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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
Figure 4.10(d) shows a schematic of the Ni-todorokite, whose large tunnel cavity is attributed to the precursor of Ni-buserite [14]. The MnO phase has a basal spacing of 10 Å, which is larger than that of Ni-birnessite (7 Å). The larger basal spacing was attributed to the presence of a second interlayer, which was caused by H2O molecules, as the birnessite was transferred to buserite during the preparation process. In addition, Ni+ ions also acted as a stabilizer to maintain the layered structure. After the Ni-buserite was hydrothermally processed, the layers were collapsed, so that a 3 × 3 tunneled structure was obtained [47, 48]. It was found that the doping metal ions were inserted in the bulk crystal as the buserite structure was transferred to the todorokite on [49]. Furthermore, the ignition method has been used transfer the layered structure into tunneled structure, where the preparation of the cryptomelane (Fig. 4.10(c)) is an example. The ignition could result in an increase in pH value of the solution, while the potassium ions could be partially depleted after washing with water, which lead to the presence of 2 × 2 tunnels. MnO2 ramsdellite (Fig. 4.10(b)) could be obtained through the oxidation of MnSO4 with (NH4)2S2O8, whereas MnO2 spinel, e.g., Li0.2Mn2O4, could be synthesized through the delithiation of LiMn2O4.
Application of birnessite-type solids prepared by sol–gel and oxidation methods in photocatalytic degradation of 4-nitrophenol
Published in Environmental Technology, 2022
S. González-Morán, B. González, M. A. Vicente, R. Trujillano, V. Rives, A. Gil, S. A. Korili
The powder X-ray diffraction diagrams of the samples synthesised by both methods are shown in Figure 1. The positions of the diffractions due to basal planes depend on the hydration degree of the layered material. In the case of buserite, a highly hydrated sample with two layers of water molecules in the interlayer above and below the potassium ion layer, the basal spacing is close to 10 Å, decreasing to 7.1–7.0 Å for birnessite, where there is a single interlayer consisting of water molecules and potassium cations, and even to 5.5 Å in the fully dehydrated phase [29,30]. In the current study, sample SG showed a basal spacing of 7.0 Å, and for sample OH it was 7.2 Å, confirming the formation of the birnessite phase in both cases; the slight difference can be due to the different hydration degree, according to the data in Table 1. As expected, other reflections were recorded at 3.6 and 2.5–2.4 Å.