160 °C, and exhibit strong piezoelectric properties, enabling them to catalyze water splitting through ultrasonic-induced piezocatalysis effect. The hydrogen evolution reaction (HER) and H2O2 generation efficiencies are measured to be 0.43 and 0.36 mmol g-1 h-1, respectively. To further boost piezocatalytic performance, cobalt oxide nanoparticles are intentionally photo-deposited onto these nanoplates as cocatalyst. This configuration results in a significantly boosted HER performance with an efficiency of 3.59 mmol g-1 h-1, which is 2.8 times higher than that of pristine nanoplates and demonstrates strong competitiveness compared to other reported piezocatalysts. The cobalt oxide cocatalyst plays a crucial role in facilitating efficient charge separation and migration, increasing the charge concentration, and ultimately enhancing piezocatalytic HER activity. Overall, this work highlights the potential of Aurivillius-layered bismuth oxide compounds as efficient piezocatalysts and provides valuable insights for designing high-performance piezocatalysts in the field of new energy.

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.

Microtubular cellulose-derived kapok fibre as a solid electron donor for boosting photocatalytic H2O2 production over C-doped g-C3N4 hybrid complexation

Cellulose continues to play an important and emerging role in photocatalysis, and its favourable properties, such as electron-rich hydroxyl groups, could enhance the performance of photocatalytic reactions. For the first time, this study exploited the kapok fibre with microtubular structure (t-KF) as a solid electron donor to enhance the photocatalytic activity of C-doped g-C₃N₄ (CCN) via ligand-to-metal-charge-transfer (LMCT) to improve hydrogen peroxide (H₂O₂) production performance. As confirmed by various characterisation techniques, the hybrid complex consisting of CCN grafted on t-KF was successfully developed in the presence of succinic acid (SA) as a cross-linker via a simple hydrothermal approach. The complexation formation between CCN and t-KF results in the CCN-SA/t-KF sample displaying a higher photocatalytic activity than pristine g-C₃N₄ to produce H₂O₂ under visible light irradiation. The enhanced physicochemical and optoelectronic properties of CCN-SA/t-KF imply that the LMCT mechanism is crucial in improving photocatalytic activity. This study promotes utilising the unique t-KF material's properties to develop a low-cost and high-performance cellulose-based LMCT photocatalyst.

Synergistic Metal-Nonmetal Active Sites in a Metal-Organic Cage for Efficient Photocatalytic Synthesis of Hydrogen Peroxide in Pure Water

Photocatalytic synthesis of hydrogen peroxide (H2 O2 ) is a potential clean method, but the long distance between the oxidation and reduction sites in photocatalysts hinders the rapid transfer of photogenerated charges, limiting the improvement of its performance. Here, a metal-organic cage photocatalyst, Co14 (L-CH3 )24 , is constructed by directly coordinating metal sites (Co sites) used for the O2 reduction reaction (ORR) with non-metallic sites (imidazole sites of ligands) used for the H2 O oxidation reaction (WOR), which shortens the transport path of photogenerated electrons and holes, and improves the transport efficiency of charges and activity of the photocatalyst. Therefore, it can be used as an efficient photocatalyst with a rate of as high as 146.6 μmol g-1  h-1 for H2 O2 production under O2 -saturated pure water without sacrificial agents. Significantly, the combination of photocatalytic experiments and theoretical calculations proves that the functionalized modification of ligands is more conducive to adsorbing key intermediates (*OH for WOR and *HOOH for ORR), resulting in better performance. This work proposed a new catalytic strategy for the first time; i.e., to build a synergistic metal-nonmetal active site in the crystalline catalyst and use the host-guest chemistry inherent in the metal-organic cage (MOC)to increase the contact between the substrate and the catalytically active site, and finally achieve efficient photocatalytic H2 O2 synthesis.

