Thermally-stable, ordered mesoporous anatase TiO 2 with large pore size and high crystallinity has been successfully synthesized through an evaporationinduced self-assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO 2 primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO 2 are characterized in detail by small-angle and wide-angle X-ray diffraction, Raman spectra, N 2 adsorption/ desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well-ordered mesoporous structure could be maintained up to 700 ° C (M700) and also possesses large pore size (10 nm), high specifi c BET surface area (122 m 2 g − 1 ), and high total pore volumes (0.20 cm 3 g − 1 ), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large-pore mesoporous anatase TiO 2 is also proposed here, which could be further confi rmed by TG/FT-IR in site analysis and X-ray photoelectron spectroscopy. The obtained mesoporous TiO 2 of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO 2 for degradation of highly toxic 2,4-dichlorophenol under UV irradiation. This enhancement is attributed to the well-ordered large-pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron-hole pairs, confi rmed by surface photovoltage spectra.
A facile template-free method has been developed for the controllable fabrication of novel hierarchical flower-like Bi 2 MoO 6 hollow spheres via a solvothermal process in the presence of ethylene glycol. The formation mechanism was proposed based on the evolution of morphology as a function of solvothermal time, which involves the initial formation of nanoparticles followed by their selfaggregation to microspheres and transformation into hierarchical flower-like hollow spheres by Ostwald ripening. The integer appearance of the hierarchical flower-like Bi 2 MoO 6 hollow spheres was maintained after calcination at 400 C for 3 h. Furthermore, the calcined hierarchical flower-like Bi 2 MoO 6 hollow spheres exhibited excellent visible-light-driven photocatalytic efficiency for the degradation of Rhodamine B, up to 95% within 2 h, which was much higher than that of Bi 2 MoO 6 prepared by solid-state reaction and TiO 2 (P25). The improved photocatalytic performance could be ascribed to the special hierarchical hollow sphere structure, good permeability and large surface area.
Stable porous TiO2 photocatalysts, with higher photocatalytic activity than Degussa P25, were synthesized
via a hydrothermal process using cetyltrimethylammonium bromide as the template, followed by a posttreatment
in the presence of ethylenediamine. The photocatalysts were characterized by X-ray diffraction, Raman
spectroscopy, N2 adsorption−desorption, transmission electron microscopy, thermogravimetric analysis, X-ray
photoelectron spectroscopy, and UV−vis diffuse reflectance spectra. The posttreatment considerably increases
the thermal stability of the porous framework and inhibits the undesirable grain growth and phase transformation
during calcination. The prepared TiO2 photocatalysts have large surface areas of about 205 and 117 m2/g
even after calcination at 700 and 800 °C, respectively. The formation mechanism of the stable porous titania
was proposed. The high crystallinity, large specific surface area, and heterojunction microstructure between
anatase and brookite may be responsible for the high photocatalytic activity in terms of the degradation of
organic pollutants such as phenol and rhodamine B under UV irradiation.
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