Figure 1. SEM images of (a) nano CaCO3, (b)
cellulose, (c) cellulose/CaCO3-0.5, (d)
cellulose/CaCO3-1 membranes and (e, f) corresponding
high magnification images.
Hydrolysis treatment is beneficial to enhance the electrolyte
wettability of porous membranes, leading to good electrochemical
performance. The reason is that acetyl groups in the CA molecular chain
are hydrolyzed under strongly alkaline conditions, and the hydrophobic
acetyl groups disappear to form hydrophilic hydroxyl groups.[34] The
FTIR was used to verify the complete hydrolysis of CA and the successful
introduction of calcium carbonate. The spectra of CA and
cellulose/CaCO3 membrane are presented in Figure
2a . It is obvious that the CA membrane exhibits a weak -OH peak at 3450
cm-1 and -CH3 stretching vibrations
peaks at 2962 cm-1 and 2872
cm-1.[35] Besides, the C=O and C-O characteristic
peaks can be seen at 1750 cm-1 and 1180
cm-1, respectively. Compared to the CA membrane, all
cellulose membranes show a strong and broad -OH peak at 3361
cm-1 and the C=O absorption peak at 1743
cm-1 disappeared, demonstrating the complete
hydrolysis of CA. What’s more, with the addition of
CaCO3, the bending vibration peak of carbonate appears
at around 874 cm-1 and the intensity of this peak
increases as the content of CaCO3 elevates.[36] From
all above, the CaCO3 was introduced to the CA membrane
successfully.
Figure 2b shows the XRD patterns of porous membranes. The peaks
at 20.4° and 21.8° correspond to the diffraction peaks of cellulose. The
crystalline peak of CaCO3 locates at 29.5°. With the
increasing content of CaCO3, the crystalline peak at
29.5° became sharper, and the corresponding CaCO3 peaks
at 35.9° as well as 39.5° appeared.[37] However, the introduction of
CaCO3 had little effect on the crystallinity of
cellulose.