## 3 Results and Discussions  
### X-ray Diffraction  
The diffraction patterns of the \(\alpha\)-MnO\({}_{2}\) type manganese oxide synthesized using the hydrothermal method are shown in Figure 1 and were collected at room temperature, over the 2\(\theta\) range of 10 to 80\({}^{\circ}\), with 0.02 degrees scan step and 0.02 s/step scan rate. The crystallography of the phase composition was confirmed with Rietveld refinement, using HighScore Plus software and the Inorganic Crystal Structure Database (ICSD). The two patterns correspond to \(\alpha\)-MnO\({}_{2}\) samples obtained under the same conditions, but with different colors--black (a) and brown (b).  
As specified in the experimental section, the hydrothermally synthesized \(\alpha\)-MnO\({}_{2}\) displayed two colors: it was observed as a brown precipitate in the middle of the autoclave and as a black precipitate on the side lines. XRD analysis confirmed that both samples were well-crystallized and can be indexed in the \(\alpha\)-MnO\({}_{2}\) structure according to JCPDS card no. 01-072-1982.  
Although the patterns indicate that the reflections of the diffraction peaks of black and brown \(\alpha\)-MnO\({}_{2}\) are similar, a small difference can be seen regarding the degree of crystallization. Thus, in the case of the brown sample, the XRD spectrum has a more irregular background because of the smaller size of the particles, outlined via SEM imagery. The differences in the diffraction peak intensities for brown and black \(\alpha\)-MnO\({}_{2}\) were reported as well in other studies, which were associated with different degrees of crystallinity and/or particle size of the compounds. Based on the literature, the properties of the \(\alpha\)-MnO\({}_{2}\) are affected by the physical treatments applied in the synthesis, such as lyophilization, drying, mechanical stirring, and maceration [33; 34].  
XRD analysis and Rietveld refinement were used to obtain the crystallographic lattice parameters of \(\alpha\)-MnO\({}_{2}\) a = b = 9.831(2) A\({}^{\circ}\), c = 2.8557(6) A\({}^{\circ}\), and \(\alpha=\beta=\gamma=90^{\circ}\) and to confirm the 14/m space group. In the XRD spectra, the peaks observed at 12.7\({}^{\circ}\), 18.1\({}^{\circ}\), 28.7\({}^{\circ}\), 37.4\({}^{\circ}\), 49.8.1\({}^{\circ}\), 60.3\({}^{\circ}\), and 69.7\({}^{\circ}\) correspond to the \(hkl\) planes (110), (200), (310), (121), (411), (521), and (451) of \(\alpha\)-MnO\({}_{2}\) nanowires, respectively. XRD patterns for brown \(\alpha\)-MnO\({}_{2}\) exhibit a high intensity peak at 28.5\({}^{\circ}\), which can be indexed as the (311) plane followed in intensity by the peaks for the planes (121) and (200). In contrast, for black samples the most dominant peak occurs at a plane (110) and a 29 value of 12.5\({}^{\circ}\) followed by planes (310) and (200), suggesting a preferential growth of \(\alpha\)-MnO\({}_{2}\) in both cases comparable with those obtained in literature by [PERSON] et al. [35].  
Figure 1: X-ray powder diffraction of the black and brown \(\alpha\)-MnO\({}_{2}\) synthesized using the hydrothermal method.  
The crystallite sizes were determined from X-ray diffraction line broadening using the Debye-Scherrer equation (Equation (2)) for the calculation of particle size:  
\[\mathrm{D}=\frac{\mathrm{K}\lambda}{\beta\cos\theta} \tag{2}\]  
where D is the mean size of crystallites (nm), K is the Scherrer constant, \(\lambda\) is wave length of the X-ray beam used (1.54, 184 A), \(\beta\) is the full width at half maximum (FWHM) of the peak, and \(\theta\) is the Bragg angle. The calculated crystallite sizes were 17.4 nm for the black \(\alpha\)-MnO\({}_{2}\) sample and 15.1 nm for the brown one.