Role of oxygen vacancies and pore structure in chloride impurity volatilization from synthetic silica

High-purity silica (SiO₂) synthesized via the sol–gel method typically retains chlorine ions (Cl^–), posing challenges to downstream processing equipment and product performance. However, the fundamental mechanisms and critical factors governing efficient dechlorination remain incompletely understood. In this study, amorphous high-purity SiO₂ particles were synthesized by sol–gel processing, and their dechlorination behavior was investigated using comprehensive characterization. Response surface methodology (RSM) identified calcination temperature and atmosphere as the dominant factors controlling dechlorination efficiency. Under the optimized conditions, the residual Cl^– content decreased to 16.89 ppm, deviating by 1.3 % from the model-predicted value (16.67 ppm). Thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) confirmed that Cl^– was released predominantly as HCl and HClO₄ during calcination. Kinetic analyses indicated that Cl^– impurities were chemically adsorbed on SiO₂, with apparent activation energies of 57.66 and 57.38 kJ/mol under air and N₂, respectively. Analysis of the crystal phase and morphology revealed that the calcination atmosphere had no discernible impact on the SiO₂ crystal form and pore structure. However, elevated temperatures increased the density of small pores, consequently impeding volatile release. Furthermore, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) demonstrated that calcination under an N₂ atmosphere promoted the formation of oxygen vacancies (Ov), which captured Cl^– and thereby limited further dechlorination. This work provides both theoretical insights and practical guidance for the deep dechlorination of high-purity SiO₂ and related materials.