Development and application of a nitrogen oxides analyzer based on the cavity attenuated phase shift technique.

Nitrogen oxides (NOx) are crucial in tropospheric photochemical ozone (O3) production and oxidation capacity. Currently, the widely used NOx measurement technique is chemiluminescence (CL) (CL-NOx), which tends to overestimate NO2 due to atmospheric oxidation products of NOx (i.e., NOz). We developed and characterized a NOx measurement system using the cavity attenuated phase shift (CAPS) technique (CAPS-NOx), which is free from interferences with nitrogen-containing species. The NOx measured by the CAPS-NOx and CL-NOx analyzers were compared. Results show that both analyzers showed consistent measurement results for NO, but the NO2 measured by the CAPS-NOx analyzer (NO2_CAPS) was mostly lower than that measured by the CL-NOx analyzer (NO2_CL), which led to the deviations in O3 formation sensitivity regime and Ox (= O3 + NO2) sources (i.e., regional background and photochemically produced Ox) determined by the ozone production efficiencies (OPE) calculated from NO2_CL and NO2_CAPS. Overall, OPE_CL exceeded OPE_CAPS by 18.9%, which shifted 3 out of 13 observation days from the VOCs-limited to the transition regime when judging using OPE_CL, as compared to calculations using OPE_CAPS. During the observation period, days dominated by regional background Ox accounted for 46% and 62% when determined using NO2_CL and NO2_CAPS, respectively. These findings suggest that the use of the CL-NOx analyzer tends to underestimate both the VOCs-limited regime and the regional background Ox dominated days. The newly built CAPS-NOx analyzer here can promote the accurate measurement of NO2, which is meaningful for diagnosing O3 formation regimes and Ox sources.

Synergizing ruthenium oxide with bimetallic Co2CrO4 for highly efficient oxygen evolution reaction.

Designing efficient and stable oxygen evolution reaction (OER) catalyst is the basis for the development of sustainable electrolytic water energy techniques. In this work, we presented a heterogeneous-structured electrocatalyst composed of bimetallic oxides-modified RuO2 nanosheets supported on nikel foam (Co2CrO4/RuO2) using a hybrid hydrothermal, ion-exchange and calcination method. The unique synergy and interfacial coupling between Co2CrO4/RuO2 heterostructures are favorable for optimizing the electronic configuration at this interface and strengthening the charge transport capacity, thus strengthening the catalytic activity of the Co2CrO4/RuO2 catalyst. The experimental data demonstrate that Cr leaching facilitates the rapid reconstruction of the catalyst into oxyhydroxides (CoOOH), which are acknowledged to be the real active species of OER. Theoretical calculations show that the Co2CrO4/RuO2 heterostructure increases the density state at the Fermi energy level and lowers the d-band center, thereby strengthening the catalytic activity. The synthesized Co2CrO4/RuO2 catalyst exhibited OER performance with an overpotential of 209 mV at 10 mA cm-2 and displayed a low Tafel slope of 78.2 mV dec-1, which outperforms most reported advanced alkaline OER catalysts. This work contributes to a new tactic for the design and development of ruthenium oxide/bimetallic oxides electrocatalysts.

Investigation into enhanced performance of toluene and Hg0 stimulative abatement over Cr-Mn oxides co-modified columnar activated coke.

In this study, a string of Cr-Mn co-modified activated coke catalysts (XCryMn1-y/AC) were prepared to investigate toluene and Hg0 removal performance. Multifarious characterizations including XRD, TEM, SEM, in situ DRIFTS, BET, XPS and H2-TPR showed that 4%Cr0.5Mn0.5/AC had excellent physicochemical properties and exhibited the best toluene and Hg0 removal efficiency at 200℃. By varying the experimental gas components and conditions, it was found that too large weight hourly space velocity would reduce the removal efficiency of toluene and Hg0. Although O2 promoted the abatement of toluene and Hg0, the inhibitory role of H2O and SO2 offset the promoting effect of O2 to some extent. Toluene significantly inhibited Hg0 removal, resulting from that toluene was present at concentrations orders of magnitude greater than mercury's or the catalyst was more prone to adsorb toluene, while Hg0 almost exerted non-existent influence on toluene elimination. The mechanistic analysis showed that the forms of toluene and Hg0 removal included both adsorption and oxidation, where the high-valent metal cations and oxygen vacancy clusters promoted the redox cycle of Cr3+ + Mn3+/Mn4+ ↔ Cr6+ + Mn2+, which facilitated the conversion and replenishment of reactive oxygen species in the oxidation process, and even the CrMn1.5O4 spinel structure could provide a larger catalytic interface, thus enhancing the adsorption/oxidation of toluene and Hg0. Therefore, its excellent physicochemical properties make it a cost-effective potential industrial catalyst with outstanding synergistic toluene and Hg0 removal performance and preeminent resistance to H2O and SO2.

