Synthesizing N-[4-morpholinecarboximidamidoyl]carboximidamidoylated graphene oxide for fabricating high-sensitive humidity sensors

Abstract

A lot of humidity sensors cannot accurately measure humidity of air containing NH3 gas due to reaction of NH3 gas with sensor materials. A guanidyl group is a strong hydrophilic group, moreover, guanidyl groups do not adsorb NH3 molecules via hydrogen or chemical bonds. In this paper, moroxydine moieties were grafted on surfaces of graphene oxide (GO) materials to synthesize N-[4-morpholinecarboximidamidoyl]carboximidamidoylated graphene oxide (MCGO) for fabricating humidity sensors. When RH increased from 11% to 95%, impedance value of the sensor decreased from 5.41 × 108 to 2.25 × 104 Ω at testing frequency 100 Hz. The change of impedance was much higher than that fabricated by GO. The sensors also exhibited short response/recovery time (2 s/20 s). Their good humidity sensing properties would be attributed to the fact that those N atoms in guanidyl groups at moroxydine moieties on the surfaces MCGO may strong interact with H atom in H2O molecules to form intermolecular hydrogen bonds and generate OH− ions to increase ionic conductivities. The impedance change of the humidity sensor at a low or high relative humidity was due to electronic or ionic conductivities, respectively.