## 3 Results and Discussion  
### Materials Characterization  
The nanocomposites prepared were characterized for their manganese concentration and the form of the impregnated manganese oxide, as well as their texture. The total Mn content for the NGO-Mn\({}_{3}\)O\({}_{4}\) and NGO-MnO\({}_{2}\) nanocomposites, estimated by ICP-MS found to be 10.4 and 19.2% _w/w_. The XRD patterns of MnO\({}_{2}\), NGO, NGO-MnO\({}_{2}\) and Mn\({}_{3}\)O\({}_{4}\), Mn\({}_{3}\)O\({}_{4}\), NGO-Mn\({}_{3}\)O\({}_{4}\), in comparison with the pattern of GO, are shown in Figure 1a,b, in order to provide information about their structure. The characteristic (001) peak of graphite oxide, obtained at 20 = 10.3\({}^{\circ}\), is indicative of the successful transformation of graphite into graphite oxide [43]. This peak appeared to be lower in the pattern for NGO, indicative of a partial exfoliation of GO. In the diffraction pattern of MnO\({}_{2}\), the main reflections at \(2\theta=11.4^{\circ}\), \(25^{\circ}\), \(37.2^{\circ}\), and \(66.7^{\circ}\) could be attributed to the (001), (002), (111) and (312) lattice planes of \(\delta\)-MnO\({}_{2}\) (birnessite) respectively [44; 45]. In addition, the broadened peaks indicated the low crystallinity of the manganese oxide. The average crystallite size (D) of MnO\({}_{2}\) as calculated applying [PERSON]'s equation for the (121) peak found to be about 35 nm [46]. The XRD pattern for the NGO-MnO\({}_{2}\) composite presented the characteristic peaks of \(\delta\)-MnO\({}_{2}\). Besides, the absence of the peak at \(2\theta=10.3^{\circ}\), indicated the complete exfoliation of GO during the preparation of the nanocomposite. The XRD pattern of Mn\({}_{3}\)O\({}_{4}\) presented peaks at 20 18\({}^{\circ}\) (101), 29\({}^{\circ}\) (112), 32.5\({}^{\circ}\) (103), 37.2\({}^{\circ}\) (211), 45\({}^{\circ}\) (220) and 60\({}^{\circ}\) (224), characteristic for Mn\({}_{3}\)O\({}_{4}\)[47]. For the NGO-Mn\({}_{3}\)O\({}_{4}\) composite, similar peaks to those appeared in the diffraction pattern for Mn\({}_{3}\)O\({}_{4}\)[48] revealed the formation of Mn\({}_{3}\)O\({}_{4}\). The diffraction peak at 25.6\({}^{\circ}\) indicated a partial reduction of graphene oxide [49; 50]. The N\({}_{2}\) adsorption isotherms for the NGO-Mn\({}_{3}\)O\({}_{4}\) and NGO-MnO\({}_{2}\) nanocomposites are shown in Figure 2 while the pore size distribution in the inset of Figure 2. The isotherms of the nanocomposites indicate an absence of variation in nitrogen uptake, corresponding to a deficiency of micropores. The nanocatalyst NGO-Mn\({}_{3}\)O\({}_{4}\) presented an isotherm of type IV, according to the IUPAC classification, indicative of the presence of mesopores. Furthermore, the isotherm exhibited a hysteresis loop at relative pressure P/Po = 0.70-0.99, classified as H3. The specific surface area was measured by the BET method and found to be 7.52 m\({}^{2}\)/g, while the pore volume found to be 0.056 cm\({}^{3}\)/g. These values are in agreement with the characteristics of hysteresis loop, indicative of lack of micropores. The N\({}_{2}\) adsorption/desorption isotherms for NGO-MnO\({}_{2}\) revealed lack of micropores while the increased N\({}_{2}\) uptake presented at P/Po > 0.95 is indicative of external surface area and the hysteresis loop at relative pressure P/Po = \(\sim\)0.50-0.99 is indicative of the mesopores. Figure 1: XRD patterns of: (**a**) graphene oxide (GO), modified graphene oxide (NGO), manganese oxide (Mn\({}_{3}\)O\({}_{4}\)) and NGO–Mn\({}_{3}\)O\({}_{4}\) nanocomposite; (**b**) GO, modified graphene oxide (NGO), manganese oxide (MnO\({}_{2}\)) and NGO–MnO\({}_{2}\) nanocomposite. The textural parameters of NGO-Mn\({}_{3}\)O\({}_{4}\) and NGO-MnO\({}_{2}\) nanocomposites are presented in Table 1 along with the parameters of NGO, Mn\({}_{3}\)O\({}_{4}\) and MnO\({}_{2}\), for the sake of comparison. From the Table, it is seen that the NGO-MnO\({}_{2}\) nanocomposite presented increase mesopores volume as well as increase Specific Surface Area.