In the present work, we address the new route for the green synthesis of manganese dioxide (MnO2) by an innovative method named the solution plasma process (SPP). The reaction mechanism of both colloidal and nanostructured MnO2 was investigated. Firstly, colloidal MnO2 was synthesized by plasma discharging in KMnO4 aqueous solution without any additives such as reducing agents, acids, or base chemicals. As a function of the discharge time, the purple color solution of MnO4 - (oxidation state +7) was changed to the brown color of MnO2 (oxidation state +4) and then light yellow of Mn2+ (oxidation state +2). Based on the UV-vis analysis we found the optimal discharging time for the synthesis of stable colloidal MnO2 and also reaction mechanism was verified by optical emission spectroscopy (OES) analysis. Secondly, MnO2 nanoparticles were synthesized by SPP with a small amount of reducing sugar. The precipitation of brown color was observed after 8 min of plasma discharge and then completely separated into colorless solution and precipitation. It was confirmed layered type of nanoporous birnessite- MnO2 by X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), and electron microscopes. The most important merits of this approach are environmentally friendly process within a short time compared to the conventional method. Moreover, the morphology and the microstructure could be controllable by discharge conditions for the appropriate potential applications, such as secondary batteries, supercapacitors, adsorbents, and catalysts.

Graphene-derived materials are an excellent electrode for electrochemical detection of heavy metals. In this study, a MnO2/ graphene supported on Ni foam electrode was prepared via ultrasonic impregnation and electrochemical deposition. The resulting electrode was used to detect Pb(II) in the aquatic environment. The graphene and MnO2 deposited on the Ni foam not only improved active surface area, but also promoted the electron transfer. The electrochemical performance towards Pb(II) was evaluated by cyclic voltammetry (CV) and square wave anodic stripping voltammetry (SWASV). The prepared electrode exhibited lower limit of detection (LOD, 0.2 μM (S/N = 3)) and good sensitivity (59.9 μAμM−1) for Pb(II) detection. Moreover, the prepared electrodes showed good stability and reproducibility. This excellent performance can be attributed to the strong adhesion force between graphene and MnO2, which provides compact structures for the enhancement of the mechanical stability. Thus, these combined results provide some technical considerations and scientific insights for the detection of heavy metal ions using composite electrodes.

Here, we have demonstrated the successful exfoliation of graphite into a layered material with scotch tape-like exfoliation. Sulfur acts as an exfoliating agent and exfoliates the loosely bounded graphite stacks. The shear force by ball milling provides the force required to overcome the van der Waals force between the layers. The MnO2 nanorods were synthesized using a KMnO4 precursor in a hydrothermal arrangement, and due to their intrinsic chemisorption capability, they were doped for polysulfide trapping. With an initial capacity of 1150 mAh/g achieved by the MnO2 nanorod-doped exfoliate-graphite/sulfur composite material, the material has displayed its application in lithium–sulfur batteries, but its use is not limited; it can be a low-cost eco-friendly solution to various energy storage systems with extensive structural qualities.

In this report, we successfully prepared nitrogen-doped porous carbon (N-PC)/manganese dioxide ( MnO2) composite for a high-performance supercapacitor. X-ray diffraction data revealed the α-MnO2 phase. Transmission electron microscopy confirmed that the nanostructured α-MnO2 nanoparticles were coated on the surface of N-PC. The N-PC/α-MnO2 composite delivered a capacitance of 525.7 F g− 1 at the charging current of 1.0 A g− 1. The higher capacitance of the composite could be owing to the synergy of MnO2 and N-PC. Besides, the electrode exhibited a 14.7% capacitance loss after 6000 charge– discharge cycles at 10 A g− 1 indicating good electrochemical stability.

MnO2 can be potentially utilized as an electrode material for redox capacitors. The deposition of MnO2 with poor electrical conductivity onto porous carbons supplies them with additional conductive paths; as a result, the capacitance of the electrical double layer formed on the porous carbon surface can be utilized together with the redox capacitance of MnO2. However, the obtained composites are not generally suitable for industrial production because they require the use of expensive porous carbons and/or inefficient fabrication methods. Thus, to develop an effective preparation procedure of the composite, a suitable structure of porous carbons must be determined. In this study, MnO2/C composites have been prepared from activated carbon gels with various pore sizes, and their electrical properties are investigated via cyclic voltammetry. In particular, mesoporous carbons with a pore size of around 20 nm form a composite with a relatively low capacitance (98 F/g-composite) and poor rate performance despite the moderate redox capacitance obtained for MnO2 (313 F/g-MnO2). On the other hand, using macro-porous carbons with a pore size of around 60 nm increases the MnO2 redox capacitance (399 F/g-MnO2) as well as the capacitance and rate performance of the entire material (203 F/g-composite). The obtained results can be used in the industrial manufacturing of MnO2/C composites for supercapacitor electrodes from the commercially available porous carbons.

