A low-cost, swift response, highly sensitive MOF-based dual sensing device enables detection of ultralow humidity levels and solvent polarity changes

Abstract

Detection of ultra-low humidity levels is very important; however, developing highly sensitive and rapid ultra-low humidity sensors is challenging due to the low water adsorption capacity, lack of hydrophilic interaction sites, and limited stabilities of most materials. Metal–organic frameworks (MOFs), a burgeoning class of porous materials, known for their high porosity and stability, could be potential candidates for designing humidity sensing devices. Herein, we report and detail the fabrication of a MOF-based capacitive dual sensor that can detect ultralow humidity levels and distinguish between polar and non-polar solvents. Solvent vapor adsorption experiments have been carried out to correlate the adsorption trends with the sensor's capability to detect different solvents such as water, methanol, ethanol, acetone, hexane, etc. [Eu(BTC)]-MOF exhibits higher water adsorption capacity over other polar and non-polar solvents. The detection limit of the sensor is as low as 0.84 ppm and it displays a very low hysteresis of ∼0.03% [ΔC/C₀ (%)]. The device also shows an exceptional atmospheric stability over a period of one month with no decline in its performance. Additionally, the [Eu(BTC)]-MOF-based device has been investigated as a real-time humidity sensor for glove box-related applications and a suitable mechanism has been proposed for the exceptional sensing behavior of the MOF device.