Visible Light-Activated Room Temperature NO 2 Gas Sensing Based on the In 2 O 3 @ZnO Heterostructure with a Hollow Microtube Structure.

The persistent challenge of poor recovery characteristics of NO 2 sensors operated at room temperature remains significant. However, the development of In 2 O 3 -based gas sensing materials provides a promising approach to accelerate response and recovery for sub-ppm of NO 2 detection at room temperature. Herein, we propose a simple two-step method to synthesize a one-dimensional (1D) In 2 O 3 @ZnO heterostructure material with hollow microtubes, by coupling metal-organic frameworks (MOFs) (MIL-68 (In)) and zinc ions. Meanwhile, the In 2 O 3 @ZnO composite-based gas sensor exhibits superior sensitivity performance to NO 2 under visible light activation. The response value to 5 ppm of NO 2 at room temperature is as high as 1800, which is 35 times higher than that of the pure In 2 O 3 -based sensor. Additionally, the gas sensor based on the In 2 O 3 @ZnO heterostructure demonstrates a significantly reduced response/recovery time of 30 s/67 s compared to the sensor based on pure In 2 O 3 (74 s/235 s). The outstanding gas sensing properties of the In 2 O 3 @ZnO heterostructure-based sensors can be attributed to the enhanced photogenerated charge separation efficiency resulting from the heterostructure effect, and the improved receptor function toward NO 2 , which can increase the reactive sites and gas adsorption capacity. In summary, this work proposes a low-cost and efficient method to synthesize a 1D heterostructure material with microtube structures, which can serve as a fundamental technique for developing high-performance room-temperature gas sensors.