Ultrasensitive Humidity Detection Using Metal–Organic Framework-Coated Microsensors

Abstract

The use of metal-organic framework (MOF) thin films to detect water vapor across a wide concentration range is demonstrated using MOF-functionalized quartz surface acoustic wave (SAW) sensors. A range of 3-14,800 ppmv was obtained with thin films of the MOF Cu(3)(benzenetricarboxylate)(2) (Cu-BTC) deposited by an automated layer-by-layer method. Devices coated by a manual technique demonstrated sensitivity from 0.28 to 14,800 ppmv, the limit of our test system. This exceeds the sensitivity of many commercially available sensors. Cu-BTC layers were covalently bonded directly to the silicon oxide surface, allowing devices to be heated beyond 100 °C to desorb water adsorbed in the pores without decomposition, thereby regenerating the sensors. Sensor response as a function of coating thickness was evaluated, showing that the SAW sensor response is bounded by maximum and minimum layer thicknesses. Computer simulation of H(2)O uptake shows a multistep adsorption isotherm defined by initial adsorption at open Cu-sites, followed by pore-filling and finally full saturation. Modeling and experimental results are consistent. Calculated uptake values suggest an efficient adsorption of H(2)O by Cu-BTC. These results provide the first convincing evidence that MOF functionalization of compact sensing technologies such as SAW devices and microcantilevers can compete with state-of-the art devices.

SAW Sensors for Chemical Vapors and Gases

“…Other widely used materials include carbon nanostructures (e.g., carbon nanotubes [99,100,101] and graphene oxide [77]), metals [102,103], ceramics [78], and composite materials [101,104,105]. More recently, interest is in relatively new materials such as metal-organic-frameworks (MOFs) [106] and porous materials for their higher sorption capacity [107]. These materials are applied using different techniques such as sputtering, evaporation, spin coating, drop casting, spray coating, and Langmuir-Blodgett methods depending upon the properties of the materials [16,108].…”

A fiber optic sensor with a metal organic framework as a sensing material for trace levels of water in industrial gases

“…Cu-BTC has been previously applied to trace water determination with a quartz surface acoustic wave (SAW) to detect weight changes caused by adsorption of gas molecules in the Cu-BTC [36]. With this method, sub-ppmv levels of water were detected with a short response time (minutes).…”

MOF@PEDOT Composite Films for Impedimetric Pesticide Sensors

“…[23,24] The use of many MOFs was extensively explored regarding its possible applications in water-based separations and chromatography, [25][26][27][28] provided that selected materials fulfill the crucial requisite of stability toward hydrolysis. [31][32][33][34][35][36][37] Based on the signal transduction possible for many configurations, sensors reported can be described as optical, [38,39] electrochemical, [40][41][42] mechanical, [43] photoelectrochemical, [44][45][46][47] or combined-miscellaneous. [30] The advantageous features of different MOFs have been rapidly applied in the development of sensors.…”