Manganese dioxide-coated biocarbon for integrated adsorption-photocatalytic degradation of formaldehyde in indoor conditions

Formaldehyde is a common indoor air pollutant with hazardous effects on human health. This study investigated the efficiency of biocarbon (BC) functionalized with variable contents of MnO2 for formaldehyde removal in ambient conditions via integrated adsorption-photocatalytic degradation technology. The sample with the highest formaldehyde removal potential was used to prepare a functional coating made of acrylic binder mixed with 20 wt% of the particles and applied on beech (Fagus sylvatica L) substrate. SEM images showed that MnO2 was deposited around and inside the pores of the BC. EDX spectra indicated the presence of Mn peaks and increased content of oxygen in the doped BC compared to pure BC, which indicated the successful formation of MnO2. Raman spectra revealed that the disorder in the BC's structure increased with increasing MnO2 loadings. FTIR spectra of BC-MnO2 samples displayed additional peaks compared to the BC spectrum, which were attributed to MnO vibrations. Moreover, the deposition of increased MnO2 loadings decreased the porosity of the BC due to pores blockage. The BC sample containing 8 % Mn exhibited the highest formaldehyde removal efficiency in 8 h, which was 91 %. A synergetic effect between BC and MnO2 was observed. The formaldehyde removal efficiency and capacity of the coating reached 43 % and 6.1 mg/m2, respectively, suggesting that the developed coating can be potentially used to improve air quality in the built environment.

Manganese dioxide decorated kiwi peel powder for efficient removal of lead from aqueous solutions, blood and Traditional Chinese Medicine extracts

For human health and environment safety, it is of great significance to develop novel materials with high effectiveness for removal of lead from not only aqueous solutions but also human body and traditional Chinese medicines. Here, functional kiwi peel composite, manganese dioxide decorated kiwi peel powder (MKPP), is proposed for the removal of Pb2+ effectively. The adsorption of Pb2+ in aqueous solution is a highly selective and endothermic process and kinetically follows a pseudo-second-order model, which can reach equilibrium with the capacity of 192.7 mg/g within 10 min. Comprehensive factors of hydration energy, charge-to-radius ratio and softness of Pb2+ make a stronger affinity between MKPP and Pb2+. The possible adsorption mechanism involves covalent bond, electrostatic force and chelation, etc. MKPP can be efficiently regenerated and reused with high adsorption efficiency after five cycles. Besides, MKPP can remove over 97% of Pb2+ from real water samples. MKPP can also alleviate lead poisoning to a certain extent and make the Pb level of TCM extract meet the safety standard. This work highlights that MKPP is a promising adsorbent for the removal of Pb2+ and provides an efficient strategy for reusing kiwi peel as well as dealing with the problem of Pb pollution.

Hierarchically core-shell structured nanocellulose/carbon nanotube hybrid aerogels for patternable, self-healing and flexible supercapacitors

The flexible and self-healing supercapacitors (SCs) are considered to be promising smart energy storage devices. Nevertheless, the SCs integrated with flexibility, lightweight, pattern editability, self-healing capabilities and desirable electrochemical properties remain a challenge. Herein, an all-in-one self-healing SC fabricated with the free-standing hybrid film (TCMP) composed of the 2,2,6,6-tetramethylpiperidin-1-yloxy-oxidized cellulose nanofibers (TOCNs) carried carbon nanotubes (CNTs), manganese dioxide (MnO2) and polyaniline (PANI) as the electrode, polyvinyl alcohol/sulfuric acid (PVA/H2SO4) gel as the electrolyte and dynamically cross-linked cellulose nanofibers/PVA/sodium tetraborate decahydrate (CNF/PB) hydrogel as the self-healing electrode matrix is developed. The TCMP film electrodes are fabricated through a facile in-situ polymerization of MnO2 and PANI in TOCNs-dispersed CNTs composite networks, exhibiting lightweight, high electrical conductivity, flexibility, pattern editability and excellent electrochemical properties. Benefited from the hierarchically porous structure and high mechanical properties of TOCNs, excellent electrical conductivity of CNTs and the desirable synergistic effect of pseudocapacitance induced by MnO2 and PANI, the assembled SC with an interdigital structure demonstrated a high areal capacitance of 1108 mF cm-2 at 2 mA cm-2, large areal energy density of 153.7 μWh cm-2 at 1101.7 μW cm-2. A satisfactory bending cycle performance (capacitance retention up to 95 % after 200 bending deformations) and self-healing characteristics (∼90 % capacitance retention after 10 cut/repair cycles) are demonstrated for the TCMP-based symmetric SC, delivering a feasible strategy for electrochemical energy storage devices with excellent performance, designable patterns and desirable safe lifespan.

MnO2-based capacitive system enhances ozone inactivation of bacteria by disrupting cell membrane

The application of ozone (O3) disinfection has been hindered by its low solubility in water and the formation of disinfection by-products (DBPs). In this study, capacitive disinfection is applied as a pre-treatment for O3 oxidation, in which manganese dioxide with a rambutan-like hollow spherical structure is used as the electrode to increase the charge density on the electrode surface. When a voltage is applied, the negative-charged microbes are attracted to the electrodes and killed by electrical interactions. The contact between microbes and capacitive electrodes leads to changes in cell permeability and burst of reactive oxygen species, thereby promoting the diffusion of O3 into the cells. After O3 penetrates the cell membrane, it can directly attack the cytoplasmic constituents, accelerating fatal and irreversible damage to pathogens. As a result, the performance of the capacitance-O3 process is proved better than the direct sum of the two individual process efficiencies. The design of capacitance-O3 system is beneficial to reduce the ozone dosage and DBPs with a broader inactivation spectrum, which is conducive to the application of ozone in primary water disinfection.

Manganese Dioxide-Based Nanomaterials for Medical Applications

Manganese dioxide (MnO2) nanomaterials can react with trace hydrogen peroxide (H2O2) to produce paramagnetic manganese (Mn2+) and oxygen (O2), which can be used for magnetic resonance imaging and alleviate the hypoxic environment of tumors, respectively. MnO2 nanomaterials also can oxidize glutathione (GSH) to produce oxidized glutathione (GSSG) to break the balance of intracellular redox reactions. As a consequence of the sensitivity of the tumor microenvironment to MnO2-based nanomaterials, these materials can be used as multifunctional diagnostic and therapeutic platforms for tumor imaging and treatment. Importantly, when MnO2 nanomaterials are implanted along with other therapeutics, synergetic tumor therapy can be achieved. In addition to tumor treatment, MnO2-based nanomaterials display promising prospects for tissue repair, organ protection, and the treatment of other diseases. Herein, we provide a thorough review of recent progress in the use of MnO2-based nanomaterials for biomedical applications, which may be helpful for the design and clinical translation of next-generation MnO2 nanomaterials.

Nanocellulose/carbon nanotube/manganese dioxide composite electrodes with high mass loadings for flexible supercapacitors

The increasing commercialization of flexible electronic products has sparked a rising interest in flexible wearable energy storage devices. Supercapacitors are positioned as one of the systems with the most potential due to their distinctive advantages: high power density, rapid charge and discharge rates, and long cycle life. However, electrode materials face challenges in providing excellent mechanical strength while ensuring sufficient energy density. This study presents a method for constructing a flexible composite electrode material with high capacitance and mechanical performance by electrochemically depositing high-quality manganese dioxide (MnO2) onto the surface of a nanocellulose (CNF) and carbon nanotube (CNT) conductive film. In this electrode material, the CNF/CNT composite film serves as a flexible conductive substrate, offering excellent mechanical properties (modulus of 3.3 GPa), conductivity (55 S/cm), and numerous active sites. Furthermore, at the interface between MnO2 and the CNF/CNT substrate, C-O-Mn bonds are formed, promoting a tight connection between the composite materials. The assembled symmetric flexible supercapacitor (FSC) demonstrates impressive performance, with an areal specific capacitance of 934 mF/cm2, an energy density of 43.10 Wh/kg, a power density of 166.67 W/kg and a long cycle life (85 % Capacitance retention after 10,000 cycles), suggesting that they hold promise for FSC applications.

