Use of XPS to identify the oxidation state of Mn in solid surfaces of filtration media oxide samples from drinking water treatment plants

Biomimetic mineralization of hydrated magnesium carbonate for hydrogel reinforcement and heavy metal adsorption

With excessive Mn(Ⅱ) and Cu(Ⅱ) pollution in aquatic environments posing potential health risks to inhabitants, the emergence of carbon capture, utilization and storage (CCUS) technology has promoted the improvement of heavy metal remediation technologies. Using hydrothermal sediment as a crystal seed, rhamnolipid was used to mediate biomimetic mineralization to prepare hydrated magnesium carbonate (HMC) composites to enhance the Mn(Ⅱ)/Cu(Ⅱ) adsorption performance of alginate hydrogels. Hydrothermal sediment is beneficial for accelerating biomimetic mineralization, while rhamnolipid can induce a crystalline phase transformation from dypingite to nesquehonite. The addition of sediment significantly enhanced the compressive mechanical properties and thermal stability of the hydrogels. The adsorption performances of the nesquehonite and dypingite hydrogels were better for Mn(II) and Cu(II), respectively. An increase in the amount of sediment improved the adsorption of Cu(II) by the hydrogels appropriately, resulting in stronger selectivity for Cu(II). The adsorption of Mn(II) and Cu(II) on the hydrogel beads was thermodynamically spontaneous. The inhibitory effects of sodium dodecyl benzene sulfonate (SDBS), fulvic acid (FA) and alginate on Cu(II) adsorption were more obvious than those of bovine serum albumin (BSA). Both the complexation of functional groups on alginate and mineralization by HMC participated in the adsorption of Mn(II) and Cu(II).

Reductive Dissolution of NCM Cathode through Anaerobic Respiration by Shewanella putrefaciens

The consumption of lithium-ion batteries (LIBs) has considerably increased over the past decade, leading to a rapid increase in the number of spent LIBs. Exposing spent LIBs to the environment can cause serious environmental harm; however, there is a lack of experimentally obtained information regarding the environmental impacts of abandoned cathode materials. Here, we report the interactions between Shewanella putrefaciens, a microorganism commonly found in diverse low-oxygen natural settings, and LiNi0.6Co0.2Mn0.2O2 (NCM622) under anaerobic conditions. We present compelling evidence that the anaerobic respiration of Shewanella putrefaciens triggers ∼59 and ∼78% dissolution of 0.2 g/L pristine and spent NCM622, respectively. We observed that Shewanella putrefaciens interacted with the pristine and the spent NCM622 under anaerobic conditions at a neutral pH and room temperature and induced the reduction of Ni, Co, and Mn, resulting in the subsequent dissolution of Li, Ni, Co, and Mn. Moreover, we found that secondary mineralization occurred on the surface of reacted NCM622. These findings not only shed light on the substantial impact of microbial respiration on the fate of discarded cathode materials in anaerobic environments but also reveal the potential for sustainable bioleaching of cathodes in spent LIBs.

Enhancing the Performance of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) Perovskites as Catalysts for CO Oxidation by Decreasing the Ba Content

Mixed oxides featuring perovskite-type structures (ABO3) offer promising catalytic properties for applications focused on the control of atmospheric pollution. In this work, a series of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) samples have been synthesized, characterized and tested as catalysts for CO oxidation reaction in conditions close to that found in the exhausts of last-generation automotive internal combustion engines. All samples were observed to be active as catalysts for CO oxidation during CO-TPRe tests, with Ba0.7MnO3 (B0.7M) being the most active one, as it presents the highest amount of oxygen vacancies (which act as active sites for CO oxidation) and Mn (IV), which features the highest levels of reducibility and the best redox properties. B0.7M has also showcased a high stability during reactions at 300 °C, even though a slightly lower CO conversion is achieved during the second consecutive reaction cycle. This performance appears to be related to the decrease in the Mn (IV)/Mn (III) ratio.

A revised digestion method to characterize manganese content in solids

Quantifying manganese (Mn) content in solids is critical for understanding its roles in aquatic ecosystems, soils, water treatment plants and distribution systems. No studies have yet used standard Mn oxides to compare the performance of the numerous digestion methods found in the literature. Nine digestion methods (including USEPA 3050B) were compared using four Mn oxides with varying oxidation states. The HCl concentrate (12.4 M) heated to at least at 40 °C provided quantitative digestion of all Mn oxides tested with ≈ 100 % recovery. HCl concentration is important only for MnO2 digestion, while temperature influences both MnO and MnO2 recovery. Complete recovery of various Al, Cu and Fe standard oxides using a 12.4 M HCl digestion at 95 °C. Digestion of environmental samples for Al, Ca, Fe, Mg and Mn content yielded higher metal content using the HCl method (except for Al). HCl 12.4 M digestion provided better performance than other digestion methods found in the scientific literature because of its high reducing capacity. •Most digestion methods found in the literature do not digest all Mn oxidation states.•Hydrochloric acid is shown to be essential to dissolve all oxidation state of Mn oxides.

Flexible microfluidic colorimetric detection chip integrated with ABTS·+ and Co@MnO2 nanozyme catalyzed TMB reaction systems for bio-enzyme free detection of sweat uric acid

BACKGROUND

The development of wearable detection devices that can achieve noninvasive, on-site and real-time monitoring of sweat metabolites is of great demand and practical significance for point-of-care testing and healthcare monitoring. Monitoring uric acid (UA) content in sweat provides a simple and promising way to reduce the risk of gout and hyperuricemia. Traditional bioenzyme based UA assays suffer from high cost, poor stability, inconvenience for storage and easy deactivation of bioenzymes. Wearable microfluidic colorimetric detection device for sweat UA detection has not been reported. The development of novel wearable microfluidic colorimetric detection chip with no requirement of bioenzymes for sweat UA detection is of great importance for health care monitoring.

