SiHARKX: Simplified Synthesis and UV-Blocking Characterization of Rice Husk Ash-Derived Silica Sol with Heavy Metal Analysis

This study aimed to synthesize silica sol from rice husk ash (RHA) using a simplified sol-gel method and evaluate its UV-blocking efficiency and heavy metal content for safe industrial and environmental applications. RHA was purified via acid leaching, extracted with sodium hydroxide, and converted into silica sol. The UV-A (315–400 nm) and UV-B (280–315 nm) transmittances of four samples were measured using UV-Visible spectrophotometry, while heavy metal contents (Pb, Cu, Zn, Cd) were analyzed via Atomic Absorption Spectrophotometry (AAS). Results showed low UV transmittance: 0.98–1.90% for UV-A and 0.074–0.275% for UV-B, well below China’s GB/T 18830-2009 limits (≤5% UV-A, ≤2% UV-B). Heavy metal concentrations were within international safety standards: Pb 9.40 ppm (≤10 ppm), Cu 0.34 ppm (≤4 ppm), Zn 5.12 ppm (≤1500 ppm), and Cd 0.07 ppm (≤50 ppm). These findings confirm that RHA-derived silica sol is a sustainable, eco-friendly, and safe material suitable for UV-protective coatings and other industrial applications.