Hydrothermal synthesis of In₂O₃ nanocubes for highly responsive and selective ethanol gas sensing

Indium oxide nanocubes (NCs) were prepared via a simple, template-free hydrothermal method at low temperature; the so-obtained structures exhibited large surface area (47.67 m²/g) and Barrett−Joyner−Halenda (BJH) adsorption average pore diameter (11.92 nm), both higher than for commercial In₂O₃ nanoparticles. At the optimal temperature of 300 °C, the In₂O₃ NCs-based sensor showed a superior response of 85–100 ppm ethanol, 3.4 times higher than that of the commercial one based on In₂O₃ NPs, and also faster response time (15 s) than the commercial device (60 s). The better sensing performance of the synthesized In₂O₃ NCs can be attributed to its unique properties that include large BET surface area and BJH adsorption average pore diameter as well as abundance of sharp edges and tips, which result in high surface to volume ratios for the gas adsorption and diffusion processes, facilitating the charge-transfer and sensing reactions at the gas–solid interfaces. In addition, the In₂O₃ NCs exhibited excellent selectivity to ethanol among other target gases (CO, CH₄, CH₃CHO, H₂, and CH₃COCH₃). This work provides an effective design pathway for ethanol sensors based on In₂O₃ NCs.