Fe-Functionalized α-Fe₂O₃/ZnO Nanocages for ppb-Level Acetone Gas Sensing

Highly sensitive and selective gas sensors hold great potential in disease diagnosis. However, the rational design of non-noble-metal-based, high-efficiency sensing materials for trace gas detection remains a crucial challenge. Herein, a chemiresistive sensor that can detect parts per billion (ppb)-level acetone was realized based on three-dimensional (3D) α-Fe 2 O 3 /ZnO nanocages, which were achieved by a simple encapsulation and calcination process. In particular, we found that Fe species play an intriguing role in the evolution from Fe-ZIF-8 to heterogeneous α-Fe 2 O 3 /ZnO nanocages. α-Fe 2 O 3 functionalization empowered the α-Fe 2 O 3 /ZnO nanocage-based sensor with a high response of 45.25, an ultrafast response (7 s) and recovery (6 s) time toward 50 ppm of acetone, a limit of detection (LOD) of 500 ppb, and superior selectivity. Moreover, in situ Fourier transform infrared analysis allowed one to devise of an acetone sensing mechanism for dissociative acetone adsorbed on the α-Fe 2 O 3 /ZnO nanocages, involving the first oxidation of acetone to form formate and acetate complexes, followed by further oxidation to CO 2 and H 2 O. The enhanced acetone sensing performance can be attributed to the high specific surface area, abundant oxygen vacancies, well-tuned heterojunction, and optimal acid–base property.