## 3 Results
### Subplate Anion  
In naturally occurring LDH, other than the commonly present CO\({}_{3}\)[2]- anion, SO\({}_{4}\)[2]- forms an additional important interlayer anion found in minerals such as honessite (Ni\({}_{6}\)Fe\({}_{2}\)SO\({}_{4}\)(OH)\({}_{16}\)-4H\({}_{2}\)O), hydrohonessite (Ni\({}_{6}\)Fe\({}_{2}\)SO\({}_{4}\)(OH)\({}_{16}\)-7H\({}_{2}\)O), and carrboydite ((Ni\({}_{4}\)Cu)\({}_{14}\)Al\({}_{9}\)(SO\({}_{4}\)CO\({}_{3}\))\({}_{6}\)(OH)\({}_{43}\)-7H\({}_{2}\)O) [61; 62; 63]. Figure 6 shows the S 2p and O 1s of sulphate-LDH. The S 2p is characterized by a single S 2p3/1 peak with a BE of 168.3 eV. This BE is slightly lower than observed for common sulfate minerals such as baryte (169.2 eV), anhydrite (168.9 eV), or gypsum (169.2 eV) [45], indicating that the sulfate in the LDH interlayer space is less strongly interacting with the LDH hydroxide layers compared to a sulfate group in a rigid crystal structure. In the O 1s, a single peak at 532.4 eV is associated not only with the oxygen in the sulfate group but also with oxygen in interlayer water that has a similar BE. This value is comparable with H\({}_{2}\)SO\({}_{4}\), which has an O 1s BE of 532.5 eV and Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) of 532.4 eV [51]. Similar results were also reported for group 1A sulfates by [PERSON] and [PERSON] [64]. Figure 6: XPS high-resolution scan of S 2p and O 1s of LDH with phosphate as the interlayer anion. [PERSON] and [PERSON] [61] described for homessite the SO4\({}^{2-}\)\(\
u_{1}\), \(\
u_{2}\), \(\
u_{3}\), and \(\
u_{4}\) infrared active modes at 980, 500, 1140, and 650 cm\({}^{-1}\), respectively. The \(\
u_{3}\) mode is obviously split, though no separate band positions were provided. Since all four modes are infrared active, the symmetry of the SO4\({}^{2-}\) anion was lowered from \(T_{d}\) (free anion) to either \(C_{3}\) or \(C_{3v}\), causing the activation of the two infrared inactive modes together with the splitting of the \(\
u_{3}\) mode ([65], p. 140). Earlier work in our group has shown that the infrared spectrum of Mg/Al-LDH containing SO4\({}^{2-}\) in the interlayer space exhibits a strong but broad \(\
u_{3}\) mode at 1126 cm\({}^{-1}\), a \(\
u_{4}\) mode at 614 cm\({}^{-1}\), and a very weak \(\
u_{1}\) mode at 981 cm\({}^{-1}\)[19]. The \(\
u_{2}\) mode was not observed as a distinct band, in contrast to homessite and hydroninesite, due to its overlap with the O-M-O bending vibration of the LDH hydroxide layer around 450 cm\({}^{-1}\)[66]. [PERSON] and [PERSON] [67] reported only a band at a significantly lower wavenumber position around 1066 cm\({}^{-1}\), which was attributed to the bending mode of interlayer sulfate ions. [PERSON] and [PERSON] [68] described a single band for Zn/Al-LDH at 1113 cm\({}^{-1}\), which is much closer to the value observed by [PERSON], [PERSON], [PERSON] and [PERSON] [19]. [PERSON] et al. [69] described for glaucocerinite (Zn,Cu)\({}_{10}\)Al\({}_{6}\)(SO4)\({}_{3}\)(OH)\({}_{32}\):18H\({}_{2}\)O, a naturally occurring LDH mineral, three strong bands at 1053, 1078 and 1109 cm\({}^{-1}\), which was attributed to the SO4\({}^{2-}\)\(\
u_{3}\) antisymmetric stretching mode. A weak band at 986 cm\({}^{-1}\) was assigned to the corresponding \(\
u_{1}\) symmetric stretching mode. They also reported that carbyodite exhibited three similar bands at 1088, 1021 and 978 cm\({}^{-1}\), with the first two bands due to \(\
u_{3}\) antisymmetric stretching modes and the last band to the \(\
u_{1}\) symmetric stretching mode. [PERSON], [PERSON], [PERSON] and [PERSON] [19] showed that the Raman spectrum of sulphate-LDH consisted of a very intense \(\
u_{1}\) mode at 982 cm\({}^{-1}\) together with medium intensity \(\
u_{2}\) and \(\
u_{4}\) modes around 453 and 611 cm\({}^{-1}\), respectively. The \(\
u_{3}\) mode was not observed as a separate band, even though broadband is visible around 1134 cm\({}^{-1}\).