Facile Preparation and Characterization of Silica Nanoparticles from South Africa Fly Ash Using a Sol–Gel Hydrothermal Method

Silica nanoparticles (SNPs) consist of several applications which include lightweight aggregates, energy storage, and drug delivery. Nevertheless, the silica reagents used in SNP synthesis are both costly and hazardous. As a result, it is critical to look for other sources of silica. For this research, a simple sol–gel hydrothermal approach is used to make SNPs from South African fly ash (SAFA). SAFA is classified as fly ash class F according to X-ray fluorescence (XRF) analysis. The wide-angle X-ray diffraction (XRD) pattern reveals the structural composition of SAFA and the amorphous phase of extracted SNPs, while Fourier transform infrared (FTIR) examination reveals the presence of silanol and siloxane groups. Basic SNPs were generally spherical with diameters of about 60 nm, according to scanning electron microscopy (SEM) and transition electron microscope (TEM) studies. The presence of SiO₂ is confirmed by energy-dispersive X-ray spectroscopy (EDX) spectrum analysis. Particle size assessment indicates particle sizes ranging from 48 nm to 87 nm in diameter, with a mean diameter of 67 nm. The application of SNPs in wastewater treatment demonstrated that they can be used to remove Cd²⁺ from an aqueous solution. This research offers new ideas for using South African fly ash in SNP manufacturing.