Increase In Oxidation Potential Research Articles

Influence of surface properties of transition metal oxides for permanganate activation: Key role of Lewis acid sites

Permanganate (PM) activation to remove contaminants in aqueous solution has gained increasing interest, and effective approaches to enhance its oxidation ability are becoming one of the hot spots. Transition metal oxides (TMOs) stand out as the most potential catalysts, but have received little attention in this area until now. Their mechanism towards PM activation also remains controversial. In this study, a series of TMOs with diverse surface properties were synthesized, and their effectiveness was compared. It was observed that α-MnO2, NiO and Co3O4 exhibited significantly higher rates of degrading sulfadiazine, levofloxacin and phenol through PM activation than CeO2, α-Fe2O3 and CuO. A performance evolution depended on the surface Lewis acid (LA) strength was established, while a less consistent correlation was observed between the degradation rate and other surface properties. Based on electrochemical analysis and density functional theory calculations, the spontaneous adsorption of MnO4- anions on LA sites in TMOs with an increase in oxidation potential of PM was further confirmed. This research would deepen the understanding of PM activation mechanism, and offer new guidance in the design of more efficient catalysts.

Abstract Tu122: Induction of Mitochondrial and Endoplasmic Reticulum Stress in Early Response to High-Fat Diet-Induced Hyperglycemia in Mouse Hearts

Background: Diabetic cardiomyopathy (DCM) is the leading cause of mortality in diabetic patients, accounting for about 80% of the death. Mitochondria and endoplasmic reticulum (ER) play a critical role in cardiomyocyte function, yet their interaction and function in diabetic hearts remains unclear. Hypothesis: We hypothesize that mitochondria and ER stress response are essential in maintaining cardiac function and preventing cardiac remodeling during early diabetic insult in the heart. Methods: Utilizing 6-month-old male and female C57BL/6 mice, we divided them into groups receiving a standard chow diet (N=8) and a 60% high-fat diet (HFD, N=8) for four months. Post-diet, we conducted glucose tolerance tests to verify hyperglycemia. We analyzed heart samples for mitochondrial stress (LonP1, ClpX, ClpP, Afg3l2, spg7, GRP75) and ER stress (XbP1, IRE1a, CHOP, PDI, Hspa5, Dnajb9, Hsp90) markers, along with mitochondrial biogenesis (mtDNA, TFAM, Mt-ND4, and Mt COII levels), and whole heart homogenate oxidative potential by electron paramagnetic resonance (EPR) spin probe (CMH). Between the groups, a p-value < 0.05 was considered significant calculated by one-way ANOVA. Results: HFD significantly increased body weight (p<0.0001) and fasting glucose levels (p<0.0001), confirming hyperglycemia. Among the mitochondrial stress response markers, LonP1 was significantly (p<0.05) elevated in HFD hearts compared to the control. However, the ER stress-associated transcription factors, CHOP and XbP1, were significantly upregulated (p<0.05) in female HFD hearts compared to the control and male groups. Further, EPR analysis showed a significant (p<0.0001) four- and two-fold increase in oxidative potential in the heart homogenate of female and male HFD groups, respectively. However, mitochondrial biogenesis was notably higher, observed only in HFD females compared to other groups. Conclusion: Our study indicates that pre-diabetic hyperglycemia enhances gender-specific mitochondrial biogenesis and triggers mitochondrial and ER stress responses, highlighting the importance of mitochondrial-ER interaction in early DCM and suggesting potential therapeutic avenues.