A Ratiometric Biosensor Containing Manganese Dioxide Nanosheets and Nitrogen-Doped Quantum Dots for 2,4-Dichlorophenoxyacetic Acid Monitoring

Nanomaterials are desirable for sensing applications. Therefore, MnO2 nanosheets and nitrogen-doped carbon dots (NCDs) were used to construct a ratiometric biosensor for quantification of 2,4-dichlorophenoxyacetic acid. The MnO2 nanosheets drove the oxidation of colorless o-phenylenediamine to OPDox, which exhibits fluorescence emission peaks at 556 nm. The fluorescence of OPDox was efficiently quenched and the NCDs were recovered as the ascorbic acid produced by the hydrolyzed alkaline phosphatase (ALP) substrate increased. Owing to the selective inhibition of ALP activity by 2,4-D and the inner filter effect, the fluorescence intensity of the NCDs at 430 nm was suppressed, whereas that at 556 nm was maintained. The fluorescence intensity ratio was used for quantitative detection. The linear equation was F = 0.138 + 3.863·C 2,4-D (correlation coefficient R2 = 0.9904), whereas the limits of detection (LOD) and quantification (LOQ) were 0.013 and 0.040 μg/mL. The method was successfully employed for the determination of 2,4-D in different vegetables with recoveries of 79%~105%. The fluorescent color change in the 2,4-D sensing system can also be captured by a smartphone to achieve colorimetric detection by homemade portable test kit.

Fabrication of MnO2 coating on aluminum honeycomb for fast catalytic decomposition of ozone at room temperature

Herein, the coating of MnO2 nanomaterials on the surface of aluminum honeycomb was carried out to meet the requirements of high air velocity, low pressure drop and high activity in ozone removal scenarios. A commercially readily available waterborne silica sol mixed with waterborne acrylate latex was creatively utilized as the binder. A series of coating samples were prepared by spray coating method and evaluated focusing on their adhesion strength and catalytic activity towards ozone decomposition in an air duct at room temperature, by varying MnO2/binder mass ratio and number of sprayings. It was found that the adhesion strength of the catalytic coatings on the aluminum honeycomb increased with the increase of binder mass ratio, but the increased binder made the catalyst particles closely packed, resulting in reduced exposure of active sites and decrease of ozone conversion. Accordingly, catalyst slurry with 81.8 wt.% MnO2 in dry coating and spraying times of two were determined as the optimal process parameters. As-prepared aluminum honeycomb filter with MnO2 layer of 50 µm thickness achieved ozone conversion of 29.3%±1.7% under conditions of air velocity 3.0 m/sec, relative humidity ∼50%, room temperature (26°C) and initial ozone concentration of 200 ppbV. This filter can be well adaptable to indoor air purification equipment operating at high air velocity with low wind resistance.

Hollow manganese dioxide-chitosan hydrogel for the treatment of atopic dermatitis through inflammation-suppression and ROS scavenging

Atopic dermatitis (AD) is a chronic inflammatory disease associated with immune dysfunction. High levels of reactive oxygen species (ROS) can lead to oxidative stress, release of pro-inflammatory cytokines, and T-cell differentiation, thereby promoting the onset and worsening of AD. In this study, we innovatively used quaternary ammonium chitosan (QCS) and tannic acid (TA) as raw materials to design and prepare a therapeutic hydrogel(H-MnO2-Gel) loaded with hollow manganese dioxide nanoparticles (H-MnO2 NPs). In this system, the hydrogel is mainly cross-linked by dynamic ion and hydrogen bonding between QCS and TA, resulting in excellent moisture retention properties. Moreover, due to the inherent antioxidant properties of QCS/TA, as well as the outstanding H2O2 scavenging ability of H-MnO2 NPs, the hydrogel exhibits significant ROS scavenging capability. In vitro experiments have shown that H-MnO2-Gel exhibits good cellular biocompatibility. Importantly, in an AD-induced mouse model, H-MnO2-Gel significantly enhanced therapeutic effects by reducing epidermal thickness, mast cell number, and IgE antibodies. These findings suggest that H-MnO2-Gel, by effectively clearing ROS and regulating the inflammatory microenvironment, provides a promising approach for the treatment of AD.

Preparation of MnO2@poly-(DMAEMA-co-IA)-conjugated methotrexate nano-complex for MRI and radiotherapy of breast cancer application

OBJECTIVE

A novel efficient pH-sensitive targeted magnetic resonance imaging (MRI) contrast agent and innovative radio-sensitizing system were synthesized based on MnO2 NPs coated with biocompatible poly-dimethyl-amino-ethyl methacrylate-Co-itaconic acid, (DMAEMA-Co-IA) and targeted with methotrexate (MTX).

MATERIALS AND METHODS

The as-established NPs were fully characterized and evaluated for MRI signal enhancement, relaxivity, in vitro cell targeting, cell toxicity, blood compatibility, and radiotherapy (RT) efficacy.

RESULTS

The targeted NPs MnO2@Poly(DMAEMA-Co-IA) and MTX-loaded NPs inhibited MCF-7 cell viability more effectively than free MTX after 24 and 48 h, respectively, with no noticeable toxicity. Additionally, the insignificant hemolytic activity demonstrated their proper hemo-compatibility. T1-weighted magnetic resonance imaging was used to distinguish the differential uptake of the produced MnO2@Poly(DMAEMA-Co-IA)-MTX NPs in malignant cells compared to normal ones in the presence of high and low MTX receptor cells (MCF-7 and MCF-10A, respectively). In MRI, the produced theranostic NPs displayed pH-responsive contrast enhancement. As shown by in vitro assays, treatment of cells with MnO2@Poly(DMAEMA-Co-IA)-MTX NPs prior to radiotherapy in hypoxic conditions significantly enhanced therapeutic efficacy.

CONCLUSION

We draw the conclusion that using MnO2@Poly(DMAEMA-Co-IA)-MTX NPs in MR imaging and combination radiotherapy may be a successful method for imaging and radiation therapy of hypoxia cells.

Dual role of soil-derived dissolved organic matter in the sulfamethoxazole oxidation by manganese dioxide

Manganese dioxide (MnO₂) can mediate organic pollutant oxidation in aquatic environments, which has been reported to be inhibited or promoted by dissolved organic matter (DOM) in different studies. It remains unresolved why conflicting results have been observed and whether such results depend on the type and concentration of DOM. Here, we used three types of well-characterized DOM derived from soil heated at 50, 250, or 400 °C (DOM_50, DOM_250, and DOM_400, respectively) to evaluate the impacts of DOM type and concentration and environmental pH on MnO₂-mediated oxidation of sulfamethoxazole, a widely detected and ecotoxic emerging pollutant. We observed that the degradation rate of sulfamethoxazole was possibly promoted by DOM_250 (pH 6‒8), while it was generally inhibited by DOM_50 and DOM_400. Furthermore, it was initially inhibited and then promoted with increasing DOM concentrations and was consistently less inhibited at a higher pH. The inter-DOM variations of sulfamethoxazole degradation could be explained by the more enriched polyphenolics in DOM_250 than in DOM_50 and DOM_400, whereas the weak promoting effect of DOM_400 indicates that high DOM aromaticity may not necessarily promote pollutant degradation. Our results reconcile the debate on the role of DOM in the oxidation of sulfamethoxazole by MnO₂ and highlight the decisiveness of the molecular composition and concentration of DOM and the reaction pH in the overall promoting or inhibiting role of DOM.

Impact of aqueous environments on hydrogen peroxide activation by manganese oxides: Kinetics and the critical role of bicarbonate

MnO₂ activating H₂O₂ is a promising way in the field of advanced oxidation processes (AOPs) and in situ chemical oxidation (ISCO) to remove contaminants. However, few studies have focused on the influence of various environmental conditions on the performance of MnO₂-H₂O₂ process, which restricts the application in real world. In this study, the effect of essential environmental factors (ionic strength, pH, specific anions and cations, dissolved organic matter (DOM), SiO₂) on the decomposition of H₂O₂ by MnO₂ (ε-MnO₂ and β-MnO₂) were investigated. The results suggested that H₂O₂ degradation was negatively correlated with ionic strength and strongly inhibited under low pH conditions and with phosphate existence. DOM had a slight inhibitory effect while Br^-, Ca²⁺, Mn²⁺ and SiO₂ placed negligible impact on this process. Interestingly, HCO₃^- inhibited the reaction at low concentrations but promoted H₂O₂ decomposition at high concentrations, possibly due to the formation of peroxymonocarbonate. This study may provide a more comprehensive reference for potential application of H₂O₂ activation by MnO₂ in different water systems.

A mesoporous MnO2-based nanoplatform with near infrared light-controlled nitric oxide delivery and tumor microenvironment modulation for enhanced antitumor therapy

A hollow mesoporous manganese dioxide-based (H-MnO₂) multifunctional nanoplatform, H-MnO₂ @AFIPB@PDA@Ru-NO@FA (MAPRF NPs), was prepared for synergistic cancer treatment, in which a histone deacetylase inhibitor AFIPB was loaded in its hollow cavity and a ruthenium nitrosyl donor (Ru-NO) and a folic acid (FA) targeting group were covalently decorated on its covered polydopamine (PDA) layer. The MAPRF NPs showed tumor microenvironment (TME)-responsive properties of depletion of glutathione (GSH) to disrupt the antioxidant defense system and on-demand drug delivery. And the released Mn²⁺ further catalyzed the decomposition of endogenous H₂O₂ to produce highly toxic hydroxyl radicals (·OH) for enhanced chemodynamic therapy (CDT). Furthermore, upon 808 nm light irradiation MAPRF NPs exhibited controlled nitric oxide (NO) delivery and simultaneously produced significant photothermal effect. Consequently, MAPRF NPs showed high mortality toward cancer cells in the presence of 808 nm light irradiation. This work provides a paradigm of multimodal synergistic therapy that combines NO-based gas therapy with TME modulation for efficient antitumor therapy.

