Unassisted Photoelectrochemical H2O2 Production with In Situ Glycerol Valorization Using α-Fe2O3.

Photoelectrochemical (PEC) H2O2 production via two-electron O2 reduction is promising for H2O2 production without emitting CO2. For PEC H2O2 production, α-Fe2O3 is an ideal semiconductor owing to its earth abundance, superior stability in water, and an appropriate band gap for efficient solar light utilization. Moreover, its conduction band is suitable for O2 reduction to produce H2O2. However, a significant overpotential for water oxidation is required due to the poor surface properties of α-Fe2O3. Thus, unassisted solar H2O2 production is not yet possible. Herein, we demonstrate unassisted PEC H2O2 production using α-Fe2O3 for the first time by applying glycerol oxidation, which requires less bias compared with water oxidation. We obtain maximum Faradaic efficiencies of 96.89 ± 0.6% and 100% for glycerol oxidation and H2O2 production, respectively, with high stability for 25 h. Our results indicate that unassisted and stable PEC H2O2 production is feasible with in situ glycerol valorization using the α-Fe2O3 photoanode.

Oxygen Vacancy-Enhanced Centrosymmetric Breaking of SrFeO3- x for Piezoelectric-Catalyzed Synthesis of H2O2.

Normally, only noncentrosymmetric structure of the materials can potentially be piezoelectric. Thus, it is limited in the field of piezoelectricity for the centrosymmetric structure of the material. In this work, the performance of piezoelectricity is successfully achieved from centrosymmetric SrFeO3- x by modulating oxygen vacancies, which have a surface piezoelectric potential up to 93 mV by using Kelvin-probe force microscopy (KPFM). Moreover, the piezoelectric effects of SrFeO3- x are also evaluated by piezoelectric catalytic effect and density functional theory calculations (DFT). The results show that the piezo-catalytic degradation of tetracycline reaches 96% after 75 min by ultrasonic mechanical vibration and the production of H2O2 by SrFeO3- x piezoelectric synthesis could reach 1821 µmol L-1. In addition, the DFT results indicate that the intrinsic effect of oxygen vacancies effectively promotes the adsorption and activation of O2 and H2O as well as intermediates and improves the piezoelectric catalytic activity. This work provides an effective basis for realizing the piezoelectricity of centrosymmetric materials and regulating the development of piezoelectric catalytic properties.

A Dual-Active Covalent Triazine Framework Film for Efficient Visible-Light-Driven Hydrogen Peroxide Production.

Photocatalytic hydrogen peroxide production from water and oxygen offers a clean and sustainable alternative to the conventional energy-intensive anthraquinone oxidation method. Compared to powdered covalent triazine frameworks (CTFs), the film morphology of CTFs provides better connectivity in 2D, yielding several advantages: more efficient connections between active sites, reduced electron-hole pair recombination, increased resistance to superoxide radical induced corrosion, and decreased light scattering. Leveraging these benefits, it has incorporated dual active sites for both the oxygen reduction reaction (ORR) and the water oxidation reaction (WOR) into a CTF film system. This dual-active CTF film demonstrated an exceptional hydrogen peroxide production rate of 19 460 µmol h⁻¹ m⁻2 after 1 h and 17 830 µmol h⁻¹ m⁻2 after 5 h under visible light irradiation (≥420 nm) without the need for sacrificial agents.

Rational Design of Conjugated Acetylenic Polymers Enables a Two-Electron Water Oxidation Pathway for Enhanced Photosynthetic Hydrogen Peroxide Generation.

