MnO2 Research Articles

Hydrothermally grown hollandite manganese dioxide nanorods: evaluation of supercapattery performance and photocatalytic efficiency

Hydrothermally grown hollandite manganese dioxide nanorods: evaluation of supercapattery performance and photocatalytic efficiency

Synthesis and performance evaluation of supercapacitor based on banana peel–derived biochar loaded manganese dioxide with polyaniline ternary composite

Synthesis and performance evaluation of supercapacitor based on banana peel–derived biochar loaded manganese dioxide with polyaniline ternary composite

Reverse osmosis silica fouling control with reactive micromixing

Silica fouling is a major challenge in groundwater reverse osmosis (RO) desalination. Dissolved silica, upon concentration during RO, forms a difficult-to-clean glassy foulant layer on membranes, limiting recoveries from brackish groundwater desalination systems. Further, dissolved silica interacts strongly with organic matter to enhance fouling and degrade membrane performance. In this work, we demonstrate an innovative coating approach employing catalytic metal oxides on polyamide RO membranes using polydopamine (PDA) that greatly mitigates fouling and alleviates concentration polarization (CP). By injecting hydrogen peroxide (H2O2) into the feed, oxygen (O2) bubbles were formed through the catalytic disproportionation of manganese dioxide (MnO2). The produced O2 bubbles increased turbulence in the boundary layer, which reduced both CP and silica fouling. Fouling was further reduced in the presence of humic acid, likely because of enhancement of the catalytic action of MnO2 in the presence of humic acid. Compared to other silica scaling control methods, which require high energy consumption, the use of H2O2 to generate bubbles consumes much less energy. Overall, PDA-encapsulated catalytic MnO2 particles in the presence of H2O2 increased the effectiveness of thin-film composite desalination membranes without impacting their integrity in short-term tests, indicating its potential for improving energy efficiency in RO systems.

Cascade catalysis nanozyme for interfacial functionalization in combating implant infections associated with diabetes via sonodynamic therapy and adaptive immune activation

Innovative solutions are required for the intervention of implant associated infections (IAIs), especially for bone defect patients with chronic inflammatory diseases like diabetes mellitus (DM). The complex immune microenvironment of infections renders implants with direct antibacterial ability inadequate for the prolonged against of bacterial infections. Herein, a synergistic treatment strategy was presented that combined sonodynamic therapy (SDT) with adaptive immune modulation to treat IAIs in diabetes patients. A multifunctional coating was created on the surface of titanium (Ti) implants, consisting of manganese dioxide nanoflakes (MnO2 NFs) with cascade catalytic enzyme activity and a responsive degradable hydrogel containing a sonosensitizer. The reactive oxygen species (ROS) generated by glucose-hydrogen peroxide (H2O2) cascade catalysis and ultrasound (US) activation sonosensitizer helped kill bacteria and release bacterial antigens. Meanwhile, Mn2+ facilitated dendritic cells (DCs) maturation, enhancing antigen presentation to activate both cellular and humoral adaptive immunity against bacterial infections. This approach effectively eliminated bacteria in established diabetic IAIs model and activated systemic antibacterial immunity, providing long-term antibacterial protection. This study presents a non-antibiotic immunotherapeutic strategy for fighting IAIs in chronic diseases.

Global sensitivity analysis with deep learning-based surrogate models for unraveling key parameters and processes governing redox zonation in riparian zone

The riparian zone constitutes an intricate redox environment, giving rise to distinct redox zones characterized by dissolved oxygen (DO), nitrate, manganese dioxide (Mn (IV)), iron hydroxide (Fe(III)), and sulfate. Processes encompassing river fluctuation, groundwater flow, microbial growth and death, as well as solute reactive transport, exert substantial influences on the spatiotemporal zonation of these redox zones in the riparian zone. Nonetheless, understanding remains elusive regarding how these processes govern the thickness of these zones. In this study, we built a one-dimensional (1-D) model which is adapted from Zhu et al. (2023) that integrates these processes to simulate the temporal variation of the thicknesses of different redox zones in riparian zone. Sobol’s sensitivity analysis method and the hierarchical sensitivity analysis framework based on Bayesian Networks (BNs) were then employed to quantify the sensitivities of the 17 selected parameters and the four generalized processes governing redox zonation, respectively. To mitigate the computational costs, multi-layer perceptron (MLP) was employed to establish the surrogate models, efficiently predicting model outputs for sensitivity analysis. The results of sensitivity analysis highlight the groundwater flow and reactive transport processes as the most important processes affecting thickness variations of the redox zones. Parameters such as the initial hydraulic conductivity (Ks0) and DOC concentration (CDOC) play a predominant role in governing the thickness variations. Parameters linked to river fluctuation and microbe growth processes exhibit very limited effects on redox zonation. These findings offer valuable insights into the factors controlling redox zones in the riparian environment.

