Polymers 2024 , 16 , 110
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Figure 1. TEM images of crosslinkers: ( A ) SiO 2 , ( B ) TiO 2 , ( C ) h-BN, and ( D ) h-BN-OH. XRD patterns of all crosslinkers (SiO 2 , TiO 2 , h-BN, and h-BN-OH) are shown in Figure 2. Both h-BN and h-BN-OH show reflections corresponding to boron nitride (2 θ =~26.7 ◦ , 41.6 ◦ , 43.7 ◦ , 54.9 ◦ , 75.6 ◦ ; ICDD PDF no. 00-034-0421). For h-BN-OH, a clear shift of peaks toward the higher angles is observed in comparison to h-BN. For example, the signal at ~26.39 ◦ , corresponding to the (002) plane of h-BN, is shifted to 26.83 ◦ . This is due to the expansion of crystallographic structure by the incorporation of the -OH functional groups into the lattice. SiO 2 exhibits one broad peak centered at around 23 ◦ , which can be assigned to the amorphous structure of silica oxide [17,18]. TiO 2 is composed of two crystal phases: anatase (ICDD PDF no. 04-014-8515) and rutile (ICDD PDF no. 00-021-1276). There are ~83.9% of anatase and ~16.1% of rutile in the sample [19]. N 2 adsorption/desorption isotherms acquired at liquid nitrogen temperature are presented in Figure 3. The isotherms for TiO 2 , SiO 2 , h-BN, and h-BN-OH are type II isotherms, where there is a wide range of pore sizes [20]. From TEM, it is clear that pores are present. The highest content is in SiO 2 , which can result in a high surface area. The highest surface area was determined for the SiO 2 , which is 275.4 m 2 /g. h-BN-OH exhibits a larger specific surface area compared to h-BN, which is 38.7 m 2 /g and 19.8 m 2 /g, respectively. This is due to the expansion of individual h-BN layers by hydroxyl groups and the creation of a larger surface area that is accessible for N 2 adsorption. The lowest specific surface area from all crosslinkers was measured for the TiO 2 (10.8m 2 /g). A similar dependence can be observed for the total pore volume (Figure 3b). The measured total pore
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