2D metal-organic framework derived co-loading of Co_3O_4 and PdO nanocatalysts on In_2O_3 hollow spheres for tailored design of high-performance breath acetone sensors

摘要

Highly dispersed Co_3O_4 nanoclusters encapsulating PdO nanoparticles were loaded on In_2O_3 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 In_2O_3 spheres by controlling the growth and self-assembly of 2D Co-ZIF-L on In_2O_3, which were converted into pure or Co_3O_4 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 Co_3O_4 or Co_3O_4/PdO nanocatalysts. The In_2O_3 sensors co-loaded with Co_3O_4/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(Co_3O_4)-n(In_2O_3) hetero-junction and the chemical sensitization due to the synergistic catalytic effect of Co_3O_4 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.