Metal–organic framework-derived ZnO hollow nanocages functionalized with nanoscale Ag catalysts for enhanced ethanol sensing properties

Abstract

Increase of porosity and functionalization with nanoscale catalysts are two significant aspects for achieving high-performance metal oxide-based resistive gas sensors. In this work, a simple metal–organic framework (MOF) route has been developed to fabricate Ag nanocatalysts functionalized ZnO hollow nanocages (NCs). Nanoscale Ag catalysts with a small size of approximately 10 nm are uniformly encapsulated within the cavities of MOFs (ZIF-8). The high porosity, hollow structure, and functionalization with uniformly-distributed nanoscale Ag catalysts have been simultaneously achieved for MOF-derived ZnO. This type of porous Ag–ZnO hollow NCs show much enhanced ethanol sensing performances and reduced operating temperature in comparison with pure ZnO nanoparticles (NPs) and ZnO NCs. In particular, the 1 mL Ag–ZnO NCs exhibit the highest response of 84.6–100 ppm ethanol at 250 °C, which is 6.4 and 3.3 times higher than those of pure ZnO NPs and ZnO NCs at the optimum operating temperature of 275 °C, respectively. The Ag–ZnO NCs also display fast response/recovery times, good ethanol selectivity, and response reproducibility. The enhanced ethanol sensing properties are attributed to the synergistic effects of several points including the electron sensitization effects and catalytic effects of nanoscale Ag catalysts, porous and hollow structures, high surface area, and high surface O− species absorbing capability of Ag–ZnO NCs.