Green synthesis of titanium oxide nanoparticles using saponin biosurfactant derived from Camellia sinensis for photocatalytic degradation of Congo Red dye

Recalcitrant synthetic dyes such as Congo Red (CR), owing to their complex aromatic structure, chemical stability, and inherent toxicity, constitute a persistent environmental contaminant. In this study, titanium oxide nanoparticles were synthesized for the photocatalytic degradation of Congo Red dye from Camellia sinensis saponin. The characterization like UV, FTIR, XRD, BET, SEM with EDAX confirms the higher structural purity. Saponin extracted by soxhlet method showed optimum results of 0.82 g/L yield, oil dispersion 75 mm and emulsification index 83.3% with high extraction and solvent penetration efficiency compared to maceration, ultrasonication and microwave extraction methods. The optical band gaps were determined to be 3.196 eV (direct) and 2.8 eV (indirect). FTIR spectra confirmed Ti–O–Ti vibrations at 879 cm −1 , while XRD peaks at 27.57° corresponded to the (110) plane of the rutile TiO 2 phase. SEM micrographs revealed uniform spherical nanoparticles with an average diameter of 41 nm. At 120 min equilibrium time, percentage CR dye degradation was increased from 39.95% to 97.22% for the dosage of 1–5 g/L. Contact time data fits well with Langmuir-Hinshelwood kinetic model. Synergistic effect of adsorption and photo catalysis in CR dye degradation was observed. Overall, the CR degradation and surface characterization affirm that biogenic TiO 2 offers a sustainable, effective, and environmentally benign solution for mitigating dye pollution in aquatic systems.