Modified rare earth waste composite material for simultaneous denitrification and recovery of phosphate in water

Nitrogen and phosphorus discharged into water bodies with sewage are the main causes of water eutrophication.Currently,the adsorption method is a cost-effective and efficient denitrification and phosphorus removal technology. In this study, waste polishing powder, manganese dioxide and sepiolite are used as raw materials, and a novel adsorbent of Sep-pp-MnO2 is prepared through co-precipitation and redox methods for simultaneous removal of ammonia nitrogen and recovery of phosphate in water.The physicochemical properties of the adsorbent are characterised, and the adsorption performances and denitrification and phosphorus removal mechanisms are determined. Results showed that,at a temperature of 25°C and pH of 8, the maximum removal of ammonia nitrogen reaches 11.47 mg/g, while the adsorption capacity for phosphates is 14.93 mg/g. Adsorption mechanisms indicated that the removal mechanism of phosphate is ligand exchange, while the removal mechanism of ammonia nitrogen involves electrostatic attraction and oxidation to nitrogen. Recycling experiments showed that after five desorption cycles, the material could achieve a removal of 4.7 mg/g for ammonia nitrogen, an adsorption capacity of 8.25 mg/g for phosphate and a phosphate recovery rate of 55 % after desorption with 0.1 M NaOH solution. Municipal wastewater validation experiments demonstrated that when the dosage of Sep-pp-MnO2 was 4 g/L,Treated water met the Class B requirements of the comprehensive emission standard for pollutants from urban sewage treatment plants in China (GB18918–2002). This study explores a new method for efficient simultaneous nitrogen and phosphorus removal in water and provides a feasible idea for alleviating the shortage of phosphate rock resources.

Significantly improved electrical conductivity and cycling stability of manganese dioxide by poly (3,4-ethylene-dioxythiophene) coating

Abstract Manganese dioxide (MnO2) is widely acknowledged as a prospective pseudocapacitive material aimed at alleviating the issue of low energy density in supercapacitors. Nevertheless, hampered by its intrinsic low conductivity and poor structural stability, MnO2-based energy storage materials often exhibit lower practical capacity in practical applications. During this investigation, the synthesis of MnO2@PEDOT (poly(3,4-ethylenedioxythiophene)) composite materials involved an in-situ oxidative polymerization approach, whereby PEDOT nanowires were integrated onto the MnO2 nanoparticle surface. Notably, the internal configuration of the MnO2@PEDOT composite material demonstrated a high surface area morphology, while the externally entwined PEDOT nanowire layer further expanded the material’s specific surface area. As a result, the MnO2@PEDOT composite material demonstrated a specific capacitance reaching 214 F g-1, a 91% improvement compared to unmodified MnO2. Furthermore, the winding of PEDOT nanowires effectively suppressed the structural disintegration of MnO2. The MnO2@PEDOT composite material exhibited a remarkable improvement in cycling stability, maintaining 81% of its initial capacity after 5000 cycles. The electron-rich PEDOT not only improved the conductivity of the inner MnO2 through electron migration but also prevented MnO2 structural degradation by tightly enveloping it. The outcomes of our study propose a method for constructing MnO2 featuring a structurally stable configuration and a prolonged cycling lifespan, offering valuable insights for designing electrode materials with high cycling stability in supercapacitors.

