Fabrication of hydroxyl group-enriched mixed-phase TiO2 nanoflowers consisting of nanoflakes for efficient photocatalytic activity

Abstract

We present hydrothermal fabrication of hydroxyl group-rich mixed-phase TiO2 nanoflowers (surface area ~ 252 m2/g) (MTNF) and their tremendous sunlight-induced photodegradation nature for methylene blue (MB), methyl orange (MO), rhodamine 6G (R6G), and oxytetracycline hydrochloride (OTC-HCl) molecules. The morphology of MTNF has been confirmed through the transmission electron microscope and scanning electron microscope studies. Microscopy studies reveal that each flower-like nanostructures formed by the assembly of nanoflakes. X-ray diffraction and Raman studies confirm the presence of mixed (anatase/rutile) phase of TiO2. The optical behavior of MTNF is explored by the UV-visible diffuse reflectance spectroscopy (UV-DRS) and photoluminescence spectroscopy (PL). Urbach energy calculation indicates the appearance of oxygen-related defects which are further assured by the PL studies. Existence of the hydroxyl group over the surface of MTNF is confirmed through Fourier transform infrared spectroscopy studies. Adsorption study results show the higher tendency of MTNF to adsorb the MB dye molecules as compared to R6G and MO dye molecules due to the presence of hydroxyl group and effective high surface area. Sunlight-driven photodegradation activity of MTNF was demonstrated by the decoloration of MB, MO, R6G, and OTC-HCl solution. Hydroxyl group functionalized MTNF with effective surface area decomposes the 16 µM MB, 10 µM MO, 10 µM R6G, and 0.5 mg/mL OTC-HCl molecules in just 12 min, 40 min, 30 min, and 60 min, respectively. Sunlight-induced photodegradation activity of MTNF can be attributed to the combined feature of hydroxyl radicals and synergistic effects in the TiO2 nanoflower-like structures.