Search Results (196)

Oxygen vacancies play a crucial role in modulating the chemical and catalytic properties of metal oxide catalysts. Herein, quercetin was used as a green reducing agent to prepare Cu-doped MnO₂ (Cu-MnO₂) composite catalysts with varying Cu doping levels via an ultrasonically assisted strategy. The structure-activity relationships were systematically investigated using XRD, Raman, XPS, H₂-TPR, and O₂-TPD. Benefiting from optimized surface lattice defects induced by an appropriate Cu doping level, the Cu-MnO₂-2 sample, which exhibited the highest oxygen vacancy concentration, achieved a HCHO removal efficiency of 99.2% for 1 ppm HCHO at room temperature (25 °C) and 50% relative humidity within 30 min. The enrichment of Mn³⁺, Cu⁺, and surface-adsorbed oxygen species (O_ads) further corroborated the increased oxygen vacancy density, indicating that moderate Cu doping effectively promotes electron transfer and oxygen activation. After five consecutive cycles, the HCHO conversion remained above 96%. Post-cycling characterizations (XRD, FTIR, EDS, and XPS) confirmed the excellent structural and chemical stability of the catalyst, with the Mn³⁺ proportion and Cu⁺/Cu²⁺ ratio well preserved. In situ DRIFTS analysis revealed that surface-adsorbed oxygen and oxygen-vacancy-activated reactive oxygen species (ROS) are key factors in the efficient HCHO oxidation over the green Cu-MnO₂-2 catalyst, promoting rapid conversion of intermediates and ultimately generating CO₂ and H₂O. This study provides a facile, low-cost, and green synthesis strategy for Cu-MnO₂ composite catalysts for indoor, room-temperature HCHO abatement, offering new insights into the design of other composite catalyst materials. Full article

Carbon monoxide (CO) is a highly toxic, colorless, and odorless gas posing significant risks to human health and the environment. Catalytic oxidation offers a promising, economically viable solution by converting CO into nontoxic CO₂ under mild conditions without energy-intensive regeneration. However, existing MnO₂-based catalysts often exhibit poor activity and stability in harsh environments, particularly at low temperatures and high humidity. In this study, we propose a Cu²⁺ ion-exchange modification strategy to activate lattice oxygen species in δ-MnO₂, thereby significantly enhancing its low-temperature CO oxidation performance. Structural characterization by XRD and SEM confirms that Cu-doped δ-MnO₂ retains its original birnessite-type structure and porous morphology. ICP-OES and XPS analyses verify that Cu²⁺ ions effectively replace interlayer K⁺ ions. The resulting MnO₂-150Cu catalyst demonstrates exceptional activity, achieving 100% CO conversion at 40 °C in dry air and maintaining full conversion at 80 °C in the presence of 1.3 vol.% H₂O at a weight hourly space velocity of 150 L/g·h. H₂-TPR and O₂-TPD results confirm that Cu doping enhances the reducibility and mobility of lattice oxygen. Furthermore, in situ DRIFTS analysis reveals that the migration of active oxygen species is the rate-limiting step at low temperatures. This work provides a novel and effective strategy for activating lattice oxygen in MnO₂-based catalysts, offering a promising pathway for developing high-performance materials for low-temperature CO oxidation under practical environmental conditions. Full article

