Structure Of MnO Research Articles

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.

Synthesis strategies toward improved ordering of [MnO6] octahedra in tunnel structured 2 × 3 and 2 × 4 MnO2

Improved homogeneity of tunnel size in Na-stabilized 2 × 3 and 2 × 4 MnO2 structures was achieved by identifying and controlling critical synthesis parameters. 2 × 3 and 2 × 4 MnO2 tunnel manganese oxide nanowires were obtained by hydrothermal treatment of Na-birnessite, a layered manganese oxide that undergoes a layer-to-tunnel transition under high pressure and temperature. Herein, the improved ordering of [MnO6] octahedra is revealed via a combined analysis of X-ray diffraction patterns and scanning transmission electron microscopy images. We show that crystallinity of the Na-birnessite precursor and the chemical composition of the system during hydrothermal treatment are crucial for achieving the targeted size of the structural tunnels with adequate uniformity.

Al-doped α-MnO2 coated by lignin for high-performance rechargeable aqueous zinc-ion batteries.

Zn/MnO2 batteries, one of the most widely studied rechargeable aqueous zinc-ion batteries, suffer from poor cyclability because the structure of MnO2 is labile with cycling. Herein, the structural stability of α-MnO2 is enhanced by simultaneous Al3+ doping and lignin coating during the formation of α-MnO2 crystals in a hydrothermal process. Al3+ enters the [MnO6] octahedron accompanied by producing oxygen vacancies, and lignin further stabilizes the doped Al3+via strong interaction in the prepared material, Al-doped α-MnO2 coated by lignin (L + Al@α-MnO2). Meanwhile, the conductivity of L + Al@α-MnO2 improves due to Al3+ doping, and the surface area of L + Al@α-MnO2 increases because of the production of nanorod structures after Al3+ doping and lignin coating. Compared with the reference α-MnO2 cathode, the L + Al@α-MnO2 cathode achieves superior performance with durably high reversible capacity (∼180 mA h g−1 at 1.5 A g−1) and good cycle stability. In addition, ex situ X-ray diffraction characterization of the cathode at different voltages in the first cycle is employed to study the related mechanism on improving battery performance. This study may provide ideas of designing advanced cathode materials for other aqueous metal-ion batteries.

Bluetooth Enabled Miniaturized Temperature Controller Device for Electrochemical Sensing Applications