Environmentally persistent free radicals on photoaging microplastics shortens longevity via inducing oxidative stress in Caenorhabditis elegans

Microplastics (MPs) are ubiquitous environmental contaminants that exert multiple toxicological effects. Current studies have mainly focused on modeled or unaged MPs, which lack environmental relevance. The generation and toxicity of environmentally persistent free radicals (EPFRs) on photoaging polystyrene (PS) have not been well studied, and the role of EPFRs on the toxic effects of photoaged PS is easily ignored. Photoaging primarily produces EPFRs, followed by an increase in reactive oxygen species (ROS) content and oxidative potential, which alter the physicochemical properties of photoaged PS. The mean lifespan and lipofuscin content were significantly altered after acute exposure to photoaged PS for 45 d (PS-45) and 60 d (PS-60) in Caenorhabditis elegans. Intestinal ROS and gst-4::GFP expression were enhanced, concomitant with the upregulation of associated genes. Treatment with N-acetyl-l-cysteine by radical quenching test significantly decreased EPFRs levels on the aged PS and inhibited the acceleration of the aging and oxidative stress response in nematodes. Pearson's correlation analysis also indicated that the EPFRs levels were significantly associated with these factors. Thus, the EPFRs generated on photoaged PS contribute to the acceleration of aging by oxidative stress. This study provides new insights into the potential toxicity and highlights the need to consider the role of EPFRs in the toxicity assessment of photoaged PS.

9-Vinyl-9H-carbazole-3,6-dicarbonitrile

Carbazole polymers attract significant attention as promising luminophores, organic electronic and photovoltaic materials, photo/electrocatalysts, energy storage materials, redox mediators and catalysts. However, the oxidation potential of the commercially available poly(vinylcarbazole) is insufficient for some applications such as high-voltage Li-Ion batteries. We have proposed a monomer for the novel polycarbazole with an increased oxidation potential, which will be compatible with high-voltage cathode materials for Li-Ion. In addition, the proposed polymer is an interesting substrate for the further carbonization to obtain N-doped carbons with a high electrocatalytic activity level.

Molecular Coupling Strategy Achieving In Situ Synthesis of Agglomeration-Free Solid Composite Electrolytes.

Solid composite electrolytes (SCEs) synergize inorganic and polymer merits for viable commercial application. However, inferior filler-polymer interfacial stability ultimately leads to the agglomeration of inorganic particles and greatly impedes Li+ migration. Herein, triethoxyvinylsilane (VTEO) is employed to form a strong chemical interaction between poly(vinylene carbonate) (PVC) and montmorillonite (MMT) via in situ solidification, which eliminates the agglomeration and improves interfacial compatibility. Consequently, the obtained solid composite electrolytes (PVC-s-MMT) achieve increased Li+ conductivity (0.4 mS cm-1 at 25 °C), enhanced transference number (0.74), and increased oxidation potential (5.2 V). The Li/PVC-s-MMT/LiFePO4 cells exhibit outstanding cycling performance (>99.5% after 600 cycles) at 1C at room temperature. Moreover, density functional theory (DFT) calculations are applied to uncover the fast interfacial conducting channels of PVC-s-MMT. Our work provides a feasible in situ synthesis method to prepare agglomeration-free SCEs, which is highly compatible with existing battery production processes of liquid electrolytes.

Hole Catalysis of Cycloaddition Reactions: How to Activate and Control Oxidant Upconversion in Radical-Cationic Diels-Alder Reactions.

In order to use holes as catalysts, the oxidized product should be able to transfer the hole to a fresh reactant. For that, the hole-catalyzed reaction must increase the oxidation potential along the reaction path, i.e., lead to "hole upconversion." If this thermodynamic requirement is satisfied, a hole injected via one-electron oxidation can persist through multiple propagation cycles and serve as a true catalyst. This work provides guidelines for the rational design of hole-catalyzed Diels-Alder (DA) reactions, the prototypical cycloaddition. After revealing the crucial role of hyperconjugation in the absence of hole upconversion in the parent DA reaction, we show how upconversion can be reactivated by proper substitution. For this purpose, we computationally evaluate the contrasting effects of substituents at the three possible positions in the two reactants. The occurrence and magnitude of hole upconversion depend strongly on the placement and nature of substituents. For example, donors at C1 in 1,3-butadiene shift the reaction to the hole-upconverted regime with an increased oxidation potential of up to 1.0 V. In contrast, hole upconversion in C2-substituted 1,3-butadienes is activated by acceptors with the oxidation potential increase up to 0.54 V. Dienophile substitution results in complex trends because the radical cation can be formed at either the dienophile or the diene. Hole upconversion is always present in the former scenario (up to 0.65 V). Finally, we report interesting stereoelectronic effects that can activate or deactivate upconversion via a conformational change.