RESULTS

Firstly, Co@MnO2 nanozyme with high oxidase-like activity was synthesized and characterized. Co@MnO2 can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) directly to generate blue-green colored ox-TMB. Green colored 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) radical (ABTS·+) was produced by the oxidation of ABTS by potassium persulfate. UA exhibits distinct quenching effect on Co@MnO2 catalyzed TMB colorimetric reaction system and ABTS·+ based colorimetric system, leading to obvious color fading of the two colorimetric systems. Then, a flexible microfluidic colorimetric detection chip for UA detection was fabricated by assembling Co@MnO2/TMB modified paper chips and ABTS·+ modified paper chips into a polydimethylsiloxane (PDMS) microfluidic chip. The fabricated microfluidic colorimetric detection chip exhibits good linear relationship for sweat UA detection. The linear range is from 20 to 200 μmol/L with detection limit as low as 6.6 μmol/L. Good results were obtained for the detection of UA in actual sweat from three volunteers.

SIGNIFICANCE

This work provides two bio-enzyme free colorimetric detection systems for UA detection. Furthermore, a simple, low-cost and selective flexible wearable microfluidic colorimetric detection chip was fabricated for noninvasive and on-site detection of sweat UA, which holds great application potential for personal health monitoring and point-of-care testing.

Carbon redirection via tunable Fenton-like reactions under nanoconfinement toward sustainable water treatment

The ongoing pattern shift in water treatment from pollution control to energy recovery challenges the energy-intensive chemical oxidation processes that have been developed for over a century. Redirecting the pathways of carbon evolution from molecular fragmentation to polymerization is critical for energy harvesting during chemical oxidation, yet the regulation means remain to be exploited. Herein, by confining the widely-studied oxidation system-Mn3O4 catalytic activation of peroxymonosulfate-inside amorphous carbon nanotubes (ACNTs), we demonstrate that the pathways of contaminant conversion can be readily modulated by spatial nanoconfinement. Reducing the pore size of ACNTs from 120 to 20 nm monotonously improves the pathway selectivity toward oligomers, with the yield one order of magnitude higher under 20-nm nanoconfinement than in bulk. The interactions of Mn3O4 with ACNTs, reactant enrichment, and pH lowering under nanoconfinement are evidenced to collectively account for the enhanced selectivity toward polymerization. This work provides an adaptive paradigm for carbon redirection in a variety of catalytic oxidation processes toward energy harvesting and sustainable water purification.

Natural sunlight-driven oxidation of Mn2+(aq) and heterogeneous formation of Mn oxides on hematite

The oxidation of dissolved Mn2+(aq) plays a critical role in driving manganese cycles and regulating the fate of essential elements and contaminants in environmental systems. Based on sluggish oxidation rate, abiotic processes have been considered less effective oxidation pathway for manganese oxidation in environmental systems. Interestingly, a recent study (Jung et al., 2021) has shown that the rapid photochemical oxidation of Mn2+(aq) could be a feasible scenario to uncover the potential significance of abiotic Mn2+(aq) oxidation. Nevertheless, the significance of photochemical oxidation of Mn2+(aq) under natural sunlight exposure remains unclear. Here, we demonstrate the rapid photocatalytic oxidation of Mn2+(aq) and the heterogeneous growth of tunnel-structured Mn oxides under simulated freshwater and seawater conditions in the presence of natural sunlight and hematite. The natural sunlight-driven photocatalytic oxidation of Mn2+(aq) by hematite showed kinetic constants of 1.02 h-1 and 0.342 h-1 under freshwater and seawater conditions, respectively. The natural sunlight-driven photocatalytic oxidation rates are quite comparable to the results obtained from the previous laboratory test using artificial sunlight, which has ∼4.5 times stronger light intensity. It is likely because of ∼5.5 times larger light exposure area in the natural sunlight-driven photocatalytic oxidation than that of the laboratory test using artificial sunlight. We also elucidate the roles of cation species in controlling the oxidation rate of Mn2+(aq) and the crystalline structure of Mn oxide products. Specifically, in the presence of large amounts of cations, the oxidation rate of Mn2+(aq) was slower likely because of competitive adsorption. Furthermore, our findings highlight that Mg2+ contributes significantly to the formation of large-tunneled Mn oxides. These results illuminate the importance of abiotic photocatalytic processes in controlling the redox chemistry of Mn in real environmental aqueous systems on the oxidation of Mn2+(aq), and provide an environmentally sustainable approach to effectively remediate water contaminated with Mn2+(aq) using natural sunlight.

Biological Oxidation of Manganese Mediated by the Fungus Neoroussoella solani MnF107

Manganese oxides are highly reactive minerals and influence the geochemical cycling of carbon, nutrients, and numerous metals in natural environments. Natural Mn oxides are believed to be dominantly formed by biotic processes. A marine Mn-oxidizing fungus Neoroussoella solani MnF107 was isolated and characterized in this study. SEM observations show that the Mn oxides are formed on the fungal hyphal surfaces and parts of the hypha are enveloped by Mn oxides. TEM observations show that the Mn oxides have a filamentous morphology and are formed in a matrix of EPS enveloping the fungal cell wall. Mineral phase analysis of the fungal Mn oxides by XRD indicates that it is poorly crystalline. Chemical oxidation state analysis of the fungal Mn oxides confirms that it is predominantly composed of Mn(IV), indicating that Mn(II) has been oxidized to Mn (IV) by the fungus.