Novel promising aqueous electrolytes for manganese dioxide/stainless steel pseudocapacitor electrode

Manganese dioxide (MnO2) films are developed by potentiostatic electrodeposition on a stainless steel sheet as a current collector using manganese acetate tetrahydrate solution at a concentration of 0.25 mol L−1. The deposited sample layer is found to be amorphous as confirmed by the scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. The capacitive property of the prepared electrodes is characterized by charging/discharging, cyclic voltammetry, and electrochemical impedance spectroscopy techniques in four different aqueous solutions; sodium sulfate, magnesium acetate, nickel acetate, and a mixture of sodium chloride + sodium bicarbonate + borax. Charge–discharge curves reveal higher specific capacitance (Cs) of 1580 F g−1 at 0.5 mA cm−2 for the investigated MnO2 film which is characterized in Ni acetate aqueous solution. The structural, morphological, and electrochemical properties of the electrodeposited manganese oxide films are also studied. The results indicate that the specific capacitance of the deposited samples showed a strong dependency on the electrolyte aqueous solutions, resulting in developing new electrolytes which is a top priority effort in comparison to seeking new electrode materials. It is found that the matching between the pore size structure of the electrode and the ion size of the electrolyte is of great importance for the improved capacity of prepared capacitors.

Gold Nanorod–Based Poly(Lactic-Co-Glycolic Acid) with Manganese Dioxide Core–Shell Structured Multifunctional Nanoplatform for Cancer Theranostic Applications [Corrigendum

Gold Nanorod–Based Poly(Lactic-Co-Glycolic Acid) with Manganese Dioxide Core–Shell Structured Multifunctional Nanoplatform for Cancer Theranostic Applications [Corrigendum

Flue gas desulfurization by natural recyclable manganese ore in packed bed reactor and its performance prediction by random pore model

Various grades of manganese dioxide ores, as a natural recyclable sorbent, can be used in dry flue gas desulfurization (FGD) at moderate temperatures (350–450 °C). This research provided low- and high-grade manganese dioxide ores to examine SO2 removal in a packed bed reactor. To obtain characteristic parameters of mineral sorbents, XRD, XRF, BET, and mercury porosimetry were employed. Then, kinetic parameters of desulfurization reaction were determined using thermogravimeter analyzer (TGA) and random pore model (RPM) for a single pellet. In desulfurization experiments of simulated flue gas in a packed bed reactor and mass spectrometer (MS) apparatus, the breakthrough times were measured under various operating conditions. The onset of these breakthrough times or life-time of MnO2 reactor for the SO2 removal was predicted successfully by RPM for a packed bed reactor using related kinetic constants from TGA. In addition, reacted sorbets were recycled multiple times after washing with water. Not only does this simple method separate MnSO4 from unreacted sorbents as a valuable byproduct to reduce the FGD cost, but it also improves pore size distribution (PSD) of mineral MnO2 by creating large pores. Modified PSD of this recycled sorbent caused increased breakthrough time.

Tumor Cell-Targeting and Tumor Microenvironment-Responsive Nanoplatforms for the Multimodal Imaging-Guided Photodynamic/Photothermal/Chemodynamic Treatment of Cervical Cancer.

Phototherapy, known for its high selectivity, few side effects, strong controllability, and synergistic enhancement of combined treatments, is widely used in treating diseases like cervical cancer. In this study, hollow mesoporous manganese dioxide was used as a carrier to construct positively charged, poly(allylamine hydrochloride)-modified nanoparticles (NPs). The NP was efficiently loaded with the photosensitizer indocyanine green (ICG) via the addition of hydrogen phosphate ions to produce a counterion aggregation effect. HeLa cell membrane encapsulation was performed to achieve the final M-HMnO2@ICG NP. In this structure, the HMnO2 carrier responsively degrades to release ICG in the tumor microenvironment, self-generates O2 for sensitization to ICG-mediated photodynamic therapy (PDT), and consumes GSH to expand the oxidative stress therapeutic effect [chemodynamic therapy (CDT) + PDT]. The ICG accumulated in tumor tissues exerts a synergistic PDT/photothermal therapy (PTT) effect through single laser irradiation, improving efficiency and reducing side effects. The cell membrane encapsulation increases nanomedicine accumulation in tumor tissues and confers an immune evasion ability. In addition, high local temperatures induced by PTT can enhance CDT. These properties of the NP enable full achievement of PTT/PDT/CDT and targeted effects. Mn2+ can serve as a magnetic resonance imaging agent to guide therapy, and ICG can be used for photothermal and fluorescence imaging. After its intravenous injection, M-HMnO2@ICG accumulated effectively at mouse tumor sites; the optimal timing of in-vivo laser treatment could be verified by near-infrared fluorescence, magnetic resonance, and photothermal imaging. The M-HMnO2@ICG NPs had the best antitumor effects among treatment groups under near-infrared light conditions, and showed good biocompatibility. In this study, we designed a nano-biomimetic delivery system that improves hypoxia, responds to the tumor microenvironment, and efficiently loads ICG. It provides a new economical and convenient strategy for synergistic phototherapy and CDT for cervical cancer.

