Robust Covalent Organic Frameworks for Photosynthesis of H2O2: Advancements, Challenges and Strategies.

Since 2020, covalent organic frameworks (COFs) are emerging as robust catalysts for the photosynthesis of hydrogen peroxide (H2O2), benefiting from their distinct advantages. However, the current efficiency of H2O2 production and solar-to-chemical energy conversion efficiency (SCC) remain suboptimal due to various constraints in the reaction mechanism. Therefore, there is an imperative to propose efficiency improvement strategies to accelerate the development of this reaction system. This comprehensive review delineates recent advances, challenges, and strategies in utilizing COFs for photocatalytic H2O2 production. It explores the fundamentals and challenges (e.g., oxygen (O2) mass transfer rate, O2 adsorption capacity, response to sunlight, electron-hole separation efficiency, charge transfer efficiency, selectivity, and H2O2 desorption) associated with this process, as well as the advantages, applications, classification, and preparation strategies of COFs for this purpose. Various strategies to enhance the performance of COFs in H2O2 production are highlighted. The review aims to stimulate further advancements in utilizing COFs for photocatalytic H2O2 production and discusses potential prospects, challenges, and application areas in this field.

Recent Advances and Challenges in Efficient Selective Photocatalytic CO2 Methanation.

Solar-driven carbon dioxide (CO2 ) methanation holds significant research value in the context of carbon emission reduction and energy crisis. However, this eight-electron catalytic reaction presents substantial challenges in catalytic activity and selectivity. In this regard, researchers have conducted extensive exploration and achieved significant developments. This review provides an overview of the recent advances and challenges in efficient selective photocatalytic CO2 methanation. It begins by discussing the fundamental principles and challenges in detail, analyzing strategies for improving the efficiency of photocatalytic CO2 conversion to CH4 comprehensively. Subsequently, it outlines the recent applications and advanced characterization methods for photocatalytic CO2 methanation. Finally, this review highlights the prospects and opportunities in this area, aiming to inspire CO2 conversion into high-value CH4 and shed light on the research of catalytic mechanisms.

Electronic Structure Modulation of Oxygen-Enriched Defective CdS for Efficient Photocatalytic H2 O2 Production.

Artificial photosynthesis for hydrogen peroxide (H2 O2 ) presents a sustainable and environmentally friendly approach to generate clean fuel and chemicals. However, the catalytic activity is hindered by challenges such as severe charge recombination, insufficient active sites, and poor selectivity. Here, a robust strategy is proposed to regulate the electronic structure of catalyst by the collaborative effect of defect engineering and dopant. The well designed oxygen-doped CdS nanorods with S2- defects and Cd2+ 4d10 electron configuration (CdS-O,Sv ) is successfully synthesized, and the Cd2+ active sites around S defects or oxygen atoms exhibit rapid charge separation, suppressed carrier recombination, and enhanced charge utilization. Consequently, a remarkable H2 O2 production rate of 1.62 mmol g-1  h-1 under air conditions is acquired, with an apparent quantum yield (AQY) of 9.96% at a single wavelength of 450 nm. This work provides valuable insights into the synergistic effect between defect and doping on catalytic activity.

Alternating 3rd- to 2nd-Order Charge Reaction Kinetics on Bismuth Vanadate Photoanodes with Ultrathin Bismuth Metal-Organic-Frameworks.

The most challenging obstacle for photocatalysts to efficiently harvest solar energy is the sluggish surface redox reaction (e. g., oxygen evolution reaction, OER) kinetics, which is believed to originate from interface catalysis rather than the semiconductor photophysics. In this work, we developed a light-modulated transient photocurrent (LMTPC) method for investigating surface charge accumulation and reaction on the W-doped bismuth vanadate (W : BiVO4) photoanodes during photoelectrochemical water oxidation. Under illuminating conditions, the steady photocurrent corresponds to the charge transfer rate/kinetics, while the integration of photocurrent (I~t) spikes during the dark period is regarded as the charge density under illumination. Quantitative analysis of the surface hole densities and photocurrents at 0.6 V vs. reversible hydrogen electrode results in an interesting rate-law kinetics switch: a 3rd-order charge reaction behavior appeared on W : BiVO4, but a 2nd-order charge reaction occurred on W : BiVO4 surface modified with ultrathin Bi metal-organic-framework (Bi-MOF). Consequently, the photocurrent for water oxidation on W : BiVO4/Bi-MOF displayed a 50 % increment. The reaction kinetics alternation with new interface reconstruction is proposed for new mechanism understanding and/or high-performance photocatalytic applications.