Simultaneous immobilization of multiple heavy metal(loid)s in contaminated water and alkaline soil inoculated Fe/Mn oxidizing bacterium.

Two strains of Fe/Mn oxidizing bacteria tolerant to high concentrations of multiple heavy metal(loid)s and efficient decontamination for them were screened. The surface of the bio-Fe/Mn oxides produced by the oxidation of Fe(II) and Mn(II) by Pseudomonas taiwanensis (marked as P4) and Pseudomonas plecoglossicida (marked as G1) contains rich reactive oxygen functional groups, which play critical roles in the removal efficiency and immobilization of heavy metal(loid)s in co-contamination system. The isolated strains P4 and G1 can grow well in the following environments: pH 5-9, NaCl 0-4%, and temperature 20-30°C. The removal efficiencies of Fe, Pb, As, Zn, Cd, Cu, and Mn are effective after inoculation of the strains P4 and G1 in the simulated water system (the initial concentrations of heavy metal(loid) were 1 mg/L), approximately reaching 96%, 92%, 85%, 67%, 70%, 54% and 15%, respectively. The exchangeable and carbonate bound As, Cd, Pb and Cu are more inclined to convert to the Fe-Mn oxide bound fractions in P4 and G1 treated soil, thereby reducing the phytoavailability and bioaccessible of heavy metal(loid)s. This research provides alternatives method to treat water and soil containing high concentrations of multi-heavy metal(loid)s.

Exploring the HONO source during the COVID-19 pandemic in a megacity in China.

HONO is a critical precursor of •OH, but its sources are controversial due to its complex formation mechanism. This study conducted comprehensive observations in Zhengzhou from April 26 to May 11, 2022. Low NOx concentrations were observed during the Covid epidemic period (EP) (10.4 ± 3.0 ppb), compared to the pre-epidemic period (PEP) (12.5 ± 3.8 ppb). The mean HONO concentration during EP (0.53 ± 0.34 ppb) was 0.09 ppb lower than that during PEP (0.62 ± 0.53 ppb). The decrease in HONO concentration during EP came mainly at night due to the reduction in the direct emission (Pemi) (0.03 ppb/hr), the homogeneous reaction between •OH and NO (POH+NO) (0.02 ppb/hr), and the heterogeneous conversion of NO2 on the ground (0.01 ppb/hr). Notably, there was no significant change in daytime HONO concentration. The daytime HONO budget indicated that the primary HONO sources during PEP were the nitrate photolysis (Pnitrate), followed by the POH+NO, Pemi, the photo-enhanced reaction of NO2 on the ground (Pground+hv) and aerosol surface (Paerosol+hv). The primary HONO sources were Pnitrate, POH+NO, Pemi, and Paerosol+hv during EP, respectively. The missing source has a high correlation with solar radiation, there might be other photo-related HONO sources or the contributions of photosensitized reactions were underestimated. In the extremely underestimated cases, HONO production rates from the Pnitrate, Pground+hv, and Paerosol+hv increased by 0.17, 0.10, and 0.10 ppb/hr during PEP, 0.23, 0.13, and 0.16 ppb/hr during EP, and Pnitrate was still the primary source during both PEP and EP.

Multifunctional HxMoO3-y-MoO2/Carbon Composite Particles for Water Remediation.

Solving a scarcity of freshwater resources is an urgent global challenge by a safe and sustainable approach using renewable energy. We demonstrate the multifunctional catalyst of HxMoO3-y-MoO2/carbon composite particles toward highly efficient water remediation. A one-step mechanochemical reaction successfully upgraded the composites from commercially available MoO3-polypropylene (PP) powders without introducing hydrogen gas. The composite particles exhibited broad light absorption in the UV-visible (Vis)-near-infrared (NIR) region (200-2000 nm), with an optical band-gap narrowing to 1.03 eV. The plasmonic properties of HxMoO3-y-MoO2 allowed a fast water evaporation rate (3.29 kg m-2 h-1) with a photothermal conversion efficiency of 88.8%. In addition, the HxMoO3-y-MoO2 heterojunction dominated wide-spectrum activity under Vis and NIR light irradiation, up to 3 orders of magnitude higher than pristine MoO3 in the photocatalytic degradation of azo-dye pollutants. Furthermore, the byproduct carbon with abundant oxygen-containing groups efficiently eliminated water pollutants as a Brønsted acid catalyst and performed exceptional adsorption capacities of heavy metal ions in the dark.

