TiO2 mesoporous microspheres self-assembled from nanoparticles were synthesized by a surfactant-free solvothermal route. The TiO2 precursors were fabricated by tetrabutyl titanate, glacial acetic acid, and urea in the ethanol solution at 140°C for 20 h, and TiO2 mesoporous microspheres were obtained by a postcalcination at temperatures of 450°C for promoting TiO2 crystallization and the removal of residual organics. The phase structure, morphology, and pore nature were characterized by XRD, SEM, and nitrogen adsorption-desorption measurements. The as-prepared TiO2 microspheres are in anatase phase, with 2-3
The existence of a close relationship between specific morphologies and unique properties in nanomaterials has ignited much attention to the synthesis of novel nanostructures for a broad domain of applications in the past decade [
Here, mesoporous TiO2 microspheres self-assembled from nanoparticles have been fabricated by a surfactant-free, convenient, and low-cost solvothermal method, which can conquer the issues above-mentioned. In addition, the diameters size, pore volume, BET surface areas, and the pore size distributions can also be tuned by adjusting synthesis parameters. This synthesis method can also be extended for the fabrication of other mesoporous metal oxide materials.
All the reagents are analytical grate and were used without further purification (from Sinopharm Chemical Reagent Ltd.). In a typical procedure, 12 mmol urea was dissolved into 60 mL of absolute ethanol; then the solution was slowly added into the other solution (mixture of 20 mL ethanol, 2 mL tetrabutyl titanate (Ti(OC4H9)4), and 1 mL glacial acetic acid (CH3COOH)) under stirring. The solution was transferred into a 100 mL Teflon-lined autoclave after stirring for 30 min. The autoclave was put into an oven and maintained at 140°C for 20 h. The precipitate was rinsed by ethanol for several times, dried at 90°C for 12 h, and then calcined at 450°C for 2 h. For comparison, different amounts of urea were added while keeping other reaction conditions constant.
XRD measurements were performed on a Bruker D8 X-ray diffractometer with Cu-K
The N2 adsorption-desorption isotherms of the TiO2 microspheres were obtained at −196°C using a Quantachrome Autosorb 1-C. Before measurements, samples were degassed under vacuum at 300°C for 4 hours. The Brunauer-Emmett-Teller (BET) approach was used to calculate specific surface area of the sample by using adsorption data over the relative pressure range of 0.05–0.30. The Barrett-Joyner-Halenda (BJH) approach was employed to determine pore size distribution and average mesopore diameter by using desorption data of the isotherms.
SEM images were obtained on a JEOL JEM 6360 scanning electron microscope with accelerating voltage of 20 kV.
Figure
Textural and structural parameters of mesoporous TiO2 samples prepared with different amounts of urea.
Urea (mmol) | Phase | Crystallite sizea |
BET surface areab |
Pore volumec |
Average pore diameterd |
---|---|---|---|---|---|
8 | Anatase | 12.2 | 1.09 | 0.002 | 3.5 |
12 | Anatase | 10.4 | 57.35 | 0.085 | 5.6 |
16 | Anatase | 9.2 | 42.45 | 0.045 | 3.8 |
20 | Anatase | 8.7 | 3.76 | 0.015 | 4.3 |
XRD patterns of mesoporous TiO2 microspheres prepared with different amounts of urea: (a) 8 mmol; (b) 12 mmol; (c) 16 mmol; (d) 20 mmol.
The morphology and size of the TiO2 samples were examined by SEM. Figures
SEM images of mesoporous TiO2 microspheres prepared with different amounts of urea: (a) 8 mmol; (b) 12 mmol; (c) 16 mmol; (d) 20 mmol.
The microstructural characteristics of the TiO2 microspheres were further investigated with the N2 adsorption/desorption analysis. The adsorption isotherms of the TiO2 microspheres are shown in Figures
N2 adsorption/desorption curves of mesoporous TiO2 microspheres prepared with different amounts of urea: (a) 8 mmol; (b) 12 mmol; (c) 16 mmol; (d) 20 mmol.
Pore size distributions of mesoporous TiO2 microspheres prepared with different amounts of urea: (a) 8 mmol; (b) 12 mmol; (c) 16 mmol; (d) 20 mmol.
It is also interesting to note that BET specific surface areas, pore volumes, and average pore diameters also changed with the amount of urea used in preparation, as shown in Table
In summary, mesoporous TiO2 microspheres self-assembled from nanoparticles are synthesized by a surfactant-free Solvothermal method combined with postcalcination route. The as-prepared TiO2 microspheres show anatase phase, high degree of crystallinity, and large BET surface areas. By adjusting the amount of urea used in synthesis, the pore size distribution and the diameters of the mesoporous TiO2 microspheres can be tuned. The new approach could be extended to the fabrication of other metal mesoporous materials.
The authors thank Liaoning Science and Technology Department Foundation (no. 2007223016), Liaoning Educational Department Foundation (L2011065), Shenyang Science and Technology Department Foundation (no. F11-264-1-76), and Scientific Research Starting Foundation for Doctor, Liaoning Province (no. 20111046), for financial support.