Adsorption and photocatalytic degradation behaviors of rhodamine dyes on surface-fluorinated TiO2 under visible irradiation

Abstract

Surface-fluorinated TiO₂ (F-TiO₂) particles was synthesized by a simple fluorosilanization method to serve as a visible-light photocatalyst for rapid degradation of Rhodamine B (RhB) dyes. The fluroalkylsilane (FAS-17) was covalently immobilized on the TiO₂ particles via robust Si–O bonds. The changes in surface properties of the F-TiO₂ particles were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and zeta potential measurements. The optical property of the F-TiO₂ particles was determined by UV-visible spectroscopy. Upon the fluorination modification, the zeta potential of TiO₂ particles switched from positive to negative, whilst the optical property of bulk TiO₂ particles remained almost unchanged. Photodegradation experimental results demonstrated that zwitterionic RhB dyes were more favorably adsorbed on F-TiO₂ rather than on the Ti(IV) sites of the pristine TiO₂, and that the photodegradation reaction of RhB on F-TiO₂ proceeded much faster than that on the pristine TiO₂. However, the adsorption and photodegradation rate of anionic methyl orange (MO) dyes did not show an obvious change on F-TiO₂. These results suggested that the molecular structure of dyes played a key role in visible-light photodegradation reactions on F-TiO₂ particles. Positive-charged diethylamine groups of RhB molecular structures were postulated to promote the adsorption of RhB dyes on the surface of F-TiO₂ particles, thus leading to easy electron injection and induction of rapid photodegradation under visible-light illumination.