Trace NO2 sensors based on reduced graphene@metal oxide/oxyhydroxide/hydroxychloride with ultrahigh sensitivity and good selectivity at room temperature via modulation of the nanograin boundary

Abstract

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 a serious threat to human health. Herein, a facile and scalable method is proposed to prepare gas sensitive materials based on reduced graphene oxide (rGO), rGO@MO/MOOH/MOHCl (MO = SnO₂, Mn₃O₄, MOOH = FeOOH, MOHCl = Cu₂(OH)₃Cl), via electrostatic interactions between rGO and metal ions of lower valence and subsequent nucleation and growth at ∼80 °C. The rGO@MO/MOOH/MOHCl sensors composed of uniformly dispersed MO/MOOH/MOHCl 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 a 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 coexisting interference gases at much higher concentrations. Complex impedance spectroscopy analysis reveals that the excellent response to trace NO₂ is ascribed to the modulation of the nanograin boundary barrier among rGO@MO/MOOH/MOHCl. The work provides an effective approach for constructing high performance sensors to detect trace gases at room temperature.