The increased oxygen vacancy by morphology regulation of MnO2 for efficient removal of PAHs in aqueous solution

Manganese dioxide (MnO₂) is considered to have a promising future in degrading polycyclic aromatic hydrocarbons (PAHs) in aqueous phase because of its low cost and environmental friendliness. In this study, various MnO₂ morphologies were prepared, and their removal performance and mechanism were evaluated using benzo(a)pyrene (B[a]P) as model molecule. Results showed that nanoflower MnO₂ with higher concentration of oxygen vacancies exhibited better oxidative and easier oxygen migration properties, and thus enhanced PAHs removal by 14.28%-43.21% compared with other MnO₂ samples. Additionally, the transformation rate of PAHs is correlated with their ionization potential (IP) values. Further mechanism studies showed that the degradation of B[a]P by MnO₂ process was first to form a combination and then oxidized by non-radical Mn species and superoxide radical (O₂^-•) to produce degradation product (B[a]P-6-one and B[a]P-6,12-quinone). The specific surface area was not the main factor affecting the removal of B[a]P by MnO₂ and oxidation was the main removal mechanism of degrading B[a]P by MnO₂. Mn³⁺ and absorbed oxygen (O_abs) played an important role in the process of removing PAHs by MnO₂. Additionally, synergistic effects of oxygen vacancy and Mn³⁺could be benefit for transforming O_abs to O₂^-•, leading to the efficient degradation of PAHs.

The role of MnO2 crystal morphological scale and crystal structure in selective catalytic degradation of azo dye

MnO₂, as a representative manganese-based catalyst with many kinds of crystal forms, has been widely used to activate PMS. However, the role of morphological scale and crystal structures on the catalytic capability of MnO₂ still lacks further study. In this study, four different crystal forms of MnO₂ (α-MnO₂, β-MnO₂, γ-MnO₂, and δ-MnO₂) are succeeded in being fabricated via hydrothermal processes and evaluated by activating PMS for the removal of Reactive Yellow X-RG, typical azo dye. Experiment results indicate that α-MnO₂ with a one-dimensional structure exhibits the best catalytic performance among the four as-prepared MnO₂, which can be attributed to its broadest crystal interplanar distance (0.692), the highest portion of Mn (III)/Mn (IV) (4.194), and lowest value of average oxidation state AOS (2.696). Correlation analysis confirms that interplanar distance is the most relative factor with the catalytic activity of MnO₂ among the three studied factors (R² = 0.99715). Meanwhile, the morphological scale structure of α-MnO₂ can also account for its highest catalytic ability among the four as-prepared MnO₂, including its large specific area and advantageous one-dimensional nanostructure. Furthermore, according to the response surface methodology, when the dosage of PMS is 2.369 g/L, the dosage of α-MnO₂ is 0.991 g/L, and the initial dye concentration is 1025 mg/L, the maximum removal rate of Reactive Yellow X-RG is up to 97.38%.

Tumor microenvironment-responsive histidine modified-hyaluronic acid-based MnO2 as in vivo MRI contrast agent

Tumor microenvironment (TME)-responsive manganese dioxide (MnO₂) nanoparticles as a good T₁ contrast agent could reduce unwanted toxicity and improve the accuracy of cancer detection. Despite these distinct advantages of MnO₂-based nanoparticles, their synthesis involves multi-step processes with relatively long synthesis times. In this study, we synthesized histidine-modified hyaluronic acid (HA-His), and the prepared HA-His conjugates quickly reduce permanganate to MnO₂, leading to facile production of HA-His/MnO₂ nanoparticles with good water-dispersibility and stability under biological conditions. The synthesized HA-His/MnO₂ nanoparticles readily responded to the TME (low pH, high H₂O₂, and high glutathione), and they were internalized into SCC7 cells with high CD44 expression. Moreover, the systemically administered HA-His/MnO₂ nanoparticles with biocompatibility were specifically accumulated in tumor tissues, thereby efficiently enhancing T₁ contrast in MRI. Therefore, the HA-His/MnO₂ nanoparticles synthesized herein can be used as a promising T₁ contrast agent for tumor MR imaging.

Preparation of C6 cell membrane-coated doxorubicin conjugated manganese dioxide nanoparticles and its targeted therapy application in glioma

In this study, we prepared a C6 cell membrane-coated doxorubicin conjugated manganese dioxide biomimetic nanomedicine system (MnO₂-DOX-C6) for the treatment of glioma. In the glioma microenvironment, manganese dioxide could alleviate tumor hypoxia by promoting the decomposition of hydrogen peroxide (H₂O₂) to generate oxygen and, through a Fenton-like reaction, increase ROS levels in tumor cells, thus inducing oxidative stress to further kill cancer cells. Doxorubicin and manganese dioxide were connected through a hydrazone bond so that doxorubicin could be released only in the acidic environment of the tumor, which helped to reduce the toxicity and side effects of doxorubicin. Encapsulation of glioma C6 cancer cell membrane in MnO₂-DOX-C6 made MnO₂-DOX possess the homologous targeting ability and also regulated drug release rate. In vitro release experiments showed that the cumulative release of doxorubicin from MnO₂-DOX-C6 at a pH of 5.0 for 48 h was 66.84 ± 3.81%, proving that it had pH sensitivity and a sustained-release effect. Cellular uptake experiments showed that MnO₂-DOX-C6 had a good ability to target syngeneic tumor cells. MTT, flow cytometry, Western blot, cell immunofluorescence staining and in vivo antitumor experiments demonstrated that MnO₂-DOX-C6 could promote C6 cell apoptosis and inhibit its proliferative ability. These results clearly suggested that MnO₂-DOX-C6 may be a promising bionic nanosystem agent for the treatment of glioma.

Oxygen-generating polymer vesicles for enhanced sonodynamic tumor therapy

The efficacy of sonodynamic therapy (SDT) is often limited by the insolubility of sonosensitizers and unfavorable hypoxia tumor microenvironment. To meet this challenge, an oxygen-generating polymer vesicle is developed to achieve enhanced SDT. The hydrophilic coronas and the hydrophobic membrane of polymer vesicles can function as different modules for the simultaneous delivery of manganese dioxide and chlorine e6 (designated as Ce6-MnO₂-PVs). These Ce6-MnO₂-PVs exhibited high catalase mimetic activity and could efficiently generate reactive oxygen species upon ultrasound activation. In vivo results showed that Ce6-MnO₂-PVs almost completely eradicated the subcutaneous tumors (94% volume reduction) without any obvious systemic toxicity. Moreover, these Ce6-MnO₂-PVs showed effective behavior for the attenuation of crucial tumor progression-releated factors. Specially, the expression levels of both hypoxia-inducible factor-1α and vascular endothelial growth factor at 4 h post-injection detected by immunofluorescence were reduced by 66% and 52%, respectively. These findings suggest that Ce6-MnO₂-PVs may serve as an effective and safe platform for enahnced SDT in hypoxic tumors.

Binary organic-inorganic nanocomposite of polyaniline-MnO2 for non-enzymatic electrochemical detection of environmental pollutant nitrite

Due to wide usage as nitrogen fertilizer in agriculture and food additive in industry, nitrite, as one of inorganic environmental pollutants, could cause detrimental effects to the ecological environment. Therefore, accurate, sensitive and rapid detection of nitrite is necessary. In this work, binary hybrid polyaniline-MnO₂ organic-inorganic nanocomposite is prepared chemically and characterized via X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Polyaniline-MnO₂ organic-inorganic nanocomposite serves as excellent electrode modifier for electrochemical sensing of nitrite by two modes of cyclic voltammetry and chronoamperometry, achieving broad linear ranges and low limits of detection for both methods. Moreover, the organic-inorganic nanocomposite displays satisfactory sensing performance in real water sample analysis. Amine and imino groups of polyaniline contribute to the better adsorption behavior of nitrite onto the nanocomposite, which improves the nanocomposite's sensing performance. In summary, the synergistic effects between polyaniline and MnO₂ is taken advantaged in the nanocomposite for effective electrochemical sensor development.

