## 3 Results and Discussion
### Kinetic Study of WPET-SiAMPy Chelating Adsorbent Nanofibres
#### 3.4.3 The Mechanism of Cu-WPET-SiAMPy Complex Formation Reaction  
The theoretical study on the mechanism of reaction of the Cu-WPET-SiAMPy complex formation was based on three things: the data of the reaction kinetics, of the obtained value of coordination number n and from the value of the rate constant \(k\). The mole ratio of Cu\({}^{2+}\) and WPET-SiAMPy nanofibres was 1:2 based on the overall equation. Based on this comparison, then the complex molecular formula formed was Cu(WPET-SiAMPy)\({}_{2}\) with a square planar geometry structure. The mechanism of formation for complex compounds Cu(WPET-SiAMPy)\({}_{2}\) is:  
\[\text{Cu}^{2+}+\text{WPET-SiAMPy}^{-}\rightarrow[\text{Cu(WPET-SiAMPy}]^{+}\]  
\[[\text{Cu(WPET-SiAMPy}]^{+}+\text{WPET-SiAMPy}^{-}\rightarrow\text{Cu(WPET-SiAMPy )}_{2}\]  
Then, the overall reaction is:  
\[\text{Cu}^{2+}+\text{2 WPET-SiAMPy}^{-}\rightarrow\text{Cu(WPET-SiAMPy)}_{2}\]  
Based on the results, it can be determined that the complex molecular formula is Cu(WPET-SiAMPy)\({}_{2}\) and this is in accordance with the kinetic data. Another fact that supports the above reaction mechanism is the value of \(k\), which is 0.0888:  
\[\text{Rate}=k[\text{Cu}^{2+}][\text{WPET-SiAMPy}^{-}]\]  
The Cu(WPET-SiAMPy)\({}_{2}\) complex compound is theoretically expected to have four coordination numbers based on the valence bond theory. This was previously proven by [PERSON] et al. when analysing the Cu\({}^{2+}\) loaded Si-AMP-M-H with X-ray photoelectron spectroscopy (XPS), compared with the unloaded Si-AMP-M-H [30]. The XPS survey scan spectra showed major peaks in Si-AMP-M-H which were Si\({}_{2p}\), O\({}_{1s}\), C\({}_{1s}\), and N\({}_{1s}\). The XPS analysis simultaneously demonstrated the Cu\({}_{2p}\) and S\({}_{2p}\) peaks in Cu\({}^{2+}\) loaded Si-AMP-M-H. This proves the legitimacy of the Cu\({}^{2+}\) ions adsorbed onto the Si-AMP-M-H surface which was accompanied by SO\({}_{4}\)\({}^{2+}\) ions, indicating that the neutral ligands form charged chelates with metal ions while anions are co-adsorbed as counter-ions to maintain electro-neutrality in both the Cu\({}^{2+}\) aqueous phase and the WPET-SiAMPy solid phase [57]. This study was supported by research showing that the Cu\({}^{2+}\) ion has an electron configuration of 1s\({}^{2}\) 2s\({}^{2}\) 2p\({}^{6}\) 3s\({}^{2}\) 3p\({}^{6}\) 3d\({}^{9}\); thus, it is possible to form the coordination bond between the bidentate ligand and the central atom and obtain sp3 tetrahedron orbitals [58]. The Cu\({}^{2+}\) ion consists of a d\({}^{9}\) configuration and is known to form 1:1 and 1:2 complexes with the AMP chelating ligands [59]. This was supported by [PERSON] et al. who reported the silica-based 2-aminomethylpyridine functionalized adsorbent for the hydrometallurgical extraction of low-grade copper ore and formed a 2:1 AMPy-Cu(II) complex ratio [60]. In this research, the Cu\({}^{2+}\) ions formed 1:2 complexes as seen in the overall reactions; however,  
Figure 14: Cu\({}^{2+}\) complexation with the WPET-SiAMPy nanofibres in aqueous solution.  
[PERSON] et al. reported that the Cu\({}^{2+}\) complex CuWRAM was closer to a 1:1 ratio than a 1:2 complex because of the steric hindrances and mobility limitations of AMP incorporated in the silica matrix [59]. Theoretically, it can be expected that the Cu complex species will have a Cu molecular formula (WPET-SiAMPy)\({}_{2}\) with square planar \(\text{dsp}^{2}\) hybridization.