The reaction of the pyridylalcohol Ph₂C(OH)CH₂-2-py-6-Me (IH) with Me₃Al in refluxing toluene led to the isolation of the dimer [AlMe₂(μ-OC(Me)Ph₂)]₂ (1), whilst at ambient temperature the complex [(I)AlMe₂]·MeCN (2·MeCN) was isolated. Complex 1 is also readily available via the interaction of diphenylethanol and Me₃Al. Similar treatment of iPr₂C(OH)CH₂-2-py-6-Me (IIH) at ambient temperature afforded [(II)AlMe₂] (3). Treatment of IH and IIH with [VO(OiPr)₃] led to oxo-bridged complexes of the type [(VO)(μ₂-O)(I/II)]₂ (I (4·0.67MeCN), II (5)). The molecular structures of 1–5 are reported. These complexes have been employed as catalysts for the ring-opening polymerization (ROP) of the cyclic esters ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL). For aluminium, complex 1/BnOH produced medium- to high-molecular-weight (M_n) PCL at 20 to 110 °C in solution, though some bi-/multi-modal behaviour was observed; for melts the M_n values were toward the lower end. For complexes 2 and 3, far lower M_n values for PCL were observed at 20 °C in solution and as melts, whilst in solution at 110 °C higher M_n values were achieved, though with less control. In general, M_n values for the PCL obtained using the vanadium complexes were low (≤8560 Da for 4, ≤2920 Da for 5). In the case of PVL, 1/BnOH in solution exhibited higher M_n values at lower temperatures with good control, and when employed as a melt, the M_n was toward the higher end (30,830 Da) observed. For 2/BnOH, much lower M_n values (≤2740 Da) were recorded both in solution and as a melt, whilst for 3, high M_n values were only observed in the absence of BnOH. Low M_n values (≤2920 Da) were also observed for the vanadium complexes 4 and 5. Kinetic results (both ε-CL and δ-VL) revealed that the vanadium complexes, particularly 4, outperformed the aluminium complexes. MALDI-ToF spectra revealed the formation of linear PCL polymers with BnO/H end groups for the aluminium/BnOH complexes in solution, and cyclic polymers when employed as melts. For vanadium, cyclic PCL polymers were the major family present. In the case of PVL, linear (BnO/H end groups) and cyclic polymers were observed when employing the Al/BnOH systems, whilst cyclic polymers were observed for vanadium. Copolymerization of ε-CL and δ-VL using 4/BnOH at 110 °C over 24 h led to incomplete conversion and formation of a random-type copolymer. Full article

The potential of La_0.2Sr_0.8MnO₃ (LSM28) perovskite oxide for thermochemical energy storage (TCES) is assessed by analyzing its thermochemical performance. The TCES capacity of LSM28 was measured using a non-stoichiometric and van’t Hoff analysis at various reduction temperatures ( T r e d ) and oxygen partial pressures ( P O 2 ). O₂ release and the associated non-stoichiometry (δ) increase with T r e d and decrease with P O 2 , according to the results, reaching a maximum δ of 0.101 at 1473 K and 0.0001 atm. The van’t Hoff research also showed that LSM28’s TCES capacity fluctuates greatly with δ, peaking at 37.1 kJ/kg under ideal circumstances. Full article

The Bagenheigqier medium-sized Pb-Zn deposit is located in central-southern segment of Great Xing’an Range, northeastern China, where its vein-type orebodies are hosted within the structural contact zone between the Lower Permian Dashi Formation and granite porphyry intrusions. Five mineralization stages are divided into skarn (I), oxide (II), quartz-pyrite-arsenopyrite (III), quartz-polymetallic sulfide (IV), and quartz-calcite-pyrite (V). Three types of fluid inclusions (FIs) are identified in Bagenheigeqier Pb-Zn deposit, including daughter mineral-bearing three-phase (SL-type), vapor–liquid two-phase (VL-type), and vapor-rich two-phase (LV-type) FIs. All FI types occur in Stages I–III, with homogenization temperatures (Th) of 423–486, 389–441, 362–408 °C, and salinities of 1.1–49.2, 0.9–43.9 and 0.9–38.8 wt.% NaCl equiv, respectively. Stage IV hosts only VL- and LV-type FIs (Th: 277–319 °C; salinity: 2.1–8.7 wt.% NaCl equiv), whereas Stage V contains exclusively VL-type FIs with Th of 173–214 °C and salinity of 1.2–5.7 wt.% NaCl equiv. The H-O isotopic results of quartz in stage II–IV (δD = −103.5‰–−99.1‰, −115.7‰–−107.8‰ and −121.5‰–−117.2‰; δ¹⁸O_H2O = 4.4‰–7.1‰, 1.1‰–3.5‰ and −4.6‰–−3.5‰) indicate the ore-forming fluids are predominantly of magmatic origin with subordinate meteoric water mixing. Fluid boiling and the mixing of meteoric water may lead to the precipitation of metal. The in situ trace elements analyses indicate that sphalerites in main mineralization stage are enriched in Fe, Mn, Co and In and depleted in Ga and Ge. The calculation results suggest that the sphalerites crystallized under moderate temperature conditions (286–330 °C) and intermediate f_S2 (−10.5 to −9.2) conditions. The geological, fluid inclusion, isotopic and trace element evidences indicate that the Bagenheigeqier deposit is classified as a skarn-type deposit. Full article