Construction and evaluation of curcumin upconversion nanocarriers decorated with MnO2 for tumor photodynamic therapy

The limited tissue penetration depth and tumor hypoxic microenvironment have become the two pivotal obstacles that alleviate the antineoplastic efficacy in tumor photodynamic therapy (PDT). In the research, MnO₂-decorated upconversion nanoparticles (UCSMn) have been designed to generate certain oxygen within the solid tumor, and also increase the light penetrating depth due to the optical conversion ability derived from upconversion nanoparticles. Furthermore, upconversion nanoparticles as the inner core are coated by mesoporous silica for the loading of curcumin as photosensitizer and chemotherapeutics, and then a MnO₂ shell is proceeding to grow via redox method. When reaching the tumor tissue, the MnO₂ nanoshells of UCSMn could be rapidly degraded into manganese ions (Mn²⁺) owing to the reaction with H₂O₂ in acidic tumor microenvironment, meanwhile producing oxygen and facilitating curcumin release. Once the tumor is illuminated by 980 nm light, the upconversion nanoparticles can transform the infrared light to visible light of 450 nm and 475.5 nm, which can be efficiently absorbed by curcumin, and then produce singlet oxygen to induce tumor cell apoptosis. Curcumin played a dual role which can not only be acted as a photosensitizer, but also a chemotherapeutic agent to further reinforce the antitumor activity. In short, the intelligent nanostructure has the potential to overcome the above-mentioned shortcomings existed in PDT and eventually do work well in the hypoxia tumors. MnO₂-decorated upconversion nanoparticle to solve the tissue penetration and tumor hypoxic microenvironment for tumor photodynamic therapy.

Engineering nanostructured Ag doped α-MnO2 electrocatalyst for highly efficient rechargeable zinc-air batteries

Engineering of highly active, and non-precious electrocatalysts are vital to enhance the air-electrodes of rechargeable zinc-air batteries (ZABs). We report a facile co-precipitation technique to develop Ag doped α-MnO₂ nanoparticles (NPs) and investigate their application as cathode materials for ZABs. The electrochemical and physical characteristics of α-MnO₂ and Ag doped α-MnO₂ NPs were compared and examined via CP, CV, TGA/DTA, FT-IR, EIS, and XRD analysis. CV result displayed higher potential and current for ORR in Ag doped α-MnO₂ NPs than α-MnO₂; but, ORR performance decreased when the Ag doping was raised from 7.5 to10 mmol. Moreover, α-MnO₂ and Ag doped α-MnO₂ NPs showed 2.1 and 3.8 electron transfer pathway, respectively, showing Ag doped α-MnO₂ performance to act as an active ORR electrocatalyst for ZABs. The EIS investigation exhibited that charge-transfer resistance for Ag doped α-MnO₂ was extremely lower associated to the MnO₂ demonstrating that the successful loading of Ag in α-MnO₂. A homemade ZAB based on Ag–MnO₂-7.5 showed a high open circuit potential, low ohmic resistances, and excellent discharge profile at a constant current density of 1 mA/g. Moreover, Ag–MnO₂-7.5 show a specific capacity of 795 mA h g⁻¹ with corresponding high energy density ∼875 Wh kg⁻¹ at 1 mA cm⁻² discharging conditions.

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Ag doped α-MnO₂ electrode for rechargeable zinc–air battery was prepared via a facile co-precipitation technique.

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Ag doped α-MnO₂ electrode shows lower charge transfer resistance associated to un-doped MnO₂ electrode.

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Ag doped α-MnO₂ shows enhanced ORR kinetics in oxygen electrode potential.

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The capacitance performance of Ag doped α-MnO₂ electrodes was highly improved.

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Ag doped α-MnO₂ electrode showed energy density of 69.3 W h kg−1 and power density of 722.9 W kg−1.

Efficient removal of organic compounds in eutrophic water via a synergy of cyanobacterial extracellular polymeric substances and permanganate

This study provides a new thinking for the efficient utilization of permanganate (Mn (VII)) in eutrophic water treatment. Eutrophic water contained a large amount of extracellular polymeric substances (EPS) with reduction and chelation; this study used phenol as typical organic matter and cyanobacteria EPS as a representative EPS to explore the mechanism by which EPS influences the oxidation of phenol by Mn(VII) at pH 5.0-9.0. The results showed that under the condition of pH 5.0-7.0, adding 0.2-10 mg/L EPS to the Mn(VII) system could effectively improve the oxidation efficiency of Mn(VII) for phenol. EPS promoted the continuous formation and stability of in situ EPS-MnO₂ colloids and significantly enhanced the oxidation of Mn(VII). EPS also combined with phenol and increased the electron cloud density to promote the oxidation of phenol by Mn(VII).

Dual-action nanoplatform with a synergetic strategy to promote oxygen accumulation for enhanced photodynamic therapy against hypoxic tumors

With the development of redox-related therapy modalities in cancer therapy, photodynamic therapy (PDT) has gradually become the most widely used type in the clinic. However, the hypoxic tumor microenvironment restricted the curative effect of PDT. Here, a strategic hypoxia relief nanodrug delivery system (SHRN) with a synergetic strategy was designed to alleviate tumor hypoxia on the basis of PDT. Specifically, the oxygen producer MnO₂, oxygen consumption inhibitor atovaquone (ATO) and photosensitizer hypericin (HY) were loaded in SHRN. MnO₂ reacted with excess H₂O₂ in the tumor microenvironment to increase oxygen generation, while ATO inhibited electron transfer in the aerobic respiratory chain to decrease oxygen consumption. Then, HY utilized this sufficient oxygen to produce ROS under irradiation to enhance the PDT effect. In vitro and in vivo assays confirmed that SHRN exhibits powerful and overall antitumor PDT effects. This formulation may provide an alternative strategy for the development of PDT effects in hypoxic tumor microenvironments. STATEMENT OF SIGNIFICANCE: We constructed a strategic hypoxia relief nanodrug delivery system (SHRN) with a synergetic strategy to alleviate tumor hypoxia on the basis of photodynamic therapy (PDT). This work uniquely aimed at not only increased O₂ generation in hypoxic tumor microenvironment but also reduced O₂ consumption. Moreover, we designed a nanodrug delivery system to enhance the tumor permeability of SHRN. In vitro and in vivo assays all confirmed that SHRN exhibited powerful and overall antitumor effects. This formulation may provide an alternative strategy for the development of the PDT effect in hypoxic solid tumor.

A Review of MnO2 Composites Incorporated with Conductive Materials for Energy Storage

Manganese dioxide (MnO₂ ) has been widely used in the field of energy storage due to its high specific capacitance, low cost, natural abundance, and being environmentally friendly. However, suffering from poor electrical conductivity and high dissolvability, the performance of MnO₂ can no longer meet the needs of rapidly growing technological development, especially for the application as electrode material in metal-ion batteries and supercapacitors. In this review, recent studies on the development of binary or multiple MnO₂ -based composites with conductive components for energy storage are summarized. Firstly, general preparing methods for MnO₂ -based composites are introduced. Subsequently, the binary and multiple MnO₂ -based composites with carbon, conducting polymer, and other conductive materials are discussed respectively. The improvement in their performance is summarized as well. Finally, perspectives on the practical applications of MnO₂ -based composites are presented.

Can the commonly used quenching method really evaluate the role of reactive oxygen species in pollutant abatement during catalytic ozonation?

Reactive oxygen species (ROS) such as hydroxyl radicals (•OH), superoxide radicals (O₂^•-), and singlet oxygen (¹O₂) have often been suggested to play a role in ozone-resistant pollutant abatement during catalytic ozonation. However, there are significant controversies regarding their relative importance in literature. Currently, the role of ROS in pollutant abatement is commonly evaluated by the quenching method based on the assumption that the added ROS quenchers (e.g., tert-butanol (TBA) and para-benzoquinone (pBQ)) quench only the target ROS, but do not considerably influence other reaction mechanisms of catalytic ozonation. However, we hypothesized that this assumption is possibly unrealistic and a main cause for the controversies reported in literature. To test this hypothesis, this study evaluated the effects of six commonly used ROS quenchers (TBA, pBQ, methanol (MeOH), 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl), furfuryl alcohol (FFA), and sodium azide (NaN₃)) on the mechanism of catalytic ozonation with manganese dioxide. The results show that rather than only quenching their target ROS, these quenchers can profoundly change the catalytic ozonation system through various mechanisms, e.g., interrupting the radical chain reaction of O₃ decomposition, blocking the active sites of catalysts, and consuming O₃ in the system. Due to the significant confounding effects of ROS quenchers on the reaction mechanism, the quenching method actually cannot reveal the role of ROS in pollutant abatement and often misinterpreted the catalytic ozonation mechanism. The results indicate that the commonly used quenching method is probably not an appropriate way to investigate the role of ROS in pollutant abatement during catalytic ozonation, and many previously reported mechanisms obtained with the quenching method may need a revisit.

