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.

Three-Dimensional-Structured Boron- and Nitrogen-Doped Graphene Hydrogel Enabling High-Sensitivity NO2 Detection at Room Temperature

Heteroatom-doping has been proved as an effective method to modulate the electronic, physical, and chemical properties of graphene (Gr). Developing a new strategy of heteroatom-doping for high-performance gas sensing is a pivotal issue. Here, we demonstrate novel Gr-based gas sensors through three-dimensional (3D)-structured B-/N-doping nanomaterials for high-performance NO₂ sensing. The 3D porous B- and N-doped reduced graphene oxide hydrogels (RGOH) are synthesized via one-step hydrothermal self-assembly and employed as transducing materials to fabricate room-temperature high-performance chemiresistors. The systematic characterizations of the as-synthesized B- and N-RGOH clearly show the uniform doping of the B and N heteroatoms and the formation of B and N components with C/O. In comparison with the pristine RGOH counterpart, the 3D B- and N-RGOH sensors exhibit 38.9 and 18.0 times enhanced responses toward 800 ppb NO₂, respectively, suggesting the remarkable doping effect of the heteroatoms in improving the sensitivity. Significantly, B- and N-RGOH display the exceptionally low limit of detection of 9 and 14 ppb NO₂, respectively, which are much lower than the threshold limit recommended by the U.S. Environmental Protection Agency. In addition, the developed NO₂ sensors show good linearity, reversibility, fast recovery, and impressive selectivity. This work opens up a new avenue to fabricate room-temperature and high-performance NO₂ sensors by incorporating B and N heteroatoms into 3D RGOH via a convenient hydrothermal self-assembly approach.

Improved Selectivity and Sensitivity of Gas Sensing Using a 3D Reduced Graphene Oxide Hydrogel with an Integrated Microheater

Low-cost, one-step, and hydrothermal synthesized 3D reduced graphene oxide hydrogel (RGOH) is exploited to fabricate a high performance NO2 and NH3 sensor with an integrated microheater. The sensor can experimentally detect NO2 and NH3 at low concentrations of 200 ppb and 20 ppm, respectively, at room temperature. In addition to accelerating the signal recovery rate by elevating the local silicon substrate temperature, the microheater is exploited for the first time to improve the selectivity of NO2 sensing. Specifically, the sensor response from NH3 can be effectively suppressed by a locally increased temperature, while the sensitivity of detecting NO2 is not significantly affected. This leads to good discrimination between NO2 and NH3. This strategy paves a new avenue to improve the selectivity of gas sensing by using the microheater to raise substrate temperature.