# Tunable Effect of the Calcination of the Silanol Groups of KIT-6 and SBA-15 Mesoporous Materials
## 3 Results and Discussion
### Effect of the Calcination Temperature on the Textural Properties of the MNS  
The porosity of calcined MNS materials under different conditions was analyzed by N\({}_{2}\) sorption. As expected for these materials, isotherms are type IVa (according to the new IUPAC [74] classification) with type I hysteresis. Figure 4 shows the SBA-15 isotherms, and Figure 5 shows the KIT-6 isotherms. The physical properties taken from these isotherms are presented in Table 4.  
For SBA-15 and KIT-6, the BET area indicates a suitable porosity with material type [13; 14; 15]. The samples of SBA-15 presented the maximum value of A\({}_{\text{BET}}\) upon calcination at 400 \({}^{\circ}\)C for 10 h. Increasing the temperature to 500 \({}^{\circ}\)C for 5 h decreased the value of A\({}_{\text{BET}}\) slightly (from 1197 to 1099 m\({}^{2}\) g\({}^{-1}\)), and maintaining the temperature at 500 \({}^{\circ}\)C but doubling the calcination time to 10 h considerably decreased the value of the total material area to 770 m\({}^{2}\) g\({}^{-1}\). This decrease in the area must be associated with the process of the dehydroxylation of the material, which begins to intensify under these heat treatment conditions. For KIT-6, a calcination at 300 \({}^{\circ}\)C for 5 h results in the lowest total area value. This is quite reasonable since it is under these conditions that the largest amount of organic material exists, as attested by the results of elemental carbon analysis. The largest BET area was obtained by calcining at 500 \({}^{\circ}\)C for 5 h. When the heat exposure time was increased from 5 to 10 h without an increase in the temperature, the BET area decreased (1174 to 874 m\({}^{2}\) g\({}^{-1}\)). This indicates that \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **A\({}_{\text{BET}}\)** & **V\({}_{\text{T}}\)** & **V\({}_{\text{Mi}}\)** & **V\({}_{\text{Me}}\)** & **D\({}_{\text{P}}\)** & **W\({}_{\text{t}}\)** \\  & **(m\({}^{2}\) g\({}^{-1}\))** & **(cm\({}^{3}\) g\({}^{-1}\))** & **(cm\({}^{3}\) g\({}^{-1}\))** & **(cm\({}^{3}\) g\({}^{-1}\))** & **(cm\({}^{3}\) g\({}^{-1}\))** & **(nm)** & **(nm)** \\ \hline SM1 & 572 & 0.78 & 0.02 & 0.76 & 7.5 & 4.5 \\ SM2 & 632 & 0.86 & 0.02 & 0.84 & 7.5 & 4.4 \\ SM3 & 641 & 0.84 & 0.03 & 0.81 & 7.8 & 4.7 \\ SM4 & 1197 & 1.52 & 0.04 & 1.48 & 7.5 & 5.0 \\ SM5 & 1099 & 1.69 & 0.00 & 1.69 & 8.9 & 3.3 \\ SM6 & 770 & 0.98 & 0.06 & 0.92 & 7.8 & 4.2 \\ KM1 & 695 & 0.82 & 0.07 & 0.75 & 7.2 & 15.8 \\ KM2 & 826 & 0.98 & 0.07 & 0.91 & 6.1 & 17.9 \\ KM3 & 905 & 1.07 & 0.07 & 1.00 & 7.5 & 16.0 \\ KM4 & 852 & 1.03 & 0.08 & 0.95 & 7.9 & 15.9 \\ KM5 & 1174 & 1.44 & 0.08 & 1.36 & 7.3 & 16.7 \\ KM6 & 874 & 1.10 & 0.05 & 1.05 & 7.4 & 15.6 \\ \hline \hline \end{tabular}  
* A\({}_{\text{BET}}\) is the specific area obtained from the Brunauer–Emmett–Teller (BET) method. The V\({}_{\text{T}}\) is the total pore volume obtained from a relative pressure p/p\({}^{0}\) equal to 0.98. The V\({}_{\text{Mi}}\) is the microporous volume obtained from the \(\alpha\)-plots method. The V\({}_{\text{Me}}\) is the mesoporous volume obtained from the \(\alpha\)-plots method. The D\({}_{\text{P}}\) is the pore diameter obtained from the Barrett–Jøyner–Halenda (BJH) method corrected from the Villarroel–Barrera–Sapag (VBS) method. The W\({}_{\text{t}}\) is the wall thickness.  
\end{table} 
Table 4: Physical properties of SBA-15 and KIT-6 samples. Figure 3: Small-angle XRD pattern of KIT-6 and SBA-15 calinated under different conditions. at temperatures above 500 \({}^{\circ}\)C, contraction of the structure begins to occur, indicating a dehydroxylation process of KIT-6 [69]. From the measurements made after the capillary condensation step at the beginning of the isotherm plateau, the total pore volume was determined from the adsorbed nitrogen volume values. Micropore and mesopore volumes were calculated according to reference [75].