Highly sensitive few-layer MoS2 nanosheets as a stable soil moisture and humidity sensor

Abstract

In this work, an MoS2 nanosheet based ultrasensitive humidity and soil moisture sensor has been developed. MoS2 nanosheets are obtained by sonication based surfactant-induced exfoliation. The performance of the sensor is examined at room temperature (25 ∘C) with respect to various relative humidity (RH) levels and soil water content (θg). A 434 fold variation (35–15200 pF) in capacitance value is seen when the relative humidity level changes from 11% to 96%. The response and recovery times of the microsensor are approximately 30 s and 40 s, respectively. The capacitance of the MoS2 based sensor increases monotonically when the soil moisture content increases from 3.6% to 53% and 2.3–45% for black and red soil, respectively. The observed variation in capacitance corresponding to θgB = 53% (black soil moisture content) and θgR = 45% (red soil moisture content) is approximately 250 and 200 times that observed for the respective dry soil samples. The error in the soil moisture response measurement for the temperature variation from 25 ∘C to 70 ∘C is ± 2.52%. The device features stable performance for six months with reasonably high accuracy (maximum error ± 1.50%). The soil sensing results show fast response (35 s), negligible hysteresis error (2.80% at θgB = 31.9%), long-term stability (6 months and more), and good reproducibility (with more than 10 cycles).