Addition Of Manganese Oxide Research Articles

New insights for simultaneous nutrient removal enhancement and greenhouse gas emissions reduction of constructed wetland by optimizing its redox environment through manganese oxide addition

Manganese oxide (MnOx) is receiving increased interest in the nutrient removal of constructed wetlands (CWs); however, its service effectiveness for simultaneous greenhouse gas (GHG) emissions reduction is still vague. In this study, three vertical flow CWs, i.e., volcanics (CCW), manganese sand uniformly mixing with volcanics (Mn-CW) and MnOx doped volcanics (MnV-CW), were constructed to investigate the underlying mechanisms of MnOx on nutrient removal enhancement and greenhouse gas (GHG) emissions reduction. The results showed that the MnOx doped volcanics optimized the oxidation–reduction potential surrounding the substrate (-164.0 ∼ +141.1 mv), and resulted in the lowest GHG emissions (CO2-equivalent) from MnV-CW, 16.8–36.5 % lower than that of Mn-CW and CCW. This was mainly ascribed to mitigation of N2O produced during the NO3−-N reduction process, according to results of 15N stable isotope labeling. Analysis of the microbial community structure revealed that due to the optimized redox conditions through chemical doping of MnOx on volcanics, the abundance of microbe involved in denitrification and Mn-oxidizing process in the MnV-CW was significantly increased at genus level, which led to a higher Mn cycling efficiency between biogenic MnOx and Mn2+, and enhanced denitrification efficiency and N2O emission reduction. This study would help to understand and provide a preferable reference for future applications for manganese-based CW.

Investigation of the Effect of Manganese Oxides on the Reduction of Hexavalent Chromium by Sodium Alginate-Dispersed Nano-Zero-Valent Iron and the Mechanism

Chromium (Cr) is a prevalent soil contaminant, and sodium alginate-modified nano-zero-valent iron (SA-NZVI) has been studied for the remediation of Cr(VI)-contaminated soils. However, the addition of manganese oxides during remediation may result in the re-release of Cr(VI), and the mechanism behind this process remains unclear. Therefore, this paper investigates the effect of different manganese oxides on the oxidation of Cr(III), the impact of manganese oxide on the reduction products of Cr(VI) and SA-NZVI, and the effect of manganese oxide addition on the remediation of Cr(VI)-contaminated soil by SA-NZVI. Solution incubation experiments, XRD characterization, and soil incubation experiments were conducted to analyze the results. Our findings show that acid birnessite (A-Bir) has the lease of Cr(VI) most influence on Cr(III) oxidation and affects the stability of the SA-NZVI and Cr(VI) reduction products. In the remediation of Cr(VI)-contaminated soils, the presence of A-Bir increases the soil pH and available Mn content and reduces the available Fe content, resulting in the re-release of Cr(VI), but the Cr converted to residue form by SA-NZVI is difficult to oxidize by A-Bir. This study suggests that A-Bir plays a crucial role in the re-release during the remediation of Cr(VI)-contaminated soils by SA-NZVI.

Accelerated reduction of nitrate by driving the manganese (Mn) cycle process with dissimilatory Mn reducing bacteria: Differential reduction pathways and cycling mechanisms

The coupling of microbial dissimilatory manganese (Mn) reduction and nitrogen transformation in anaerobic environment affects the fate of many elemental geochemical cycles. A strain of dissimilatory manganese reducing bacteria (DMRB) named Pantoea sp. MFG10 was isolated for simultaneous reduction of Mn(IV) oxides and NO3--N to explore the differential reduction mechanism. The post-reaction precipitates were investigated for researching potential persistent products. The strain MFG10 could achieve 99.86% NO3--N removal (1.176 mg L−1 h−1) and 20.97 mg L−1 (0.583 mg L−1 h−1) free Mn(II) yield within 12 and 36 h, respectively. The transient intermediate Mn(III) formed after the reduction of strain MFG10 was utilized in the denitrification process. The restricted Mn reduction behavior in the NO3--N and manganese oxide co-reduction system led to the formation of large amounts of Mn(III) by single electron transfer of Mn(IV). Mn(III) acts as electron donor and re-oxidized to constitute a dynamic manganese cycle pathway. Thus, the addition of manganese oxide significantly improved the denitrification efficiency and the fast electron flow formed an abundant Mn(III) secondary minerals on the surface of the manganese oxide. This work will help to understand the more subtle environmental and process-based manganese cycle and inspire new strategies to develop efficient manganese recycling processes for groundwater pollution control.

