Highly responsive and selective ppb-level NO2 gas sensor based on porous Pd-functionalized CuO/rGO at room temperature

For the first time, Pd nanoparticle-functionalized, rGO nanosheet-modified 3D rod-like CuO (Pd–CuO/rGO) with a nanowire hierarchical structure was successfully synthesized using a facile hydrothermal strategy. Interestingly, the developed Pd–CuO/rGO sensor exhibited more prominent features compared with the CuO, Pd–CuO and CuO/rGO sensors towards trace NO2 gas at room temperature (RT, 23 °C). In particular, the Pd–CuO/rGO sensor demonstrated an ultra-high response of 64.2 towards 100 ppm NO2 gas at RT, which was approximately 3.4 times that of the pristine CuO sensor, 2.7 times that of the Pd–CuO sensor and 2 times that of the CuO/rGO sensor, respectively. Simultaneously, a response/recovery time of 10.7/9.2 s towards 10 ppm NO2 gas at RT was indicated for the Pd–CuO/rGO sensor, and the extremely low limit of detection was down to 50 ppb, ensuringreal-time detection at a ppb-level NO2 gas concentration. Furthermore, the fabricated sensors had reliable consistency, excellent repeatability and long-term stability. In addition to the contribution from the porous rGO-modified CuO providing abundant active places for gas adsorption and diffusion, Pd and partially oxidized Pd NPs that chemically and electronically sensitized the CuO supporter greatly improved the sensitivity and selectivity of the fabricated Pd–CuO/rGO sensor. Moreover, abundant surface oxygen vacancies were also to some extent beneficial for the sensing performance. Our scientific and systematic work has great potential for practical applications in extremely harsh environments.