## 3 Results
### XRD  
In Figure 2, the XRD pattern for MWCNTs and composites are shown. As can be seen, in the case of MWCNTs, an intense peak is observed at 20 = 25.5\({}^{\circ}\), which corresponds to the (002) reflection. The shift towards small angles by 1\({}^{\circ}\) relative to graphite (26.15\({}^{\circ}\); ICDD (PDF-2/Release 2011 01-073-5918 01-073-5918) and the broadening of the CNT (002) peak indicates an increase in the interplanar spacing (up to 3.5 A) [43]. This result is associated with the pretreatment of MWCNTs in nitric acid, which damages their outer layers. Another diffraction peak near 43\({}^{\circ}\) is associated with reflection from (100) planes. The XRD spectrum of the Mn-0 composite differs from that of the MWCNTs by the presence of two additional peaks at angles of 36.65 and 65.63\({}^{\circ}\), which correspond to (110) and (020) planes, with d = 2.45 A and d = 1.42 A of K-birnessite manganese oxide (8-MnO\({}_{2}\)), respectively. The existence of the latter may be due to the fact that part of the MnO\({}_{2}\) formed as a result of the redox reaction between MWCNTs and KMnO\({}_{4}\) (4 MnO\({}_{4}\) + 3C + H\({}_{2}\)O\(\rightarrow\)4 MnO\({}_{2}\) + CO\({}_{3}\)\({}^{2-}\) + 2 HCO\({}^{3-}\)) being doped with K [44; 45]. The presence of low-intensity peaks and their broadening indicates a low concentration of manganese oxide in the sample and, most likely, it is in a nanocrystalline state; this is also evidenced by SEM data (Figure 1). The thermal treatment of Mn-0 composite (sample Mn-580) leads to the appearance of a series of new peaks in the diffraction pattern. According to the ICDD database (PDF-2/Release 2011 DB card number 01-071-6262), the peaks at 32.5, 35.97, 40.53 and 59.4\({}^{\circ}\) correspond to dimanganese(III) (Mn\({}_{3}\)O\({}_{4}\)). As in the case of Mn-0, manganese in this sample is most likely in the nanocrystalline state, as evidenced by the presence of diffuse and low-intensity diffraction peaks. The analysis of the diffractogram of the Re-360 sample showed the presence of peaks at angles of 16.5, 26.17 and 30.24\({}^{\circ}\). According to [46], these peaks can be attributed to the reflection from the (011), (112) and (020) planes of ammonium tetraoxorhenate (VII). The presence of the latter is due to incomplete thermal decomposition. In this case, the rhenium oxide formed as a result of heating NH\({}_{4}\)ReO\({}_{4}\) is most likely in a nanocrystalline or amorphous state. The XRD patterns of the last two samples (Mn-580 + Re and Mn-700 + Re) contain a large number of peaks that belong to the two types of phases Mn\({}_{3}\)O\({}_{4}\) (dimanganese(III)) and KReO\({}_{4}\) (ICDD PDF-2/Release 2011 DB card number  
Figure 1: SEM images for (**a**) MWCNTs and composites: (**b**) Mn-0; (**c**) Mn-580; (**d**) Re-360; (**e**) Mn-580 + Re; (**f**) Mn-700 + Re.  
01-071-6262 and PDF-2/Release 2011 DB card number 00-008-0044, respectively). Wherein, the phase composition does not change depending on the treatment temperature.  
The presence of the KReO\({}_{4}\) phase can be explained by a number of processes: (i) thermal decomposition of KMnO\({}_{4}\) with the formation of products containing potassium [47]; (ii) thermal decomposition of NH\({}_{4}\)ReO\({}_{4}\) with the formation of intermediate products, including ReO\({}_{2}\)[48]; (iii) the interaction of potassium-containing products with ReO\({}_{2}\) to form KReO\({}_{4}\).