Structural Design of 5 mol.% Yttria Partially Stabilized Zirconia (5Y-PSZ) by Addition of Manganese Oxide and Direct Firing

In this study, 5Y-PSZ-based ceramics with 15 mol.% of manganese oxide were obtained from PSZ + MnO2 powders mixtures by pressing and direct firing. The resulting materials show a stable cubic fluorite structure with only minor traces of segregated manganese oxides and relative density from 90% to 98%. The linear thermal expansion coefficient is in the order of 10−5 K−1 at 500 K and increases gradually with temperature, due to the onset of a contribution of chemical expansion, reaching about 13 × 10−6 K−1 at 1100 K. These results are suitable for prospective applicability as buffer layers to minimize degradation and delamination of electrolyte/oxygen electrode interfaces in solid electrolyte cells. The electrical conductivity remains close to 1 S/m at 973 K and close to 7 S/m at 1273 K, suggesting mixed conductivity with a prospective contribution to electrode processes occurring at electrode/electrolyte interfaces. Guidelines for further improvement were also established by a detailed analysis of the impact of heating/cooling rate, firing temperature, and time on those properties, based on Taguchi planning.

Mechanism of strengthening electroless plated copper films with extremely dilute oxide dispersion alloying: The optimal MnO addition

Surface engineering via alloying opens up a new route to tune the strength of an alloy film, thus it is critical to determine an optimal alloy addition. Here, the effect of varying the content of extremely dilute manganese oxide (MnO), namely 0.04, 0.10 and 0.17%, on microstructure stability and reliability of electroless plated colloidal Cu alloy thin films upon annealing is studied. An intermediate MnO content (0.10%) noticeably gives the best performance in terms of stabilizing Cu grains and enhancing film reliability against thermal stressing. Transmission electron microscopy and secondary ion mass spectroscopy reveal that the strengthening mechanism is related to interfacial segregation of MnO (serving as a barrier) and grain-boundary segregation of MnO (pinning and stabilizing Cu grains). However, the stabilization of Cu grains by the segregation of MnO are both missing from the other two films with MnO additions of 0.04% and 0.17%, and an identical annealing thus leads to their premature failure. Thin-film properties of adhesion strength, residual stress, surface energy, and MnO segregation tendency are comprehensively studied elucidating the strengthening mechanism.

Catalytic N2O Decomposition over Cu/Mn/Zn Doped Ceo2 Composite Oxides

Cu/Mn/Zn oxides were firstly prepared by coprecipitation with molar ratio of Cu/Zn, 0.17, and Mn/(Cu+Zn) by 0.0∼0.06, respectively. The temperature of N2O conversion ca. 10% over Cu/Zn and Cu/Mn0.03/Zn was 370°C and 325°C, respectively, by using 6.8(v)% N2O+balanced N2, and GHSV of 30000h−1, indicating the addition of manganese oxide could improve Cu/Zn oxide activity on N2O decomposition. The Cu/Mn/Zn doped CeO2 composite oxides were further prepared with molar ratio of Ce/Cu by 0.0∼1.4. The temperature of N2O conversion ca. 10% over Ce1.0/Cu/Mn0.03/Zn was 260°C as same conditions applied over Cu/Zn and Cu/Mn0.03/Zn samples. Stability test by using simulated mixture, 6.8(v)% N2O+5.0(v)% O2+3.0(v)% H2O+balanced N2, 580°C, GHSV of 30000h−1, showed that N2O conversion remained stable. Characterization demonstrated that the synergistic action of active components was the main origin of Ce1.0/Cu/Mn0.03/Zn sample had good performance on N2O abatement.

