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Zeitschriftenartikel zum Thema „Γ-MnO2“

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Autor: Grafiati

Veröffentlicht am 22. Juni 2024

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1

Chen, Lin, Shan Ren, Tao Chen, Xiaodi Li, Mingming Wang, Zhichao Chen und Qingcai Liu. „Low-Temperature NH3-SCR Performance and In Situ DRIFTS Study on Zeolite X-Supported Different Crystal Phases of MnO2 Catalysts“. Catalysts 13, Nr. 4 (31.03.2023): 682. http://dx.doi.org/10.3390/catal13040682.

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In this study, a series of zeolite-X-supported different crystal phases of MnO2 (α-MnO2, β-MnO2, γ-MnO2, and σ-MnO2) catalysts were prepared via a solid-state diffusion method and high-heat treatment method to explore their low-temperature NH3-SCR performance. All of the catalysts featured typical octahedral zeolite X structures and manganese dioxides species of various crystal types dispersed across the support surface. Throughout the entire temperature range of the reaction, γ-MnO2/X catalyst had the highest NO conversion. Additionally, β-MnO2/X, γ-MnO2/X, and σ-MnO2/X catalysts had nearly 100% of N2 selectivity, whereas the α-MnO2/X catalyst had the lowest N2 selectivity (about 90%) below 125 °C. Moreover, the γ-MnO2/X catalyst demonstrated superior acidity capacity and reduction ability compared with the other three catalysts. All the catalysts contained the essential intermediates NH2NO and NH4NO3 species, which are essential to the SCR reaction. More acid sites and nitrate species existed on the γ-MnO2/X catalyst than on the other catalysts, thereby boosting the SCR reaction.

2

Yang, Wein-Duo, Yi-Rong Chou, Cheng-Ching Kuo und Yu-Min Kang. „Controlling the Molar Ratios of Cation to Anion of Precursors for High Performance Capacitive Properties of MnO2 Hybridized Carbon-Based Materials Electrode“. Batteries 9, Nr. 5 (16.05.2023): 273. http://dx.doi.org/10.3390/batteries9050273.

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Controlling the cation to anion (Mn2+/MnO4−) molar ratios of the precursors was used to obtain a highly performance capacitive properties of nanostructural MnO2 hybridized carbon-based materials on nickel foam (NF) through successive ionic layer adsorption and reaction technology. SEM, XRD, BET, and XPS analyses are utilized to investigate the influence of cation/anion molar ratios of precursors on the as-obtained MnO2 electrode materials. At a lower molar ratio of cation/anion of 1, the prepared manganese oxide deposited on the NF with obvious δ-MnO2 phase. The average pore size distribution of BET analysis of the as-obtained δ-MnO2 is about 4.6 nm, the specific surface area is 155.7 m2 g−1, exhibiting a mesoporous structure. However, when the molar ratio of cation/anion is higher than 5, the deposited film produced by the reaction exhibits a γ-MnO2 crystal phase. The capacitance of δ-MnO2/NF electrode is 280 F g−1 at 1 A g−1 in a 1 M Na2SO4 aqueous electrolyte solution. In addition, reduced graphene oxide (rGO) mixed with multi-wall carbon nanotube (MWCNT) was added to synthesize γ-MnO2/rGO-MWCNT/NF electrode, which has a high capacitance of 377.4 F g−1 under the charge/discharge current density at 1 A g−1.

3

Yu, Zhi Ming, Jia Xiu Hu, Jian Zhao und Yun Song Niu. „The Preparation, Texture and Electrodeposition Mechanism of Reticular MnO₂ Catalytic Materials with High Porosity“. Advanced Materials Research 311-313 (August 2011): 1784–88. http://dx.doi.org/10.4028/www.scientific.net/amr.311-313.1784.

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The Ni-based reticular MnOx catalytic materials with high porosity and high specific area were prepared by the electrodeposition method. XRD and SEM were employed to characterize the phase structure and morphology of the MnOx films before and after heat treatment. The phase structure has changed from irregular amorphous structure to compacting crystal structure on the effect of heat treatment. The results show that the phase in the film is γ-MnO2 after aging. The electrodeposition mechanism of MnO2 has also been studied in this paper. MnO2 was deposited by the hydrolysis reaction of Mn2+ in electrolyte and the disproportionation reaction of unstable Mn3+ ions. A large number of hydrogen was released during the whole deposition process.

4

Jalinan Izzah, Dewi, Nazriati Nazriati und Sumari Sumari. „Green Synthesis of MnO₂ Nanoparticles with Aqueous Extract of Star Apple Leaves (Chrysophyllum cainito L.)“. E3S Web of Conferences 481 (2024): 05003. http://dx.doi.org/10.1051/e3sconf/202448105003.

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Nanomaterials are materials with a size of ≤100 nm and are important for technology in today’s digital era. MnO2 is one of the most studied metal oxides nowadays because of its abundance, low toxicity, and environmentally friendly. This material can be synthesized via redox reactions. The reagents commonly used in this reaction are typically toxic and environmentally unfriendly, such as H2SO4, HCl and HNO3. Therefore, through this research, the synthesis of MnO2 was carried out using an aqueous extract of star apple leaves. Because the aqueous extract of star apple leaves is known to contain secondary metabolites which have -OH, -C=O, and -C-N groups. These groups act as reducing and capping agents for the synthesis of MnO2 NPs. In addition, this study investigated the effect of the various synthesis methods on the formation of MnO2 NPs. Based on the results of LC-MS characterization, the aqueous extract of star apple leaves contains myricetin. Myricetin has -C=O and -OH groups which are reactive to MnO4- ions in aqueous solution, so that MnO4- is reduced to MnO4. This fact is supported by the results of the P-XRD characterization, which proves the presence of R-MnO2 and γ- MnO2 were obtained.

5

Sun, Chang, Yingxin Mu und Yuxin Wang. „A Pd/MnO2 Electrocatalyst for Nitrogen Reduction to Ammonia under Ambient Conditions“. Catalysts 10, Nr. 7 (19.07.2020): 802. http://dx.doi.org/10.3390/catal10070802.

