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In Situ Metal Immobilization and Phytostabilization of Contaminated Soils
Published in Norman Terry, Gary Bañuelos, of Contaminated Soil and Water, 2020
M. Mench, J. Vangronsveld, H. Clijsters, N. W. Lepp, R. Edwards
The hydroxyl groups of the hydrous oxides form an ideal template for bridging trace metals because the OH-OH distance matches well with the coordination polyhedra of trace metals (Manceau et al., 1992a, b; Charlet and Manceau, 1993; Spadini et al., 1994; Hargé, 1997). As2O42- and Pb2+ form isolated innersphere surface complexes with ferrihydrite (HFO), while Cu2+ forms similar complexes on MnO2. Zn2+, Cd2+, and Pb2+ form similar mononuclear complexes on goethite and ferrihydrite surfaces (Manceau et al., 1992a; Spadini et al., 1994; Hargé, 1997). Pb2+ binds to HMO at various surface sites: edge-, double-, corner-, and triple corner-polyhedra linkages being observed (Hargé, 1997). At a similar density of surface coverings, Pb(II) showed greater polymerization on the surface of Mn-dioxide birnessite than on HFO. The birnessite group of minerals are commonly occurring Mn oxides characterized by mixed Mn valency and disordered structures. Zn, Pb, and Cu form innersphere complexes with birnessite (Na4Mn14O27·9H2O) or bimessite-like structures (Manceau et al., 1997). In a sludged sandy soil, Zn was mainly bound at lattice vacancy sites of the phyllomanganate chalcophanite (ZnMn3O7-3·H2O), whose structure shows similarities to birnessite (Manceau et al., 1997; Hargé, 1997).
Mn, 25]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Manganese occurs mainly at +2 oxidation stage, but may change valences up to +7. It is a member of the Fe family, and is highly associated with Fe, in all geochemical processes. There are many Mn minerals, mainly together with other metals, especially with Fe. The most common is pyrolusite, β-MnO2; other minerals are manganite, γ-MnOOH; hausmannite, Mn3O4; and rodochrozite; MnCO3. The Mn oxide mineral birnessite, (Na0.3Ca0.1K0.1)(Mn4+,Mn3+)2O4·1.5 H2O, of an unconfirmed composition, is formed due to precipitation in lakes, oceans, and groundwater. It is a major component of desert varnish and deep sea Mn nodules, exhibits a large adsorption capacity to several metals (Cd, Co, Cu, Pb, and Zn), and has a high oxidizing potential (Feng et al. 2007). Sorption capacity of MnO2 for several metals is comparable to that of goethite and hematite.
Oxide Based Supercapacitors I-Manganese Oxides
Published in Ling Bing Kong, Nanomaterials for Supercapacitors, 2017
Ling Bing Kong, Wenxiu Que, Lang Liu, Freddy Yin Chiang Boey, Zhichuan J. Xu, Kun Zhou, Sean Li, Tianshu Zhang, Chuanhu Wang
A hydrothermal method was reported to synthesize lamellar birnessite δ-MnO2 structures with different interlayer spacings, which could be simply controlled by adjusting pH value of the initial reaction solutions [70]. As the precursor, α-NaMnO2, was prepared by using the conventional solid-state process [72]. Na2CO3 and Mn2O3 were mixed and calcined at 650°C for 40 hours in Ar flow to form α-NaMnO2. Birnessite-type MnO2 was synthesized by using hydrothermal reaction. 1 g α-NaMnO2 was dispersed in 30 mL distilled water at pH values of 0.63, 2.81 and 8.24, which were adjusted with 10% HNO3 solution. One more solution had a pH value of 12.43, which was obtained without the presence of HNO3. Hydrothermal reaction was conducted at 120°C for 12 hours.
Thermodynamic modelling of decomposition processes in the Mn-O and Mn-O-H systems
Published in Canadian Metallurgical Quarterly, 2023
These various manganese oxides are relatively inexpensive and are being considered for a number of potential engineering applications such as energy conversion and storage devices [33], supercapacitors [34], magnetic materials [35], biomedical applications [36] and catalysts [37]. They can adsorb a large number of different ions and therefore can be utilised in wastewater treatment [38,39]. As mentioned previously, manganese (Mnx+) can exist in a number of valence states and this characteristic can be utilised to facilitate both catalytic oxidation and reduction reactions. Furthermore, some manganese oxides such as the birnessite-type manganese oxides can form tunnel-like structures consisting of the MnO6 octahedra. The presence of these tunnels can facilitate both the access of species to active sites and the absorption of species into the structure. Additionally, the presence of oxygen vacancies in some manganese oxides can further enhance the availability of active sites, particularly for reactions involving oxygen.
Low-temperature degradation of toluene over Ag-MnOx-ACF composite catalyst
Published in Environmental Technology, 2023
Jiahui Shi, Qiang Liu, Rui Liu, Dan Zhao, Ximeng Xu, Jiahao Cui, Hui Ding
Additionally, the 500 nm SEM images of the catalysts calcined at different temperatures were performed. As shown in the Figure 4, the surface of the catalyst is loose and porous due to the presence of water molecules between the formed manganese oxides. These water molecules interact with cations to form a layered crystal structure. The increase of calcination temperature leads to the alteration of surface structure owing to the removal of water molecules, which also proves that the formed manganese oxides are birnessite with a layered structure. The interlayer spacing has been verified to be related to the cation radius and interlayer water content [50, 51].