Comparison between Linear and Branched Polyethylenimine and Reduced Graphene Oxide Coatings as a Capture Layer for Micro Resonant CO₂ Gas Concentration Sensors

• Main Authors: Alberto Prud’homme, Frederic Nabki
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Sensors
• Subjects: polyethylenimine; micro-resonator; co₂ sensor; gas sensor; humidity sensor; reduced graphene oxide; coatings; mass sensor
• Online Access: https://www.mdpi.com/1424-8220/20/7/1824

The comparison between potential coatings for the measurement of CO₂ concentration through the frequency shift in micro-resonators is presented. The polymers evaluated are linear polyethylenimine, branched polyethylenimine and reduced graphene oxide (rGO) by microwave reduction with polyethylenimine. The characterization of the coatings was made by using 6 MHz gold-plated quartz crystals, and a proof-of-concept sensor is shown with a diaphragm electrostatic microelectromechanical systems (MEMS) resonator. The methods of producing the solutions of the polymers deposited onto the quartz crystals are presented. A CO₂ concentration range from 0.05 % to 1 % was dissolved in air and humidity level were controlled and evaluated. Linear polyethylenimine showed superior performance with a reaction time obtained for stabilization after the concentration increase of 345 s, while the time for recovery was of 126 s, with a maximum frequency deviation of 33.6 Hz for an in-air CO₂ concentration of 0.1%.