We present a useful ammonia gas sensor based on chemically reduced graphene oxide (rGO) sheets by self-assembly technique to create conductive networks between parallel Au electrodes. Negative graphene oxide (GO) sheets with large sizes (>10 μm) can be easily electrostatically attracted onto positive Au electrodes modified with cysteamine hydrochloride in aqueous solution. The assembled GO sheets on Au electrodes can be directly reduced into rGO sheets by hydrazine or pyrrole vapor and consequently provide the sensing devices based on self-assembled rGO sheets. Preliminary results, which have been presented on the detection of ammonia (NH₃) gas using this facile and scalable fabrication method for practical devices, suggest that pyrrole-vapor-reduced rGO exhibits much better (more than 2.7 times with the concentration of NH₃ at 50 ppm) response to NH₃ than that of rGO reduced from hydrazine vapor. Furthermore, this novel gas sensor based on rGO reduced from pyrrole shows excellent responsive repeatability to NH₃. Overall, the facile electrostatic self-assembly technique in aqueous solution facilitates device fabrication, the resultant self-assembled rGO-based sensing devices, with miniature, low-cost portable characteristics and outstanding sensing performances, which can ensure potential application in gas sensing fields.

Graphene is a promising material for gas sensing, but high-performance gas sensors often require a robust structural design in order to endow the resultant sensing devices with batch uniformity, good response, sensitivity, and selectivity. In this study, a novel gas sensor based on assembled porous reduced graphene oxide (rGO) multilayer frameworks was designed and fabricated for gas sensing. To this end, negatively charged holey graphene oxide (GO) and positively charged holey graphene oxide (rGO) were assembled on gold (Au) electrodes through electrostatic interactions to form a porous structural framework. A reduction process was then performed to ensure the formation of a porous framework composed of the r(GO/rGO)_n multilayers. The combined chemical assembly, etching and modification methods resulted in porous r(GO/rGO)_n multilayers with an increased specific surface area. This improved the gas sensor response towards dimethyl methylphosphonate (DMMP) vapour at room temperature. The sensor that was assembled with 12 layers of porous graphene (r(GO/rGO)₁₂) showed a resistance change reaching 8.95% in the presence of 50 ppm DMMP vapour. This value was 3-fold higher than that obtained with the sensor constructed with one-layered graphene. At the low DMMP vapour concentration of 1 ppm, the resistance change in (r(GO/rGO)₁₂) reached a substantial 2.21%. Furthermore, the assembled porous r(GO/rGO)₁₂ sensor showed good repeatability, excellent stability, good uniformity, and elevated selectivity towards DMMP vapour. Overall, the proposed concept looks promising for the design of future high-performance gas sensing devices with broad applications.

The nanosheet stacking phenomenon in graphene thin films significantly deteriorates their gas-sensing performance. This nanosheet stacking issue should be

Nowadays, metal oxide semiconductors (MOS)-reduced graphene oxide (rGO) nanocomposites have attracted significant research attention for gas sensing applications. Herein, a novel composite material is synthesized by combining two p-type semiconductors, i.e., Cu₂O and rGO, and a p-p-type gas sensor is assembled for NO₂ detection. Briefly, polypyrrole-coated cuprous oxide nanowires (PPy/Cu₂O) are prepared via hydrothermal method and combined with graphene oxide (GO). Then, the nanocomposite (rGO/PPy/Cu₂O) is obtained by using high-temperature thermal reduction under Ar atmosphere. The results reveal that the as-prepared rGO/PPy/Cu₂O nanocomposite exhibits a maximum NO₂ response of 42.5% and is capable of detecting NO₂ at a low concentration of 200 ppb. Overall, the as-prepared rGO/PPy/Cu₂O nanocomposite demonstrates excellent sensitivity, reversibility, repeatability, and selectivity for NO₂ sensing applications.

This study presents three-dimensional (3D) MoS₂/reduced graphene oxide (rGO)/graphene quantum dots (GQDs) hybrids with improved gas sensing performance for NO₂ sensors. GQDs were introduced to prevent the agglomeration of nanosheets during mixing of rGO and MoS₂. The resultant MoS₂/rGO/GQDs hybrids exhibit a well-defined 3D nanostructure, with a firm connection among components. The prepared MoS₂/rGO/GQDs-based sensor exhibits a response of 23.2% toward 50 ppm NO₂ at room temperature. Furthermore, when exposed to NO₂ gas with a concentration as low as 5 ppm, the prepared sensor retains a response of 15.2%. Compared with the MoS₂/rGO nanocomposites, the addition of GQDs improves the sensitivity to 21.1% and 23.2% when the sensor is exposed to 30 and 50 ppm NO₂ gas, respectively. Additionally, the MoS₂/rGO/GQDs-based sensor exhibits outstanding repeatability and gas selectivity. When exposed to certain typical interference gases, the MoS₂/rGO/GQDs-based sensor has over 10 times higher sensitivity toward NO₂ than the other gases. This study indicates that MoS₂/rGO/GQDs hybrids are potential candidates for the development of NO₂ sensors with excellent gas sensitivity.