## 3 Results and Discussion
### Adsorption Studies of Cu\({}^{2+}\) Metal Ion
#### 3.2.1 Effect of Cu\({}^{2+}\) Aqueous Solution pH Using Modified WPET-SiAMPy Composite Nanofibres  
The effect of aqueous solution pH on Cu\({}^{2+}\) recovery was studied using PET, WPET, and modified nanofibres (WPET-SiAMPy composite nanofibres). The Cu\({}^{2+}\) aqueous solution pH experiments were made up to pH 6 in order to prevent the precipitation of the Cu\({}^{2+}\) (see Figure 4). The experiments were carried out in 100 mL of 100 mgL\({}^{-1}\) of Cu\({}^{2+}\) aqueous solution using 0.01 g of the nanofibres dosage by manually adjusting the Cu\({}^{2+}\) aqueous solution with 0.1 M of HNO\({}_{3}\) or NaOH solution to the desired pH value (1, 2, 3, 4, 5 and 6). The equilibrium data shown in Figure 4 were correlated using adsorption capacity (q\({}_{e}\)) Equation (1). Figure 4 shows the pH for optimum adsorption when the modified nanofibres (WPET-SiAMPy) were exposed to 100 mgL\({}^{-1}\) of Cu\({}^{2+}\) metal ions in the solution at pH 1 to 6. The results show that the adsorption capacity increased as the pH was increased from 1 to 2. The adsorption capacity started to decline after pH 2 until pH 4 and increased at pH 5 achieving 1.30 mmol/g using WPET-SiAMPy nanofibres. The decline in the Cu\({}^{2+}\) binding capacity may be due to the hydrogen (H\({}^{+}\)) ions being more dominant than Cu\({}^{2+}\) ions in an aqueous solution [26]. The adsorption capacity gradually increased as the pH of the Cu\({}^{2+}\) aqueous solution increased from 5 to 6 with the adsorption capacity for Cu\({}^{2+}\) of 0.04 mmol/g (PET) or 0.046 mmol/g (WPET) at pH 5. Above pH 7, the Cu\({}^{2+}\) aqueous solution is more alkaline, thus, Cu\({}^{2+}\) ions start to precipitate and form hydroxides (Cu(OH)\({}_{2}\)) [27]. Thus, pH 5 was confirmed as the optimum pH for further adsorption studies in this research. 2.2 Effect of Cu\({}^{2+}\) Contact Time Using the Modified PET-SiAMPy or WPET-SiAMPy Composite Nanofibres  
The effect of contact time on Cu\({}^{2+}\) recovery by the modified chelating adsorbent nanofibres (PET-SiAMPy or WPET-SiAMPy) was studied over different contact times of 1, 5, 10, 20, 30, 60, 90, and 120 min. The main objective in the recovery of Cu\({}^{2+}\) using the modified chelating adsorbents is the improved adsorption rate at shorter period of adsorption time to reach equilibrium. The adsorption capacity (q\({}_{e}\)) calculated according to Equation (1) of the modified chelating adsorbent nanofibres was analysed as shown in Figure 5. The adsorbate results of this experiment were used for comparison in further adsorption experiments. The effect of contact time on the recovery of Cu\({}^{2+}\) metal ions by the PET, WPET, PET-SiAMPy, and WPET-SiAMPy nanofibres is shown in Figure 5--showing that low adsorption occurred over time for PET or WPET but high adsorption was attained within the first minute using the modified WPET-SiAMPy composite nanofibre adsorbent. It was found that the adsorption of Cu\({}^{2+}\) ions achieved equilibrium at 1 min. In the first 1 min, the  
Figure 4: Adsorption capacity of Cu\({}^{2+}\) from aqueous solution pH using (**a**) PET, WPET, and (**b**) WPET-SiAMPy nanofibres (Cu\({}^{2+}\) concentration 100 mgL\({}^{-1}\), 120 min, dosage average, 0.01 g). Cu\({}^{2+}\) quantity adsorbed was 1.24 mmol/g (96.04%) of the metal ion concentration present in the Cu\({}^{2+}\) aqueous solution using the chelating adsorbent WPET-SiAMPy composite nanofibres. WPET-SiAMPy composite nanofibres had the fastest adsorption attributed to the amount of the SiAMPy (0.01 wt%) incorporated in WPET-SiAMPy when compared with the unmodified WPET that achieved 0.05 mmol/g adsorption capacity, which is 35.45% Cu\({}^{2+}\) recovery efficiency. The PET-SiAMPy nanofibres achieved 0.98 mmol/g in the first minute of adsorption. The adsorption capacity of the unmodified PET nanofibres reached equilibrium from the first minute of adsorption contact time until the adsorption experiment reached 30 min, where slight fluctuations started.