Surface characteristic and sinking behavior modifications of microplastics during potassium permanganate pre-oxidation

Microplastics (MPs) occur in the source water of worldwide drinking water treatment plants (DWTPs). Pre-oxidation treatments become the initial stage for MPs treatment in DWTPs. Investigating the modifications of MPs after pre-oxidations is important to understand their fate in DWTPs. In this study, potassium permanganate oxidation (PPO) was applied to treat four high abundant MPs in DWTPs, including polyethylene (PE), polyethylene terephthalate (PET), polyvinylchloride (PVC) and polystyrene (PS). Influences of polymer types, sizes and pH were considered. After 10 mg L^-1 PPO, only slight corrosions were observed on all MPs. Whereas, the appearances of O-Mn spectrum and the observation of nano-scale particles indicated the generation of nascent state Mn-oxides (MnO₂) on MPs surface. This adhesion of MnO₂ contributed to increasing density and hydrophilicity. As a result, the sinking performance of MPs was enhanced, e.g. the sinking ratio of 6.5 µm MPs increased 30% (PET), 20% (PVC) and 30% (PS) compared with pristine ones upon pH 7 PPO. These results implied that the practical PPO can enhance the sinking behavior of MPs. Of note, PE seems to be persistent and requires special concern.

Cytocompatible manganese dioxide-based hydrogel nanoreactors for MRI imaging

The application of nanoparticles in magnetic resonance imaging (MRI) has been greatly increasing, due to their advantageous properties such as nanoscale dimension and tuneability. In this context, manganese (Mn²⁺)-based nanoparticles have been greatly investigated, due to their valuable use as a contrast agent, improving signal intensity and specificity in MRI (manganese-enhanced MRI, MEMRI). Additionally, Mn²⁺ can act as scavengers of reactive oxygen species (ROS), commonly present in the inflammatory processes of neurodegenerative diseases. The aim of the present study was to develop nanoreactors, which can be used as contrast-agent in MEMRI. Several blends of methacrylated gellan gum (GG-MA) and hyaluronic acid (HA) were embedded with different types of manganese dioxide (MnO₂) nanoparticles and further physico-chemically characterized. Dynamic light scattering, scanning electron microscopy, water uptake and degradation studies were performed. In vitro cytotoxicity of the different formulations was also evaluated using an immortalized rat fibroblast cell line L929, up to 72 h of culturing. Synthesized nanoparticles were obtained with an average size of 70 nm and round-shaped morphology. The stability of the different formulations of hydrogels was not affected by nanoparticles' concentration or HA ratio. The presence of synthesized MnO2 (MnO2_S) nanoparticles reduced hydrogels' cytocompatibility, whereas the commercially available type 1 (MnO2_C1) nanoparticles were less toxic to cells. Additionally, cell proliferation and viability were enhanced when a lower content of HA was present. Higher concentrations (75 and 100 ng/mL) of MnO2_S and MnO2_C1 nanoparticles did not negatively affected cell viability, whereas the opposite effect was observed for the commercial type 2 (MnO2_C2) nanoparticles. Further studies are required to evaluate the potential application of the most promising nanoreactors' formulations for combined application in MEMRI and as ROS scavengers.

A novel γ-like MnO2 catalyst for ozone decomposition in high humidity conditions

MnO₂ catalysts have been widely studied for catalytic gaseous ozone decomposition. However, their poor moisture resistance often leads to undesirable catalytic effects in the presence of high humidity. In this study, a novel catalyst with γ-like MnO₂ was synthesized using the selective dissolution method on LaMnO₃ perovskites. The as-prepared catalyst exhibited quite stable ozone conversion of ~90% within 12 h under 75% relative humidity (400-800 ppm of ozone, 30 °C, 150 000 mL·g^-1·h^-1 of WHSV). In contrast, traditional γ-MnO₂ catalyst showed deficient resistance to H₂O and sensitivity to space velocity. Detailed characterizations showed that the larger number of oxygen vacancies induced by structure reconstruction of the γ-like MnO₂ and residual La³⁺ cations facilitated ozone decomposition in humid atmosphere. Finally, the reaction rate of ozone decomposition was proposed by a kinetic study, which further proved that the amount and hydrophilicity of oxygen vacancies are the determinants of the first-order reaction rate constant.

Green fabrication of porous microspheres containing cellulose nanocrystal/MnO2 nanohybrid for efficient dye removal

Microspheres based on cellulose nanocrystal (CNC)/metal oxide hybrid materials have great application prospects in wastewater treatment due to simultaneously adsorption, degradation ability, easily separation and recycling properties. However, the relatively small porosity and specific surface area of the CNC-based microspheres limit their adsorption ability. Herein, we reported a facile strategy to prepare porous microsphere based on CNC/MnO₂ by freeze-drying the air-bubble templated emulsion, in which the sodium alginate (SA) was used as the crosslinked matrix. Thus-obtained CNC/MnO₂/SA microspheres showed low density of 0.027 g/cm³ and high porosity of 98.23%. Benefiting from the high porosity, synergetic effect of CNC electrostatic adsorption and oxidative degradation ability of MnO₂, the decolorization ratio of methylene blue (800 mg/mL) could be up to 95.4% in 10 min, and the equilibrium decolorization could reach 114.5 mg/g. This study provides a green and facile strategy to design porous CNC-based material for dye wastewater treatment.

Innate tumor-targeted nanozyme overcoming tumor hypoxia for cancer theranostic use

Introduction

Hypoxic tumor microenvironment (TME) is the major contributor to cancer metastasis, resistance to chemotherapy, and recurrence of tumors. So far, no approved treatment has been available to overcome tumor hypoxia.

Objectives

The present study aimed to relieve tumor hypoxia via a nanozyme theranostic nanomaterial as well as providing magnetic resonance imaging (MRI)-guided therapy.

Methods

Manganese dioxide (MnO₂) was used for its intrinsic enzymatic activity co-loaded with the anti-cancer drug Doxorubicin (Dox) within the recombinant heavy-chain apoferritin cavity to form MnO₂-Dox@HFn. Following the synthesis of the nanomaterial, different characterizations were performed as well as its nanozyme-like ability. This nanoplatform recognizes tumor cells through the transferrin receptors 1 (TfR1) which are highly expressed on the surface of most cancer cells. The cellular uptake was confirmed by flow cytometry and fluorescence spectroscopy. In vitro and in vivo studies have been investigated to evaluate the hypoxia regulation, MRI ability and anti-tumor activity of MnO₂-Dox@HFn.

Results

Being a TME-responsive nanomaterial, MnO₂-Dox@HFn exerted both peroxidase and catalase activity that mainly produce massive oxygen and Mn²⁺ ions. Respectively, these products relieve the unfavorable tumor hypoxia and also exhibit T1-weighted MRI with a high longitudinal relaxivity of 33.40 mM. s⁻¹. The utility of MnO₂-Dox@HFn was broadened with their efficient anti-cancer activity proved both in vitro and in vivo.

Conclusions

MnO₂-Dox@HFn successfully overcome tumor hypoxia with double potentials enzymatic ability and diagnostic capacity. This investigation could ignite the future application for cancer theranostic nanozyme therapy.

Online evaluation of the catalytic performance of MnO2 and its application in H2S cataluminescence sensing

As a catalyst widely used in industry, manganese dioxide (MnO₂) has different crystalline forms and shows excellent performance in catalytic reactions. Therefore, it is of significance to rapidly evaluate the catalytic performance of MnO₂ online. In this paper, a highly efficient evaluation method based on H₂S cataluminescence (CTL) sensing was proposed for MnO₂ with different crystalline forms. Firstly, α-, β- and δ-MnO₂ were synthesized successfully and performed diacritical CTL behaviours in the catalytic oxidation of H₂S. Based on these interesting phenomena, the catalytic performance of α-, β- and δ-MnO₂ was efficiently evaluated online through CTL method for the first time. Results showed that β-MnO₂ had the best catalytic oxidation performance, followed by α- and δ-MnO₂, and the reactive oxygen species of MnO₂ was the most significant influencing factor. Subsequently, β-MnO₂ was selected to design a CTL sensor for H₂S detection with a wide linear range (2.43-29.1 μg/mL) and a low limit of detection (LOD, S/N = 3, 0.280 μg/mL). This work not only provided a new and feasible method for online evaluation of the catalytic performance of materials, but also designed a CTL sensor for H₂S determination with high selectivity and sensitivity.