Tolerance of Silicon Oxide‐Coated Pt/C Catalyst Toward CO and H2S Contamination in Hydrogen for Proton Exchange Membrane Fuel Cells

Platinum on graphitized low surface area carbon (Pt/C) is coated with a silicon oxide thin film and is employed as anode catalyst to manipulate the tolerance of proton exchange membrane fuel cells toward carbon monoxide and hydrogen sulfide contamination. The SiO2 coating, prepared by successive hydrolysis of 3‐aminopropyl‐triethoxisilane and tetraethoxysilane, forms clusters in proximity to Pt in sizes comparable to the catalyst particles, leaving most of the carbon surfaces free. The performance with and without CO is investigated in situ at relative humidities (RH) of 100%, 70%, and 40%. When operated with neat hydrogen, SiO2‐Pt/C shows marginally better performance owing to an improved protonic conduction due to the water retaining hydrophilic SiO2. Upon operation with CO‐contaminated fuel, the SiO2‐Pt/C performs worse than that of Pt/C particularly at high RH. CO stripping measurements reveal an increase in CO oxidation potential for the SiO2‐Pt/C, suggesting an increased CO coverage and consequently higher anode overpotentials during operation with CO‐contaminated fuel. Upon operation with H2S in the fuel, the SiO2 coating extends the lifetime until the cell voltage broke down, which is attributed to the enhanced water retention due to SiO2 and the solubility of sulfuric species.

Permanganate activation with Mn oxides at different oxidation states: Insight into the surface-promoted electron transfer mechanism

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO4) is a hot topic in water treatment. While Mn oxides have been extensively used in Advanced Oxidation Processes through an electron transfer mechanism, the field of KMnO4 activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn2O3 and α-MnO2, exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO4. The MnO4- species initially formed stable complexes with the surface Mn(III/IV) species and showed an increased oxidation potential and electron transfer reactivity, caused by the electron-withdrawing capacity of the Mn species acting as Lewis acids. Conversely, for MnO and γ-Mn3O4 with Mn(II) species, they reacted with KMnO4 to produce cMnO2 with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO2/KMnO4 system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO2 in complicated waters indicated its potential for application in water treatment. Overall, the findings shed light on the development of Mn-based catalysts for organic pollutants degradation via KMnO4 activation and understanding of the surface-promoted mechanism.

Sustainable removal of uranium from acidic wastewater using various mineral raw materials

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

Mineralogical and textural evolution of the Alvo 118 copper-bearing gossan: Implications for supergene metallogenesis in Carajás Mineral Province, Brazil

