Titania nanocoating on MnCO3 microspheres via liquid-phase deposition for fabrication of template-assisted core-shell- and hollow-structured composites.

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.