Little is known of a large black shale belt within the Naij Tal Group in the East Kunlun region, which hosts polymetallic deposits, including manganese, vanadium, and cobalt. The recently discovered Dagangou vanadium mineralization is the first black rock series-type vanadium deposit in the East Kunlun region and Qinghai Province and represents a significant find owing to its intermediate scale. This study investigated the mineralogy, major and trace elements, rare earth elements, and platinum group element geochemistry of the Dagangou vanadium deposit. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed that the main vanadium-bearing minerals are micas, followed by limonite, clay minerals, feldspar, and jarosite. The SiO₂/Al₂O₃, Co/Zn, Sr/Ba, and Pd/Ir ratios, as well as the Ir content of the ores, indicated strong involvement of hydrothermal activity in the mineralization process. The V/Cr, Ni/Co, and U/Th ratios, as well as the δU values and significant negative δCe anomalies, suggested that the vanadium-bearing black rock series formed in a strongly anoxic reducing environment. The Al₂O₃/(Al₂O₃ + Fe₂O₃) and MnO/TiO₂ ratios, along with weak positive δEu anomalies and strong enrichment of heavy rare earth elements, indicated that mineralization occurred in an extensional tectonic setting. The black shale-hosted vanadium polymetallic deposit formed in a setting that transitioned from an open oceanic deep-sea environment to a progressively shallower continental margin. Full article

The South Sakhalin mud volcano (Sakhalin Island, Russia) emits HCO₃-Cl/Na-Mg water, emanates CO₂ prevailing over CH₄ in the gas phase, and extrudes mud bearing five carbonate mineral species. The study focuses on the distribution, diversity, and origin of the carbonate minerals from the mud volcano (MV) ejecta, in terms of carbon cycle processes. The data presented include a synthesis of field observations, compositions of MV gases and waters, chemistry of carbonate minerals, as well as stable isotope geochemistry of MV waters (δ¹³C, δD, and δ¹⁸O) and carbonates (δ¹³C and δ¹⁸O). The sampled MV waters are isotopically heavy, with δ¹⁸O = +5.7‰ to +7.5‰ VSMOW, δD = −18.0‰ to −11.0‰ VSMOW, and ¹³C (δ¹³C_DIC = +6.9‰ to +8.1‰ VPDB). This composition may be due to the dilution of basinal water with dehydration water released during the diagenetic illitization of smectite. Carbonates in the sampled mud masses belong to three genetically different groups. Mg-rich siderite, (Fe_0.54–0.81Mg_0.04–0.30Ca_0.05–0.23Mn_0.00–0.08)CO₃, disseminated in abundance throughout the mud masses, coexists with common calcite and sporadic ankerite. The trace-element chemistry of Mg-siderite, as well as the oxygen (δ¹⁸O = +34.4‰ to +36.8‰ VSMOW) and carbon (δ¹³C = −1.3‰ to +0.6‰ VPDB) isotopic signatures, confirms its authigenic origin. Siderite formed during early diagenesis of the Upper Cretaceous sandy and clayey marine sediments mobilized by mud volcanism in the area. Another assemblage, composed of dawsonite, siderite, and vein calcite (±kaolinite), represents altered arkose sandstones found as few fragments in the mud. This assemblage may be a marker of later CO₂ flooding into the sandstone aquifer in the geological past. The trace-element chemistry, particular morphology, and heavy C (δ¹³C = +5.5‰ to +7.0‰ VPDB) and O (δ¹⁸O = +39.1‰ to +39.5‰ VSMOW) isotope compositions indicate that aragonite is the only carbonate species that is related to the current MV activity. It crystallized in a shallow reservoir and was maintained by CO₂ released from rapidly ascending liquefied mud and HCO₃-Cl/Na-Mg-type of MV waters. Full article

