Decorated cenosphere surface with bioreduced silver nanoparticles for environmental applications

Abstract

Cenospheres (CF) are hollow spherical particles primarily composed of silica (SiO2) and alumina (Al2O3), known as aluminosilicate ceramic microspheres. In this study, CF were fractionated into the four size ranges (40–80 μm, 80–125 μm, 125–160 μm, 160–200 μm), purified, and activated using piranha solution (PS). Acid treatment activation was followed by the CF functionalization with biosynthesized silver colloidal nanoparticles (AgNPs). Silver integration was confirmed using elemental analysis (5.8–7.1 wt% of Ag), and electron microscopy revealed AgNPs (∼45 nm) unevenly distributed and locate at surface defects. X-ray diffraction (XRD) analysis confirmed the presence of quartz and mullite phases in both raw and modified CF, indicating structural stability during processing. Sound absorption tests revealed that while larger CF particles—especially the 160–200 μm fraction—initially demonstrated the highest noise reduction coefficient (NRC), with a maximum NRC of 0.210 at 80 mm powder bed heigh, the modification with AgNP significantly diminished the dependency of sound absorption performance on particle size. Ag-modified samples showed NRC values, CF with a particle size fraction pf 160–200 μm: 0.158, at 80 mm, confirming uniform acoustic performance. Mechanical stiffness, expressed by bulk modulus, increased with both particle size and powder bed density, reaching a maximum of 64.26 MPa for CF_160200_2 PS_Ag. Leaching tests under static, dynamic, and rotation conditions revealed limited silver release, with only slightly increased leaching observed for larger particles under rotation. Silver release from CF_160200_2 PS_Ag was 0.007 wt% (static), 0.008 wt% (dynamic), and 0.010 wt% (rotation). Overall, Ag release remained low, confirming high material stability. These results show that silver-modified CF retain their structural and chemical integrity, offer tunable acoustic and mechanical properties, and show excellent potential for long-term use in environmental remediation, sound insulation, and catalytic applications.