## 2 Results and Discussion  
FTIR results in Figure 1 can be described as, in the case of CeO\({}_{2}\) nanoparticles (Figure 1a), having a peak at 673 cm\({}^{-1}\) that corresponds to the stretching vibration of Ce-O group. The peak of 1290 cm\({}^{-1}\) being weak corresponds to Ce-OH overtone band, while the sharp peak at 1461 cm\({}^{-1}\) is assigned to the bending vibrations of C-H bond, and the wide band at 3410 cm\({}^{-1}\) corresponds to stretching vibrations of O-H functional groups, respectively [18; 19; 20]. In Ce/GOCNIO NPs, the weaker peak at 1290 cm\({}^{-1}\) decreased, while all other peaks can be clearly seen in Figure 1c and d Considering Figure 1b for analyzing FTIR peaks of pure Yb\({}_{2}\)O\({}_{3}\) nanoparticles, the peak at 618 cm\({}^{-1}\) is correlated to the stretching vibrations Yb-O-H, 1368 cm\({}^{-1}\) shows bending vibrations of C-O bonds, and 1621 cm\({}^{-1}\) is assigned to stretching mode of C-O vibrations, while the broad band at 3445 cm\({}^{-1}\) is due to O-H stretching vibrations, respectively [21; 22; 23]. In Yb/GOCNIO NPs, the intensity of the peak at 618 cm\({}^{-1}\) increased due to the intercalated Fe-O group within the nanocomposite structure [24], while the remaining three peaks are available with slight changes as shown in Figure 1d. The peak of 1450 cm\({}^{-1}\) shows the reported range of stretching vibrations of the heterocyclic aromatic C-N linkage correlating the triazine rings of graphitic carbon nitride, respectively [25]. Common peaks in both nanocomposites are 2346 cm\({}^{-1}\), 2919 cm\({}^{-1}\), and 3748 cm\({}^{-1}\), respectively. All three of these peaks can be elucidated as significant peaks for C-C stretching, C-H stretching vibrations, and O-H stretching vibrations, respectively [26]. Moreover, peaks present in the range of 3500 cm\({}^{-1}\) to 3800 cm\({}^{-1}\) correspond to N-H functional groups of amino acids, confirming the presence of nanosheet-based graphitic carbon nitride as reported in the literature. There is a broadening of the peak area between 700 cm\({}^{-1}\) and 900 cm\({}^{-1}\) due to the presence of cerium and ytterbium nanoparticles, thus making small and weak the peaks for iron oxide onto graphene oxide sheets. XRD patterns of pure CeO\({}_{2}\) NPs and Yb\({}_{2}\)O\({}_{3}\) NPs are shown in Figure 2a,b, respectively. XRD patterns have been checked and confirmed using JCPDS card numbers of 01-081-0792 for CeO\({}_{2}\) NPs, and 00-018-0463 has been used for Yb\({}_{2}\)O\({}_{3}\) NPs. Ce/GOCNIO NPs and Yb/GOCNIO NPs are depicted in Figure 2. The various diffraction peaks of Ce/GOCNIO NPs at 2-theta are of 10.7\({}^{\circ}\), 19.6\({}^{\circ}\), 27.8\({}^{\circ}\), 32.9\({}^{\circ}\), 35.5\({}^{\circ}\), 47.9\({}^{\circ}\), 54.1\({}^{\circ}\), 57.3\({}^{\circ}\), and 62.5\({}^{\circ}\), indexed to planes (001), (113), (002), (200), (199), (220), (311), (428), and (203), respectively. The diffraction peaks at 2-theta of 19.6\({}^{\circ}\) and 27.8\({}^{\circ}\) could be attributed to g-C\({}_{3}\)N\({}_{4}\)[27]. The characteristic diffraction peaks at 32.9\({}^{\circ}\), 47.9\({}^{\circ}\), and 54.1\({}^{\circ}\) were observed due to the presence of cerium oxide [19; 28]. The crystallite size calculated from the Scherrer's formula (D = K\(\lambda\)/(\(\beta\) cos \(\theta\))) is 19 nm. The various diffraction peaks of Yb/GOCNIO NPs at 2-theta are of 10.7\({}^{\circ}\), 19.6\({}^{\circ}\), 22.0\({}^{\circ}\), 27.8\({}^{\circ}\), 29.6\({}^{\circ}\), 35.5\({}^{\circ}\), 57.3\({}^{\circ}\), and 62.5\({}^{\circ}\), indexed to planes (001), (113), (211), (002), (222), (119), (428), and (203), respectively. The characteristic diffraction peaks at 22.0\({}^{\circ}\) and 29.6\({}^{\circ}\) were observed due to the presence of ytterbium oxide [29; 30; 31]. The crystallite size for ytterbium ions was calculated to be 14 nm. The existence of only distinctive peaks and the absence of any other peak due to impurities in XRD patterns revealed the purity of as-prepared samples.