Herein, the design of conjugated acetylenic polymers (CAPs) featuring diverse spatial arrangements and intramolecular spacers of diacetylene moieties (─C≡C─C≡C─) for photocatalytic hydrogen peroxide (H2 O2 ) production from water and O2 , without the need for sacrificial agents, is presented. It is shown that the linear configuration of diacetylene moieties within conjugated acetylenic polymers (CAPs) induces a pronounced polarization of electron distribution, which imparts enhanced charge-carrier mobility when compared to CAPs' networks featuring cross-linked arrangements. Moreover, optimizing the intramolecular spacer between diacetylene moieties within the linear structure leads to the exceptional modulation of the band structures, specifically resulting in a downshifted valence band (VB) and rendering the two-electron water oxidation pathway thermodynamically feasible for H2 O2 production. Consequently, the optimized CAPs with a linear configuration (LCAP-2), featuring spatially separated reduction centers (benzene rings) and oxidation centers (diacetylene moieties), exhibit a remarkable H2 O2 yield rate of 920.1 µmol g-1 h-1 , superior than that of the linear LCAP-1 (593.2 µmol g-1 h-1 ) and the cross-linked CCAP (433.4 µmol g-1 h-1 ). The apparent quantum efficiency (AQE) and solar-to-chemical energy conversion (SCC) efficiency of LCAP-2 are calculated to be 9.1% (λ = 420 nm) and 0.59%, respectively, surpassing the performance of most previously reported conjugated polymers.

Middle-age abolishes cardioprotection conferred by thioredoxin-1 in mice.

Thioredoxin-1 (Trx1) has cardioprotective effects on ischemia/reperfusion (I/R) injury, although its role in ischemic postconditioning (PostC) in middle-aged mice is not understood. This study aimed to evaluate if combining two cardioprotective strategies, such as Trx1 overexpression and PostC, could exert a synergistic effect in reducing infarct size in middle-aged mice. Young or middle-aged wild-type mice (Wt), transgenic mice overexpressing Trx1, and dominant negative (DN-Trx1) mutant of Trx1 mice were used. Mice hearts were subjected to I/R or PostC protocol. Infarct size, hydrogen peroxide (H2O2) production, protein nitration, Trx1 activity, mitochondrial function, and Trx1, pAkt and pGSK3ß expression were measured. PostC could not reduce infarct size even in the presence of Trx1 overexpression in middle-aged mice. This finding was accompanied by a lack of Akt and GSK3ß phosphorylation, and Trx1 expression (in Wt group). Trx1 activity was diminished and H2O2 production and protein nitration were increased in middle-age. The respiratory control rate dropped after I/R in Wt-Young and PostC restored this value, but not in middle-aged groups. Our results showed that Trx1 plays a key role in the PostC protection mechanism in young but not middle-aged mice, even in the presence of Trx1 overexpression.

Aeration-Free In Situ Fenton-like Reaction: Specific Adsorption and Activation of Oxygen on Heterophase Oxygen Vacancies.

Aeration accounts for 35-51% of the overall energy consumption in wastewater treatment processes and results in an annual energy consumption of 5-7.5 billion kWh. Herein, a solar-powered continuous-flow device was designed for aeration-free in situ Fenton-like reactions to treat wastewater. This system is based on the combination of TiO2-x/W18O49 featuring heterophase oxygen vacancy interactions with floating reduced graphene/polyurethane foam, which produces hydrogen peroxide in situ at the rates of up to 4.2 ppm h-1 with degradation rates of more than 90% for various antibiotics. The heterophase oxygen vacancies play an important role in the stretching of the O-O bond by regulating the d-band center of TiO2-x/W18O49, promoting the hydrogenation of *·O2- or *OOH by H+ enrichment, and accelerating the production of reactive oxygen species by spontaneous adsorption of hydrogen peroxide. Furthermore, the degradation mechanisms of antibiotics and the treatment of actual wastewater were thoroughly investigated. In short, the study provides a meaningful reference for potentially undertaking the "aeration-free" in situ Fenton reaction, which can help reduce or even completely eradicate the aeration costs and energy requirements during the treatment of wastewater.

Azobenzene-bridged Covalent Organic Frameworks Boosting Photocatalytic Hydrogen Peroxide Production from Alkaline Water: One Atom Makes a Significant Improvement.