Nanoporous carbon/MnO2 (C–MnO2) composites with foam-like structure based on modified nitrile butadiene rubber were achieved by thermal treatment, followed by alkaline solution etching and dipping method. The XRD, nitrogen adsorption and desorption, and SEM and TEM were used to characterize the microstructure of the obtained C–SiO2, C and C–MnO2. Finally, all the obtained samples have been used in three-electrode system to study the electrochemical properties including cyclic voltammetry, galvanostatic charge/discharge and AC impedance for supercapacitor. The study found that the specific capacity of C–MnO2 electrode material for supercapacitor could reach as high as 109 F/g under the current density of 0.5 A/g, which is much higher than those of the other two. These superior electrochemical properties are attributed to the synergistic effect MnO2 particles with the C matrix which functions as a conductive support.

This study describes the doping effect of Yb2O3 on microstructure, electrical and dielectric properties of ZnO-V2O5- MnO2-Nb2O5 (ZVMN) ceramic semiconductors sintered at a temperature as low as 900°C. As the doping content of Yb2O3 increases, the ceramic density slightly increases from 5.50 to 5.54 g/cm3; also, the average ZnO grain size is in the range of 5.3-5.6 μm. The switching voltage increases from 4,874 to 5,494 V/cm when the doping content of Yb2O3 is less than 0.1 mol%, whereas further doping decreases this value. The ZVMN ceramic semiconductors doped with 0.1 mol% Yb2O3 reveal an excellent nonohmic coefficient as high as 70. The donor density of ZnO gain increases in the range of 2.46-7.41×1017 cm−3 with increasing doping content of Yb2O3 and the potential barrier height and surface state density at the grain boundaries exhibits a maximum value (1.25 eV) at 0.1 mol%. The dielectric constant (at 1 kHz) decreases from 592.7 to 501.4 until the doping content of Yb2O3 reaches 0.1 mol%, whereas further doping increases it. The value of tanδ increases from 0.209 to 0.268 with the doping content of Yb2O3.

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of 0.96(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3-0.04BaZrO3, which has a rhombohedral-tetragonal phase boundary composition. MnO2 and CuO-added 0.96(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3-0.04BaZrO3 ceramics sintered at a relatively low temperature of 1020 oC show a pure perovskite phase with no secondary phase. As the addition of MnO2 and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of MnO2.

The composites of carbon nanotube (CNT) supported by Sn-doped MnO2 with enhanced capacitance have been fabricated with varying dopant concentrations. The composites have been subjected to physiochemical, configurational, and morphological analyses by FTIR, UV–Vis spectroscopy, X-ray diffraction and field emission scanning electron microscopy, high resolution transmission electron microscopy and selected area electron diffraction studies. The electrochemical performance of the composite has been evaluated by cyclic voltammetry and charge/discharge techniques. Highest specific capacitances of 940 F g−1 at a current density of 0.35 A g−1 and 927 F g−1 at 5 mV s−1 in 1 M Na2SO4 electrolyte solution was achieved in the case of 5% Sn doped composite. Moreover, the electrode demonstrated good cycling performance and retaining 79.7% of the initial capacitance over 3000 cycles. The superior electrochemical performance is accredited mainly to the porous sheath hierarchical architecture, which consist of inter connected MnO2 nanoneedles uniformly coated over the CNT surface. This peculiar architecture is responsible for fast ion/electron transfer and easy access of the active material.

Plastic pollution is threatening human health and ecosystems, resulting in one of the biggest challenges that humanity has ever faced. Therefore, this study focuses on the preparation of macroporous carbon from biowaste (MC)-supported manganese oxide (MnO2) as an efficient, reusable, and robust catalyst for the recycling of poly(ethylene terephthalate) (PET) waste. As-prepared MnO2/MC composites have a hierarchical pore network and a large surface area (376.16 m2/g) with a narrow size distribution. MnO2/MC shows a maximum yield (98%) of bis(2-hydroxyethyl)terephthalate (BHET) after glycolysis reaction for 120 min. Furthermore, MnO2/MC can be reused at least nine times with a negligible decrease in BHET yield. Based on this remarkable catalytic performance, we expect that MnO2-based heterogeneous catalysts have the potential to be introduced into the PET recycling industry.

