Controlled synthesis of TiO2 mesoporous microspheres via chemical vapor deposition

Graphical abstract: Highlights: → Anatase titanium dioxide (TiO2) mesoporous microspheres with core-shell and hollow structure were successfully prepared on a large scale by a simple template-free chemical vapor deposition method. → The as-synthesized products are high uniformity, and the porosity could be well controlled by optimizing the reaction conditions. → The possible growth mechanism of the multi core-shell and hollow nanostructures has been discussed. - Abstract: Anatase titanium dioxide (TiO2) mesoporous microspheres with core-shell and hollow structure were successfully prepared on a large scale by a one-step template-free chemical vapor deposition method. The effects of various reaction conditions on the morphology, composition and structure of the products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) technique and photoluminescence (PL) method. The results indicate that the product near the source was composed of core-shell structure TiO2 microspheres with diameters from 3 to 5 μm. With increasing the distance between the source materials and the substrate, the hollow TiO2 spheres with 1-2 μm dominant the products. A localized Ostwald ripening can be use to explain the formation of core-shell and hollow structures, and the size of the initial TiO2 solid nanoparticles plays an important role in determining the evacuation manner of the solid in the ripening-induced hollowing process. The surface area of TiO2 hollow microspheres determined by the adsorption isotherms was measured to be 74.67 m2/g. X-ray photoelectron spectroscopy (XPS) analysis revealed that the O-H peaks of hollow structures have a chemical shift compared with the core-shell structures. The optical property of the products was also discussed.