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The textile industry consumes a large volume of organic dyes and water. These organic dyes, which remained in the effluents, are usually persistent and difficult to degrade by conventional wastewater treatment techniques. If the wastewater is not treated properly and is discharged into water system, it will cause environmental pollution and risk to living organisms. To mitigate these impacts, the photo-driven catalysis process using semiconductor materials emerges as a promising approach. The semiconductor photocatalysts are able to remove the organic effluent through their mineralization and decolorization abilities. Besides the commonly used titanium dioxide (TiO 2 ), manganese dioxide (MnO 2 ) is a potential photocatalyst for wastewater treatment. MnO 2 has a narrow bandgap energy of 1~2 eV. Thus, it possesses high possibility to be driven by visible light and infrared light for dye degradation. This paper reviews the MnO 2 -based photocatalysts in various aspects, including its fundamental and photocatalytic mechanisms, recent progress in the synthesis of MnO 2 nanostructures in particle forms and on supporting systems, and regeneration of photocatalysts for repeated use. In addition, the effect of various factors that could affect the photocatalytic performance of MnO 2 nanostructures are discussed, followed by the future prospects of the development of this semiconductor photocatalysts towards commercialization.

In recent days, manganese oxide nanoparticles (MnO 2 NPs) have intrigued material science researches extensively due to its wide range of applications. They are widely used in energy storage devices (lithium-ion batteries, capacitors), catalysts, adsorbent, sensors and imaging, therapeutic activity, etc. Since they hold a lot of distinguished potentials, a robust protocol for cheap, stable, biocompatible and eco-friendly MnO 2 NPs is necessary. They can be categorized into different phases like α, β, δ and others. Thus, owing to their peculiar character, they could be utilized for various purposes depending on the mode of action and applications. Hence, this review has summarized conventional methods, such as hydrothermal, sol–gel, oxidation–reduction used for the generation of MnO 2 NPs. Likewise, morphological characterization by various spectroscopic techniques also outlined. It is found that the particular method of generation of MnO 2 NPs is useful for a specific phase. Graphic Abstract Graphical representation of manganese dioxide nanoparticles: synthesis and application

As a new type of secondary ion battery, aqueous zinc‐ion battery has a broad application prospect in the field of large‐scale energy storage due to its characteristics of low cost, high safety, environmental friendliness, and high‐power density. In recent years, manganese dioxide (MnO2)‐based materials have been extensively explored as cathodes for Zn‐ion batteries. Based on the research experiences of our group in the field of aqueous zinc ion batteries and combining with the latest literature of system, we systematically summarize the research progress of Zn−MnO2 batteries. This article first reviews the current research progress and reaction mechanism of Zn−MnO2 batteries, and then respectively expounds the optimization of MnO2 cathode, Zn anodes, and diverse electrolytes and their effects on battery performance. Additionally, primary challenges related to different components and their respective strategies for mitigating them are discussed, with the ultimate objective of offering comprehensive guidance for the design and fabrication of high‐performance Zn−MnO2 batteries. Finally, the future research and development direction of aqueous Zn−MnO2 batteries with high energy density, high safety and long life is envisioned. In recent years, Zn−MnO2 batteries have attracted more and more attention. This review not only summarizes the battery mechanism under different pH, but also discusses the main challenges encountered and latest developments in anode and cathode materials and various electrolyte materials (liquid, solid and gel), which are crucial for enabling the design of high‐performance batteries. In the end, prospects of the sustainable development of Zn−MnO2 batteries are summarized.

The consumption of electrical energy grows alongside the development of global industry. Generating energy storage has become the primary focus of current research, examining supercapacitors with high power density. The primary raw material used in supercapacitor electrodes is activated carbon (AC). To improve the performance of activated carbon, we used manganese dioxide (MnO2), which has a theoretical capacitance of up to 1370 Fg−1. The composite-based activated carbon with a different mass of 0–20% MnO2 was successfully introduced as the positive electrode. The asymmetric cell supercapacitors based on activated carbon as the anode delivered an excellent gravimetric capacitance, energy density, and power density of 84.28 Fg−1, 14.88 Wh.kg−1, and 96.68 W.kg−1, respectively, at 1 M Et4NBF4, maintaining 88.88% after 1000 test cycles.

Manganese dioxide nanoparticles/activated carbon (MnO 2 /AC) composites and manganese dioxide nanoparticles (MnO 2 NPs) are prepared through chemical reduction method. Morphological study shows that MnO 2 NPs had cylindrical and spherical shape. The morphological study also revealed that MnO 2 NPs were well dispersed on AC while neat Mn NPs present both in dispersed and in agglomerated form. The FT-IR study confirms the synthesis of MnO 2 NPs. Zetasizer study presented that the Mn NPs had uniform size and below 100 nm in size and had zeta potential of − 20 mV, which represent its stability in the suspension form. The synthesized Mn/AC composite and Mn NPs were utilized as photocatalysts for the photodegradation of Congo red (CR) dye. The degradation study shows that MnO 2 /AC composite degraded CR dye more efficiently than MnO 2 NPs under UV and normal light irradiation. The efficient degradation of dye by Mn/AC composite is due to the synergistic effect between dye adsorption on AC and rapid photodegradation by supported MnO 2 NPs. The results revealed that Mn/AC composite degraded about 98.53% of CR dye within 5 min while MnO 2 NPs degraded 66.57% of dye within the same irradiation time. The recycled catalyst also significantly degraded dye which verifies its sustainability. The effect of catalyst dosage and initial dye concentration was conducted. The degradation rate of dye was found drastically faster in tap water (in presence of catalyst), which might be due to the presence of various mineral ions in the tap water.

