Room Temperature H2S Sensing by rGO-MoS2 Composite

Diagnosis of diseases by analyzing the constituents of breath or mouth vapor, owing to its ease of operation, is emerging as a promising alternative to the existing diagnostics. H2S is one of the known biomarkers of hepatocellular carcinoma. This work reports detection of H2S using reduced graphene oxide (rGO) and molybdenum disulfide (MoS2) composite. rGO was synthesized by thermally reducing graphene oxide that was obtained using modified Hummers' method and MoS2 nanoflakes were synthesized using a facile liquid exfoliation technique. The composite was synthesized by mixing the two nanomaterials in specific proportion and ultrasonicating the dispersion. The 2-D morphologies of all the intrinsic nanomaterials and the composite were confirmed using electron microscopies. The bandgaps of rGO, MoS2, and rGO-MoS2 composites were found to be 4.1, 1.7, and 2.2 eV, respectively, when studied using ultraviolet-visible spectroscopy. All the nanomaterials were tested exhaustively for 5-54 ppm of H2S at room temperature. The rGO exhibited 0.5%-1.5% response toward 13-54 ppm H2S while the responses of MoS2 and rGO-MoS2 composite were found to vary between 20%-50% and 15%-33%, respectively, for 5-54 ppm H2S at room temperature. The incorporation of rGO in the MoS2 network led to stabilization of the baseline resistance of the sensors, which was otherwise varying largely in case of intrinsic MoS2. The composite was found to be fast with the response times varying from 21 to 50 s and the recovery time was found to vary from 10 to 33 s for 5-54 ppm H2S at room temperature. The composite also exhibited excellent selectivity toward the target gas.