Chromium(VI) Adsorption and Reduction in Soils under Anoxic Conditions: The Relative Roles of Iron (oxyhr)oxides, Iron(II), Organic Matters, and Microbes.

Chromium (Cr) transformation in soils mediated by iron (Fe) (oxyhr)oxides, Fe(II), organic matter (OM), and microbes is largely unexplored. Here, their coupling processes and mechanisms were investigated during anoxic incubation experiments of four Cr(VI) spiked soil samples with distinct physicochemical properties from the tropical and subtropical regions of China. It demonstrates that easily oxidizable organic carbon (EOC, 55-84%) and microbes (16-48%) drive Cr(VI) reduction in soils enriched with goethite and/or hematite, among which in dryland soils microbial sulfate reduction may also be involved. In contrast, EOC (38 ± 1%), microbes (33 ± 1%), and exchangeable and poorly crystalline Fe (oxyhr)oxide-associated Fe(II) (29 ± 3%) contribute to Cr(VI) reduction in paddy soils enriched with ferrihydrite. Additionally, exogenous Fe(II) and microbes significantly enhance Cr(VI) reduction in ferrihydrite- and goethite-rich soils, and Fe(II) greatly promotes but microbes slightly inhibit Cr passivation. Both Fe(II) and microbes, especially the latter, promote OM mineralization and result in the most substantial OM loss in ferrihydrite-rich paddy soils. During the incubation, part of the ferrihydrite converts to goethite but microbes may hinder the transformation. These results provide deep insights into the geochemical fates of redox-sensitive heavy metals mediated by the complicated effects of Fe, OM, and microbes in natural and engineered environments.

Enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation with addition of red mud: Performance and mechanisms.

Red mud (RM) as hazardous waste produced from aluminum refining industry has threatened the environment and human health. In this study, RM was added into the fermenter to promote short chain fatty acids (SCFAs) production from waste activated sludge (WAS) anaerobic fermentation. Results showed that the addition of RM could effectively improve the SCFAs production, especially, acetic acid. In particular, the production of total SCFAs and acetic acid in 20 g/L RM added fermenter were 1108.1 mg COD/L and 415.5 mg COD/L, which were 116.0% and 1308.0% higher than that in control fermenter. Batch experiment revealed that RM could enhance the hydrolysis and acidification process. Further study indicated that the activity of enzyme related to hydrolysis-acidification, abundance of fermentative bacteria for SCFAs production and functional metabolism genome were all improved with the addition of RM. The potential mechanism maybe that the RM promoted the hydrolysis-acidification process with the contained varies Fe(Ⅲ) oxides as electron acceptor, and the produced Fe2+ could serve as necessary trace elements to synthesize enzyme and then stimulate the expression of enzyme genes.

Quantifying kinetically relevant species on Zr-SiO2 materials for MPV reduction.

On supported metal catalysts such as Zr-SiO2, it can be challenging to isolate characteristics that result from intrinsic properties of the active site from those that result from the environment surrounding the active site. In this report, we utilize in situ titration of Lewis acid sites with phosphonic acid to accurately and quantitatively describe kinetically relevant Zr species on Zr-SiO2 materials for the MPV reduction of cyclohexanone. We find that rate of MPV reduction on Zr-SiO2 materials can be described as a combination of rate over titratable Zr, that is likely well dispersed Zr, and rate over non-titratable Zr, that is likely supported ZrOx. The fraction of Zr that is well dispersed on the SiO2 is dependent on the surface density at which Zr is grafted but not the choice of Zr precursor. We demonstrate that phosphonic acid titration can offer a more relevant, quantitative description of Zr dispersion than UV-vis and can be used to quantitatively describe changes that occur to the material during regeneration.

New Suggestion of Highly Durable Electrode Design for Ordered Mesoporous Ni-Mn Binary Transition Metal Oxide Anode Material in Lithium-Ion Batteries.