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Electrochemical ammonia synthesis, which is an alternative approach to the Haber–Bosch process, has attracted the attention of researchers because of its advantages including mild working conditions, environmental protection, and simple process. However, the biggest problem in this field is the lack of high-performance catalysts. Here, we report high-efficiency electroreduction of N2 to NH3 on γ-MnO2-supported Pd nanoparticles (Pd/γ-MnO2) under ambient conditions, which exhibits excellent catalytic activity with an NH3 yield rate of 19.72 μg·mg−1Pd h−1 and a Faradaic efficiency of 8.4% at −0.05 V vs. the reversible hydrogen electrode (RHE). X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization shows that Pd nanoparticles are homogeneously dispersed on the γ-MnO2. Pd/γ-MnO2 outperforms other catalysts including Pd/C and γ-MnO2 because of its synergistic catalytic effect between Pd and Mn.

6

Ngobeni, P., PE Ngoepe und KP Maenetja. „Structural and electronic properties of β-MnO2 employing DFTB technique“. Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 40, Nr. 1 (24.01.2022): 133–36. http://dx.doi.org/10.36303/satnt.2021cosaami.26.

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MnO2 is presently under massive review for its capacitance properties. MnO2 recrystallizes into several crystallographic structures such as α, β, γ, δ, and λ structure. These structures vary in the way MnO6 octahedra are connected, they possess tunnels or interlayers with gaps of different magnitudes. However, upon lithium intercalation in β-MnO2, LiMnO2 suffers from capacity loss due to undesirable structural phase transformation into spinel like LixMn2O4. One of the major demands is to modify and strengthen the structural stability of MnO2 to prevent phase transformation during lithium intercalation and rapid capacity fading during cycling. DMol3 is a density functional theory-based program used to calculate the lattice parameter of ferromagnetic MnO2. After successfully parameterized MnO2, the lattice parameters were compared with the results from experiments. Density functional tight-binding (DFTB) was employed to investigate the electronic properties of MnO2 such as density of states (DOS) and band structures. The DOS was calculated to check the conductivity of MnO2. The electronic band structures calculated indicate the absence of a gap at the Fermi level, thus MnO2 is metallic. These findings are important in preserving the crystal structure of LiMnO2 and the maintenance of capacity during cycling.

7

Cai, Bohang, Fawei Lin, Xuan Guo und Yongtao Li. „Catalytic Acetone Oxidation over MnOx Catalysts: Regulating Their Crystal Structures and Surface Properties“. Processes 12, Nr. 2 (02.02.2024): 326. http://dx.doi.org/10.3390/pr12020326.

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This study investigates the catalytic oxidation of acetone by different crystal phases of MnO2 prepared via different methods. Compared with β-MnO2 and γ-MnO2, α-MnO2 exhibited superior catalytic activity. Moreover, as replacements for traditional hydrothermal methods and air calcination, the use of microwave hydrothermal methods and N2 calcination significantly enhanced the catalytic performance of the MnO2 catalyst. The optimal catalyst, MnO2-WN (α-MnO2 synthesized via microwave hydrothermal method and N2 calcination), converted 100% of 100 ppm acetone below 150 °C, with the CO2 yields reaching 100%. Further, the stability of the catalyst and its potential for other volatile organic compounds (VOCs) were also determined. The experimental data demonstrated that its outstanding activity primarily stemmed from the improved preparation method, enhancing the specific surface area of the catalyst, optimizing the pore structure, improving the redox performance, and generating more acidic sites and active oxygen species, thereby creating a synergistic effect. Finally, the reaction pathway of acetone oxidation on the catalyst surface has been explored. This work provides a new perspective for developing economically efficient MnOx catalysts for removing VOCs.

8

Zhang, Guangyi, Gui Chen, Haomin Huang, Yexia Qin, Mingli Fu, Xin Tu, Daiqi Ye und Junliang Wu. „Insights into the Role of Nanorod-Shaped MnO2 and CeO2 in a Plasma Catalysis System for Methanol Oxidation“. Nanomaterials 13, Nr. 6 (13.03.2023): 1026. http://dx.doi.org/10.3390/nano13061026.

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Published papers highlight the roles of the catalysts in plasma catalysis systems, and it is essential to provide deep insight into the mechanism of the reaction. In this work, a coaxial dielectric barrier discharge (DBD) reactor packed with γ-MnO2 and CeO2 with similar nanorod morphologies and particle sizes was used for methanol oxidation at atmospheric pressure and room temperature. The experimental results showed that both γ-MnO2 and CeO2 exhibited good performance in methanol conversion (up to 100%), but the CO2 selectivity of CeO2 (up to 59.3%) was much higher than that of γ-MnO2 (up to 28.6%). Catalyst characterization results indicated that CeO2 contained more surface-active oxygen species, adsorbed more methanol and utilized more plasma-induced active species than γ-MnO2. In addition, in situ Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) were applied with a novel in situ cell to reveal the major factors affecting the catalytic performance in methanol oxidation. More reactive oxygen species (O22−, O2−) from ozone decomposition were produced on CeO2 compared with γ-MnO2, and less of the intermediate product formate accumulated on the CeO2. The combined results showed that CeO2 was a more effective catalyst than γ-MnO2 for methanol oxidation in the plasma catalysis system.

9

Kuan, W. H., C. Y. Chen und C. Y. Hu. „Removal of methylene blue from water by γ-MnO2“. Water Science and Technology 64, Nr. 4 (01.08.2011): 899–903. http://dx.doi.org/10.2166/wst.2011.262.

