Dual Channel H2O2 Photosynthesis in Pure Water over S-Scheme Heterojunction Cs3PMo12/CC Boosted by Proton and Electron Reservoirs

Dual channel photo-driven H2O2 production in pure water on small-scale on-site setups is a promising strategy to provide low-concentrated H2O2 whenever needed. This process suffers, however, strongly from the fast recombination of photo-generated charge carriers and the sluggish oxidation process. Here, insoluble Keggin-type cesium phosphomolybdate Cs3PMo12O40 (abbreviated to Cs3PMo12) is introduced to carbonized cellulose (CC) to construct S-scheme heterojunction Cs3PMo12/CC. Dual channel H2O2 photosynthesis from both H2O oxidation and O2 reduction in pure water has been thus achieved with the production rate of 20.1 mmol L-1 gcat. -1 h-1, apparent quantum yield (AQY) of 2.1% and solar-to-chemical conversion (SCC) efficiency of 0.050%. H2O2 accumulative concentration reaches 4.9 mmol L-1. This high photocatalytic activity is guaranteed by unique features of Cs3PMo12/CC, namely, S-scheme heterojunction, electron reservoir, and proton reservoir. The former two enhance the separation of photo-generated charge carriers, while the latter speeds up the torpid oxidation process. In situ experiments reveal that H2O2 is formed via successive single-electron transfer in both channels. In real practice, exposing the reaction system under natural sunlight outdoors successfully results in 0.24 mmol L-1 H2O2. This work provides a key practical strategy for designing photocatalysts in modulating redox half-reactions in photosynthesis.

Unraveling the Synergistic Mechanism of Boosted Photocatalytic H2O2 Production over Cyano-g-C3N4/In2S3/Ppy Heterostructure and Enhanced Photocatalysis-Self-Fenton Degradation Performance

In this work, cyano contained g-C3N4 comodified by In2S3 and polypyrrole (C≡N─CN/IS/Ppy) materials are synthesized for the photocatalytic production of H2O2 and photocatalysis-self-Fenton reaction for highly efficient degradation of metronidazole. The results from UV-vis spectrophotometry, surface photovoltage, and Kelvin probe measurements reveal the promoted transport and separation efficiency of photoinduced charges after the introduction of In2S3 and Ppy in the heterojunction. The existence of a built-in electric field accelerates the photoinduced charge separation and preserves the stronger oxidation ability of holes at the valence band of C≡N─CN. Linear sweep voltammetry measurements, zeta potential analyzations, nitroblue tetrazolium determination, and other measurements show that Ppy improves the conversion ratio of •O2 - to H2O2 and the utilization ratio of •O2 -, as well as suppresses decomposition of H2O2. Accordingly, the H2O2 evolution rate produced via a two-step single-electron reduction reaction reaches almost 895 µmol L-1 h-1, a value 80% and 7.2-fold higher than those obtained with C≡N─CN/IS and C≡N─CN, respectively. The metronidazole removal rate obtained via photocatalysis-self-Fenton reaction attains 83.7% within 120 minutes, a value much higher than that recorded by the traditional Fenton method. Overall, the proposed synthesis materials and route look promising for the H2O2 production and organic pollutants degradation.

In Situ Generation of H2O2 over MoOx Decorated on Cu2O@CuO Core-Shell Particle Nanoarchitectonics for Boosting Photocatalytic Oxidative Desulfurization

Photocatalytic oxidation desulfurization (PODS) has emerged as a promising, ecofriendly alternative to traditional, energy-intensive fuel desulfurization methods. Nevertheless, its progress is still hindered due to the slow sulfide oxidation kinetics in the current catalytic systems. Herein, we present a MoOx decorated on a Cu2O@CuO core-shell catalyst, which enables a new, efficient PODS pathway by in situ generation of hydrogen peroxide (H2O2) with saturated moist air as the oxidant source. The photocatalyst delivers remarkable specific activity in oxidizing dibenzothiophene (DBT), achieving a superior rate of 7.8 mmol g-1 h-1, while maintaining a consistent performance across consecutive reuses. Experimental investigations reveal that H2O2 is produced through the two-electron oxygen reduction reaction (ORR), and both H2O2 and the hydroxyl radicals (•OH) generated from it act as the primary reactive species responsible for sulfide oxidation. Importantly, our catalyst accomplishes complete PODS of real diesel fuel, underscoring an appealing industrial prospect for our photocatalyst.

