Kaolin phyllosilicate-derived silica quantum dots via acid-base hydrothermal synthesis for anti-cancer applications

This study presents a green and sustainable approach for synthesizing silica quantum dots (QDs) from kaolin phyllosilicate collected in Cipatujah, West Java, Indonesia, via a two-step hydrothermal acid–base method. Kaolin, a naturally abundant and low-cost phyllosilicate mineral composed primarily of Al₂Si₂O₅(OH)₄, served as the silica precursor. In the first step, kaolin was hydrothermally treated with hydrochloric acid (HCl) to remove impurities such as Fe and Mn and to extract orthosilicic acid. In the second step, the purified material was treated with sodium hydroxide (NaOH) under identical hydrothermal conditions, inducing bond scission and promoting the formation of nanoscale silica via silicate intermediates. This method successfully yielded high-purity silica QDs. X-ray fluorescence (XRF) analysis confirmed a Silica (SiO₂) content of 90.2 %. High-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FESEM) revealed spherical and amorphous particles. Cytotoxicity assay demonstrated significant dose-dependent inhibitory effects on B16F0 melanoma and MCF-7 breast cancer cells, with half-maximal inhibitory concentration (IC₅₀) values during 24 h incubation of 134 ppm and 147 ppm, respectively. This environmentally friendly synthesis strategy minimizes the use of hazardous reagents while utilizing natural mineral resources, aligning with the principles of sustainable nanotechnology. The findings underscore the potential of kaolin-derived silica QDs as biocompatible and eco-friendly nanomaterials for cancer therapy.