Modifier-induced structural evolution in CTAB-assisted SiO2–CaO–CeO2 sol–gel systems

CTAB-assisted SiO 2 –CaO–CeO 2 materials were synthesized via a sol–gel route under strongly basic conditions (pH 10) and calcined at 600 °C. Three nominal oxide compositions (mol%) were investigated: 100SiO 2 (Si), 70SiO 2 –30CaO (SiCa), and 65SiO 2 –25CaO–10CeO 2 (SiCaCe). Thermal analysis revealed composition-dependent decomposition behavior associated with surfactant removal and nitrate precursor breakdown. X-ray diffraction showed that Si and SiCa remain predominantly amorphous after calcination, whereas the SiCaCe composition exhibits the formation of CeO 2 nanocrystals with average sizes of 6–8 nm. Fourier-transform infrared spectroscopy provides evidence consistent with progressive depolymerization of the silicate network upon calcium incorporation, reflected by an increased fraction of non-bridging oxygen species. Electron microscopy reveals aggregated, rounded particles characteristic of base-catalyzed sol–gel processing, together with composition-dependent variations in nanoscale structural arrangement. The SiCa composition exhibits increased structural heterogeneity, while XRD demonstrates the formation of nanocrystalline CeO 2 in the cerium-containing composition, consistent with cerium-induced phase separation within the amorphous matrix. TEM observations indicate continuous nanoscale contrast domains extending across the particles, without direct compositional assignment. These results indicate that structural evolution in these systems arises from the combined effects of alkaline condensation, calcium-induced network modification, cerium-driven phase separation, and surfactant-assisted condensation processes during sol–gel synthesis.