Synthesis of In₂O₃ nanocubes, nanocube clusters, and nanocubes-embedded Au nanoparticles for conductometric CO sensors

Cubic indium oxide (In₂O₃) of different sizes, In₂O₃ nanocube clusters, and In₂O₃ nanocube clusters embedded Au nanoparticles were obtained using solvothermal method. Compared with the large size or monodispersed In₂O₃ nanocubes, In₂O₃ nanocube clusters shows a higher response to carbon monoxide (CO), due to increased surface area and pore structures. Moreover, In₂O₃ nanocube clusters with an Au nanoparticle core (Au@In₂O₃) leads to a further increase of response to CO. Our results also show that 1 at% Au@In₂O₃ system presents the best sensing properties with response of 42.1–100 ppm CO, response/recovery speed of 2/2 s and ultra-low limit detection. The CO concentration dependence of the sensor response implies that ∼0.5 ppb and ∼28 ppb could be detected with a response value of 1.4 under 20 % and 93 % relative humidity, respectively. This increase in sensing response is due to the fact that Au nanoparticles can enhance the receptor function of the semiconductor gas sensor. Remarkably, Au@In₂O₃ system unifies three key factors of a semiconductor gas sensor, i.e., high specific surface area, high porosity, and noble metal loading.