Visible-Light-Driven Photodegradation of Methylene Blue Dye and Pathogenic Escherichia coli by Mn-Doped TiO2 Nanoparticles

Abstract

A sol–gel method was used to synthesize TiO2 nanoparticles doped with varying amounts of Mn. The physico-chemical properties of the synthesized nanoparticles were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and diffuse reflection spectroscopy (DRS). The XRD results indicated that the anatase phase was the major phase of TiO2, while a minor rutile phase was observed in the Mn-doped TiO2 0.2 wt.% and 0.3 wt.% samples. The TEM analysis showed that the Mn atoms existed in different oxidation states, including Mn[Formula: see text], Mn[Formula: see text], Mn[Formula: see text] and Mn[Formula: see text], and that the nanoparticles had a spherical-like morphology with a size ranging from 10[Formula: see text]nm. The narrowest band gap of 2.80[Formula: see text]eV was observed in the Mn-doped TiO2 0.2 wt.% sample. The photocatalytic activity of the synthesized nanoparticles was evaluated for methylene blue (MB) photodegradation and Escherichia coli (E. coli) photokilling under visible light irradiation. The MB degradation efficiency was found to be the highest in the Mn-doped TiO2 0.2 wt.% sample, with a removal efficiency of 96% and a degradation rate constant of 0.08 1/min. The degradation efficiency decreased in the following order: Mn-doped TiO2 0.1 wt.%, 0.3 wt.% and undoped TiO2. Similarly, complete E. coli photokilling was achieved only in the Mn-doped TiO2 0.2 wt.% sample, while some residual E. coli was observed in the other doping nanoparticles and undoped TiO2. In summary, the results suggest that Mn doping significantly improved the photocatalytic activity of TiO2 nanoparticles, and the Mn-doped TiO2 0.2 wt.% sample exhibited the highest efficiency in both MB photodegradation and E. coli photokilling under visible light irradiation.