Efficient exfoliation of g-C3N4 and NO2 sensing behavior of graphene/g-C3N4 nanocomposite

In this work, graphitic carbon nitride (g-C3N4) nanosheets were prepared and employed to improve the gas sensitivity performance of graphene. g-C3N4 nanosheets (NS-CN) were exfoliated from bulk powder using a proton-enhanced liquid-phase exfoliation method, where the co-ordinate bonds between nitrogen of g-C3N4 and proton H+ of HCl benefit the swelling of bulk and improve the delamination process. The thickness and size of the exfoliated nanosheets were about 4 nm and 1-2 mu m, respectively. A slight increment of the bandgap of g-C3N4 was observed after exfoliation. It was found that the proton functionalization of g-C3N4 powder before exfoliation facilitates the production of uniform nanosheets. A certain amount ranging from 0% to 90% of as-prepared g-C3N4 was added to a graphene solution and ultrasonically mixed to prepare a graphene/g-C3N4 nanocomposite (G/NS-CN). The performances of pure graphene-based and nanocomposite-based sensors in sensing NO2 gas were systematically investigated and compared. We found compositing g-C3N4 with graphene significantly enhanced the sensing performance of the graphene sensor. A trade-off effect on sensing response was observed as the weight ratio of NS-CN to graphene in the nanocomposite sensor was changed, suggesting the specific roles of g-C3N4 and graphene in sensing behavior. It was found that the nanocomposite sensor with 15 wt% of NS-CN exhibited the best sensing response. The sensor in this optimized composition presented a linear and stable response as well as good recovery toward NO2 gas. The sensing mechanism of the nanocomposite sensor was also proposed. (C) 2017 Elsevier B.V. All rights reserved.