# Rare Earth Elements Uptake by Synthetic Polymeric and Cellulose-Based Materials: A Review
## 8 Cellulosic Materials for RE Capture  
Cellulose is a biopolymer composed of glucose units bonded by glycosidic bonds \(\beta\)-1,4 (Figure 4). It is the most abundant biomass-derived substance on earth, and it is found as an integral part of the cell walls in bacteria and plants [55; 56; 57].  
Cellulose has been a substance of interest for researchers because of its abundance, availability, renewability, biocompatibility, biodegradability, and low cost. It also shows high versatility due to the following physical and chemical properties: mechanical stability, chemical stability, high surface area, and modifiable surface chemistry. Cellulosic materials could be chemically modified through incorporation of chemical groups in their structure by means of substitution of hydroxyl groups present in their structure [55; 56; 57] (see Figure 4).  
Cellulose and modified cellulose could be incorporated together with functional polymers and inorganic substances, forming composites and hydrogels. These hydrogels and composites could be used as adsorbent/ion exchange materials for metal ion removal from water [55; 56; 57; 58]. Cellulosic materials have been evaluated to remove toxic heavy metal  
Figure 4: Chemical structure and modifications of interest for cellulosic-based materials.  
cations, such as Pb (II), Hg (II), Cd (II), and Cr (III); semiprecious metal cations, such as Ag (I); precious metals, such as Au (III), Pt (II), and Pd (IV); and less toxic metal cations, such as Cu (II), Zn (II), and Fe (III) [58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78]. Additionally, cellulosic materials have been studied for removing the toxic metal anions Cr (VI) and As (V) [77; 78; 79; 80; 81; 82; 83; 84]. In most cases, cellulosic materials show high capture capacities and selectivity toward specific metal groups [58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78].  
Recently, cellulosic materials have been studied for REE recovery through adsorption/ion exchange processes. As observed from cellulosic materials for metal cation capture from aqueous media, chemical modifications to cellulose and/or using organic functional polymers and inorganic hybrid cellulosic composites allow the capture of REEs (Table 3).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Cellulosic Material** & **Functional Groups** & **Captured Ion** & **Capacity q** & **Conditions** & **Ref** \\  & **Involved** & **Captured Ion** & **(mg/g)** & **T\({}^{\circ}\)C, pH** & **Ref** \\ \hline  & & Eu (III) & 5.7 & & & \\ Nutshell cellulose & & Gd (III) & 5.1 & & & \\  & & Sm (III) & 6.1 & & 25, 4.0 & [86] \\  & & La (III) & 6.0 & & & \\ \hline  & & Nd (III) & 73.0 & & & \\ Thiourae functionalized cellulose & & Eu (III) & 27.0 & & & \\ \hline  & & Tb (III) & 25.2 & 25, 5.0 & [88] \\ \hline  & & La (III) & 33.7 & 25, 6.0 & [89] \\ \hline  & & La (III) & 100.7 & 25, 7.0 & [90] \\ \hline  & & Nd (III) & 264.0 & 25, 4.0–6.0 & [91] \\ \hline  & & La (III) & 84.8 & & \\ \hline  & & Eu (III) & 101.7 & 25, 5.4–6.5 & [92] \\ \hline  & & Er (III) & 120.2 & & \\ \hline  & & La (III) & 262.0 & & \\ \hline  & & Ce (III) & 255.0 & & \\ \hline  & & Pr (III) & 244.0 & & 25, 6.0 & [93] \\ \hline  & & Nd (III) & 241.0 & & \\ \hline \hline  & & & & \\ \hline \end{tabular}
\end{table}
Table 3: Cellulosic materials for REE capture from aqueous media.