*2.2. Synthesis of Hydrogels*

The synthesis of the hydrogels containing CNF was performed via free-radical polymerization. For all experiments, the mass of ClAETA monomer was fixed at 5.0 g in 30 mL of deionized water type I. The synthesis was performed in a polymerization tube (Schlenk) under an inert atmosphere of nitrogen gas, which was immersed in a glycerine bath at 70 ◦C for 2.5 h. At the end of the reaction, the samples were dried in an oven (BIOBASE, model BOV-T50F, Jinan, Shandong, China) to obtain a constant weight. Subsequently, the samples were lyophilized (LABCONCO FREEZONE, Kansas City, USA).

Figure 1 shows the chemical structures of MO, poly(ClAETA), and the synthesis scheme.

**Figure 1.** (**a**) Chemical structure of MO dye (molecular formula: C14H14N3O3SNa), (**b**) chemical structure of CNF, (**c**) chemical structure of poly(ClAETA), and (**d**) illustrative representation of the synthesis process of the exchange hydrogels obtained from this work.