Ozone assisted oxidation of gaseous PCDD/Fs over CNTs-containing composite catalysts at low temperature

Ozone assisted carbon nanotubes (CNTs) supported vanadium oxide/titanium dioxide (V/Ti-CNTs) or vanadium oxide-manganese oxide/titanium dioxide (V-Mn/Ti-CNTs) catalysts towards gaseous PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) catalytic oxidations at low temperature (150 °C) were investigated. The removal efficiency (RE) and decomposition efficiency (DE) of PCDD/Fs achieved with V-Mn/Ti-CNTs alone were 95% and 45% at 150 °C under a space velocity (SV) of 14000 h−1; yet, these values reached 99% and 91% when catalyst and low concentration (50 ppm) ozone were used in combined. The ozone promotion effect on catalytic activity was further enhanced with the addition of manganese oxide (MnOx) and CNTs. Adding MnOx and CNTs in V/Ti catalysts facilitated the ozone decomposition (creating more active species on catalyst surface), thus, improved ozone utilization (demanding relatively lower ozone addition concentration). On the other hand, this study threw light upon ozone promotion mechanism based on the comparison of catalyst properties (i.e. components, surface area, surface acidity, redox ability and oxidation state) before and after ozone treatment. The experimental results indicate that a synergistic effect exists between catalyst and ozone: ozone is captured and decomposed on catalyst surface; meanwhile, the catalyst properties are changed by ozone in return. Reactive oxygen species from ozone decomposition and the accompanied catalyst properties optimization are crucial reasons for catalyst activation at low temperature.

Are the phosphorus-rich Na2O–CaO–B2O3–SiO2–P2O5glasses bioactive and what is an influence of doping with manganese oxide?

AbstractA series of glasses of the composition 20Na2-O-15CaO-5B2O3-5SiO2-(55 - x) P2O5:xMnO2, was prepared and characterized by XRD, DSC, SEM, and Raman techniques. The samples were later immersed in simulated body fluid (SBF) for checking the potential growth of hydroxyapatite layer (HA). Experiments confirmed that addition of manganese oxide leads to structural changes of the glasses. With increasing content of MnO2, the surface of the samples became more congenial for improving the growth of HA. The formation of HA layer on the surface of the samples was confirmed just after seven days of immersion. The growth rate of HA has gradually increased with the increase of MnO2content.

Modification of PdO/CeO2–ZrO2 catalyst by MnO x for water–gas shift reaction: redox property and valence state of Pd

A PdO/MnO x /CeO2–ZrO2 catalyst was prepared by a two-step impregnation method. PdO/CeO2–ZrO2, PdO/Al2O3, PdO/MnO x /Al2O3, CeO2–ZrO2, and MnO x /CeO2–ZrO2 catalysts were also prepared for reference. The textural and surface properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller, Raman spectroscopy, X-ray photoelectron spectroscopy, ultraviolet visible spectroscopy, and CO chemisorption. The redox properties and catalytic activity of the catalysts were evaluated by H2 temperature-programmed reduction (H2-TPR) and water–gas shift (WGS) reaction measurements, respectively. The addition of manganese oxide enhances the WGS activity of PdO/CeO2–ZrO2 catalyst significantly. It is ascribed to the improved redox property of the catalyst arising mainly from the Mn–Ce interaction at the interface and the formation of metallic Pd species that resulted from interacting with manganese oxide.

Effects of Manganese Oxide Addition on Coking Behavior of Ni/YSZ Anodes for SOFCs

AbstractSolid oxide fuel cells with Ni‐MnO/yttria‐stabilized‐zirconia (YSZ) tricomposite anode supports were fabricated with different MnO concentrations, and the coking tolerances and catalytic activities were investigated in wet CH4 atmosphere. Ni0.9(MnO)0.1/YSZ (10MnO) anode support cell exhibited a maximum power density of 210, 354, 505, and 620 mWcm−2 at 700, 750, 800, and 850 °C, respectively, in H2. Moreover, a maximum power density in wet CH4 reaches 504 mWcm−2 at 800 °C; while the Ni/YSZ cell showed poorer performances. The coking tolerance improved with an increase in their MnO content, and the 10MnO anode showed the highest tolerance. 10MnO exhibited stable performance for more than 40 h in wet CH4 without undergoing deactivation. Furthermore, it showed negligible coke formation of 0.0045 g of coke per catalyst, during testing under steam reforming‐like conditions at a steam‐to‐carbon (S/C) ratio of 1. Outlet gas chromatography analysis indicated that MnO suppresses CH4 cracking, while only minimally lowering the catalytic activity of steam reforming. Thus, it can be inferred that MnO promotes the adsorption of steam and oxygen on the reaction sites, owing to its high basicity and oxygen storage capacity. The increase in the local S/C and oxygen‐to‐carbon ratios suppresses CH4 cracking and promotes coke gasification.

