Facile and eco-friendly synthesis of TiO2 NPs using extracts of Verbascum thapsus plant: an efficient photocatalyst for reduction of Cr(VI) ions in the aqueous solution

In this study, a fast and green synthesis of TiO2 nanoparticles (TiO2 NPs) is investigated using Verbascum thapsus (V. thapsus) plant aqueous extract as a reducing and stabilizing agent at room temperature. The TiO2 NPs formation and the optical properties were followed by the absorption spectra in ultraviolet–visible spectroscopy. This spectrum showed a strong absorption peak of around 356 nm. Moreover, the green synthesized TiO2 NPs were characterized by different techniques, for example, X-ray powder diffraction was used to analyze the phase and crystal structure, Fourier-transform infrared spectroscopy was conducted to know the functional groups involved in the NPs TiO2, and transmission electron microscopy was carried out to determine the morphology and size. The results showed a successful synthesis and anatase phase with spherical shape and smaller than 13 nm and also the presence of a few phytochemicals of the extracts around the synthesized TiO2 NPs, which acted as stabilizing the NPs. X-ray photoelectron spectroscopy analysis was carried out to characterize TiO2 NPs for evaluating the chemical states of the elements. The catalytic activity of the green synthesized TiO2 NPs was examined on photoreduction of Cr(VI) ions in the aqueous solution. The found conditions are as follows: [TiO2 NPs] = 750 mg/L, pH = 3.5, T = 25 °C and after 120 min of reaction photocatalytic reduction of Cr(VI) ions, 79.6% reduction efficacy (RE) was achieved. It was found that the reduction kinetic fitted the pseudo-first-order model. Finally, the photocatalyst reusability was investigated after five times of recovery; RE was reduced to 78.1%.