## 2 Materials and Methods  
### Synthesis and Characterization of Silica Pillared Clays (Si-PILC)  
The raw material used in this work was bentonite (natural clay, NC) from Pellegrini Lake in the province of Rio Negro, Argentina, described in detail in a previous work [16]. The silica pillared clays (Si-PILC) were prepared following the methodology described by [PERSON] et al. [26] with some modifications. The silica sol solution used as pillaring agent was obtained by mixing tetraethyl orthosilicate (TEOS: Si(OEt)\({}_{4}\), Merck \(>\) 99%), 2 M HCl (Cicarelli, 36.5-38%), and ethanol in a molar ratio of 1:0.1:1. The resulting solution was then aged at room temperature and mixed with a 0.25 M ferric nitrate (Fe(NO\({}_{3}\))\({}_{3}\).9H\({}_{2}\)O, Anedra 99%) solution in a molar ratio of Si/Fe 10:1. This mixture was titrated with a 0.2 M NaOH (Anedra, 98%) solution up to a pH of 2.7. Then, the pillaring agent obtained was added drop-wise to an NC suspension of 1 wt % deionized water and, considering its cation exchange capacity (CEC), the molar ratio chosen was Si:Fe:CEC 50:5:1, respectively. During the cation exchange, the mixture was stirred 3 h at 60 \({}^{\circ}\)C and the solid was separated by centrifugation at 3500 rpm for 15 min by a Sorvall RC 5C centrifuge. This solid was washed with a solution of ethanol/water 50% \(v/v\) and then was dispersed in a 0.2 M HCl solution under stirring for 3 h. This last step was carried out four more times. Finally, the solid material was washed with deionized water several times and then dried to finally obtain the Si-pillared clay precursor. Three materials were synthetized by this procedure varying the molar ratio between the Si and natural clay CEC and obtaining Si-PILC precursors with ratios of 25, 50, and 75 mol Si.g\({}^{-1}\) of natural clay. Finally, the precursors of the Si-PILC were calcined at 500 \({}^{\circ}\)C for 1 h in order to obtain the Si-PILC 25, 50, and 75, respectively.  
The structural properties of the materials were analyzed by X-Ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The XRD were obtained using a RIGAKU Geigerflex X-ray diffractometer with CuK\(\alpha\) radiation at 20 mA and 40 kV. The scans were recorded between 2\({}^{\circ}\) and 70\({}^{\circ}\) (20) with a step size of 0.02\({}^{\circ}\) and a scanning speed of 2\({}^{\circ}\) min\({}^{-1}\). The FTIR spectra were acquired using an Infralum FT-08 from 300 to 4000 cm\({}^{-1}\), the samples were prepared by potassium bromide pressed disc technique (3 mg of sample with 300 mg of KBr). The textural properties were studied by nitrogen adsorption-desorption isotherms at \(-\)196 \({}^{\circ}\)C. These measurements were carried out using an Autosorb 1 MP and iQ (Quantachrome Instruments). All the samples were previously degassed for 12 h up to a residual pressure lower than 0.5 Pa at 200 \({}^{\circ}\)C. Textural properties were obtained from these isotherms by different methods. The specific surface area (S\({}_{\text{BET}}\)) was assessed by the Brunauer, Emmet, and Teller (BET) method, using the [PERSON]'s criteria [27]. The micropore volumes (V\({}_{\text{HP}}\)) were calculated with the \(\alpha\)-plot method using the corresponding sample calcined at 1000 \({}^{\circ}\)C as reference material [28].  
The total pore volume (V\({}_{\text{T}}\)) was obtained using the Gurvich rule (at 0.97 of relative pressure) [27]. Pore size distributions (PSD) were obtained by the Horvarth-Kawazoe method, considering the adsorption branch and that the PIL have slit shape pores within the interlayer region.