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Methylene blue (MB) is a cationic dyestuff, which is particularly resistant to biodegradation. The molecular sieved γ-MnO2 was used as an adsorbent/oxidant to remove the MB at room temperature and in visible light. The removal efficiency was mainly evaluated by X-ray diffractometer (XRD), UV–Vis spectrometer (UV–Vis), total organic carbon (TOC). The results revealed that the mechanisms of MB removal by γ-MnO2 are significantly influenced by the pH. In acidic conditions, hypsochromic effects (i.e. blue shifts of UV–Vis spectra) resulting from N-demethylation of the dimethylamino group in MB may occur concomitantly with oxidative degradation by γ-MnO2. However, the TOC in solution after γ-MnO2 treatment in acidic conditions did not show a dramatic decrease. At near neutral pH conditions, there was almost no UV–Vis absorption for the MB solution, however, only 50% TOC removal was observed. It indicated that MB was not only adsorbed onto γ-MnO2 but also partially oxidatively degraded to other organic compounds which were colourless for UV–Vis.

10

Huang, Xian Ping, und Chun Xu Pan. „Absorbing Manganese Oxide on Multi-Walled Carbon Nanotubes“. Solid State Phenomena 121-123 (März 2007): 85–88. http://dx.doi.org/10.4028/www.scientific.net/ssp.121-123.85.

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A layer of Manganese dioxides (γ-MnO2) was absorbed upon carbon nanotubes (CNTs) surface by using a chemical deposit process. The morphologies of the MnO2/CNTs composite were characterized using transmission electron microscopy (TEM), energydispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and laser Raman spectroscopy (RS). It is found that absorbed layer belongs to the γ-MnO2 nanoparticles in size about 10 nm, and coated homogeneously around the CNTs. It is expected that this MnO2/CNTs composite will be widely applied to make supercapacitors.

11

Kozhina, G. A., A. N. Ermakov, V. B. Fetisov, A. V. Fetisov, K. Y. Shunyaev, A. N. Dmitriev, S. A. Petrova und Robert Grigorievich Zakharov. „Effect of Mechanical Activation on the Electrochemical Behavior of MnO₂“. Defect and Diffusion Forum 334-335 (Februar 2013): 369–74. http://dx.doi.org/10.4028/www.scientific.net/ddf.334-335.369.

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Electrochemical behaviour of mechanoactivated β-MnO2 powders has been studied by the method of cyclic voltammetry with a carbon-paste electroactive electrode. Mechanical activation was carried out by dry grinding in an AGO-2 planetary ball mill. It was found that the grinding process results in a mechanochemical effect in the surface layer of the oxide particles: Mn (IV) cations are reduced to Mn (III). Voltammetry test detects that mechanical activation of β-MnO2 leads to a new state, which is characteristic for the γ-modification of manganese dioxide (β-MnO2 γ-MnO2).

12

Shi, Baicheng, Zhaoying Di, Xiaonan Guo, Ying Wei, Runduo Zhang und Jingbo Jia. „Facet control of manganese oxides with diverse redox abilities and acidities for catalytically removing hazardous 1,2-dichloroethane“. Materials Advances 3, Nr. 2 (2022): 1101–14. http://dx.doi.org/10.1039/d1ma00943e.

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Four kinds of α-, β-, γ-, and δ-type MnO2 with distinct crystal phases and spatial structures were prepared for catalytic combustion of 1, 2-dichloroethane with γ-MnO2 exhibiting a superior activity due to synergy of redox property and acidity.

13

Li, Lu, Yuwei Liu, Jingyin Liu, Bing Zhou, Mingming Guo und Lizhong Liu. „Catalytic Degradation of Toluene over MnO2/LaMnO3: Effect of Phase Type of MnO2 on Activity“. Catalysts 12, Nr. 12 (18.12.2022): 1666. http://dx.doi.org/10.3390/catal12121666.

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Series of α, β, γ, δ type MnO2 supported on LaMnO3 perovskite was developed by a one-pot synthesis route. Compared with α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and LaMnO3 oxides, all MnO2/LaMnO3 showed promotional catalytic performance for toluene degradation. Among them, α-MnO2/LaMnO3 holds the best active and mineralization efficiency. By the analysis of N2 adsorption-desorption, XPS and H2-TPR, it can be inferred that the improved activity should be ascribed to the higher proportion of lattice oxygen, better low-temperature reducibility and larger specific surface area. Besides, the byproducts from the low-temperature reaction of toluene oxidation were detected by a TD/GC-MS, confirming the presence of the intermediates. Combined with the in-situ DRIFTS, the catalytic degradation path of toluene oxidation has also been discussed in depth.

14

Sarciaux, S., A. Le Gal La Salle, A. Verbaere, Y. Piffard und D. Guyomard. „γ-MnO2 for Li batteries“. Journal of Power Sources 81-82 (September 1999): 661–65. http://dx.doi.org/10.1016/s0378-7753(98)00230-4.

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15

Sarciaux, S., A. Le Gal La Salle, A. Verbaere, Y. Piffard und D. Guyomard. „γ-MnO2 for Li batteries“. Journal of Power Sources 81-82 (September 1999): 656–60. http://dx.doi.org/10.1016/s0378-7753(99)00095-6.

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16

Wu, Xu, Heqin Guo, Litao Jia, Yong Xiao, Bo Hou und Debao Li. „Effect of MnO2 Crystal Type on the Oxidation of Furfural to Furoic Acid“. Catalysts 13, Nr. 4 (28.03.2023): 663. http://dx.doi.org/10.3390/catal13040663.

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The base-free oxidation of furfural by non-noble metal systems has been challenging. Although MnO2 emerges as a potential catalyst application in base-free conditions, its catalytic efficiency still needs to be improved. The crystalline form of MnO2 is an important factor affecting the oxidation ability of furfural. For this reason, four crystalline forms of MnO2 (α, β, γ, and δ-MnO2) were selected. Their oxidation performance and surface functional groups were analyzed and compared in detail. Only δ-MnO2 exhibited excellent activity, achieving 99.04% furfural conversion and 100% Propo.FA (Only furoic acid was detected by HPLC in the product) under base-free conditions, while the furfural conversion of α, β, and γ-MnO2 was below 10%. Characterization by XPS, IR, O2-TPD and other means revealed that δ-MnO2 has the most abundant active oxygen species and surface hydroxyl groups, which are responsible for the best performance of δ-MnO2. This work achieves the green and efficient oxidation of furfural to furoic acid over non-noble metal catalysts.

