3.3.6. FTIR Analysis

The functional groups of cellulose, hemicellulose and lignin in the *C. pentandra* fiber can be analyzed using FTIR analysis. Generally, the cellulose fiber structure consists of carbonyl, carboxyl and aldehyde groups [32]. These compositions untreated and alkaline treated on *C. pentandra* fiber were investigated based on the peak shifting of the related functional groups in the FTIR spectra. The FTIR spectra of untreated *C. pentandra* fiber appeared its absorption bands were at 3346, 2918, 1736, 1314, 1238, 1037 and 604 cm−<sup>1</sup> as shown in Figure 13a. The peak at 3346 cm−<sup>1</sup> is responsible for the hydroxyl group stretching of the hydrogen bonding network. At the peak of 2918 cm−<sup>1</sup> is related to the functional groups of C–H stretching vibration of methyl and methylene groups in cellulose or hemicellulose structure [33]. The peak at 1736 cm−<sup>1</sup> is corresponding to the C=O stretching vibration of hemicellulose [25]. The peak at 1314 cm−<sup>1</sup> is corresponding to the C–H bending of aldehyde groups of cellulose structure. The peak at 1238 cm−<sup>1</sup> is corresponding to the C–O stretching of the acetyl groups in the hemicellulose. The peak at 1037 cm−<sup>1</sup> is responsible for due to the presence of xylane and the glycosidic linkages of hemicellulose [25]. The peak at 604 cm−<sup>1</sup> related to the bonding of oxygen from the hydroxyl groups.

After alkaline treatment of *C. pentandra* fiber, the FTIR spectrum showed the shift in wavenumber or changes in peak intensity explains the types of functional groups involved in the fiber as shown in Figure 13b. The treated *C. pentandra* fiber showed the peak shifted from 3346 to 3337 cm−<sup>1</sup> suggests the hydroxyl group stretching of the hydrogen bonding network in the treated *C. pentandra* fiber. The peak at 2899 cm−<sup>1</sup> was shifted from 2918 cm−<sup>1</sup> for untreated *C. pentandra* fiber suggests the C–H stretching vibration of methyl and methylene groups in the cellulose structure [25]. The peak 1735 cm−<sup>1</sup> in the untreated *C. pentandra* fiber was disappeared in the treated *C. pentandra* fiber spectra was due to the removal of hemicellulose after alkaline treatment. The peak 1314 cm−<sup>1</sup> of untreated *C. pentandra* fiber was shifted to 1321 cm−<sup>1</sup> suggesting C–H bending of aldehyde groups of cellulose structure of treated *C. pentandra* fiber. The intensity of the peak at 1280 cm−<sup>1</sup> was decreased after alkaline treatment suggesting that the C–O stretching of the acetyl groups. The peak at 1037 cm−<sup>1</sup> of untreated fiber was shifted to 1027 cm−<sup>1</sup> with strong peak intensity relate to the presence of xylane and the glycosidic linkages. This major peak shifted can be related to the removal of the hemicellulose structure of treated *C. pentandra* fiber after alkaline treated. This result supported the finding in TGA analysis asserted that the hemicellulose of *C. Pentandra* fiber was removed after alkaline treatment. The peak shifted at 560 cm−<sup>1</sup> is related to the bonding of oxygen from the hydroxyl groups.

**Figure 13.** Fourier Transform Infrared (FTIR) spectra of (**a**) untreated *C. pentandra* fiber, (**b**) treated *C. pentandra* fiber and (**c**) *C. pentandra*/Ag-NPs.

The FTIR spectrum of *C. pentandra*/Ag-NPs showed the absorption bands at 3335, 2900, 1307, 1028 and 526 cm−<sup>1</sup> as shown in Figure 13c. After loaded with Ag-NPs, the peak shifted to the 3335 cm−<sup>1</sup> suggesting to the hydroxyl group stretching of the hydrogen bonding network. The peak shifted to the 2899 cm−<sup>1</sup> suggesting the C–H stretching vibration of methyl and methylene groups in cellulose and hemicellulose structure. The cellulose structure has an aldehyde group (–CHO) which was oxidized to carboxylic acid, while Ag<sup>+</sup> ion was reduced to Ag-NPs. This mechanism caused the incorporation of Ag-NPs in *C. pentandra* fiber by strong attachment between Ag-NPs and *C. pentandra* fiber. The peak at 1280 cm−<sup>1</sup> in the treated *C. pentandra* fiber was disappeared suggesting that the involvement of C–O stretching of the acetyl groups in the hemicellulose for loading Ag-NPs into *C. pentandra* fiber. The peak intensity at 1028 cm−<sup>1</sup> was decreased after loaded with Ag-NPs suggesting the C–OH of a primary group of the gluco–pyranose ring. The peak shifted at 526 cm−<sup>1</sup> is related to the bonding of oxygen from the hydroxyl groups in the *C. pentandra* fiber. The FTIR analysis shows the functional groups of *C. pentandra* fiber cellulose structures which consist of carbonyl, carboxyl and aldehyde groups. These functional groups are responsible for the reduction of Ag<sup>+</sup> ions to Ag-NPs.
