Amorphous SiO₂ nanoparticles from natural sands: Structure and porosity

Silica (SiO₂) nanoparticles (NPs) generally include mesoporous materials (2-50 nm), having broad application prospects, such as for drug delivery systems. In this study, we report the porosity of amorphous SiO₂ NPs by investigating their crystal structure, morphology, diameter, and volume of pores. Amorphous SiO₂ NPs have been prepared from quartz sand, heated at a temperature range from 500 to 1,200 °C. The identification of the crystal structure was performed using XRD, the morphology and grain growth particles were considered using SEM, and the diameter and volume of pores were investigated using BET. An FTIR analysis was used to analyze the -Si-O and Si-OH functional groups. The results of this study presented that at a calcination temperature range of 500-800 °C, the crystal structure disappeared. However, at a temperature of 1,000 °C, a new crystalline tridymite structure was observed. Furthermore, the structural transformation was observed at a temperature of 1,200 °C from the amorphous phase to the polycrystalline phase consisted of quartz, cristobalite, and tridymite structures. During the calcination process, as the particles' pore size grew more significantly, the number of grain boundaries decreased, influencing the particle porosity sizes. The results of the analysis using BET presented that the pore surface area and pore volume of the samples tended to be smaller, along with increasing calcination temperature.