Undeniably, Nanoparticles are of prodigious significance because of their tremendous applications in diverse fields. The structure and throughput of nanomaterials are profoundly reliant on the process utilized for their synthesis due to their unique physical and chemical properties. Synthesizing of the nanomaterials process plays a vital role in shaping the structures of nanoparticles effectively and efficiently for better yield, further these nanoparticles can be used for electrochemical sensing applications. The existing conventional technique requires very expensive and massive thermal instruments, a huge volume of reagents, a customized vessel like autoclave, stainless steel container, entails huge time with tedious and laborious approaches. In this process, the thermal management systems are considered to be an important and indispensable platform in several biological and biochemical applications. The miniaturized temperature controller device extends its usage with cost-effectiveness, rapidity, and portability. To make use of a thermal management device in micro-scale applications, it is very imperative to have an easy-to-use, effective and efficient design in the thermal management technique. This paper focuses on developing a miniaturized temperature controller system with key aspects such as cost-effective, precise, easy-to-operate, stability, automation, and compact device that can be used for electrochemical sensing applications. Such a platform is amenable to be used for biomedical or biochemical applications such as nanoparticle synthesis, DNA amplification using polymerase chain reaction (PCR) technique and rheological applications, etc. The portable device was incorporated with the arduino controller board which comes using a proportional-derivative-integral (PID) controlling approach. A PID controller is integrated with a response loop that includes an open-source library available in arduino IDE that offers a decent outcome performance constancy perceived through fine-tuning of KP=150, KI=1, and KD=70 as per the prerequisite with low tolerance. Further, a customized cartridge heater was calibrated to achieve a peak temperature of 300°C in 30 minutes, managed by a self-designed driver switching circuit and a k-type thermocouple sensor. The MAX6675 is a breakout module used with the k-type thermocouple, responsible to minimize the error, signal variation, and noise of the sensing parameters. The characterization of a cartridge heater was carried out using a feedback loop sensor. The setpoint temperature of the proposed device was around 75°C. The device showcased a temperature sensitivity of +/-2°C. Herein, an inexpensive, easy-to-operate automated and integrated device is being designed and developed for universal biological and biochemical applications. It includes a 32-bit arduino based microcontroller with 4 MB of memory and it operates in 3 – 5V range. Pro-mini usually works on 5V/16MHz and exhibits a maximum output current of 150 mA. Arduino pro mini is responsible for controlling, coordinating, and monitoring the inputs (k-type temperature sensor) and outputs (cartridge heater) respectively. The proposed device is IoT (ESP 8266-01) and Bluetooth (HC-05) enabled, with features like geotagging of data and cloud computing are the advantages of the device, wherein ThingSpeak platform allows user to analyze, access, store, and visualize live data streaming facilities. The device has been unified with additional features like real-time data accessing with a smartphone-enabled Bluetooth app storage facility. The complete device was powered up with plug-and-play by the 12V/3A adapter and dimension comes with 10.4cm*7cm*3.8cm respectively. As a proof-of-concept, the proposed thermal management device was utilized for synthesizing manganese oxide (MnO2) Nanoparticle, and the reaction sample were heated to 75°C for 8 hours, a 5 ml of beaker was used as a container for storing the reaction sample for the synthesis of nanoparticles. Further obtained MnO2 nanoflakes were subjected to characterization methods such as FESEM and EDX to examine and review the superficial morphology. A unique nanoflakes structure of MnO2 were successfully produced by the proposed temperature controller device. The obtained mean size of MnO2 nanoflakes is 22 nm. Further, the acquired MnO2 Nanoparticles can be utilized for biological and electrochemical sensing applications such as for various neurotransmitters like dopamine, histamine, and acetylcholine. Overall, the miniaturized thermal device can be used for performing diverse thermal-based reactions on a micro-scale as environment-friendly technology, with a microfluidic environment for point-of-care (POC) applications. Index Terms- Arduino pro mini, Nanoparticles (NPs), Proportional-Derivative-Integral (PID), Manganese oxide (MnO2), Field Emission Scanning Electron microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDX), Electrochemical Figure 1

(Invited) Manganese Dioxide Positive Electrodes for Aqueous Zinc-Ion Batteries

Tremendous work has been made in a relatively short period of time on developing the rechargeable aqueous zinc-ion battery (ZIB). The ZIB using inexpensive/abundant raw active materials is a cheaper and safer alternative to Li-ion batteries (LIBs), particularly where portability is not of primary importance. The ZIB is also considered by many to be the most promising rechargeable zinc battery technology because it addresses many of the short-comings of traditional zinc battery chemistries. By using a near-neutral pH electrolyte as compared to a strong alkaline solution, cycling of the zinc metal electrode is improved drastically. The coulombic efficiency of zinc plating/stripping is increased and internal short circuits due to dendritic growth of zinc metal are suppressed. The slightly acidic (pH 4-6) electrolyte also allows for new reversible (de)intercalation mechanisms to occur at the positive electrode. This has led to the development of several novel classes of electrode materials which store zinc cations.One such electrode material which is capable of intercalating Zn2+ cations is manganese dioxide. Compared to the alkaline Zn-MnO2 battery in which both the zinc negative electrode and the manganese dioxide positive electrodes undergo conversion reactions, the chemistry of the ZIB is simplified. Zn2+ is stripped from the negative electrode and intercalates into the positive electrode during discharge. Upon charge, Zn2+ cations de-intercalate from the positive electrode active material and plate back onto the negative electrode as zinc metal. In this work, various forms of manganese dioxide were explored in detail for use as the positive electrode active material for zinc intercalation. Different crystal structures of MnO2 were studied and several additional factors, such as particle size and morphology were found to impact the performance of Zn2+ intercalation. The diffusion coefficients were calculated and each material was cycled in a zinc-ion battery to determine its suitability as a Zn2+ intercalation electrode in a near-neutral aqueous system. Through this structure-properties correlation, general material design rules can be drawn, guiding future R&D efforts on ZIB chemistry. Figure 1