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Removal of chromium from water using manganese (II, III) oxides coated sand: adsorption and transformation of Cr(VI) and Cr(III)

A manganese coated sand (MCS) sorbent containing manganese (II,III) oxides was developed for adsorption and transformation of chromium [Cr(VI) and Cr(III)] with potential application in flow-through permeable media adsorption filters. Characterization of the MCS sorbent using XRD and XPS showed that the oxides of manganese (II) and manganese (III) were present on the MCS sorbent surface. Adsorption of both Cr(VI) and Cr(III) onto the MCS sorbent occurred over a broad pH range from 3 to 10. Surface charge analysis of the MCS sorbent determined a pHPZC of 7.8, which may facilitate the uptake of both oxy-anionic Cr(VI) species and cationic Cr(III) species. Favorable adsorption of Cr(VI) and Cr(III) onto the MCS sorbent occurred according to the Langmuir and the Freundlich adsorption equations, with a higher adsorption capacity for Cr(III) than Cr(VI). Adsorption parameters from the Langmuir, the Freundlich and the Temkin adsorption equations showed a stronger binding of Cr(VI) than Cr(III). Adsorption of Cr(III) decreased with increasing calcium concentration while adsorption of Cr(VI) decreased with increasing concentration of common anions found in natural water in the following order: phosphate > sulfate> bicarbonate. Transformation of chromium occurred on the surface of the MCS sorbent due to the partial reduction of Cr(VI) and the partial oxidation of Cr(III), which may be attributed to the role of surface manganese (II,III) oxides as either reducing or oxidizing agents. The MCS sorbent is a recyclable and sustainable adsorbent for removal of chromium from water with an environmental impact comparable to ion-exchange technology.

Removal of pharmaceutical in a biogenic/chemical manganese oxide system driven by manganese-oxidizing bacteria with humic acids as sole carbon source

Bioaugmented sand filtration has attracted considerable attention because it can effectively remove contaminants in drinking water without additional chemical reagent addition. In this study, a synthesized chemical manganese dioxide (MnO₂)-coated quartz sand (MnQS) and biogenic manganese oxide (BioMnO_x) composite system was proposed to simultaneously remove typical pharmaceutical contaminants and Mn²⁺. We demonstrated a manganese-oxidizing bacterium, Pseudomonas sp. QJX-1, could oxidize Mn²⁺ to generate BioMnO_x using humic acids (HA) as sole carbon source. The coaction of MnQS, QJX-1, and the generated BioMnO_x in simultaneously removing caffeine and Mn²⁺ in the presence of HA was evaluated. We found a synergistic effect between them. MnQS and BioMnO_x together significantly increased the caffeine removal efficiency from 32.8% (MnQS alone) and 21.5% (BioMnO_x alone) to 61.2%. Meanwhile, Mn²⁺ leaked from MnQS was rapidly oxidized by QJX-1 to regenerate reactive BioMnO_x, which was beneficial for continuous contaminant removal and system stability. Different degradation intermediates of caffeine oxidized by MnQS and BioMnO_x were detected by LC-QTOF-MS analysis, which implied that caffeine was oxidized by a different pathway. Overall, this work promotes the potential application of bioaugmented sand filtration in pharmaceutical removal in the presence of natural organic matter in drinking water.

Coupled mixotrophic denitrification and utilization of refractory organics driven by Mn redox circulation for significantly enhanced nitrogen removal

Coupled mixotrophic denitrification and degradation of organics driven by redox transition of Mn for nitrogen removal has attracted much attention. Herein, this study explored the removal performance and mechanisms for nitrogen and refractory organics from secondary effluent in up-flow MnOx biofilter. Results showed that the removal of organics and nitrate was significantly enhanced by the synergistic process of heterotrophic denitrification and Mn(II)-driven autotrophic denitrification (MnAD), which were originated from the facilitation of Mn circulation. But nitrate removal was closely related to the types of carbon source and Mn(II) concentration. Single small molecular carbon source (glucose) performed better than mixed carbon source (humic acid and glucose) in nitrate removal process (74.8% in stage 1-2 vs. 54.1% in stage 3-5). And raising external Mn(II) concentration increased the contribution of MnAD (60.2% in stage 5 vs. 46.5% in stage 3) to nitrate removal. Furthermore, the relationship between Mn/N transformation and microbial community structure shifts revealed that the redox transition between Mn(II) and Mn(IV) promoted the enrichment of denitrogenation bacteria and functional genes, thus contributing to pollutants removal. Our studies expand the knowledge of MnOx-mediated pollutants removal processes and support the potential application of MnOx for removal of residual refractory organics and nitrogen.

Coordination of Pt(IV) by {P8W48} Macrocyclic Inorganic Cavitand: Structural, Solution, and Electrochemical Studies

Hydrothermal reaction of a macrocyclic inorganic POM cavitand Li₁₇(NH₄)₂₁H₂[P₈W₄₈O₁₈₄] with [Pt(H₂O)₂(OH)₄] results in coordination of up to six {Pt(H₂O)_x(OH)_4-x} fragments to the internal surface of the polyoxoanion. The product was isolated as K₂₂(NH₄)₉H₃[{Pt(OH)₃(H₂O)}₆P₈W₄₈O₁₈₄]·79H₂O (1) and characterized by multiple techniques in the solid state (SCXRD, XRPD, XPS, FTIR, and TGA) and in solution (NMR, ESI-MS, and HPLC-ICP-AES). Electrochemical properties were studied both in solution and as components of the paste electrode. The complex shows electrocatalytic activity in water oxidation.