Covalent organic frameworks (COFs) have been demonstrated as promising photocatalysts for hydrogen peroxide (H2O2) production. However, the construction of COFs with new active sites, high photoactivity, and wide-range light absorption for efficient H2O2 production remains challenging. Herein, we present the synthesis of a novel azobenzene-bridged 2D COF (COF-TPT-Azo) with excellent performance on photocatalytic H2O2 production under alkaline conditions. Notably, although COF-TPT-Azo differs by only one atom (-N=N- vs. -C=N-) from its corresponding imine-linked counterpart (COF-TPT-TPA), the COF-TPT-Azo exhibits a significantly narrower band gap, enhanced charge transport, and prompted photoactivity. Remarkably, when employed as a metal-free photocatalyst, COF-TPT-Azo achieves a high photocatalytic H2O2 production rate up to 1498 µmol g-1 h-1 at pH =11, which is 7.9 times higher than that of COF-TPT-TPA. Further density functional theory (DFT) calculations reveal that the -N=N- linkages are the active sites for photocatalysis. This work provides new prospects for developing high-performance COF-based photocatalysts.

Structural Modulation of Covalent Organic Frameworks for Efficient Hydrogen Peroxide Electrocatalysis.

The electrochemical production of hydrogen peroxide (H2O2) using metal-free catalysts has emerged as a viable and sustainable alternative to the conventional anthraquinone process. However, the precise architectural design of these electrocatalysts poses a significant challenge, requiring intricate structural engineering to optimize electron transfer during the oxygen reduction reaction (ORR). Herein, we introduce a novel design of covalent organic frameworks (COFs) that effectively shift the ORR from a four-electron to a more advantageous two-electron pathway. Notably, the JUC-660 COF, with strategically charge-modified benzyl moieties, achieved a continuous high H2O2 yield of over 1200 mmol g-1 h-1 for an impressive duration of over 85 hours in a flow cell setting, marking it as one of the most efficient metal-free and non-pyrolyzed H2O2 electrocatalysts reported to date. Theoretical computations alongside in situ infrared spectroscopy indicate that JUC-660 markedly diminishes the adsorption of the OOH* intermediate, thereby steering the ORR towards the desired pathway. Furthermore, the versatility of JUC-660 was demonstrated through its application in the electro-Fenton reaction, where it efficiently and rapidly removed aqueous contaminants. This work delineates a pioneering approach to altering the ORR pathway, ultimately paving the way for the development of highly effective metal-free H2O2 electrocatalysts.

Metal-Free Electrocatalysts for the Selective 2 e- Oxygen Reduction Reaction: A Never-Ending Story?

Hydrogen peroxide (H2 O2 ) electrosynthesis via the 2e- Oxygen Reduction Reaction (ORR) represents a highly challenging, environmentally friendly and cost-effective alternative to the current anthraquinone-based technology. Various lightweight element hetero-doped carbon nanostructures are promising and cheap metal-free electrocatalysts for H2 O2 synthesis, particularly those containing O-functionalities. The exact role of O-containing functional groups as electroactive sites for the process remains debated if not highly controversial. Herein, we have reported on the covalent exohedral functionalization of the outer surface of extra-pure multi-walled carbon nanotubes (MWCNTs) with discrete O-functional groups as a unique approach to prepare selective electrocatalysts for the process. This kind of decoration has added fundamental tiles to the puzzling structure/reactivity relationship of O-containing carbon-based catalysts for ORR, clearing doubts on the controversial role of hydroxyl/phenol groups as key functionalities for the design of more performing 2e- ORR electrocatalysts.

Construction of Atomic Metal-N2 Sites by Interlayers of Covalent Organic Frameworks for Electrochemical H2 O2 Synthesis.