Efficient transformation of DDT with peroxymonosulfate activation by different crystallographic MnO2

In this study, three different structures of MnO2 were synthesized and used to activate peroxymonosulfate (PMS) for the degradation of DDT in aqueous solutions. It was found that DDT was efficiently degraded in the MnO2/PMS system and the degradation rate was dependent on the properties of MnO2 including crystal structure (followed the order: α-MnO2 > γ-MnO2 > β-MnO2), surface area and Mn(III) content. Sulfate radicals (SO4−) was primarily responsible for the degradation of DDT based on the results of electron paramagnetic resonance (EPR) and quenching experiments. The degradation of DDT was suppressed at alkaline pH because the formation of SO4− was inhibited. The results of GC–MS indicated that dichlorobenzophenone, 4-chlorobenzoic acid and benzylalcohol were the dominant intermediates for DDT degradation. The possible pathways of DDT degradation were proposed according to the identified products.

Study on Magnetic Properties and the Phase Structure of MnO2 and LiFePO4/C Composite Materials

MnO2 and LiFePO4/C composite materials were prepared by two-step sol-gel. The main peak patterns of lithium iron phosphate and manganese dioxide appeared in the analysis of the phase structure of composite materials. The SEM analysis shows that the particle quality of composite materials is obvious and the dispersion is better, and the particle size is mainly 168 nm. Magnetic hysteresis loops at room temperature show that the introduction of manganese dioxide causes the saturated magnetization strength of composite materials Ms (emu/g), residual magnetization strength Mr (emu/g) and the area of hysteresis loops (kOe emu/g) to increase with the increase of manganese dioxide. The Mossbauer spectrum of MnO2 and LiFePO4/C indicates that the main component of composite materials is high spin Fe2+ compounds.

Electrochemical Behaviors of MnO2 on Lead Alloy Anode during Pulse Electrodeposition for Efficient Manganese Electrowinning

The electrochemical performances of deposited MnO2 on lead alloy anode by pulse current (PC) and direct current (DC) electrodeposition in manganese sulfate solution were investigated by performing measurements of galvanostatic polarization, cyclic voltammetry (CV), and Tafel tests. The composition and morphology of MnO2 were observed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The anode deposited with MnO2 layers by PC electrodeposition presented a lower anodic potential of 60 mV and more uniform potential oscillating attractor with fractal dimension of 1.0337 compared with those of DC electrodeposition. In addition, MnO2 layers exhibited excellent corrosion resistance because less intermediate oxide Mn(III) appeared in anode deposits. Furthermore, the cathodic current efficiency improved by 3.11∼3.77% and energy consumption decreased by 5.30∼8.17% after galvanostatic electrolysis for 2∼8 h by using PC instead of DC for manganese metal electrodeposition. As an external control method, PC electrodeposition not only regulated the structure and surface morphology of MnO2 but also affected the anode electrochemical behaviors and cathode manganese metal deposition. Electrochemical oscillations and other characteristics of anode reaction described in this study could inspire future work on promoting the whole electrowinning process.

