Thermal Behavior and structural evolution of silica nanospheres synthesized at controlled ammonia concentration and temperature

This study examined how synthesis temperature and reagent formulation were related to morphology, electrokinetic behavior, and thermal evolution of Stöber silica in a 4 × 4 synthesis matrix. Characterization included scanning electron microscopy (SEM) with equivalent-circle-diameter (ECD) analysis, dynamic light scattering (DLS), zeta-potential and conductivity measurements, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetry/differential scanning calorimetry coupled with quadrupole mass spectrometry (TG/DSC-QMS). Mean ECD values ranged from 108 to 1015 nm, with the largest corresponding to coalesced structures. Higher nominal NH 4 OH concentrations were associated with larger objects. At higher NH 4 OH concentrations, increasing temperature was associated with smaller particles, narrower SEM-ECD distributions, and fewer coalesced structures. DLS followed the SEM particle-size trend. Samples prepared at 0.150 mol L −1 NH 4 OH formed the smallest particles, had natural suspension pH values of 5.8–6.1 and zeta potentials of −21.27 to −30.07 mV, and showed lower mass-normalized m/z 18 areas at 30–250 °C (4.18–6.63 A s mg −1 ) than the remaining samples (8.42–11.77 A s mg −1 ). They also showed stronger low-temperature organic-fragment signals, particularly at m/z 31. TG mass losses were 4.31–6.50%, 3.98–5.59%, and 0.66–1.00% at 30–250, 250–600, and 600–1000 °C, respectively. After calcination at 1000 °C, hydroxyl-, water-, and C–H-related bands were below the ATR-FTIR detection limit, while Si–O–Si band changes were consistent with further network condensation. Overall, this distinct cross-technique grouping links synthesis conditions with electrokinetic and thermal behavior relevant to subsequent dispersion, calcination, and surface functionalization.