Pore-size-dependent sensing property of hierarchical SnO2 mesoporous microfibers as formaldehyde sensors

Distinct from SnO2 nanoparticulates whose gas-sensing properties depend deeply on grain size and specific surface area, hierarchical SnO2 mesoporous structures has been found to possess remarkable gas-sensing performance due to their large accessible surface area. Interestingly, our obtained hierarchical SnO2 mesoporous microfibers shows an increase in the response to formaldehyde (HCHO) gas with decreasing specific surface area and increasing pore size, characterized by TEM, BET and performance analysis. The pore-size-dependent gas-sensing properties are mainly attributed to the transport of detected gases inside SnO2 mesoporous microfibers. Smaller pores can not provide efficient gas transport to more active sites while larger pores can allow most detected gas molecules diffuse easily inside the deeper region of the mesoporous SnO2 microfibers and react with oxygen species adsorbed on the surface (these reactive surface can be called as effective surface), resulting in a large sensor response. Therefore, the pore size and its resultant effective surface area rather than specific surface area play a dominant role in the gas-sensing properties of mesoporous materials, which can provide us with new insight on the design of high-performance gas sensors in the future.