UV-activated formaldehyde sensing properties of hollow TiO2@SnO2 heterojunctions at room temperature

Abstract Hollow TiO2@SnO2 nanospheres were synthesized via a hydrothermal process. Comparing to pure hollow TiO2 nanospheres, the hollow TiO2@SnO2 heterojunction nanospheres based sensor exhibited better sensing properties to formaldehyde under Ultraviolet (UV) irradiation at room temperature. The response time and recovery time were 20 s and 56 s, respectively, which are reduced compared to the pure one. The enhanced sensing properties could be ascribed to the formation of heterojunction between SnO2 and TiO2 together with hollow nanosphere architectures. The decorated TiO2 nanocrystals are even more depleted at the shallow Debye region which is equivalent to the reduction in the effective particle size of TiO2 significantly contributing to the enhanced response. After the targeted gases were removed, the chemisorbed oxygen on the surface of the metal oxides trapped electrons to the surface of the heterojunction sample. This process can also be promoted by energy barriers, which can explain the faster recovery speed of the heterojunction based sensor compared to that of the pure hollow TiO2 based one.