*3.1. Characterization Studies of Alkaline Treated C. pentandra Fiber*

The surface morphology of untreated *C. pentandra* fiber was observed using SEM analysis. The smooth surface of untreated *C. pentandra* fiber in the SEM images at different magnification is observed in Figure 3a,b. After alkaline treatment, it clearly showed the treated *C. pentandra* fiber have rougher, more flaky or grooved surface and less attached as seen in Figure 3c,d, respectively. The plant fiber surface becomes rougher and compressed due to the collapse of the lumen structure and removal of the hemicellulose and lignin covered on the cellulose region [24,25]. It is assumed that in the absence

of hemicellulose and lignin-containing compositions on the fiber surface enhances the compatibility between fiber and matrix for the deposition of metal nanoparticles [26].

**Figure 3.** SEM images of (**a**,**b**) untreated *C. pentandra* fiber and (**c**,**d**) treated *C. pentandra* fiber at 6000× and 50,000× magnification, respectively.

The EDX spectra of untreated *C. pentandra* fiber show the major peak of Carbon (C) and Oxygen (O) elements with a percentage of 57.9% and 36.9%, respectively as shown in Figure 4a. These elements are attributed to the hemicellulose and cellulose as the main compositions in the untreated *C. pentandra* fiber. For the EDX spectra of treated *C. pentandra* fiber, besides the C (47.6%) and O (47.4%) as the major element, Na peak appeared at 1.0 KeV with a percentage of 3.8% as shown in Figure 4b. This peak was due to the treatment of *C. pentandra* fiber with NaOH solution. The peak of platinum (Pt) (1.2%) also appeared for both untreated and treated *C. pentandra* fiber due to the fiber was coated with the platinum for the analysis. The percentage of oxygen was increased from 36.9% to 47.4% after alkaline treatment proved that the increased of oxygen density after alkaline treatment. This was due to the disruption of the fiber clusters, removing the hemicellulose and lignin covered on the cellulose region [9,27].

**Figure 4.** EDX spectra of (**a**) untreated *C. pentandra* fiber and (**b**) treated *C. pentandra* fiber.

The porosity of the treated *C. pentandra* fiber was further confirmed using surface area analysis based on Langmuir plots. The values of SL surface area obtained for untreated *C. pentandra* fiber was 33.96 m2/g. However, after treated with the alkaline solution, the treated *C. pentandra* fiber showed the values of *S*<sup>L</sup> surface area was increased to 49.65 m2/g. This result proved that the porosity of treated *C. pentandra* fiber was increased after treatment and also increased the surface area of *C. pentandra* fiber. The large surface area of treated *C. pentandra* fiber assisted the deposition of Ag-NPs in the fiber surface.

The decomposition profile of absorbed water, hemicellulose, cellulose and lignin-containing in *C. pentandra* fiber are depending on their weight compositions. The initial decomposition peak of fibers at a lower temperature (25 to 150 ◦C) is corresponding to the vaporization of absorbed water in the samples [7,25]. According to [28], hemicellulose starts to decompose at 220–315 ◦C, while the temperature range of 315–400 ◦C corresponds to the cellulose decomposition. However, lignin is decomposed at a wider temperature range (200 to 720 ◦C) [29]. The TGA and derivative thermogravimetry DTG curves of untreated *C. pentandra* fiber and treated *C. pentandra* fiber as a function of temperature are shown in Figure 5. The initial decomposition peak of untreated *C. pentandra* fiber approximately at ~100 ◦C (5%) is corresponding to vaporization of absorbed water in the samples as shown in Figure 5a. The main *C. pentandra* fiber decomposition occurred at perature around 200–370 ◦C. This peak region is corresponding to the peak of hemicellulose and lignin [25]. The weight loss of treated *C. pentandra* fiber was slightly decreased than untreated *C. pentandra* fiber from 71% to 69%, respectively. The DTG curve also showed the main *C. pentandra* fiber decomposition occurred in the region from 200–370 ◦C. The DTG peak was shifted from 320 to 341 ◦C for untreated and treated *C. pentandra* fiber, respectively corresponding to the cellulose decomposition. This result proved that the base treatment removed the hemicellulose and lignin in the *C. pentandra* fiber and exposed cellulose crystalline region for the attachment of Ag-NPs. The DTG curves of untreated *C. pentandra* fiber also show the small peak of decomposition at 221 ◦C. This peak is corresponding to the hemicellulose decomposition of untreated *C. pentandra* fiber. This peak is in line with the invisible peak at this region suggesting the removal of hemicellulose of the treated *C. pentandra* fiber during the alkaline treatment. In addition, a more intense peak was observed at 320 ◦C was due to the decomposition of hemicellulose and lignin. This finding proved that the removal of these compositions during the alkaline treatment to increase the roughness of *C. pentandra* fiber surface and increased the reactive site exposed on the surface for loading of Ag-NPs. The same observation was also reported by Fiore et al. [7], who reported that the removal of hemicellulose from the fiber after treated with NaOH solution. In Figure 5b, the degradation at 390–628 ◦C show slightly increased to 23% weight loss in comparison with untreated *C. pentandra* fiber corresponding to the increasing number of the macromolecules of *C. pentandra* fiber making it difficult to degrade at a higher temperature only and increased the thermal stability of treated *C. pentandra* fiber. A similar finding was reported by Komal et al. [30] proved that the effective removal of hemicellulose and waxes present on the surface of plant fiber resulted in the enhancement of the thermal stability of plant fiber after alkaline treatment.

**Figure 5.** TGA and DTG curves of (**a**) untreated *C. pentandra* fiber and (**b**) treated *C. pentandra* fiber.

*3.2. In-Situ Biofabrication of Ag-NPs in C. pentandra Fiber(C. pentandra*/*Ag-NPs)*

The success of treated *C. pentandra* fiber incorporated with Ag-NPs can be preliminarily determined visually based on the color of the fiber. The photograph showed that the color of treated *C. pentandra*/Ag-NPs was changed to brown after the bio-fabrication process as shown in Figure 6. The schematic illustration of predicted mechanisms of Ag-NPs got in-situ deposited in the *C. pentandra* fiber also shown in Figure 6. This happened might be due to the interaction of Ag<sup>+</sup> ions

with the functional groups like hydroxyl, carbonyl, ether, aldehyde and acetyl groups that is present in the cellulose of *C. pentandra* fiber and terpenoidal saponin compound of *E. spiralis* extract. The addition of *E. spiralis* extract in the bio-fabrication process help to control the size, shape and stability of Ag-NPs loaded into treated *C. pentandra* fiber.

**Figure 6.** Schematic illustration predicted the formation of in-situ bio-fabrication of Ag-NPs using *E. spiralis* extract in *C. pentandra* fiber.
