## 3 Results
### Phosphate Anion
However, only the triply degenerate v\({}_{3}\) (\(F_{2}\)) and v\({}_{4}\) (\(F_{2}\)) modes are infrared active. The observation of the v\({}_{1}\) mode must be due to either the presence of some nitrate or carbonate instead [19]. In contrast, [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [53], in a paper a year earlier, claimed the presence of not only PO4\({}^{3-}\) in the interlayer space but also HPO4\({}^{2-}\). Though the spectrum provided is of rather low quality and they do not show the band fit, they claim that the broadband in the 1020 cm\({}^{-1}\) region consists of the v\({}_{3}\) vibrational mode of PO4\({}^{3-}\) anion and two additional bands assigned to the v\({}_{3}\) and v\({}_{2}\) modes of HPO4\({}^{2-}\) anion [57]. In contrast, [PERSON], [PERSON], [PERSON] and [PERSON] [52] assigned the bands at 1045 cm\({}^{-1}\) and 565 cm\({}^{-1}\) corresponding to the v\({}_{3}\) and v\({}_{4}\) band vibrations of HPO4\({}^{2-}\) or H\({}_{2}\)PO4\({}^{-}\) without further explanation. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [22] reported only a single band at 1088 cm\({}^{-1}\) attributed to the vibration of P-O. [PERSON] et al. [58] reported that three bands attributed to HPO4\({}^{2-}\) coalesce into a single broad band around 1056 cm\({}^{-1}\). In addition, a shoulder band was detected at 870 cm\({}^{-1}\) near the theoretical antisymmetric stretching mode of P-OH. Others also described the characteristic band related to phosphate in the interlayer of Zn/Al LDH at 1040 cm\({}^{-1}\)[59] and 1048 cm\({}^{-1}\)[60]. In earlier work, we reported on the Raman spectra of phosphate-LDH and addressed the possibility of determining the presence of H\({}_{2}\)PO4\({}^{-}\) and HPO4\({}^{2-}\) in addition to PO4\({}^{3-}\)[17]. The Raman spectra will change if hydrogen is linked to the phosphate unit as the symmetry will change from \(T_{d}\) to C\({}_{3v}\) to C\({}_{2v}\). This will cause a loss of degeneracy, and other bands may become visible. The sample synthesized at pH 12.5 exhibited a strong, sharp band at 960 cm\({}^{-1}\) with a broader band at 1026 cm\({}^{-1}\) assigned to the PO4\({}^{3-}\) symmetric and antisymmetric stretching vibrational modes identical to that of the PO4\({}^{3-}\) ion. Similar bands were observed for the pH 11.9 sample at 957 cm\({}^{-1}\) and 1032 cm\({}^{-1}\). [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [54] reported the formation of bands in the region between 940 cm\({}^{-1}\) and 960 cm\({}^{-1}\) after exchange with phosphate. Slight changes were also detected in the band positions in the 1050 cm\({}^{-1}\) region. A different Raman spectrum was obtained for the pH 9.3 sample with four bands at 964, 989, 1033 and 1138 cm\({}^{-1}\). In aqueous systems, the PO4\({}^{3-}\) ion has a strong band at 936 cm\({}^{-1}\), while HPO4\({}^{2-}\) anion exhibits a strong band at 990 cm\({}^{-1}\). Therefore, the spectrum can be interpreted as a combination of the PO4\({}^{3-}\) anion (964 and 1033 cm\({}^{-1}\)) and the HPO4\({}^{2-}\) ion (989 and 1138 cm\({}^{-1}\)). However, it is questionable whether these are actually present in the interlayer space of LDH, as XRD showed the material mainly as amorphous. For the oxyanion PO\({}_{4}\)[3]- the symmetric bending mode (v\({}_{2}\)) and the v\({}_{4}\) mode are observed at 420 cm\({}^{-1}\) and 567 cm\({}^{-1}\), respectively. For the phosphate LDH at pH 12.5, a band of 474 cm\({}^{-1}\) was observed. A similar band was found at 472 cm\({}^{-1}\) for the pH 11.9 sample, while a broad band around 441 cm\({}^{-1}\) was present in the Raman spectrum of the pH 9.3 sample. Infrared and Raman spectroscopy of phosphate-LDH has shown that the nature of the anion present in the interlayer space is affected by the synthesis conditions. In this study, three different pH values were studied despite the fact that in the literature, the presence of H\({}_{2}\)PO\({}_{4}\)\({}^{-}\) and HPO\({}_{4}\)\({}^{2-}\) have been claimed [52; 53].