17

Thackeray, M. M., und A. De Kock. „Synthesis of γ-MnO2 from LiMn2O4 forLi/MnO2 battery applications“. Journal of Solid State Chemistry 74, Nr. 2 (Juni 1988): 414–18. http://dx.doi.org/10.1016/0022-4596(88)90373-8.

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18

POINSIGNON, C., J. AMARILLA und F. TEDJAR. „Electrochemical reduction of βMnO2, ramsdellite, γ- and εMnO2“. Solid State Ionics 70-71 (Mai 1994): 649–53. http://dx.doi.org/10.1016/0167-2738(94)90387-5.

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19

Maksyuta, I., E. Shembel, V. Kyrychenko, V. Redko, T. Pastushkin und N. Zaderey. „Melanin as biological organic polymer with semiconductor properties is unique effective modifier for MnO₂ cathode and increases the energy of Li-MnO₂ battery“. Journal of Physics: Conference Series 2382, Nr. 1 (01.11.2022): 012008. http://dx.doi.org/10.1088/1742-6596/2382/1/012008.

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This article presents results on the modification of a composite mass based on MnO2 with an organic polymer – melanin. The main goal was to evaluate the possibility of increasing the efficiency of electrode processes during cycling and their stabilization. MnO2, synthesized chemically on the basis of Ukrainian manganese ores, was used for modification. This manganese dioxide has a high density (about 2.64 g/cm3), a high specific surface area (28 m2/g), and electronic conductivity also. The final product of the synthesis is γ-MnO2 powder with 5% admixture of γ-Mn2O3.

20

Özcan, Şeyma, Aslıhan Güler, Tugrul Cetinkaya, Mehmet O. Guler und Hatem Akbulut. „Freestanding graphene/MnO2 cathodes for Li-ion batteries“. Beilstein Journal of Nanotechnology 8 (14.09.2017): 1932–38. http://dx.doi.org/10.3762/bjnano.8.193.

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Different polymorphs of MnO2 (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers’ method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge–discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm−2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg−1, 198 mAhg−1, and 251 mAhg−1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg−1 after 200 cycles with 72% capacity retention.

21

Hill, Jörg-R., Clive M. Freeman und Margaretha H. Rossouw. „Understanding γ-MnO2 by molecular modeling“. Journal of Solid State Chemistry 177, Nr. 1 (Januar 2004): 165–75. http://dx.doi.org/10.1016/s0022-4596(03)00393-1.

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22

Huang, Xiangping, Zhao Wang, Changyuan Zhang, Huili Wei und Mao Feng. „γ-MnO2/CNTs Nanocomposite for Supercapacitors“. Journal of Scientific Conference Proceedings 1, Nr. 2 (01.06.2009): 117–20. http://dx.doi.org/10.1166/jcp.2009.1024.

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23

Huang, Xiaoyan, Aijuan Xie, Xingmeng Zhou, Jianwen Xia, Shiping Luo, Chao Yao und Xiazhang Li. „Fabrication of γ-MnO2-Ce Pillared Montmorillonite for Low Temperature NH3-SCR“. Zeitschrift für Physikalische Chemie 232, Nr. 12 (27.11.2018): 1755–69. http://dx.doi.org/10.1515/zpch-2017-1064.

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Abstract A series of γ-MnO2-Ce/MMT catalyst materials synthesized by homogeneous precipitation method was investigated for the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction and specific surface areas were utilized for micro structure and layer spacing investigation. And NH3-TPD, Pyridoxine IR, H2-TPR and XPS were used to investigate Brønsted acid and Lewis acid, redox properties, atomic concentrations and element chemical state for as-prepared catalysts. The results showed that the γ-MnO2-Ce/MMT had superior NOx conversion compared to the bulk particles, among which 6 wt.% γ-MnO2-Ce/MMT displayed the best deNOx of 95.3% for the low temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) under the GHSV of 25,000 h−1, therefore it is a promising catalyst for low temperature NH3-SCR.

24

Zhang, Bentian, Gao Cheng, Wenjin Ye, Xiaoying Zheng, Hengfa Liu, Ming Sun, Lin Yu, Yuying Zheng und Xiaoling Cheng. „Rational design of MnO2@MnO2 hierarchical nanomaterials and their catalytic activities“. Dalton Transactions 45, Nr. 47 (2016): 18851–58. http://dx.doi.org/10.1039/c6dt03523j.

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Lavender-like α-MnO₂@α-MnO₂ and balsam pear-like α-MnO₂@γ-MnO₂ were prepared and α-MnO₂@γ-MnO₂ exhibited a better performance than that of α-MnO₂@α-MnO₂ in dimethyl ether combustion.

25

Shao, Wei, Xiu Juan Chu, Kai Gao und Hua Zhang. „Mangnese Dioxide Nano-Crystal as Catalyst to Remove Formaldehyde“. Advanced Materials Research 298 (Juli 2011): 147–52. http://dx.doi.org/10.4028/www.scientific.net/amr.298.147.

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The purification technology and material of indoor formaldehyde is a hot spot in the field of material at present. In this paper, MnSO4, KMnO4, NaOH and H2O2 etc. are used to make manganese dioxide nanocrystal with the method of liquid precipitation. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and properties. The results show that the products are nano-crystals of γ- MnO2 and δ-MnO2. The catalyze oxidation of formaldehyde using bothγ- MnO2 and δ-MnO2 as catalysts was investigated; and acetyl acetone method was used to characterize formaldehyde chroma. The catalytic ability ofγ-MnO2 nanocrystal to catalyze formaldehyde oxidation is better than that ofδ-MnO2.

26

Devi, Raman, Vinay Kumar, Sunil Kumar, Mamta Bulla, Shruti Sharma und Ashutosh Sharma. „Electrochemical Analysis of MnO2 (α, β, and γ)-Based Electrode for High-Performance Supercapacitor Application“. Applied Sciences 13, Nr. 13 (05.07.2023): 7907. http://dx.doi.org/10.3390/app13137907.

