*3.3. Silane Modification of Cellulose Aerogel*

As hydrophilicity is the inherent nature of cellulose due to its hydroxyl groups, a silane coating was carried out for cellulose aerogels to make them both hydrophobic and oleophilic. To achieve this, a simple thermal chemical vapor deposition procedure was performed for the aerogel with MEMO silane at 110 ◦C in a vacuum desiccator, as described in the above. To become "active", the silane must first be hydrolyzed. The reaction of the silicon end of the molecule was initiated by the hydrolysis of the alkoxy group, usually after exposure to ambient moisture to form a silanol that releases alcohol as follows:

$$-\text{Si(OCH}\_3)\_3 + \text{H}\_2\text{O} \rightarrow -\text{Si(OH)}\_3 + \text{3CH}\_3\text{OH}$$

Once in the silanol state, the silane can be condensed on the aerogel surface, forming a direct covalent bond with the surface. The silanization process of the interior surface of as-prepared cellulose aerogel and silanized cellulose aerogel was shown in Figure 4.

**Figure 4.** Silanization processing.

As shown in Figure 5, the open porous microstructure of the cellulose aerogel was preserved after coating. In addition, there was no change in the surface of the cellulose aerogel after coating, which might be due to the very thin silane coating layer.

**Figure 5.** FE-SEM images of cross-section of CA and silane-coated cellulose aerogel (SCA).

Successful silanization on the surface of the cellulose aerogel was confirmed by FTIR spectroscopy, as shown in Figure 6. The FTIR spectrum of SCA showed four new peaks compared to the spectrum of the uncoated aerogel. The absorption bands at ~731 cm−<sup>1</sup> and ~1269 cm−<sup>1</sup> were attributed to the stretching and bending vibrations of the C–Si linkage, respectively. This confirmed the condensation of silane on the CA surface. In addition, the peak at 1720 cm−<sup>1</sup> on the SCA spectrum was assigned to the characteristic vibrations of the carbonyl group of MEMO silane attached to the aerogel surface. The absorption band at ~815 cm−<sup>1</sup> was attributed to the vibration of the Si-O-Si linkage, which might have formed due to the self-condensation of the silanols.

**Figure 6.** FTIR spectrums of cellulose aerogel and cellulose aerogel (CA) silanization with MEMO silane (SCA).

Silanization was confirmed by energy dispersive X-ray spectroscopy (EDX). The EDX spectrum of the uncoated CA revealed carbon and oxygen peaks but no silicon peak. After silanization, EDX showed peaks for carbon, oxygen, and silicon, as shown in Figure 7.

**Figure 7.** Energy dispersive X-ray spectroscopy (EDX) spectrum of (**a**) cellulose aerogel (CA) and (**b**) cellulose aerogel silanization with MEMO silane (SCA).