Reactivities of α-Oxo BMIDA Gold Carbenes Generated by Gold-Catalyzed Oxidation of BMIDA-Terminated Alkynes.

An oxidative strategy is reported to access α-oxo BMIDA gold carbenes directly from BMIDA-terminated alkynes. Besides offering expedient access to seldom studied boryl metal carbenes, these BMIDA gold carbene species undergo facile insertions into methyl, methylene, methine, and benzylic C-H bonds in the absence of the Thorpe-Ingold effect. They also undergo efficient OH insertion, cyclopropanation, and F-C alkylations. This chemistry provides rapid access to structurally diverse α-BMIDA ketones, which are scarcely documented. In combination with DFT studies, the role of BMIDA is established to be an electron-donating group that attenuates the high electrophilicity of the gold carbene center.

Highly Selective and Efficient Solar-Light-Driven CO2 Conversion with an Ambient-Stable 2D/2D Co2 P@BP/g-C3 N4 Heterojunction.

Renewable solar-driven carbon dioxide (CO2 ) conversion to highly valuable fuels is an economical and prospective strategy for both the energy crisis and ecological environment disorder. However, the selectivity and activity of current photocatalysts have great room for improvement due to the diversification and complexity of products. Here, an ambient-stable 2D/2D Co2 P@BP/g-C3 N4 heterojunction is designed for highly selective and efficient photocatalytic CO2 reduction reaction. The resulting Co2 P@BP/g-C3 N4 material has a remarkable conversion of CO2 to carbon monoxide (CO) with an ≈96% selectivity, coupled with a dramatically increased CO generation rate of 16.21 µmol g-1 h-1 , which is 5.4 times higher than pristine graphitic carbon nitride (g-C3 N4 ). In addition, this photocatalyst exhibits good ambient stability of black phosphorus (BP) without oxidation even over 180 days. The excellent photocatalytic selectivity and activity of Co2 P@BP/g-C3 N4 heterojunction are attributed to its lower energy barriers of *COOH, *CO, and *+CO in the process of CO2 reduction, coupled with rapid charge transfer at the heterointerfaces of BP/g-C3 N4 and Co2 P/BP. This is solidly verified by both density functional theory calculation and mechanism experiments. Therefore, this work holds great promise for an ambient-stable efficient and high selectivity photocatalyst in solar-driven CO2 conversion.

Spatially Separating Redox Centers on Z-Scheme ZnIn2 S4 /BiVO4 Hierarchical Heterostructure for Highly Efficient Photocatalytic Hydrogen Evolution.

Photocatalysis technology using solar energy for hydrogen (H2 ) production still faces great challenges to design and synthesize highly efficient photocatalysts, which should realize the precise regulation of reactive sites, rapid migration of photoinduced carriers and strong visible light harvest. Here, a facile hierarchical Z-scheme system with ZnIn2 S4 /BiVO4 heterojunction is proposed, which can precisely regulate redox centers at the ZnIn2 S4 /BiVO4 hetero-interface by accelerating the separation and migration of photoinduced charges, and then enhance the oxidation and reduction ability of holes and electrons, respectively. Therefore, the ZnIn2 S4 /BiVO4 heterojunction exhibits excellent photocatalytic performance with a much higher H2 -evolution rate of 5.944 mmol g-1 h-1 , which is about five times higher than that of pure ZnIn2 S4 . Moreover, this heterojunction shows good stability and recycle ability, providing a promising photocatalyst for efficient H2 production and a new strategy for the manufacture of remarkable photocatalytic materials.

Charge reactions on crystalline/amorphous lanthanum nickel oxide cocatalyst modified hematite photoanode.

