Enhancement of Photocatalytic Activity of Mesporous TiO₂ Powders by Hydrothermal Surface Fluorination Treatment

Abstract

Mesporous surface-fluorinated TiO 2 (F-TiO 2 ) powders of anatase phase with high photocatalytic activity are prepared by a one-step hydrothermal strategy in a NH 4 HF 2 -H 2 O-C 2 H 5 OH mixed solution with tetrabutylorthotitanate (Ti(OC 4 H 9 ) 4 , TBOT) as precursor. The prepared samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N 2 adsorption-desorption isotherms, UV-vis absorption spectroscopy, and transmission electron microscopy. The production of hydroxyl radicals ( • OH) on the surface of UVilluminated TiO 2 is detected by a photoluminescence (PL) technique with use of terephthalic acid as a probe molecule. The photocatalytic activity is evaluated by photocatalytic oxidation decomposition of acetone in air under UV light illumination. The results show that the photocatalytic activity of F-TiO 2 powders is obviously higher than that of pure TiO 2 and commercial Degussa P25 (P25) powders due to the fact that the strong electron-withdrawing ability of the surface tTi-F groups reduces the recombination of photogenerated electrons and holes, and enhances the formation of free OH radicals. Especially, the F-TiO 2 powder prepared at the nominal atomic ratio of fluorine to titanium (R F ) of 0.5 shows the highest photocatalytic activity and its rate constant k exceeds that of P25 by a factor of more than 3 times.

Photocatalytic oxidation of gaseous ammonia over fluorinated TiO2 with exposed (001) facets

“…The as-prepared anatase TiO 2 presented a 140.1 m 2 /g BET surface area, 5.44 nm pore diameter and 0.19 cm 3 /g pore volume. The surface fluorination resulted in a sharp drop in the BET surface area but a sharp increase in the pore size and pore volume of F-TiO 2 due to growth of TiO 2 crystallites [23,39]. In contrast, the defluorination process did not induce much difference in BET surface area, pore diameter and pore volume of samples.…”

“…The fluoride peak at binding energy 684.5 eV (F 1s) only appears in the F-TiO 2 sample, indicating the formation of surface fluoride ( Ti-F) by a ligand exchange reaction between F − and the surface hydroxyl group on the TiO 2 surface [40][41][42][43][44]. No peak for F − ions in the lattice at 688.5 eV was observed in the spectra, because the hydrothermal process could prevent the substitution of F − for O 2− in the lattice of TiO 2 [21,39,40,45]. The fluoride peak in the D-TiO 2 almost disappeared after defluorination, indicating that the surface fluorine atoms were removed by NaOH washing for 10 h [46].…”

Graphene supported plasmonic photocatalyst for hydrogen evolution in photocatalytic water splitting

“…The enhancement in the H 2 evolution in presence of graphene in TiO 2 could be due to excellent electron accepting and transferring capability, and the capacity to restrain the recombination of the photo-excited electrons and holes effectively. It has been reported that the two-dimensional π-conjugation structure of graphene sheets facilitates the transfer of photo-induced electrons and can act as an excellent electron acceptor [57,58]. A further increase in graphene content leads to a reduction of the photo-catalytic activity.…”

Synergistic effect of Ag deposition and nitrogen doping in TiO2 for the degradation of phenol under solar irradiation in presence of electron acceptor

“…Peaks at 3400, 2930, 2850 cm −1 are attributed to the Ti-OH bond [39]. The TiO 2−x N x sample shows additional peaks at 1450, 1160 cm −1 attributed to nitrogen atom in the TiO 2 matrix [40]. The peak at 600 cm −1 can be assigned to the absorption bands of Ti-O and O-Ti-O.…”

“…The practical applications of TiO 2 have been suppressed by the low quantum yield that arises from the rapid recombination of photo-induced charge carriers and the other drawback is the poor solar absorption efficiency that is determined by its band gap. It was found that doping with nonmetals (e.g., boron [4], carbon [5], nitrogen [6] and fluorine [7]), especially nitrogen can successfully modify the electronic structure of TiO 2 , extending the photoresponse of TiO 2 to the visible light region. Many studies have been reported that loading of noble metals (e.g., Pt, Au, or Ag) on the surface of TiO 2 can effectively hinder the recombination and promote the transfer of photo-induced electrons to these metal deposits [8][9][10][11][12].…”