Fabrication of phase and morphology controlled pure rutile and rutile/anatase TiO₂ nanostructures in functional ionic liquid/water

Graphical abstract: - Highlights: • Synthesised pure rutile and anatase-rutile TiO₂ nanocrystals in functional IL/aq. media. • Avoided the use of environmentally hazardous corrosive mineral acids. • Nano-flowers and well-defined rutile solid nanorods of TiO₂ were obtained. • Sample S-2 showed higher photocatalytic activity than P-25 upon UV irradiation. - Abstract: In this paper, pure rutile and anatase-rutile TiO₂ nanoparticles have been successfully synthesised via a green route by hydrolysis of titanium tetrachloride with room temperature acidic ionic liquid 3-methyl-1-(3-sulfonylpropyl) imidazolium trifluoromethanesulfonate [HO₃S(CH₂)₃MIM][CF₃SO₃] in aqueous medium. The influence of pH of the solution by varying molar ratio of substrate and ionic liquid has been investigated in both sol–gel and hydrothermal synthesis of TiO₂ with significant variation in phase, phase composition (ratio of rutile to anatase) and morphology as indicated by various structural analysis such as XRD, TEM, BET, Raman and UV–vis absorption spectroscopy. The results indicate formation of a bunch of aligned thin flaky nano-rods of TiO₂ which look like nano-flowers with a crystal size of 3–5 nm by sol–gel method, while in case of hydrothermal method well-defined rutile solid nanorods of TiO₂ were formed with variable length in the range of 120–170 nm and 20–24 nm in width. The photocatalytic activity of the prepared TiO₂ samples has been determined by the photodegradation of methyl orange dye (20 ppm) under UV light. Best photocatalytic activity was exhibited by sample S-2 prepared via sol–gel method.