Understanding the charge reactions at the semiconductor/cocatalyst interface is of great interest for boosting photoelectrochemical water splitting since the charge transfer to water molecules is the sluggish one. Besides the dopants, porosity, or ion-penetration of the cocatalyst, the crystallinity of the cocatalyst may also influence the charge reactions at the interface. Herein, we prepared amorphous LaNiOx and crystalline La-doped NiO (c-LaNiOx) cocatalysts through photochemical decomposition and ion-exchange of Ni(OH)2 precipitation, respectively. Both lanthanum nickel oxides (LaNiOx) showed considerable improvement of hematite photoanodes. By using electrochemical impedance measurements, we confirmed that the catalyst could store photogenerated charges with reduced transfer resistance and passivate the surface state, resulting in the overall charge transfer rate enhancement. This study may lead to a chance to uncover the kinetic bottleneck with an efficient cocatalyst in well-controlled crystallinity in the future.

Z-Scheme 2D/2D Heterojunction of Black Phosphorus/Monolayer Bi2 WO6 Nanosheets with Enhanced Photocatalytic Activities.

Black phosphorus (BP), a star-shaped two-dimensional material, has attracted considerable attention owing to its unique chemical and physical properties. BP shows great potential in photocatalysis area because of its excellent optical properties; however, its applications in this field have been limited to date. Now, a Z-scheme heterojunction of 2D/2D BP/monolayer Bi2 WO6 (MBWO) is fabricated by a simple and effective method. The BP/MBWO heterojunction exhibits enhanced photocatalytic performance in photocatalytic water splitting to produce H2 and NO removal to purify air; the highest H2 evolution rate of BP/MBWO is 21042 µmol g-1 , is 9.15 times that of pristine MBWO and the NO removal ratio was as high as 67 %. A Z-scheme photocatalytic mechanism is proposed based on monitoring of . O2 - , . OH, NO2 , and NO3 - species in the reaction. This work broadens applications of BP and highlights its promise in the treatment of environmental pollution and renewable energy issues.

3D Aerogel of Graphitic Carbon Nitride Modified with Perylene Imide and Graphene Oxide for Highly Efficient Nitric Oxide Removal under Visible Light.

3D materials are considered promising for photocatalytic applications in air purification because of their large surface areas, controllability, and recyclability. Here, a series of aerogels consisting of graphitic-carbon nitride (g-C3 N4 ) modified with a perylene imide (PI) and graphene oxide (GO) are prepared for nitric oxide (NO) removal under visible-light irradiation. All of the photocatalysts exhibit excellent activity in NO removal because of the strong light absorption and good planarity of PI-g-C3 N4 coupled with the favorable charge transport properties of GO, which slow the recombination of electron-hole pairs. The aerogel containing thiophene displays the most efficient NO removal of the aerogel series, with a removal ratio of up to 66%. Density functional theory calculations are conducted to explain this result and recycling experiments are carried out to verify the stability and recyclability of these photocatalysts.

Palladium-Catalyzed ortho-Olefination of Phenyl Acetic and Phenyl Propylacetic Esters via C-H Bond Activation.

A highly regioselective palladium-catalyzed ester-directed ortho-olefination of phenyl acetic and propionic esters with olefins via C-H bond activation has been developed. A wide variety of phenyl acetic and propionic esters were tolerated in this transformation, affording the corresponding olefinated aromatic compounds. The ortho-olefination of heterocyclic acetic and propionic esters also took place smoothly giving the products in good yields, thus proving the potential utility of this protocol in synthetic chemistry.

Selective synthesis of polyfunctionalized pyrido[2,3-b]indoles by multicomponent domino reactions.

A series of novel polyfunctionalized pyrido[2,3-b]indoles were synthesized by three- or four-component domino reactions under microwave irradiation. This protocol has the advantages of readily available starting materials, short reaction times, high yields, easy workup, and high chemo- and regioselectivities.

Recent advances in ambient-stable black phosphorus materials for artificial catalytic nitrogen cycle in environment and energy.

Nitrogen cycle is crucial for the Earth's ecosystem and human-nature coexistence. However, excessive fertilizer use and industrial contamination disrupt this balance. Semiconductor-based artificial nitrogen cycle strategies are being actively researched to address this issue. Black phosphorus (BP) exhibits remarkable performance and significant potential in this area due to its unique physical and chemical properties. Nevertheless, its practical application is hindered by ambient instability. This review covers the synthesis methods of BP materials, analyzes their instability factors under environmental conditions, discusses stability improvement strategies, and provides an overview of the applications of ambient-stable BP materials in nitrogen cycle, including N2 fixation, NO3- reduction, NOx removal and nitrides sensing. The review concludes by summarizing the challenges and prospects of BP materials in the nitrogen cycle, offering valuable guidance to researchers.