Identifying chemical and physical changes in wide-gap semiconductors using real-time and near ambient-pressure XPS

Photoelectron spectroscopy is a powerful characterisation tool for semiconductor surfaces and interfaces, providing in principle a correlation between the electronic band structure and surface chemistry along with quantitative parameters such as the electron affinity, interface potential, band bending and band offsets. However, measurements are often limited to ultrahigh vacuum and only the top few atomic layers are probed. The technique is seldom applied as an in situ probe of surface processing; information is usually provided before and after processing in a separate environment, leading to a reduction in reproducibility. Advances in instrumentation, in particular electron detection has enabled these limitations to be addressed, for example allowing measurement at near-ambient pressures and the in situ, real-time monitoring of surface processing and interface formation. A further limitation is the influence of the measurement method through irreversible chemical effects such as radiation damage during X-ray exposure and reversible physical effects such as the charging of low conductivity materials. For wide-gap semiconductors such as oxides and carbon-based materials, these effects can be compounded and severe. Here we show how real-time and near-ambient pressure photoelectron spectroscopy can be applied to identify and quantify these effects, using a gold alloy, gallium oxide and semiconducting diamond as examples. A small binding energy change due to thermal expansion is followed in real-time for the alloy while the two semiconductors show larger temperature-induced changes in binding energy that, although superficially similar, are identified as having different and multiple origins, related to surface oxygen bonding, surface band-bending and a room-temperature surface photovoltage. The latter affects the p-type diamond at temperatures up to 400 °C when exposed to X-ray, UV and synchrotron radiation and under UHV and 1 mbar of O₂. Real-time monitoring and near-ambient pressure measurement with different excitation sources has been used to identify the mechanisms behind the observed changes in spectral parameters that are different for each of the three materials. Corrected binding energy values aid the completion of the energy band diagrams for these wide-gap semiconductors and provide protocols for surface processing to engineer key surface and interface parameters.

MnO2 Electrocatalysts Coordinating Alcohol Oxidation for Ultra-Durable Hydrogen and Chemical Productions in Acidic Solutions

Electrocatalytic hydrogen production under acidic conditions is of great importance for industrialization in comparison to that in alkaline media, which, unfortunately, still remains challenging due to the lack of earth-abundant, cost-effective and highly active anodic electrocatalysts that can be used durably under strongly acidic conditions. Here we report an unexpected finding that manganese oxide, a kind of common non-noble catalysts easily soluble in acidic solutions, can be applied as a highly efficient and extremely durable anodic electrocatalyst for hydrogen production from an acidic aqueous solution of alcohols. Particularly in a glycerol solution, a potential of as low as 1.36 V (vs. RHE) is needed at 10 mA cm^-2 , which is 270 mV lower than that of oxygen evolution reaction (OER), to oxidize glycerol into value-added chemicals such as formic acid, without oxygen production. To our surprise, the manganese oxide exhibits extremely high stability for electrocatalytic hydrogen production in coupling with glycerol oxidation for longer than 865 hours compared to shorter than 10 h for OER. Moreover, the effect of the addition of glycerol on the electrochemical durability has been probed via in situ Raman spectroscopic analysis and density functional theory (DFT) calculations. This work demonstrates that acid-unstable metal oxide electrocatalysts can be used robustly in acidic media under the presence of certain substances for electrochemical purposes, such as hydrogen production.

Excellent electrochemical properties, Li ion dynamics and room temperature work function of Li2MnO3cathode thin films

We report on excellent electrochemical properties, Li ion diffusion coefficient and work function of Li₂MnO₃thin films fabricated by RF sputtering technique. The x-ray diffraction study confirms the formation of Li₂MnO₃thin film in layered structure. The x-ray photoelectron spectroscopy study confirms the existence of Li and Mn ions and their appropriate oxidation states in Li₂MnO₃thin film. Work function of the Li₂MnO₃thin film has been measured using scanning Kelvin probe microscopy and is found to be 5.51 eV. Electrochemical studies show that the Li₂MnO₃thin film exhibits oxidation and reduction peaks at 2.98 V and 2.81 V respectively with the discharging capacity of 10μAh cm^-2in the first cycle and 9μAh cm^-2in the 100th cycle at aCrate of 25μA cm^-2. Electrochemical stability of Li₂MnO₃thin film is probed by measuring the charge discharge profile with high sweep rate of 500 mV s^-1. Li ion diffusion coefficient value is seen to 1.6 × 10^-14cm²s^-1and 2.56 × 10^-14cm²s^-1before and after the cycling respectively. Electrochemical studies indicate that Li₂MnO₃thin films can be utilized as a promising cathode layer in all-solid thin film battery fabrication.

Spray Pyrolysis Synthesis of Pure and Mg-Doped Manganese Oxide Thin Films

Pure and Mg-doped manganese oxide thin films were synthesized on heated glass substrates using the spray pyrolysis technique. The surface chemical composition was investigated by the use of X-ray photoelectron spectroscopy (XPS). Structural and morphological properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscopy (AFM). Optical properties were characterized by UV-visible spectroscopy. XPS spectra showed typical Mn (2p3/2), (2p1/2) and O (1s) peaks of Mn3O4 with a slight shift attributed to the formation of different chemical states of manganese. XRD analysis revealed the tetragonal phase of Mn3O4 with a preferred (211) growth orientation that improved with Mg-doping; likewise, grain size is observed to increase with the Mg doping. SEM images of Mn3O4 films showed rough surfaces composed of uniformly distributed nanograins whose size decreases with the Mg-doping. The manganese oxide films surface observed in AFM show a textured, rough and porous surface. The combination of transmittance and absorption data in the UV-visible range allowed determining the energy values of the Eg band gap (1.5–2.5 eV). The decrease of the band gap with the Mg-doping increase is attributed to the influence of the greater size of the Mg2+ ion in the manganese oxide lattice.

