A facile solvothermal process combined with a precursor thermal transformation method has been developed for preparing porous TiO₂ hollow nanospheres with a high surface area and a good thermal stability. The porous TiO₂ hollow spheres were obtained by using TiOSO₄ as a titanium source and carbon nanospheres as a sacrificial template. Their particle size, diameter and morphology can be readily controlled by varying growth parameters, including reaction temperature, time and reagent concentration. The calcination temperature of TiO₂–C core-shell nanospheres was found to have a profound effect on the structure and properties of the final products. The photocatalytic activities of the products were evaluated by the photodegradation of methyl orange (MO). The TiO₂ hollow spheres obtained from 450 °C thermal treatment exhibited higher photocatalytic activity than commercial Degussa P25 in the presence of Cr(VI). The possible photodegradation mechanism was also investigated.

In this work, SnO₂ hierarchical nanostructures were successfully prepared via a simple and surfactant-free hydrothermal process starting from stannous sulfate (SnSO₄) and trisodium citrate dihydrate (Na₃C₆H₅O₇·2H₂O) in a suitable ethanol–water system. TEM and HRTEM images showed that the obtained SnO₂ products are uniform, well-dispersed, and have spherical architectures, composed of tiny primary nanocrystals, and the diameters are about 50 nm. It was found that the amount of Na₃C₆H₅O₇·2H₂O and the volume ratio of ethanol and water played important roles in determining the final morphologies of the products. The gas sensing results indicated that the sensor made from porous SnO₂ nanostructures calcined at 400 °C exhibited excellent gas sensing performance to butanol at the low temperature compared with those under higher calcination temperature and commercial SnO₂. The SnO₂ hierarchical nanostructures possess uniform size and large surface areas, making them ideal candidates for more potential applications such as battery electrodes and as opto-electronic devices.