Metal–Organic Framework Templated Catalysts: Dual Sensitization of PdO–ZnO Composite on Hollow SnO2 Nanotubes for Selective Acetone Sensors

Metal–organic framework (MOF)-derived synergistic catalysts were easily functionalized on hollow SnO2 nanotubes (NTs) via electrospinning and subsequent calcination. Nanoscale Pd NPs (∼2 nm) loaded Zn-based zeolite imidazole framework (Pd@ZIF-8, ∼80 nm) was used as a new catalyst-loading platform for the effective functionalization of a PdO@ZnO complex catalyst onto the thin wall of one-dimensional metal oxide NTs. The well-dispersed nanoscale PdO catalysts (3–4 nm) and multiheterojunctions (PdO/ZnO and ZnO/SnO2) on hollow structures are essential for the development of high-performance gas sensors. As a result, the PdO@ZnO dual catalysts-loaded hollow SnO2 NTs (PdO@ZnO–SnO2 NTs) exhibited high acetone response (Rair/Rgas = 5.06 at 400 °C @ 1 ppm), superior acetone selectivity against other interfering gases, and fast response (20 s) and recovery (64 s) time under highly humid atmosphere (95% RH). In this work, the advantages of hollow SnO2 NT structures with high surface area and open porosity were clearly demonstrated by the comparison to SnO2 nanofibers (NFs). Moreover, the sensor arrays composed of SnO2 NFs, SnO2 NTs, PdO@ZnO–SnO2 NFs, and PdO@ZnO–SnO2 NTs successfully identified the patterns of the exhaled breath of normal people and simulated diabetics by using a principal component analysis.