Dielectric and magnetic response of mechanically activated Mn-doped SrTiO3 ceramics

This research was focused on the influence of manganese (Mn) incorporation at Sr and/or Ti sites on the microstructure, relative dielectric permittivity and specific magnetization of strontium titanate (SrTiO3) ceramics. A solid-state method was used for the preparation of mechanically activated (10, 30 and 120 min) Mn-doped SrTiO3 ceramics with various manganese dioxide (MnO2) weight percentages (1.5, 3 and 6 wt%). Rietveld's analysis showed that the mean crystallite size in doped-activated SrTiO3 ceramics is smaller than in undoped ceramics, which is a consequence of additional crystal structure distortion due to ion substitution. Changes in the Raman spectra indicated dopant incorporation in the SrTiO3 lattice. The microstructural analysis pointed out a decrease in the mean grain size with increasing dopant concentration and time of activation. The highest values of permittivity and magnetization were observed for Mn-doped SrTiO3 ceramic mechanically activated for 120 min. Based on all the above, the optimal electrical and magnetic properties of SrTiO3 ceramics can be achieved by the appropriate choice of mechanical activation time and dopant concentration.

A complete and sustained organic/inorganic reaction mechanism of Baeyer’s test

The Baeyer’s test for unsaturation has been used in Qualitative Organic Analysis for a long time. However, if an alkaline reagent is used, compounds having an active hydrogen (carbon acids) also give a positive test with potassium permanganate, detracting the test for unsaturation. The first steps of the reaction sequence have been described but the next stages are missing. These are very important because they involve the formation mode of the observed end product, brown manganese dioxide. In this communication, a complete and sustained reaction mechanism is provided for both reaction mediums, neutral and alkaline. It is in accordance with observed experimental facts. The missing steps are a redox reaction between hypomanganate and permanganate ions, and a second cyclic intermediate now formed with manganate ion. The instability of this intermediate leads directly to manganese dioxide and alkalinization of the neutral medium, as observed experimentally.

Endogenous glucose-driven cascade reaction of nano-drug delivery for boosting multidrug-resistant bacteria-infected diabetic wound healing

Multidrug-resistant (MDR) bacteria-infected wound healing remains greatly challenging, especially in diabetic patients. Herein, a novel nano-drug delivery based on endogenous glucose-driven cascade reaction is proposed for boosting MDR bacteria-infected diabetic wound healing with high efficacy by improving wound microenvironment and enhancing photodynamic antibacterial activity. The composite nanoagent is first self-assembled by integrating berberine (BBR) and epigallocatechin gallate (EGCG) from natural plant extracts, named as BENPs, which is successively coated with manganese dioxide nanoshells (MnO2 NSs) and glucose oxidase (GOX) to form the final BEMGNPs. The cascade reaction is triggered by glucose at the wound site of diabetes which is specifically catalyzed by GOX in the BEMGNPs to produce gluconic acid and hydrogen peroxide (H2O2). That is subsequently to decompose MnO2 NSs in the BEMGNPs to generate oxygen (O2). The BEMGNPs as photosensitizers effectively produce reactive oxygen species (ROS) to enhance the eradication of bacteria with the assistance of O2. Under the synergistic function of the cascaded reaction, the BEMGNPs present excellent antibacterial efficacy even for MDR bacteria. The in vivo experiments explicitly validate that the constructed nano-drug delivery can augment the MDR bacteria-infected diabetic wound healing with excellent biosafety. The as-proposed strategy provides an instructive way to combat ever-threatening MDR bacteria, which particularly is beneficial for diabetic patients.

