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

Abstract

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.