Anode materials storing large-scale lithium ions gradually decrease electrochemical performance due to severe volume changes during cycling. Therefore, there is an urgent need to develop anode materials with high electrochemical capacity and durability, without deterioration arising due to the volume changes during the electrochemical processes. To date, mesoporous materials have received attention as anode materials due to their ability to mitigate volume expansion, offer a short pathway for Li+ transport, and exhibit anomalous high capacity. However, the nano-frameworks of transition metal oxide collapse during conversion reactions, demanding an improvement in nano-framework structure stability. In this study, ordered mesoporous nickel manganese oxide (m-NMO) is designed as an anode material with a highly durable nanostructure. Interestingly, m-NMO showed better cycle performance and higher electrochemical capacity than those of nickel oxide and manganese oxide. Operando small-angle X-ray scattering and ex situ transmission electron microscopic results confirmed that the binary m-NMO sustained a highly durable nanostructure upon cycling, unlike the single metal oxide electrodes where the mesostructures collapsed. Ex situ X-ray absorption spectroscopy proved that nickel and manganese showed different electrochemical reaction voltages, and thus undergoes sequential conversion reactions. As a result, both elements can act as complementary nano-propping buffers to maintain stable mesostructure.

Crystalline-Amorphous IrOx Supported on Perovskite Nanotubes for pH-Universal OER.

Designing catalysts with desirable oxygen evolution reaction (OER) performance under pH-universal conditions is of great significance to promote the development of hydrogen production. Herein, we successfully synthesized a crystalline-amorphous IrOx supported on perovskite oxide nanotubes to obtain IrOx@La0.6Ca0.4Fe0.8Ni0.2O3 with superior OER performance in whole pH media. The overpotential of the IrOx@La0.6Ca0.4Fe0.8Ni0.2O3 catalyst in media of pH 14, 7.2, and 1 has been demonstrated to be 120, 400, and 143 mV, respectively, with no significant element dissolution as well as double-layer capacitance decay after the durability test. Through comparative experiments with IrOx@CNT and the physical mixture of IrOx and La0.6Ca0.4Fe0.8Ni0.2O3, it is found that the strong metal-support interaction (SMSI) in IrOx@La0.6Ca0.4Fe0.8Ni0.2O3 makes IrOx exist in an amorphous state rich in Ir3+, which is closely associated with the surface-active species Ir-OH. Through the regulation of Ir by a perovskite oxide support at the heterointerface, the reaction breaks through the limitation of the adsorbate evolution mechanism (AEM) and converts to a lattice-oxygen-mediated mechanism (LOM), which was fully demonstrated by the addition of the probe tetramethylammonium cation (TMA+), a LOM reaction intermediate, to the electrolyte. This work fills the research gap of perovskite oxide supported Ir-based catalysts with heterogeneous structures, providing an excellent strategy for the structural design of efficient pH-universal OER catalysts for hydrogen production systems.

Improving the Performance of the Layered Nickel Manganese Oxide Cathode of Sodium-Ion Batteries by Direct Coating with Sodium Niobium Oxide.

This research highlights the efficacy of NaNbO3 as a coating for P2-Na2/3Ni1/3Mn2/3O2 cathodes in sodium-ion batteries. The coating enhances the kinetic behavior and cyclability of the electrochemical cells, as shown by electrochemical measurements. XRD analysis indicates that Nb does not incorporate into the cathode structure, implying a physical interaction between the coating and the cathode material. XRF analysis and EDX mapping confirm the actual composition and uniform dispersion of elements throughout the sample, while the electron micrographs evidence the occurrence of NaNbO3 particles modifying the surface of the layered oxide. The Ni4+/Ni3+ and Ni3+/Ni2+ redox pairs, along with the partially reversible oxidation of oxide to peroxide anions, contribute significantly to cell capacity, as revealed by XPS spectra. This last effect and the appearance of a co-intercalated phase at high voltage are positive factors to provide fast kinetics. Cyclic voltammograms show that samples coated with 2-3% NaNbO3 have superior rate capability, with high capacitive response and apparent diffusion coefficients. These samples also have low impedance at the electrode-electrolyte interface, which helps deliver a high capacity at 5C. Further cycling at 1C shows improved cyclability in the bare and 3% coated samples, due to their higher diffusion coefficients on charging. Notably, the 3% NaNbO3-coated sample exhibits excellent cyclability below 0 °C, making it a promising cathode material for sodium-ion batteries.