S-Scheme Heterojunction Photocatalysts for H2O2 Production

Photocatalysis opens a new door to H₂O₂ formation via a low-cost, clean, mild, and sustainable process, which holds great promise for the next generation of massive H₂O₂ production. However, fast photogenerated electron-hole recombination and slow reaction kinetics are the main obstacles for its practical application. An effective solution is to construct the step-scheme (S-scheme) heterojunction, which remarkably promotes carrier separation and boosts the redox power for efficient photocatalytic H₂O₂ production. Considering the superiority of S-scheme heterojunctions, this Perspective summarizes the recent advances of S-scheme photocatalysts for H₂O₂ production, including photocatalysts for building S-scheme heterojunctions, H₂O₂-production performance, and S-scheme photocatalytic mechanisms. Lastly, some prospects are given to motivate future research in this promising field, other promising strategies are provided to further improve H₂O₂ yields, and future research directions are suggested.

A Targeted Review of Current Progress, Challenges and Future Perspective of g-C3 N4 based Hybrid Photocatalyst Toward Multidimensional Applications

The increasing demand for searching highly efficient and robust technologies in the context of sustainable energy production totally rely onto the cost-effective energy efficient production technologies. Solar power technology in this regard will perceived to be extensively employed in a variety of ways in the future ahead, in terms of the combustion of petroleum-based pollutants, CO₂ reduction, heterogeneous photocatalysis, as well as the formation of unlimited and sustainable hydrogen gas production. Semiconductor-based photocatalysis is regarded as potentially sustainable solution in this context. g-C₃ N₄ is classified as non-metallic semiconductor to overcome this energy demand and enviromental challenges, because of its superior electronic configuration, which has a median band energy of around 2.7 eV, strong photocatalytic stability, and higher light performance. The photocatalytic performance of g-C₃ N₄ is perceived to be inadequate, owing to its small surface area along with high rate of charge recombination. However, various synthetic strategies were applied in order to incorporate g-C₃ N₄ with different guest materials to increase photocatalytic performance. After these fabrication approaches, the photocatalytic activity was enhanced owing to generation of photoinduced electrons and holes, by improving light absorption ability, and boosting surface area, which provides more space for photocatalytic reaction. In this review, various metals, non-metals, metals oxide, sulfides, and ferrites have been integrated with g-C₃ N₄ to form mono, bimetallic, heterojunction, Z-scheme, and S-scheme-based materials for boosting performance. Also, different varieties of g-C₃ N₄ were utilized for different aspects of photocatalytic application i. e., water reduction, water oxidation, CO₂ reduction, and photodegradation of dye pollutants, etc. As a consequence, we have assembled a summary of the latest g-C₃ N₄ based materials, their uses in solar energy adaption, and proper management of the environment. This research will further well explain the detail of the mechanism of all these photocatalytic processes for the next steps, as well as the age number of new insights in order to overcome the current challenges.

