## 3 Results and Discussion
### Characterization of the Zeolite Samples
#### 3.1.6 Raman Analysis  
The Raman spectra of fresh, P-adsorbed and P-desorbed iron-Z-A have been shown in Figure 6. The Raman analysis of phosphate adsorbed Iron-Z-A showed changes in the peak position and intensity as compared with the pristine Iron-Z-A. The peak at 200 cm\({}^{-1}\) region, T\(-\)O\(-\)T angle at 490 cm\({}^{-1}\), and asymmetric stretching at 1000\(-\)1100 cm\({}^{-1}\) region in all the three samples is due to characteristic stretching and bending of Z-A. The bands between 650 and 750 cm\({}^{-1}\) are due to the presence of a double four rings (D4R) of Z-A [52]. The bands at 800-900 cm\({}^{-1}\), 500 cm\({}^{-1}\) regions, and 1250-1350 cm\({}^{-1}\) region show P\(-\)O\(-\)P bridges, bending vibrations of P\(-\)O bonds, and P\(=\)O stretching respectively [53], where the intensity of band increases at 800\(-\)900 cm\({}^{-1}\) and decreases at 1300 cm\({}^{-1}\) with the increase in phosphate content. The peaks observed at 1300 cm\({}^{-1}\) and 1600 cm\({}^{-1}\) in all the three samples claims the formation of Fe\({}_{2}\)O\({}_{3}\) in the zeolite structure [54; 55]. In the region of 1250 and 1350 cm\({}^{-1}\), it showed symmetric stretching of P\(-\)O [53]. The change in peak's intensity in the region of 1300 cm\({}^{-1}\) of P-adsorbed and P-desorbed Z-A is due to the formation of Fe-O-P bond. In P-adsorbed Z-A, there is a rise in the intensity of the band centered at 1104 cm\({}^{-1}\) was due to the peaks of adsorbed PO\({}_{4}\)\({}^{3-}\) appeared in the range of 800-900 cm\({}^{-1}\) and thus broadened the band, whereas we can see the absence of any peak in the same region 850-900 cm\({}^{-1}\), due to desorption of PO\({}_{4}\)\({}^{3-}\) from iron-Z-A. The spectrum of phosphate desorbed iron-Z-A showed a noteworthy shift (from 1004 cm\({}^{-1}\) to 1050 cm\({}^{-1}\)) along with increased intensity for the interlayer anion band. The RRUFF database proves that the peaks near 400 cm\({}^{-1}\) and between 1200 cm\({}^{-1}\) and 1400 cm\({}^{-1}\) in the fresh, P-adsorbed, and P-desorbed Iron-Z-A are due to Fe\({}_{2}\)O\({}_{3}\) in the zeolite framework [56].  
coefficients of correlation applied to both the adsorption isotherm models are also presented in Table 2. [PERSON]'s isotherm demonstrated a better fit than that of [PERSON]'s isotherm with higher correlation coefficient values. In addition, the value of \(\mathsf{Q}_{\mathsf{m}}\) was also significantly high in the case of [PERSON], as compared to [PERSON], whose \(\mathsf{Q}_{\mathsf{m}}\) values are found to be negative. This result indicated that the phosphate is uniformly adsorbed on the adsorbent's surface, and the adsorbed adsorbate's amount depends on the dosage of adsorbent or the exposed adsorbent's surface, irrespective of phosphate concentration.  
By considering the amount of \(\mathsf{PO}_{4}\)[3]- being adsorbed by Z-A (only Al) and iron-Z-A (Fe + Al), we calculated the amount \(\mathsf{PO}_{4}\)[3]- being adsorbed by Fe and Al individually. From Table 3, it is clear that the adsorption capacity \(\mathsf{PO}_{4}\)[3]- increased seven times by adding Fe to the Z-A framework.  
It can easily be calculated from the above data that the amount of P captured by Fe is greatly high or ten folds higher than that of Al. These results are considered consistent with the results perceived in the adsorption kinetics study.