Excellent acetone sensing enabled by tunable metal organic framework derived TiO₂ nanodisks

Annealing plays a crucial role for in enhancing the gas sensing properties of MOF-derived TiO₂ (MIL-125). Generally, TiO₂ transforms into different polymorphs (anatase, rutile, and brookite) during annealing, each with unique crystal structures and gas sensing properties. The aim of this research was to investigate the impact of annealing (500-650 °C) on the properties of MIL-125, which had not been previously studied. Through precise control, a 3D nanodisk morphology was obtained, where the MIL-125 surface gradually becomes rough at 600 °C (MT600). At 650 °C (MT650), anatase transforms completely into rutile, resulting in significant collapse and a decrease in diameter size from 700 nm to 300 nm. The XPS and EPR study showed that the MIL-125 nanodisks contain high amount of oxygen vacancies, thus giving higher response to various gases, specifically to acetone. The MT600 sensor maintained a good sensor response (for instance S_R∼21 toward 500 ppm acetone) at 250 °C for isntance SR. Even at 1 ppm, it exhibited an S_R value of ∼6.7. A fast response (T_Res ∼13 s) and recovery time (T_Rec ∼12 s) of MT600 sensor at 100 ppm acetone was obtained. The gas sensing mechanism is thoroughly discussed, and the electron migration process in acetone detection is analyzed, offering new sensitive materials and insights for improving metal-oxide-semiconductor gas sensors.