One-step green synthesis of Cu2O/CuO@rGO composites for ppt level detection of NO2 at room temperature

Conventional metal oxide semiconductor gas sensors often suffer from high operating temperatures, low selectivity, and complex synthesis processes for NO2 detection. In this work, reduced graphene oxide (rGO) nanosheets are coated on NaOH-etched Cu2O/CuO urchin-like spheres to form Cu2O/CuO@rGO composites via a one-step green synthesis method at room temperature (RT). The gas sensor based on this material has been utilized for detecting NO2 at RT (25 °C), and the effects of Cu2O addition and reaction time on the morphology as well as gas-sensing properties of the as-prepared sensor are investigated. Of interest, the sensor based on the 550Cu2O/CuO@rGO-5 composite has an ultra-high response (S = 871) to 5 ppm NO2 gas at RT with a response/recovery time of 32/73 s, and the detection limit is as low as 90.6 ppt. In addition, the gas sensor shows excellent selectivity and repeatability. The excellent sensing performance of the as-prepared 550Cu2O/CuO@rGO sensor is attributed to the framework structure of Cu2O/CuO@rGO, the urchin-like hierarchical structure of the Cu2O/CuO and the synergistic effect of the p–p (Cu2O–CuO) heterojunction. This exploration of the present work offers a good reference for mass, green, and low-power sensing material preparation.