Green synthesis of Titanium (IV) oxide nanoparticles via citrus fruit peel for antibacterial and photocatalytic applications

This study reports the green synthesis of Titanium (IV) oxide nanoparticles (TiO 2 NPs) using peel extracts of Mandarin ( Citrus reticulata ), Sweet Orange ( Citrus sinensis ) and Lime ( Citrus aurantifolia ) as reducing agents. Optimization of flavonoid extraction by UV-Vis spectrophotometry identified deionized water with a 3-hour extraction time as the most effective condition, yielding the maximum total flavonoid content. To synthesize TiO 2 nanoparticles (NPs), varying volumes (1, 5, 10, 15, and 20 mL) of mandarin (ME), sweet orange (SE) and lime (LE) extracts were reacted with titanium (IV) isopropoxide. A 10 mL volume of each extract proved optimal for successful synthesis. The resulting samples are hereafter referred to as TiO 2 -10-ME, TiO 2 -10-SE and TiO 2 -10-LE, respectively. X-ray diffraction (XRD) confirmed the formation of the anatase phase, with crystallite sizes of 1.918, 2.460 and 2.591 nm for TiO 2 -10-ME, TiO 2 -10-SE and TiO 2 -10-LE, respectively. Initial FTIR analysis revealed residual organic impurities, which were subsequently removed by calcination at 350 °C; the durations required to obtain high-purity TiO 2 were 72, 6 and 24 h for ME, SE and LE, respectively. Among all samples, TiO 2 -10-LE which calcined at 350 °C for 24 h (TiO 2 -10-LE-24 h) exhibited the highest MB removal performance, with an apparent removal of 92.95% after 50 min of UV irradiation. Antibacterial efficacy, evaluated by the disc diffusion method, showed effective inhibition of both Gram-negative ( E. coli ) and Gram-positive ( S. aureus ) bacteria, with the largest inhibition zones of 9.95 ± 0.34 mm and 10.41 ± 0.22 mm, respectively, again for TiO 2 -10-LE-24 h. These results highlight the potential of citrus-mediated TiO 2 NPs for sustainable environmental remediation and biomedical applications.