Physicochemical characteristics of calcined MnFe2O4 solid nanospheres and their catalytic activity to oxidize para-nitrophenol with peroxymonosulfate and n-C7 asphaltenes with air

Manganese ferrite solid nanospheres (MSNs) were prepared by a solvothermal method and calcined at various temperatures up to 500 °C. Their surface area, morphology, particle size, weight change during calcination, surface coordination number of metal ions, oxidation state, crystal structure, crystallite size, and magnetic properties were studied. The MSNs were used as catalysts to activate potassium peroxymonosulfate (PMS) for the oxidative degradation of para-nitrophenol (PNP) from water and for the oxidation of n-C₇ asphaltenes in flowing air at atmospheric (0.084 MPa) and high pressure (6 MPa). Mn was in oxidation states (II) and (III) at calcination temperature of 200 °C, and the crystalline structure corresponded to jacobsite. Mn was in oxidation states (III) and (IV) at 350 °C and in oxidation states (II), (III), and (IV) at 500 °C, and the crystalline structure was maghemite at both temperatures. MSN catalysts generated hydroxyl (HO·) and sulfate (SO₄^·-) radicals in the PMS activation and generated HO· radicals in the n-C₇ asphaltene oxidation. In both reactions, the best catalyst was MSN calcined at 350 °C (MSN350), because it has the highest concentration of Mn(III) in octahedral B sites, which are directly exposed to the catalyst surface, and the largest total and lattice oxygen contents, favoring oxygen mobility for Mn redox cycles. The MSN350 sample reduces the decomposition temperature of n-C₇ asphaltenes from 430 to 210 °C at 0.084 MPa and from 370 to 200 °C at 6.0 MPa. In addition, it reduces the effective activation energy by approximately 77.6% in the second combustion (SC) region, where high-temperature oxidation reactions take place.

Electronic and structural properties of single-crystal Jahn-Teller active Co1+x Mn2-x O4 thin films

Recent investigations on spinel CoMn2O4 have shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline Co1+x Mn2-x O4 thin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry. Our results indicate that excess Co ions occupy tetrahedral interstitial sites at lower excess Co stoichiometries, and become substitutional for octahedrally-coordinated Mn at higher Co levels. We compare these results with density functional theory models of stoichiometric CoMn2O4 to understand how the Jahn-Teller distortion and hybridization in Mn-O bonds impact the ability to hole dope the material with excess Co. The findings provide important insights into CoMn2O4 and related spinel oxides that are promising candidates for inexpensive oxygen reduction reaction catalysts.

Microplotter-Printed On-Chip Combinatorial Library of Ink-Derived Multiple Metal Oxides as an "Electronic Olfaction" Unit

Information about the surrounding atmosphere at a real timescale significantly relies on available gas sensors to be efficiently combined into multisensor arrays as electronic olfaction units. However, the array's performance is challenged by the ability to provide orthogonal responses from the employed sensors at a reasonable cost. This issue becomes more demanded when the arrays are designed under an on-chip paradigm to meet a number of emerging calls either in the internet-of-things industry or in situ noninvasive diagnostics of human breath, to name a few, for small-sized low-powered detectors. The recent advances in additive manufacturing provide a solid top-down background to develop such chip-based gas-analytical systems under low-cost technology protocols. Here, we employ hydrolytically active heteroligand complexes of metals as ink components for microplotter patterning a multioxide combinatorial library of chemiresistive type at a single chip equipped with multiple electrodes. To primarily test the performance of such a multisensor array, various semiconducting oxides of the p- and n-conductance origins based on pristine and mixed nanocrystalline MnO_x, TiO₂, ZrO₂, CeO₂, ZnO, Cr₂O₃, Co₃O₄, and SnO₂ thin films, of up to 70 nm thick, have been printed over hundred μm areas and their micronanostructure and fabrication conditions are thoroughly assessed. The developed multioxide library is shown to deliver at a range of operating temperatures, up to 400 °C, highly sensitive and highly selective vector signals to different, but chemically akin, alcohol vapors (methanol, ethanol, isopropanol, and n-butanol) as examples at low ppm concentrations when mixed with air. The suggested approach provides us a promising way to achieve cost-effective and well-performed electronic olfaction devices matured from the diverse chemiresistive responses of the printed nanocrystalline oxides.

Oxidation of Mn(III) Species by Pb(IV) Oxide as a Surrogate Oxidant in Aquatic Systems

Dissolved Mn(III) species have been recognized as a significant form of Mn in redox transition environments, but a holistic understanding of their geochemical properties still lacks the characterization of their reactivity as reductants. Through using PbO₂ as a surrogate oxidant and pyrophosphate (PP) as a model ligand, we evaluated the thermodynamic and kinetic constrains of dissolved Mn(III) oxidation under environmentally relevant pH. Without disproportionation, Mn(III) complexes could be directly oxidized by PbO₂ to produce Mn oxides. The reaction rates decreased with increasing PP:Mn(III) ratio and became negligible when the ratio was above a threshold value. Particulate manganite could also be oxidized by PbO₂ with detectable production of Pb(II). The favorability of Mn(III) oxidation by PbO₂ as a function of the PP:Mn ratio could be predicted by the stability constant of the Mn(III)-PP complex. We developed kinetic models that couple multiple pathways of Mn oxidation by PbO₂ to simulate the dynamics of Pb release, loss of dissolved Mn, as well as Mn(III) production and consumption. Beyond the context of Mn geochemistry, the interactions between Pb and various Mn species, including its trivalent forms, may also have important implications to the water quality in lead service lines within distribution systems.

Tuning oxygen vacancy concentration of MnO2 through metal doping for improved toluene oxidation

Oxygen vacancy acts an important role in adjusting the chemical properties of MnO₂. In this paper, two-dimensional MnO₂ catalysts with different oxygen vacancy concentration are obtained by doping Cu²⁺. It is researched that the K⁺ species in the interlayer of birnessite-type MnO₂ can be substituted during the Cu²⁺ doping process. Meanwhile, this process will generate the oxygen vacancy. Interestingly, the formation of an appropriate numbers of oxygen vacancy in MnO₂ distinctly enhances the low-temperature reducibility and oxygen species activity, which improves the catalytic activity for the toluene oxidation (T₁₀₀ = 220 °C, E_a=43.6 kJ/mol). However, an excessive concentration of oxygen vacancy in MnO₂ sample performs against the activity improvement for toluene oxidation. In situ DRIFTS are applied to elucidate the main intermediates and conversion pathway on MnO₂-OV3 with moderate concentration of oxygen vacancy. The results demonstrate that the adsorbed toluene can interact with oxygen species of catalyst to form physisorbed benzaldehyde, aldehydic adsorbate and benzoate species. In addition, it is found that the oxygen vacancy concentration plays an important effect on the oxidation of benzoate species owing to the acceleration effect of oxygen vacancy in the activation of gaseous oxygen.

