Humidity Sensing Mechanism on 2-D/3-D MoS2 in the Light of Watersorption, Morphology, and Hydrophilicity: A Holistic Understanding

This article represents a holistic approach to understand the humidity sensing mechanism on MoS2 surfaces by judiciously correlating the three pivotal determining factors, viz: 1) volumetric watersorption; 2) morphology; and 3) hydrophilicity. To ascertain the distinguishable difference in the three abovementioned parameters, 2-D and 3-D nanoforms of MoS2 were synthesized via electrodeposition and hydrothermal routes, respectively. Detailed morphological (field emission scanning electron microscopy (FESEM) and Brunauer–Emmett–Teller (BET) surface area), hydrophilicity [water contact angle (WCA)], and volumetric watersorption characterizations were carried out. The 3-D nanoflowers-based sensors showed significantly better performance than that of 2-D nanosheets-based ones. MoS2 nanoflowers exhibited a significantly larger BET surface area (5.833 m2/gm) than that of the MoS2 nanosheets (0.025 m2/gm). The WCA of the MoS2 nanosheets (83°) was found to be higher than that of the MoS2 nanoflowers (60°), while the maximum volumetric water vapor uptake for the nanoflowers (176.1 cc/gm) was found to be ~1166 times greater than that of the nanosheets (0.151 cc/gm). Sensitivity was found to be the function of the three parameters mentioned above, while the recovery time was found to be the function of WCA and volumetric watersorption mainly (inversely proportional to WCA and directly with volumetric watersorption). In contrast, the response time exhibited an inverse relationship with the surface area and a direct relationship with the WCA with minimal influence of volumetric watersorption. A quantitative model was developed, where a single equation reflects the effects of all the factors and helps in a complete understanding of the phenomenon and its correlation with performance parameters.