2. Experimental
2.1. Development of hydrophilic recycled cellulose aerogels Recycled cellulose fibers (2 wt%) is dispersed into sodium
hydroxide/urea solutions (1.9 wt%/10 wt%) by sonicating for 6 min. Thereafter, the solution is placed in refrigerator for more than 24 h to allow gelation of the solution. After the solution has been frozen, it is then thawed at room temperature and then followed by immersing into ethanol (99 vol%) for coagulation. The specimen thickness is controlled at 1 cm with a diameter of 3.5 cm using a beaker as a mold. After coagulation, solvent exchange is carried out by immersing the gel in de-ionized (DI) water for two days. The sample is then frozen in a freezer at −18 ◦C for 12 h. After that, freeze drying is carried out for two days with a ScanVac CoolSafe 95-15 Pro freeze dryer (Denmark) to obtain the desired aerogel.