Tuning electronic structure of δ-MnO2 by the alkali-ion (K, Na, Li) associated manganese vacancies for high-rate supercapacitors

Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution. In this work, δ-MnO2 with alkali-ion (K, Na, Li) associated manganese (Mn) vacancies is fabricated by a simple hydrothermal reaction, and the correlation between their electronic structure and pseudocapacitance are systematically investigated. FESEM/TEM images have shown that the morphology of MnO2 is obviously changed after the introducing of cation vacancies. The position of alkali-ion in MnO2 structure can be controlled by adjusting the ion concentration. XRD patterns and Raman spectra demonstrate that the alkali-ion is embedded in Mn vacancies at low concentration, while entered the interlayer of MnO2 at high concentration. The existence of Mn vacancies will resulting in the distortion of neighboring atoms, leading to the electronic delocalization, and thus enhancing the conductivity, pseudocapacitance and rate capability of MnO2. Accordingly, the specific capacitances of optimized 0.4KMO, 0.4NaMO and 0.4LiMO samples are enhanced about 1.9, 1.6 and 1.6 times compared to pure MnO2. Meanwhile, the rate performance has also been improved about 76%, 46% and 42%, respectively. Theoretical calculations further confirm that the Mn vacancies can generate additional occupancy states and cause an increase in carrier concentration, which will improve the conductivity and further boost the pseudocapacitance of MnO2. This result open up a promising approach to explore active and durable electrode materials.

Preparation of Anisotropic MnO2 Nanocatalysts for Selective Oxidation of Benzyl Alcohol and 5-Hydroxymethylfurfural

Anisotropic MnO2 nanostructures, including α-phase nanowire, α-phase nanorod, δ-phase nanosheet, α + δ-phase nanowire, and amorphous floccule, were synthesized by a simple hydrothermal method through adjusting the pH of the precursor solution and using different counterions. The catalytic properties of the as-synthesized MnO2 nanomaterials in the selective oxidation of benzyl alcohol (BA) and 5-hydroxymethylfurfural (HMF) were evaluated. The effects of micromorphology, phase structure, and redox state on the catalytic activity of MnO2 nanomaterials were investigated. The results showed that the intrinsic catalytic oxidation activity was mainly influenced by the unique anisotropic structure and surface chemical property of MnO2. With one-dimensional and 2D structures exposing highly active surfaces, unique crystal forms, and high oxidation state of Mn, the intrinsic activities for MnO2 catalysts synthesized in pH 1, 5, and 10 solutions (denoted as MnO2-pH1, MnO2-pH5, and MnO2-pH10, respectively) were twice higher than those of other MnO2 catalysts in oxidation of BA and HMF. With a moderate aspect ratio, the α + δ nanowire of MnO2-pH10 exhibited the highest average oxidation state, most abundant active sites, and the best catalytic oxidation activity.

Core-Shell-Structured Sulfur Cathode: Ultrathin δ-MnO2 Nanosheets as the Catalytic Conversion Shell for Lithium Polysulfides in High Sulfur Content Lithium-Sulfur Batteries.

Owing to their low cost and high theoretical energy density, lithium-sulfur (Li-S) batteries are highly promising as a contender for the post-lithium-ion battery era. However, the intrinsic low reversible conversion ability of lithium polysulfides to sulfur/Li2S during charging/discharging seriously hinders the sulfur utilization, resulting in poor cycling life of batteries. Herein, we report an improvement of core-shell-structured sulfur nanospheres@ultrathin δ-MnO2 nanosheet electrode materials prepared by a simple precipitation reaction method, in which the ultrathin δ-MnO2 nanosheets as a catalytic layer can promote the chemical adsorption of lithium polysulfides and their conversion rates to sulfur/Li2S. Using a combination of the UV-visible adsorption spectra and first-principles calculation, the results indicate that the Mn-O coordination center on the surface of the MnO2 structure plays an efficient catalytic role in the conversion reaction of lithium polysulfides to insoluble S/Li2S. The sulfur nanospheres@ultrathin δ-MnO2 nanosheet composite with a high S mass ratio of 82 wt % reveals a high specific capacity of 846 mA h g-1 at 1 C rate and good cycling stability. Moreover, the areal capacity of the electrode with a high sulfur loading mass of 10 mg cm-2 is 5.2 mA h cm-2, approaching the practical application standard at a current density of 1 mA cm-2.

