Cyclic Redox Research Articles

Enhanced removal of sulfamethoxazole by an anaerobic/aerobic SBR with an oxidation-reduction cycle of magnetite

This study aims to evaluate an advanced activated sludge process that integrates activated sludge process with biological Fenton reaction to enhance antibiotic treatment in wastewater. The target antibiotic used in this study was sulfamethoxazole (SMX). An anaerobic/aerobic sequencing batch reactor (SBR) containing magnetite was proposed. Anaerobic and aerobic sludge was exposed to alternating anaerobic and aerobic conditions for treating synthetic wastewater containing 1 mg/L SMX and 405 mg/L chemical oxygen demand (COD). Stable and enhanced SMX removal was observed in the SBRs with magnetite, which achieved more than 86% removal, 40% higher than that without magnetite. Magnetite dosage at 1 and 3 g/L did not significantly affect SMX removal. Fluorescence observations indicated the formation of hydroxyl radicals (·OHs) in the matrix of magnetite-sludge aggregates. This elucidated the primary mechanism of the significant SMX removal. It was shown that Fe (III) in the magnetite was reduced to Fe (II) and then oxidized to Fe (III) under anaerobic and aerobic conditions respectively, creating continuous oxidation-reduction of magnetite. Moreover, hydrogen peroxide (H2O2) was microbially generated under aerobic conditions and drove the biological Fenton reaction. Approximately 90% of COD was removed under steady-state conditions in the SBRs containing magnetite. The higher COD removal in SBRs with magnetite was due to microbial Fe (III) reduction.

Synergistic effect of Ce-Mn on cyclic redox reactivity of pyrite cinder for chemical looping process

Pyrite cinder (Pc) is a solid waste from sulfuric acid production. The cleaner and efficient utilization of pyrite cinder is of great significance to achieve the recycling of industrial solid waste. In this study, we prepared different doped pyrite cinder-based oxygen carriers (Ce-Pc, Ce-Mn-Pc, Mn-Pc), and investigated the synergistic effect of Ce-Mn on cyclic redox reactivity of pyrite cinder in chemical looping process. The synergy between Ce and Mn in the modified pyrite cinder for fuel combustion reactivity was discussed in detail. The addition of Mn enhanced the cyclic stability of CeO2-doped pyrite cinder during sequential chemical looping cycles. The synergistic effect of Ce-Mn facilitated the generation of oxygen vacancies, which improved the mobility of lattice oxygen and enhanced the reducibility. The results indicated that the effect of CeO2 and MnOx on the cyclic redox reactivity of pyrite cinder was relatively weak compared with the synergistic effect of CeO2-MnOx. In addition, Ce-Mn could prevent grain growth and agglomeration of pyrite cinder. After the 20th cycle, the oxygen carrying capacity (OCC) of raw pyrite cinder decreased significantly from 3.63% in the 1st cycle to 2.45%. During the multiple redox cycles, the Ce-Mn-Pc presented the highest OCC (about 3.6%). The Ce-Mn co-doped pyrite cinder presented excellent cyclic durability with CH4 conversion more than 85% during successive cycles. This study provides an approach for the rational design of pyrite cinder-based oxygen carriers with high cyclic redox reactivity and durability.

Mesoporous Silica Encapsulated Platinum-Tin Intermetallic Nanoparticles Catalyze Hydrogenation with an Unprecedented 20% Pairwise Selectivity for Parahydrogen Enhanced Nuclear Magnetic Resonance.

Supported noble metals offer key advantages over homogeneous catalysts for in vivo applications of parahydrogen-based hyperpolarization. However, their performance is compromised by randomization of parahydrogen spin order resulting from rapid hydrogen adatom diffusion. The diffusion on Pt surfaces can be suppressed by introduction of Sn to form Pt-Sn intermetallic phases. Herein, an unprecedented pairwise selectivity of 19.7 ± 1.1% in the heterogeneous hydrogenation of propyne using silica encapsulated Pt-Sn intermetallic nanoparticles is reported. This high level of selectivity exceeds that of all supported metal catalysts by at least a factor of 3. Moreover, the pairwise selectivity for alkyne hydrogenation is about 2 times higher than for alkene hydrogenation, an observation attributed to the higher coverage of the former and its effect on diffusion. Lastly, PtSn@mSiO2 nanoparticles exhibited improved coking resistance, and any loss of activity is shown to be fully reversible through high-temperature oxidation-reduction cycling.

