The Effect of Heat Treatment on Photocatalytic Performance and Antibacterial Activity of TiO 2 Nanoparticles Prepared by Sol-Gel Method

The effect of post-heat treatment process on TiO2 nanoparticles (NPs), prepared by hydrothermal-assisted sol-gel method, was investigated through measurement of the band gap energy, crystal size, photocatalytic activity and antibacterial efficiency of TiO2 NPs. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and UV-Vis spectroscopy were used to characterize treated as well as untreated TiO2 nanoparticles. Methylene blue (MB) dye was used as a pollutant model in order to investigate the photocatalytic activity of as-prepared TiO2 nanoparticles. The antibacterial activity of TiO2 nanoparticles was assessed under UV-A irradiation by testing the growth inhibition of two bacterial strains: a Gram negative bacteria Stenotrophomonas maltophilia (S. maltophilia) and a Gram positive bacteria Micrococcus luteus (M. luteus). The results indicate that the crystal size increases from 13 to 20 nm for untreated (NT) and treated nanoparticles, respectively. FTIR results show that heat treatment eliminates inorganic impurity. SEM micrographs prove that annealing does not modify the morphology of nanoparticles, however, particle size increases due to calcination. In addition, post-heat treatment at 500 °C for 2 h decreases the band gap energy (from 4.35 to 3.25 eV) and consequently enhances significantly the photocatalytic activity as well as the antibacterial performance of as-synthesized TiO2 nanoparticles.