Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath

The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co₃O₄ hollow nanocages (HNCs) by using metal-organic framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and separate Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co₃O₄ HNCs (PdO-Co₃O₄ HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co₃O₄ HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co₃O₄ HNCs exhibited improved acetone sensing response (R_gas/R_air = 2.51-5 ppm) compared to PdO-Co₃O₄ powders (R_gas/R_air = 1.98), Co₃O₄ HNCs (R_gas/R_air = 1.96), and Co₃O₄ powders (R_gas/R_air = 1.45). In addition, the PdO-Co₃O₄ HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy people's breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.