Synthesis of mesoporous silica and calcium fluoride nanoparticles from hexafluorosilicic acid waste: A circular economy approach

Abstract

The growing demand for sustainable industrial practices has intensified the need for innovative approaches to managing hazardous waste. In this study, we propose a circular economy-driven method for the synthesis of mesoporous silica nanoparticles (MSNs) and calcium fluoride (CaF₂) nanoparticles from hexafluorosilicic acid (H₂SiF₆), a highly corrosive and toxic by-product of the phosphate fertilizer industry. The process involves reacting H₂SiF₆ with ammonia (NH₃) under controlled conditions to yield high-purity MSNs with tunable properties, including particle sizes ranging from 32 to 85 nm and pore diameters of 2-5 nm. In a second step, the ammonium fluoride (NH₄F) solution obtained as a by-product during the MSN synthesis was treated with calcium hydroxide (Ca(OH)₂) to synthesize CaF₂ nanoparticles with an average particle size of 38 nm. The resulting nanoparticles were characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), confirming their high purity and nanoscale dimensions. This dual-synthesis approach not only addresses the environmental concerns associated with H₂SiF₆ disposal but also provides valuable nanomaterials for various industrial applications, thus contributing to a circular economy.