## 3 Results
### Effect of the Heat-Treatment Temperature on the Properties of the Porous Diatomic Granules
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Designation**} & **Total Pore Volume** & **Average Pore** & **BET Specific Surface** \\  & **(cm\({}^{3}\) g\({}^{-1}\))** & **Diameter (nm)** & **Area (m\({}^{2}\) g\({}^{-1}\))** \\ \hline D43-0 & 0.0107 & 14.70 & 2.92 \\ D43-9 & 0.0091 & 14.83 & 2.45 \\ D43-10 & 0.0088 & 16.94 & 2.08 \\ D43-11 & 0.0089 & 23.01 & 1.55 \\ D43-12 & 0.0081 & 35.34 & 0.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main properties deduced from the N\({}_{2}\) adsorption/desorption isotherms of the porous diatomic granules heat-treated between 900 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C as compared with the green body. Figure 11: N\({}_{2}\) adsorption/desorption isotherms of porous diatomic granules heat-treated between 900 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C as compared to the green body. (The adsorbed capacity values and the offsets of the isotherms are included in the label). of 0.714 \(\pm\) 0.07 g/cm\({}^{3}\)). The D43-9 specimens (0.51 \(\pm\) 0.09 MPa, macropores: 1.765 \(\upmu\)m, mesopores: 14.83 nm) showed a compressive strength value comparable to that of boehmite-derived \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules (0.95 MPa, pore size: 11.60 nm) obtained under similar processing conditions (sodium alginate gelation) [11]. Furthermore, the D43-12 specimens exhibited a five-hold higher compressive strength (5.17 \(\pm\) 0.31 MPa, macropores: 2.777 \(\upmu\)m, mesopores: 35.34 nm) compared to boehmite-derived \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules, despite having larger mesopores [11]. Additionally, the newly developed D43-12 granules showed compressive strength comparable to that of porous diatomic granules (5.09 MPa, pore size: \(\sim\)1.8 \(\upmu\)m) [84] prepared by pan rotation granulation under similar heat-treatment conditions, while also exhibiting hierarchical meso/macroporosity and approximate sphericity of 0.9. The compressive strength of the granules increased from 0.51 \(\pm\) 0.09 MPa to 5.17 \(\pm\) 0.31 MPa as the heat-treatment temperatures increased from 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C, while the specific surface area decreased from 2.45 m\({}^{2}\) g\({}^{-1}\) to 0.91 m\({}^{2}\) g\({}^{-1}\). This indicates a trade-off relationship between these two properties. Nevertheless, the specimens exhibited a hierarchical meso/macropore structure irrespective of the heat-treatment condition. Despite having a lower specific surface area, the D43-9 and D43-12 specimens showed mesopore sizes comparable to those of boehmite-derived \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules (S\({}_{\text{BET}}\): 244.0 m\({}^{2}\) g\({}^{-1}\), 14.83 nm) [11] and oil-molding derived \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules (S\({}_{\text{BET}}\): 7.0 m\({}^{2}\) g\({}^{-1}\), 39.92 nm) [16], which were obtained through similar heat treatments and are applicable as catalytic supports. Furthermore, the newly developed D43-9 granules (2.45 m\({}^{2}\) g\({}^{-1}\), mesopore size: 14.83 nm) exhibited a specific surface area comparable to that of the CaO/carbon catalyst beads used in CO\({}_{2}\) reduction (2.03 m\({}^{2}\) g\({}^{-1}\), 1.8 nm, N\({}_{2}\) calcination, 500 \({}^{\circ}\)C) [85]. Additionally, the D43-9 and D43-12 specimens displayed mesoporousity and macroporosity ranges similar to those of non-consolidated diatomic supports (mesopore size: \(\sim\)30 nm [38], macropore size: \(\sim\)0.1-3.2 \(\upmu\)m [81]) of the type used for the adsorption of organic pollutants [36; 38] and heavy metals [36]. The macroporosity in these systems is considered highly beneficial for adsorption applications, as it enhances the efficiency of the mass transport and diffusion process [38]. In summary, our newly developed D43-9 specimens showed compressive strength comparable to that of sodium alginate gelation-derived \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules [11] along with comparable mesoporosity.