Mesoporous silica-encaged ultrafine ceria–nickel hydroxide nanocatalysts for solar thermochemical dry methane reforming

Reforming of methane to produce synthesis gas for the Fischer–Tropsch process provides an alternative to fossil fuels. Silica-encaged ceria–nickel hydroxide catalysts were produced by an in situ synthesis method to obtain ultrafine bimetallic species dispersed evenly within the mesoporous silica matrix. Dry reforming and reduction-oxidation cycling was undertaken with the materials. Catalysts with high content of nickel showed good activity during dry reforming, with conversions rates close to equilibrium in equimolar conditions. Insignificant deactivation of the catalysts was observed over 5 h and 50 h of reaction at 900 °C. Syngas production via reduction–oxidation cycling was shown to be insignificant as compared to continuous catalytic reforming.

CO2 gasification of petroleum coke with use of iron-based waste catalyst from F-T synthesis

In this study, the influence of iron-based waste catalyst (IWC) from F-T synthesis as a cheap additive on the gasification reaction characteristics of petroleum coke (PC) with CO2 at 1000–1300°C was investigated by thermogravimetric analyzer. The gasification kinetics of PC was analyzed by free model method. The surface complexes of PC were determined through temperature-programmed desorption (TPD) methods to reveal the mechanism of IWC catalytic PC gasification. The results show that IWC is an efficient PC gasification catalyst and can reduce the activation energy of PC CO2 gasification. The induction of iron in IWC makes the surface of PC have more activated carbon sites, thereby forming more oxygen-containing intermediates, and the cyclic redox reaction of iron can act as an oxygen carrier to accelerate the reaction of CO2 and carbon, both of these may be the essential reasons for the CO2 gasification of PC catalyzed by IWC.

Novel magnetic manganese-iron materials for separation of solids used in high-temperature processes: Application to oxygen carriers for chemical looping combustion

Different chemical looping processes allow burning or gasify solid fuels with inherent CO2 capture because the oxygen is transferred from air to the fuel through a metal oxide based material, which is named oxygen carrier. To improve process efficiency and CO2 capture, highly reactive synthetic materials could be used. One of the challenges of using solid fuels is the oxygen carrier separation from the ash, because loss of oxygen carrier particles is expected during ash drainage. So, their costs would have necessary the recovery of the synthetic oxygen carrier. Mn-Fe based materials show magnetic properties in the spinel phase, which could be used for a magnetic separation. When these Mn-Fe materials are used at high temperature under oxidizing or reducing atmospheres, stability of the spinel phase should be guaranteed in order to take advantage of the magnetic properties. The design of low reactive Mn-Fe based materials with magnetic properties, which can be used as a support material for other highly reactive and active phases, was the main objective of this work. In this sense, the support must have high crushing strength, low reactivity under oxidation and reduction atmospheres at high temperatures and permanent magnetism at low temperature for solids separation. Materials prepared with different Mn/(Mn + Fe) molar ratios and calcination conditions were evaluated regarding mechanical strength, inerticity and magnetic properties. A Cu-based oxygen carrier prepared on the optimal support was prepared and evaluated along 240 oxidation-reduction cycles in thermobalance (25 h experiment), exhibiting suitable mechanical and magnetic characteristics as well as high reactivity.

Degradation of methylene blue through Fenton-like reaction catalyzed by MoS2-doped sodium alginate/Fe hydrogel

In this study, a low-cost and high-performance MoS2/sodium alginate (SA)/Fe (MSF) hydrogel catalyst was prepared. It was found that the MSF hydrogel could efficiently catalyze the degradation of methylene blue (MB) through the Fenton reaction without the addition of Fe2+. The reaction was initiated by Fe2+ which was derived from the cyclic redox reaction between MoS2 and Fe3+ and produced large quantities of ·OH to degrade the MB. The effect of MoS2 concentration, FeCl3·6H2O concentration, H2O2 dosage, solution pH, and light on the degradation was systematically studied. The MoS2 concentration of 0.5 mg/ mL, FeCl3·6H2O concentration of 0.25 g/mL, 50 μL H2O2, and the pH of 4.0 were the optimized parameters. Moreover, it was found that the MB degraded faster under the infrared radiation. The MB removal rate reached as high as 98% within 15 min in the presence of a low concentration of H2O2 and the procedure could be repeated 5 times. The MSF hydrogel provided an effective and simple strategy for the sustainable degradation of organic pollutants in wastewater.

