Nanoscale PdO Catalyst Functionalized CoO 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 CoO 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 CoO HNCs (PdO-CoO HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of CoO HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-CoO HNCs exhibited improved acetone sensing response (R/R = 2.51-5 ppm) compared to PdO-CoO powders (R/R = 1.98), CoO HNCs (R/R = 1.96), and CoO powders (R/R = 1.45). In addition, the PdO-CoO 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.