Improved near-resonant two photon absorption of α-MnO2 nanowires surface functionalized reduced graphene oxide sheets

The versatile study of graphene derivatives has resurgence of interest on understanding its nonlinear optical response at different nanoscales. Nanostructured manganese dioxide: reduced graphene oxide (MnO2: rGO) hybrids were synthesized by reduction method by varying the content of rGO (5, 10, 15 & 20 wt%). X-ray Photoelectron Spectroscopy studies confirmed the surface functionalization of MnO2 on rGO. Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Tunnelling Electron Microscopy (HRTEM) witness that with respect to the content of rGO, the morphology of MnO2 varies radically from clusters to nanorods to nanowires over the surface of rGO sheets. Ground state absorption spectra of the hybrids have absorption edge at 268 nm corresponding to combined metal oxide charge transfer between rGO (π-π* transition of CC and n-π transition of C-O bonds) and MnO2 (d-d transition). Moreover, hierarchical MnO2 nanowire network resided on 2D rGO sheets involves broad absorption at the visible spectral domain due to polaron transition as well the localization of π- π* transited electrons that facilitates the probability of occurrence of excited state absorption. Intensity dependent open aperture Z-scan technique of the prepared hybrids using Q-switched Nd: YAG 532 nm nanopulsed laser reveals unusual transitions and enhanced nonlinear absorption. MnO2:(5 wt%) rGO shows saturable absorption (SA) at low intensity and changeover dynamically to reverse saturable absorption (RSA) at higher intensity. MnO2:(10 & 15 wt%) rGO exposes coupled nonlinear absorption (SA + RSA) owing to the combined effect of graphene (π-states) and MnO2 (σ-states). MnO2:(20 wt%) rGO exhibits a stronger RSA ascribed to sequential two photon absorption. The third-order nonlinear absorption coefficient and limiting threshold of MnO2: rGO (20 wt%) are 4.04 ×10-10 m/W and 0.84 ×1012 W/m2, which shows five-fold increase compared to bare rGO and MnO2. The obtained results propose that the optical nonlinearity of MnO2 nanowires surface functionalized rGO sheets can significantly be tuned to meet the requirements for fabricating laser safety devices.

Tumor microenvironment-regulated drug delivery system combined with sonodynamic therapy for the synergistic treatment of breast cancer.

Co-loading of sonosensitizers and chemotherapeutic drugs into nanocarriers can improve the biocompatibilities, stabilities, and targeting of drugs and reduce the adverse reactions of drugs, providing a robust platform to orchestrate the synergistic interplay between chemotherapy and sonodynamic therapy (SDT) in cancer treatment. In this regard, biodegradable manganese dioxide (MnO2) has attracted widespread attention because of its unique properties in the tumor microenvironment (TME). Accordingly, herein, MnO2 nanoshells with hollow mesoporous structures (H-MnO2) were etched to co-load hematoporphyrin monomethyl ether (HMME) and doxorubicin (DOX), and DOX/HMME-HMnO2@bovine serum albumin (BSA) obtained after simple BSA modification of DOX/HMME-HMnO2 exhibited excellent hydrophilicity and dispersibility. H-MnO2 rapidly degraded in the weakly acidic TME, releasing loaded HMME and DOX, and catalysed the decomposition of H2O2 abundantly present in TME, producing oxygen (O2) in situ, significantly increasing O2 concentration and downregulating the hypoxia-inducible factor 1α (HIF-1α). After irradiation of the tumor area with low-frequency ultrasound, the drug delivery efficiency of DOX/HMME-HMnO2@BSA substantially increased, and the excited HMME generated a large amount of reactive oxygen species (ROS), which caused irreversible damage to tumor cells. Moreover, the cell death rate exceeded 60% after synergistic SDT-chemotherapy. Therefore, the pH-responsive nanoshells designed in this study can realize drug accumulation in tumor regions by responding to TME and augment SDT-chemotherapy potency for breast cancer treatment by improving hypoxia in tumors. Thus, this study provides theoretical support for the development of multifunctional nanocarriers and scientific evidence for further exploration of safer and more efficient breast cancer treatments.

