Impact of Ionic Liquids on the Crystal Growth and Surface Morphology of Ruthenium-doped TiO₂ Nano Heterojunction Structures for Improved Photocatalytic Degradation of Evans Blue Dye and the Associated Antibacterial Activities

Novel Ru-doped TiO₂ nanocomposites (Ru/TiO₂ NCs) were synthesized at a 130 °C temperature and 24-h incubation period using hydrothermal methods with and without ionic liquids (ILs). NCs were synthesized using 1-butyl-2,3-dimethylimidazolium tetrafluoroborate as the ILs and titanium(IV) isopropoxide and ruthenium(III) nitrate as the precursors. The presence of Ru in the NCs was analyzed using different characterization techniques. Powder X-ray diffraction and transmission electron microscopy confirmed the presence of anatase and rutile phases as well as the nanocrystalline texture of the prepared Ru/TiO₂ NCs. The presence of Ru, Ti, and O was confirmed via energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The optical properties and bandgap energies of Ru/TiO₂ NCs were determined via ultraviolet (UV)–visible (Vis) diffuse reflectance spectroscopy; the optical properties exhibited a redshift in the optical response toward the visible region owing to the reduced bandgap energy of Ru/TiO₂ NCs in the visible region after doping Ru into the TiO₂ nanocrystalline structure. Scanning electron microscopy images revealed a highly voluminous and porous network of Ru/TiO₂ NCs. Moreover, different concentrations of Ru were doped into the TiO₂ matrix to investigate the photocatalytic and antibacterial activities. Among all the synthesized NCs, 0.3-wt% Ru/TiO₂ NCs exhibited high photocatalytic degradation efficiency and was therefore considered the optimum concentration. Moreover, it exhibited the highest BET surface area and quantum efficiency compared with other Ru/TiO₂ NCs. Results revealed that Ru/TiO₂ NCs synthesized via IL-assisted hydrothermal method, i.e., R₃TL, exhibited considerably enhanced photocatalytic and antibacterial activities compared to the NCs synthesized without the ILs, i.e., R₃TH. The inhibition pattern showed an excellent zone of inhibition (p < 0.001) in several strains with both NCs (R₃TL and R₃TH). However, Gram-positive Staphylococcusaureus exhibited a remarkably increased zone of inhibition (35 mm) compared with all the other strains used for R₃TH. In contrast, Bacillus sp. exhibited the second largest zone of inhibition (21 mm) for R₃TL after S. aureus (34 mm). In summary, this study emphasized the role of ILs and reaction mechanisms.