# Rare Earth Elements Uptake by Synthetic Polymeric and Cellulose-Based Materials: A Review
## 8 Cellulosic Materials for RE Capture
### Low-Molecular-Weight-Moleule-Modified Cellulose Materials  
Cellulose by itself has low REE uptake, up to 6 mg/g [84]. However, thiourea functionalized cellulose captures up to 73 and 27 mg/g of Nd (III) and Eu (III), respectively [86]. Thiourea acts as a complexity agent for REEs, and many thiourea-metal complexes have been reported [100; 101]. Researchers do not specify pH conditions in their experiments; however, thiourea has been studied alone as an extracting agent for REEs from acid leaching [102], which indicates the thiourea-cellulose materials could be applied in mining wastewaters or AMD, although more direct evidence is needed to support this claim.  
On the other hand, carboxylated cellulose captures up to 25 and 33 mg/g Tb (III) and La (III), which could also suggest selectivity toward light REEs [88; 89]. Interestingly, when carboxylated cellulose is on the nanoscale, the capture capacity for La (III) increases considerably, up to 100 mg/g [90]. However, this capture capacity is reported when carboxylated nanofibrilated cellulose (NFC) is found as a suspension in aqueous media, and researchers also evaluated freeze-dried carboxylated NFC, reporting 59 mg/g of La (III) captured at neutral pH [90]. Substituting hydroxyl groups found in nanocrystalline cellulose (NCC) by a dicarboxylic acid and combining it with NCC as a support to form a composite allowed the capture of Nd (III) up to 264 mg/g at low acidic pH [91]. It should be noted that most experiments related to REEs and carboxylated cellulose were reported at neutral pH, which favors both coordinative and ion exchange effects for REE uptake. Based on the information previously discussed about polymeric materials for  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Cellulosic Material** & **Functional Groups** & **Capacity q** & **Conditions** & **Ref** \\  & **Involved** & **Captured Ion** & **(mg/g)** & **T\({}^{\circ}\)(\({}^{\circ}\)C, pH)** & **Ref** \\ \hline Microcrystalline cellulose & & & & & \\ Tetrahylenepentamine-g-cellulose & & & & & \\ Poly(carboxymethyl)-cellulose & & & La (III) & 101.0 & 25, 3–4 & [94] \\  & & & & 107.0 & & \\ \hline Graphene & & & & & \\ oxide/polyethylene & & & & & \\ glycol/carboxylated & & & & & \\ bacterial cellulose IIP & & & & & \\ \hline Phosphorylated & & & & & \\ nanocrystalline cellulose (NCC)/carbon nanotubes & & & La (III) & 45.9 & 25, 4.0 & [96] \\  & & & & & \\ \hline Carboxylated NCC/carbon nanotubes IIP & & & & & \\ \hline Cellulose@SiO\({}_{2}\) & & & & & \\  & & & & & \\ \hline Cellulose@Zn/Al layered & & & & & \\ double hydroxide (LDH) & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: _Cont._REE uptake related to carboxylic acid moieties, especially focused on the dicarboxylic acid-cellulosic material, which was evaluated in acidic conditions, it could be possible to apply carboxylated cellulosic materials for REE capture from mining wastewaters or AMD sources. However, more suitable studies should be performed to support this claim. Moreover, it should be highly recommended to include more REEs, because only a few were considered in the selected works.