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MnO2 is the most favorable material in power storage due to its technological significance and potential applications in pseudocapacitance (due to various oxidative states allowing efficient charge transfer to meet energy demands), where its properties are considerably influenced by its structure and surface morphology. In the present study, a facile hydrothermal route was used to produce different phases of MnO2 (α, β, and γ) with different morphologies. The electrochemical performance of the synthesized phases was studied in aqueous sodium sulfate as an electrolyte. X-ray diffraction, UV–Vis spectroscopy, and Fourier-transform infrared spectroscopy were used to characterize the synthesized material. The surface morphology and topography were examined using field-emission scanning electron microscopy. The direct band gap of α-, β-, and γ-MnO2 was found to be 1.86 eV, 1.08 eV, and 1.68 eV, lying in the semiconducting range, further enhancing the electrochemical performance. It was found that α-MnO2 had a maximum specific capacitance of 138 F/g at 1 A/g, and the symmetric device fabricated using α-MnO2 had a specific capacitance of 86 F/g at 1 A/g.

27

CUI, DEYUAN, KUN GAO, PAI LU, HONG YANG, YINONG LIU und DONGFENG XUE. „MILD SOLUTION ROUTE TO MIXED-PHASE MnO2 WITH ENHANCED ELECTROCHEMICAL CAPACITANCE“. Functional Materials Letters 04, Nr. 01 (März 2011): 57–60. http://dx.doi.org/10.1142/s1793604711001683.

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Mild chemical bath route at 60–80°C led to the redox reaction between MnSO 4 and KMnO 4 to form MnO 2. The as-synthesized MnO 2 was a mixture of both α- and δ-phases, which has enhanced electrochemical capacitance performances. Pure α-, δ- and γ- MnO 2 were also chemically prepared in the current solution system. The electrochemical performances of the as-prepared MnO 2 samples were evaluated as an electrode for supercapacitor by recording cyclic voltammograms and galvanostatic charge-discharge curves. The crystallographic structure of MnO2 was found to be determined by the chemical bath reaction temperature and time. In the current work, we purposefully designed the optimum reaction parameters to synthesize high performance mixed-phase MnO 2 through mild chemical bath route, ultimately for enhancing the capacitance of powder-based electrodes.

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Tangphanit, K., N. Boonraksa, S. Maensiri, E. Swatsitang und K. Wongsaprom. „The facile one-step hydrothermal method to prepare MnO₂ nanoparticles: Structural and electrochemical properties“. Journal of Physics: Conference Series 2145, Nr. 1 (01.12.2021): 012034. http://dx.doi.org/10.1088/1742-6596/2145/1/012034.

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Abstract MnO2 nanoparticles were successfully prepared via one-step hydrothermal method. The surface are properties of the MnO2 nanoparticles were determined by BET nitrogen adsorption-desorption measurement. The XRD analyses confirm the pure phase of γ-MnO2 and α-MnO2, having orthorhombic crystal structure (JCPDS file no.14-0644 and 44-0141). FE-SEM analysis reveals the combination of massively small spherical particles with average particle size 54.8 nm. The electrochemical results revealed that the MnO2 nanoparticles delivered the specific capacitance of 200.83 F/g at a current density of 1A/g. The cycle stability was usability 30% after 500 cycles at a current density of 5 A/g. The MnO2 nanoparticles reveal a energy density of 3.62 Wh/kg under a power density of 43.11 W/kg.

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Yamada, N., und M. Ohmasa. „Determination of defect structure in γ-MnO2“. Acta Crystallographica Section A Foundations of Crystallography 43, a1 (12.08.1987): C311. http://dx.doi.org/10.1107/s0108767387077067.

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Caltagirone, Scott, und James Massingill. „Developing γ-MnO2 Models for XRD Analysis“. ECS Transactions 11, Nr. 32 (19.12.2019): 29–35. http://dx.doi.org/10.1149/1.2992491.

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Li, Guicun, Li Jiang, Hongtao Pang und Hongrui Peng. „Synthesis of γ-MnO2 single-crystalline nanobelts“. Materials Letters 61, Nr. 16 (Juni 2007): 3319–22. http://dx.doi.org/10.1016/j.matlet.2006.11.021.

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Tedjar, F., und J. Guitton. „Considérations sur la surface de γ-MnO2“. Surface and Coatings Technology 35, Nr. 1-2 (Oktober 1988): 1–10. http://dx.doi.org/10.1016/0257-8972(88)90051-5.

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Dose, Wesley M., und Scott W. Donne. „Kinetic analysis of γ-MnO2 thermal treatment“. Journal of Thermal Analysis and Calorimetry 105, Nr. 1 (24.03.2011): 113–22. http://dx.doi.org/10.1007/s10973-011-1445-5.

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Wang, Jian, Hainan Zhao, Jianfei Song, Tingyu Zhu und Wenqing Xu. „Structure-Activity Relationship of Manganese Oxide Catalysts for the Catalytic Oxidation of (chloro)-VOCs“. Catalysts 9, Nr. 9 (28.08.2019): 726. http://dx.doi.org/10.3390/catal9090726.

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Manganese oxide catalysts, including γ-MnO2, Mn2O3 and Mn3O4, were synthesized by a precipitation method using different precipitants and calcination temperatures. The catalytic oxidations of benzene and 1,2-dichloroethane (1,2-DCE) were then carried out. The effects of the calcination temperature on the catalyst morphology and activity were investigated. It was found that the specific surface area and reducibility of the catalysts decreased with the increase in the calcination temperature, and both the γ-MnO2 and Mn3O4 were converted to Mn2O3. These catalysts showed good activity and selectivity for the benzene and 1,2-DCE oxidation. The γ-MnO2 exhibited the highest activity, followed by the Mn2O3 and Mn3O4. The high activity could be associated with the large specific surface area, abundant surface oxygen species and excellent low-temperature reducibility. Additionally, the catalysts were inevitably chlorinated during the 1,2-DCE oxidation, and a decrease in the catalytic activity was observed. It suggested that a higher reaction temperature could facilitate the removal of the chlorine species. However, the reduction of the catalytic reaction interface was irreversible.

