Au Nanocage/In₂O₃ Nanoparticle-Based Hybrid Structures for Formaldehyde Sensors

Detecting the trace ppb level of formaldehyde (HCHO) in indoor ambient and human exhaled breath using a metal oxide semiconductor gas sensor has attracted increasing attention. A hybrid nanostructure consisting of In2O3 nanoparticles grown on a Au nanocage (NC) surface was synthesized using a one-step solvothermal method, which was then used to be fabricated as HCHO sensors. The 0.5 wt % Au NC/In2O3 sensor featured an ultrahigh response of 8.8 for 1 ppm of HCHO at a low operating temperature (145 °C), which was nearly 2.5 times higher than that of the pure In2O3 sensor. Furthermore, it possessed outstanding selectivity and a low detection limit (25 ppb) toward HCHO. This excellent sensing property was possibly due to the increase in chemisorbed oxygens on its surface due to the Au NC spillover mechanism, an enhanced adsorption capability for HCHO because of the phase transition from cubic to rhombohedral In2O3, good gas diffusion, and a large surface area with a Au NC/In2O3 3D hierarchical structure, as well as the widened electron depletion layer derived from the Schottky barriers and homojunctions between the components of Au NC/In2O3.