Synthesis of mesoporous magnetic MnFe2O4@CS-SiO2 microsphere and its adsorption performance of Zn2+ and MB studies

Because of its superior physical and chemical properties, MnFe₂O₄ is regarded as one of the best magnetic material alternatives for Fe₃O₄. However, MnFe₂O₄ alone cannot remove heavy metal ions and dyes. Here, we report on a new mesoporous magnetic MnFe₂O₄@CS-SiO₂ microsphere material that was synthesised via the hydrothermal method to remove Zn²⁺ and methylene blue (MB) in simulated textile wastewater. The composite was characterised using a vibrating sample magnetometer, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and a Brunauer-Emmett Teller analysis. The pH, adsorbent dosage, initial adsorbate concentration, and reaction time effects on the removal of Zn²⁺ and MB were studied under different conditions, and a possible removal mechanism was proposed and discussed. The experimental results show that the suitable pH range for MB adsorption was extremely wide, and the adsorption equilibrium can be reached within 30 min. In addition, the prepared material has excellent stability. With an excellent removal efficiency as high as 56.1% and 93.86% for Zn²⁺ and MB, respectively, after five consecutive cycles and a superior adsorption capacity compared with other materials, the prepared composite in this paper proved to be a promising and effective magnetic adsorbent for the removal of Zn²⁺ and MB from textile wastewater.

Preparation of road base material by utilizing electrolytic manganese residue based on Si-Al structure: Mechanical properties and Mn2+ stabilization/solidification characterization

Electrolytic manganese residue (EMR) is a potentially harmful industrial solid waste that should be addressed. In the study, the red mud, carbide slag and blast furnace slag were used as stabilization/solidification (S/S) agents to S/S Mn²⁺, and simultaneous reused it as raw material to prepare road base material. The S/S behavior of manganese, unconfined compressive strength (UCS) of road base material with different Al/Si ratios, leaching test and the S/S mechanisms were investigated. The results showed that the Mn²⁺ can be well solidified when the S/S agents reach up to 20 %. The 7-day UCS of the road base material was 6.1 MPa with the Al/Si ratio of 0.48, which meets the highway standards. When Al/Si = 0.48, the formation amount of CaAl₂Si₂O₈·4H₂O and ettringite increased, which promoted the adsorption and wrap of Mn²⁺. The content of active Al^Ⅳ and Al^Ⅵ increased after S/S. Mn₂SiO₄ and Ca₄Mn₄Si₈O₂₄ were produced by the charge balance effect, and the new chemical bond was formed. Meanwhile, the Mn²⁺ is oxidized to more stable MnO₂ to achieve the S/S of Mn²⁺. This research provides an effective way to solidify Mn²⁺ and solves the problem of large-scale utilization of EMR and other solid waste.

Co-precipitation of MnO and Cu in an ionic liquid as a first step toward self-formed barrier layers

Mixed MnO–Cu nanoparticles are synthesised in an ionic liquid, and the suspensions are spread and annealed directly on technological substrates to form films suitable for the metallisation of through-Si vias.

Ferroelectric Diode Effect with Temperature Stability of Double Perovskite Bi2NiMnO6 Thin Films

Double perovskite Bi₂NiMnO₆ (BNMO) thin films grown on p-Si (100) substrates with LaNiO₃ (LNO) buffer layers were fabricated using chemical solution deposition. The crystal structure, surface topography, surface chemical state, ferroelectric, and current-voltage characteristics of BNMO thin films were investigated. The results show that the nanocrystalline BNMO thin films on p-Si substrates without and with LNO buffer layer are monoclinic phase, which have antiferroelectric-like properties. The composition and chemical state of BNMO thin films were characterized by X-ray photoelectron spectroscopy. In the whole electrical property testing process, when the BNMO/p-Si heterojunction changed into a BNMO/LNO/p-Si heterojunction, the diode behavior of a single diode changing into two tail to tail diodes was observed. The conduction mechanism and temperature stability were also discussed.

Impact of dissolved O2 on phenol oxidation by δ-MnO2

Although redox reactions of organic contaminants with manganese oxides have been extensively studied, the role of dissolved O2 in these processes has largely been overlooked. In this study, the oxidative degradation of phenol by δ-MnO2 was investigated under both oxic and anoxic conditions. Dissolved O2 inhibited phenol degradation due to its promoting role in the reoxidation and precipitation of reduced Mn(ii) to Mn(iii) on the δ-MnO2 surface, resulting in partial transformation of δ-MnO2 to "c-disordered" H+-birnessite at pH 5.5 and feitknechtite, manganite, and hausmannite at pH 7.0 and 8.5. The reformed Mn(iii) phases could reduce phenol oxidation by blocking reactive sites of δ-MnO2. In addition, dissolved O2 caused a higher degree of particle agglomeration and a more severe specific surface area decrease, and hence lower reactivity of δ-MnO2. These findings revealed that after reductive dissolution by phenol and reoxidation by dissolved O2 throughout continuous redox cycling, δ-MnO2 became less reactive rather than being regenerated. These results can provide new insights into the understanding of the oxidation of organic contaminants by manganese oxides in the natural environment.