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Tao, Ying, Rong Li, Ai-Bin Huang, Yi-Ning Ma, Shi-Dong Ji, Ping Jin und Hong-Jie Luo. „High catalytic activity for formaldehyde oxidation of an interconnected network structure composed of δ-MnO2 nanosheets and γ-MnOOH nanowires“. Advances in Manufacturing 8, Nr. 4 (28.08.2020): 429–39. http://dx.doi.org/10.1007/s40436-020-00321-2.

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AbstractAmong the transition metal oxide catalysts, manganese oxides have great potential for formaldehyde (HCHO) oxidation at ambient temperature because of their high activity, nontoxicity, low cost, and polybasic morphologies. In this work, a MnO2-based catalyst (M-MnO2) with an interconnected network structure was successfully synthesized by a one-step hydrothermal method. The M-MnO2 catalyst was composed of the main catalytic agent, δ-MnO2 nanosheets, dispersed in a nonactive framework material of γ-MnOOH nanowires. The catalytic activity of M-MnO2 for HCHO oxidation at room temperature was much higher than that of the pure δ-MnO2 nanosheets. This is attributed to the special interconnected network structure. The special interconnected network structure has high dispersion and specific surface area, which can provide more surface active oxygen species and higher surface hydroxyl groups to realize rapid decomposition of HCHO.

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Yang, Fan, Xichuan Liu, Rui Mi, Lei Yuan, Xi Yang, Minglong Zhong, Zhibing Fu, Chaoyang Wang und Yongjian Tang. „A Novel Radiation Method for Preparing MnO2/BC Monolith Hybrids with Outstanding Supercapacitance Performance“. Nanomaterials 8, Nr. 7 (14.07.2018): 533. http://dx.doi.org/10.3390/nano8070533.

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A novel facile process for fabrication of amorphous MnO2/bamboo charcoal monolith hybrids (MnO2/BC) for potential supercapacitor applications using γ-irradiation methods is described. The structural, morphological and electrochemical properties of the MnO2/BC hybrids have been investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. The combination of BC (electrical double layer charge) and MnO2 (pseudocapacitance) created a complementary effect, which enhanced the specific capacitance and good cyclic stability of the MnO2/BC hybrid electrodes. The MnO2/BC hybrids showed a higher specific capacitance (449 F g−1 at the constant current density of 0.5 A g−1 over the potential range from –0.2 V to 0.8 V), compared with BC (101 F g−1) in 1 M of Na2SO4 aqueous electrolyte. Furthermore, the MnO2/BC hybrid electrodes showed superior cycling stability with 78% capacitance retention, even after 10,000 cycles. The experimental results demonstrated that the high performance of MnO2/BC hybrids could be a potential electrode material for supercapacitors.

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Li, Mingdong, Jiawei Wang, Dejin Fu, Bibo Gou, Xiaoliang Chen und Haifeng Wang. „Preparation of nano manganese oxides by H₂O₂ in-situ oxidation: effect of regulation mechanism on physical and chemical properties“. Materials Research Express 8, Nr. 11 (01.11.2021): 115007. http://dx.doi.org/10.1088/2053-1591/ac3535.

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Abstract Manganese oxides showed many special physicochemical properties in many fields such as electrochemistry, adsorption and catalysis. They were widely used in cathode materials for lithium batteries, molecular sieves, catalytic materials and adsorbents. In this paper, in situ oxidation of manganese sulfate solution was conducted with H2O2 as oxidant, and the characterization means of XRD, SEM and BET were used. The purpose was to study the effects of different regulation mechanisms on the physical and chemical properties of manganese oxides such as morphology, phase composition, surface properties and specific surface area. The adsorption properties of γ-MnO2 for Co and Ni in manganese ore leaching solution were tested. The results showed as follows. Under alkaline conditions, the main product of manganese sulfate solution oxidized by H2O2 was Mn3O4 spherical particles with a radius of about 50 nm, these particles had micropores or mesopores, the oxidation reaction rate was rapid, and the specific surface area and N2 adsorption capacity changed with the change of reaction conditions.The temperature had a great influence on the micro morphology of the product.The micro morphology was slender nanorod when the temperature was 20 °C. With the increase of temperature, the length of nanorod became shorter. When the temperature rises to 50 °C, the rod became spherical. When the pH value decreased from 9 to 7, the diffraction peak of each crystal plane in the product Mn3O4 decreased gradually. The diffraction peak of γ-MnO2 appeared when the pH value decreased to 5. All the products were γ-MnO2 when the pH value decreased to 3. With the increase of Mn2+ concentration, the grain size decreased and agglomeration was easy to occur. The optimum conditions were obtained as follows: the temperature was 30 °C, pH was 3, reaction time was 90 min, the mole ration of H2O2 to Mn2+ was 1:1, and Mn2+ concentration was 10 g l−1. Under the optimum conditions, γ-MnO2 with high specific surface area (172.41 m2 g−1) was prepared. This γ-MnO2 has a good adsorption effect on Co and Ni in manganese ore leaching solution, and the adsorption efficiency could be reached 94.75% and 95.67%. This study would provide a reference for the preparation of manganese oxides with different physical and chemical properties.

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Lin, H. Y., Y. P. Sun, B. J. Weng, C. T. Yang, N. T. Suen, K. H. Liao, Y. C. Huang, J. Y. Ho, N. S. Chong und H. Y. Tang. „Factors influencing the structure of electrochemically prepared α-MnO2 and γ-MnO2 phases“. Electrochimica Acta 52, Nr. 23 (Juli 2007): 6548–53. http://dx.doi.org/10.1016/j.electacta.2007.04.095.

