Abstract: High-purity SiO₂ nanoparticles (SNPs) play a crucial role in various electronic applications, such as semiconductors, solar cells, optical fibers, lenses, and insulating layers, given their purity and particle size, which significantly impact device efficiency. This study focuses on the synthesis and characterization of pure SNPs through the chemical etching of greater club rush. White powder SNPs were prepared using HCl etching, and their thermal behaviors were analyzed via thermogravimetric analysis/differential scanning calorimetry. Structural properties were investigated using X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. X-ray absorption near-edge structure was employed to assess the oxidation state of the SNPs. The morphology of the SNPs after the first etching was amorphous, with sizes ranging from 50 to 100 nm, which increased to 50–200 nm after the second etching. Despite this size variation, the SNPs maintained a high purity level of 99.8wt% SiO₂, comparable with industry standards. Notably, the second etching with 0.1-M HCl significantly enhanced the purity level, achieving 99.8wt% SiO₂ mass. Furthermore, HCl etching facilitated the formation of SiO₂ in the Si⁴⁺ oxidation state, akin to industrial SNPs. These findings underscore the critical role of HCl etching in synthesizing high-purity SNPs, with potential applications in advanced electronic devices.