Imperfect makes perfect: defect engineering of photoelectrodes towards efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting for hydrogen evolution has been considered as a promising technology to solve the energy and environmental issues. However, the solar-to-hydrogen (STH) conversion efficiencies of current PEC systems are far from meeting the commercial demand (10%) due to the lack of efficient photoelectrode materials. The recent rapid development of defect engineering of photoelectrodes has significantly improved the PEC performance, which is expected to break through the bottleneck of low STH efficiency. In this review, the category and the construction methods of different defects in photoelectrode materials are summarized. Based on the in-depth summary and analysis of existing reports, the PEC performance enhancement mechanism of defect engineering is critically discussed in terms of light absorption, carrier separation and transport, and surface redox reactions. Finally, the application prospects and challenges of defect engineering for PEC water splitting are presented, and the future research directions in this field are also proposed.

Functionalized 2D defect g-C3N4 for artificial photosynthesis of H2O2 and synchronizing tetracycline fluorescence detection and degradation

Artificial photosynthesis of H₂O₂ is a clean production technology, which brings the synergistic effect to photodegradation of pollutants. Inspired by defect engineering, 2D defective carbon nitride (g-C₃N₄) photocatalyst was obtained via potassium ion assisted synthesis. Defective g-C₃N₄ is protonated and applied to photosynthesis of H₂O₂, H₂O₂ concentration produced reached 477.7 μM, which was approximately 5.27 times that by pristine g-C₃N₄. Additionally, defective g-C₃N₄ materials are borrowed to synchronizing tetracycline (TC) fluorescence detection and degradation, suggesting the catalyst existed bifunctional characteristics of TC detection and degradation. Meanwhile, metal impregnation engineering (molybdenum) was borrowed enhancing the electron-trapping ability in local region of defective g-C₃N₄, which takes advantages to the efficient degradation of TC. Furthermore, optical and electrical properties of photocatalysts were investigated in details by advanced material characterization testing. This work provides potential applications in the field of artificial photosynthesis and pollution degradation.

Enhanced piezocatalytic hydrogen evolution performance of bismuth vanadate by the synergistic effect of facet engineering and cocatalyst engineering

Developing piezocatalysts with excellent piezocatalytic hydrogen evolution reaction (HER) performance is highly desired but also challenging. Here, facet engineering and cocatalyst engineering are employed to synergistically improve the piezocatalytic HER efficiency of BiVO₄ (BVO). Monoclinic BVO catalysts with distinct exposed facets are synthesized by adjusting pH of hydrothermal reaction. The BVO with highly exposed {110} facet exhibits a superior piezocatalytic HER performance (617.9 μmol g^-1h^-1) compared with that with {010} facet, owing to the strong piezoelectric property, high charge transfer efficiency, and excellent hydrogen adsorption/desorption capacity. The HER efficiency is enhanced by 44.7% by selectively depositing cocatalyst of Ag nanoparticles specifically on the reductive {010} facet of BVO, where the Ag-BVO interface provides the directional electron transport for high-efficiency charge separation. Under the collaboration between cocatalyst of CoO_x on {110} facet and the hole sacrificial agent of methanol, the piezocatalytic HER efficiency is evidently enhanced by 2 times because CoO_x and methanol can impede the water oxidation and improve the charge separation. This easy and simple strategy provides an alternative perspective on designing high-performance piezocatalysts.

Spatial Specific Janus S-Scheme Photocatalyst with Enhanced H2 O2 Production Performance

Photocatalytic oxygen reduction reaction (ORR) for H₂ O₂ production in the absence of sacrificing agents is a green approach and of great significance, where the design of photocatalysts with high performance is the central task. Herein, a spatial specific S-scheme heterojunction design by introducing a novel semiconducting pair with a S-scheme mechanism in a purpose-designed Janus core-shell-structured hollow morphology is reported. In this design, TiO₂ nanocrystals are grown inside the inner wall of resorcinol-formaldehyde (RF) resin hollow nanocakes with a reverse bumpy ball morphology (TiO₂ @RF). The S-scheme heterojunction preserves the high redox ability of the TiO₂ and RF pair, the spatial specific Janus design enhances the charge separation, promotes active site exposure, and reduces the H₂ O₂ decomposition to a large extent. The TiO₂ @RF photocatalyst shows a high H₂ O₂ yield of 66.6 mM g^-1  h^-1 and solar-to-chemical conversion efficiency of 1.11%, superior to another Janus structure (RF@TiO₂ ) with the same heterojunction but a reversed Janus spatial arrangement, and most reported photocatalysts under similar reaction conditions. The work has paved the way toward the design of next-generation photocatalysts for green synthesis of H₂ O₂ production.

