Photocatalytic and antimicrobial activity of TiO2 particles, obtained by Mentha spicata leaves–mediated synthesis

The TiO₂ anatase nanoparticles were obtained by plant-assisted synthesis using Mentha spicata (MS) leaves water extract and titanium isopropoxide solution. The hydrothermal activation of plant extract-modified titanium solution was carried out at two different temperatures and treated thermally at 400 °C. The prepared powders were characterized by the following techniques: powder X-ray diffraction analysis (PXRD), Fourier transform infrared (FT-IR) spectroscopy, Scanning Electron microscopy (SEM), Energy dispersive X-ray analysis (EDS), Transmission Electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Diffuse reflectance spectroscopy (DRS), Electron paramagnetic resonance (EPR) and BET analyses. It was established that the plant-assisted samples possess higher specific area and better dispersion than those of the reference powders. The samples obtained at higher hydrothermal temperature (HT) possess the smallest particles sizes in the range 8–12 nm, according to TEM analyses. When both the HT and activation time increase, the amount of hydroxyl groups increases, while the amount of lattice oxygen decreases. The addition of plant extract during the synthesis process leads to changes of the textural and structural features of the obtained samples, which result in increasing of the band gap values for the M0 (3.22 eV) and M0-H powders (3.25 eV). All above mentioned physicochemical features cause better adsorption of the dye and inner surface illumination, thus resulting in improved photocatalytic activity of the plant-assisted synthesized particles towards Reactive Black 5 dye UV-initiated discoloration (96 %). The obtained photocatalysts exhibit high stability during three consecutive cycles. The synergistic effect of UV-light and particles on E. coli, P. aeruginosa, B. subtilis and O. paurometabola bacterial strains was demonstrated. The plant-assisted synthesized powders showed a stronger inhibitory effect compared to that of the reference TiO₂.