N-doped TiO2-SBA-15 (denoted as N-TiO2-SBA-15) material has been successfully synthesized by a two-step procedure. Firstly, TiO2-SBA-15 was prepared by impregnating tetraisopropyl orthotitanate on SBA-15 and followed by calcination at 550°C. In the second step, TiO2-SBA-15 was modified by doping nitrogen with the assistance of urea. The resulting material, N-TiO2-SBA-15, was characterized by XRD, TEM, SEM, N2 adsorption/desorption at 77 K, DR UV-Vis, and XPS. The results showed that N-TiO2-SBA-15 material maintains its ordered hexagonal mesostructure and exhibits the absorption of visible region. The photocatalytic activity of N-TiO2-SBA-15 sample was evaluated by the photodegradation of methylene blue under visible light.
Heterogeneous photodegradation of organic pollutants with semiconductors has attracted much of the attention of researchers because of its efficiency and promises of economy [
Many efforts have been made on supporting TiO2 on porous materials for increasing surface area of TiO2 [
Over the past decades, in order to extend the useful spectral range into the visible region, metal-doped TiO2 photocatalysts were intensively studied. However, metal-doped TiO2 exhibits several drawbacks: thermal instability, electron trapping by the metal centers, and requirement of more expensive ion-implantation facilities [
These reports all showed that the doping can bring a significant enhancement for the photocatalytic activity of TiO2 under visible light. Among the nonmetals, N is the most typical nonmetal dopant and has been intensively investigated so far. There are numerous publications on preparation of N-doped TiO2 by various methods, including sol-gel [
A combination of modified TiO2 and SBA-15 can take advantage of both SBA-15 and TiO2. In this paper, we report a facile preparation of N-doped TiO2-SBA-15 using urea as a nitrogen source. The as-synthesized material showed visible-light response and potential application in photodegradation of methylene blue under visible light.
Triblock copolymer Pluronic P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H), tetraethyl orthosilicate (TEOS, (C2H5O)4Si), methylene blue, and titanium isopropoxide (Ti(C3H7O)4) were purchased from Merck. Hydrochloric acid and urea were purchased from Shanghai Chemical Company. All chemicals were used as received without any further purification.
The mesoporous silica SBA-15 was prepared according to the literature [
X-ray diffraction (XRD) patterns for the samples were measured on a Bruker D8 Advance diffractometer using CuK
For the photocatalytic test, 100 mg of the catalyst was suspended in 50 mL of 100 mg/L methylene blue (MB) aqueous solution, and then the mixture was stirred for 2 h in dark to obtain the equilibrium adsorption. The reaction mixture was exposed to visible light from a 300 w lamp with a UV cutoff filter (>420 nm). After a given irradiation time, about 4 mL of the mixture was withdrawn and the catalysts were separated by centrifugation. The selected solutions were measured using a UV-Vis spectrophotometer (Jenway 6800).
The small-angle X-ray diffraction patterns of pure SBA-15, TiO2-SBA-15, and N-TiO2-SBA-15 are shown in Figure
Structural, textural properties of the pure SBA-15, TiO2-SBA-15, and N-TiO2-SBA-15.
Material |
|
Pore diameter (nm) |
|
Wall thickness (nm) |
---|---|---|---|---|
SBA-15 | 689.8 | 7.5 | 11.1 | 3.6 |
TiO2-SBA-15 | 529.4 | 6.6 | 10.9 | 4.3 |
N-TiO2-SBA-15 | 462.6 | 6.0 | 11.1 | 5.1 |
(a) Small-angle XRD patterns of the pure SBA-15 (A), TiO2-SBA-15 (B), and N-TiO2-SBA-15 (C); (b) Large-angle XRD patterns of the pure SBA-15 (A), TiO2-SBA-15 (B), and N-TiO2-SBA-15 (C).
The large-angle X-ray diffraction for N-TiO2-SBA-15 was also studied to characterize the structure of TiO2 grafted on SBA-15 (Figure
The periodicity in the mesostructure of the three materials is confirmed directly by transmission electron microscopy (Figure
TEM images of the pure SBA-15 (a), TiO2-SBA-15 (b), and N-TiO2-SBA-15 (c).
The morphology of rope-like domains with a uniform size was obtained for the materials SBA-15 and TiO2-SBA-15 (Figures
SEM images of the pure SBA-15 (a), TiO2-SBA-15 (b), and N-TiO2-SBA-15 (c).
The N2 adsorption/desorption isotherms at 77 K of the calcined SBA-15 and the modified SBA-15 samples are shown in Figure
N2 adsorption-desorption isotherms and pore size distribution (the inset) of the pure SBA-15 (A), TiO2-SBA-15 (B), and N-TiO2-SBA-15 (C).
The doping of TiO2 on SBA-15 with nitrogen was further supported by the diffuse reflectance UV-Vis spectroscopy. Figure
Diffuse reflectance UV-Vis spectra of TiO2-SBA-15 (a) and N-TiO2-SBA-15 (b).
Chemical states of the doped nitrogen in N-TiO2-SBA-15 were investigated by XPS. It can be seen from Figure
XPS spectra of N 1s (a), Ti 2p (b), and O 1s (c) for N-TiO2-SBA-15.
Compared to Ti-N, a relatively higher binding energy at 397.6 eV for N-Ti-O may be explained by the high electronegativity of oxygen leading to the reduction of electron density on the nitrogen [
The photocatalytic activity of the samples was determined by the degradation of methylene blue in water under visible light. Figure
Photocatalytic degradation of methylene blue on TiO2-SBA-15 (A) and N-TiO2-SBA-15 (B) with initial methylene blue concentration of 100 mg/L under visible light.
The visible-light-sensitive nitrogen-doped TiO2-SBA-15 material was synthesized by a two-step process. TiO2 nanoparticles with homogeneous dispersion on the SBA-15 silica were treated with urea to form nitrogen-doped TiO2-SBA-15 material. The absorption of visible light for the material comes from the partial substitution of the oxygen in TiO2 by nitrogen atoms. The nitrogen-doped TiO2-SBA-15 material exhibits a good photocatalytic activity for the degradation of methylene blue in the aqueous solution under visible light.
The financial support from the National Foundation for Science and Technology Development of Vietnam (NAFOSTED, 104.03.2011.11) is gratefully acknowledged.