## 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 adsorption capacity fluctuated for the unmodified nanofibres adsorbent (WPET), the Cu\({}^{2+}\) recovery declined from 5 to 10 min of adsorption and increased from 10 to 20 min, only to further decline from 20 to 90 min and slightly increased from 90 to 120 min. The adsorption capacity using all the material, respectively, reached the adsorption equilibrium at 1 min, with the fluctuation of the copper binding capacity of the unmodified nanofibres. The PET and WPET nanofibres achieved only 0.06 mmol/g and 0.05 mmol/g in the first minute with a low adsorption capacity of 0.07 mmol/g noticed at 60 min for PET and 0.08 mmol/g noticed at 20 min for WPET. The 1 min was set as the necessary time needed to attain equilibrium for the modified nanofibre adsorbents. The fast adsorption during the first minute was related to the large amount of active vacant adsorption sites of the SiAMPy incorporated into the nanofibres (see kinetic study in Section 3.4). The obtained average adsorption efficiency results in Figure 6 showed that the modified WPET using the chelating ligand SiAMPy had the highest Cu\({}^{2+}\) metal ion binding capacity compared to that of the PET-SiAMPy because the WPET nanofibres had more SiAMPy compared to PET nanofibre as seen in Figure 1e,f, indicating that the WPET-SiAMPy had an enlarged surface area compared to PET-SiAMPy and therefore more Cu\({}^{2+}\) adsorption sites. The adsorption performance occurred rapidly when the number of available sites was greater than the number of Cu\({}^{2+}\) ions to be adsorbed. In the initial stage of adsorption, there is excess active adsorption sites vacant on the adsorbent surface for Cu\({}^{2+}\) recovery. Thereafter, the adsorption rate dropped slightly due to the aggregation of Cu\({}^{2+}\) metal ions on adsorbent nanofibres or more likely on excess adsorption sites. Thus, the active sites of WPET-SiAMPy nanofibres were fully exposed to Cu\({}^{2+}\) ions in aqueous solution, causing the rapid saturation of the surface and yielding high adsorption capacity as seen in Figure 6. The Cu\({}^{2+}\) recovery rate demonstrated the high rate of binding kinetics, thus suggests that the WPET-SiAMPy composite nanofibres has very high adsorption efficiency and thus has high potential in Cu\({}^{2+}\) recovery. The modification of WPET polymers using the SiAMPy was beneficial in Cu\({}^{2+}\) adsorption efficiency, as the SiAMPy was previously proven to be selective for Cu\({}^{2+}\)[28]. The WPET-SiAMPy composite nanofibres showed  
Figure 5: Effect of contact time on the recovery of Cu\({}^{2+}\) from aqueous solution using (**a**) PET, WPET; and (**b**) PET-SiAMPy and WPET-SiAMPy nanofibres (Cu\({}^{2+}\) concentration 100 mgL\({}^{-1}\), pH 5, dosage 0.01 g). high Cu\({}^{2+}\) uptake of 1.24 mmol/g (96.04%). This research agrees with the efficient activity of the 2-aminomethylpyridine resin (AMPy) which could only achieve 0.22 mmol/g Cu uptake on its own [29]. Incorporating it into nanofibres significantly improved the Cu\({}^{2+}\) adsorption capacity, which is in agreement with the adsorption capacity achieved using the fixed-bed column adsorption process for the deep removal of Cu\({}^{2+}\) from simulated cobalt electrolyte with polystyrene-supported 2-aminomethylpyridine chelating resin [30].