# Natural Clays as Potential Amino Acids Carriers for Animal Nutrition Application
## 3 Results  
### Carriers Characterization  
Mineral clays were fully characterized by XRD (Supporting S1), granulometry (Supporting S2), and morphological analysis. Results are summarized in Table 1.  
As reported above, among others, Adsorbene(r) (ADS, in the following) was selected as possible carrier, in view of its sorption capability and its common use in feed application. Therefore, it was fully characterized (Table 1). It is evident that ADS is a complex mixture of different mineral clays and zeolites. With such a composition, the result is a reasonably high surface area (93 m\({}^{2}\)/g), which makes it a good methionine carrier candidate. Such a complex phase composition could make it difficult to understand the behavior of the material during intercalation and also not allow establishment of a direct correlation between the adsorption and the interaction with the carrier. This information is of paramount importance to understand the behavior of the MET-carrier system in the final application. Therefore, other two mineral clays, namely Veegum K(r) (VEG in the following), i.e., a pure expandable montmorillonite, and BioKi(r) (BIO, in the following), i.e., a fully zeolite-based material, were selected for comparison, and fully characterized, also (Table 1). ADS and BIO were characterized by very close surface area, pore volume,and pore diameter. Due to this close similarity, it can be assumed that ADS morphology is predominantly due to the zeolite components. Similar characterization was performed by FTIR. The spectrum of pristine ADS clay is characterized by the broad and complex absorption in the 1200-900 cm\({}^{-1}\) region, consistent with vibrational modes due to the presence of SiO in the structure. The zeolite fraction detected in this material is also characterized by weak peaks in the low-frequency region due to SiO deformation modes, and structural OH bending. Other minor features overlapping in this region can be assigned to oxide impurities. In the high-frequency region of the spectrum, a band due to structural OH groups are detected centered at 3620 cm\({}^{-1}\), partially masked by the broad absorption due to vibration modes of adsorbed molecular water (Supporting S3). The strong band at 1450 cm\({}^{-1}\), with very weak signals around 2900 cm\({}^{-1}\), associated to CH bending, was probably due to the presence of some organic compounds, such as tetramethylmonium (TMA) [31]. This compound and its derivates are reported to be used to expand the clay interlayer to increase the adsorption capability of the carrier [32; 33]. These molecules are so strongly bonded to the clay that they should not be released during utilization. The skeletal spectrum of BIO shows the same main features assigned to SiO vibrational modes, that is, a broad band centered at 1030 cm\({}^{-1}\) and assigned to structural SiO stretching modes, and weaker bands at lower frequencies due to deformation modes. The Veegum spectrum shows a main split band at 1036 cm\({}^{-1}\), due to structural SiO vibrations, and features in the range 950-500 cm\({}^{-1}\) related to the presence of AlO and MgO components. In the high frequency region, a broad absorption centered at 3450 cm\({}^{-1}\) is due to OH stretching of adsorbed water [31; 32; 33; 34]. As already remarked, it has been demonstrated that the adopted experimental procedures allow for the intercalation of an organic molecule without ion exchange [24], and this approach was proven on a variety of substances with different chemical natures and structures [18; 19; 20; 21; 22; 23]. This procedure guarantees that the properties of the intercalated molecule (e.g., methionine) are thus preserved until it reaches the absorption site. It was also reported that the operating parameters, such as contact time, pH, and solution concentrations, were fundamental for the setting up and the success of the reaction.