Resistive- and capacitive-type humidity and temperature sensors based on a novel caged nickel sulfide for environmental monitoring

In this work for the first time, a new bis(4-benzylpiperazine-1-carbodithioato-k²S,Sʹ)nickel(II) complex (hereafter caged nickel sulfide) has been used to fabricate the capacitive-type and resistive-type sensor. The surface consisted of 2D plates, pores and pore-channels of various shapes and size. These 2D plates and pores played a pivotal role in the sensing mechanism of the sensor. The conduction mechanism is based on Von Grotthuss mechanism. In the relative humidity (RH) range 30–90%, the resistance of the sensor was decreased by two orders of magnitude (from 2.94 × 10⁸ Ω at 30%RH to 2.34 × 10⁶ Ω at 90%RH at operational frequency of 120 Hz). While at applied frequency of 120 Hz, capacitance of the sensor was increased from 15.95 pF to 38.1 pF in the range of 30–90%RH. At higher frequency (10 kHz) the capacitance of the sensor is reduced to 6.285 pF. The maximum hysteresis of 1.54% is noted which is less than the reported in the literature. The response and recovery time of the sensor were 25 and 30 s, respectively, which are either far smaller or greater than the response and recovery time of the various sensors reported in the literature.