Iodinated disinfection byproduct formation in a MnO2/I-/EPS system

Manganese dioxide (MnO₂) is a Mn deposit widely accumulated in the corrosion layer of pipelines, and iodide (I^-) is a halogen ion frequently detected in waters. The biofilm dwelling on the corrosion scales often secretes extracellular polymeric substances (EPS) into drinking water. The paper aimed to study the I^- oxidation by MnO₂ and iodinated disinfection byproducts (I-DBPs) formation with biofilm EPS as a precursor. More than 93% of formed free iodine was finally converted into organic iodine in the MnO₂/I^-/EPS system. Compared with humic acid, EPS had a lower carbonaceous I-DBPs (C-IDBPs) formation while a higher nitrogenous I-DBPs (N-IDBPs) formation. The formation of iodomethanes (I-THMs), iodoacetonitriles (I-HANs) and iodoacetic acids (I-HAAs) decreased with the increase of pH due to the weakening of polarization effect and redox potential, while the iodoacetamides (I-HAcAms) formation achieved the maximum at pH 6.0 due to the difference between the hydrolysis rate of I-HANs and decomposition rate of I-HAcAms. The I-DBPs formation was positively correlated with I^- concentration, while negatively correlated with MnO₂ dose. Protein components displayed a higher formation of N-IDBPs and C-IDBPs than polysaccharide components due to higher nitrogen proportion and more iodination sites. Among 20 protein monomers, aspartic acid was considered as the most important precursor of the four investigated I-DBPs species. The paper is helpful to understand the I-DBPs formation when I^- in the bulk water come into contact with Mn deposits attached by biofilm.

Construction of Z-scheme g-C3N4 / MnO2 /GO ternary photocatalyst with enhanced photodegradation ability of tetracycline hydrochloride under visible light radiation

A facile wet-chemical method was adopted to synthesize g-C₃N₄/MnO₂/GO heterojunction photocatalyst for visible-light photodegradation of tetracycline hydrochloride (TC). The addition of MnO₂ and GO increased the absorption of visible light and the specific surface area of the photocatalyst. The results of photoluminescence, electrochemical impedance spectroscopy, and photocurrent response indicated that CMG-10 had the lowest electron-hole recombination probability, which was beneficial for the photocatalytic reaction. The ternary photocatalyst exhibited enhanced photoelectric performance and superior photocatalytic activity with 91.4% removal of TC (10 mg/L) under a mere 60 min visible light illumination, which showed enhanced photocatalytic degradation when compared with binary (CM, 77.95%; CG, 78.83%) and single (C₃N₄, 55.5%; MnO₂, 36.41%) photocatalysts. A pH of 6 was optimal for the CMG-10 photocatalytic degradation of TC, and the optimal photocatalyst dosage was 0.5 g/L. Common coexisting ions influenced the removal of TC by influencing the production of active species. The catalyst is stable and reusable with only a 10% reduction in removal efficiency after four cycles. According to the active species analysis, the Z-scheme mechanism was a charge transfer behavior in the composite photocatalyst, which could prevent the recombination of photogenerated carriers. This study presents a photocatalytic approach to the effective removal of TC from water bodies, which provides practical implications to advance the use of photocatalytic technology in the restoration of aqueous environmental pollution.

Synthesis of membrane-type graphene oxide immobilized manganese dioxide adsorbent and its adsorption behavior for lithium ion

Recently, there has been an urgent need to develop new materials and technologies for extracting lithium ions. Herein, the membrane-type adsorbent of manganese dioxide (MnO₂) is prepared by a vacuum filtration method using graphene oxide (GO) as a binder and amino-β-cyclodextrin (amino-β-CD) as an adjuvant. The results of thermogravimetric analysis show that MnO₂ is successfully immobilized on GO layers with a content of about 24 wt%, which enabled rapid adsorb lithium ions from the ionic solution. In addition, the permeation experiment shows the membrane has specific selectivity for lithium ion transport and adsorption, which is manifested in the selectivity ratios of K⁺/Li⁺, Na⁺/Li⁺ and K⁺/Na⁺ to 2.5, 3.2 and 0.8, respectively. Adsorption experiments show that GO-β-CD/MnO₂ membrane has a high adsorption capacity for lithium ions (37.5 mg g^-1). The adsorption kinetic curve indicates that the lithium adsorption process is controlled by the chemical adsorption mechanism. In the enrichment experiment, the concentration of lithium ions from seawater can be enriched to 1.2 mg L^-1 after 100 cycles. The results suggest that the developed GO-β-CD/MnO₂ membrane could effectively extract lithium ions from seawater.

Reducing substances-enhanced degradation of pollutants by permanganate: The role of in situ formed colloidal MnO2

Permanganate is one of common oxidants used for organic pollutant abatement in water treatment. This study showed that the degradation rate of bisphenol A (BPA) by permanganate at pH 5.0 in the presence of aniline is much higher than that in the absence of aniline. 2, 5, and 10 μM of aniline enhanced BPA degradation rate by 104%, 326% and 601%, respectively. Colloidal MnO₂ was formed through the reduction of permanganate by aniline and contributed to BPA oxidation considerably. The reactivity of MnO₂ is sensitive to pH and is high under acidic conditions, resulting in the observed enhancement of aniline on BPA removal by permanganate at pH < 7.0. The role of MnO₂ was further confirmed by the relationship of MnO₂ formation and BPA/aniline removal, the inhibitory effect of Ca²⁺ on the oxidation of BPA in the presence of aniline. Besides the aniline/BPA system, the pollutants which react with permanganate rapidly are likely to enhance the degradation of coexisting pollutants which show high reactivity towards MnO₂. Due to the reduction of permanganate and stabilization of the in situ formed colloidal MnO₂ by water matrix, the oxidation rate of pollutant in real water is higher than that in pure water.

Oxygen-generating glycol chitosan-manganese dioxide nanoparticles enhance the photodynamic effects of chlorin e6 on activated macrophages in hypoxic conditions

This study aimed to investigate the use of glycol chitosan (GC) for the synthesis of MnO₂ nanoparticles (NPs) and to evaluate whether the prepared GC-MnO₂ NPs enhance the light-triggered photodynamic effects of chlorin e6 (Ce6) via the generation of oxygen and alleviation of hypoxia in lipopolysaccharide (LPS)-activated macrophages (RAW 264.7), which produce excessive amounts of reactive oxygen species (ROS). GC-MnO₂ NPs were synthesized by a simple reaction between GC and KMnO₄ in water. The prepared GC-MnO₂ NPs were spherical in shape, with a mean diameter of approximately 60 nm. The particles effectively generated oxygen via H₂O₂-induced degradation under hypoxic conditions, which led to an increase in the singlet oxygen levels upon laser irradiation. Furthermore, GC-MnO₂ NPs significantly enhanced the light-triggered photodynamic effects of Ce6 on activated macrophages under hypoxic conditions, as shown by the increased levels of cell death and cell membrane damage in activated macrophages. Therefore, these results suggest that GC can be used as an alternative natural polymer for the synthesis of MnO₂ NPs and that oxygen-generating GC-MnO₂ NPs enhance the light-triggered photodynamic effects of Ce6 on activated macrophages by alleviating hypoxia.

Hydrous manganese dioxide modified poly(sodium acrylate) hydrogel composite as a novel adsorbent for enhanced removal of tetracycline and lead from water

In this study, hydrous manganese dioxide (HMO) modified poly(sodium acrylate) (PSA) hydrogel was produced for the first time to remove tetracycline(TC) and lead(Pb(II)) from water. The as-prepared composite was characterized using various techniques, such as SEM-EDS, FTIR, XRD, BET, and XPS, to elucidate the successful loading of HMO and analyze subsequent sorption mechanisms. Different influencing parameters such as adsorbent dose, initial concentration of adsorbates, reaction time, solution pH, and temperature were also investigated. The adsorption kinetic studies of both TC and Pb(II) removal indicated that equilibrium was achieved within 12 h, with respective removal rates of 91.9 and 99.5%, and the corresponding adsorption data were fitted to the second-order kinetics model. According to the adsorption isotherm studies, the sorption data of TC best fitted to the Langmuir isotherm model while the adsorption data of Pb(II) were explained by the Freundlich isotherm model. The maximum adsorption capacities of both TC and Pb(II) were found to be 475.8 and 288.7 mg/g, respectively, demonstrating excellent performances of the adsorbent. The uptake capacity of PSA-HMO was significantly influenced by the level of solution pH, in which optimum adsorption amount was realized at pH 4.0 in the TC and Pb(II) systems, respectively. Thermodynamic studies showed the process of TC and Pb(II) adsorptions were endothermic and spontaneous. Overall this study elucidated that PSA-HMO composite can be a promising candidate for antibiotics and heavy metal removal in water treatment applications.

Detection of silver through amplified quenching of fluorescence from polyvinyl pyrrolidone-stabilized copper nanoclusters

Silver ion detection with ultra-high sensitivity was established. We synthesized copper nanoclusters (CuNCs) with blue fluorescence through a one-pot process. Instead of a direct quencher toward the CuNCs, silver ions activated the strong oxidation from persulfate and subsequently converted divalent manganese ion into manganese dioxide (MnO₂). The surface charges of MnO₂ and the CuNCs brought them together and quenched the fluorescence from the latter. Due to silver ions' role as the catalyst in the process, it cycled and even a small amount leads to a significant fluorescence change. This signaling provided the determination of  silver ions in the range 5 pM~1 nM, with a detection limit of  1.2 pM. The method is selective, and its applicability was validated through practical water sample analyses.

