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.
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