Jahn-Teller Disproportionation Induced Exfoliation of Unit-Cell Scale ϵ-MnO2

Sensitive and Selective Dual-Mode Responses to Reactive Oxygen Species by Chiral Manganese Dioxide Nanoparticles for Antiaging Skin

Excessive accumulation of reactive oxygen species (ROS) can lead to oxidative stress and oxidative damage, which is one of the important factors for aging and age-related diseases. Therefore, real-time monitoring and the moderate elimination of ROS is extremely important. In this study, a ROS-responsive circular dichroic (CD) at 553 nm and magnetic resonance imaging (MRI) dual-signals chiral manganese oxide (MnO2 ) nanoparticles (NPs) are designed and synthesized. Both the CD and MRI signals show excellent linear ranges for intracellular hydrogen peroxide (H2 O2 ) concentrations, with limits of detection (LOD) of 0.0027 nmol/106 cells and 0.016 nmol/106 cells, respectively. The lower LOD achieved with CD detection may be attributable to its higher anti-interference capability from the intracellular matrix. Importantly, ROS-induced cell aging is intervened by chiral MnO2 NPs via redox reactions with excessive intracellular ROS. In vivo experiments confirm that chiral MnO2 NPs effectively eliminate ROS in skin tissue, reduce oxidative stress levels, and alleviate skin aging. This approach provides a new strategy for the diagnosis and treatment of age-related diseases.

Elucidating the Reaction Mechanism of Mn2+ Electrolyte Additives in Aqueous Zinc Batteries

Aqueous zinc batteries (ZIBs) have attracted considerable attention in recent years because of their high safety and eco-friendly features. Numerous studies have shown that adding Mn2+ salts to ZnSO4 electrolytes enhanced overall energy densities and extended the cycling life of Zn/MnO2 batteries. It is commonly believed that Mn2+ additives in the electrolyte inhibit the dissolution of MnO2 cathode. To better understand the role of Mn2+ electrolyte additives, the ZIB using a Co3 O4 cathode instead of MnO2 in 0.3 m MnSO4 + 3 m ZnSO4 electrolyte is built to avoid interference from MnO2 cathode. As expected, the Zn/Co3 O4 battery exhibits electrochemical characteristics nearly identical to those of Zn/MnO2 batteries. Operando synchrotron X-ray diffraction (XRD), ex situ X-ray absorption spectroscopy (XAS), and electrochemical analyses are carried out to determine the reaction mechanism and pathway. This work demonstrates that the electrochemical reaction occurring at cathode involves a reversible Mn2+ /MnO2 deposition/dissolution process, while a chemical reaction of Zn2+ /Zn4 SO4 (OH)6 ∙5H2 O deposition/dissolution is involved during part of the charge/discharge cycle due to the change in the electrolyte environment. The reversible Zn2+ /Zn4 SO4 (OH)6 ∙5H2 O reaction contributes no capacity and lowers the diffusion kinetics of the Mn2+ /MnO2 reaction, which prevents the operation of ZIBs at high current densities.

Two-Dimensional Iron Silicide (FeSix) Alloys with Above-Room-Temperature Ferromagnetism

Two-dimensional (2D) materials with intrinsic room-temperature ferromagnetism have gathered tremendous interest as promising candidates for next-generation spintronics. Here, on the basis of first-principles calculations, we report a family of stable 2D iron silicide (FeSi_x) alloys via dimensional reduction of their bulk counterparts. Our results demonstrate that 2D Fe₄Si₂-hex, Fe₄Si₂-orth, Fe₃Si₂, and FeSi₂ nanosheets are lattice-dynamically and thermally stable, confirmed by the calculated phonon spectra and Born-Oppenheimer dynamic simulation up to 1000 K. 2D FeSi_x nanosheets are ferromagnetic metals with estimated Curie temperatures ranging from 547 to 971 K due to strong direct exchange interaction between Fe sites. In addition, the electronic properties of 2D FeSi_x alloys can be maintained on silicon substrates, providing an ideal platform for spintronics applications in the nanoscale.

