Transformation of novel TiOF2 nanoparticles to cluster TiO2-{001/101} and its degradation of tetracycline hydrochloride under simulated sunlight

Abstract

The anatase type cluster TiO₂-{001/101} was rapidly generated by a one-step hydrothermal method. The transformation process of coral-like TiOF₂ nanoparticles to cluster TiO₂-{001/101} was investigated for the first time, and the sensitization between cluster TiO₂-{001/101} and tetracycline hydrochloride (TCH) was also discussed. The degradation rate of TCH by cluster TiO₂-{001/101} under simulated sunlight was 92.3%, and the total removal rate was 1.76 times that of P25. Besides, cluster TiO₂-{001/101} settles more easily than P25 in deionized water. The study showed that cluster TiO₂-{001/101} derived from coral-like TiOF₂ nanoparticles had a strong adsorption effect on TCH, which was attributed to the oxygen vacancy (O_v) and {001} facets of cluster TiO₂-{001/101}. The strong adsorption effect promoted the sensitization between cluster TiO₂-{001/101} and TCH, and widened the visible light absorption range of cluster TiO₂-{001/101}. In addition, the fluorescence emission spectrum showed that cluster TiO₂-{001/101} had a lower luminous intensity, which was attributed to the heterojunction formed by {001} facets and {101} facets that reduces the recombination rate of carriers. It should be noted that cluster TiO₂-{001/101} still has good degradation performance for TCH after five cycles of degradation. This study provides a new idea for the synthesis of cluster TiO₂-{001/101} with high photocatalytic performance for the treatment of TCH wastewater.

Fig. 1. XRD patterns of the prepared samples.

Fig. 2. The high-magnification FE-SEM images of (a) T-0.5h, (b) T-1h, (c) T-3h, (d) T-4h; the element mapping of (e) Ti, (f) O, (g) F in T-4h.

Fig. 3. TEM images of as-prepared samples (a) T-0.5h, (b) T-1h, (c) T-3h, (d) T-4h, and HRTEM images of (e and f) T-4h.

Fig. 4. Nitrogen adsorption and desorption isotherms of T-0.5h, T-1h, T-3h, T-4h and P25. The inset is the corresponding pore size distribution.

Fig. 5. FT-IR (a) and EPR (b) spectra of different samples.

Fig. 6. (a) Survey XPS spectra of the samples; (b, c and d) high-resolution XPS data of Ti2p, O1s and F1s for samples respectively.

Fig. 7. (a) UV-Vis absorbance spectra of the samples and (b) the corresponding plots of (αhv)^1/2versus hv.

Fig. 8. The photoluminescence spectra with the excitation wavelength λ_ex = 300 nm for T-0.5h, T-1h, T-3h, T-4h and P25.

Fig. 9. (a) Photodegradation of TCH solution (10 mg L⁻¹, 100 mL) using different samples under simulated sunlight; (b) kinetic linear simulation curves of TCH solution photodegradation; (c) the effect of different concentration of TCH solution on the photocatalytic performance of T-4h (30 mg) under simulated sunlight; (d) the effect of different dosage of T-4h photocatalyst on degradation of TCH solution (10 mg L⁻¹, 100 mL) under simulated sunlight.

Fig. 10. (a) Photo stability tests over T-4h for TCH degradation; (b) XRD patterns of T-4h before and after five cycling runs; (c) effect of different scavengers on the degradation of TCH (10 mg L⁻¹, 100 mL) efficiencies over T-4h.

Fig. 11. Photographs of P25 suspension and T-4h suspension in deionized water at pH 7.0 at different settling times.

Fig. 12. Effect of different scavengers on the degradation of TCH (10 mg L⁻¹, 100 mL) efficiencies over T-4h.

Fig. 13. Schematic illustration of the photocatalytic mechanism for TCH removal over the T-4h photocatalyst.