Sensing Alzheimer’s Disease Utilizing Au Electrode by Controlling Nanorestructuring

This paper reports the development of Alzheimer’s disease (AD) sensor through early detection of amyloid-beta (Aβ) (1–42) using simple nanorestructuring of Au sheet plate by oxidation-reduction cycle (ORC) via the electrochemical system. The topology of Au substrates was enhanced through the roughening and Au grains grown by a simple ORC technique in aqueous solutions containing 0.1 mol/L KCl electrolytes. The roughened substrate was then functionalized with the highly specific antibody β-amyloid Aβ (1–28) through HS-PEG-NHS modification, which enabled effective and direct detection of Aβ (1–42) peptide. The efficacy of the ORC method had been exhibited in the polished Au surface by approximately 15% larger electro-active sites compared to the polished Au without ORC. The ORC polished structure demonstrated a rapid, accurate, precise, reproducible, and highly sensitive detection of Aβ (1–42) peptide with a low detection limit of 10.4 fg/mL and a wide linear range of 10−2 to 106 pg/mL. The proposed structure had been proven to have potential as an early-stage Alzheimer’s disease (AD) detection platform with low-cost fabrication and ease of operation.

Redox reaction between solid-phase humins and Fe(III) compounds: Toward a further understanding of the redox properties of humin and its possible environmental effects

Redox reactions between humic substances and Fe(III) compounds play a critical role in the biogeochemical cycle of pollutants. Most humic substances in soils and sediments are in a solid form (i.e. humin (HM)). In order to assess the contribution of electron shuttling via HM within the electron transfer network in natural environments and to predict environmental fate of pollutants associated with iron oxides, it is necessary to understand the electron transfer processes from HM to the environmentally relevant Fe(III) minerals, and to examine the redox reversibility of HM. The results of this study demonstrated that non-reduced HMs could only donate electrons to dissolved ferric citrate and poorly crystalline ferrihydrite, but reduced HMs could also reduce hematite and magnetite that had high crystallinity. The degree of reduction depended on the difference in redox potential and the crystallinity of the Fe(III) compounds. The electron-accepting capacities of different HMs correlated well with their organic carbon content, and quinones and Fe-bound organic component were important electron-accepting groups in HMs. Furthermore, the redox reversibility experiments demonstrated that HMs could maintain stable electron transfer capacities over three reduction-oxidation cycles, indicating that the HM could be an environmentally sustainable electron shuttle. Our results suggest that (1) HM may play an unrecognized and important role in biogeochemical cycles of pollutants in Fe(III) mineral-rich environments; (2) electron shuttling through HM to ferric citrate and ferrihydrite can occur even in the presence of O2; and (3) HM would be a promising material for environmental remediation.

Recent Developments in the Syntheses of Aluminum Complexes Based on Redox-Active Ligands

Applications of aluminum as a catalyst for organic/inorganic transformation reactions are ideal because of its easy availability, inexpensiveness, and non-toxicity. However, successful implementation of Al(III) complexes as catalysts require an easy reduction-oxidation cycle between Al(III) and Al(I). Nevertheless, molecular complexes of Al(I) are not common, often require special efforts for their synthesis and isolation. Additionally, the Al(I)→Al(III) oxidation reaction is facile whereas the corresponding Al(III)→Al(I) reduction occurs only under highly reducing conditions. This creates a problem in developing Al(I)/Al(III) couple catalytic cycle for practical application. But, for aluminum complexes to be applicable in redox transformations, complexes must readily undergo reversible oxidation and reduction processes. One can envision applying a redox-active ligand where instead of aluminum the ligand would be reversibly oxidized and reduced to perform a certain electron transfer process. So, the development of a large pool of aluminum complexes supported by redox-active ligands is very important. In this review article, we have summarized recent developments on the syntheses of aluminum complexes with some redox-active ligands. This may help in designing new catalysts for future applications.

