Three-Dimensional Graphene Hydrogel Decorated with SnO₂ for High-Performance NO₂ Sensing with Enhanced Immunity to Humidity

A facile, one-step hydrothermal route was exploited to prepare SnO2-decorated reduced graphene oxide hydrogel (SnO2/RGOH) with three-dimensional (3D) porous structures for NO2 gas detection. Various material characterizations demonstrate the effective deoxygenation of graphene oxide and in situ growth of rutile SnO2 nanoparticles (NPs) on 3D RGOH. Compared with the pristine RGOH, the SnO2/RGOH displayed much lower limit of detection (LOD) and an order of magnitude higher sensitivity, revealing the distinct impact of SnO2 NPs in improving the NO2-sensing properties. An exceptional low theoretical LOD of 2.8 ppb was obtained at room temperature. The p–n heterojunction formed at the interface between RGOH and SnO2 facilitates the charge transfer, improving both the sensitivity in NO2 detection and the conductivity of hybrid material. Considering that existing SnO2/RGO-based NO2 sensors suffer from great vulnerability to humidity, here we employed integrated microheaters to effectively suppress the response to humidity, with nearly unimpaired response to NO2, which boosted the selectivity. Notably, a flexible NO2 sensor was constructed on a liquid crystal polymer substrate with endurance to mechanical deformation. This work indicates the feasibility of optimizing the gas-sensing performance of sensors by combining rational material hybridization, 3D structural engineering with temperature modulation.