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 SnO 2 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/SnO 2 ) on hollow structures are essential for the development of high-performance gas sensors. As a result, the PdO@ZnO dual catalysts-loaded hollow SnO 2 NTs (PdO@ZnO–SnO 2 NTs) exhibited high acetone response ( R air / R gas = 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 SnO 2 NT structures with high surface area and open porosity were clearly demonstrated by the comparison to SnO 2 nanofibers (NFs). Moreover, the sensor arrays composed of SnO 2 NFs, SnO 2 NTs, PdO@ZnO–SnO 2 NFs, and PdO@ZnO–SnO 2 NTs successfully identified the patterns of the exhaled breath of normal people and simulated diabetics by using a principal component analysis.