Soil Moisture Sensing Properties of the Ti₃C₂T _x Mxene-Based Soil Moisture Sensor on Vadose Zone Soils

One of the crucial variables for accurate irrigation models is soil moisture data. Recent advancement in microsensors has opened avenues to fabricate low-cost and highly sensitive soil moisture sensors for in situ measurements. For these microsensors, sensing films play a pivotal role, considering the selectivity and sensitivity. In this work, we have explored the Ti3C2Tx MXene two-dimensional (2D) nanomaterials as the soil moisture sensor's sensing film. For this purpose, the interdigitated electrodes (IDEs) have been fabricated on the silicon substrate using the micromanufacturing method. To understand the characteristics of the Ti3C2Tx MXene 2D nanomaterials, X-ray diffraction (XRD) is adopted to confirm the structural analysis. Fourier transform infrared (FTIR) spectroscopy is carried out to identify the exciting chemical bonds for Ti3C2Tx MXene. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis are used to study the morphology and elemental composition of Ti3AlC2 MAX and Ti3C2Tx MXene phases, respectively. Further, the sensor transfer function has been studied for three different soil samples, viz., clayey soil, loamy sand soil, and sandy loam soil, under laboratory conditions. The performed measurements indicate that the response of fabricated soil moisture sensors is about 500, 2400, and 1700% for the clayey, loamy sand, and sandy loam soils at 300 Hz, respectively, for the gravimetric water content (GWC) ranging from 1 to 18% GWC. Interestingly, the hysteresis of the fabricated sensor on the loamy sand soil is about +/- 1% GWC, whereas for the sandy loam and clayey soils, it is around +/- 3 and +/- 6% GWC, respectively. Further, the fabricated sensor shows a high selectivity toward the water molecule when compared with the other ions (Cu+, Cd+, Na+, and K+) in the soil samples.