## 3 Results
### Effect of the Heat-Treatment Temperature on the Properties of the Porous Diatomic Granules
This observation suggests that with an increase in the heat treatment temperature of the porous diatomic granules from 900-1100 \({}^{\circ}\)C to 1100-1200 \({}^{\circ}\)C, a portion of the log differential intrusion shifts towards larger pore sizes (i.e., an increased presence of larger pores). This shift is illustrated in Figure 9c, depicting the emergence of larger-sized pores (approximately 7 \(\upmu\)m). The N\({}_{2}\) adsorption/desorption isotherms and main properties deduced from the isotherms for the D43-0, D43-9, D43-10, D43-11, and D43-12 specimens are shown in Figure 11 and Table 2, respectively. Overall, the specimens exhibited a minimal amount of N\({}_{2}\) adsorption at low pressures (p/p\({}_{0}\) < 0.1), indicating the filling of small micropores (<2 nm) [36; 81]. An intermediate region (0.1 < p/p\({}_{0}\) < 0.9) was attributed to the adsorption of mesopores (2-50 nm), while a sharp adsorption region at high pressures (p/p\({}_{0}\) > 0.9) suggested the presence of abundant macropores (>50 nm) [36; 38; 81]. Moreover, the samples displayed a hysteresis loop in the high p/p\({}_{0}\) range. According to the IUPAC classification [82], the N\({}_{2}\) adsorption/desorption isotherms of the D43 specimens corresponded to type II isotherms with a H3 hysteresis loops. These characteristics are typically observed in porous solids with hierarchical features and are consistent with diatomic-derived supports [36; 38; 39; 81; 83]. Such features are associated with the exis  
Figure 10: Porosity and bulk density properties (**a**), and pore size distributions (determined by mercury porosimetry) (**b**) of porous diatomic granules heat-treated between 900 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C.  
tence of meso/macroporosity [39, 81] and the presence of slit-shaped pores and non-rigid aggregates of plate-like particles [82]. The D43 specimens displayed an increase in the average pore size from 14.83 nm to 35.34 nm, accompanied by a decrease in the specific surface area from 2.45 m\({}^{2}\) g\({}^{-1}\) to 0.91 m\({}^{2}\) g\({}^{-1}\) for the D43-9 to D43-12 specimens (Table 2). Additionally, it is suggested that the slight increase in the average pore size of the D43-9 specimen (from 14.70 nm to 14.83 nm) compared to the D43-0 sample can be attributed to the burn-out of the gaseous species from crosslinked alginate chains [11, 75]. Figure 11 shows that the adsorption region, with a range of 0.1 \(<\) p/p\({}_{0}\)\(<\) 0.9, becomes flatter as the heat-treatment temperature increases, indicating a decrease in the mesoporosity of the specimens [38]. Consequently, the decrease in the specific surface area is mainly governed by a reduction in the mesoporosity due to the filling and merging of smaller pores in the mesopore range, which aligns with the trend observed in the pore size distribution derived from mercury porosimetry (Figure 10b) [3, 77, 78]. Ultimately, the newly developed porous diatomic granules that were heat-treated between 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C exhibited hierarchical meso/macroporosity, with mesopores in the range of 14.83 nm to 35.34 nm and abundant macroporosity with pore sizes ranging from 1.765 \(\upmu\)m to 2.777 \(\upmu\)m [39, 81]. Figure 12, shows the compressive strengths of the D43 specimens heat-treated between 900 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C as a function of the pore size. The compressive strength outcomes of the newly developed D43 granules were in the corresponding ranges of 0.51 \(\pm\) 0.09 MPa, 1.17 \(\pm\) 0.18 MPa, 3.35 \(\pm\) 0.48 MPa, and 5.17 \(\pm\) 0.31 MPa for the specimens that were heat-treated at 900 \({}^{\circ}\)C, 1000 \({}^{\circ}\)C, 1100 \({}^{\circ}\)C, and 1200 \({}^{\circ}\)C. These results showed that the compressive strengths of the specimens increased with the heat-treatment temperature, which can be attributed to the promoted inter-particle partial densification and decreased porosity [71], particularly evidenced at 1200 \({}^{\circ}\)C (porosity of 69.0 \(\pm\) 2.9% and bulk density