The Carajás Mineral Province is home to one of the most extensive copper-gold belts globally, where hypogene orebodies were partially transformed into gossans. The Carajás Mountains host mature gossan profiles modified by lateritization. Conversely, the surrounding denuded landscape holds deep immature gossans characterized by generation mechanisms that remain poorly understood. Alvo 118 is a typical deposit from this area, with numerous drill cores available for evaluation. Mineralogical, textural, and mineral chemistry investigations showed that the hypogene mineralization, consisting of massive and disseminated chalcopyrite with minor nukundamite, was partially oxidized. The resulting gossan comprises a range of copper-bearing minerals, including malachite, pseudomalachite, cuprite, tenorite, native copper, ramsbeckite, chrysocolla, and libethenite, with relics of a secondary sulfide zone represented by chalcocite. The host rocks are relatively well-preserved from supergene alteration near the gossan due to the chalcopyrite's low acidifying potential and the deep occurrence of the gossan orebody, resulting in an immature profile. The gossan orebody is sectioned into four zones; the mineral succession of each zone indicates independent evolution, with a general transition from slightly acidic to alkaline conditions and increasing oxidation potential, with local oscillations related to water table fluctuations. This environment was established by the interaction of acid solutions derived from sulfide dissolution with gangue minerals (calcite and apatite) and secondarily with host rocks (chloritites and granodiorites), leading to system buffering. Ti, Mn, Zn, Ni, V, and Co were incorporated into the gossan mainly by goethite, while malachite contains Ba, Ca, Cr, Mn, and Zn. Gold and Pb were detected in goethite, cuprite, tenorite, and native copper. This set of mineralogical zones and mineral successions record an important and unique stage of the supergene evolution of the Carajás Mineral Province, with prominent copper-gold mineralization showing no effects from lateritization.

Mechanism of slag-based silicate fertilizer suppressing methane emissions from paddies

The addition of electron acceptors to boost soil microbes competitive to methanogens could minimize methane (CH4) emissions from paddy soils. To study the microbiological mechanisms underlying the suppression of CH4 emissions, silicate fertilizer made from blast furnace slag that contains electron acceptors, such as Fe, was applied to Japonica and Indica rice at a rate of 2 Mg ha−1. We found that silicate fertilization significantly reduced CH4 emissions from Japonica and Indica rice by 21.1% and 25.7%, respectively, and the decrease in CH4 emissions coincided with an increase in iron reduction in paddy soils. Silicate fertilization markedly suppressed several methanogens and abundance of genes involved in acetoclastic and hydrogenotrphic methanogenesis, albeit the suppression of acetoclastic gene abundance was larger. Conversely, it increased methanotrophs, their gene abundance, and CH4 oxidation potential of paddy soils, which could be explained by an increase in root oxidation potential. Iron-reducing and oxidizing microbes, and their gene abundance significantly increased by silicate fertilization. Structural equation modeling showed that the suppression of CH4 emissions was mainly due to the competitive inhibition of methanogens by iron-reducing bacteria and the proliferation of methonotrophs. These findings have implications for understanding the CH4 biogeochemistry under silicate fertilization, as it has the potential to mitigate CH4 emissions from paddies.

Comparative Analysis of Mononuclear 1:1 and 2:1 Tetravalent Actinide (U, Th, Np) Complexes: Crystal Structure, Spectroscopy, and Electrochemistry.

Six mononuclear tetravalent actinide complexes (1-6) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (HLpr). The HLpr is treated with tetravalent actinide elements in varied stoichiometries to afford mononuclear 1:1 complexes [MCl3-Lpr·nTHF] (1-3) and 2:1 complexes [MCl2-L2pr] (4-6) (M = Th4+ (1 and 4), U4+ (2 and 5), and Np4+ (3 and 6)). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography. UV-vis spectroscopy revealed more red-shifted absorption spectra for 2:1 complexes as compared to 1:1 complexes. 1H NMR of Th(IV) complexes exhibit diamagnetic spectra, whereas U(IV) and Np(IV) complexes revealed paramagnetically shifted 1H NMR. Interestingly, NMR signals are paramagnetically shifted between -70 and 40 ppm in 2 and 3 but are confined within -35 to 25 ppm in 2:1 complexes 5 and 6. Single-crystal structures for 1:1 complexes revealed an eight-coordinated Th(IV) complex (1) and seven-coordinated U(IV) (2) and Np(IV) (3) complexes. However, all 2:1 complexes 4-6 were isolated as eight-coordinated isostructural molecules. The geometry around the Th4+ center in 1 is found to be trigonal dodecahedral and capped trigonal prismatic around U(IV) and Np(IV) centers in 2 and 3, respectively. However, An4+ centers in 2:1 complexes are present in dodecahedral geometry. Importantly, 2:1 complexes exhibit increased bond distances in comparison to their 1:1 counterparts as well as interesting bond modulation with respect to ionic radii of An(IV) centers. Cyclic voltammetry displays an increased oxidation potential of the ligand by 300-500 mV, after coordination with An4+. CV studies indicate Th(IV)/Th(II) reduction beyond -2.3 V, whereas attempts were made to identify redox potentials for U(IV) and Np(IV) centers. Spectroscopic binding studies reveal that complex stability in 1:1 stoichiometry follows the order Th4+ ≈ U4+ > Np4+.