The HBx protein from hepatitis B virus coordinates a redox-active Fe-S cluster

The viral protein HBx is the key regulatory factor of the hepatitis B virus (HBV) and the main etiology for HBV-associated liver diseases, such as cirrhosis and hepatocellular carcinoma. Historically, HBx has defied biochemical and structural characterization, deterring efforts to understand its molecular mechanisms. Here we show that soluble HBx fused to solubility tags copurifies with either a [2Fe-2S] or a [4Fe-4S] cluster, a feature that is shared among five HBV genotypes. We show that the O2-stable [2Fe-2S] cluster form converts to an O2-sensitive [4Fe-4S] state when reacted with chemical reductants, a transformation that is best described by a reductive coupling mechanism reminiscent of Fe-S cluster scaffold proteins. In addition, the Fe-S cluster conversions are partially reversible in successive reduction–oxidation cycles, with cluster loss mainly occurring during (re)oxidation. The considerably negative reduction potential of the [4Fe-4S]2+/1+ couple (−520 mV) suggests that electron transfer may not be likely in the cell. Collectively, our findings identify HBx as an Fe-S protein with striking similarities to Fe-S scaffold proteins both in cluster type and reductive transformation. An Fe-S cluster in HBx offers new insights into its previously unknown molecular properties and sets the stage for deciphering the roles of HBx-associated iron (mis)regulation and reactive oxygen species in the context of liver tumorigenesis.

Ethane conversion in the presence of CO2 over Co-based ZSM-5 zeolite: Co species controlling the reaction pathway

Two cobalt-based ZSM-5 catalysts CoZ-IE and CoZ-IM were prepared by ion-exchange and incipient wetness impregnation method, respectively, and characterized by XRD, N2 adsorption, TEM, XPS, UV–vis, H2-TPR and Py-IR. The catalytic performance towards ethane conversion over the two catalysts in the presence of CO2 was compared. Despite of their similar textual properties and Co contents, the product distributions over the two catalysts were quite different. Ethylene with high selectivity of 95% formed over CoZ-IE while syngas was produced as the main product on CoZ-IM, indicating dry reforming becomes the dominant reaction pathway instead of dehydrogenation. The difference pathway can be ascribed to the different nature of Co species in two catalysts. The isolated Co2+ anchored at zeolitic framework in CoZ-IE is quite stable and can only act as Lewis acid sites for ethane dehydrogenation. In contrast, the cobalt oxides on the zeolitic surface in CoZ-IM can proceed oxidation-reduction cycles in the CO2-C2H6 system, facilitating the activation of CO2 and the scission of C−C bonds, leading to the dry reforming of ethane.

Reticulated Porous Perovskite Structures for Thermochemical Solar Energy Storage

AbstractThe inherent capability of concentrated solar power (CSP) plants for sensible thermal energy storage ensures their continuous operation and is considered their most crucial competitive edge versus other renewable energy sources. The storage density of air‐operated CSP plants can be significantly increased by hybridizing sensible with thermochemical storage of solar heat, exploiting reversible air–solid oxide reduction–oxidation reactions. Thermochemical storage‐relevant‐protocols testing of in‐house manufactured lab‐scale reticulated porous ceramic foams made entirely of CaMnO3 perovskite reveals fully reversible reduction‐oxidation in up to 46 cycles between 300 and 1100 °C under air, without any deterioration of the foams’ structural integrity and exploitable endothermic/exothermic heat effects between 890 and 920 °C linked to an orthorhombic‐to‐cubic phase transition. Dilatometry experiments with CaMnO3 bars under identical cyclic conditions demonstrate the correlation of this phase transition to an increase in the thermal expansion coefficient but nevertheless, complete recovery of the initial specimen dimensions upon completion of a full heat‐up/cooldown redox cycle. The possibility of shaping into sturdy reticulated porous ceramic structures which exhibit complete dimensional reversibility upon cyclic redox operation, combined with the low cost, earth abundance and environmentally benign character of the constituting elements, render such perovskite compositions extremely attractive for the manufacture of large‐scale porous structured objects for exploitation in various thermochemical processes.

