## 1 Introduction  
Hydrotalcites, also referred to as layered double hydroxides (LDHs), are categorized as anionic clays due to their distinctive layered architecture [1, 2]. This structure is characterized by positively charged hydroxy layers, in stark contrast to cationic (silicate) clays such as smectites, which possess a negative layer charge. Within the interlayer space of these positively charged layers, anions are present to balance the overall charge. A more comprehensive understanding of hydrdtalcite's structure reveals positively charged hydroxide layers that resemble those found in brucite [Mg(OH)\({}_{2}\)]. In this configuration, a portion of the Mg\({}^{2+}\) ions can be substituted with trivalent metals, such as Al\({}^{3+}\), while charge-compensating anions, typically in a hydrated form, occupy the interstitial regions between the hydroxide layers (Figure 1) [2,3]. The composition of LDH is very versatile, commonly represented by the formula [M\({}^{2+}\)\({}_{1-x}\)M\({}^{3+}\) x (OH)\({}_{2}\)][A\({}^{n-1}\)\({}_{\text{N/m}}\)yH\({}_{2}\)O, where M\({}^{2+}\) and M\({}^{3+}\) denote the divalent and trivalent cations residing in octahedral coordination within the hydroxide layers. The variable x usually ranges from 0.17 to 0.33, indicating the proportion of M\({}^{3+}\) ions. Notably, it is imperative that the ionic radii of M\({}^{2+}\) and M\({}^{3+}\) do not exhibit significant disparity--specifically, a deviation of no more than 30%--to maintain structural integrity. For instance, the ionic radii for Mg\({}^{2+}\) and Al\({}^{3+}\) are approximately 0.65 A and 0.45 A, respectively. Furthermore, sound chemical principles dictate that the solubility products, \(S_{1}\) for M\({}^{2+}\)(OH)\({}_{2}\) and \(S_{2}\) for M\({}^{2+}\)CO\({}_{3}\), must adhere to the conditions where the difference p\(S_{1}\)-p\(S_{2}\) is maintained within the range of 0 and 10, ensuring the stability of the hydrdtalcite phase [2, 3, 4]. The variety of anions that can exist within the LDH framework is relatively unconstrained, provided that these anions do not engage in complexation with the cations within the octahedral sheets during the synthesis process. Such complexation would inhibit the formation of a viable LDH structure [5]. The inherent flexibility in both cationic and anionic compositions of hydrdtalcite enables the engineering of tailor-made materials suitable for a broad array of applications. These may include their utilization as basic catalysts or precursors for synthesizing mixed metal oxide catalysts. Additionally, hydrdtalcites serve functional roles as adsorbents, fillers, UV stabilization agents, chloride scavengers, and thermal stabilizers, positioning them as versatile components in various industrial and technological contexts [6, 7, 8, 9, 10, 11]. Figure 1: Simplified structure of LDH showing the Mg/Al hydroxide layers with the OH-groups (filled grey spheres) on its surfaces exposed to the interlayer space filled with water and interlayer anions such as CO\({}_{3}\)\({}^{2-}\), in this case. Infrared spectroscopy, along with the less frequently employed Raman spectroscopy, has proven instrumental in elucidating the structural and compositional characteristics of LDH containing varied cations and anions. These spectroscopic techniques have facilitated comprehensive examinations of anionic intercalation and thermal degradation processes in these materials, primarily serving to identify a range of exchangeable anions. Among the anions detected in such studies are carbonate (CO\({}_{3}\)\({}^{2-}\)), chloride (Cl\({}^{-}\)), perchlorate (ClO\({}_{4}\)\({}^{-}\)), nitrate (NO\({}_{3}\)\({}^{-}\)), sulfate (SO\({}_{4}\)\({}^{2-}\)), arsenate (AsO\({}_{4}\)\({}^{3-}\)), vanadate (VO\({}_{4}\)\({}^{3-}\)), molybate (MoO\({}_{4}\)\({}^{2-}\)) and chromate (CrO\({}_{4}\)\({}^{2-}\)) [12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27].