Manganese dioxide (MnO2) is one of the most important cathode materials used in both aqueous and non-aqueous batteries. The MnO2 polymorph that is used for lithium primary batteries is synthesized either by electrolytic (EMD-MnO2) or chemical methods (CMD-MnO2). Commonly, electrolytic manganese dioxide (EMD) is used as a cathode mixture material for dry-cell batteries, such as a alkaline batteries, zinc-carbon batteries, rechargeable alkaline batteries, etc. The characteristics of lithium/manganese-dioxide primary cells fabricated with EMD-MnO2 powders as cathode were compared as a function of the parameters of a manufacturing process. The flexible primary cells were prepared with EMD-MnO2, active carbon, and poly vinylidene fluoride (PVDF) binder (10 wt.%) coated on an Al foil substrate. A cathode sheet with micro-porous showed a higher discharge capacity than a cathode sheet compacted by a press process. As the amount of EMD-MnO2 increased, the electrical conductivity decreased and the electrical capacity increased. The cell subjected to heat-treatment at 200˚C for 1 hr showed a high discharge capacity. The flexible primary cell made using the optimum conditions showed a capacity and an average voltage of 220 mAh/g and 2.8 V, respectively, at 437.5μA.

Significant improvements in the switching voltage distribution are required for the development of unipolar resistivememory devices using MnOx thin films. The Vset of the as-grown MnOx film ranged from 1 to 6.2 V, whereas the Vset of theoxygen-annealed film ranged from 2.3 to 3 V. An excess of oxygen in an MnOx film leads to an increase in Mn4+ contentat the MnOx film surface with a subsequent change in the Mn4+/Mn3+ ratio at the surface. This was attributed to the changein Mn4+/Mn3+ ratios at the MnOx surface and to grain growth. Oxygen annealing is a possible solution for improving theswitching voltage distribution of MnOx thin films. In addition, crystalline MnOx can help stabilize the Vset and Vreset distributionin memory switching in a Ti/MnOx/Pt structure. The improved uniformity was attributed not only to the change of thecrystallinity but also to the redox reaction at the interface between Ti and MnOx.

La0.6Sr0.4MnO3 (LSMO) thin films, which are known as colossal magnetoresistance materials, were prepared on fused silica thin films by conventional RF magnetron sputtering, and the interfacial reactions between them were investigated by rapid thermal processing. Various analyses, namely, X-ray diffraction, transmission electron microscopy combined with energy adispersive X-ray spectrometry, and secondary ion mass spectrometry, were performed to explain the mechanism of the interfacial reactions. In the case of an LSMO film annealed at 800˚C, the layer distinction against the underplayed SiO2 was well preserved. However, when the annealing temperature was raised to 900˚C, interdiffusion and interreaction occurred. Most of the SiO2 and part of the LSMO became amorphous silicate that incorporated La, Sr, and Mn and contained a lot of bubbles. When the annealing temperature was raised to 950˚C, the whole stack became an amorphous silicate layer with expanded bubbles. The thermal instability of LSMO on fused silica should be an important consideration when LSMO is integrated into Si-based solid-state devices.

Perovskite manganites such as RE1-xAxMnO3 (RE = rare earth, A = Ca, Sr, Ba) have been the subject of intense research in the last few years, ever since the discovery that these systems demonstrate colossal magnetoresistance (CMR). The CMR is usually explained with the double-exchange (DE) mechanism, and CMR materials have potential applications for magnetic switching, recording devices, and more. However, the intrinsic CMR effect is usually found under the conditions of a magnetic field of several Teslas and a narrow temperature range near the Curie temperature (Tc). This magnetic field and temperature range make practical applications impossible. Recently, another type of MR, called the low-field magnetoresistance(LFMR), has also been a research focus. This MR is typically found in polycrystalline half-metallic ferromagnets, and is associated with the spin-dependent charge transport across grain boundaries. Composites with compositions La0.7(Ca1-xSrx)0.3MnO3)]0.99/(BaTiO3)0.01 [(LCSMO)0.99/(BTO)0.01]were prepared with different Sr doping levels x by a standard ceramic technique, and their electrical transport and magnetoresistance (MR) properties were investigated. The structure and morphology of the composites were studied by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). BTO peaks could not be found in the XRD pattern because the amount of BTO in the composites was too small. As the content of x decreased, the crystal structure changed from orthorhombic to rhombohedral. This change can be explained by the fact that the crystal structure of pure LCMO is orthorhombic and the crystal structure of pure LSMO is rhombohedral. The SEM results indicate that LCSMO and BTO coexist in the composites and BTO mostly segregates at the grain boundaries of LCSMO, which are in accordance with the results of the magnetic measurements. The resistivity of all the composites was measured in the range of 90-400K at 0T, 0.5T magnetic field. The result indicates that the MR of the composites increases systematically as the Ca concentration increases, although the transition temperature Tc shifts to a lower range.