Electrosynthesis of H2 O2 is a promising alternative to the anthraquinone oxidation process because of its low energy utilization and cost-effectiveness. Heteroatom-doped carbons-based catalysts have been widely developed for H2 O2 synthesis. However, their doping degree, defective degree, and location of active sites are difficult to be preciously controlled at molecular level. Herein, a dioxin-linked covalent organic framework (COF) is used as the template to preciously construct different metal-N2 sites along the porous walls for H2 O2 synthesis. By tuning the metal centers, the catalyst with Ca-N2 sites enables to catalyze H2 O2 production with selectivity over 95% from 0.2 to 0.6 V versus RHE, while the H2 O2 yields for Co sites or Ni sites are 20% and 60% in the same potential range. In addition, the turnover frequency (TOF) values for Ca-N2 sites are 11.63 e-1 site-1 s-1 , which are 58 and 20 times higher than those of Co and Ni sites (0.20 and 0.57 e-1 site-1 s-1 ). The theoretical calculations further reveal that the OOH* desorption on Ca sites is easier than those on Co or Ni sites, and thus catalyzes the oxygen reduction reaction in the 2e- pathway with high efficiency.

High Concentrations of Genistein Decrease Cell Viability Depending on Oxidative Stress and Inflammation in Colon Cancer Cell Lines.

Genistein could play a crucial role in modulating three closely linked physiological processes altered during cancer: oxidative stress, mitochondrial biogenesis, and inflammation. However, genistein's role in colorectal cancer remains unclear. We aimed to determine genistein's effects in two colon cancer cells: HT29 and SW620, primary and metastatic cancer cells, respectively. After genistein treatment for 48 h, cell viability and hydrogen peroxide (H2O2) production were studied. The cell cycle was studied by flow cytometry, mRNA and protein levels were analyzed by RT-qPCR and Western blot, respectively, and finally, cytoskeleton remodeling and NF-κB translocation were determined by confocal microscopy. Genistein 100 µM decreased cell viability and produced G2/M arrest, increased H2O2, and produced filopodia in SW620 cells. In HT29 cells, genistein produced an increase of cell death, H2O2 production, and in the number of stress fibers. In HT29 cells, mitochondrial biogenesis was increased, however, in SW620 cells, it was decreased. Finally, the expression of inflammation-related genes increased in both cell lines, being greater in SW620 cells, where NF-κB translocation to the nucleus was higher. These results indicate that high concentrations of genistein could increase oxidative stress and inflammation in colon cancer cells and, ultimately, decrease cell viability.

Nanospatial Charge Modulation of Monodispersed Polymeric Microsphere Photocatalysts for Exceptional Hydrogen Peroxide Production.

Photocatalysis offers a sustainable strategy for hydrogen peroxide (H2 O2 ) production, which is an essential oxidant and emerging energy carrier in modern chemical industry. The development of polymer-based photocatalysts to produce H2 O2 has great potential but is limited by lower efficiency due to the limitation of light utilization and the low charge separation efficiency. Herein, a series of monodispersed mesoporous resorcinol-formaldehyde resin spheres (MRFS) are reported with a rational designed spatial charge distribution, exhibiting wide light absorption with a solar-to-chemical conversion (SCC) efficiency of 1.1%. Surface photovoltage microscopy (SPVM) measurements unraveled the charge separation in nanospace with uneven distribution of donor (D) and acceptor (A) sites. A density functional theory (DFT) calculation elucidated the origin of photogenerated electrons and holes. Moreover, MRFS demonstrates photocatalytic water oxidation ability. The findings in this work open a new avenue for the development of porous polymeric photocatalysts toward highly efficient solar energy conversion.

Investigation of 8-methoxy-3-(4-nitrobenzoyl)-6-propyl-2H-chromen-2-one as a promising coumarin compound for the development of a new and orally effective antileishmanial agent.