Enhanced methanol electro-oxidation activity of Pt/MWCNTs electro-catalyst using manganese oxide deposited on MWCNTs

Electro-oxidation of methanol on platinum nanoparticles supported on a nanocomposite of manganese oxide (MnOx) and multi-wall carbon nanotubes (MWCNTs) is investigated. The morphology, structure, and chemical composition of the electro-catalysts are characterized by TEM, XRD, EDS, TGA, and H2-TPR. The electro-catalytic properties of electrodes are examined by cyclic voltammetry, CO-stripping, electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). Compared to Pt/MWCNTs, the Pt/MnOx-MWCNTs electro-catalyst exhibits about 3.3 times higher forward peak current density, during cyclic voltammetry, and 4.6 times higher exchange current density in methanol electro-oxidation reaction. In addition, deposition of manganese oxide onto MWCNTs dramatically increases the electrochemical active surface area from 29.7 for Pt/MWCNTs to 89.4m2g−1Pt for Pt/MnOx-MWCNTs. The results of long-term cyclic voltammetry show superior stability of Pt nanoparticles upon addition of manganese oxide to the support. Furthermore, the kinetics of formation of the chemisorbed OH groups improves upon manganese oxide incorporation. This leads to a lower onset potential of COads oxidation on Pt/MnOx-MWCNTs than on Pt/MWCNTs.

Nonextractable residue formation of sulfonamide antimicrobials: New insights from soil incubation experiments

Soil incubation experiments using 14C-labelled sulfamethazine were carried out to assess the factors governing its nonextractable residue (NER) formation via nucleophilic addition reactions. Circumstantial evidence on possible mechanisms of NER formation was derived from a selective manipulation of soil samples. The amount of quinones in soil available for nucleophilic addition was a limiting factor as indicated by (i) an (initial) increase of NER formation by adding quinone precursors or enhancing their formation by manganese oxide addition and (ii) a decrease of NER formation by limiting the formation of quinones under anaerobic conditions. A slow NER formation with time under aerobic conditions is likely caused by covalent bonding as well, because no slow NER formation phase was observed under anaerobic conditions.

Effects of manganese oxide addition and reductive atmosphere annealing on the phase stability and microstructure of yttria stabilized zirconia

Abstract The effects of Mn3O4 addition and reductive atmosphere (N2:H2 = 97:3) annealing on the microstructure and phase stability of yttria stabilized zirconia (YSZ) ceramics during sintering at 1500 °C for 3 h in air and subsequent annealing in a reductive atmosphere were investigated. Mn3O4 added 6 mol% YSZ (6YSZ) and 10 mol% YSZ (10YSZ) ceramics were prepared via the conventional solid-state reaction processes. The X-ray diffraction results showed that a single cubic phase of ZrO2 was obtained in 1 mol% Mn3O4 added 6YSZ ceramic at a sintering temperature of 1500 °C for 3 h. A trace amount of monoclinic ZrO2 phases were observed for 1 mol% Mn3O4 added 6YSZ ceramics after annealing at 1300 °C for 60 cycles in a reductive atmosphere by transmission electron microscopy. Furthermore, a single cubic ZrO2 phase existed stably as Mn3O4 added 10YSZ ceramics was annealed at 1300 °C for 60 cycles in reductive atmosphere.