The effects of doping on the crystal structure, ferroelectric, and piezoelectric properties of (K,Na) (KNN) ceramics have been investigated. was found to be effective in enhancing the densification and grain growth during sintering. X-ray diffraction analysis indicated that Mn ions substituted B-site Nb ions up to 2 mol%, however, further doping induced unwanted secondary phases. In comparison with undoped KNN ceramics, the well developed microstructure and the substitution to B-sites in 2 mol% Mn-doped KNN ceramics resulted in significant improvements in both piezoelectric coupling coefficient and electromechanical quality factor.

The (1-x)La0.7Sr0.3MnO3(LSMO)/xZnFe2O4(ZFO) (x = 0, 0.01, 0.03, 0.06 and 0.09) composites were prepared by a conventional solid-state reaction method. We investigated the structural properties, magnetic properties and electrical transport properties of (1-x)LSMO/xZFO composites using X-ray diffraction (XRD), scanning electron microscopy (SEM), field-cooled dc magnetization and magnetoresistance (MR) measurements. The XRD and SEM results indicate that LSMO and ZFO coexist in the composites and the ZFO mostly segregates at the grain boundaries of LSMO, which agreed well with the results of the magnetic measurements. The resistivity of the samples increased by the increase of the ZFO doping level. A clear metal-to-insulator (M-I) transition was observed at 360K in pure LSMO. The introduction of ZFO further downshifted the transition temperature (350K-160K) while the transition disappeared in the sample (x = 0.09) and it presented insulating/semiconducting behavior in the measured temperature range (100K to 400K). The MR was measured in the presence of the 10kOe field. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR) was observed in the composites. It was clearly observed that the magnetoresistance effect of x = 0.03 was enhanced at room temperature range. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together.

For use in ultrasonic actuators, we investigated the structural and piezoelectric properties of (1 - x)Pb(Zr0.515Ti0.485)O3 - xPb(Sb1/2Nb1/2)O3 + 0.5 wt% MnO2 [(1 - x)PZT - xPSN + MnO2] ceramics with a variation of x (x = 0.02, 0.04, 0.06, 0.08). All the ceramics, which were sintered at 1250˚C for 2 h, showed a typical perovskite structure, implying that they were well synthesized. A homogeneous micro structure was also developed for the specimens, and their average grain size was slightly decreased to 1.3μm by increasing x to 0.8. Moreover, a second phase with a pyrochlore structure appeared when x was above 0.06, which resulted in the deterioration of their piezoelectric properties. However, the 0.96PZT-0.04PSN+MnO2 ceramics, which corresponds with a morphotropic phase boundary (MPB) composition in the (1 - x)PZT - xPSN + MnO2 system, exhibited good piezoelectric properties: a piezoelectric constant (d33) of 325 pC/N, an electromechanical coupling factor (kp) of 70.8%, and a mechanical quality factor (Qm) of 1779. The specimens with a relatively high curie temperature (Tc) of 305˚C also showed a significantly high dielectric constant (εr) value of 1109. Therefore, the 0.96PZT - 0.04PSN + MnO2 ceramics are suitable for use in ultrasonic vibrators.

In this study, the thermoelectric power and resistivity of the perovskite manganiteLa0.75Ba0.25MnO3 were investigated in the temperature range 300K-1200K. The electrical resistivity andthermoelectric power indicate a transport mechanism dominated by adiabatic small-polaron hopping. Thepower factor increases from 2×10−6W/mK2 to 1×10−5W/mK2 as to the temperature increases from 400K to1200K, which indicates that the compound is highly feasible as a thermoelectric material at high temperatures.