Boosted Photoreforming of Plastic Waste via Defect-Rich NiPS3 Nanosheets

Sustainable conversion of plastic waste to mitigate environmental threats and reclaim waste value is important. Ambient-condition photoreforming is practically attractive to convert waste to hydrogen (H₂); however, it has poor performance because of mutual constraint between proton reduction and substrate oxidation. Here, we realize a cooperative photoredox using defect-rich chalcogenide nanosheet-coupled photocatalysts, e.g., d-NiPS₃/CdS, to give an ultrahigh H₂ evolution of ∼40 mmol g_cat^-1 h^-1 and organic acid yield up to 78 μmol within 9 h, together with excellent stability beyond 100 h in photoreforming of commercial waste plastic poly(lactic acid) and poly(ethylene terephthalate). Significantly, these metrics represent one of the most efficient plastic photoreforming reported. In situ ultrafast spectroscopic studies confirm a charge transfer-mediated reaction mechanism in which d-NiPS₃ rapidly extracts electrons from CdS to boost H₂ evolution, favoring hole-dominated substrate oxidation to improve overall efficiency. This work opens practical avenues for converting plastic waste into fuels and chemicals.

Photoredox-Promoted Co-Production of Dihydroisoquinoline and H2 O2 over Defective Zn3 In2 S6

One of the most sustainable and promising approaches for hydrogen peroxide (H₂ O₂ ) production in a low-cost and environment-friendly way is photosynthesis, which, however, suffers from poor carrier utilization and low H₂ O₂ productivity. The addition of proton donors such as isopropanol or ethanol can increase H₂ O₂ production, which, unfortunately, will inevitably elevate the entire cost while wasting the oxidizing power of holes (h⁺ ). Herein, the tetrahydroisoquinolines (THIQs) is employed as a distinctive proton donor for the thermodynamically feasible and selective semi-dehydrogenation reaction to highly valuable dihydroisoquinolines (DHIQs), and meanwhile, to couple with and promote H₂ O₂ generation in one photoredox reaction under the photocatalysis by dual-functional Zn₃ In₂ S₆ photocatalyst. Surprisingly, the suitably defective Zn₃ In₂ S₆ offers an excellent and near-stoichiometric co-production performance of H₂ O₂ and DHIQs at unprecedentedly high rates of 66.4 and 62.1 mmol h^-1 g^-1 under visible light (λ ≥ 400 nm), respectively, which outperforms all the previously available reports even though sacrificial agents were employed in those reports. Additionally, photocatalytic redox reaction mechanism demonstrates that H₂ O₂ can be generated through multiple pathways, highlighting the synergistic effect among ROS (·O₂ ^- and ¹ O₂ ), h⁺ and proton donor, which has been ignored in previous studies.

Photochemically Etching BiVO4 to Construct Asymmetric Heterojunction of BiVO4 /BiOx Showing Efficient Photoelectrochemical Water Splitting

BiVO₄ as a promising semiconductor candidate of the photoanode for solar driven water oxidation always suffers from poor charge carrier transport property and photo-induced self-corrosion. Herein, by intentionally taking advantage of the photo-induced self-corrosion process, a controllable photochemical etching method is developed to rationally construct a photoanode of BiVO₄ /BiO_x asymmetric heterojunction from faceted BiVO₄ crystal arrays. Compared with the BiVO₄ photoanode, the resulting BiVO₄ /BiO_x photoanode gains over three times enhancement in short-circuit photocurrent density (≈3.2 mA cm^-2 ) and ≈75 mV negative shift of photocurrent onset potential. This is due to the formation of the strong interacted homologous heterojunction, which promotes photo-carrier separation and enlarges photovoltage across the interface. Remarkably, the photocurrent density can remain at ≈2.0 mA cm^-2 even after 12 h consecutive operation, while only ≈0.1 mA cm^-2 is left for the control photoanode of BiVO₄ . Moreover, the Faraday efficiency for water splitting is determined to be nearly 100% for the BiVO₄ /BiO_x photoanode. The controllable photochemical etching process may shed light on the construction of homologous heterojunction on other photoelectrode materials that have similar properties to BiVO₄ .

