## 4 Application of Cyclodextrin-Based Adsorbents
### Removal of Organic Compounds
#### 4.3.1 Endocrine Disruptors
The CDGO membranes were produced by vacuum filtration and laying CDGO nanosheets onto spongy compounds. Nanosheets were produced by chemically grafting \(\beta\)-CD particles on both sides of graphene oxide nanosheets. The BPA adsorption efficiency by the synthesized material wss several times higher than that of the affinity membranes that were earlier used. In addition, this material was readily regenerated by treatment with ethanol. After a few cycles, it was possible to restore the effectiveness of BPA removal to almost 100% [123]. In 2020, a porous membrane made of cellulose nanofibers with modified \(\beta\)-cyclodextrintrin (CA-P-CDP) was produced and tested. The impurities used were model bisphenol compounds bisphenol A, bisphenol S, and bisphenol F. In addition, temperature, adsorbent dosage, and pH were tested during the adsorption process, and it was shown that they had a significant effect on the adsorption efficiency. Under chosen conditions (25 \({}^{\circ}\)C, 7.0 pH, and 0.1 g/L dose of material), the removal of model pollutants reached equilibrium within 15 min, and the qmax parameter was 50.37, 48.52, and 47.25 mg/g for bisphenol A, S and bisphenol F, respectively. The work focused on the interaction of hydrophobic effects, hydrogen bond interactions, and \(\pi\)-\(\pi\) stacking interactions. In addition, it was proved that the amount of treated solution by CA-P-CDP was 14.5 times greater than that of a pristine-cellulose membrane. In addition, the authors also indicated the complete removal of pollutants during the treatment of natural water samples, which proved that the tested material could be used in practice [133]. Another example of the application of CD-based adsorbents may be using a new, environmentally friendly adsorbent formed by cross-linking with \(\beta\)-cyclodextrintrin diatomic  
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(DA@-CD) for the removal of EDCs. The synthesized DA@-CD had 1.4 to 2.5 times higher BPA removal capacity than DA. The test material was steady and reusable after washing with an alkaline solution. A removal held after three regeneration cycles, still achieved a stable removal rate of 91.15% [118]. Cyclodextrin-based materials can remove many contaminants other than BPA. For example, in one study, Fe3O4@CD MNPs were produced by chemical co-precipitation, and could quickly be isolated from the water phase by a magnet. The efficiency of 1-naphthol removal by the mentioned material was tested according to the batch technique. The qmax parameter of Fe3O4@CD MNPs was higher than that of several adsorbing materials tried before. Moreover, the paper showed the cost-effective and advantageous removal of Co(II) and 1-naphthol simultaneously by Fe3O4@CD MNPs [134]. In addition, core-shell nanoparticles can also be used to adsorb harmful compounds. An example may be the magnetic and photocatalytic Fe3O4@TiO2 prepared and described by researchers. It is formed when cyclodextrin cavities are anchored in TiO2 coating. The model pollutant used in the study was butyl phthalate. An undeniable advantage of this type of material was the possibility of separating the functionalized nanoparticles by magnetic action and reusing them. The dispersibility of nanoparticles in water captured organic impurities, due to the presence of cyclodextrin in the composite material. Moreover, the desirable feature of these adsorbents was that they could be removed entirely and reused, while maintaining the current adsorption capacity [135]. Researchers also undertook the removal of estrogens (including estradiol and estrone) from the environment using Zr/CM-\(\beta\)CD, i.e., the Zr(IV)-cross-linked carboxymethyl-\(\beta\)-cyclodextrinrin, which was constructed by an easy, all-purpose and environmentally friendly method. Namely, this material could be obtained by a chelation reaction between Zr(IV) and the carboxyl group of the cyclodextrin used. Furthermore, the CD cavities encapsulated estrogenic contaminants through inclusion complexes.