## 2 Results and Discussion
### Characteristics of Synthesized REEIIPs and Hybrid Materials
Figure 5: Dependency of elongation on standard force for: (**a**) Gd sensitive hybrid membranes with various additions of modified MWCNT-GdIIPs (from 0 to 5 wt.%), and (**b**) Nd sensitive hybrid membranes with various additions of modified MWCNT-NdIIPs (from 0 to 4 wt.%). Namely, the dark gray matrix represents modified chitosan, in which there are lighter bands representing a higher density material, such as the added second NdIIP, and white inclusions represent modified nanotubes (Figure 6a). The following figures show cross-sections and 3D models of the light phase (green), which represents the distribution of MWCNTs in the polymer matrix (Figure 6b). The next figures show cross-sectional views parallel and perpendicular to the membrane plane, with pores and voids marked in blue (Figure 6c). The membrane with the addition of MWCNT-NdIIPs was characterized by high porosity, in which the structure consisted of many individual pores. In the membrane with a smaller addition of nanotubes, there were mostly single pores, but as the MWCNT concentration increased, the porous structure changed and consisted of single pores that merged into larger longitudinal ones. It could be seen from Figure 6a that the modified chitosan NdIIP was dispersed uniformly. While, after the addition of modified MWCNT-NdIIPs, they were dispersed homogeneously and created a developed 3D structure inside the polymer matrix. So, the obtained materials were characterized by a homogeneous internal structure and well-dispersed pore networks appropriate for transport and adsorption processes. SEM analysis was also performed on the newly developed membranes, and the corresponding images are presented in Figure 7.  
Figure 7 illustrates the suitable MWCNT dispersion that may be caused by the application of an external magnetic field during membrane production. Such a dispersion may result not only from direct interaction of the magnetic field with magnetic functionalized MWCNTs, but also from the interaction of the polymer matrix itself with MWCNTs modified with appropriate REEIIPs. The Nd- and Gd-sensitive adsorption membranes made of two polymers (Figure 7d,g) exhibited porous textures and small cracks, which could be caused by excessive drying of the membranes (during transport) before the SEM measurements. The membranes were usually stored in deionized water. SEM images of the hybrid membranes with the addition of MWCNT-REEIIPs showed a decent dispersion and the formation of an expanded 3D structure. The modification of MWCNTs with REEIIPs allowed obtaining membranes with a more uniform structure achieved by increasing the compatibility between the inorganic additives and the polymer matrix, even when the amount of the additive increased. In the case of membranes with nanotube additives without any modifications to the external structure, the compatibility between the polymer matrix of IIPs and the inorganic additive was found to be lower. Modification of the structure of nanotubes, especially by introducing REEIIP groups, resulted in a much better interaction between the inorganic and organic phases and more evenly distributed nanotube-polymer domains. The increase in MWCNT content led to denser, interconnected morphologies, potentially beneficial for barrier properties or selective adsorption. Modification with IIPs also provided certain benefits in the form of stronger interactions between  
Figure 6: Results of X-ray tomography for a Nd sensitive hybrid membrane with 1 wt.% MWCNT-NdIIPs: (**a**) cross-section, (**b**) 3D model of bright phase, and (**c**) 3D model of pores and voids. those phases, which, in turn, translated into better separation properties of the membranes and an improved stability in the working environment. The magnetic properties of newly developed adsorptive membranes were also tested, with the results presented in Table 2 and Figure 8. The hysteresis loops and magnetic parameters of REE ion-imprinted polymers indicated that they were ferromagnetic, but mostly with weak saturation magnetization (Ms \(\sim\)0.04-0.15 emu/g).