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Dinh, Van-Phuc, Ngoc-Chung Le, Ngoc-Tuan Nguyen, Quang-Thien Tran, Van-Dong Nguyen, Anh-Tuyen Luu, N. Quang Hung, Tran Duy Tap und Thien-Hoang Ho. „Determination of Cobalt in Seawater Using Neutron Activation Analysis after Preconcentration by Adsorption onto γ-MnO2 Nanomaterial“. Journal of Chemistry 2018 (2018): 1–8. http://dx.doi.org/10.1155/2018/9126491.

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The γ-MnO2 nanomaterial has been used to adsorb cobalt in the seawater at Phan Thiet City, Binh Thuan Province, Vietnam. Its concentration is determined by using the neutron activation analysis (NAA) method at the Dalat nuclear research reactor. Factors affecting the uptake of cobalt on the γ-MnO2 material such as the pH, adsorption time, and initial cobalt(II) concentration are investigated. The irradiated experiment data are calculated using the K0-Dalat program. The results obtained show that the trace dissolved cobalt in Phan Thiet seawater is found equal to 0.25 ± 0.04 μg/L (n=5, P=95%) with the adsorption efficiency being higher than 95% (n=4, P=95%).

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Dong, Jie, Zhenzhong Hou, Qiuli Zhao und Qinghao Yang. „Synthesis and Characterization of Nickel-doped Manganese Dioxide Electrode Materials for Supercapacitors“. E3S Web of Conferences 79 (2019): 03002. http://dx.doi.org/10.1051/e3sconf/20197903002.

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Nickel-doped manganese dioxide (Ni-MnO2) synthesized by sol-gel method has been used as an electrode material for supercapacitors. The structure and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectrometry (EIS). Results showed that the nickel-doped manganese dioxide sample exhibited irregular particles with the diameter of about 500 nm. The crystallographic structure of MnO2 was the poorly crystallized γ-MnO2. The doping ratio had a great influence on the electrochemical properties of the materials. When the molar ratio of Ni/Mn was 3/100, the specific capacitance of Ni-MnO2 achieved to 252.61 F/g. After 2000 charge/discharge cycles, the specific capacitance of Ni-MnO2 was still maintained at 74.36%, which was attributed to its excellent cycling stability.

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Huang, Xiangping, Chunxu Pan und Xingtang Huang. „Preparation and characterization of γ-MnO2/CNTs nanocomposite“. Materials Letters 61, Nr. 4-5 (Februar 2007): 934–36. http://dx.doi.org/10.1016/j.matlet.2006.06.040.

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Thackeray, M. M., A. De Kock, L. A. De Picciotto und G. Pistoia. „Synthesis and characterization of γ-MnO2 from LiMn2O4“. Journal of Power Sources 26, Nr. 3-4 (Mai 1989): 355–63. http://dx.doi.org/10.1016/0378-7753(89)80146-6.

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Tedjar, Farouk, und Jacques Guitton. „Structural modification on heat treatment of γ-MnO2“. Thermochimica Acta 181 (Mai 1991): 13–22. http://dx.doi.org/10.1016/0040-6031(91)80408-b.

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Chiu, Hsin-Ya, und Chun-Pei Cho. „Impacts of Mn Content and Mass Loading on the Performance of Flexible Asymmetric Solid-State Supercapacitors Using Mixed-Phase MnO2/N-Containing Graphene Composites as Cathode Materials“. C 9, Nr. 3 (10.09.2023): 88. http://dx.doi.org/10.3390/c9030088.

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MnO2/nitrogen-containing graphene (x-NGM) composites with varying contents of Mn were used as the electrode materials for flexible asymmetric solid-state supercapacitors. The MnO2 was a two-phase mixture of γ- and α-MnO2. The combination of nitrogen-containing graphene and MnO2 improved reversible Faraday reactions and charge transfer. However, excessive MnO2 reduced conductivity, hindering ion diffusion and charge transfer. Overloading the electrode with active materials also negatively affected conductivity. Both the mass loading and MnO2 content were crucial to electrochemical performance. x-NGM composites served as cathode materials, while graphene acted as the anode material. Operating by two charge storage mechanisms enabled a synergistic effect, resulting in better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 exhibited the highest conductivity, efficient charge transfer, and superior capacitive characteristics. It showed a superior specific capacitance of 579 F·g−1, leading to high energy density and power density. Flexible solid-state supercapacitors using x-NGM composites demonstrated good cycle stability, with a high capacitance retention rate of 86.7% after 2000 bending cycles.

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Chang, Yali, Hao Zhang, Weijun Xiang, Shengping Wang, Xiaoyan Zhu und Jingxian Yu. „Thermodynamics, kinetics and crystal structure of γ/β-MnO2 in Li/MnO2 primary batteries“. Electrochimica Acta 339 (April 2020): 135918. http://dx.doi.org/10.1016/j.electacta.2020.135918.

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Hu, Ching-Yao, Yu-Jung Liu und Wen-Hui Kuan. „pH-Dependent Degradation of Diclofenac by a Tunnel-Structured Manganese Oxide“. Water 12, Nr. 8 (05.08.2020): 2203. http://dx.doi.org/10.3390/w12082203.

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The mechanism of diclofenac (DIC) degradation by tunnel-structured γ-MnO2, with superior oxidative and catalytic abilities, was determined in terms of solution pH. High-performance liquid chromatography with mass spectroscopy (HPLC–MS) was used to identify intermediates and final products of DIC degradation. DIC can be efficiently oxidized by γ-MnO2 in an acidic medium, and the removal rate decreased significantly under neutral and alkaline conditions. The developed model can successfully fit DIC degradation kinetics and demonstrates electron transfer control under acidic conditions and precursor complex formation control mechanism under neutral to alkaline conditions, in which the pH extent for two mechanisms exactly corresponds to the distribution percentage of ionized species of DIC. We also found surface reactive sites (Srxn), a key parameter in the kinetic model for mechanism determination, to be exactly a function of solution pH and MnO2 dosage. The main products of oxidation with a highly active hydroxylation pathway on the tunnel-structured Mn-oxide are 5-iminoquinone DIC, hydroxyl-DIC, and 2,6-dichloro-N-o-tolylbenzenamine.