Recent Advancement of the Current Aspects of g-C3 N4 for its Photocatalytic Applications in Sustainable Energy System

Being one of the foremost enticing and intriguing innovations, heterogeneous photocatalysis has also been used to effectively gather, transform, and conserve sustainable sun's radiation for the production of efficient and clean fossil energy as well as a wide range of ecological implications. The generation of solar fuel-based water splitting and CO₂ photoreduction is excellent for generating alternative resources and reducing global warming. Developing an inexpensive photocatalyst can effectively split water into hydrogen (H₂ ), oxygen (O₂ ) sources, and carbon dioxide (CO₂ ) into fuel sources, which is a crucial problem in photocatalysis. The metal-free g-C₃ N₄ photocatalyst has a high solar fuel generation potential. This review covers the most recent advancements in g-C₃ N₄ preparation, including innovative design concepts and new synthesis methods, and novel ideas for expanding the light absorption of pure g-C₃ N₄ for photocatalytic application. Similarly, the main issue concerning research and prospects in photocatalysts based g-C₃ N₄ was also discussed. The current dissertation provides an overview of comprehensive understanding of the exploitation of the extraordinary systemic and characteristics, as well as the fabrication processes and uses of g-C₃ N₄ .

Inorganic Metal-Oxide Photocatalyst for H2 O2 Production

Hydrogen peroxide (H₂ O₂ ) is a mild but versatile oxidizing agent with extensive applications in bleaching, wastewater purification, medical treatment, and chemical synthesis. The state-of-art H₂ O₂ production via anthraquinone oxidation is hardly considered a cost-efficient and environment-friendly process because it requires high energy input and generates hazardous organic wastes. Photocatalytic H₂ O₂ production is a green, sustainable, and inexpensive process which only needs water and gaseous dioxygen as the raw materials and sunlight as the power source. Inorganic metal oxide semiconductors are good candidates for photocatalytic H₂ O₂ production due to their abundance in nature, biocompatibility, exceptional stability, and low cost. Progress has been made to enhance the photocatalytic activity toward H₂ O₂ production, however, H₂ O₂ photosynthesis is still in the laboratory research phase since the productivity is far from satisfaction. To inspire innovative ideas for boosting the H₂ O₂ yield in photocatalysis, the most well-studied metal oxide photocatalysts are selected and the modification strategies to improve their activity are listed. The mechanisms for H₂ O₂ production over modified photocatalysts are discussed to highlight the facilitating role of the modification methods. Besides, methods for the quantification of H₂ O₂ and associated radical intermediates are provided to guide future studies in this field.

Augmentation of microbial fuel cell and photocatalytic polishing technique for the treatment of hazardous dimethyl phthalate containing wastewater

In the present paper, the potentiality of integrating microbial fuel cells (MFCs) with a photocatalytic reactor to maximize the wastewater treatment efficiency with concurrent power generation was explored. Dimethyl phthalate (DMP) and acetic acid (AA) were the employed substrate and the co-substrate, respectively, using Pseudomonas aeruginosa as a biocatalyst. MFCs operated by single substrate showed the maximum power generation of 0.75-3.84 W m^-3 whereas an addition of AA as the co-substrate yielded 3-12 fold higher power generation. Pseudomonas aeruginosa produced phenazine-1-carboxylic acid in DMP-fed MFC as the metabolite whereas AA along with DMP yielded pyocyanin which reduced the charge transfer resistance. Chemical oxygen demand (COD) removal efficiency in the MFCs was circa 62% after 11 days of operation. Thereafter, it further increased albeit with a drastic reduction in power generation. Subsequently, the MFC anolyte was treated in a photocatalytic reactor under visible light irradiation and catalyzed by CuO-gC₃N₄. The performance of photocatalytic reactor was evaluated, with COD and total organic carbon (TOC) removal efficiency of 88% and 86% after 200 min of light irradiation. The present work suggests that the MFC can be integrated with photocatalysis as a sustainable wastewater treatment method with concurrent power generation.

Nanostructured CuO with a thin g-C3N4 layer as a highly efficient photocathode for solar water splitting

A g-C₃N₄/CuO nanostructure featuring improved photoelectrochemical properties was successfully prepared using a facile and cost-effective method involving electrodeposition and thermal oxidation.

