A Resonant CO2 Sensor Functionalized with a Polymerized Ionic Liquid

Abstract

Carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is a commonly monitored gas; however, few commercially available sensors exist that can accurately measure CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations with low cost and low power consumption. This work presents initial assessments of microelectromechanical sensors based upon small-scale resonators embedded in an oscillator circuit for CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas concentration measurement. Devices were functionalized with a polymerized ionic liquid via an inkjet printing technique. An imidazolium cation functionality with a hexafluorophosphate anion chemistry (poly(1-methyl-3-(4-vinylbenzyl)-1H-imidazol-3-ium) hexafluorophosphate [PMVBI-PF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ]) was added to a polystyrene backbone motif, as this combination has previously shown significant CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interactions when utilized as a sorbent material for the capture of carbon dioxide from the atmosphere. Assessments were performed in a bench-top environmental test chamber by introducing a known amount of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> balanced with nitrogen, down to 100 ppm. The oscillation frequency was measured using a custom digital logic-based frequency counter circuit implemented in a field-programmable gate array (FPGA). The results show that the proposed approach, with additional development, could serve as an alternative to current commercially available CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensing technologies.