Green Synthesis of TiO₂ Nanoparticles Using Ocimum tenuiflorum and Wrightia tinctoria Leaf Extracts: Characterization, Antibacterial Activity, and Machine Learning-Based Cytocompatibility Prediction
J. Environ. Nanotechnol., Volume 15, No 3 (September 2026) pp. 292-307
Abstract
This study reports the microwave-assisted green synthesis of TiO₂ nanoparticles (TiO₂ NPs) using Ocimum tenuiflorum (Tulsi), Wrightia tinctoria, and their combined leaf extracts, with titanium (IV) isopropoxide (TTIP) as the titanium precursor. XRD confirmed the formation of anatase TiO₂ without detectable secondary phases, with average crystallite sizes of 13, 15, and 18 nm for the O. tenuiflorum, W. tinctoria, and combined-extract samples, respectively. The combined-extract sample contained quasi-spherical primary nanoparticles with a comparatively narrow size range of 18–38 nm; however, larger micron-scale agglomerates were observed by FESEM, potentially resulting from particle association during drying. FTIR spectra indicated the involvement of hydroxyl, carbonyl-related, C–O, and C–O–C functional groups in nanoparticle formation and surface stabilization, together with characteristic Ti–O–Ti vibrations. DLS measurements showed hydrodynamic diameters of 103.6, 87.1, and 71.9 nm, with corresponding reported fractions below 100 nm of 57.7%, 85.5%, and 96.5%, respectively. Zeta potentials of −24.8, −27.1, and −31.2 mV suggested progressively stronger electrostatic stabilization under the measurement conditions, although long-term colloidal stability was not evaluated. All TiO₂ NP formulations exhibited concentration-dependent antibacterial activity against Escherichia coli DH5α, Enterobacter 2282, and Bacillus subtilis 1305. At 250 µg mL⁻¹, the combined-extract sample produced the largest inhibition zones of 15, 16, and 14 mm against E. coli, Enterobacter, and B. subtilis, respectively. A gradient boosting regression model was developed using a computationally constructed dataset of 240 observations, representing three TiO₂ NP formulations, ten concentration levels within 10–500 µg mL⁻¹, two exposure periods (24 and 48 h), and four mammalian cell lines—HeLa, HEK-293, J774A.1, and HepG2. Ten-fold cross-validation yielded R² = 0.9869, RMSE = 0.8267, MAE = 0.6819, and MAPE = 0.7609%, indicating strong internal predictive performance. These outcomes highlight the effectiveness of plant extracts as sustainable bioresources for TiO₂ NPs with promising biomedical applications.
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