A porous material excited by near-infrared light for photo/chemodynamic and photothermal dual-mode combination therapy

Photodynamic therapy (PDT) and photothermal therapy (PTT) are well-developed light therapy methods for cancer; however, both have a few areas that need improvement. A sustained PDT effect depends on the sustained generation of reactive oxygen species (ROS); therefore, adjusting the type of photosensitizer or the reaction mechanism to prolong the duration of the oxidation-reduction reaction is a possible solution for the continuation of the PDT effect. Further, if PTT could be combined with other treatments, it would bring about a more satisfactory therapeutic effect. To increase the treatment effect of the above two therapeutic methods, a collaborative treatment model of photo/chemodynamic therapy (PCDT) and PTT is needed and is the focus of this study. On the one hand, PCDT is a therapy that integrates PDT with Fenton-like reactions, and Fenton-like reactions can help PDT to produce more ROS by making better use of H₂O₂ in the tumor microenvironment. On the other hand, the PTT effect can also promote PCDT effects to some extent because rising temperature can elevate the redox reaction rate. Therefore, a copper oxide semiconductor photosensitizer was selected in this research to realize the abovementioned therapeutic purposes and experimental concepts. A porous silica carrier can facilitate the uniform attachment of the copper oxide photosensitizer to the SiO₂ surface to form a relatively uniform nanostructure, and the nanoporous structure can increase the performance of the whole material to a certain extent. Based on these perspectives, SiO₂@CuO nanotube (NT), an agent of both Fenton-like photosensitization and photothermal reagent, is synthesized by the hydrothermal co-precipitation template approach to shrink the tumor through the combined effect of PCDT and PTT. In this system, copper ions can participate in the Fenton-like reactions and make better use of H₂O₂ to generate more ROS. Herein, 808 nm light was chosen for irradiation because of its suitable excitation ability, applicable penetration and low intrinsic damage. The experimental results show that SiO₂@CuO NT is a promising agent that combines PCDT and PTT for cancer treatment. This work provides guidance for the synthesis of Fenton-like photosensitizers for the PCDT effect.

Acetylene and Diacetylene Functionalized Covalent Triazine Frameworks as Metal-Free Photocatalysts for Hydrogen Peroxide Production: A New Two-Electron Water Oxidation Pathway

Metal-free polymer photocatalysts have shown great promise for photocatalytic H₂ O₂ production via two-electron reduction of molecular O₂ . The other half-reaction, which is the two-electron oxidation of water, still remains elusive toward H₂ O₂ production. However, enabling this water oxidation pathway is critically important to improve the yield and maximize atom utilization efficiency. It is shown that introducing acetylene (CC) or diacetylene (CCCC) moieties into covalent triazine frameworks (CTFs) can remarkably promote photocatalytic H₂ O₂ production. This enhancement is inherent to the incorporated carbon-carbon triple bonds which are essential in modulating the electronic structures of CTFs and suppressing charge recombinations. Furthermore, the acetylene and diacetylene moieties can significantly reduce the energy associated with OH* formation and thus enable a new two-electron oxidation pathway toward H₂ O₂ production. The study unveils an important reaction pathway toward photocatalytic H₂ O₂ production, reflecting that precise control over the chemical structures of polymer photocatalysts is vital to achieve efficient solar-to-chemical energy conversion.

Fabrication of a full-spectrum-response Cu2(OH)2CO3/g-C3N4 heterojunction catalyst with outstanding photocatalytic H2O2 production performance via a self-sacrificial method

Over the past few decades, near infrared light (NIR), as an important part of sunlight, has seldom been utilized in photocatalytic reactions.

Construction of a wide-spectrum-driven VN-g-C3N4/Cu2(OH)2CO3 heterojunction catalyst from VIS to NIR light via the in situ self-sacrificial method: the effect of oxygen on the N2 photofixation ability

In this work, an N vacancy-doped g-C₃N₄/Cu₂(OH)₂CO₃ (V_N-GCN/CuCOH) heterojunction catalyst with superior wide-spectrum-driven (from VIS to NIR) N₂ photofixation ability was synthesized via the in situ self-sacrificial method.