A dual-signal optical sensing platform of CDs-MnO2 NS composites for facile detection of ascorbic acid based on a combination of Tyndall effect scattering and fluorescence.

A dual-signal optical sensing platform was successfully developed for the determination of ascorbic acid (AA) based on blue fluorescent carbon dots (CDs) and manganese dioxide nanosheets (MnO2 NSs) with strong Tyndall effect (TE) scattering and fluorescence quenching capabilities. In this nanosystem, CDs-MnO2 NS composites were employed as probes to evaluate the AA concentration. Owing to the strong reduction, the presence of the target AA could reduce the MnO2 NSs to Mn2+ and induce the degradation of the MnO2 NSs, resulting in a significant decrease in the TE scattering intensity of the MnO2 NSs and the fluorescence recovery of the CDs. Therefore, a novel optical sensor based on TE scattering and fluorescence dual detectors was developed for the sensitive determination of AA. Under optimized conditions, the limits of detection (LODs) of the two modes were 113 and 3 nM, respectively. Furthermore, the dual-signal optical sensing platform was successfully applied for the detection of AA in human serum.

Impacts of MnO2 on tomato (Lycopersicon esculentum Mill.) growth: A study with MnO2-amended organic fertilizer

Manganese dioxide (MnO2), as a catalyst in composting processes, can accumulate in soil over multiple fertilizations. However, its impact on crop growth remains to be explored. In this study, a pot experiment was conducted to investigate the impacts of MnO2 on the tomato plant performance across various growth stages. Results showed that MnO2 reduced the plant height, leaf number and length by 35.53 %, 27.61 %, and 37.00 %, respectively, and decreased the fruit weight (23.16 %) and sugar-acid ratio (29.7 %) of fruits compared to the MnO2-free control. The adverse impacts of MnO2 on plant growth might be attributed to the inhibition of microbial activity in soil reflected by the reduction of soil urease (9.30 %) and acid phosphatase (12.52 %) activities, which decreased the efficiency of nutrients conversion and uptake. The decrease of nutrient elements in roots resulted in oxidative stress in the plant, inhibiting the plasma membrane H+-ATPase activity thereby reducing the translocation of nutrients (e.g., calcium, magnesium, and phosphorus) translocation from roots to leaves. Furthermore, the phytohormones indolebutyric acid, gibberellin, and jasmonic acid of leaves were disturbed. This study reveals the risks associated with the application of MnO2-containing organic fertilizers.

Customization of Manganese Oxide Cathodes via Precise Electrochemical Lithium-Ion Intercalation for Diverse Zinc-Ion Batteries.

Manganese oxide-based aqueous zinc-ion batteries (ZIBs) are attractive energy storage devices, owing to their good safety, low cost, and ecofriendly features. However, various critical issues, including poor conductivity, sluggish reaction kinetics, and unstable structure still restrict their further development. Oxygen defect engineering is an effective strategy to improve the electrochemical performance of manganese oxides, but challenging in the accurate regulation of oxygen defects. In this work, an effective and controllable defect engineering strategy-controllable electrochemical lithium-ion intercalation - is proposed to tackle this issue. The incorporation of lithium ions and oxygen defects can promote the conductivity, lattice spacing, and structural stability of Mn2O3 (MO), thus improving its capacity (232.7mAhg-1), rate performance, and long-term cycling stability (99.0% capacity retention after 3000 cycles). Interestingly, the optimal ratio of intercalated lithium-ion varies at different temperature or mass-loading of MO, which provides the possibility to customize diverse ZIBs to meet different application conditions. In addition, the fabricated ZIBs present good flexibility, superior safety, and admirable adaptability under extreme temperatures (-20-100°C). This work provides an inspiration on the structural customization of metal oxide nanomaterials for diverse ZIBs, and sheds light on the construction of future portable electronics.

Kinetic study of sulfur dioxide removal reaction with manganese dioxide by random pore model using thermogravimetry

Kinetic study of sulfur dioxide removal reaction with manganese dioxide by random pore model using thermogravimetry