Iron plays a role in sulfasalazine-induced ferroptosis with autophagic flux blockage in K7M2 osteosarcoma cells.

Osteosarcoma is the most common primary bone malignancy in children and young adults, with a very poor prognosis. It is of great importance to develop targeted therapeutic strategies for osteosarcoma. Sulfasalazine (SAS) is an FDA-approved drug for the treatment of Crohn's disease, rheumatoid arthritis, and inflammatory bowel disease. It acts as an inhibitor of cystine/glutamate system, which is important for cellular glutathione synthesis and maintenance of GPx4 activity. Nowadays, SAS has been repurposed as an antitumor drug for inducing ferroptosis in cancers. This study aimed to uncover the role of iron in SAS-induced ferroptotic cell death in K7M2 osteosarcoma cells. Herein, SAS led to an iron-dependent cell death mode in K7M2 cells, accompanied with decreased antioxidant defense and increased production of cytosolic and lipid reactive oxygen species. Results also showed that iron supplement with ferric ammonium citrate (FAC) or ferrous ammonium sulfate (FAS) exacerbated the declined cell viability of SAS-treated K7M2 cells, while in the case of iron depletion, it weakened such suppression. Furthermore, iron promoted SAS-induced alterations on cell cycle, cytoskeleton, mitochondria morphology and function, and redox system. Iron also induced the dysfunction of autophagic activity in SAS-treated K7M2 cells. In conclusion, our study uncovered the essential role of iron in SAS's effects on K7M2 cells and provided the potential combined therapy of inhibition on antioxidant defense and an increase in oxidative potential, which further disturbed the redox status in tumor cells.

Preparation of WO3 gel electrochromic device by simple two-step method

Gel electrochromic devices (gel ECDs) have promising application prospects in smart windows due to their energy-saving effects and superior electrochromic performance. However, the rapid preparation of gel electrolytes is one of the reasons limiting the further promotion of gel ECDs. In this work, we proposed a simple doctor blade method to prepare PVDF gel electrolytes with high ionic conductivity (3.7 * 10−3 S cm−1) and excellent mechanical properties (268% strain), accompanied by high transmittance (exceeding 95% within 600–1100 nm). And we also prepared WO3 gel ECDs by using PVDF gel electrolytes as electrolyte layer. Compared with liquid ECDs, WO3 gel ECDs' lifetime has increased by 33%, mainly due to the increased oxidation potential with PVDF gel electrolyte addition, enhancing oxidation resistance. In addition, the large-area flexible gel ECDs (6 * 10 cm2) were assembled, which provides practical guidance for preparing large-area flexible gel ECDs in the future.

The insights into the catalytic performance of rare earth metal ions on lactic acid formation from biomass via microwave heating