Adsorption/desorption of acid violet-7 onto magnetic MnO2 prior to its quantification by UV–visible spectroscopy: optimized by fractional factorial design

A highly efficient magnetic adsorbent is presented to preconcentrate acid violet-7 (AV-7) prior quantifying by UV–visible spectroscopy (λmax = 520 nm). The adsorbent consisting of MnO2 and Fe3O4 was synthesized via precipitation method. The green preparation method was simple and fast; it was performed at room temperature, without consuming organic solvents and thermal treatment. The synthesis strategy is based on using cetrimonium bromide as a surfactant. The surfactant was adsorbed onto negative sites of Fe3O4 then trapped Mn2+ ions and finally by adding NH3, nanoparticles of MnO2 were formed. The nanocomposite was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, alternating gradient force magnetometer and Brunauer–Emmett–Teller. The strong magnetic property of Fe3O4 and porous structure of MnO2 with positive charges enable efficient adsorption of AV-7 via magnetic solid phase extraction. The optimum conditions with respect to circumscribed fractional factorial design were pH (4.0 ± 0.2), sorbent amount (20 mg), adsorption time (20 min), adsorption temperature (308 K), eluent kind [ethanol/NaNO3 (1 mL/50 mg)], desorption time (10 min) and desorption temperature (283 K). The adsorption mechanism of AV-7 onto adsorbent was explained based on FT-IR spectra. The swelling behavior of adsorbent was investigated. Limit of detection (0.86 ng mL−1), relative standard deviation (n = 5) (1.61%), preconcentration factor (50) and linearity of dynamic range (20–400 μg L−1) perform the applicability of adsorbent in AV-7 preconcentration. The adsorbent is reusable for 15 times and durable for 100 days. The swelling behavior was investigated. The effects of interference ions and three dyes on the preconcentration recovery were studied. Temkin model and pseudo-second order were fitted with isotherm adsorption and kinetic adsorption, respectively. According to thermodynamic parameters, the adsorption is endothermic and spontaneous. The adsorbent was successfully applied to quantify AV-7 from a leather sample.

Effective improvement of electrochemical performance of electrodeposited MnO2 and MnO2/reduced graphene oxide supercapacitor materials by alcohol pretreatment

Abstract In this work, basing on the traditional electrodeposition method, we improve the structure and electrochemical performance of MnO2 and MnO2/reduced graphene oxide (MnO2/RGO) electrode materials by alcohol infiltrated substrate process that introduces ethanol oxidation reaction on nickel foam substrate surface. After alcohol treatment, the deposited MnO2 on substrate obtains more uniform thickness and looser distribution, RGO obtains larger deposition area with compact distribution. In addition, the capacity, rate, specific energy, specific power and cycle performance have been greatly improved. MnO2 electrode shows the specific capacitance increasing from 153 and 103 F g − 1 to 270 and 190 F g − 1 at the current densities of 1 and 5 A g − 1, respectively. MnO2/RGO electrode shows specific capacitance increasing from 343 to 254 F g − 1 to 467 and 307 F g − 1 at 1 and 5 A g − 1, respectively. Moreover, the specific capacitance of MnO2 and MnO2/RGO electrodes keep 83.9% and 93.1% retention after 2500 cycles at the large current density of 5 A g − 1, respectively. Based on some scientific universals, we look forward to the proposed alcohol infiltrated substrate process for this work, which may be favorable for the performance enhancement of a series of MnO2-based supercapacitor materials, not only for MnO2 and MnO2/RGO.

