Template-Free Construction of Tin Oxide Porous Hollow Microspheres for Room-Temperature Gas Sensors.

Porous hollow microsphere (PHM) materials represent ideal building blocks for realizing diverse functional applications such as catalysis, energy storage, drug delivery, and chemical sensing. This has stimulated intense efforts to construct metal oxide PHMs for achieving highly sensitive and low-power-consumption semiconductor gas sensors. Conventional methods for constructing PHMs rely on delicate reprogramming of templates and may suffer from the structural collapse issue during the removal of templates. Here, we propose a template-free method for the construction of tin oxide (SnO2) PHMs via the competition between the solvent evaporation rate and the phase separation dynamics of colloidal SnO2 quantum wires. The SnO2 PHMs (typically 3 ± 0.5 µm diameter and approximately 200 nm shell thickness) exhibit desirable structural stability with desirable processing compatibility with various substrates. This enables the realization of NO2 gas sensors having a superior response and recovery process at room temperature. The superior NO2-sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels, enhancing the interaction of metal oxide solids with gas molecules in terms of the receptor function, transducer function, and utility factor. In addition, the one-step deposition of SnO2 PHMs directly onto device substrates simplifies the fabrication conditions for semiconductor gas sensors. The desirable structural stability of PHMs combined with the functional diversity of metal oxides may open new opportunities for the design of functional materials and devices.