As a potential strategic resource of critical metals, deep-sea cobalt-rich crusts represent one of the most promising metal reservoirs within oceanic seamount systems, and their metallogenic mechanism constitutes a frontier topic in deep-sea geoscience research. This review focuses on the cobalt-rich crusts from the Magellan Seamount region in the northwestern Pacific and synthesizes existing geological, mineralogical, and geochemical studies to systematically elucidate their mineralization processes and metal enrichment mechanisms from a microstructural perspective, with particular emphasis on cobalt enrichment and its controlling factors. Based on published observations and experimental evidence, the formation of cobalt-rich crusts is divided into three stages: (1) Mn/Fe colloid formation—At the chemical interface between oxygen-rich bottom water and the oxygen minimum zone (OMZ), Mn²⁺ and Fe²⁺ are oxidized to form hydrated oxide colloids such as δ-MnO₂ and Fe(OH)₃. (2) Key metal adsorption—Colloidal particles adsorb metal ions such as Co²⁺, Ni²⁺, and Cu²⁺ through surface complexation and oxidation–substitution reactions, among which Co²⁺ is further oxidized to Co³⁺ and stably incorporated into MnO₆ octahedral vacancies. (3) Colloid deposition and mineralization—Mn–Fe colloids aggregate, dehydrate, and cement on the exposed seamount bedrock surface to form layered cobalt-rich crusts. This process is dominated by the Fe/Mn redox cycle, representing a continuous evolution from colloidal reactions to solid-phase mineral formation. Biological processes play a crucial catalytic role in the microstructural evolution of the crusts. Mn-oxidizing bacteria and extracellular polymeric substances (EPS) accelerate Mn oxidation, regulate mineral-oriented growth, and enhance particle cementation, thereby significantly improving the oxidation and adsorption efficiency of metal ions. Tectonic and paleoceanographic evolution, seamount topography, and the circulation of Antarctic Bottom Water jointly control the metallogenic environment and metal sources, while crystal defects, redox gradients, and biological activity collectively drive metal enrichment. This review establishes a conceptual framework of a multi-level metallogenic model linking macroscopic oceanic circulation and geological evolution with microscopic chemical and biological processes, providing a theoretical basis for the exploration, prediction, and sustainable development of potential cobalt-rich crust deposits. Full article

A deterministic platform for engineering epitaxial strain in CaMnO_3-δ (CMO) thermoelectric thin films is demonstrated using pulsed laser deposition, enabling precise control of the interplay between strain state and oxygen vacancy formation. High-quality epitaxial CMO films are grown on four different single crystalline substrates, which impose fully relaxed, partially relaxed, low tensile, and high tensile strain states, respectively. Increasing tensile strain induces a monotonic expansion of the unit cell volume and a systematic rise in oxygen vacancy concentration. Oxygen vacancies increase carrier concentration but decrease mobility due to enhanced scattering. Reducing tensile strain suppresses scattering of electrons by oxygen vacancies and increases both electrical conductivity (σ) and the Seebeck coefficient (S), mitigating the conventional inverse relationship between S and σ. Fully relaxed films exhibit σ approximately four orders of magnitude higher at room temperature than highly tensile strained films. These relaxed films also show the highest power factor (PF = S²·σ), exceeding strained films by up to six orders of magnitude. Strain-controlled oxygen vacancies thus provide a direct route to optimize charge transport and maximize the thermoelectric performance of CMO thin films. Full article