Changes in host immunity and parasite resistance to drugs are among the factors that contribute to decreased efficacy of antiparasitic drugs such as the antimonial compounds pentamidine, amphotericin (AMP B) and miltefosine. Bioactive natural products could be alternatives for the development of new drugs to treat neglected human diseases such as leishmaniasis. Natural coumarins and synthetic analogues have shown leishmanicidal activity, mainly in vitro. This study investigated the in vitro and in vivo leishmanicidal activity of synthetic coumarin compounds (C1-C5) in parasites Leishmania (L.) amazonensis and L. (L.) infantum chagasi. The cytotoxicity of these compounds in mammalian cells and their influence on production of reactive oxygen species was also investigated. In vitro assays showed that 8-methoxy-3-(4-nitrobenzoyl)-6-propyl-2H-chromen-2-one (C4) was as active as AMP B mainly in the amastigote form (p < 0.05); C4 presented a selectivity index (65.43) four times higher than C2 (15.4) in L. amazonensis and six times higher (33.94) than C1 (5.46) in L. infantum chagasi. Additionally, coumarin C4 reduced the H2O2 concentration 32.5% more than the control group in L. amazonensis promastigotes during the lag phase of proliferation. No interference of C4 was observed on the mitochondrial membrane potential of the parasites. In vivo, coumarin C4 in corn oil (oral route) led to a reduction in the number of amastigotes from L. infantum chagasi to 1.31 × 106 and 4.09 × 104 in the spleen and liver, respectively (p < 0.05). Thus, C4 represents a candidate for further studies aiming at new treatments of leishmaniasis.

Hybrid microbial electrolytic/UV system for highly efficient organic pollutants removal.

This study for the first time proposed an efficient microbial electrolyte/UV system for Methyl Orange decomposition. With an external applied voltage of 0.2 V and cathode aeration of 20 mL/min, H2O2 could be in-situ generated from two-electron reduction of oxygen in cathode, reaching to 8.1 mg/L in 2 hr and continued to increase. The pollutant removal efficiency of approximate 94.7% was achieved at initial neutral pH, with the activation of •OH in the presence of UV illumination. Although the nature of its guiding principles remain on the vista of practical exploration, this proof-of-concept study provides an alternative operation pattern of solar-microbial hybrid technology for future wastewater treatment from a basic but multidisciplinary view.

Does Acinetobacter calcoaceticus glucose dehydrogenase produce self-damaging H2O2?

The soluble glucose dehydrogenase (sGDH) from Acinetobacter calcoaceticus has been widely studied and is used, in biosensors, to detect the presence of glucose, taking advantage of its high turnover and insensitivity to molecular oxygen. This approach, however, presents two drawbacks: the enzyme has broad substrate specificity (leading to imprecise blood glucose measurements) and shows instability over time (inferior to other oxidizing glucose enzymes). We report the characterization of two sGDH mutants: the single mutant Y343F and the double mutant D143E/Y343F. The mutants present enzyme selectivity and specificity of 1.2 (Y343F) and 5.7 (D143E/Y343F) times higher for glucose compared with that of the wild-type. Crystallographic experiments, designed to characterize these mutants, surprisingly revealed that the prosthetic group PQQ (pyrroloquinoline quinone), essential for the enzymatic activity, is in a cleaved form for both wild-type and mutant structures. We provide evidence suggesting that the sGDH produces H2O2, the level of production depending on the mutation. In addition, spectroscopic experiments allowed us to follow the self-degradation of the prosthetic group and the disappearance of sGDH's glucose oxidation activity. These studies suggest that the enzyme is sensitive to its self-production of H2O2. We show that the premature aging of sGDH can be slowed down by adding catalase to consume the H2O2 produced, allowing the design of a more stable biosensor over time. Our research opens questions about the mechanism of H2O2 production and the physiological role of this activity by sGDH.

Engineered Composite Interfacial Electric Field Boosts Piezocatalysis of Perovskite Ferroelectrics.

Reducing the level of annihilation of electrons and holes is considered to be a feasible strategy to promote piezocatalytic activities. But this strategy is only achieved through cumbersome sample preparation technologies, hindering its practical applications. Herein, we introduce a simple and efficient technique, the conventional solid-state method, to engineer a composite interfacial electric field to solve this problem, and validate it in a composite piezocatalysis composed of potassium sodium niobate ((K, Na)NbO3, KNN) and multiwalled carbon nanotubes (MWCNTs). The KNN-1CNT sample, a piezocatalyst doped with 1 wt % MWCNTs, shows a degradation rate (k) of 127 × 10-3 min-1 for Rhodamine B (RhB) dye and a hydrogen peroxide (H2O2) production rate of 36 µmol/h, about 27 times more than a reported ferroelectric composite piezocatalyst. The excellent piezocatalytic activities are attributed to the good crystallinity, slightly increased oxygen vacancies, and especially the optimal composite interface electric field. Therefore, our proposed method provides a paradigm for obtaining large-scale perovskite piezocatalysts with high piezocatalytic activities.

