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Detection of volatile organic compounds (VOCs) at room temperature (RT) currently remains a challenge for metal oxide semiconductor (MOS) gas sensors. Herein, for the first time, we report on the utilization of porous SnO2 thin films for RT detection of VOCs by defect engineering of oxygen vacancies. The oxygen vacancies in the three-dimensional-ordered SnO2 thin films, prepared by a colloidal template method, can be readily manipulated by thermal annealing at different temperatures. It is found that oxygen vacancies play an important role in the RT sensing performances, which successfully enables the sensor to respond to triethylamine (TEA) with an ultrahigh response, for example, 150.5-10 ppm TEA in a highly selective manner. In addition, the sensor based on oxygen vacancy-rich SnO2 thin films delivers a fast response and recovery speed (53 and 120 s), which can be further shortened to 10 and 36 s by elevating the working temperature to 120 °C. Notably, a low detection limit of 110 ppb has been obtained at RT. The overall performances surpass most previous reports on TEA detection at RT. The outstanding sensing properties can be attributed to the porous structure with abundant oxygen vacancies, which can improve the adsorption of molecules. The oxygen vacancy engineering strategy and the on-chip fabrication of porous MOS thin film sensing layers deliver great potential for creating high-performance RT sensors.

Multishelled hollow micro/nanostructures hold great potential for a variety of important applications due to their fascinating properties. However, the synthesis of multishelled hollow micro/nanostructures mainly relies on template-involved methods. A template-free protocol for multishelled hollow structures remains quite challenging. In this work, a solution strategy based on inside-out and outside-in Ostwald ripening is developed to manipulate hematite hollow spheres with single or double shells without using any hard or soft templates. The structure evolution of the hematite hollow spheres is comprehensively studied to reveal the formation mechanism. As a potential application, the hematite hollow spheres have been utilized for chemical gas sensors to investigate the structure–property correlations. Results demonstrate that the double-shelled hematite spheres exhibit much higher response than the single-shelled ones due to structure sensitization. An improved sensor response is further obtained by cata...