HighlightsA novel hydrogel with high water retention and Zn2+ transference number of 0.604 was constructed by copolymerizing sulfobetaine and acrylamide in Zn(ClO4)2 solution.The designed electrolyte configuration enables in situ generation of the organic–inorganic hybrid interface, which contributes to the electrodeposition uniformity and corrosion resistance of the anode.Zn–Zn and Zn–MnO2 cells based on hydrogel electrolyte exhibit outstanding cycling stability (over 3000 h under 0.5 mA cm−2/0.5 mAh cm−2 after two-time shelving).Aqueous zinc metal batteries are noted for their cost-effectiveness, safety and environmental friendliness. However, the water-induced notorious issues such as continuous electrolyte decomposition and uneven Zn electrochemical deposition remarkably restrict the development of the long-life zinc metal batteries. In this study, zwitterionic sulfobetaine is introduced to copolymerize with acrylamide in zinc perchlorate (Zn(ClO4)2) solution. The designed gel framework with hydrophilic and charged groups can firmly anchor water molecules and construct ion migration channels to accelerate ion transport. The in situ generated hybrid interface, which is composed of the organic functionalized outer layer and inorganic Cl− containing inner layer, can synergically lower the mass transfer overpotential, reduce water-related side reactions and lead to uniform Zn deposition. Such a novel electrolyte configuration enables Zn//Zn cells with an ultra-long cycling life of over 3000 h and a low polarization potential (~ 0.03 V) and Zn//Cu cells with high Coulombic efficiency of 99.18% for 1000 cycles. Full cells matched with MnO2 cathodes delivered laudable cycling stability and impressive shelving ability. Besides, the flexible quasi-solid-state batteries which are equipped with the anti-vandalism ability (such as cutting, hammering and soaking) can successfully power the LED simultaneously. Such a safe, processable and durable hydrogel promises significant application potential for long-life flexible electronic devices.

Hydrogen energy is the cleanest energy at present because its combustion product and no carbon emission. Electrolysis of water to produce hydrogen is generally considered to be the most promising method to produce hydrogen in large quantities. But electrolysis of water to produce hydrogen is without the use of a catalyst. Manganese dioxide is an efficient and green catalyst. MnO 2 dioxide-polyaniline electrode was prepared by CV method and CV/CA method respectively. The properties of dioxide-polyaniline were studied with the linear sweep cyclic voltammetry test, electrochemical impedance test and tafel slope test, and the results were compared with those of MnO 2 electrode. It was found the MnO 2 dioxide-polyaniline electrode properties were outstanding. It was further showed that performance of manganese dioxide-polyaniline electrode was superior by preparation of CV/CA with the testes of XPS and SEM and stability test.

Manganese dioxide (MnO2) has drawn attention as a sensitiser to be incorporated in graphene-based chemoresistive sensors thanks to its promising properties. In this regard, a rGO@MnO2 sensing material was prepared and deposited on two different substrates (silicon and Kapton). The effect of the substrate nature on the morphology and sensing behaviour of the rGO@MnO2 material was thoroughly analysed and reported. These sensors were exposed to different dilutions of NO2 ranging from 200 ppb to 1000 ppb under dry and humid conditions (25% RH and 70% RH) at room temperature. rGO@MnO2 deposited on Kapton showed the highest response of 6.6% towards 1 ppm of NO2 under dry conditions at RT. Other gases or vapours such as NH3, CO, ethanol, H2 and benzene were also tested. FESEM, HRTEM, Raman, XRD and ATR-IR were used to characterise the prepared sensors. The experimental results showed that the incorporation of nanosized MnO2 in the rGO material enhanced its response towards NO2. Moreover, this material also showed very good responses toward NH3 both under dry and humid conditions, with the rGO@MnO2 sensor on silicon showing the highest response of 18.5% towards 50 ppm of NH3 under 50% RH at RT. Finally, the synthetised layers showed no cross-responsiveness towards other toxic gases.

In this work, nano-manganese dioxide (nMnO2)-modified biochar (BC) was synthesized in order to improve BC’s adsorption capacity for di-n-butyl phthalate (DBP) and oxytetracycline (OTC). The results showed that nMnO2 on the BC surface exhibited a poor crystallinity and oxidation state (Mn (IV)). Sorption experiments showed that, compared to BC, DBP sorption capacity of nMnO2-BC (1:20) and OTC sorption capacity of nMnO2-BC (1:10) were 0.0364 and 0.0867 mmol/g, respectively, which are significantly higher than that of BC (0.0141 and 0.0151 mmol/g). Kinetics and isotherm experiments indicated that physical adsorption and chemical interactions have both exerted their impacts on the adsorption process. Further X-ray photoelectron spectroscopy (XPS) analysis showed that part of the Mn (IV) in nMnO2-BC was reduced to Mn (III) and Mn (II) after DBP or OTC adsorption. Therefore, we suggest the nMnO2 also acted as an oxidizer on modified BC, which may accelerate the degradation of DBP and OTC.

A kind of single-layer carbon based dots (CDs) with abundant carboxyl functional groups was hybridized with manganese dioxide (MnO 2 ). The resulting nanohybrid is stable and can be well dispersed in water. MnO 2 is capable of oxidizing the substrate 3,3′5,5′-tetramethylbenzidine (TMB) to form a blue product whose absorption (peaking at 655 nm) fades in the presence of glutathione (GSH). A sensitive and selective colorimetric GSH assay was worked out that has a linear response in the 10 to 0.1 µM GSH concentration range, with a 0.095 μM detection limit. The method was applied to the determination of GSH in spiked fetal calf serum where it gave excellent recoveries. Graphical abstract Schematic of the preparation of a nanohybrid composed of manganese dioxide and carbon based dots (MnO 2 /CDs). They can be used for the colorimetric detection of glutathione (GSH) based on the color change of 3,3′5,5′-tetramethylbenzidine (TMB).