Ultrathin In₂O₃ Nanosheets with Uniform Mesopores for Highly Sensitive Nitric Oxide Detection

Nitric oxide (NO_x, including NO and NO₂) is one of the most dangerous environmental toxins and pollutants, which mainly originates from vehicle exhaust and industrial emission. The development of sensitive NO_x gas sensors is quite urgent for human health and the environment. Up to now, it still remains a great challenge to develop a NO_x gas sensor, which can satisfy multiple application demands for sensing performance (such as high response, low detection temperature, and limit). In this work, ultrathin In₂O₃ nanosheets with uniform mesopores were successfully synthesized through a facile two-step synthetic method. This is a success due to not only the formation of two-dimensional (2D) nanosheets with an ultrathin thickness of 3.7 nm based on a nonlayered compound but also the template-free construction of uniform mesopores in ultrathin nanosheets. The sensors based on the as-obtained mesoporous In₂O₃ ultrathin nanosheets exhibit an ultrahigh response (R_g/R_a = 213) and a short response time (ca. 4 s) toward 10 ppm NO_x, and a quite low detection limit (10 ppb NO_x) under a relatively low operating temperature (120 °C), which well satisfies multiple application demands. The excellent sensing performance should be mainly attributed to the unique structural advantages of mesopores and 2D ultrathin nanosheets.