The Effect of Remelting on the Physical Properties of Borotellurite Glass Doped with Manganese

A systematic set of borotellurite glasses doped with manganese (1–x) [(B2O3)0.3(TeO2)0.7]-xMnO, with x = 0.1, 0.2, 0.3 and 0.4 mol%, were successfully synthesized by using a conventional melt and quench-casting technique. In this study, the remelting effect of the glass samples on their microstructure was investigated through density measurement and FT-IR spectra and evaluated by XRD techniques. Initial experimental results from XRD evaluation show that there are two distinct phases of glassy and crystallite microstructure due to the existence of peaks in the sample. The different physical behaviors of the studied glasses were closely related to the concentration of manganese in each phase. FTIR spectra revealed that the addition of manganese oxide contributes the transformation of TeO4 trigonal bipyramids with bridging oxygen (BO) to TeO3 trigonal pyramids with non-bridging oxygen (NBO).

Mesoporous Silica Nanoparticle‐Stabilized and Manganese‐Modified Rhodium Nanoparticles as Catalysts for Highly Selective Synthesis of Ethanol and Acetaldehyde from Syngas

AbstractWell‐defined and monodispersed rhodium nanoparticles as small as approximately 2 nm were encapsulated in situ and stabilized in a mesoporous silica nanoparticle (MSN) framework during the synthesis of the mesoporous material. Although both the activity and selectivity of MSN‐encapsulated rhodium nanoparticles in CO hydrogenation could be improved by the addition of manganese oxide as expected, the carbon selectivity for C2 oxygenates (including ethanol and acetaldehyde) was unprecedentedly high at 74.5 % with a very small amount of methanol produced if rhodium nanoparticles were modified by manganese oxide with very close interaction.

Catalytic behaviors of CuO supported on Mn 2O 3 modified γ-Al 2O 3 for NO reduction by CO

CuO supported on γ-Al 2O 3 and Mn 2O 3 modified γ-Al 2O 3 was prepared and characterized by XRD, UV–vis, XPS, TPR and in situ adsorption IR. NO reduction by CO over these catalysts was also investigated. For the modification of γ-Al 2O 3 by Mn 2O 3, manganese oxide was highly dispersed on γ-Al 2O 3 surface to form a monolayer with a dispersion capacity of about 1.0 mmol Mn 3+/100 m 2 γ-Al 2O 3 corresponding to 8.1 wt.% of Mn. For supported copper oxide, CuO dispersion capacity was 0.75 mmol Cu 2+/100 m 2 γ-Al 2O 3 on γ-Al 2O 3, and increased to 1.1 mmol Cu 2+/100 m 2 γ-Al 2O 3 on 1.0 MnO x –γ-Al 2O 3, indicative of an elevated CuO dispersion capacity upon Mn 2O 3 modification. For NO reduction by CO, the addition of manganese oxide generally enhanced NO conversion and N 2 selectivity. Furthermore, the catalyst with the loading amounts of Cu and Mn of 0.6 mmol and 0.3/100 m 2 γ-Al 2O 3 respectively exhibited the most prominent catalytic efficiency among the tested catalysts in terms of NO conversion and N 2 selectivity. Additionally, these catalysts showed stable NO conversion and N 2 selectivity.

Desulfurization performance of iron-manganese-based sorbent for hot coal gas

A series of iron-manganese-based sorbents were prepared by co-precipitation and physical mixing method, and used for H2S removal from hot coal gas. The sulfidation tests were carried out in a fixed-bed reactor with space velocity of 2000 h−1(STP). The results show that the suitable addition of manganese oxide in iron-based sorbent can decrease H2S and COS concentration in exit before breakthrough due to its simultaneous reaction capability with H2S and COS. Fe3O4 and MnO are the initial active components in iron-manganese-based sorbent, and FeO and Fe are active components formed by reduction during sulfidation. The crystal phases of iron affect obviously their desulfurization capacity. The reducibility of sorbent changes with the content of MnO in sorbent. S7F3M and S3F7M have bigger sulfur capacities (32.68 and 32.30 gS/100 g total active component), while S5F5M has smaller sulfur capacity (21.92 gS/100 g total active component). S7F3M sorbent has stable sulfidation performance in three sulfidation-regeneration cycles and no apparent structure degradation. The sulfidation performance of iron-manganese-based sorbent is also related with its specific surface area and pore volume.

Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite

99Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O 4 −) and its possible uptake into the food chain cause 99Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII)O 4 − to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) than at acidic and basic pHs when Fe(II) concentration was low (< 1 mmol/g). The effect of pH, however, was insignificant at higher Fe(II) concentrations. The reduction of Tc(VII) by Fe(II) associated with NAu-2 was also studied in the presence of common subsurface oxidants including iron and manganese oxides, nitrate, and oxygen, to evaluate the effect of these oxidants on the enhancement and inhibition of Tc(VII) reduction, and reoxidation of Tc(IV). Addition of iron oxides (goethite and hematite) to the Tc(VII)-NAu-2 system, where Tc(VII) reduction was ongoing, enhanced reduction of Tc(VII), apparently as a result of re-distribution of reactive Fe(II) from NAu-2 to more reactive goethite/hematite surfaces. Addition of manganese oxides stopped further Tc(VII) reduction, and in case of K +-birnessite, it reoxidized previously reduced Tc(IV). Nitrate neither enhanced reduction of Tc(VII) nor promoted reoxidation of Tc(IV). Approximately 11% of Tc(IV) was oxidized by oxygen. The rate and extent of Tc(IV) reoxidation was found to strongly depend on the nature of the oxidants and concentration of Fe(II). When the same oxidants were added to aged Tc reduction products (mainly NAu-2 and TcO 2•nH 2O), the extent of Tc(IV) reoxidation decreased significantly relative to fresh Tc(IV) products. Increasing NAu-2 concentration also resulted in the decreased extent of Tc(IV) reoxidation. The results were attributed to the effect of NAu-2 aggregation that effectively retained Tc(IV) in the solid and decreased its vulnerability to reoxidation. Overall, our results implied that bioreduced clay minerals could play an important role in reducing Tc(VII) and in maintaining the long-term stability of reduced Tc(IV).

Sintering and Oxygen Transport in Ce0.8Pr0.2O2 − δ: A Comparative Study of Mn and Co Oxide Additives

Minor additions of manganese oxide and cobalt oxide are both shown to be good sintering aids for , a promising ceramic membrane material with comparable values of partial oxygen-ionic and electronic conductivities, to offer dense ceramics with submicron grain sizes under . Transmission electron microscopy and X-ray energy dispersive spectroscopy suggest the transition-metal oxide addition to be located in the grain boundary regions. The smallest grain size is observed in the case of materials with Mn additions. Whereas the addition of cobalt oxide radically improves the transport properties of , boosting the level of electronic conductivity by two to three times and leaving the ionic conductivity intact, the addition of manganese oxide is shown to be detrimental, increasing the activation energy for ionic conductivity while offering no benefit to electronic conductivity. These characteristic transport properties impact on levels of oxygen permeation. The flux is significantly improved in the case of Co additions due to an increased ambipolar conductivity and improved oxygen surface kinetics, whereas no improvement in oxygen permeation flux is observed for Mn additions in comparison to the base composition . It has been suggested that a very slight increase in solubility of the transition oxide addition in the grain bulk in the Mn-doped case may offer an explanation of the resultant properties.

Microstructure and Electrical Properties of MnO‐Doped (Na0.5Bi0.5)0.92Ba0.08TiO3 Lead‐Free Piezoceramics

Microstructure and electrical properties of manganese oxide (MnO)‐doped (Na0.5Bi0.5)0.92Ba0.08TiO3 (NBBT) piezoceramics were investigated in this work. X‐ray diffraction analysis shows that the suitable substitution of Mn ion into the B site induces the lattice distortion of perovskite NBBT: the solution limit is at 0.3 wt% MnO. Besides, it is observed that the sintering properties can be improved by adding a small amount of MnO, thus increasing the grain size and the relative density. Further, the temperature dependence of the dielectric permittivity of NBBT ceramics indicates that the MnO addition reconstructs the disorder array destroyed by joining BaTiO3 in the Na0.5Bi0.5TiO3 system due to the sizable radius of the B‐site cations. Combining these effects of MnO addition, the optimal electrical properties were acquired for NBBT ceramic with addition of 0.30 wt% MnO. The excellent electrical properties of MnO‐doped NBBT ceramics indicate its promising application in large displacement actuators.