Size-Dependent Core-Shell Fine Structures and Oxygen Evolution Activity of Electrochemical IrOx Nanoparticles Revealed by Cryogenic Electron Microscopy.

Electrochemically oxidized amorphous iridium oxides (IrOx) offer significantly improved electrocatalytic activities on the oxygen evolution reaction (OER) compared to crystalline IrO2, yet the origin of their decent activity and their size-dependent properties have not been fully understood. An important argument is the formation of deprotonated oxygen species not only at the topmost surface but also at the near surface, which creates an electrophilic character that activates the OER electrocatalysis. However, high spatial resolution identification of the electrophilic oxygen species remains unachieved. We address this hitherto-unresolved problem on size-selected electrochemical IrOx nanoparticles (NPs) by using cryogenic scanning transmission electron microscopy combined with electron energy loss spectroscopy, which enables simultaneous atomic detection of the near surface compositional and electronic structures with minimal damage that are further correlated with their size-dependent OER activities. Depending on the particle size, the electrochemical IrOx NPs showed distinctly different core-shell fine structures ranging from amorphous and hydrous IrOxHy NPs to a "metallic Ir core/sub-stoichiometric IrOx interlayer/amorphous IrOxHy shell" NP structure. Moreover, the formation of deprotonated, electrophilic oxygen is directly identified at the substoichiometric IrOx interface layer. These features account for a previously unestablished particle size effect of the electrochemical IrOx NPs, showing increasing water oxidation reactivity with an increasing nanoparticle size. Our results provide important insights into how subsurface oxygen chemistry controls the surface reactivity in the nanoscale Ir-based OER electrocatalysts.

Fe (hydr)oxides and organic colloids mediate colloid-bound chromium mobilization in Cr(VI) contaminated paddy soil.

The association of chromium (Cr) with colloidal particles transport in contaminated sites can affect hexavalent chromium (Cr(VI)) migration and transformation, which is an important mechanism for Cr pollutants in soil and groundwater systems. Here, we investigated colloid and particle-bound Cr migration and transformation effects on rice Cr accumulation during different rice growth stages and different redox conditions in Cr(VI) contaminated soil by pot experiment. Results showed that 13-29% of soil Cr was water dispersible colloid-bound (100-1000 nm) form during rice growth. Using transmission electron microscopy - energy dispersion spectroscopy and asymmetric flow field - flow separation, we identified colloid-bound organic matter (OM) and iron (Fe), most likely in the form of Fe (hydr)oxides - clay composites, as the primary Cr carrier. Specifically, colloid-bound Cr was mainly associated with 125-350 nm soil particle size. Under different redox conditions, colloid- and nanoparticle-bound Cr concentration decreased with increasing nanoparticles zero-valent iron (nZVI) dose. Soil reoxidation promoted the colloid- and nanoparticle-bound Cr release due to the weakly crystalline Fe-(hydr)oxides reprecipitation. Further quantitative analysis showed that colloid-bound Cr concentrations were positively correlated with colloid-bound Mn concentrations during the whole rice growth soils. Most important of all, Cr content in rice grain was positively correlated with colloid-bound Cr significantly. This study provides a quantitative and size-resolved understanding of particle-bound Cr in paddy soils, highlighting the importance of colloid-bound Cr and Fe interactions in Cr geochemical cycle of paddy soil.

Electronic structure, global reactivity descriptors and nonlinear optical properties of glycine interacted with ZnO, MgO and CaO for bacterial detection.