Studies of MnO2/g-C3N4 hetrostructure efficient of visible light photocatalyst for pollutants degradation by sol-gel technique

MnO2 and g-C3N4 heterostructure were constructed by simple sol-gel technique combined with annealing process were characterized different variety of techniques to understand the structural, morphological, optical and elemental composition were using XRD, TEM, Raman, UV, PL, BET and EDAX analysis. In fact, XRD and FESEM results shows that α-phase MnO2 structure were individually spherical shaped - like morphology nanostructures the average diameter 25 nm to 40 nm was observed apparently. In order to understand, the optical bandgap properties and specific surface area of MnO2/g-C3N4 nanocomposites were ranging from 2.55 eV - 2.78 eV & 67.23 - 105.21 m2/g, which is confirmed through UV–vis DRS and N2 nitrogen absorption desorption study. Therefore, the photocatalytic activity of the photocatalysts were estimated by degradation effect of methyl orange (MO) and toxic phenol pollutants. Among the results reveal that the MnO2/g-C3N4 hybrid catalyst have showed to owing the degradation effect 98% and high stability (only loss 3.5%) towards phenol dye concentration. This can be attributed to the separation of photogenerated electron-hole (e−/h+) pairs, overwhelms the recombination of free charges were reported in detail.

Influence of Ag Doping on the Electrochemical Supercapacitor Characteristics of Manganese Dioxide Prepared by Pulsed Potentiostatic Electrodeposition

Manganese dioxide (MnO2) is a promising electrode material for electrochemical supercapacitor applications due to its low cost, eco-friendly and high theoretical specific capacitance in a wide potential window. In this study, MnO2 and Ag-doped MnO2 are prepared by cathodic electrodeposition on graphite substrate from electrolyte with the main compound of potassium permanganate using pulse potentiostatic technique. The effect of Ag doping on the morphology, structure and electrochemical properties of MnO2 materials are investigated. Scanning electron microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), cyclic voltammetry (CV), galvanostatic charge-discharge measurement and electrochemical impedance spectroscopy (EIS) are used for characterization of the prepared materials. The results show that doping Ag into the MnO2 structure has improved electrochemical characteristics of materials. The specific capacitances are calculated for pure MnO2 and Ag-doped MnO2 to be 272.84 and 277.48 F/g, respectively. The prepared materials exhibit the high charge-discharge stability, maintaining at about 92 % for MnO2 and 95 % for Ag-doped MnO2 after 500 cycles of the charge-discharge operation.

Kinetics and mechanism of distribution of lanthanum ions in MnO2 structure in the presence of fluoride ions

Kinetics and mechanism of distribution of lanthanum ions in MnO2 structure in the presence of fluoride ions

Zn2+ Pre‐Intercalation Stabilizes the Tunnel Structure of MnO2 Nanowires and Enables Zinc‐Ion Hybrid Supercapacitor of Battery‐Level Energy Density

Although there has been tremendous progress in exploring new configurations of zinc-ion hybrid supercapacitors (Zn-HSCs) recently, the much lower energy density, especially the much lower areal energy density compared with that of the rechargeable battery, is still the bottleneck, which is impeding their wide applications in wearable devices. Herein, the pre-intercalation of Zn2+ which gives rise to a highly stable tunnel structure of Znx MnO2 in nanowire form that are grown on flexible carbon cloth with a disruptively large mass loading of 12 mg cm-2 is reported. More interestingly, the Znx MnO2 nanowires of tunnel structure enable an ultrahigh areal energy density and power density, when they are employed as the cathode in Zn-HSCs. The achieved areal capacitance of up to 1745.8 mF cm-2 at 2 mA cm-2 , and the remarkable areal energy density of 969.9 µWh cm-2 are comparable favorably with those of Zn-ion batteries. When integrated into a quasi-solid-state device, they also endow outstanding mechanical flexibility. The truly battery-level Zn-HSCs are timely in filling up of the battery-supercapacitor gap, and promise applications in the new generation flexible and wearable devices.

Noninterference Revealing of "Layered to Layered" Zinc Storage Mechanism of δ-MnO2 toward Neutral Zn-Mn Batteries with Superior Performance.

