Investigation of structural, optical, antibacterial, and dielectric properties of sol-gel and biosynthesized TiO2 nanoparticles

This study explored the structural, optical, antibacterial, and dielectric properties of TiO₂ nanoparticles synthesized using two distinct approaches: sol-gel and biosynthesis. Density functional tight binding (DFTB+) and density functional theory (DFT) calculations were employed alongside experimental techniques to gain a comprehensive understanding of the electronic-property relationships. <i>Allium sativum</i> peel extract was utilized for the biosynthesis method. X-ray diffraction (XRD) affirmed the anatase phase formation for both nanoparticles. Rietveld technique was employed for a detailed structural analysis. The FESEM analysis revealed the diminutive particle size of TiO₂ nanoparticles with a comparable size distribution for both variants. However, the biosynthesized variant exhibited smaller average particle size (26.74 nm) than the sol-gel variant (32.22 nm). Optical studies showed an absorption redshift for the biosynthesized variant (352 nm) relative to the sol-gel variant (347 nm). The band gap energy is higher for the sol-gel variant (3.17 eV) compared to the biosynthesized variant (3.02 eV). The biosynthesized nanoparticles showed strong antibacterial activity, with inhibition zones of 15 mm against <i>E. coli</i> and <i>S. flexneri</i> bacteria. Dielectric analysis revealed that the sol-gel synthesized nanoparticles exhibited a higher dielectric permittivity of 27.80 and a lower dielectric loss of 0.37 at 1 kHz, compared to the biosynthesized nanoparticles, which showed a dielectric permittivity of 19.48 and a dielectric loss of 0.69.