High-performance reversible aqueous zinc-ion battery based on iron-doped alpha-manganese dioxide coated by polypyrrole

The development of zinc-ion storage cathode materials for aqueous zinc-ion batteries (AZIBs) is a necessary step for the construction of large-scale electrochemical energy conversion and storage devices. Iron-doped alpha-manganese dioxide (α-MnO₂) nanocomposites were achieved in this study via pre-intercalation of Fe³⁺ during the formation of α-MnO₂ crystals. A polypyrrole (PPy) granular layer was fabricated on the surface of α-MnO₂ using acid-catalyzed polymerization of pyrroles. The pre-intercalation of Fe³⁺ effectively enlarges the lattice spacing of α-MnO₂ and consequently decreases the hindrance for Zn²⁺ insertion/extraction in the iron-doped α-MnO₂ coated by PPy (Fe/α-MnO₂@PPy) composite. Meanwhile, the PPy buffer layer can ameliorate electron and ion conductivity and prevent dissolution of α-MnO₂during the charge/discharge process. This unique structure makes the Fe/α-MnO₂@PPy composite an efficient zinc-ion storage cathode for AZIBs. The targeted Fe/α-MnO₂@PPy cathode achieves superior performance with reversible specific capacity (270 mA h g^-1 at 100 mA g^-1) and exhibits highdiffusioncoefficientof 10^-10-10^-14 cm^-2 s^-1. Therefore, a feasible approach is implemented on advanced electrode materials using in AZIBs for practical applications.

Degradation of ciprofloxacin by the Mn cycle system (MnCS): Construction, characterization and bacterial analysis

The release of Mn(II) occurs in the degradation of organic matters by manganese ore (MnO₂), resulting in a reduced efficiency. During the degradation of ciprofloxacin (CIP), in a biofilter, this paper put forward a novel method that similar to the geo-cycle of Mn (MnCS) on the Earth to regenerate MnO₂. The freshly prepared MnO₂ was suitable for the use in the MnCS. It indicated that the mutual conversion between Mn(II), Mn(III), and Mn(IV) in the MnCS, which was driven by CIP and manganese oxidizing bacteria (MnOB), could maintain the activity of MnO₂. The MnCS showed feasibility in the coexistence of ammonia or humic acid, and provided a kinetic degradation. The physicochemical features of MnO₂ before and after bio-regeneration were characterized by TEM, XRD, BET, and XPS. It was found that the morphological structure of MnO₂ became loose and the maximum peak of pore size distribution became smaller, but the increase of surface area, the change of Mn(III/IV) content, and the decrease of crystallinity favored the bio-regeneration process. Moreover, as a mediator in the MnCS, the group of MnOB was dramatically inhibited by CIP, and the bacterial community had changed significantly. The typical MnOB shared low abundance in the biofilter, while the rarely reported genera (e.g. Sphingomonas) that related to the formation of Mn deposits appeared to be involved in the MnCS.

Immobilization of chitosan-templated MnO2 nanoparticles onto filter paper by redox method as a retrievable Fenton-like dip catalyst

By exploiting the hydrophilicity of cellulose filter paper (FP) and the excellent chelating property of chitosan (CH) for Mn²⁺, we have designed an efficient and retrievable dip catalyst MnO₂/CH-FP for Fenton-like degradation of methylene blue (MB) over a wide pH range from 2.8 to 11.2. The MnO₂ nanoparticles were uniformly immobilized in the CH-FP matrix by in-situ redox precipitation method where Mn(NO₃)₂ was treated with KMnO₄ at mild conditions. A series of MnO₂/CH-FP hybrids with different MnO₂ loading were fabricated via varying concentration of Mn(NO₃)₂ solution, and their structure-function relationships were discussed based on detailed characterization. The optimal catalyst 1.0MnO₂/CH-FP could cooperate with multiple low-concentration dosages of H₂O₂ to efficiently degrade 95.6% MB in 90 min (50 mg L^-1 MB, 1 g L^-1 catalyst, 30 mg L^-1 H₂O₂, pH 7). It is also shown that 1.0MnO₂/CH-FP could still keep 83.3% degradation efficiency of MB after six cycles. Moreover, the activity of this composite greatly surpassed that of bare MnO₂ for nearly 50%, owing to its larger surface area and more accessible active sites. This method for preparing MnO₂/CH-FP could effectively avoid the agglomeration of MnO₂ nanoparticles and make the reaction turn on/off almost instantaneously by mere insertion/removal.

A comparison study of levofloxacin degradation by peroxymonosulfate and permanganate: Kinetics, products and effect of quinone group

Permanganate (Mn(VII)) as a selective oxidant has been widely used in water treatment process. Recently, peroxymonosulfate (PMS) was recognized as an emerging selective oxidant, which showed appreciable reactivity toward organic compounds containing electron-rich functional groups. In this study, the oxidation of a model fluoroquinolone antibiotic levofloxacin (LEV) by Mn(VII) and PMS was comparatively investigated. Degradation of LEV by PMS followed second-order kinetics and showed strong pH dependency with apparent second-order rate constants (k_app) of 0.15-26.52 M^-1 s^-1 at pH 5.0-10.0. Oxidation of LEV by Mn(VII) showed autocatalysis at pH 5.0-7.0, while no autocatalysis was observed at pH 8.0-10.0 (k_app = 2.23-4.16 M^-1 s^-1). Such unusual oxidation kinetics was attributed to the in-situ formed MnO₂ from Mn(VII) consumption. The performance of PMS and Mn(VII) for the degradation of LEV was also examined in real waters. PMS primarily react with the aliphatic N4 amine on the piperazine ring of LEV, and Mn(VII) reacted with both the aliphatic N4 amine and aromatic N1 amine. Both PMS and Mn(VII) could efficiently eliminate the antibiotic activity of LEV. Benzoquinone showed activating effect on both PMS and Mn(VII) oxidation, but their activation mechanisms were totally different.

Rod-like MnO2 boost Pd/reduced graphene oxide nanocatalyst for ethylene glycol electrooxidation

Anode catalyst is one of the core components of fuel cell, but its poor catalytic activity, short lifespan, and high price are tricky problems to the commercialization of fuel cell. Herein, a novel rod-like MnO₂ decorated reduced graphene oxide (RGO) supported Pd hybrid (Pd/RGO-MnO₂) has been designed, which manifests more negative onset oxidation potential, higher peak current density, and better long-term stability relative to Pd/RGO and pure Pd catalysts when serving for ethylene glycol electrooxidation. This enhancement may be due to the addition of MnO₂, which can effectively promote the adsorption of hydroxyl at a lower potential and produce a strong electronic interaction with Pd, as confirmed by X-ray photoelectron spectroscopy (XPS) technique. In view of its excellent performance and low cost, Pd/RGO-MnO₂ is considered to be a potential and effective anode catalyst for DEGFCs.

Role of MnO2 in controlling iron and arsenic mobilization from illuminated flooded arsenic-enriched soils

This study examined the role of intermittent illumination/dark conditions coupled with MnO₂-ammendments to regulate the mobility of As and Fe in flooded arsenic-enriched soils. Addition of MnO₂ particles with intermittent illumination led to a pronounced increase in the reductive-dissolution of Fe(III) and As(V) from flooded soils compared to a corresponding dark treatments. A higher MnO₂ dosage (0.10 vs 0.02 g) demonstrated a greater effect. Over a 49-day incubation, maximum Fe concentrations mobilized from the flooded soils amended with 0.10 and 0.02 g MnO₂ particles were 2.39 and 1.85-fold higher than for non-amended soils under dark conditions. The corresponding maximum amounts of mobilized As were at least 92 % and 65 % higher than for non-amended soils under dark conditions, respectively. Scavenging of excited holes by soil humic/fulvic compounds increased mineral photoelectron production and boosted Fe(III)/As(V) reduction in MnO₂-amended, illuminated soils. Additionally, MnO₂ amendments shifted soil microbial community structure by enriching metal-reducing bacteria (e.g., Anaeromyxobacter, Bacillus and Geobacter) and increasing c-type cytochrome production. This microbial diversity response to MnO₂ amendment facilitated direct contact extracellular electron transfer processes, which further enhanced Fe/As reduction. Subsequently, the mobility of released Fe(II) and As(III) was partially attenuated by adsorption, oxidation, complexation and/or coprecipitation on active sites generated on MnO₂ surfaces during MnO₂ dissolution. These results illustrated the impact of a semiconducting MnO₂ mineral in regulating the biogeochemical cycles of As/Fe in soil and demonstrated the potential for MnO₂-based bioremediation strategies for arsenic-polluted soils.