Aluminum-ion batteries (AIBs) are emerging as promising alternatives to lithium-ion batteries due to their cost-effectiveness and resource abundance. However, their practical application is hindered by low capacity, poor cycle life, and limited rate capability. In this study, δ-MnO₂ and δ-MnO₂/Graphene composite cathodes are developed and tested in aqueous aluminum-ion batteries (AAIBs) using a mixture of 0.5 M Al₂(SO₄)₃ and 0.4 M MnSO₄ as the electrolyte. The electrochemical properties are evaluated alongside treated aluminum (TAl) and Zn–Al alloy anodes. Among the configurations tested, the δ-MnO₂/Graphene|0.5 M Al₂(SO₄)₃, 0.4 M MnSO₄|Zn–Al system showed the best performance, achieving a high discharge voltage of 1.63 V, a specific capacity of 746 mAh g⁻¹, and excellent cycling stability over 352 cycles. The stabilizing effect of graphene, due to increased oxygen vacancies and the formation of Mn–O–C bonds, enhances electron and ion transport, thereby improving cathode integrity and the overall performance of the AAIB. Additionally, the Zn–Al alloy anode extends the battery’s cycle life compared to the TAl anode. This work demonstrates the potential for low-cost, high-performance AAIBs, paving the way for more sustainable and scalable energy storage solutions. Full article

Photothermal catalysis has emerged as a promising approach for the efficient and cost-effective removal of volatile organic compounds (VOCs). Pt@MnO₂ catalysts have demonstrated excellent performance in the photothermal catalytic oxidation of VOCs. However, current research has predominantly focused on the interaction between Pt and MnO₂, while often overlooking the influence of the MnO₂ crystal phase. Therefore, in this study, we synthesized Pt supported on four crystal phases (α, β, γ, and δ) of MnO₂ and established the structure–activity relationships through performance evaluation and characterization. Among the prepared catalysts, Pt@Mn[δ] exhibited excellent performance and possessed outstanding stability. Crystal structure characterization revealed that the larger specific surface area and lower crystallinity of Pt@Mn[δ] exposed more active sites. XPS analysis indicated the transformation of Mn⁴⁺ to Mn³⁺ on Pt@Mn[δ], leading to the formation of oxygen vacancies. O₂-TPD and H₂-TPR further confirmed the activation of lattice oxygen and the promoted redox cycle of Pt@Mn[δ]. UV-Vis DRS and electrochemical measurements demonstrated that Pt@Mn[δ] exhibited the most pronounced visible-light absorption, the highest photocurrent density, the lowest charge transfer resistance and superior charge carrier mobility. TD-GC-MS analysis indicated that o-xylene underwent alkylation and isomerization, with subsequent oxidation following the Mars–van Krevelen (MvK) mechanism. Full article

Aqueous zinc-ion batteries (ZIBs) have emerged as a promising candidate for large-scale energy storage due to their inherent safety, low cost, and environmental friendliness. However, manganese dioxide (MnO₂)-based cathodes, which are widely studied for ZIBs owing to their high theoretical capacity and low cost, face severe capacity fading issues that hinder the commercialization of ZIBs. This performance degradation mainly stems from the weak van der Waals forces between MnO₂ layers leading to structural collapse during repeated Zn²⁺ insertion and extraction; it is also exacerbated by irreversible Mn dissolution via Mn³⁺ disproportionation that depletes active materials, and further aggravated by dynamic electrolyte pH fluctuations promoting insulating zinc hydroxide sulfate (ZHS) formation to block ion diffusion channels. To address these interconnected challenges, in this study, a synergistic strategy was developed combining crystal engineering and pH buffer regulation. We synthesized three MnO₂ polymorphs (α-, δ-, γ-MnO₂), identified δ-MnO₂ with flower-like microspheres as optimal, and introduced sodium dihydrogen phosphate (NaH₂PO₄) as a pH buffer (stabilizing pH at 2.8 ± 0.2). The modified electrolyte improved δ-MnO₂ wettability (contact angle of 17.8° in NaH₂PO₄-modified electrolyte vs. 26.1° in base electrolyte) and reduced charge transfer resistance (Rct = 78.17 Ω), enabling the optimized cathode to retain 117.25 mAh g⁻¹ (82.16% retention) after 2500 cycles at 1 A g⁻¹. This work provides an effective strategy for stable MnO₂-based ZIBs, promoting their application in renewable energy storage. Full article

