*2.5. Silver Content Analysis and Silver Ions Release of C. pentandra*/*Ag-NPs*

The amount of silver (Ag) content in the *C. pentandra*/Ag-NPs was determined using the method proposed by Rehan et al. [15]. The Ag content in *C. pentandra*/Ag-NPs was extracted by immersing 0.2 g dried *C. pentandra*/Ag-NPs with 20 mL of 15% aqueous nitric acid in a conical flask. The mixture was immersed for 2 h in a water bath shaker at 80 ◦C. After immersed, the filtrate was filtered on Whatman No. 42 filter paper and the Ag<sup>+</sup> ions concentration was measured using Inductively Coupled Plasma Optical Emissions Spectrophotometer (ICP-OES) (Avio 500, Perkin Elmer, Medtech Park, Singapore) at 328.1 nm wavelength. The Ag content in the *C. pentandra*/fiber sample was calculated using Equation (1):

$$\frac{\mathbb{C} \times V}{\left[ W \times \left( 1 - \frac{\text{MC}}{1000} \right) \right]} = X \tag{1}$$

where *X* is the Ag content in the fiber (g/kg), *C* is the Ag<sup>+</sup> ions concentration (mg/L) in extracted solution; *V* is the volume of the extracted solution (L); *W* is the weight of dried *C. pentandra*/Ag-NPs (g); *MC* is the moisture content in dried *C. pentandra*/Ag-NPs (%). The *MC* of *C. pentandra*/Ag-NPs was measured using an oven drying method (method No. 44-15A) as followed by Hussain et al. [16]. The *C. pentandra*/Ag-NPs sample was conditioned at ambient temperature for 24 h. The conditioned sample was then dried in the oven at 105 ◦C for 2 h. Equation (2) was used to calculate the percentage of moisture content as shown below:

$$\text{Moisture} \left( \% \right) = \frac{W\_b - W\_d}{W\_b} \times 100 \tag{2}$$

where *Wb* is mass of the sample and *Wd* is mass of the *C. pentandra*/Ag-NPs after dried in the oven.

The release rate of silver ions from *C. pentandra*/Ag-NPs was investigated by following the method by Zhang et al. [17] and Liu et al. [18]. A mass of 0.05 g of each sample of *C. pentandra*/Ag-NPs at different stirring reaction times (6–144 h) was put into 50 mL of deionized water in the different conical flasks. The mixture was shaken in a water bath shaker at 105 stroke/min and at room temperature. During the shaking time process, 10 mL solution was withdrawn from the release media and another 10 mL of fresh deionized water was added at time intervals of 6, 12, 24, 48, 72 and 96, 120, 144 h. The amount of released Ag<sup>+</sup> ions was measured using ICP-OES at 328.1 nm wavelength. The procedure was repeated for the sample of *C. pentandra*/Ag-NPs and the results were compared. The experiments

were conducted in duplicate and the results were reported in average value. The percentage of Ag<sup>+</sup> ions release rate was calculated using Equation (3) as below:

$$\text{Iors release rate } \left( \% \right) = \frac{\mathcal{C}\_b - \mathcal{C}\_a}{\mathcal{C}\_b} \times 100 \tag{3}$$

where *Cb* and *Ca* are Ag<sup>+</sup> ions concentration before and after adsorption (mg/L), respectively.