MnO2 is one of the most studied cathodes for aqueous neutral zinc‐ion batteries. However, the diverse reported crystal structures of MnO2 compared to δ‐MnO2 inevitably suffer a structural phase transition from tunneled to layered Zn‐buserite during the initial cycles, which is not as kinetically direct as the conventional intercalation electrochemistry in layered materials and thus poses great challenges to the performance and multifunctionality of devices. Here, a binder‐free δ‐MnO2 cathode is designed and a favorable “layered to layered” Zn2+ storage mechanism is revealed systematically using such a “noninterferencing” electrode platform in combination with ab initio calculation. A flexible quasi‐solid‐state Zn–Mn battery with an electrodeposited flexible Zn anode is further assembled, exhibiting high energy density (35.11 mWh cm−3; 432.05 Wh kg−1), high power density (676.92 mW cm−3; 8.33 kW kg−1), extremely low self‐discharge rate, and ultralong stability up to 10 000 cycles. Even with a relatively high δ‐MnO2 mass loading of 5 mg cm−2, significant energy and power densities are still achieved. The device also works well over a broad temperature range (0–40 °C) and can efficiently power different types of small electronics. This work provides an opportunity to develop high‐performance multivalent‐ion batteries via the design of a kinetically favorable host structure.

Recovery of strontium (Sr2+) from seawater using a hierarchically structured MnO2/C/Fe3O4 magnetic nanocomposite

The recovery of strontium ions (Sr2+) from seawater has attracted much attention as an approach to securing Sr resources to meet increasing industrial demand. In this study, we synthesized a magnetic MnO2 nanocomposite (MnO2/C/Fe3O4) using a simple redox reaction under ambient conditions and applied this nanocomposite to the extraction of Sr2+ from natural seawater. The synthesized nanocomposite exhibited a hierarchical structure of MnO2, carbon, and Fe3O4 with a saturation magnetization of 25 emu/g that enabled effective separation under an external magnetic force. Regardless of the initial Sr2+ concentration, the adsorption of Sr2+ onto MnO2/C/Fe3O4 proceeded rapidly (within <10 min) following a pseudo-second-order kinetic model and agreed well with the Langmuir isotherm model, indicating a maximum adsorption capacity of 42 mg/g. Among the competitive ions, Mg2+ and Ca2+ significantly hindered Sr2+ adsorption onto MnO2/C/Fe3O4, whereas Na+ and K+ had little effect on Sr2+ adsorption. A detailed study of the distribution coefficient (Kd) revealed 11.2-fold and 1.8-fold higher selectivities toward Sr2+ than toward Mg2+ and Ca2+, respectively. The Sr2+ ions adsorbed onto MnO2/C/Fe3O4 were completely recovered through desorption in 0.1 M HCl eluent. Finally, a Sr2+-enriched solution with a concentration of 501 mg/L could be obtained via seawater adsorption and subsequent acid desorption over 8 iterative cycles, demonstrating its effectiveness for practical applications of Sr2+ recovery from seawater.

Influence of calcination temperature on physical and electrochemical properties of MnO2 nanoparticles synthesized by co-precipitation method

Manganese dioxide nanoparticles were successfully synthesized by co-precipitation method using manganese acetate and potassium permanganate as the starting materials and calcined at 200–500 °C for 4 h in ambient air. Structural, morphological and electrochemical properties of all samples were investigated by X-ray diffraction technique (XRD), scanning electron microscope (SEM) and cyclic voltammetry technique (CV), respectively. The symmetric electrochemical cells were fabricated on 304-stainless steel as the electrode by doctor blade technique using polyvinylpyrrolidone (PVP)-KI as the gel electrolyte. The XRD results reveal that tetragonal structure of MnO2 could be synthesized by co-precipitation process with calcinations temperature at 400 °C for 4 hr. SEM images indicate that the size of MnO2 quasi-spherical powders are in nanoscale and transform into short rod under calcination temperature at 500 °C. The electrochemical properties results indicate that the electrochemical cell of MnO2 calcined at 300 °C with PVP-KI as the gel electrolyte shows a highest specific capacitance about 90.87 F/g at a scan rate of 100 mV/s.