Recent advances of pure/independent covalent organic framework membrane materials: preparation, properties and separation applications.

Covalent organic frameworks (COF) are porous crystalline polymers connected by covalent bonds. Due to their inherent high specific surface area, tunable pore size, and good stability, they have attracted extensive attention from researchers. In recent years, COF membrane materials developed rapidly, and a large amount of research work has been presented on the preparation methods, properties, and applications of COF membranes. This review focuses on the research on independent/pure continuous COF membranes. First, based on the membrane formation mechanism, COF membrane preparation methods are categorized into two main groups: bottom-up and top-down. Four methods are presented, namely, solvothermal, interfacial polymerization, steam-assisted conversion, and layer by layer. Then, the aperture, hydrophilicity/hydrophobicity and surface charge properties of COF membranes are summarized and outlined. According to the application directions of gas separation, water treatment, organic solvent nanofiltration, pervaporation and energy, the latest research results of COF membranes are presented. Finally, the challenges and future directions of COF membranes are summarized and an outlook provided. It is hoped that this work will inspire and motivate researchers in related fields.

Biomimetic cellulose-nanocrystalline-based composite membrane with high flux for efficient purification of oil-in-water emulsions.

The massive discharge of oily wastewater and oil spills are causing serious pollution to water resources. It is urgent to require clean and efficient method of purifying oily emulsions. Although the separation membranes with selective wettability have been widely used in the efficient purification of oil/water emulsions. It is still very challenging to develop functional films that are environmentally friendly, fouling resistant, inexpensive, easy to prepare, easy to scale, and highly efficient. Cellulose nanocrystalline-based composite membranes (CCM) were prepared by surface-initiated atom transfer radical polymerization (SATRP) and vacuum self-assembly. The prepared CCM is superhydrophilic and superoleophobic underwater due to the hydrophilic nature of the modified cellulose-nanocrystalline and the micro-nano surface structure. The CCM shows high separation efficiency (> 99.9 %), high flux (16,692 L-1·m-2·h-1·bar-1) for surfactant-stabilized oil-in-water emulsions, good cycle stability and anti-fouling performance. This biomass-derived membrane is green, cheap, easy to manufacture, scalable, super-wettability, and durability, it promises to be an alternative to separation membranes in today's market.

A polydimethylsiloxane-based sponge for water purification and interfacial solar steam generation.

A better knowledge for the design and synthesis of low-cost, novel porous materials is highly desirable in various fields such as recyclable solar desalination and liquid recycling. Herein, a polydimethylsiloxane-based sponge with a web-like three-dimensional (3D) interconnected porous structure was developed for effective recovery of liquids and the continuous interfacial solar steam generation (ISSG). The sponge is capable of conducting directional transport of oil or organic solvents at temperatures above 32 °C while automatically controlling the desorption of the organic phase below 28 °C. The synergistic combination between high light absorption (above 95 %) and light-to-heat conversion efficiency (99.87 %) resulted in a considerably high seawater evaporation rate (1.66 Kg m-2h-1) under 1 sun. The self-regeneration of the evaporator is facilitated by the salt barrier function of the large channels of the smart sponge with high hydraulic conductivity. This sponge can maintain a maximum evaporation rate up to the 5 consecutive days operation with the co-benefit of real-time regeneration and the reversible switching of the wettability. The reusable smart sponge evaporators are highly efficient in generating clean water from seawater with satisfactory ion rejection rates (above 99.6 %). As such, the prepared sponge shows great potential in environmental restoration, metal recovery, and water regeneration.

A 3D smart wood membrane with high flux and efficiency for separation of stabilized oil/water emulsions.