Oxidation-Reduction Molecular Junction Covalent Organic Frameworks for Full Reaction Photosynthesis of H2 O2

The full reaction photosynthesis of H₂ O₂ that can combine water-oxidation and oxygen-reduction without sacrificial agents is highly demanded to maximize the light-utilization and overcome the complex reaction-process of anthraquinone-oxidation. Here, a kind of oxidation-reduction molecular junction covalent-organic-framework (TTF-BT-COF) has been synthesized through the covalent-coupling of tetrathiafulvalene (photo-oxidation site) and benzothiazole (photo-reduction site), which presents visible-light-adsorption region, effective electron-hole separation-efficiency and photo-redox sites that enables full reaction generation of H₂ O₂ . Specifically, a record-high yield (TTF-BT-COF, ≈276 000 μM h^-1  g^-1 ) for H₂ O₂ photosynthesis without sacrificial agents has been achieved among porous crystalline photocatalysts. This is the first work that can design oxidation-reduction molecular junction COFs for full reaction photosynthesis of H₂ O₂ , which might extend the scope of COFs in H₂ O₂ production.

A general interfacial-energetics-tuning strategy for enhanced artificial photosynthesis

The demands for cost-effective solar fuels have triggered extensive research in artificial photosynthesis, yet the efforts in designing high-performance particulate photocatalysts are largely impeded by inefficient charge separation. Because charge separation in a particulate photocatalyst is driven by asymmetric interfacial energetics between its reduction and oxidation sites, enhancing this process demands nanoscale tuning of interfacial energetics on the prerequisite of not impairing the kinetics and selectivity for surface reactions. In this study, we realize this target with a general strategy involving the application of a core/shell type cocatalyst that is demonstrated on various photocatalytic systems. The promising H₂O₂ generation efficiency validate our perspective on tuning interfacial energetics for enhanced charge separation and photosynthesis performance. Particularly, this strategy is highlighted on a BiVO₄ system for overall H₂O₂ photosynthesis with a solar-to-H₂O₂ conversion of 0.73%.

Long-range ordered amino acid assemblies exhibit effective optical-to-electrical transduction and stable photoluminescence

Bio-endogenous peptide molecules are ideal components for fabrication of biocompatible and environmentally friendly semiconductors materials. However, to date, their applications have been limited due to the difficulty in obtaining stable, high-performance devices. Herein, simple amino acid derivatives fluorenylmethoxycarbonyl-leucine (Fmoc-L) and fluorenylmethoxycarbonyl-tryptophan (Fmoc-W) are utilized to form long-range ordered supramolecular nanostructures by tight aromatic stacking and extensive hydrogen bonding with mechanical, electrical and optical properties. For the first time, without addition of any photosensitizers, pure Fmoc-L microbelts and Fmoc-W microwires exhibit Young's modulus up to 28.79 and 26.96 GPa, and unprecedently high values of photocurrent responses up to 2.2 and 2.3 μA/cm², respectively. Meanwhile, Fmoc-W microwires with stable blue fluorescent emission under continuous excitation are successfully used as LED phosphors. Mechanism analysis shows that these two amino acids derivatives firstly formed dimers to reduce the bandgap, then further assemble into bioinspired semiconductor materials using the dimers as the building blocks. In this process, aromatic residues of amino acids are more conducive to the formation of semiconducting characteristics than fluorenyl groups. STATEMENT OF SIGNIFICANCE: Long-range ordered amino acid derivative assemblies with mechanical, electrical and optical properties were fabricated by a green and facile biomimetic strategy. These amino acid assemblies have Young's modulus comparable to that of concrete and exhibit typical semiconducting characteristics. Even without the addition of any photosensitizer, pure amino acid assemblies can still produce a strong photocurrent response and an unusually stable photoluminescence. The results suggest that amino acid structures with hydrophilic C-terminal and aromatic residues are more conducive to the formation of semiconducting characteristics. This work unlocks the potential for amino acid molecules to self-assemble into high-performance bioinspired semiconductors, providing a reference for customized development of biocompatible and environmentally friendly semiconductor materials through rational molecular design.

