Comparative photocatalytic and antibacterial performance of TiO ₂ nanoparticles synthesized by precipitation, microwave and hydrothermal methods

The textile and printing industries extensively use synthetic dyes, which can severely pollute the environment when their dye effluents are directly discharged into water bodies. Metal oxide-based photocatalytic dye degradation is an effective approach for degrading the complex structures of synthetic dye pollutants. Titanium dioxide (TiO ₂ ) nanoparticles (NPs) are widely investigated as photocatalysts owing to their excellent chemical stability, non-toxic nature and low cost. In addition to dye pollution, pathogens such as bacteria have another significant environmental problem for human beings. In this work, three different chemical growth methods such as precipitation, microwave and hydrothermal were used to synthesize TiO ₂ NPs. The influence of the synthesis method on the photocatalytic and antibacterial activities of the prepared TiO ₂ NPs was systematically studied. The synthesized TiO ₂ NPs have been characterized using advanced physico-chemical techniques. The XRD pattern confirmed that TiO ₂ NPs synthesized by all three methods have the anatase phase with a tetragonal structure. The prepared TiO ₂ NPs show a low band gap energy value of 2.89 eV. The photocatalytic efficiency of the synthesized TiO ₂ NPs under solar and UV light irradiation was examined by decolorization of 10 ppm methylene blue (MB) dye. A higher decolorization efficiency of 95.4 % was obtained for the hydrothermally synthesized TiO ₂ NPs after 180 min of solar light irradiation. The hydrothermally synthesized TiO ₂ NPs demonstrated a higher rate constant value ( k ) of 0.99467 min ⁻¹ under sunlight irradiation, which surpasses that of the microwave ( k = 0.99059 min ⁻¹ ) and precipitation ( k = 0.97921 min ⁻¹ ) synthesized samples. Additionally, the antibacterial activity of TiO ₂ NPs against Klebsiella pneumoniae and Streptococcus pneumoniae was examined using the disc diffusion method. The hydrothermally synthesized TiO ₂ NPs exhibited the maximum zones of inhibition for both gram-negative Klebsiella pneumoniae (25 mm) and gram-positive Streptococcus pneumoniae (21 mm) compared to those synthesized by the precipitation and microwave methods. The current investigation clearly reveals that the prepared TiO ₂ NPs can be considered as a promising candidate for photocatalytic and antibacterial applications.