## 4 Application of Cyclodextrin-Based Adsorbents  
### Removal of Dyes  
Dyes are being removed with high efficiency by using CD-based adsorbents. Various studies related to dye adsorption. Adsorption efficiency depends upon the interactions of analyte molecules with the adsorbent [92]. Various adsorbents have different abilities to uptake the dye in their matrix. The \(\beta\)-CD surface is rich in oxygen, and 0.1 m\({}^{2}\)/g surface area adsorbs CR and MB with a maximum capacity of \(1.80-10^{-2}\) mmol/g but a higher affinity for CR, because of the CD and hydrophobic dye interactions. In contrast, MB has weak interaction of forces at the hydrophilic surface of \(\beta\)-CD [93]. Host-guest complexation has become the advanced and economical adsorption technique. In a new study, \(\beta\)-CD and oil orange SS (OOSS) azo dye complexes were formed by the coprecipitation method to check their water purification ability. OOSS dye encapsulation with the \(\beta\)-CD hydrophobic cavity was confirmed by thermal analysis and FTIR. The complexation induced stability in the matrix, due to host-guest complex formation [94]. In another study, \(\beta\)-CD and \(\varepsilon\)-polycaprolactone (PCL) composite fibers were prepared by the electrospinning method through the host-guest complexation mechanism, as shown in Figure 4. The adsorbents were characterized by SEM, XRD, EDXS, and FT-IR. The synthesized fiber exhibited selective response for the 4-aminoazobenzene and MB solutions. The dye elusion efficiency was achieved at 24.1 mg/g towards 4-aminoazobenzene. Adsorption stability, sensitivity, and selectivity of the electrospun fibers encourage their potential use at a large scale for dye adsorption [95]. Natural polysaccharides can perform surface modification of GO due to various active functional groups. In a new study, the GO/\(\beta\)-CD composite was prepared by the cross-linking method to study its performance in MB adsorption. The new material was characterized by SEM, XRD, FT-IR, Raman and TGA analysis. GO/ \(\beta\)-CD exhibited the maximum adsorption capacity of 76.4 mg/g in six consecutive adsorption-desorption cycles [96]. Functionalized polymer composites gained much attention due to their high sensitivity, easy availability, good separation, and various active groups in the polymeric chain. Combining functionalized polymers with nanoparticles induces excellent properties in adsorbent materials. [PERSON] et al. reported a magnetic polymer nanocomposite by the addition of Fe\({}_{3}\)O\({}_{4}\) nanoparticles (NPs) with \(\beta\)-CD/activated charcoal (AC)/sodium alginate (Alg). Figure 5 shows the SEM images and elemental analysis of the synthesized adsorbent. Langmuir isotherm fitted on the adsorption studies and prepared polymer composite exhibited the adsorption capacity of 10.63 mg g\({}^{-1}\) for MB with an elution rate of 99.53% [97]. Figure 3: Fragment of the structure of the cyclodextrin adsorbent interacting with dyes and metal cations. A combination of adsorption and membrane technology enhances the adsorbent performance. [PERSON] et al. modified filter paper with CD and citric acid to remove dual molecules, including dyes and Cu ions. Adsorption capacities of 39.1 mg g\({}^{-1}\), 99.7 mg/g, 124.6 mg g\({}^{-1}\), and 130.4 mg g\({}^{-1}\) were determined for the Cu(II), Rhodamine-B (RB), Methylene Blue (MB),  
Figure 4: Schematic representation for the synthesis and adsorption mechanism of \(\beta\)-CD/PCL composite fibers for MB [95]. Figure 5: SEM-Energy Dispersive X-ray Spectrometry (EDX) images of Fe\({}_{3}\)O\({}_{4}\)/AC/CD/Alg polymer beads before (**A**) and after (**B**) adsorption. Fe\({}_{3}\)O\({}_{4}\)/AC/CD/Alg elemental analysis before (**C**) and after (**D**) adsorption [97]. and Brilliant Green (BG), respectively.