• Ln 3+ showed special activity for lactic acid formation from biomass. • The activity increased monotonically with the atomic number of Ln 3+ . • Smaller ionic radius of Ln 3+ led to stronger interaction with glucose. • Ln 3+ with smaller ionic radius exhibited higher electron-withdrawing ability. • The orbital-stabilization ability of transition state increased with atomic number. The unique properties of rare earth metal offer attractive potentials for the application as catalyst in biomass valorization. In present work, we found that rare earth metal ions exhibited specific catalytic activity for lactic acid production from biomass, giving 75.9% and 71.0% carbon molar yield of lactic acid from glucose and furfural residue, respectively. The activity of lanthanide(III) ions increased monotonically with the atomic number, as well as the decreasing ionic radius, from La 3+ to Lu 3+ . The increasing oxidation potential with atomic number might facilitate the disproportionation reaction in glucose conversion via an intramolecular H-shift. DFT calculation further revealed that smaller ionic radius of lanthanide(III) ions led to stronger interaction between lanthanide(III) ions and glucose/fructose, as well as the less composition of 4 f in LUMO that enabled more activation of glucose. More importantly, lanthanide(III) with smaller ionic radius exhibited higher electron-withdrawing ability from the oxygen atom in -C = O. This enhanced the electrophilicity of C2, C3, and C4 atoms, and led to the more exposure especially for C4 atom, thereby significantly weakening C3-C4 bond. In addition to the increasing orbital-stabilization ability at the bond-breaking site in the corresponding transition state with atomic number, the energy barrier for C3-C4 cleavage in fructose was greatly reduced by heavy lanthanide(III) ions. These factors contributed to the special activity for lactic acid formation from biomass. The insights in this work might give some useful clues for the widespread application of rare earth metal in biomass valorization.

Time-Related Alteration of Aqueous-Phase Anthracene and Phenanthrene Photoproducts in the Presence of TiO2 Nanoparticles.

Polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) are photoactive environmental pollutants that can contaminate aquatic environments. Aqueous-phase interactions between PAHs and TiO2-NPs are of interest due to their emerging environmental relevance, particularly with the deliberate application of TiO2-NPs to remediate pollution events (e.g., oil spills). Our objective was to investigate anthracene (ANT) and phenanthrene (PHE) photoproduct formation and transformation following ultraviolet A (UVA) irradiation in the presence and absence of TiO2-NPs. ANT and PHE solutions were prepared alone or in combination with TiO2-NPs, UVA-irradiated, and either exposed to larval zebrafish or collected for chemical analyses of diverse hydroxylated PAHs (OHPAHs) and oxygenated PAHs (OPAHs). The expression profiles of genes encoding for enzymes involved in PAH metabolism showed PAH-specific and time-dependent inductions that demonstrated changes in PAH and photoproduct bioavailability in the presence of TiO2-NPs. Chemical analyses of PAH/NP solutions in the absence of zebrafish larvae identified diverse photoproducts of differing size and ring arrangements, which suggested photodissociation, recombination, and ring re-arrangements of PAHs occurred either during or following UVA irradiation. Both ANT and PHE solutions showed heightened oxidative potential following irradiation, but TiO2-NP-related increases in oxidative potential were PAH-specific. The exploitation of multiple analytical methods provided novel insights into distinct PAH photoactivity, TiO2-NP influence on photoproduct formation in a PAH-specific manner, and the significant role time plays in photochemical processes.

Preparation of nanoporous Cu/Cu2O composites by anodic oxidation and their electrocatalytic performance towards methanol oxidation

Nanoporous Cu/Cu2O (NP-Cu/Cu2O) composites with a three-dimensional bicontinuous heterostructure are prepared by anodic oxidation of nanoporous copper (NP-Cu). The effects of electrolyte (pH 7–13) and anodic oxidation potential (0.1–1.0 V vs. SCE) on the morphologies and electrocatalytic performances of NP-Cu/Cu2O composites are investigated. The Cu2O/Cu content ratio increases with the increase of anodic oxidation potential, but decreases with the increase of pH value. The pore/ligament width ratio of NP-Cu/Cu2O composites prepared in pH 9–13 electrolytes is in the range of 0.6–1.0. The onset potential of NP-Cu/Cu2O negatively shifts, and the oxidation peak current density of NP-Cu/Cu2O composites prepared in pH 7–11 electrolytes is higher than that of NP-Cu. NP-Cu/Cu2O composite prepared in pH 11 electrolyte at anodic oxidation potential of 0.7 V exhibits the best electrocatalytic performance towards methanol oxidation.

