Trace NO2 Sensors Based on Reduced Graphene@Metal Oxide /Oxyhydroxide/ Hydroxychloride with Ultrahigh Sensitivity and Good Selectivity at Room Temperature via Modulation of Nanograin Boundary

Developing gas sensors with high sensitivity and good selectivity at room temperature is essential for the detection and control of trace toxic gases which pose great threats to human health. Herein, a facile and scalable method is proposed to prepare gas sensitive materials of reduced graphene oxide (rGO)@MOX (MOX = SnO2, Mn3O4, FeOOH, Cu2(OH)3Cl) via electrostatic interactions between rGO and metal ions of lower valence and subsequent nucleation and growth at ~80oC. The rGO@MOX sensors composed of uniformly dispersed MOX on rGO sheets, exhibit significantly higher sensitivity to trace NO2 at room temperature than that based on rGO alone. Remarkably, rGO@Cu2(OH)3Cl presents the state-of-the-art response of 220% to trace NO2 (5 parts per billion) and ultra-low limit of detection of 5.0 parts per trillion. Furthermore, the sensor shows good repeatability, long-term stability and high selectivity as revealed by little change of the response by coexistent interference gases of much higher concentrations. Complex impedance spectroscopy analysis reveals that the excellent response to trace NO2 is ascribed to the modulation of nanograin boundary barrier among rGO@MOX. The work provides an effective approach for constructing high performance sensors to detect trace gases at room temperature.