Extended Conjugation Tuning Carbon Nitride for Non-sacrificial H2 O2 Photosynthesis and Hypoxic Tumor Therapy

Artificial photocatalysis offers a clean approach for producing H₂ O₂ . However, the poor selectivity and activity of H₂ O₂ production hamper traditional industrial applications and emerging photodynamic therapy (PDT)/chemodynamic therapy (CDT). Herein, we report a C₅ N₂ photocatalyst with a conjugated C=N linkage for selective and efficient non-sacrificial H₂ O₂ production in both normoxic and hypoxic systems. The strengthened delocalization of π-electrons by linkers in C₅ N₂ downshifted the band position, thermodynamically eliminating side H₂ evolution reaction and kinetically promoting water oxidation. As a result, C₅ N₂ had a competitive solar-to-chemical conversion efficiency of 0.55 % in overall H₂ O₂ production and exhibited by far the highest activity under hypoxic conditions (698 μM h^-1 ). C₅ N₂ was further applied to hypoxic PDT/CDT with outstanding performance in apparent cancer cell death and synchronous bioimaging. The study sheds light on the photosynthesis of H₂ O₂ by carbon nitrides for health applications.

Intracluster Reaction Dynamics of Ionized Micro-Hydrated Hydrogen Peroxide (H2O2): A Direct Ab Initio Molecular Dynamics Study

Hydrogen peroxide (H₂O₂) is a unique molecule that is applied in various fields, including energy chemistry, astrophysics, and medicine. H₂O₂ readily forms clusters with water molecules. In the present study, the reactions of ionized H₂O₂-water clusters, H₂O₂ ⁺(H₂O) _n , after vertical ionization of the parent neutral cluster were investigated using the direct ab initio molecular dynamics (AIMD) method to elucidate the reaction mechanism. Clusters with one to five water molecules, H₂O₂-(H₂O) _n (n = 1-5), were examined, and the reaction of [H₂O₂ ⁺(H₂O) _n ]_ver was tracked from the vertical ionization point to the product state, where [H₂O₂ ⁺(H₂O) _n ]_ver is the vertical ionization state (hole is localized on H₂O₂). After ionization, fast proton transfer (PT) from H₂O₂ ⁺ to the water cluster (H₂O) _n was observed in all clusters. The HOO radical and H₃O⁺(H₂O) _n-1 were formed as products. The PT reaction proceeds directly without an activation barrier. The PT times for n = 1-5 were calculated to be 36.0, 9.8, 8.3, 7.7, and 7.1 fs, respectively, at the MP2/6-311++G(d,p) level, indicating that PT in these clusters is a very fast process, and the PT time is not dependent on the cluster size (n), except in the case of n = 1, where the PT time was slightly longer because the bond distance and angle of the hydrogen bond in n = 1 were deformed from the standard structure. The reaction mechanism was discussed based on these results.

Highly Active and Renewable Catalytic Electrodes for Two-Electron Oxygen Reduction Reaction

This study has shown that antimony-doped tin oxide (ATO) works as a robust "renewable catalyst" for the electrochemical synthesis of hydrogen peroxide (H₂O₂) from water and oxygen. Antimony doping into SnO₂ gives rise to remarkable electrocatalytic activity for two-electron oxygen reduction reaction (2e^--ORR) by water with a volcano-type relation between the activity and doping levels (x_Sb). Density functional theory simulations highlight the importance of an isolated Sb atom of ATO inducing the high activity and selectivity for 2e^--ORR due to the effects of O₂ adsorption enhancement, decrease in the activation energy, and lowering the adsorptivity of H₂O₂. Electrolysis by a normal three-electrode cell using ATO (x_Sb = 10.2 mol %) at -0.22 V (vs reversible hydrogen electrode) stably and continuously produces H₂O₂ with a turnover frequency of 6.6 s^-1. This remarkable activity can be maintained even after removing the surface layer of ATO by argon-ion sputtering.

Construction of a Bi2MoO6/CoOx/Au system with a dual-channel charge transfer path for enhanced tetracycline degradation

The introduction of two cocatalysts CoOx and Au constructs dual carrier transfer channels, which improves the photogenerated electron–hole pairs separation efficiency and photocatalytic performance.