Modern laboratory medicine relies on analytical instruments for bacterial detection, focusing on biosensors and optical sensors for early disease diagnosis and treatment. Thus, Density Functional Theory (DFT) was utilized to study the reactivity of glycine interacted with metal oxides (ZnO, MgO, and CaO) for bacterial detection. Total dipole moment (TDM), frontier molecular orbitals (FMOs), FTIR spectroscopic data, electronic transition states, chemical reactivity descriptors, nonlinear optical (NLO) characteristics, and molecular electrostatic potential (MESP) were all investigated at the B3LYP/6-31G(d, p) level using DFT and Time-Dependent DFT (TD-DFT). The Coulomb-attenuating approach (CAM-B3LYP) was utilized to obtain theoretical electronic absorption spectra with the 6-31G(d, p) basis set to be more accurate than alternative quantum chemical calculation approaches, showing good agreement with the experimental data. The TDM and FMO investigation showed that glycine/CaO model has the highest TDM (10.129Debye) and lowest band gap (1.643 eV). The DFT computed IR and the experimental FTIR are consistent. The calculated UV-vis spectra showed a red shift with an increase in polarity following an increase in the absorption wavelength due to the interaction with ZnO, MgO, and CaO. Among the five solvents of water, methanol, ethanol, DMSO and acetone, the water and DMSO enhances the UV-Vis absorption. Glycine/CaO model showed high linear polarizability (14.629 × 10-24esu) and first hyperpolarizability (23.117 × 10-30esu), indicating its potential for nonlinear optical applications. The results showed that all model molecules, particularly glycine/CaO, contribute significantly to the development of materials with potential NLO features for sensor and optoelectronic applications. Additionally, MESP confirmed the increased electronegativity of the studied structures. Additionally, glycine/ZnO nanocomposite was synthesized and characterized using IR and UV-visible spectroscopy to determine their structural and spectroscopic features. It was discovered that there was good agreement between the DFT computed findings and the related experimental data. The antibacterial activity of glycine/ZnO nanocomposites against Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa were studied in terms of concentration and time. The results showed that increasing the concentration of glycine/ZnO nanocomposite significantly enhanced its antibacterial efficacy by lowering optical density. Notably, Pseudomonas aeruginosa exhibited lower susceptibility to the nanocomposite compared to S. aureus, requiring higher concentrations for effective bactericidal action. In summary, this study contributes novel insights into the dual functionality of glycine-metal oxide complexes, with significant implications as optical biosensor for microbial detection.

Crystalline iron oxide mineral (magnetite) accelerates methane production from petroleum hydrocarbon biodegradation.

Methane (CH4) emissions are a factor in climate change; in addition, CH4 production may affect reclamation of fluid fine tailings (FFT) in tailings ponds, and end-pit lakes (EPLs). In laboratory cultures, we investigated the effect of crystalline iron mineral (magnetite) on CH4 production from the biodegradation of hydrocarbons added to FFT collected from methanogenically more and less active sites in a demonstration EPL. Magnetite enhanced CH4 production from both sites, having a greater effect in more active FFT, where it increased the CH4 production rate as much as 48% (from 6.67 µmol d-1 to 9.87 µmol d-1) compared to FFT without magnetite. Correspondingly, magnetite hastened biodegradation of hydrocarbons (monoaromatics, n-alkanes and iso-alkanes), with a pronounced effect on o-xylene, ethylbenzene, m/p-xylenes, n-octane, n-nonane, and 2-methyloctane, where biodegradation rates increased by 46, 117, 11, 45, 28 and 37%, respectively, compared to FFT without magnetite. Little FeII was produced, suggesting that magnetite is not being used as an electron acceptor but rather functions as a conduit for electron transfer. Thus, magnetite may be a suitable amendment to enhance bioremediation of anaerobic environments contaminated with hydrocarbons. Importantly, our observations imply that magnetite may increase CH4 emissions from terrestrial ecosystems, thus affecting carbon budget estimations.

Enhanced nitrogen removal in constructed wetlands with multivalent manganese oxides: Mechanisms underlying ammonium oxidation processes.

The ammonium (NH4+) removal efficiency in constructed wetlands (CWs) is often limited by insufficient oxygen. In this study, an extract of Eucalyptus robusta Smith leaves was used to prepare multivalent manganese oxides (MVMOs) as substrates, which were used to drive manganese oxide (MnOx) reduction coupled to anaerobic NH4+ oxidation (Mnammox). To investigate the effects and mechanisms of MVMOs on ammonium nitrogen (NH4+-N) removal, four laboratory-scale CWs (0 %/5 %/15 %/25 % volume ratios of MVMOs) were set up and operated as continuous systems. The results showed that compared to controlled C-CW (0 % MVMOs), Mn25-CW (25 % MVMOs) improved the average NH4+-N removal efficiency from 24.31 % to 80.51 %. Furthermore, N2O emissions were reduced by 81.12 % for Mn25-CW. Isotopic tracer incubations provided direct evidence of Mnammox occurrence in Mn-CWs, contributing to 18.05-43.64 % of NH4+-N removal, primarily through the N2-producing pathway (73.54-90.37 %). Notably, batch experiments indicated that Mn(III) played a predominant role in Mnammox. Finally, microbial analysis revealed the highest abundance of the nitrifying bacteria Nitrospira and Mn-cycling bacteria Pseudomonas, Geobacter, Anaeromyxobacter, Geothrix and Novosphingobium in Mn25-CW, corresponding to its superior NH4+-N removal efficiency. The enhancement of NH4+ oxidation, first to hydroxylamine and then to nitrite, in Mn25-CW was attributed to the upregulation of ammonia monooxygenase genes (amoABC and hao). This study enhanced our understanding of Mnammox and provided further support for the use of manganese oxide substrates in CWs for efficient NH4+-N removal.