Effect of MnO2 Polymorphs' Structure on Low-Temperature Catalytic Oxidation: Crystalline Controlled Oxygen Vacancy Formation

MnO₂ polymorphs (α-, β-, and ε-MnO₂) were synthesized, and their chemical/physical properties for CO oxidation were systematically studied using multiple techniques. Density functional theory (DFT) calculations and temperature-programmed experiments reveal that β-MnO₂ shows low energies for oxygen vacancy generation and excellent redox properties, exhibiting significant CO oxidation activity (T₉₀ = 75 °C) and stability even under a humid atmosphere. For the first time, we report that the specific reaction rate for β-MnO₂ (0.135 molecule_CO·nm^-2·s^-1 at 90 °C) is roughly approximately 4 and 17 times higher than that of ε-MnO₂ and α-MnO₂, respectively. The specific reaction rate order (β-MnO₂ > ε-MnO₂ > α-MnO₂) is not only in good agreement with reduction rates (CO-TPSR measurements) but also agrees with the DFT calculation. In combination with in situ spectra and intrinsic kinetic studies, the mechanisms of CO oxidation over various crystal structures of MnO₂ were proposed as well. We believe the new insights from this study will largely inspire the design of such a kind of catalyst.

Atomically dispersed Ag on δ-MnO2via cation vacancy trapping for toluene catalytic oxidation

Atomic dispersion of Ag on δ-MnO2 was achieved via H2O2-induced Mn vacancy trapping. Single-atom Ag could activate adjacent lattice oxygen, facilitating methyl oxidation and benzene ring cleavage to improve toluene oxidation activity.

Investigation into the Phase-Activity Relationship of MnO2 Nanomaterials toward Ozone-Assisted Catalytic Oxidation of Toluene

Manganese dioxide (MnO₂ ), with naturally abundant crystal phases, is one of the most active candidates for toluene degradation. However, it remains ambiguous and controversial of the phase-activity relationship and the origin of the catalytic activity of these multiphase MnO₂ . In this study, six types of MnO₂ with crystal phases corresponding to α-, β-, γ-, ε-, λ-, and δ-MnO₂ are prepared, and their catalytic activity toward ozone-assisted catalytic oxidation of toluene at room temperature are studied, which follow the order of δ-MnO₂  > α-MnO₂  > ε-MnO₂  > γ-MnO₂  > λ-MnO₂  > β-MnO₂ . Further investigation of the specific oxygen species with the toluene oxidation activity indicates that high catalytic activity of MnO₂ is originated from the rich oxygen vacancy and the strong mobility of oxygen species. This work illustrates the important role of crystal phase in determining the oxygen vacancies' density and the mobility of oxygen species, thus influencing the catalytic activity of MnO₂ catalysts, which sheds light on strategies of rational design and synthesis of multiphase MnO₂ catalysts for volatile organic pollutants' (VOCs) degradation.

Autologous manganese phosphates with different Mn sites for electrocatalytic water oxidation

Herein, we report two autologous phosphates obtained from the same parent material for electrocatalytic water oxidation. These two phosphates have many similarities except the coordination structure of the Mn centers. It has been straightforwardly observed that the highly asymmetric geometry of Mn2P2O7 can stabilize the active Mn(iii) to promote water oxidation.

Degradation of antibiotics in aqueous media using manganese nanocatalyst-activated peroxymonosulfate

ε-MnO₂ effectively activates peroxymonosulfate (PMS) for the efficient degradation of emerging pollutants. ε-MnO₂ was synthesized by a facile thermal-treatment method and its long-term stability and efficiency for the elimination of emerging pollutants, including sulfamethoxazole (SMX), sulfachloropyridazine (SCP), sulfamethazine (SMT), ciprofloxacin (CIP), and azithromycin (AZI), from aqueous media were evaluated. ε-MnO₂ was found to activate PMS more efficiently than α-MnO₂, β-MnO₂, or δ-MnO₂, owing to its high - OH-group content, unique structure, and high surface area. Sulfate (SO₄^•-), hydroxyl (•OH), and superoxide (O₂^•-) radicals, as well as singlet oxygen (¹O₂) were generated, with O₂^•- acting as the ¹O₂ precursor. The ε-MnO₂/PMS system proved to be effective in the pH range of 3.5-9.0 and the rate of SMX degradation was not significantly affected by the presence of inorganic anions or natural organic matter. The proposed pathway for the activation of PMS by ε-MnO₂ includes inner-sphere interactions between ε-MnO₂ and PMS, and electron transfer to PMS via the MnIII ↔ MnIV redox cycle, which generates reactive oxygen species. These findings provide new insight into PMS activation by less-toxic metal oxides as catalysts and demonstrate that Mn-based materials can be used to effectively treat water matrices containing emerging pollutants.