Novel Zn-doped In₂O₃ nanocages and hollow spindle-like nanostructures (HSNs) have been prepared by calcining precursors obtained via a facile template-free hydrothermal method. The change in morphology, size, and phase compositions in a controlled synthesis of the Zn-doped In₂O₃ nanostructures are achieved by simple adjustments of the amount of water. The result of this formation mechanism investigation reveals that the amount of water and the reaction time make significant contributions to the growth of Zn-doped In₂O₃ nanostructures. The driving forces for the formation of the nanostructures are the precipitation–dissolution–renucleation–growth and Ostwald ripening processes based on time-dependent experimental results. The gas-sensing properties of Zn-doped In₂O₃ nanocages and HSNs have shown high sensitivity toward formaldehyde (HCHO) vapor at a relatively low operating temperature. Note that the gas sensor fabricated with Zn-doped In₂O₃ HSNs exhibit a higher and faster response than those fabricated with Zn-doped In₂O₃ nanocages due to the larger surface area and the decreasing size of the particle.

In this paper, copper-doped ceria oxides with different hollowness and size are fabricated by changing the Cu²⁺ doping concentration in the mixed water-glycol system. Results show that the copper-doped CeO₂ oxides undergo a morphology transformation from the solid nanospheres to core–shell, then to hollow nanospheres with the increase of the Cu²⁺ doping concentration. The corresponding size becomes smaller during this transfer process. The Cu²⁺ doping induced acceleration in the nucleation and growth process is further investigated. The resultant Cu²⁺-doped CeO₂ oxides exhibit enhanced CO conversion performance and better reduction behaviors.