Challenges and Modification Strategies on High-voltage Layered Oxide Cathode for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted great attention due to their advantages on resource abundance, cost and safety. Layered oxide cathodes (LOCs) of SIBs possess high theoretical capacity, facile synthesis and low cost, and are promising candidates for large scale energy storage application. Increasing operating voltage is an effective strategy to achieve higher specific capacity and also high energy density of SIBs. However, at high operating voltages, LOCs will undergo a series of phase transitions in bulk phase, leading to huge change of volume and layer spacings accompanied by severe lattice stress and cracking formation. Degeneration of surface also occurs between LOCs and electrolytes, resulting in sustained growth of cathode electrolyte interphase (CEI) and release of O2 and CO2. These induce structural destruction and electrochemical performance degradation in high voltage regions. Recently, many strategies have been proposed to improve electrochemical performance of LOCs under high voltages, including bulk element doping, structural design, surface coating and gradient doping. This review describes pivotal challenges and occurrence mechanisms at high voltages, and summarizes strategies to improve stability of bulk and surface. Viewpoints will be provided to promote development of high energy density SIBs.

Quantum Spin Exchange Interactions Trigger O p Band Broadening for Enhanced Aqueous Zinc-Ion Battery Performance.

The pressing demand for large-scale energy storage solutions has propelled the development of advanced battery technologies, among which zinc-ion batteries (ZIBs) are prominent due to their resource abundance, high capacity, and safety in aqueous environments. However, the use of manganese oxide cathodes in ZIBs is challenged by their poor electrical conductivity and structural stability, stemming from the intrinsic properties of MnO2 and the destabilizing effects of ion intercalation. To overcome these limitations, our research delves into atomic-level engineering, emphasizing quantum spin exchange interactions (QSEI). These essential for modifying electronic characteristics, can significantly influence material efficiency and functionality. We demonstrate through density functional theory (DFT) calculations that enhanced QSEI in manganese oxides broadens the O p band, narrows the bandgap, and improves both proton adsorption and electron transport. Empirical evidence is provided through the synthesis of Ru-MnO2 nanosheets, which display a marked increase in energy storage capacity, achieving 314.4 mAh g-1 at 0.2 A g-1 and maintaining high capacity after 2000 cycles. Our findings underscore the potential of QSEI to enhance the performance of TMO cathodes in ZIBs, pointing to new avenues for advancing battery technology.

Engineering a superionic conductor surface enables fast Na+ transport kinetics for high-stable layered oxide cathode.

Unstable cathode/electrolyte interphase and severe interfacial side reaction have long been identified as the main cause for the failure of layered oxide cathode during fast charging and long-term cycling for rechargeable sodium-ion batteries. Here, we report a superionic conductor (Na3V2(PO4)3, NVP) bonding surface strategy for O3-type layered NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode to suppress electrolyte corrosion and near-surface structure deconstruction, especially at high operating potential. The strong bonding affinity at the NVP/NFM contact interface stabilizes the crystal structure by inhibiting surface parasitic reactions and transition metal dissolution, thus significantly improving the phase change reversibility at high desodiation state and prolonging the lifespan of NFM cathode. Due to the high-electron-conductivity of NFM, the redox activity of NVP is also enhanced to provide additional capacity. Therefore, benefiting from the fast ion transport kinetics and electrochemical Na+-storage activity of NVP, the composite NFM@NVP electrode displays a high initial coulombic efficiency of 95.5 % at 0.1 C and excellent rate capability (100 mAh g-1 at 20 C) within high cutoff voltage of 4.2 V. The optimized cathode also delivers preeminent cyclic stability with ∼80 % capacity retention after 500 cycles at 2 C. This work sheds light on a facile and universal strategy on improving interphase stability to develop fast-charging and sustainable batteries.