2D metal-organic framework derived co-loading of Co3O4 and PdO nanocatalysts on In2O3 hollow spheres for tailored design of high-performance breath acetone sensors

Abstract

Highly dispersed Co3O4 nanoclusters encapsulating PdO nanoparticles were loaded on In2O3 hollow spheres to design high-performance breath acetone sensors. Nanolayers of two-dimensional (2D) metal-organic frameworks (MOFs), pure and Pd-intercalated leaf-like cobalt zeolitic-imidazolate frameworks (Co-ZIF-L), were uniformly coated (thickness: approximately 10 nm) on the surface of the In2O3 spheres by controlling the growth and self-assembly of 2D Co-ZIF-L on In2O3, which were converted into pure or Co3O4 nanoclusters (size: 10 nm) encapsulating PdO nanoparticles (size: approximately 4 nm) by thermal annealing. The gas response, selectivity, and optimal sensing temperature could be tuned by loading different quantities and configurations of the Co3O4 or Co3O4/PdO nanocatalysts. The In2O3 sensors co-loaded with Co3O4/PdO exhibited ultra-high responses (ratio of resistances in air and gas) to 5 ppm of acetone (145.9) as well as high selectivity over the interference of other biomarker gases at 225 °C, even in high humidity conditions (80% relative humidity), thereby demonstrating the promising potential for monitoring diabetes and the ketogenic diet. This unprecedented acetone sensing performance can be explained by the electronic sensitization due to the formation of p(Co3O4)-n(In2O3) heterojunction and the chemical sensitization due to the synergistic catalytic effect of Co3O4 and PdO. Ultrathin 2D-MOFs incorporating metallic nanoparticles provide a promising template for co-loading two different nanocatalysts in a highly dispersed and well-mixed configuration that can be used to establish diverse catalyst-oxide hetero-nanostructures for various functional applications, including high-performance gas sensors.