## 2 Results and Discussion
### Characteristics of Synthesized REEIIPs and Hybrid Materials
The shape of these peaks changes slightly, e.g., after introducing larger amounts of additives, especially in the case of MWCNTs modified with REEIIPs, they become sharper, and an additional small overlapping peak appears. The decrease in these peaks' intensity could be caused by structural disorder and improved matrix homogenization. In the case of membranes modified by the GdIIPs and the introduction  
Figure 2: XRD spectra for Nd, Pr, and Gd sensitive adsorption membranes: (**a**) REEIIP dense membranes, (**b**) hybrid membranes with 0.5 wt.%, 1 wt.%, and 2 wt.% addition of MWCNT-GdIIPs, and (**c**) hybrid membranes with 2 wt.% and 4 wt.% addition of MWCNT-NdIIPs. of a larger addition of modified MWCNTs, the movement of peak maximum with the greatest intensity in the direction of a higher angle of 2 Theta was observed. In addition, a slight increase in the intensity of this peak was also observed as the addition of modified nanotubes increased for all types of tested adsorption membranes. The TGA was conducted for all synthesized membranes (Figure 3). The TGA curve for modified chitosan (Figure 3a) contains a few stages. There is a small weight decrease (about 2%) in the range between 50 and 93 \({}^{\circ}\)C, which could be related to the moisture release. In the next step, i.e., between 245 \({}^{\circ}\)C and 370 \({}^{\circ}\)C, a weight loss of 47% was observed, which could be caused by the loss of heterocyclic rings and phenyl groups attached to the backbone of chitosan during depolymerization [43]. In the last stage, the recorded weight loss was about 16%, leaving, eventually, a residue amounting to approximately 20 wt.%. This behavior indicated that up to 800 \({}^{\circ}\)C, not the whole modified chitosan was decomposed, and the observed weight loss was caused by the decomposition of the unreacted amino groups. Comparing the abovementioned results with the literature results for the pure chitosan (i.e., a weight loss of 11.5% between 27 and 105 \({}^{\circ}\)C, 51% between 255 and 363 \({}^{\circ}\)C, 22% in the third stage, and the residual mass of 8%), it can be concluded that after modification, the thermal stability of the chitosan had improved. The TGA results for the REEIIP (Figure 3a) indicate several stages. The first stage (49-124 \({}^{\circ}\)C) can be assigned to the evaporation of the entrapped solvent. The second stage (124-270 \({}^{\circ}\)C) corresponds to the pyrolysis of quinolinol (the melting point of 5,7-dichloroquinoline-8-ol is 180 \({}^{\circ}\)C). And the next stage (270-570 \({}^{\circ}\)C) relates to the further decomposition of the REE (5,7-dichloroquinoline-8-ol)\({}_{3}\) complex and polymer material. The residual mass was in the 10-20% range. Figure 3: **(a–d)** TGA curves of polymer membranes made of modified chitosan, REEIIPs, and hybrid membranes based on synthesized polymers with various modified MWCNT-REEIIP additions. In the case of Pr selective membranes with the addition of MWCNT modified with PrIIPs, a faster decomposition of the polymer matrix was observed. However, they were still stable until 250 \({}^{\circ}\)C, considered to be adequate for their potential application as adsorption membranes for REE recovery. However, in the case of other membranes selective for Nd and Gd, the tendency was opposite. Namely, their thermooxidative stability increased, and the temperatures at which decomposition was observed shifted to higher values.