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.

Fragmented Polymetric Carbon Nitride with Rich Defects for Boosting Electrochemical Synthesis of Hydrogen Peroxide in Alkaline and Neutral Media.

Electrocatalytic oxygen reduction reaction via 2e- pathway is a safe and friendly route for hydrogen peroxide (H2O2) synthesis. In order to achieve efficient synthesis of H2O2, it is essential to accurately control the active sites. Here, fragmented polymetric carbon nitride with rich defects (DCN) is designed for H2O2 electrosynthesis. The multi-type defects, including the sodium atom doping in six-fold cavities, the boron atom doping at N-B-N sites and the cyano groups, are successfully created. Owing to the synergistic effect of these defects, the fragmented DCN achieves a high H2O2 yield of 2.28 mol gcat.-1 h-1 and a high Faradic efficiency of nearly 90% in alkaline media at 0.4 V vs. RHE in H-type cell. In neutral media, the H2O2 concentration produced by DCN can reach 1815 mM within 6 h at a potential of 0.2 V vs. RHE, and the H2O2 production rate of DCN is 0.23 mol gcat.-1 h-1. In addition, DCN shows excellent long-term durability in alkaline and neutral media. This study provides a new approach for the design and development of the boron, nitrogen doped carbon-based electrocatalysts for H2O2 electrochemical synthesis.

Error Awareness in the Volcano Plots of Oxygen Electroreduction to Hydrogen Peroxide.

Electrocatalysis holds the key to the decentralized production of hydrogen peroxide via the two-electron oxygen reduction reaction (ORR, O2g+2H++e-→H2O2aq). However, cost-effective, active, and selective catalysts are still sought after. While density functional theory (DFT) has already led to the discovery of various enhanced catalysts, it has a severe yet often unnoticed drawback: the ill description of O2 and H2O2. Here, we analyze the impact of the errors in those two species on the most widespread activity plots in the literature, namely free-energy diagrams and Sabatier-type volcano plots. Uncorrected or partially corrected gas-phase energies lead to appreciably different activity plots that may provide inaccurate predictions. Indeed, we show for a variety of electrocatalysts that only when the errors in O2 and H2O2 are corrected can DFT mimic the experiments. In sum, this work provides concrete guidelines to avoid a common pitfall of computational models for electrocatalytic hydrogen peroxide production.

Dual Regulation of Charge Separation and the Oxygen Reduction Pathway by Encapsulating Phosphotungstic Acid into the Cationic Covalent Organic Framework for Efficient Photocatalytic Hydrogen Peroxide Production.

Previous research on covalent organic framework (COF)-based photocatalytic H2O2 synthesis from oxygen reduction focuses more on charge carrier separation but less on the electron utilization efficiency of O2. Herein, we put forward a facile approach to simultaneously promote charge separation and tailor the oxygen reduction pathway by introducing phosphotungstic acid (PTA) into the cationic COF skeleton. Experiments verified that PTA, as an electron transport medium, establishes a fast electron transfer channel from the COF semiconductor conductor band to the substrate O2; meanwhile, the reaction path is optimized by its catalytic cycle for preferable dioxygen capture and reduction in oxygen reduction reaction (ORR) kinetics. The existence of PTA promotes the rate and tendency of converting O2 into •O2- intermediates, which is conducive to boosting the photocatalytic activity and selectivity toward the sequential two-step single-electron ORR. As expected, compared to the pristine TTB-EB, the optimal PTA0.5@TTB-EB achieves a 2.2-fold improvement of visible-light-driven photocatalytic performance with a H2O2 production rate of 897.94 µmol·L-1·h-1 in pure water without using any sacrificial agents. In addition, owing to the robust electrostatic interaction and the confinement effect of porous TTB-EB channels, the PTA@TTB-EB composite possessed favorable stability.