Light-Triggered p-n Junction Switching in Hierarchical GaxIn2-xO3@MIL-68(GaIn) Nanotube Gas Sensors with Thermally Adaptive Dual-Selectivity toward Acetic Anhydride and Isopropanol.

Acetic anhydride and isopropanol are essential chemical raw materials, and their accurate and efficient detection is of great significance. Conventionally, the sensing of these two gases requires two distinct types of sensors, which increases the complexity of the detection device. Meanwhile, sensors still face challenges regarding detection limits and power consumption. To address these issues, this study constructed a heterogeneous structure of hierarchical GaxIn2-xO3@MIL-68(GaIn) nanotubes based on the bimetallic metal-organic framework (BMOF) precursor MIL-68(GaIn). This heterogeneous structure exhibits novel and interesting phenomena: (1) It has an unusual temperature-dependent selectivity for acetic anhydride and isopropanol. At room temperature, it strongly favors isopropanol, but at 260 °C, it switches to favoring acetic anhydride, with a detection limit of as low as 10 ppb (0.01 ppm). (2) It also shows light-induced selectivity under ultraviolet (UV) light. With UV exposure at room temperature, it exhibits p-n switching response characteristics for isopropanol. The low detection limit and low power consumption likely come from the combined effects of the hierarchical porous structure that improves gas transport, the heterointerface that tunes charge distribution, and the oxygen vacancies that create highly active adsorption sites. At room temperature, the sensor responds to isopropanol in a typical p-type manner. But under UV light, the response shifts from p-type to n-type, showing how light-induced carrier regulation works. This study provides a deeper look into how to engineer the structure of metal-organic framework (MOF)-derived multicomponent gas-sensing materials and how to achieve multimode gas detection.