## 3 Results and Discussion  
The crystal structures of Samples A, B, C, D, and E were analyzed using powder X-ray diffraction methods. The XRD pattern of Sample A, which was processed only by grinding in ethanol, displays the clear crystalline peaks, as shown in Figure 2. However, the spectrum cannot be indexed into any manganese oxide structure. When compared with either KMnO\({}_{4}\) or MnSO\({}_{4}\) spectrum, it can be found that the XRD spectrum of Sample A is not the simple mixture of two starting materials. This result indicates that, after the grinding process, the material is formed with an intermediate phase. A further process is required to form the MnO\({}_{2}\) structures. It was proved that, if the material is processed in an alcohol-based environment, a fine growth unit for formation of metal oxide is likely to form [33; 34]. Figure 1: Illustration synthesis steps and sampling conditions. To avoid a process at high temperatures that can result in a reduction of the surface area, further treatments were conducted in an H\({}_{2}\)SO\({}_{4}\) acid solution at 25 \({}^{\circ}\)C or 80 \({}^{\circ}\)C for comparative studies. It is believed that the acid, such as H\({}_{2}\)SO\({}_{4}\), would be able to accelerate the oxidation process of MnSO\({}_{4}\)[30], probably due to the presence of H\({}^{+}\). For preparing other samples, Sample A as a starting material was then added to the H\({}_{2}\)SO\({}_{4}\) solution. Sample B, C, and D were then extracted during the process at a duration of 15 h to obtain Sample B, 20 h to obtain Sample C, and 40 h to obtain Sample D. The XRD analysis of these three samples (B, C, and D) (only XRD pattern of Sample D is shown in Figure 2 since the XRD patterns for both Sample B and C are similar to Sample D) indicates that all the samples show a well-defined \(\alpha\)-MnO\({}_{2}\) crystal structure without any other phase presented. It implies that the clean \(\alpha\)-MnO\({}_{2}\) structure can be formed in less than 15 h, and the structure was stabilized as time went on. In other words, only \(\alpha\)-MnO\({}_{2}\) could be produced at this synthetic condition. The \(\gamma\)-MnO\({}_{2}\) phase described in [30] was not observed in this process. As we will discuss later, even though the duration of the treatments in acid solution does not impact the crystal structure of MnO\({}_{2}\), the process does affect the development of the morphology and the shape of formed materials. To evaluate the temperature effect on crystal structures of MnO\({}_{2}\) and its morphology, Sample A as a starting material was treated in acid solution for 3 h at 80 \({}^{\circ}\)C to produce Sample E. As shown in Figure 2, Sample E displays a crystal structure similar to Samples B, C, and D, indicating that a stable \(\alpha\)-MnO\({}_{2}\) crystal structure can be formed in such a process at a slightly-high-temperature conditions. We will see later that such a process changes the morphology of developed materials dramatically via an accelerated crystal growth rate. The morphologies of Samples B, C, D, and E that correspond to the illustration in Figure 1 were also examined by the Scanning Electron Microscope (SEM) technique, and Figure 3 shows the SEM images of four samples. For Samples B, C, and D, treated at only 25 \({}^{\circ}\)C at different durations, the Staghorn coral-shaped aggregates can be observed as in Figure 3a-c, respectively. A gradual development of the morphology and shape on each sample at subsequent growth stages can be seen. Sample B shows the rather dense aggregates packed by nanometer spherical particles. The high magnification image in Figure 4a shows the fine features on the surface of each particle, which looks like the skin of a Staghorn coral. Such a feature on the surface increases the roughness of the particles, yielding a large surface area. Table 1 lists the BET surface area for Samples B, C, and D. Sample B shows a 220 m\({}^{2}\)/g BET surface area, which is the largest among all the samples.