Activated peroxymonosulfate (PMS) processes have emerged as a highly effective advanced oxidation technique for the removal of emerging organic contaminants in water. This study successfully converted δ-MnO₂ into α-MnO₂ through a crystal phase transformation method via the application of a mild water bath heating process, enhancing its catalytic properties. α-MnO₂ (k = 0.092 ± 0.0059 min⁻¹) exhibited significantly higher activity than δ-MnO₂ (k = 0.027 ± 0.0075 min⁻¹) in the PMS-activated degradation of sulfamethoxazole (SMX). Importantly, ¹O₂ was identified as the primary reactive oxygen species in the α-MnO₂ + PMS system for SMX degradation. XPS and O₂-TPD characterizations demonstrated that α-MnO₂ possesses a higher concentration of active lattice oxygen a and lower concentration of Mn(III) than δ-MnO₂. Further analysis reveals that both surface Mn(III) and active lattice oxygen in α-MnO₂ are crucial for PMS activation. Notably, ¹O₂ is predominantly generated through the interaction between PMS and reactive lattice oxygen. Moreover, a heterogeneous PMS activation mechanism toward α-MnO₂ was proposed. This research underscores the critical role of active lattice oxygen in MnO₂ for PMS activation, providing valuable insight relevant to the design of catalysts aimed at pollutant elimination in environmental applications. To the best of our knowledge, our study is the first to report a pathway for MnO₂ crystal phase transition under relatively mild conditions. Full article

In this study, cerium with different ratios (x = 0 (zero), 0.1, 0.15, 0.5) was added to the PrMn structure as an A-site material to evaluate characteristic behavior as a potential cathode material for solid oxide fuel cells. The Pr_xCe_1−xMnO_3−δ electrocatalysts were synthesized using the sol–gel combustion method and were assessed for their electrochemical, phase, and structural properties, as well as desorption and reducibility capabilities. Phase changes, from orthorhombic to cubic structures observed upon cerium additions, were evaluated via the X-Ray diffraction method. X-Ray photoelectron spectroscopy (XPS) showed the valence states of the surface between the Ce⁴⁺/Ce³⁺ and Pr⁴⁺/Pr³⁺ redox pairs, while oxygen temperature programmed desorption (O₂-TPD) analysis was used to evaluate the oxygen adsorption and desorption behavior of the electrocatalysts. Redox characterization, evaluated via hydrogen atmosphere temperature-programmed reduction (H₂-TPR), revealed that a higher cerium ratio in the structure lowered the reduction temperature, suggesting a better dynamic oxygen exchange capability at a lower temperature for the Pr_0.5Ce_0.5MnO_3−δ catalyst compared to the electrochemical behavior analysis by the electrochemical impedance spectroscopy method. Moreover, the symmetrical cell tests with Pr_0.5Ce_0.5MnO_3−δ electrodes showed that, when combined with scandia-stabilized zirconia (ScSZ) electrolyte, the overall polarization resistance was reduced by approximately 28% at 800 °C compared to cells with yttria-stabilized zirconia (YSZ) electrolyte. Full article

Due to its unique layered structure that facilitates ion intercalation and deintercalation, δ-MnO₂ has emerged as a promising cathode material for aqueous zinc-ion batteries (ZIBs). However, its structural collapse and Mn dissolution during prolonged cycling significantly limit its practical application. In this study, we demonstrate that metal ion doping, particularly with Fe³⁺, can effectively stabilize the δ-MnO₂ structure and enhance its electrochemical performance. Through a hydrothermal synthesis approach, δ-MnO₂ materials with varying Fe³⁺ doping ratios are prepared and systematically investigated. Among them, the sample with a Mn:Fe molar ratio of 20:1 exhibits the best performance, maintaining the layered δ-MnO₂ phase while significantly increasing Mn³⁺ content and promoting the formation of oxygen vacancies. At a current density of 0.5 A·g⁻¹, the iron-doped sample exhibited an initial specific capacity of 116.24 mAh·g⁻¹, with a capacity retention rate of 41.7% after 200 cycles. In contrast, the undoped δ-MnO₂ showed an initial specific capacity of only 85.15 mAh·g⁻¹, with a capacity retention rate of merely 19.9% after 200 cycles. The results suggest that Fe³⁺ doping not only suppresses Mn dissolution but also improves structural stability and Zn²⁺ transport kinetics. This work provides new insights into the development of durable Mn-based cathode materials for aqueous ZIBs. Full article