Mn-based catalysts for sulfate radical-based advanced oxidation processes: A review

Sulfate radical-based advanced oxidation processes (AOPs) have drawn increasing attention during the past two decades, and Mn-based materials have been proven to be effective catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS) to degrade many contaminants. This article presents a comprehensive review of various Mn-based materials to activate PMS and PDS. The activation mechanisms of different Mn-based catalysts (i.e., Mn oxides MnO_x, MnO_x hybrids, and MnO_x‑carbonaceous material composites) were first summarized and discussed in detail. Besides the commonly reported free radicals (SO₄^-• and ^•OH), non-radical mechanisms such as singlet oxygen and direct electron transfer have also been discovered for selected materials. The effects of pH, inorganic ions, natural organic matter (NOM), dissolved oxygen content, temperature, and the crystallinity of the materials on the catalytic reactivity were also discussed. Then, important instrumentations and technologies employed to characterize Mn-based materials and to understand the reaction mechanisms were concisely summarized. Three common overlooks in the experimental designs for examining the PMS/PDS-MnO_x systems were also discussed. Finally, future research directions were suggested to further improve the technology and to provide a guidance to develop cost-effective Mn-based materials to activate PMS/PDS.

Oxidative nucleation and growth of Janus-type MnOx-Ag and MnOx-AgI nanoparticles

Janus nanoparticles (NPs) containing two chemically distinct materials in one system are of great significance for catalysis in terms of harnessing catalytic synergies that do not exist in either component. We herein present a novel synthetic method of two Janus-type MnOx-Ag and MnOx-AgI NPs. The synthesis of Janus-type MnOx-AgI NPs is based on the oxidative nucleation and growth of Ag domains on MnO first and the subsequent iodization of Ag. A mild and non-disruptive iodization strategy is developed to yield Janus MnOx-AgI NPs, in which converting Ag to AgI domains with iodomethane (CH3I) is achieved through partial iodization. Simultaneously, Mn2+ species in the primary MnO octahedra are oxidized during the growth of Ag NPs, leading to the formation of amorphous p-type MnOx domains. Therefore, the as-resultant Janus-type MnOx-AgI NPs combining two semiconductors into an integrated nanostructure can be used as an efficient photocatalyst for visible-light-driven water oxidation. Janus MnOx-AgI NPs show an expected photocatalytic activity even in the absence of Ru(bpy)3Cl2 as an electron mediator. This intriguing synthesis may offer a new opportunity to develop asymmetric nanostructures of two semiconductors that will potentially be efficient photocatalysts for solar-driven water splitting.

Portraying manganese biofilms via a merger of EPR spectroscopy and cathodic polarization

Microbial biofilms on stainless steel surfaces exposed to water from a freshwater pond were dominated by manganese-oxidizing bacteria, as initially diagnosed by microscopy and elemental analysis. The application of electron paramagnetic resonance (EPR) spectroscopy revealed conspicuous sextet (six-line) patterns that intensified with immersion time, implying the gradual accumulation of Mn(II) in the biofilms. Correspondingly, cathodic polarization designated the manganese oxide (MnO_x) reduction peak in the form of a distinctive 'nose', which grew increasingly more negative with biofilm growth. The progressive expansion of cathodic current densities and the concurrent area-under-the-curve also allowed the quantification of microbially mediated MnO_x deposition_. Furthermore, the merger of EPR and cathodic polarization techniques yielded key insights, in tandem with Mn speciation data, into the pathways of microbial manganese transformations in biofilms, besides providing meaningful interpretations of prevailing literature. Accordingly, the natural freshwater biofilm was inferred as one supporting a complete manganese cycle encompassing multiple redox states.

Osteogenic potential of sol-gel bioactive glasses containing manganese

Bioactive glasses (BGs) are widely used for bone regeneration, and allow the incorporation of different ions with therapeutic properties into the glass network. Amongst the different ions with therapeutic benefits, manganese (Mn) has been shown to influence bone metabolism and activate human osteoblasts integrins, improving cell adhesion, proliferation and spreading. Mn has also been incorporated into bioceramics as a therapeutic ion for improved osteogenesis. Here, up to 4.4 mol% MnO was substituted for CaO in the 58S composition (60 mol% SiO₂, 36 mol% CaO, 4 mol% P₂O₅) and its effects on the glass properties and capability to influence the osteogenic differentiation were evaluated. Mn-containing BGs with amorphous structure, high specific surface area and nanoporosity were obtained. The presence of Mn²⁺ species was confirmed by X-ray photoelectron spectroscopy (XPS). Mn-containing BGs presented no cytotoxic effect on human mesenchymal stem cells (hMSCs) and enabled sustained ion release in culture medium. hMSCs osteogenic differentiation stimulation and influence on the mineralisation process was also confirmed through the alkaline phosphatase (ALP) activity, and expression of osteogenic differentiation markers, such as collagen type I, osteopontin and osteocalcin, which presented higher expression in the presence of Mn-containing samples compared to control. Results show that the release of manganese ions from bioactive glass provoked human mesenchymal stem cell (hMSC) differentiation down a bone pathway, whereas hMSCs exposed to the Mn-free glass did not differentiate. Mn incorporation offers great promise for obtaining glasses with superior properties for bone tissue regeneration.

Powdered activated carbon enhanced Manganese(II) removal by chlorine oxidation

Chlorine is not effective in the oxidative removal of soluble manganese(II) ions at neutral pH. Powdered activated carbon (PAC) also has a very limited capacity for Mn(II) removal through adsorption in drinking water treatment practice. This study explored the combined use of PAC and chlorine for Mn(II) removal and found that PAC dramatically catalyzed Mn(II) oxidation by chlorine under diverse conditions. At a dose as low as 5.0 mg/L, two different commercial PACs increased Mn(II) oxidation rate by two orders of magnitude respectively and reduced Mn(II) concentration from 200 μg/L to < 10 μg/L in tens of minutes. First-order kinetics with respect to aqueous Mn(II) concentration were observed. Typically, homogeneous Mn(II) oxidation by chlorine depends strongly on alkaline pH. In the presence of PAC, however, the reaction was still rather fast at pH 6.0. Increasing PAC doses linearly increased Mn(II) oxidation rate, indicating that the reaction was highly PAC surface active sites dependent. The efficacy of PAC was further corroborated in removing Mn(II) from natural water. SEM-EDS and XPS demonstrated that a MnO₂ coating was formed on PAC surface after reaction, which resulted from heterogeneous oxidation of Mn(II) on PAC surface rather than the precipitation of Mn oxides formed through homogeneous oxidation in solution. Adsorption of free Mn(II) ions onto PAC surface was proved to directly correlate with Mn(II) oxidation rate. Two kinds of electron transfer pathways from adsorbed Mn(II) species to chlorine, enhanced by surface-complexation and electrically-conductive carbon surface respectively, were hypothesized.