Oily sewage discharged from indiscriminate industrial and frequent oil spills have become a serious global problem. There is an urgent need to separate stable oil/water emulsions by efficient and environmentally friendly methods. Membrane separation technology has the advantages of low energy consumption and low cost, thus is an effective solution to the problems of oily wastewater. However, the manufacture of multifunctional membranes with high efficiency, high flux and self-cleaning using renewable materials remains a challenge. Herein, three-dimensional (3D) smart membranes with switchable superhydrophobic-hydrophilic surfaces were prepared by grafting photo-responsive poly-spiropyran (PSP) on wood-based substrates via surface atom transfer radical polymerization. This novel membrane can efficiently separate stabilized water-in-oil and oil-in-water emulsions due to reversible hydrophilic-hydrophobic transition by switching UV and visible light irradiation. Remarkably, after immobilization, the PSP grafted on the wood substrate exhibited a faster photo response effect than the free spiropyran (SP). More importantly, the prepared 3D smart membranes showed exceptional high flux (4392 L•m-2•h-1) and efficiency (above 99.99 %), good cycle stability (99.99 % after 12 times) and durability (available for at least 60 days) for the separation of surfactant-stabilized water-in-oil emulsions. This work opens a new avenue for the design of functional biomass-derived membranes for efficient and sustainable oily wastewater treatment with high flux, easy scale-up, and green regeneration.

Two-dimensional nanomaterials: synthesis and applications in photothermal catalysis.

Photothermal catalysis, as one of the emerging technologies with synergistic effects of photochemistry and thermochemistry, is highly attractive in the fields of environment and energy. Two-dimensional (2D) nanomaterials have received extensive attention toward photothermal catalysis because of their ultrathin layer structures, superior physical and optical properties, and high surface areas. These merits are beneficial for shortening the transfer distance of charge carriers, improving the efficiency of solar to thermal, and providing a great opportunity for the development of photothermal chemistry. In this review, we have summarized the state-of-art advances in various 2D nanomaterials with emphasis on the driving force and relevant mechanism of photothermal catalysis, including the involved three types, namely, localized surface plasmonic resonance (LSPR), nonradiative relaxation, and thermal vibrations of molecules. Moreover, the synthesis strategies of 2D materials and their photothermal applications in carbon dioxide (CO2) conversion, hydrogen (H2) production, volatile organic compounds (VOCs) degradation, and water (H2O) purification have been discussed in detail. Ultimately, the existing challenges and prospects of future development in the field are proposed. It is believed that this review will afford a great reference for the exploration of the high-efficiency 2D nanomaterials and their structure-activity relationship.

Multifunctional Solar Evaporator with Adjustable Island Structure Improves Performance and Salt Discharge Capacity of Desalination.

Interfacial solar steam generation (ISSG) is the main method to get fresh water from seawater or wastewater. The balance between evaporation rate and salt resistance is still a major challenge for ISSG. Herein, a wood aerogel island solar evaporator (WAISE) with tunable surface structure and wettability by synthesizing poly(n-isopropylacrylamide)-modified multi-walled carbon nanotube photothermal layers. Compared to dense surface structure evaporators, interfacial moisture transport, thermal localization, and surface water vapor diffusion of WAISE are greatly promoted, and the evaporation rate of WAISE increased by 87.64%. WAISE allows for record performance of 200 h continuous operation in 20% NaCl solution without salt accumulation. In addition, the photo-thermal-electric device is developed based on WAISE with continuous water purification, power generation, and irrigation functions. This work provides a new direction for the development of multifunctional water purification systems.

Construction of BiVO4/NiCo2O4 nanosheet Z-scheme heterojunction for highly boost solar water oxidation.

The sluggish water oxidation process is a severe obstacle for solar-driven water splitting. Therefore, it is imperative to develop a suitable photocatalyst with reduced energy barrier for strong oxidation. In this study, a Z-scheme BiVO4/NiCo2O4 (BVO/NCO) heterojunction system was designed by decorating ultrathin nickel-cobalt (NiCo2O4) spinel nanosheets on BiVO4 as an efficient photocatalyst for water oxidation. The unique structure of the system significantly reduced the energy barrier and improved the oxidation ability of BiVO4 to efficiently enhance the separation and transfer of the photogenerated carriers. Thus, the photocatalyst delivered an excellent O2 evolution performance of 1640.9 µmol∙g-1∙h-1 and showed 124% improved efficiency as compared to pristine BiVO4 and a quantum efficiency of 5.39% at 400 nm for O2 evolution. Additionally, the theoretical calculations revealed that the formation of *OOH was the rate-determining step for water oxidation. The decoration with NiCo2O4 significantly reduced the energy barrier between *O and *OOH, which eventually improved the photocatalytic performance of BVO/NCO. The results hold great promise for the potential application of spinel-based materials in efficient photocatalytic O2 evolution and offer fundamental insights into the design of efficient water oxidation heterojunctions.