Investigating the stability of graphitic carbon materials in electrocatalysis using electronic structure methods

As carbon materials are cheap and versatile, they are widely used materials for heterogeneous catalysis in general and for electrocatalysis in particular. However, they are prone to degradation, particularly under oxidative conditions. While electronic structure theory has been applied to study structure and thermodynamics in materials science, in many cases kinetic stability is the key feature which is associated with mechanisms and barriers. To compute these in aqueous medium and under electrode potential, we devise a DFT + implicit solvation scheme using a constant potential approach. Considering both pH and potential on a polycyclic aromatic hydrocarbon (PAH) model, we find a low energy pathway for graphitic carbon degradation. Depending on the pH and the potential, barrierless hydroxylation followed by deprotonation is observed at the PAH’s edges. At low pH and potential, the material is expected to remain pristine, at intermediate potential it exhibits few ketone and alcohol groups at its edges, and at high potential no barriers are found for hydroxylation processes, leading to CO2 formation and significant deformation of the material. We also observe smaller PAHs and nitrogen doped PAHs exhibit increased stability, which we attribute to their increased oxidation potentials.

Filamentous green algae Spirogyra regulates methane emissions from eutrophic rivers.

Excessive growth of filamentous green algae in rivers has attracted much attention due to their functional importance to primary production and carbon cycling. However, comprehensive knowledge of how filamentous green algae affect carbon cycling, especially the CH4 emissions from river ecosystems, remains limited. In this study, incubation experiments were conducted to examine the factors regulating CH4 emissions from a eutrophic river with dense growth of filamentous green algae Spirogyra through combinations of biogeochemical, molecular biological, and stable carbon isotope analyses. Results showed that although water dissolved oxygen (DO) in the algae+sediment (A+S) incubation groups increased up to 19 mg L-1, average CH4 flux of the groups was 13.09 μmol m-2 day-1, nearly up to two times higher than that from sediments without algae (S groups). The significant increase of sediment CH4 oxidation potential and methanotroph abundances identified the enhancing sediment CH4 oxidation during Spirogyra bloom. However, the increased water CH4 concentration was consistent with depleted water [Formula: see text] and decreased apparent fractionation factor (αapp), suggesting the important contribution of Spirogyra to the oxic water CH4 production. It can thus be concluded that high DO concentration during the algal bloom promoted the CH4 consumption by enhancing sediment CH4 oxidation, while algal-linked oxic water CH4 production as a major component of water CH4 promoted the CH4 emissions from the river. Our study highlights the regulation of Spirogyra in aquatic CH4 fluxes and will help to estimate accurately CH4 emissions from eutrophic rivers with dense blooms of filamentous green algae. Graphical abstract.

Catalytic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran using V-containing heteropoly acid catalysts

2,5-Diformylfuran (DFF) is an attractive and challenging compound that can be synthesized with good selectivity by the oxidation of bio-based 5‐hydroxymethylfurfural (5-HMF) using specific catalysts. Vanadium-containing heteropoly acids (PMoV HPAs) are highly active oxidation catalysts whose activity can be tuned by changing vanadium(V) (VV) content. This study reports the preparation of a number of PMoV HPAs with different VV amount and type of outer-sphere cation and investigating their catalytic performance in 5-HMF-to-DFF conversion. The characterization of synthesized HPAs by simple instrumental methods (pH-measurement, potentiometry, and titration analysis) and NMR revealed retaining Keggin structure and increasing oxidation potential with rising VV amount. The complete optimization of reaction conditions allowed one to reach a DFF yield of 92% using Co2H6P3Mo18V7O84 at 110 °C in water/MIBK for 90 min under atmospheric pressure. The described method of 5-HMF oxidation is based on using effective soft oxidants that can be easily recycled and reused at least five times without significant loss of catalytic activity.