Manganese Increases Lead Release to Drinking Water

Lead and manganese are regulated in drinking water due to their neurotoxicity. These elements have been reported to co-occur in drinking water systems, in accordance with the metal-scavenging properties of MnO₂. To the extent that manganese is a driver of lead release, controlling it during water treatment may reduce lead levels. We investigated transport of lead and manganese at the tap in a full-scale distribution system: consistent with a cotransport phenomenon, the two metals were detected in the same colloidal size fraction by size-exclusion chromatography with multielement detection. We also studied the effect of manganese on lead release using a model distribution system: increasing manganese from 4 to 215 μg L^-1 nearly doubled lead release. This effect was attributed primarily to deposition corrosion of lead by oxidized phases of manganese, and we used 16S rRNA sequencing to identify bacteria that may be relevant to this process. We explored the deposition corrosion mechanism by coupling pure lead with either MnO₂-coated lead or pure lead exposed to MnO₂ in suspension; we observed galvanic currents in both cases. We attributed these to reduction of Mn(IV) under anaerobic conditions, and we attributed the additional current under aerobic conditions to oxygen reduction catalyzed by MnO₂.

Slow-releasing permanganate ions from permanganate core-manganese oxide shell particles for the oxidative degradation of an algae odorant in water

In this work, potassium permanganate particles (KMnO₄) were modified with a manganese oxide (MnOx) shell comprising passages for the slow release of permanganate ions (MnO₄^-) in aquatic systems. The bare particle (KMnO₄) and KMnO₄ core-MnOx shell particles (CP-60) were characterized by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The CP-60 were evaluated as a slow source of MnO₄^- for the oxidative treatment of pure and lake water containing dimethyl trisulfide (DMTS), a water odorant produced by cyanobacteria in many eutrophic waters. XPS and ATR-FTIR results confirmed the presence of MnOx surface shell (diameter ∼ 1 μm) on CP-60. SEM images revealed cracks on CP-60, which serve as outlets for MnO₄^-. Approximately 0.76 ± 0.07 g KMnO₄/g of CP-60 was released from the core of CP-60 after 120 min. The CP-60 degraded 88.9 ± 2.5% and 70.8 ± 6.3% of DMTS in pure water and lake water matrix within 120 min, respectively. The degradation was slightly more effective than the degradation using aqueous KMnO₄ (74.2%) reported in literature. The release kinetics of the particles is consistent with a pseudo-first order equation with correlation coefficients of 0.99 and 0.97 in pure water and lake water matrix, respectively. The CP could serve as low cost slow-release particles for the degradation of micropollutants, even in cyanobacteria laden water. Notably, the in situ MnOx formed during the KMnO₄ oxidation reaction can facilitate adsorption of organics and metal ions, improving water quality.

La0.75Sr0.25XO3 (X = Fe, Mn or Cr) with coking tolerance for CH4/H2O reaction: effect of H2S on catalytic performance

The influence of the B type cation from the ABO₃ perovskite formulation La_0.75Sr_0.25XO₃ (LSX, where X is Fe, Mn or Cr) on the C and H₂S tolerance and its catalytic activity for the methane/water reaction has been studied.

Hydrotreatment Followed by Oxidative Desulfurization and Denitrogenation to Attain Low Sulphur and Nitrogen Bitumen Derived Gas Oils

To lower the sulphur content below 500 ppm and to increase the quality of bitumen derived heavy oil, a combination of hydrotreating followed by oxidative desulfurization (ODS) and oxidative denitrogenation (ODN) is proposed in this work. NiMo/γ-Al2O3 catalyst was synthesized and used to hydrotreat heavy gas oil (HGO) and light gas oil (LGO) at typical operating conditions of 370–390 °C, 9 MPa, 1–1.5 h−1 space velocity and 600:1 H2 to oil ratio. γ-Alumina and alumina-titania supported Mo, P, Mn and W catalysts were synthesized and characterized using X-ray diffractions, N2 adsorption-desorption using Brunauer–Emmett–Teller (BET) method, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). All catalysts were tested for the oxidation of sulphur and nitrogen aromatic compounds present in LGO and HGO using tert-butyl hydroperoxide (TBHP) as oxidant. The oxidized sulphur and nitrogen compounds were extracted using adsorption on activated carbon and liquid-liquid extraction using methanol. The determination of oxidation states of each metal using XPS confirmed the structure of metal oxides in the catalyst. Thus, the catalytic activity determined in terms of sulphur and nitrogen removal is related to their physico-chemical properties. In agreement with literature, a simplistic mechanism for the oxidative desulfurization is also presented. Mo was found to be more active in comparison to W. Presence of Ti in the support has shown 8–12% increase in ODS and ODN. The MnPMo/γ-Al2O3-TiO2 catalyst showed the best activity for sulphur and nitrogen removal. The role of Mn and P as promoters to molybdenum was also discussed. Further three-stage ODS and ODN was performed to achieve less than 500 ppm in HGO and LGO. The combination of hydrotreatment, ODS and ODN has resulted in removal of 98.8 wt.% sulphur and 94.7 wt.% nitrogen from HGO and removal of 98.5 wt.% sulphur and 97.8 wt.% nitrogen from LGO.