## 4 Application of Cyclodextrin-Based Adsorbents
### Removal of Heavy Metals  
Generally, metals can be eliminated through complexation, interaction, or ion exchange mechanisms. The efficiency of the adsorbent depends upon various factors, especially on the preparation technique and optimal pH. The CD polymer has deprotonated hydroxyl groups, which bind the metal strongly under primary conditions. The stability towards environmental conditions is enhanced by polymerizing Poly-CD/metal ion complex with polyacids. Anceschi reported Poly-CD/PVA fibers by the electrospinning of various Poly-CD and PVA solutions for the adsorption of Cu (II) ions. The fiber morphology was investigated by SEM, and physical-chemical properties were examined by FTIR and TGA. The ability of the insoluble CD-based fibers to eliminate heavy metals from wastewater was examined by analyzing the adsorption of Cu\({}^{2+}\) and Cd\({}^{2+}\) using ICP-OES. Poly-CD/PVA fibers exhibited an excellent response, especially towards the Cu(II), with a maximum adsorption capacity of 48.15 mg/g [101]. In another study, nano-sponges were fabricated through a complexation mechanism by cross-linking linecaps and CD with citric acid. Another pyromellitate nano-sponge was synthesized by the same reaction with pyromellitic dianhydride to compare the responses. The response was recorded at the 500 pm metal concentration, and pyromellitate exhibited a higher retention capability than the citrate-based nano-sponges. Pyromellitate adsorbent showed an adsorption capacity of 272 mg/g and 81 mg/g for the Pb(II) and Cu(II) [102]. Dual adsorbents are a new addition to adsorption technology. Single class pollutants have been reported, and it is challenging to eliminate organic and inorganic contaminants with the same adsorbents. Recently, [PERSON] et al. reported \(\beta\)-CD-CS-EDTA adsorbent for the extraction of heavy metals (Ni(II), Cu(II), and Pb(II)) and ciprofloxacin (CIP). Figure 6 represents the synthesis mechanism of the adsorbent material. The adsorption mechanism was examined using EDX, FTIR, and elemental mapping methods. Heavy metals adsorption was more rapid than the CIP, with an adsorption capacity of 118.90, 161, and 330.90 mg/g for Ni(II), Cu(II), and Pb(II), respectively, while the CIP adsorption capacity was found to be 25.40 mg/g. It is a direction toward new research related to the elimination of organic and inorganic pollutants from water at the same time by a single adsorbent [103]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**adsorbent** & **Dye** & \
\begin{tabular}{c} **adsorption** \\ **Capacity** \\ \end{tabular} &
\begin{tabular}{c} **Removal** \\ **Efficiency (\%)** \\ \end{tabular} & **pH** & **References** \\ \hline Fe3O4/AC/CD/Alg & MB & 10.63 mg/g & 99.53 & 6.0 & [97] \\ \(\beta\)-CD/GO & MB & 76.4 mg/g & 90.00 & 7.0 & [96] \\  & MB & 124.6 mg/g & & 5.5–6 & \\ \(\beta\)-CD filter paper & BG & 130.4 mg/g & 92.94 & 5.5–6 & [98] \\  & RB & 99.7 mg/g & & 5.5–6 & \\ Fe3O4/b-CD/GO & MG & 990.1 & 98.00 & 7.0 & [99] \\ Fe3O4-PEI/b-CD & MO & 192.2 & 83.90 & 1 & [76] \\ \(\beta\)-CD & CR & 12 mg/g & 65.00 & - & [93] \\ PA-\(\beta\)-CD & MB & 1095 & & 6–10 & \\  & BG 4 & 2005.58 & 90.00 & 6–10 & [100] \\ PA-\(\beta\)-CD & CV & 1930.23 & & 6–10 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Adsorption capacities of various CD-based adsorbents for dyes. Magnetic composites are frequently used in adsorption due to their strong hydrophilicity, greater surface area, and various active sites [104; 105]. The addition of magnetic composite with poly (vinylidene fluoride) PVDF membranes is due to the characteristics mentioned above. [PERSON] et al. modified PVDF with \(\beta\)-CD/GO/Fe\({}_{3}\)O\({}_{4}\) to remove Cu(II) metal ions. The morphological and structural properties of the nanocomposite were investigated by TEM, XRD, FTIR, EDX and VSM techniques. The prepared adsorbent exhibited an adsorption capacity of 0.94 mg/g, and pH > 6 enhanced Cu's elimination rate (II).