Influence of plant extract type and volume on the structural, morphological, and antibacterial properties of sol–gel derived TiO2

We investigated the synthesis of TiO 2 via the sol–gel route using titanium tetrabutoxide as the precursor and aqueous extracts of Buddleja cordata (B-TiO 2 ) and spent Humulus lupulus (L-TiO 2 ) as biogenic modulating agents, at volumes of 5, 10, 20, and 30 mL. X-ray diffraction confirmed a stable anatase phase in all B-TiO 2 samples (crystallite size 8.98–9.58 nm), while L-TiO 2 showed progressive crystallinity loss with increasing extract volume, becoming amorphous above 10 mL. FTIR and EDS analyses linked this behavior to greater retention of organic/carbonaceous residues in L-TiO 2 than in B-TiO 2 , which instead yielded smaller, more homogeneous agglomerates (0.220 ± 0.044 μm) and a denser, more uniform Ti/O distribution by STEM mapping. At the optimal 5 mL volume, antibacterial assays showed B-TiO 2 inhibiting E. coli and S. aureus at concentrations two to three orders of magnitude lower (0.05–0.14 μg/mL) than L-TiO 2 (40–60 μg/mL), with UV irradiation further enhancing activity. Overall, the botanical source and extract volume strongly influenced TiO 2 formation and its resulting properties, with B. cordata mediated TiO 2 showing the most favorable structural characteristics and antibacterial performance.