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Sun, Hongmei, Hongyu Chen, Dong Shu, Zhengyi Xie, Chun He und Liangbo Peng. „Study on degradation of acid orange II in aqueous solution using one-dimensional MnO2 nanorods“. Water Science and Technology 61, Nr. 8 (01.04.2010): 1995–2001. http://dx.doi.org/10.2166/wst.2010.103.

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MnO2 nanorods were prepared by the reaction of KMnO4 and MnSO4 in aqueous media and subsequently followed by hydrothermal methods. The structure and surface morphology of as-prepared powder were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results indicated that the prepared MnO2 possessed α- and γ structure. SEM observations showed that the obtained MnO2 powder possessed a well-defined one-dimensional nanorod-like shape 100 nm wide and 700 nm long. The surface area of the MnO2 nanorods was 92 m2 g−1. The degradation efficiency of MnO2 nanorods towards the organic pollutants in aqueous solution was evaluated using acid orange II as a model dye. It was found that the degradation efficiency of MnO2 nanorods was a function of initial acid orange II concentration, MnO2 nanorods concentration, and the proton concentration. The apparent reaction orders for the initial acid orange II concentration, MnO2 nanorods concentration and the proton concentration were determined to be −0.76, 0.37 and 0.12, respectively. It was found that the degradation efficiency for 60 ppm acid orange II reached 99% with 0.5 g L−1 MnO2 nanorods concentration at pH 2.0 after 60 min, demonstrating its higher degradation efficiency in aqueous solution. The apparent activation energy of the degradation reaction of acid orange II was calculated to be 17.3 kJ mol−1. Furthermore, MnO2 nanorods were demonstrated to have superior durability during regeneration tests.

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Li, Xu, und Yuhui Ma. „MnO₂ nanodrug mediates the expression of antigen-presenting cell through combined chemotherapy to enhance the antineoplastic curative function“. Materials Express 13, Nr. 6 (01.06.2023): 935–41. http://dx.doi.org/10.1166/mex.2023.2432.

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Nano-conjugated compounds are studied in tumor treatment. However, little is known on the function of MnO2 nanodrug mediated by combined chemotherapy. This study explored the efficacy of MnO2 nanodrug applied in combined chemotherapy and evaluated its antineoplastic efficacy in vivo. Confocal microscope was used to detect the transfection efficiency in tumor cells. Nanoparticles with MnO2 as core (MnO2 NPs) were prepared. The antineoplastic activity efficiency of MnO2 NPs loaded with doxorubicin (DOX) was tested by cell viability test and cell biological behaviors. And the proliferation activity of the co-loading complex on tumor cells was tested in mice in vivo. RT-PCR and flow cytometry detected the expression of adenomatous polyposis coli (APC) mediated by MnO2 nanodrug combined chemotherapy. Co-loading MnO2 NPs and DOX showed a high activity on cells. The mobility of MnO2 NPs DOX cells was weakened and co-loading could inhibit cell invasion. The in vivo studies showed that the metastasis of tumor cells was inhibited after the mice received co-loading. Compared with DOX group, ki67 and APC in co-loading group decreased significantly and the expression of IFN-γ mediated by co-loading drugs was higher than control group, indicating that APC is involved in inhibiting tumor cell growth and metastasis by co-loading. MnO2 nanodrug can enhance the antineoplastic function through APC mediated by combined chemotherapy and inhibit the tumor growth by enhancing the synergistic function of inhibiting the growth, migration, and invasion of tumor cells.

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Khamsanga, Sonti, Mai Thanh Nguyen, Tetsu Yonezawa, Patchanita Thamyongkit, Rojana Pornprasertsuk, Prasit Pattananuwat, Adisorn Tuantranont, Siwaruk Siwamogsatham und Soorathep Kheawhom. „MnO2 Heterostructure on Carbon Nanotubes as Cathode Material for Aqueous Zinc-Ion Batteries“. International Journal of Molecular Sciences 21, Nr. 13 (30.06.2020): 4689. http://dx.doi.org/10.3390/ijms21134689.

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Due to their cost effectiveness, high safety, and eco-friendliness, zinc-ion batteries (ZIBs) are receiving much attention nowadays. In the production of rechargeable ZIBs, the cathode plays an important role. Manganese oxide (MnO2) is considered the most promising and widely investigated intercalation cathode material. Nonetheless, MnO2 cathodes are subjected to challenging issues viz. limited capacity, low rate capability and poor cycling stability. It is seen that the MnO2 heterostructure can enable long-term cycling stability in different types of energy devices. Herein, a versatile chemical method for the preparation of MnO2 heterostructure on multi-walled carbon nanotubes (MNH-CNT) is reported. Besides, the synthesized MNH-CNT is composed of δ-MnO2 and γ-MnO2. A ZIB using the MNH-CNT cathode delivers a high initial discharge capacity of 236 mAh g−1 at 400 mA g−1, 108 mAh g−1 at 1600 mA g−1 and excellent cycling stability. A pseudocapacitive behavior investigation demonstrates fast zinc ion diffusion via a diffusion-controlled process with low capacitive contribution. Overall, the MNH-CNT cathode is seen to exhibit superior electrochemical performance. This work presents new opportunities for improving the discharge capacity and cycling stability of aqueous ZIBs.

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He, Huixia, Caihong Fu, Yongling An, Jinkui Feng und Jianxi Xiao. „Biofunctional hollow γ-MnO₂ microspheres by a one-pot collagen-templated biomineralization route and their applications in lithium batteries“. RSC Advances 11, Nr. 59 (2021): 37040–48. http://dx.doi.org/10.1039/d1ra06899g.

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Recombinant collagen with unique rod-like structure has been demonstrated as a robust template to create novel dandelion-like hollow microspheres of γ-MnO2 mesocrystals, which display superior biocompatibility and electrochemical performance.