3D Porous Graphene Films with Large‐Area In‐Plane Exterior Skins

AbstractConstruction of macroscopic 3D architectures of graphene is crucial to harness the advantageous properties of planar 2D graphene and to enable integration to many conventional and novel applications. Ideally, the 3D structure of graphene should be free of defects, covalently interconnected, and can be produced at large‐scale. Among various assembly techniques, fabrication using chemical vapor deposition (CVD) enables the production of high‐quality graphene where selection of template is the key that determines its consequent crystalline quality and structural morphology. Herein, a new method is presented to synthesize high‐quality porous graphene film by incorporating an in situ reduction–oxidation cycling treatment to generate micrometer‐sized pores on commercial Ni foil using an all‐CVD process route. Owing to the unique morphological features of the modified Ni template, the graphene film exhibits a holey surface with large‐area exterior skin coverage of >94% and many interconnected ligaments within its porous interior. This extraordinary configuration gives rise to superior in‐plane electrical conductivity despite its low density. In comparison to state‐of‐the‐art materials for electromagnetic interference shielding, this porous graphene film is among the best performing materials with a specific shielding effectiveness of >550 dB cm3 g−1 and absolute effectiveness of >220 000 dB cm2 g−1.

Solar bipolar cell facilitating carbon dioxide for efficient coproduction of electricity and syngas

Herein, a novel solar system is first reported for the efficient generation of syngas and electricity by feeding solar energy plus carbon dioxide into a solar bipolar cell. The solar bipolar cell, fully driven by solar energy, is a rechargeable cycle system to realize the highly efficient co-production of electricity and syngas. The solar bipolar cell consists of hydroxide molten Cell (Ⅰ) for hydrogen production and carbonate molten Cell (Ⅱ) for carbon monoxide production, simultaneously plus the a generation of rechargeable electricity. Due to the combined utilization of solar thermal and electric effect, the solar system can charged/recharged by the potential difference of the cyclic redox reaction. The system could store electric energy (Charge) and generate syngas under solar and then release electric energy (Discharge) and syngas during not input of solar energy. The charge-discharged processes could be operated circularly for a release of fuel. The results demonstrated that the solar bipolar cell presented an overall maximum Coulomb efficiency of 85% at 450/800 °C. This work provides a new route to design a system which combines the renewable energy with the undesirable carbon dioxide for the clean and pollution-free discharged products.

Time series proteome profile analysis reveals a protective role of citrate synthase in angiotensin II-induced atrial fibrillation.

Background:Angiotensin (Ang) II and elevated blood pressure are considered to be the main risk factors for atrial fibrillation. However, the proteome profiles and key mediators/signaling pathways involved in the development of Ang II-induced atrial fibrillation remain unclear.Methods:Male wild-type C57BL/6 mice (10-week old) were infused with Ang II (2000 ng/kg per min) for 1, 2, or 3 weeks, respectively. Time series proteome profiling of atrial tissues was performed using isobaric tags for relative and absolute quantitation and liquid chromatography coupled with tandem mass spectrometry.Results:We identified a total of 1566 differentially expressed proteins (DEPs) in the atrial tissues at weeks 1, 2, and 3 after Ang II infusion. These DEPs were predominantly involved in mitochondrial oxidation-reduction and tricarboxylic acid cycle in Ang II-infused atria. Moreover, coexpression network analysis revealed that citrate synthase, a rate-limiting enzyme in the tricarboxylic acid cycle, was localized at the center of the mitochondrial oxidation-reduction process, and its expression was significantly downreguated in Ang II-infused atria at different time points. Cardiomyocyte-specific overexpresion of citrate synthase markedly reduced atrial fibrillation susceptibility and atrial remodeling in mice. These beneficial effects were associated with increased ATP production and mitochondrial oxidative phosphorylation system complexes I–V expression and inhibition of oxidative stress.Conclusion:The current study defines the dynamic changes of the DEPs involved in Ang II-induced atrial fibrillation, and identifies that citrate synthase plays a protective role in regulating atrial fibrillation development, and increased citrate synthase expression may represent a potential therapeutic option for atrial fibrillation treatment.

