Bacterial Compatibility/Toxicity of Biogenic Silica (b-SiO₂) Nanoparticles Synthesized from Biomass Rice Husk Ash

Biogenic silica (b-SiO₂) nanopowders from rice husk ash (RHA) were prepared by chemical method and their bacterial compatibility/toxicity was analyzed. The X-ray diffractometry (XRD) patterns of the b-SiO₂ nanopowders indicated an amorphous feature due to the absence of any sharp peaks. Micrographs of the b-SiO₂ revealed that sticky RHA synthesized SiO₂ nanopowder (S1) had clustered spherical nanoparticles (70 nm diameter), while b-SiO₂ nanopowder synthesized from red RHA (S2) and b-SiO₂ nanopowder synthesized from brown RHA (S3) were purely spherical (20 nm and 10 nm diameter, respectively). Compared to the S1 (11.36 m²g^-1) and S2 (234.93 m²g^-1) nanopowders, the S3 nanopowders showed the highest surface area (280.16 m²g^-1) due to the small particle size and high porosity. The core level of the X-ray photoelectron spectroscopy (XPS) spectra showed that Si was constituted by two components, Si 2p (102.2 eV) and Si 2s (153.8 eV), while Oxygen 1s was observed at 531.8 eV, confirming the formation of SiO₂. The anti-bacterial activity of the b-SiO₂ nanopowders was investigated using both gram-positive (Escherichia coli) and gram-negative (Staphylococcus aureus) microorganisms. Compared to S2 and S3 silica nanopowders, S1 demonstrated enhanced antibacterial activity. This study signifies the medical, biomedical, clinical, and biological importance and application of RHA-mediated synthesized b-SiO₂.