RESUMO
Porous TiO2 structures have been of great interest in various photocatalytic applications over the past decade. However, the synthetic methods reported so far in the literature are complex and time consuming. This study presents a simple one-pot fabrication method of hollow porous TiO2 nanospheres using a sol-gel process involving CO2 generation in aqueous solution. The CO2 nanobubbles produced in the reaction act as a template for the crystal growth of TiO2 resulting in highly porous hollow nanospheres. The unique nanocrystal structure with a hollow nanosphere centre surrounded by an outer shell of prickle-like porous nanocrystals was observed. The prepared hollow porous TiO2 nanospheres exhibited excellent adsorption properties as demonstrated by the adsorption measurements and dynamic extraction of methylene blue in aqueous solution. Furthermore, the hollow porous TiO2 nanospheres hydrothermally treated at 180 °C exhibit 3.2 times higher photocatalytic performance in the decomposition of methylene blue than the commercial P25 TiO2. The idea of this work provides a new direction for facile green synthesis routes of various metal oxides with cavities, channels or crevices for various technological applications.
RESUMO
A novel class of core-shell- and hollow-structured MnCO3/TiO2 composites was synthesized by titania nanocoating on MnCO3 microspheres via two-step liquid-phase deposition at room temperature. Morphological change from core-shell to hollow microparticles was possible in the prepared samples by controlling prereaction time of MnCO3 and [NH4]2TiF6. Upon the prereaction process, the core of the core-shell MnCO3/TiO2 became highly porous, and a honeycomb-like surface that resembled the orientation of self-assembled MnCO3 nanocrystals was developed. The MnCO3 core was completely removed after 6 h prereaction. Calcination at 600 °C resulted in the transformation of both core-shell- and hollow-structured composites to Mn2O3/TiO2 anatase microspheres that retained their original morphologies. X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and electron probe microanalysis were employed for microsphere characterization. As the first trial for application of the synthesized materials, solid-extraction of organics from aqueous media was examined using methylene blue (MB). Both types of Mn2O3/TiO2 composites showed very fast adsorption of MB with high extraction values of 5.2 and 6.4 µmol g(-1) for the core-shell and hollow structures, respectively. Current work provides a new approach for facile fabrication of titania-metal oxide nanocomposites with unique morphological features and promising application possibilities.