MnO2-decorated biochar composites of coconut shell and rice husk: An efficient lithium ions adsorption-desorption performance in aqueous media

Lithium (Li⁺) is used in various applications involving pharmaceuticals, textile dyes, and batteries. Therefore, the demand for environmentally friendly and effective materials for Li⁺ uptake and recovery continues to increase. Herein, rice husk (RH) and coconut shell (CS) biomasses were used to fabricate honeycomb-networked biochar (BC) precursors via slow pyrolysis. RHBC- and CSBC-based MnO₂ composites were synthesized by depositing MnO₂ in various ratios onto RHBC and CSBC by varying the KMnO₄ concentration (2%, 3%, and 4%), followed by simple ultrasonication and heat-treatment methodologies. The structural and physicochemical properties of all of the fabricated composites were analyzed using several different instrumental methods. The batch adsorption experiments were performed for comparative Li⁺-adsorption studies of RHBC-Mnx and CSBC-Mnx composites by optimizing several parameters (pH, adsorbent dose, Li⁺ initial concentration, and contact time). The comparative adsorption analysis revealed that the RHBC-Mnx composites exhibited stronger Li⁺-adsorption ability than the CSBC-Mnx composites and that increasing the MnO₂ deposition to 3% in both cases led to maximum Li⁺ adsorption capacities (62.85 mg g^-1 and 57.8 mg g^-1), respectively. The kinetic studies show that Li⁺ adsorption proceeds through the pseudo-second-order mechanism. Li⁺ recovery was successfully carried out using HCl (eluting agent), thereby demonstrating the benefits of synthesized composites at the industrial scale. The current work indicates that the fabricated RHBC-Mnx and CSBC-Mnx composites may have potential for use as economical composites in eco-friendly applications such as Li⁺ adsorption and recovery from aqueous media.

MnO2-decorated N-doped carbon nanotube with boosted activity for low-temperature oxidation of formaldehyde

Low-temperature oxidative degradation of formaldehyde (HCHO) using non-noble metal catalysts is challenging. Herein, novel manganese dioxide (MnO₂)/N-doped carbon nanotubes (NCNT) composites were prepared with varying MnO₂ content. The surface properties and morphologies were analyzed using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). Comparing with MnO₂/carbon nanotubes (CNTs) catalyst, the 40% MnO₂/NCNT exhibited much better activity and selectivity for HCHO oxidation, mineralizing 95% of HCHO (at 100 ppm) into CO₂ at 30 °C at a gas hourly space velocity (GHSV) of 30,000 mL h^-1  g^-1. Density functional theory (DFT) calculation was used to analyze the difference in the catalytic activity of MnO₂ with CNTs and NCNT carrier. It was confirmed that the oxygen on NCNT was more active than CNTs, which facilitated the regeneration of MnO₂. This resulted in remarkably boosted activity for HCHO oxidation. The present work thus exploited an inexpensive approach to enhance the catalytic activity of transition metal oxides via depositing them on a suitable support.

Wet-spinning assembly and in situ electrodeposition of carbon nanotube-based composite fibers for high energy density wire-shaped asymmetric supercapacitor

Wire-shaped supercapacitors (WSC) have attracted tremendous attention for powering portable electronic devices. However, previously reported WSC suffered from a complicated fabrication process and high cost. The objective of this study is to develop a facile and scalable process for the fabrication of high energy density WSC. We coupled the wet-spinning assembly with an in situ electrodeposition technique to prepare carbon nanotube (CNT)-based composite fibers. The charge balance between the electrodes was realized by controlling the deposition time of the pseudocapacitive materials. A wire-shaped asymmetric supercapacitor (WASC) was fabricated by twisting MnO₂/CNT fiber cathode and PPy/CNT fiber anode with LiCl/PVA electrolyte. The flexible MnO₂/CNT//PPy/CNT WASC operated in a broadened voltage range of 0-1.8 V exhibited a high capacitance of 17.5F cm^-3 (10.7F g^-1). In addition, it delivered a maximum energy and power densities of 7.88 mWh cm^-3 (4.82 Wh kg^-1) and 2.26 W cm^-3 (1382 W kg^-1), respectively. The WASC device demonstrated satisfactory cycling stability with 86% capacitance retention, and its Coulombic efficiency remained at 96% after 5000 charge-discharge cycles. The contributions of the diffusion-controlled insertion and the surface capacitive effect were theoretically quantified to investigate the energy storage mechanism. The fabrication approaches hold potential for the construction of cost-effective and high-performance WSC.

Detrimental role of residual surface acid ions on ozone decomposition over Ce-modified γ-MnO2 under humid conditions

In the study, the catalyst precursors of Ce-modified γ-MnO₂ were washed with deionized water until the pH value of the supernatant was 1, 2, 4 and 7, and the obtained catalysts were named accordingly. Under space velocity of 300,000 hr^-1, the ozone conversion over the pH = 7 catalyst under dry conditions and relative humidity of 65% over a period of 6 hr was 100% and 96%, respectively. However, the ozone decomposition activity of the pH = 2 and 4 catalysts distinctly decreased under relative humidity of 65% compared to that under dry conditions. Detailed physical and chemical characterization demonstrated that the residual sulfate ions on the pH = 2 and 4 catalysts decreased their hydrophobicity and then restrained humid ozone decomposition activity. The pH = 2 and 4 catalysts had inferior resistance to high space velocity under dry conditions, because the residual sulfate ion on their surface reduced their adsorption capacity for ozone molecules and increased their apparent activation energies, which was proved by temperature programmed desorption of O₂ and kinetic experiments. Long-term activity testing, X-ray photoelectron spectroscopy and density functional theory calculations revealed that there were two kinds of oxygen vacancies on the manganese dioxide catalysts, one of which more easily adsorbed oxygen species and then became deactivated. This study revealed the detrimental effect of surface acid ions on the activity of catalysts under humid and dry atmospheres, and provided guidance for the development of highly efficient catalysts for ozone decomposition.

Removal of tetracycline from an aqueous solution using manganese dioxide modified biochar derived from Chinese herbal medicine residues

Biochar (BC) derived from Chinese herbal medicine residues has been investigated for its performance as a potential adsorbent in tetracycline (TC) removal. In the present study, a chemical co-precipitation method was carried out to prepare manganese dioxide modified biochar (Mn-BC) to increase its sorption capacity. The properties of the modified biochar were characterized for further enhancing TC removal from an aqueous solution. Mn-BC was successfully synthesized and resulted in a much higher specific surface area, total pore volume and pore diameter. The sorption kinetics of TC on Mn-BC was described by the pseudo-second-order model. The sorption data of Mn-BC were fitted by Langmuir and Freundlich models. The study findings revealed a maximum adsorption capacity of Mn-BC (1:10) to TC was up to 131.49 mg/g. The adsorption process was endothermic and spontaneous. The degradation of TC was further enhanced by MnO₂ acting as an oxidizer on Mn-BC. Overall, the modified biochar derived from Chinese herbal medicine residues is a superior alternative for the removal of TC from an aqueous solution.

A sensitive non-enzymatic electrochemical sensor based on acicular manganese dioxide modified graphene nanosheets composite for hydrogen peroxide detection

In this work, a novel manganese dioxide-graphene nanosheets (MnO₂-GNSs) composite was synthesized by a facile one-step hydrothermal method, in which manganese dioxide (MnO₂) was fabricated by hydrothermal reduction of KMnO₄ with GNSs. The structure and morphology of MnO₂-GNSs composite were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS). A sensitive non-enzymatic electrochemical sensor based on MnO₂-GNSs composite for the detection of low concentration hydrogen peroxide (H₂O₂) was fabricated. The electrochemical properties of MnO₂-GNSs composite modified glassy carbon electrode (MnO₂-GNSs/GCE) were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometry. The observations confirmed that the fabricated sensor exhibited high electrocatalytic activity for oxidation of H₂O₂ owing to the catalytic ability of MnO₂ particles and the conductivity of GNSs. Under the optimum conditions, the calibration curve was linear for the amperometric response versus H₂O₂ concentration over the range 0.5-350 μM with a low detection limit of 0.19 μM (S/N = 3) and high sensitivity of 422.10 μA mM^-1 cm^-2. The determination and quantitative analysis of H₂O₂ in antiseptic solution on MnO₂-GNSs/GCE exhibited percent recovery of 96.50%-101.22% with relative standard deviation (RSD) of 1.48%-4.47%. The developed MnO₂-GNSs/GCE might be a promising platform for the practical detection of H₂O₂ due to its prominent properties including excellent reproducibility, good anti-interference and repeatability.