Metal–Organic Framework Templated Catalysts: Dual Sensitization of PdO–ZnO Composite on Hollow SnO2Nanotubes for Selective Acetone Sensors

Metal–organic framework (MOF)-derived synergistic catalysts were easily functionalized on hollow SnO2nanotubes (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 SnO2NTs (PdO@ZnO–SnO2NTs) 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 SnO2NT structures with high surface area and open porosity were clearly demonstrated by the comparison to SnO2nanofibers (NFs). Moreover, the sensor arrays composed of SnO2NFs, SnO2NTs, PdO@ZnO–SnO2NFs, and PdO@ZnO–SnO2NTs successfully identified the patterns of the exhaled breath of normal people and simulated diabetics by using a principal component analysis.