Fluidized Bed Technology: Challenges and Perspectives

Fluidized beds are recognized as important gas-solid contacting technology in chemical synthesis reactors, in combustion/gasification/pyrolysis of coal and biomass, in multiple drying applications, in solar thermal energy capture and storage, and more recently also in the production of hydrogen by either catalytic steam reforming of organic feedstock, or thermal water splitting using oxidation-reduction cycles. Although the process understanding and operational experience has significantly been expanded over the past decades, some challenges remain the be dealt with, as discussed in the paper. These challenges are mostly of gas-solid hydrodynamic nature.

Removal, Recovery, and Recycles of Au(III) from Tetrachloroauric Acid Solution Using Immobilized <i>Pseudomonas</i> Cells by Biomineralization and Thiourea Oxidation

Removal, recovery, and recycles of gold(III) from aqueous tetrachloroauric acid solution using immobilized <i>Pseudomonas saccharophila</i> was investigated. The effect of pH, cell amounts on gold removal, and the time course of gold removal by <i>P. saccharophila</i> cells, which removed large amounts of gold from a solution containing hydrogen tetrachloroauric(III) acid were reported in detail. Additionally, to approve the amount of gold recovery much higher, the removal of gold(III) by biosorption and biomineralization from aqueous systems using microbial cells, gold(III) removal by those using microbial cells was investigated. The oxidative recovery of gold after reduced gold(0) by the oxidation using aqueous thiourea solution, and recycles of gold reduction-oxidation cycles were also investigated.

Микро- и наномодификация структуры при циклической окислительно-восстановительной обработке пористого никеля, спеченного с использованием порообразователя

By performing high-temperature cyclic oxidation-reduction (redox) post-treatment of biporous nickel fabricated in the sintering-dissolution process using micron nickel powder and sodium chloride as a space holder, permeable materials with multilevel hierarchical porosity were created. After an oxidation stage in an air atmosphere, a porous material with a core-shell Ni – NiO structure and a cellular underlayer of micron-sized Kirkendall pores was formed. Subsequent reduction in hydrogen led to the formation of a developed nanoporous bumpy surface at sintered nickel particles. The obtained metallic nickel and ceramic nickel-oxide materials contain a hierarchical system of pores of different origin of four types: (a) macropores formed after the removal of the space holder; (b) interparticle micropores remaining due to incomplete sintering of the nickel powder; (c) intraparticle Kirkendall pores created at the oxidation stage and (d) nanopores formed during reduction. Depending on the dispersion of the space holder, the porosity and hydraulic permeability of the nickel samples were 80 – 82 % and 35·10–12 – 101·10–12 m2, respectively.

Ru-promoted perovskites as effective redox catalysts for CO2 splitting and methane partial oxidation in a cyclic redox scheme.

The current study reports AxA'1-xByB'1-yO3-δ perovskite redox catalysts (RCs) for CO2-splitting and methane partial oxidation (POx) in a cyclic redox scheme. Strontium (Sr) and iron (Fe) were chosen as A and B site elements with A' being lanthanum (La), samarium (Sm) or yttrium (Y), and B' being manganese (Mn) or titanium (Ti) to tailor their equilibrium oxygen partial pressures (PO2s) for CO2-splitting and methane partial oxidation. DFT calculations were performed for predictive optimization of the oxide materials whereas experimental investigation confirmed the DFT-predicted redox performance. The redox kinetics of the RCs improved significantly by 1 wt% ruthenium (Ru) impregnation without affecting their redox thermodynamics. Ru-impregnated LaFe0.375Mn0.625O3 (A = 0, A' = La, B = Fe, and B' = Mn) was the most promising RC in terms of its superior redox performance (CH4/CO2 conversion >90% and CO selectivity ∼95%) at 800 °C. Long-term redox testing over Ru-impregnated LaFe0.375Mn0.625O3 indicated a stable performance during the first 30 cycles followed by an ∼25% decrease in the activity during the last 70 cycles. Air treatment was effective to reactivate the redox catalyst. Detailed characterizations revealed the underlying mechanism of the redox catalyst deactivation and reactivation. This study not only validated a DFT-guided mixed oxide design strategy for CO2 utilization but also provides potentially effective approaches to enhance redox kinetics and long-term redox catalyst performance.